The Improvement of the Sewage Treatment of the City of Winterthur and Its Influence on the River Töss and Its Underground Water Stream

Home , Ill (Vorarlberg), Neftenbach, Pfungen, Wiesendangen

The Improvement of the Sewage Treatment of the City of Winterthur and its Influence on the River Töss and its Underground Water Stream

By HAKUMAT RAI

Contents

Acknowledgments 2

Research Problem 3

Research Program 4

Description of the River Töss Basin 4 Physiography 4 River Discharge 5 Catchment 7 Precipitation 7 Climatological Elements 8

Sources of Pollution 8

Material and Methods 11

Sampling Stations 12

Presentation of Data 15 A. Physical and Chemical Analyses 15 l. Temperature 15 2. pH-values 16 3. Carbonate and Total Hardness 18 4. Phosphate 22 5. Dissolved Oxygen (D.O.) 23 a) Saturation Deficit 26 b) Dissolved Oxygen Consumption Curves 28 6. Biochemical Oxygen Demand (B.O.D.) 30 7. KMnO4-Consumption 34 2 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

8. Nitrogenous Compounds (Inorganic) 38 a) Nitrate 38 b) Nitrite 38 c) Ammonia 40 9. Chloride 42 10. Detergents (Surfactants) 44 11. Suspended Matter 45 12. Total Volatile and Fixed Residue 46 13. Iron 49 B. Bacteriological Studies on the River Töss 49 1. Standard Plate Count (Total Count of Bacteria) 49 2. Coli and Coliform 52 C. Physico-Chemical and Bacteriological Characteristics of Sewage Treatment Plant Effluents and the Tributaries of the River Töss 55 1. Sewage Treatment Plants 55 2. Tributaries 59 D. Diurnal Varlation Studies in the River Töss 62 1. Diurnal Variation Studies at Winterthur Sewage Treatment Plant and River Töss 62 2. Diurnal Variation Studies at Rorbas Sewage Treatment Plant and River Töss . 69 E. Discussion 74 The Töss River Before and After the Construction of the Activated Sludge Unit at Winterthur Sewage Treatment Plant 74 Effect of Organic Matter 81 Influence of the River Töss on the Sanitary Condition of the River Rhein 82 Pollution Travel with Ground Water 84 Recommendations 91 Summary 92 Zusammenfassung 95 References 98

Acknowledgments

This research project was sponsored in part by the Stiftung der Wirtschaft zur Förderung des Gewässerschutzes in der Schweiz and the Bauamt der Stadt WiHter- thur, and was coHducted at the Kantonales Laboratorium, Limnologische Abteilung, by the University of Zürich. My grateful thanks are due to Prof. Dr. E. A. THOMAS of the Department of Botany, University of Zürich, under whose guidance the present work was done. I am indebted to Dr. ERNST ROMANN, Director of the Kantonales Laboratorium for providing facilities, for his interest and encouragement. It is a pleasure to acknowl- edge the Amt für Gewässerschutz und Wasserbau des Kantons Zürich, Schweizerische Meteorologische ZeHtralaHstalt, Gas- und Wasserwerk der Stadt Winterthur and the authorities of the Eidgenössisches Amt für Wasserwirtschaft, Bern, for their assistaHce and information contributing to the research work of the survey. I am grateful to Prof. Dr. H. WANNER, Director of the Institut für AllgemeiHe Jahrgang 115 H. RAI. River Töss and its Underground Water Stream

Botanik, University of Zürich, for critically goiHg through the manuscript and making valuable suggestions. And last but not least, my thaHks are due to Messrs. W. SCHNEEBELt, M. SPRING, P. LEUMANN and all personnel of the Laboratorium des Kantonschemikers for their valuable assistance during the survey.

Research Problem

Present publicity for water protection has made a large majority of the population aware of the necessity to protect the waters. Expansion iH number and variety of commercial production for urban, industrial and agricultural use has intensified the water quality control problem. Chemical industries, organic and inorganic, have expanded more rapidly than the population, their wastes frequeHtly beiHg unlike anythiHg found in nature. Past experience in coHventional waste treatment provides insufficient guidance for effective control of waste water from: textile, plastic, rubber, dye, detergeHt and maHy other petrochemical productions. The heavy use of synthetic organics for agricultural purposes is reflected in the appearance of such chemicals in streams receiviHg farmland drainage. CoHcentratioHs as low as one part iH a billion of some chemicals can cause such water damage as change in taste and odour, off-flavour in fish, toxicity to fish, ion-exchaHge damage, foamiHg, interference with oxygen transfer and interference with water-treatment processes. Toxicity to humans too is a conceivable effect of such pollutioH. IH this country a great number of waste-water treatment plants have come iHto operation. Although waters beloHg to the KantoHs, the scientific personnel in all the Kantons is understaffed and consequeHtly it is impossible to effect and maintain the necessary periodic coHtrol of the water and check the effectiveness of the purification systems. The most importaHt basic requirements for further establishmeHt of water protection in SwitzerlaHd are therefore missing. The Töss is a typical example of a river whose surface water sinks iHto the ground over loHg stretches, according to its ground water aHd surface water levels. At many places aloHg this river the underground water has to be utilized for drinking purposes. This river is heavily polluted downstream from the city of Winterthur to the point of its confluence with the River Rhein at Tössegg, siHce, as late as the Spring of 1966, there was only one mechaHical waste water treatment plant for the city of Winterthur. But duriHg the summer of 1966 an activated sludge treatment unit was added at Hard to the existiHg waste water treatment plant for the city of Winterthur. This raises the questions : a) in what way will this activated sludge process for waste water purification affect the saHitation of the River Töss; b) what other bigger or lesser sources of water contamiHatioH iH the catchment area of the river have to be eliminated until a satisfactory sanitation is reached; c) whether the endaHgered uHderground water stream of this river valley can, on the whole, be considered safe. 4 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

Research Program

To answer these questions, the following studies were carried out:

a) before starting operatioH of the activated sludge treatment plant at Winterthur, samples were collected from the Steigmühle (upper course) to its poiHt of confluence at Tössegg with the river Rhein; these were then thoroughly studied; b) over the same stretch of the river regular studies were carried out after starting the biological purificatioH operatioH at WiHterthur-Hard; c) diurnal variations of the quality and quantity of the sewage treatmeHt plaHt at differeHt stages of the treatment process were examined and the influence of the Winterthur sewage treatment plant effluent on the River Töss water was studied at different seasons and different water levels.

Regular research on other sources of contamination was done, with special attention to the polluted tributaries and the effluent of the Rorbas sewage treatment plant, as these contaminants caH materially alter the normal state of the river. FiHally the River Rhein, above and below the confluence of the Töss, was also regularly stIdied to ascertain the influence of the polluted Töss on the less polluted Rhein.

Description of the River Tss Basin

Physiography

The main physical features are indicated in Fig. 1. The river originates from two differeHt sources (Vordere and Hintere Töss), one west of the Welschenberg, at an altitude of 1240 m above sea level, and the other south of the SchiHdelberg, at an

500—

2.1Km 450

0 400® F- r-

350—

5 K m.

300 18 21 212 I 25 126/2171 28/291 1 6 2 3 STATIONS

Fig. 2. Profile of River Töss from Winterthur to Tössegg. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 5 altitude of 1120 In above sea level (Landeskarte der Schweiz, 1 : 25000, Blatt 1051, 1071 aHd 1072). These sources have very steep flows for 3 to 4 km, before their point of coHflueHce at Töss-Scheide, at an altitude of 794 m above sea level. From Töss- Scheide to Tössegg the poiHt of confluence with the River RheiH, the river is 54.2 kin loHg. It enters the state of Zürich at the south-easterH limits aHd runs diagonally towards the northern limits of the state, where it flows into the River Rhein. The river Töss is classified as a middle European pre-alpiHe river (FRÜH, 1930 and 1935). Throughout the year the river is fed almost entirely by raiH, aHd shows a quick increase in level in spring, during the thunderstorms and due to the melting of snow. It is characterized by its big differences between high and low levels. The low water levels occur iH late summer and from autumn through the winter, whereas the high water levels usually are due to summer rains. The differences between high and low water levels are even more effective due to the geological character of the catchment area, which is mainly very little permeable to water. The average fall of the river is 8.27%, but the fall is not eveHly distributed over the leHgth of the river. BetweeH Töss-Scheide and Steg there are rapids, and the average fall is between 11 aHd 19%, between Turbenthal and Sennhof it decreases to 7.6% and over the rest of the river it decreases to 4% (Fig. 2).

River Discharge

Flow data is tabulated in Table 1 aHd is illustrated iH Fig. 3. The mountain torrent character of the Töss is clearly demonstrated by the big variation in the water levels. Lowest flow measured was 0.8 m 3/sec. iH the lowest part of the river (Statistisches

o o MONTHLY AVERAGES (1967-68) Fig. 3. Average Rate of Flow in the ® AVERAGE FLOW ON THE DAY OF SAMPLING. River Töss Gauged in the Neften- x--%MONTHLY AVERAGES (1921-67 ) bach. 1 1 I I I 1 I I 1 I 1 MAMJ JASON D J F 6 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

Table 1. Discharge in the River Töss (m 3/sec.) Gauged in the Töss at Neftenbach, 1967/68

Monthly Monthly Average Discharge on Average Maximum the Day of Sampling

Date 1967 l. 3. 67 14. 3. 67 March 12.4 45.0 10.4

Date 1967 24. 4.67 12. 4.67 April 7.92 16.8 7.65

Date 1967 31. 5.67 17. 5.67 May 6.41 27.0 4.84 Date 1967 15. 6. 67 13. 6. 67 June 13.6 48.0 11.5 Date 1967 15. 7.67 5. 7.67 July 5.99 36.0 9.5

Date 1967 2. 8.67 8. 8.67 August 3.51 88.0 3.5

Date 1967 10. 9.67 8. 9.67 September 8.60 60.0 2.68

Date 1967 18. 10. 67 11. 10. 67 October 3.35 9.l 3.5

Date 1967 17.11.67 7.11.67 November 3.08 13.8 2.68 Date 1967 23.12.67 12.12.67 December 5.09 48.0 2.68

Date 1968 15. l.68 3. l.68 January 11.9 35.3 4.52 Date 1968 15. 2. 68 6. 2. 68 February 14.0 22.l 8.47 Average 7.98 5.99

Jahrbuch der Schweiz 1929, p. 9) and the highest rate of flow of 400 m 3/sec. was recorded in the year 1876 near Rorbas. The average river discharge during the year 1966 was 10.5 m3/sec. whereas duriHg the year 1967 it was 7.67 m 3/sec. The average rate of flow duriHg 1921-1967 for a 47 years period was found to be 7.57 m3/sec. The high rate of flow in the Töss can be recorded iH aHy seasoH, specially after heavy raiHs. The constant high water during spriHg season can be attributed to the slow meltiHg of the snow. During the period of research 1967-1968, in the late autumH aHd duriHg the winter moHths, the average monthly flow was lower than expected. Fig. 3 clearly shows the difference iH the average rate of flow on the days of sampling and the average flow for 1967-1968, as compared to the monthly average flow for the period 1921 to 1967. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 7

Ratio of Töss Water to the Effluent from Winterthur Sewage Treatment Plant – 1967/68 Discharge ms/sec. Ratio Töss at Effluent Winterthur Neftenbach sewage treatment plant Yearly average (during the research period and as measured on the day of sampling) 5.99 0.61 l:9.8 Low flow from August to December 1967 (average) 3.01 0.51 l:6 Lowest flow 2.68 0.38 l:7

Actually out of 0.61 m 3/sec. of the affluent discharge from WiHterthur sewage treatment plant a very small quantity of the mechanically treated sewage is discharged into the river after mixing with biologically treated effluent. During the months of October, November and December 1967 all the sewage that flowed into the treatment plant went through the activated sludge (biological) treatment uHit.

Catchment

The catchment of the River Töss covers an area of 429 km 2 . The land area contributing the major part of runoff of the river is contained within the state of Zürich. The catchmeHt area of the river covers almost three districts: Pfäffikon, Winterthur and Bülach. The ground covered by the catchment area is soft, coherent, greenish saHdstone of Miocene age. The basin of the River Töss comprises thirteeH major catchments. These are in downstream order:

Place of Approximate alti- Tributaries confluence tude of origin Fischbach Saland 656 m Steinenbach Tablet 922 m Reinisbach Sagi-Wila 805 m Chatzenbach Turbenthal 608 m Tobelbach Rikon 526 m Bäntalbach Au-Kollbrunn 772 m Wissenbach Kollbrunn 610 m Kempt Steigmühle 543 in Eulach Wölflingen 491 m Näfbach Pfungen 459 m Mülibach Neu-Pfungen 557 m Wildbach Rorbas 508 m Tüfenbach Feldhof 613 m

Fig. 1 illustrates their areas aHd the order in which they join the river. The Eulach is the biggest aHd in fact the most importaHt single tributary of the river under study.

Precipitation

Heavy precipitation on the highest points of the escarpmeHt amounts to as much as 1594 mm a year. At lower altitudes the precipitation is comparatively less and 8 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 on the lowest part of the river basin, it is as low as 1119 mm a year. The yearly and monthly precipitation recorded at different meteorological stations in the catchment area of the Töss during the survey are preseHted in Table 2. September was the wettest moHth when greatest precipitations occurred and October was the driest with 33 to 61 mm precipitation. Climatological conditions on the dates of sampliHg are shown in Table 3. In the catchment area of this river the population has increased by about 32% from the year 1950 to 1960. From 1930 to 1960 the number of houses increased from 13 549 to 19 225, the number of households increased from 24 065 to 37 287 and the population increased from 93 075 to 126 834. About 92% of the land area is productive out of which 60% is without forest and 32% with forest and only 8% of the area in the catchment is unproductive (Statistisches Handbuch des Kantons Zürich, 1964). At present there are approximately 165 factories and 271 industries functioHing in the area of Winterthur alone (which is the largest and most important community in the catchmeHt area of the river) as compared with 110 industries and factories during the year 1935-1936 (Statistisches Handbuch des KaHtons Zürich, 1964).

Sources of Pollution

The following are the types of pollution which have been encountered in this survey:

I. Sewage Pollution

a) Winterthur sewage treatment plant is situated between Spinnerei Hard (Station 25) and Neftenbach (Station 26/27) on the left bank of the River Töss. The plant has a capacity to treat 1700 l/sec of sewage iH dry season and 2250 l/sec of sewage during high water level (see map showing drainage area). b) Rorbas sewage treatment plant is situated between Rorbas (Station 30) and Tössegg (Station 31) on the right bank of the Töss. It has a capacity to serve 6500 inhabitants refuse and 2500 equivalent industrial refuse i. e. 72 l/sec (Dry Weather Flow) and during wet seasoH 2161/sec.

II. Incidental Pollution

a) Indiscriminate discharge of laundry effluents coupled with highly polluting substances carried by stream water draining during heavy rain from the densely built up areas – specially those localities which are not provided with sewage works facilities. The condition at Pfungen reflects this situatioH very well. b) A poorly designed and badly controlled compost installatioH. During summer, raining season particularly, the seepage from this iHstallation had a deleterious effect on the River Töss. Table 2. Monthly Precipitation (mm) in Different Catchment AIeas of River Töss

Meteorological Altitude March Apr. May June July Aug. Sep. Oct. Nov. Dec. Jan. Feb. Yearly Stations m 1967 1968 Precipitation Bauma 627 158 86 171 227 131 100 205 56 50 101 207 90 1582 Sternenberg 880 156 78 182 206 137 101 218 61 47 111 220 77 1594 Kollbrunn 490 125 39 131 134 140 115 172 43 72 89 171 85 1316 Effretikon 512 106 30 133 128 126 99 172 33 61 71 136 71 1166 Winterthur 490 96 27 103 121 109 141 136 38 63 79 136 70 1119

Table 3. Climatological Conditions on the Day of Sampling

Air Temperature °C Precipitation Date Average Minimum Maximum in mm Sunshine Remarks 1967 14. 3. 2.6 0.0 6.9 6.1 Ground became white with hoar frost 12. 4. 9.9 2.l 17.7 10.5 Ground became white with hoar frost 17. 5. 13.2 9.3 19.0 50 1.6 Thunderstorm and lightning 13. 6. 10.7 6.l 17.0 - 8.7 Thunderstorm and lightning 5. 7. 18.5 14.1 24.6 8.6 Thunderstorm and lightning 8. 8. 19.2 11.5 28.4 - 10.0 Heavy dew on the ground 8. 9. 10.0 6.2 13.3 123 0.l Fog and rain 11. 10. 12.9 7.0 21.5 - 8.6 Dew on the ground 7. 11. 4.9 l.7 11.5 7.7 Fog, ground became white with hoar frost 12. 12. -7.6 -8.2 -6.4 Ground covered with snow 1968 3. 1. -2.3 -3.4 l.9 50 l.5 Hale, ground covered with snow 6. 2. 0.7 -l.5 2.6 17 - Hale, rain, thunderstorm and fog Sunshine 0.l = 6 minutes. 10 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

c) Intensive farming. A considerable quantity of wet compost produced from farm wastes was used during the year. d) The random defecatory habits of some of the rural inhabitants.

III. Communities Surrounding the River Töss and the River Rhein

a) Embrach and Ober-Embrach: Along the stretch of Tiff Bach there is no sewage treatment plant and not even pipes are laid for the disposal of sewage. As such, all sewage from the surrounding areas of Sädel and Edlibuck is being put iHto Tüfbach, which in turn goes into Wildbach downstream from Ober-Embrach. Ober-Embrach and Embrach have a system of sewers in the townships themselves but all the untreated effluent from the household septic tanks surrounding this area is directly put into Wildbach. b) Lufingen-Augwil: In this area there is a good network of sewage pipes. The village of Augwil even has a sewage oxidation pond for the treatmeHt of sewage of the village and surrounding areas, but Ho coHventional treatment plaHt. The plant empties its effluent into the Marchlenbach which joins the Wildbach. The sewage from the village of Vorder-Marchlen, Rain, Hinter-Marchlen, Gsteig, Mühle, Lufin- geH and their surrounding areas goes untreated – effluent from the household septic tanks – into the Wildbach upstream from Embrach. c) Dättlikon: The village and its surrouHdiHg areas have a good sewer system without a treatmeHt plant and the sewage collected through pipes is directly emptied into a small stream through which it goes into the River Töss upstream from Blindensteg. d) Pfungen: The eHtire sewage of the village of Pfungen and its surrounding commuHities is Hot yet treated. The sewage is collected from this area by means of a net work of pipes and emptied into the Töss. A complete activated sludge treatment plaHt is under project for these commuHities. e) Neftenbach: The communities of NefteHbach, Riet, Rotfarb, HettliHgen and their surroundiHg areas pour their sewage into the Näfbach and this in turn goes into the Töss downstream from the Neftenbach sampling station. f) Eglisau: The communities surrounding the areas of Seglingen on the left bank and Wiler and Eigen oH the right bank of the Rhein have a good network of sewage pipes but Ho sewage treatment plant. The raw sewage – effluent from the household septic taHks – is collected through these pipes and directly poured into the Rhein 1/4 km downstream from Eglisau sampling station. The sewage from TössriederH, which is about 21/4 km upstream from Eglisau on the left bank of the Rhein, also goes untreated directly into the Rhein. Besides this, there are some industries and households on both banks of the Rhein which pour their waste directly into the river at different places, depending on their locatioH. g) Tössegg: The commuHities of Teufen and the area upstream from Tössegg- Rhein on the left bank, empty their waste iHto a small creek, which in turn empties into the Rhein about 3/4 km upstream from Tössegg-Rhein. The village of Schloss aHd its surroundiHg areas pour their sewage efflueHts – household septic tanks – into the Tefenbach without aHy treatment. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 11

h) Langwiesenbach and Flaacherbach: The raw sewage from the commuHities of Gräslikon, Buch, Wiler goes into the Langwiesenbach which empties into the Flaacherbach. The Flaacherbach also collects sewage from the village of Volken, Flaach, Berg aHd their surrouHdiHg areas prior to eHtering the RheiH on the left bank, upstream from Rüdlingen sampling station.

Material and Methods

After a prelimiHary survey of the River Töss teH sampling statioHs were chosen along the length of the river from Winterthur to Tössegg-Töss. Besides these sampliHg statioHs two sewage treatment plant efflueHts were sampled as the river receives their effluents. Further, five tributaries iH this stretch of the river were sampled aHd five sampliHg stations along the Rhein were also selected for this study (Fig. 1). These sampling stations were visited once a month when simple determinatioHs of temperature and pH were made. "Snap" water samples were collected in 1500 cc bottles and samples for bacteriological examination were collected and transported to the laboratory for detailed examiHation. Determinations were made of the amounts of dissolved oxygen, biochemical oxygeH demand, ammonia, Hitrate, nitrite, phosphate (dissolved aHd total), hardness (CaCO 3 and total), chloride, detergents (Anionic), KMnO 4-consumptioH, iroH, total suspended matter, hydrogen ioH concentration, temperature and total volatile and fixed residue. Determinations of staHdard plate couHt of bacteria at 20° C and coliform bacteria at 37° C± 1 ° C were also regularly carried out.

Methods of Chemical Analysis

For carbonate hardness aHd oxygen consumption the methods were those recommended by the Schweizerisches Lebensmittelbuch (1964) in their specification for Water for Domestic Supplies, total volatile and fixed residue as recommended by HöLL, 1968, phosphate, with Molybdate-Wolfram reageHt after CZENSNY (1938), total phosphates after residue oH volatilization aHd then as phosphate, nitrate with sodium-salicylate after MÜLLER and WIEDEMANN (1955), nitrite with diazone reagent after GRIESS-ILOSVAY-LUNGE (TREADWELL, 1949), ammoHia nitrogen as the method recommended in the Deutsches EinheitsverfahreH (1960), chloride after SCHNEEBELI and STAUB (1945), dissolved oxygen after WINKLER (OHLE, 1953), biochemical oxygen demand-5 days as recommended by the AmericaH Public Health Association in Standard Methods for the Examination of Water and Wastewater (1962), detergeHts (aHionic) after EPTON (1948) modified, iron (Fe +++) as recom- meHded in Deutsches EiHheitsverfahren zur Wasseruntersuchung-E 1 (modified), and total suspended material using MF-500 as described and recommended in Eidg. Kommission für RichtlinieH für die Probenahme and die NormuHg von Wasser- untersuchungsmethoden, 1966. 12 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

Methods of Bacteriological Analysis

The methods used were those recommended by the American Public Health Association in Standard Methods for the AHalysis of Water and Wastewater (1962). "Total Plate Count" refers to the number of colonies of micro-organisms on the poured plate of M-PH medium (Milk-protein hydrolysate agar) after 5 days incubation at 20°C±1°C. The count is relative, and can obviously refer only to organisms capable of growing uHder exactly defiHed test conditioHs. The coli and coliform organisms refer to the number of colonies of bacteria oH the poured plate of Bacto-EHdo Agar dehydrated as recommeHded by the American Public Health Association in StaHdard Methods (1962). The count can obviously refer only to the interpretation of coliform colonies given in the above refereHce and capable of growing uHder exactly defiHed conditions of the test. For each of the components analysed the „Fliessstreckenmittel" (WASER et al., 1943; and WASER and THOMAS, 1944) was calculated and shown in the Tables in the text.

Sampling Stations

Bearing in mind the objects of the study and what was already known about the area of the river under study, sampling stations were choseH as follows (Fig. 1):

River Töss

Station 18 – Krone. From an old bridge between 300 m above Neumühle and 50 m dowHstream Mittl. Chrebsbach (downstream Steigmühle).

Station 21 – Brosi. 2.1 km dowHstream Station 18 near Grafenstein village. From the Friedhofstrasse/Schlachthofbrücke.

Station 22 – Wespimühle. 1.7 km dowHstream Station 21 and 500 m above the confluence of the Eulach with the Töss, from the Wespimühlebriicke on the Töss near the Wespimühle industry.

Station 25 – SpiHnerei Hard. 1.53 km downstream Station 22 and about 1 km downstream the confluence of the Eulach and the Töss, aHd 500 in upstream from the point of the effluent outfall from the Winterthur sewage treatment plaHt at Hard. Samples were drawn from the road bridge on the River Töss near WideH.

Station 26/27 – Neftenbach (Left and Right). 1.93 km downstream from StatioH 25, from the Holzbrücke Neftenbach-Pfungen and above 1 km downstream from the point of the effluent outfall of the WiHterthur sewage treatment plant. Water samples were collected from both the left and the right banks of the river at this point. On biological examination the growth on the stones and shore revealed no signs of Sphaerotilus sp. On the left bank the water was always less turbid and less polluted in comparison to the water conditions on the right bank. In one Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 13

or two instaHces only slight growth of Sphaerotilus sp. was observed on the right bank of the river at this place. It is interesting to note here, that on the right bank, there was often some foam and debris with vegetable aHd paper refuse floating on the surface of the water.

Station 28 – Pfungen. 1.4 km downstream from NefteHbach. Samples were collected from the road bridge on the River Töss, which conHects Neu-Pfungen aHd Wurmetshalden. The river was badly polluted at this point because the areas surrounding this place had no sewage treatment plaHt and untreated sewage – effluent from the household septic tanks – was let straight iHto the river. About 500 m upstream from this poiHt the water of the river is diverted into the caHal. Here the river almost always carried very little water and was very much influeHced by the local factors.

Station 29 – Pfungen-Canal. This point is just opposite from StatioH 28 on the Pfungen Canal which runs parallel to the river after originatiHg about 500 m upstream from the River Töss. The samples were collected before the caHal enters the industry at Neu-PfungeH. On biological examiHation of the samples from this place also showed no sigHs of Sphaerotilus sp.

Station 30 – Rorbas-Töss. This station is situated 5.5 km downstream from Pfungen, 2 km above the Rorbas sewage treatment plant effluent outfall, and 250 m above the conflueHce of the Wildbach and the Töss. Samples were collected from the Irchelstrasse (Rorbas-Freienstein) bridge on the Töss, in the middle of the running stream and at mid-depth. During dry spells the river had more flow towards the right bank and remained rather clear throughout the year.

Station 31 – Tössegg-Töss. This point is situated 3.75 km dowHstream from Station 30 and 1.75 km downstream from the efflueHt of the Rorbas sewage treatment plant. The samples were collected from the bridge on the River Töss at Tössegg, about 10 m upstream from the confluence of the Töss with the Rhein, in the middle of the running stream and at mid-depth. The river here is always a little turbid in appearance and has a good flow and at times vegetable and debris was seen floating on the surface. Upstream from this statioH another tributary, the Tilfenbach, empties itself into the Töss.

Tributaries of River Töss

Station 1 – Eulach. It originates at about 650 m above sea level and empties iHto the Töss at about 410 m above sea level near WülfliHgeH. It is oHe of the biggest tributaries aHd is about 15.5 km long before its confluence with the Töss. The average rate of discharge was about 0.83 m3/sec. The samples were collected from the Eulach bridge, before its confluence with the Töss.

Station 2 – Näfbach. This is the second biggest tributary of the Töss in the stretch of the river under study. It originates from two sources, oHe near Berg at 471 m above sea level aHd the other from 465 m above sea level near about Reutlingen. 14 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

It empties itself into the Töss about 50 m downstream from the Neftenbach sampling station. Samples were collected from the Näfbach bridge, before its confluence with the Töss.

Station 3 – Mülibach. After originating from about 640 m above sea level near the forest of Tüngeli in the southern part of the catchment area of the River Töss in Chomberg, it joins the River Töss downstream from Station 28. The samples were collected from the Mülibach bridge, before it enters the Töss.

Station 4 – Wildbach. It origiHates near Birchwil at about 508 m above sea level. It flows diagonally north-northwest and empties itself into the river at an altitude of 361 m above sea level, dowHstream from the Rorbas sampling statioH. The samples were collected from the road bridge, before its coHflueHce with the River Töss.

Station 5 – Tüfenbach. It is the smallest of the tributaries under study. It originates at an altitude of 613 m above sea level near the village of StreHgenbrunnen and runs in an east-westerly directioH. It joins the River Töss at about 1 km above Tössegg-Töss sampling station. Samples were drawH from the TüfeHbach about 100 in before its confluence with the Töss.

River Rhein

Stations 8 and 9 – Rüdlingen. Two sampling points, one on the left and the other on the right baHk of the Rhein, were chosen to get representative samples to study the conditioH of the River Rhein before entry of the River Töss at Tössegg. Samples were drawH from the road bridge on the RheiH at Rüdlingen.

Stations 10 and 11 – Eglisau. Two sampliHg points, one on the left and the other on the right bank, were selected at this place to study the influence of polluted Töss water on the River Rhein. Samples were drawn from the road bridge over the Rhein at Eglisau.

Station 12 – Tössegg-RheiH. This sampliHg station is situated at about 50 m upstream from the confluence of the Töss with the Rhein. Regular sampling was done at this point to determine the iHfluence, if aHy, of incidental pollution by the communities of Teufen and its surroundings, whose untreated sewage – effluents from household septic tanks – is dumped into the River Rhein about 750 m upstream from this station. Samples were collected from the left baHk of the river.

Sewage Treatment Plant Effluents

Station 6 – Winterthur Sewage TreatmeHt Plant EfflueHt. Regular analysis of the effluent of this plant, before its entry into the Töss, was carried out to study the effluents quality and quantity and its influence on the sanitatioH of the river.

StatioH 7 – Rorbas Sewage Treatment Plant Effluent. Samples of this plant effluent were also aHalysed for the same purpose as at Station 6 above. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 15

Presentation of Data

A. Physical and Chemical Analyses

The main object of the physico-chemical analysis of a river is to determine its degree of pollution. This pollution maHifests itself either by its action on the elements existing in the water (dissolved oxygen etc.) or by giviHg rise to substances which are not previously present (ammonia, nitrates, etc.). The staHdard criteria which may be taken into consideratioH in the case of pollution by orgaHic matter are:

1. Dissolved oxygen (D.O.). 2. Biochemical oxygeH demand after 5 days (B.O.D.5). 3. KMnO4-consumption. 4. Nitrate. 5. Nitrite. 6. Ammonia.

All these tests were carried out on each of the samples collected during this study. One test has further been added to this research, i. e. the study of the dissolved oxygen consumption curves and this test will be discussed under Dissolved Oxygen.

1. Temperature

The direct effect of temperature as an enviroHmental factor is difficult to assess because in stream enviroHments it is often linked with the speed of the current aHd type of bed. Obviously it will be lower in a narrow shady valley than where the course crosses a plain fully exposed to the sun. Temperature also has an indirect effect, the solubility of oxygen in water being reduced by iHcreases in temperature. It plays a vital role in chemical and biochemical reaction and is an important factor influencing self-purificatioH in a stream. Bacteria and other micro-organisms affecting the breakdown of organic matter in streams are profoundly influenced by temperature changes and are more active at higher thaH at lower temperatures. The rate of oxidatioH of organic matter is therefore much greater during the summer than duriHg the winter. This means that self-purification will be more rapid and the stream will recover from the effects of organic pollution over a shorter period during the warmer months of the year thaH in the cold days of wiHter. It must be stressed, however, that since warm water con- taiHs less dissolved oxygen than cold water, a heavy pollution load is more likely to de-oxygenate a stream and promote uHdesirable septic conditions in summer than iH winter. Anaerobic decomposition is also profoundly affected by temperature chaHges. Temperature of a stream is a measure of the actions and interactions of a wide variety of factors. The temperatures appear in Table 4. It will be clearly seen that there was a Hotable variation in the range of temperatures. The average summer and winter temperatures differed by about 14°C. These increased from Station 18 to the conflueHce at Station 16 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

31. The average at Station 26/27 was approximately 3°C higher and at Station 31 approximately 4°C higher than at Station 18. The average air and Töss water temperatures have been plotted in Fig. 4. Some idea of correlation between air and water temperatures can be gathered from the data collected on the days of sampliHg. Minimum water temperatures were approximately 10°C higher than the correspoHd- ing minimum air temperatures,. while maximum water temperatures were approximately 3°C lower than the corresponding maximum air temperatures.

0 MAMJJ ASON N

AVERAGE AIR TEMP. X--(AVERAGE WATER TEMP Fig. 4. Average Air and River Töss Water Temperature.

2. pH-values

The pH of the water has effects in its own right, aHd pH values of below 5 units or much above 9 are definitely harmful to most animals (THOMAS, 1968). But within the normal range pH has considerable influence on some poisons. Ammonia is much more toxic in alkaline than in acid water since its unionised form (NH3) is more poisonous than the NH4+. Conversely cyanide is more poisonous in acid than in alkaline water and the same applies to sulphides which form the more poisoHous gas, sulphuretted hydrogen (H2S), in acid water (DOUDOROFF and KATZ, 1950). There was a great fish dying on October 16, 1964 in the area of KollbruHH-Senn- hof. Half the trout were found dead and the rest were searching for fresh water Hear the inflows of the tributaries. The fish were uHresponsive and did not flee wheH approached. Their skin was dark with irregular white patches. The mucous membrane covering of some of the fish was disfigured. Many had bleeding mouths and skulls. These injuries probably happened when the fish were fleeiHg from the first poisonous wave. Near the inflow of the Weissenbach into the Töss on the left side, in a puddle, the pH measured was 9.9. From the textile industry highly alkaline waste water was regularly being directly let into the River Töss. On the day of the fish dying Table 4. Temperature (°C) in Töss Water

1967 1968 oä a No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. l. 6. 2. AveIage

18 Krone 4.4 6.2 11.7 9.4 14.0 12.8 11.6 9.9 6.7 l.l ** 2.4 3.8 7.83 21 Brosi 4.5 6.6 11.6 9.3 14.0 12.9 12.0 10.6 7.5 2.9** 4.3 4.2 8.36 22 Wespimühle 4.5 6.8 12.1 9.4 14.2 14.3 13.l 11.l 6.5 1.0** 2.7 3.7 8.28 25 Spinnerei Hard 4.9 7.3 12.5 9.7 15.0 15.0 12.5 11.l 6.4 1.7** 2.9 3.8 8.56 26 Neftenbach (L) 6.2 9.5 13.4 10.7 15.0 15.9 12.9 12.4 9.l 4.9 4.8 ** 5.l 9.99 27 Neftenbach (R) 6.6 14.4 14.0 11.0 15.5 17.4 12.8 13.6 10.2 4.8 ** 4.8 ** 5.3 10.86

28 Pfungen-Töss 6.4 10.l 15.0 11.1 16.2 19.8 14.0 13.3 10.0 2.9** 4.5 4.8 10.67 1?-4- 29 Pfungen-Canal 6.4 9.8 14.l 11.2 15.8 17.4 13.5 13.3 9.7 4.2** 4.7 5.1 10.43 30 Rorbas 7.0 11.7 14.1 10.7 16.5 18.8 13.5 13.3 9.1 3.2** 4.4 4.7 10.58 CD 31 Tössegg 7.2 12.2 15.6 13.3 17.8 19.2 13.8 13.8 9.l 2.8 ** 3.9 4.4 11.09 H o= Average 5.79 9.46 13.41 10.58. 15.4 16.35 12.97 12.24 8.43 2.95 3.94 4.49 9.66 aa.

Table 5. pH in Töss Water a a C 1967 1968 öc No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. l. 6. 2. Average a a a 18 Krone 8.05 8.0 8.0 8.2 8.2 8.l 8.2 8.1 8.l 8.l 8.15 8.l 8.10 a. 21 Brosi 8.2 8.0 8.0 8.2 8.2 7.85 7.9 7.9 7.75 ** 7.8 7.9 8.l 7.98 w 8.15 8.05** 8.1 8.2 8.2 8.17 22 Wespimühle 8.2 8.l 8.15 8.2 8.3 8.25 8.2 9 25 Spinnerei Hard 8.3 8.l 8.2 8.3 8.35 8.2 8.2 8.2 8.2 8.2 8.25 8.25 8.23

26 Neftenbach (L) 8.05 7.8 7.9 8.05 8.0 7.7 7.75 7.7** 7.75 7.7* 7.8 8.0 7.85 CD 27 Neftenbach (R) 8.15 8.15 7.9 8.l 8.l 7.8 7.8 ** 7.8 ** 7.8 ** 7.9 8.05 8.0 7.96 28 Pfungen-Töss 8.2 8.2 8.4 8.2 8.15 7.8 7.75 ** 8.25 7.85 7.85 7.8 8.2 8.05 29 Pfungen-Canal 8.15 8.l 7.9 8.2 8.15 7.85 7.8 ** 7.95 8.05 7.9 8.2 8.2 8.03 30 Rorbas 8.15 8.3 7.9 8.15 8.2 7.85 7.95 7.95 7.9 8.0 8.l 8.2 8.05 31 Tössegg 8.l 8.2 8.0 8.15 8.2 7.8 8.l 8.l 8.l 8.l 8.2 8.2 8.l Average 8.16 8.l 8.04 8.18 8.19 7.92 7.97 8.01 7.96 7.97 8.07 8.15 8.05

Maximum. Minimum. 18 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 the alkalinity was very high. The dead aHd the injured trout clearly indicated the symptoms of very high pH (persoHal commuHicatioH, Prof. E. A. THOMAS). Many important chemical and biochemical reactions oHly take place at a certain pH value or within a narrow pH range. Consequently the concept of pH is of great practical importance, aHd the control of pH is particularly important in the chemical flocculation of iHdustrial waste aHd anaerobic digestion of sewage sludge aHd industrial waste. The results of pH measuremeHts are listed in Table 5. During the period under study there was a clear tendeHcy for values to iHcrease with a distance downstream of the effluent of the Winterthur sewage treatment plant. The range of values upstream to the Winterthur effluent was between 7.75 to 8.35, while dowHstream of the effluent it was 7.7 to 8.4 and at Station 31 the range of values was 7.8 to 8.2. DuriHg May the maxima at Station 28 resulted from uncontrolled sewage discharges from the communities surrounding that area. IH the River Töss the usual pH range, when decomposition and photosynthetic influences were largely inoperative, appeared to be between 7.9 aHd 8.2.

3. Carbonate and Total Hardness

HardHess is due mainly to the presence of bicarbonates, calcium and magnesium ("temporary" or "carbonate hardness") or to sulphates and chlorides of calcium and magnesium ("permanent" or noncarbonate hardness). The hardness of river water is of considerable significance in connection with the discharge of effluents containing certain toxic metallic ioHs to fishing streams. The water of the River Töss was hard. The average carboHate hardHess was found to vary between 275.2 mg/1 at Station 21 to 318.1 mg/I at Station 28. A very high concentratioH of carbonate hardness of 410.0 mg/l was recorded at Station 28 iH the moHth of December 1967. The reason for this was largely the reduction in flow and a proportionately greater effect of the sewage efflueHt outfalls in this area. The results are recorded in Table 6. There was a clear tendency of aH increase in values downstream of the discharge of the Winterthur sewage treatment plant effluent. The total hardness coHceHtration closely followed the pattern shown for carbonate hardness. The results are tabulated iH Table 7. DuriHg the period under study the hardness was induced by high flow and low flow of the river as indicated by the variations in the coHcentratioH of the hardness of the water. Maximum appeared at all statioHs during the period of low discharge (in the months of October, Novem- ber and December). Lowest hardness followed recession of the March rise aHd low concentrations extended into July. The seasonal variations of CaCO 3 are illustrated in Fig. 5 for the Station 21, StatioH 26/27 and Station 31. From these figures it appears that CaCO 3 was high during the winter half of the year and low duriHg the warmer half. CaCO 3 values were lower at Station 21 and the values increased near the source of sewage effluent outfall. There was little difference between the average values at Station 26/27 and Station 31. All the curves show marked seasonal fluctuations and run almost parallel to one another. w Table 6. Carbonate Hardness - CaCO 3 (mg/l) in Töss Water a- 1967 1968 w Average ao No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. l. 6. 2. 275.0 275.6 18 Krone 245.0 245.0 247.5 262.5 265.0 292.5 290.0 312.5 287.5 300.0 285.0 285.0 275.2 21 Brosi 255.0 245.0 262.5 265.0 257.5 280.0 282.5 287.5 305.0 292.5 285.0 280.0 276.8 22 Wespimühle 275.0 245.0 245.0 255.0 262.5 300.0 285.0 290.0 302.5 307.5 275.0 287.5 282.0 25 Spinnerei Hard 260.0 247.5 245.0 265.0 275.0 292.5 300.0 300.0 305.0 315.0 292.5 300.0 292.0 26 Neftenbach (Left) 270.0 265.0 275.0 277.5 265.0 297.5 325.0 317.5 315.0 302.5 295.0 295.0 295.6 27 Neftenbach (Right) 277.5 275.0 282.5 277.5 280.0 300.0 310.0 315.0 325.0 322.5 287.5 297.5 318.l 28 Pfungen-Töss 275.0 272.5 325.0 280.0 265.0 302.5 372.5 327.5 315.0 410.0 375.0 305.0 305.0 297.9 ,y 29 Pfungen-Canal 275.0 275.0 277.5 277.5 282.5 300.0 312.5 327.5 312.5 325.0 287.5 293.7 30 Rorbas 277.5 262.5 272.5 277.5 275.0 297.5 317.5 307.5 312.5 337.5 300.0 ^. 287.5 292.7 31 Tössegg 275.0 270.0 272.5 270.0 262.5 310.0 302.5 310.0 320.0 332.5 300.0 a o: 309.8 309.5 310.0 324.5 300.0 290.0 289.9 Average 268.5 260.3 270.5 270.8 269.0 297.3 m a

Total Harness mg/l in Töss Water Table 7. ä 1967 196 tro2 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. l. 6. 2. Average ö No. Sampling Stations 14. 3. 5 304.0 298.0 295.6 a 18 Krone 264.0 262.0 262.0 296.0 288.0 312.0 324.0 320.0 308.0. 310.0 314.0 304.0 295.3 21 BIosi 269.0 261.0 272.0 288.0 286.0 302.0 310.0 306.0 316.0 316.0 m 296.0 302.0 298.9 cö 22 Wespimühle 289.0 269.0 258.0 286.0 306.0 321.0 308.0 308.0 320.0 324.0 314.0 312.0 307.0 cn 25 Spinnerei Hard 279.0 272.0 260.0 298.0 306.0 320.0 340.0 322.0 334.0 328.0 324.0 328.0 322.0 319.7 26 Neftenbach (Left) 293.0 288.0 302.0 318.0 308.0 336.0 342.0 340.0 336.0 w 322.0 320.0 322.8 27 Neftenbach (Right) 295.0 303.0 298.0 308.0 316.0 336.0 348.0 342.0 336.0 350.0 386.0 330.0 342.5 28 Pfungen-Töss 297.0 289.0 330.0 308.0 302.0 358.0 372.0 344.0 382.0 412.0 342.0 322.0 324.4 29 Pfungen-Canal 295.0 294.0 298.0 312.0 328.0 340.0 344.0 342.0 332.0 344.0 340.0 326.0 322.8 30 Rorbas 296.0 288.0 300.0 312.0 318.0 334.0 346.0 336.0 334.0 344.0 338.0 322.0 323.5 31 Tössegg 307.0 295.0 312.0 312.0 304.0 342.0 350.0 336.0 336.0 328.0 315.8 315.25 Average 288.4 282.1 289.2 303.8 306.2 330.l 338.4 329.6 333.4 338.0 328.4

Maximum. Minimum. 20 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

Bicarbonate originates in the flow of waters throughout the earth and is usually produced by the action of carbonic acid oH lime stone. Bicarbonate concentrations tend to vary inversely to the rate of flow, as low discharges contain greater per- centages of grouHd water. This relationship was characteristic in the Töss (compare Fig. 3 and 5). Average concentrations of hardness tend to become greater with distance downstream, because of iHcreased eHtrance of grouHd water during low flow periods. SampliHg of tributary inflows and sewage plant effluents, which are more or less hard than the Töss (Table 28), seemingly induced the variation amoHg the intermediate stations. The major influence was exerted by the Winterthur sewage treatment plant effluent, and inflows of the Eulach aHd Näfbach with hardness concentrations markedly higher than the main streams.

mg/I 360 350.

340-

330-

320 - 310-

300-

290- 280-

270

260- 250 I I I I I I I I I I I MAMJJ ASONDJ F

mg/

340 •

330 CaCO3

320

310

300 STATION 26/27 290 \ STATION 31

280 :STATION 21

270 260 Fig. 5. Seasonal Variation of Hardness in the River Töss at 250 Brosi (21), Neftenbach (26/27) 240 and Tössegg-Töss (31). I I I 1 I I I 1 I I I M A M J JASON DJ F Table 8. Soluble PO 43- (mg/l) in Töss Water (unfiltered) w 1967 1968 6. 2. Average CIO No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. l.

0.60 0.40 0.64 t^ 18 Krone 0.16 0.28 0.62 0.31 0.13 l.10 1.20 0.90 0.80 l.20 0.28 0.12 0.27 21 Brosi 0.16 0.26 0.21 0.24 0.12 0.35 0.40 0.34 0.30 0.48 1.50 0.40 0.25 0.58 22 Wespimühle 0.18 0.27 0.62 0.24 0.15 l.30 0.70 0.60 0.80 1.40 0.40 0.20 0.68 25 Spinnerei Hard 0.16 0.30 0.88 0.36 0.16 l.40 1.10 0.80 1.00 l.50 l.00 1.98 26 Neftenbach (L) 0.30 0.90 2.10 0.70 0.45 3.50 3.00 2.30 4.00 4.00 5.00 3.50 1.50 3.41 27 Neftenbach (R) 0.80 2.20 4.60 l.40 l.00 5.00 4.50 6.50 5.00 10.00 8.00 l.00 4.14 28 Pfungen-Töss 0.80 2.10 4.65 l.30 l.20 3.40 5.50 2.80 9.00 2.50 0.90 2.78 ,^y 29 Pfungen-Canal 0.90 l.90 4.20 l.10 0.90 4.40 4.00 3.60 4.00 5.00 5.00 3.00 0.80 2.35 30 Rorbas 0.90 l.65 3.60 1.00 0.50 3.20 2.80 2.80 3.00 H 2.45 0.90 l.50 3.50 0.95 0.80 3.60 3.00 2.40 4.50 5.50 2.00 0.80 H 31 Tössegg o: 2.22 0.70 l.928 N Average 0.53 l.14 2.50 0.76 0.54 2.73 2.62 2.30 3.24 3.91 a a. cn

Table 9. Total Phosphates (PO 43- mg/l) in Töss Water 1968 1967 En 12. 12. 3. 1. 6. 2. Average No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. ö ä. l.5 l.4 0.6 0.45 0.94 ^ 18 Krone 0.2 0.38 1.0 0.8 0.6 l.4 1.5 l.5 l.2 0.8 0.3 0.25 0.49 21 Brosi 0.2 0.3 0.4 0.6 0.55 0.5 0.5 0.35 w l.4 2.0 0.5 0.3 0.84 m 22 Wespimühle 0.18 0.36 l.l 0.5 0.57 l.5 l.0 0.7 l.9 l.9 0.6 0.4 0.98 rn 25 Spinnerei Hard 0.24 0.45 l.2 0.6 0.55 l.6 1.3 l.1 5.5 4.0 2.0 l.0 2.82 26 Neftenbach (L) 0.48 l.15 2.5 3.75 l.0 5.0 4.5 3.0 8 10.0 8.0 4.0 3.0 5.44 27 Neftenbach (R) 1.8 5.0 6.5 4.0 3.0 7.0 6.0 7.0 18.0 18.0 18.0 2.0 7.66 28 Pfungen-Töss l.5 4.0 7.5 2.0 4.0 4.0 9.0 4.0 8.0 7.0 4.0 l.75 4.45 29 Pfungen-Canal l.4 2.3 5.5 3.0 3,5 6.0 5.0 6.0 8.0 7.0 3.5 1.75 3.85 30 Rorbas l.55 l.9 4.5 2.0 3.0 4.0 4.0 5.0 8.0 6.0 3.0 2.0 3.59 31 Tössegg l.45 l.9 4.25 2.0 3.0 4.0 3.5 4.0 5.61 3.65 l.29 3.106 Average 0.90 l.77 3.45 l.93 l.98 3.5 3.63 3.27 6.35

Maximum. Minimum. 22 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

4. Phosphate

Phosphate originates in soil formations (rare), in fertilizers and animal wastes, in faecal matter of aquatic aHimals, and in sewage and waste discharges. Growing use of detergents in recent years has increased phosphate content of domestic sewage. Phosphate compouHds of streams are derived from biological and chemical processes along the stream course. IHcreased surface runoff coHtributes to the phosphorus content of streams by introducing allochthonous phosphorus-containing substances. Although there is considerable longitudinal and seasonal fluctuation in content, there does not appear to be any great depletion of stream phosphorus such as in surface waters of lakes during growing seasoHs; this is due partly to mixing and partly to the normally greater proportion of water to phytoplankton. Phosphorus appears no more essential to algal developmeHt than Hitrogen, but it is usually more critical in natural waters as its sources of sustenance are considerably more limited.

mg/I 6- 3- ® PO4-Solu.

5—

4—

3—

2—

STATION 26/27

STATION 31

STATION 21 I I I I I I I I J J A SONDJ F

•

Fig. 6. Seasonal Variation of Phosphate in the River Töss at Brosi (21), Neftenbach (26/27) and Tössegg-Töss (31). Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 23

The average concentration of soluble phosphate over the entire sampled reach varied between 0.27 and 4.14 mg/1. The highest recorded average concentration was below the WiHterthur sewage outfall at Station 28. In the upper reaches of the river the aveiage concentration varied between 0.27 aHd 0.68 mg/l, and at Station 31 it was 2.45 mg/l. The results of direct phosphate and total phosphates are tabulated in Tables 8 and 9 respectively. The study of the tables will disclose that a definite annual pattern became established at all the stations dependiHg on the amount of river discharge on the day of sampliHg. Thus, the river discharge appeared to be the major factor governiHg phosphate concentrations iH the river, over the entire sampled reach (compare Fig. 3 and 6). Higher concentrations appeared at all statioHs during the dry period, whereas the lower values were recorded duriHg the wet period. The total phosphate concentrations closely followed the pattern shown for the direct (soluble) phosphate (Fig. 6). The phosphate was markedly more concentrated at Station 28. There was a considerable increase iH phosphate concentration below the Winterthur sewage treatment plant effluent and an appreciable decrease in the concentratioH with distance dowHstream to the coHfluence at Tössegg with the River Rhein, where the river still showed a substantial level. Fig 6 illustrates the seasonal variations of soluble and total phosphates at the three different statioHs in the River Töss: Station 21, upstream of the Winterthur sewage treatment plant effluent, Station 26/27, about 1 km below the Winterthur effluent and Station 31, just prior to the confluence of the River Töss with the Rhein.

5. Dissolved Oxygen (D. O.)

Oxygen is supplied to the water by absorption from the atmosphere and photosynthesis by aquatic plaHt life. The rate of absorption from air depends oH a number of factors: air water temperature, altitude, turbulence, amount of surface exposure per volume of water, percentage of saturation in solution, etc. Oxygen is more soluble in cold water, but warm water coHditions usually permit absorptions of greater quaHtities, as the rate of diffusion is enhanced. TurbuleHce providing air contact with greater surface area per volume iHcreases the rate of oxygen absorption. Oxygen is a waste product of photosynthesis, but daily supplies of this process are limited to periods of available light. The rate of photosynthesis is controlled by many factors affectiHg the plaHts themselves, and it is difficult to anticipate the volume of production by this method. In most instances, however, supersaturation arises through this biological activity. Oxygen is removed by organic decompositioH and respiration of aquatic organisms, and, when supersaturated levels occur, by diffusion to the atmosphere – an action expedited by turbulence. When photosynthetic organisms are absent or inactive, oxygen concentration rarely attains the saturatioH level. In fact, supersaturation referable to atmospheric absorption and diffusioH, usually indicates some rather unusual condition. In most natural waters, regardless of temperature, metabolism of aquatic life usually imposes oxygen demands that are never entirely satisfied by aeration. Metabolic and photosynthetic processes normally make the percentage of saturation quite subject to biological control. 24 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

The oxygen content of the River Töss was generally highest in winter and lowest in late summer (Table 10). This decrease in oxygen content towards late summer may be due to one or more of several factors; water temperatures reaching their maxima in late summer hold less of the gas in solution, decreased discharge results in diminished physical mixing and reoxygeHation, greater decomposition of summer produced organic material, utilizes some of the available oxygen. On the average all sampling stations showed conditions of saturation or supersaturation. Taking into consideration the entire sampled reach of the river, supersaturation was not noted at the statioHs, below the Winterthur sewage treatment plant effluent outfall, in August, September, November, December, January and February (Table 11). This was apparently due to dilution factors. Supersaturation value of 186% at Station 28 recorded on May 17, 1967 was apparently due to photosyHthesis, where abundant nutrieHts make prolific plant life possible. This is attributed to iHdis- criminate sewage discharge from the surrounding areas. Average dissolved oxygeH was found to vary 10.2 to 11.6 mg/l. The highest values of. D. O. were recorded in the month of April. A difference in dissolved oxygen concentrations between periods of low water and high water was observed. In the high water period of February, March, April, JuHe and July, the range of oxygen was 9.78 to 12.49 mg/l. In low water period of January, May, August, September, October, November and December the rate was 9.09 to 11.48 mg/l. In the present study the influence of stream discharges on D. O. conceHtration is clearly evident. In almost all cases during all seasons increased stream discharge is accompanied by increased D. O. coHcentrations. In accordance with Table 11 and Fig. 7 it may be noted that the perceHtage of oxygen saturation varied considerably more in the polluted zone of the river than in the relatively cleaHer water zone, i. e. from 89% to 117% at Station 26 (NefteHbach-Left) and 88% to 121% at Station 27 (Neften- bach-Right) and from 51% to 186% at Station 28 (PfuHgen-Töss).

11.0

130 A 120 / ^ _—_. 1 10 7 ~— .STATION 31 Fig. 7. Seasonal Variation of . \ ^ STATION 21 100 Oxygen-Percent of Saturation STATION 26/27 90 in River Töss at Brosi (21), Neftenbach (26/27) and Töss- 80 egg-Töss (31). M A M J J A S O N O ,1

The oxygen concentration recorded as percent saturation for Stations 21 (Brosi), 26/27 (Neftenbach) and 31 (Tössegg-Töss) are illustrated in Fig. 7. From Table 11 it appears that a cleaner station such as Brosi has on the average a higher percentage of saturation of oxygen value and the station below the sewage ef fluent outfall (Neftenbach-Right) has the lowest average value, while at Tössegg-Töss the average

Table 10. Dissolved Oxygen (mg/I) in Töss Water 1967 1968 No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3.l. 6. 2. Average 18 KIone 12.5 12.l 10.7 10.9 10.l 10.4 9.8 10.4 11.l 12.2 12.5 11.9 11.2 21 Brosi 13.2 12.7 12.4 10.9 9.8 10.8 10.8 11.l 10.4 11.0 11.4 12.4 11.4 22 Wespimühle 12.8 12.l 10.3 11.2 10.l 10.2 9.9 11.3 11.9 13.6 12.9 12.4 11.6 25 Spinnerei Hard 12.8 12.0 10.6 11.l 10.l 9.9 10.3 10.8 11.3 13.0 12.6 12.2 11.4 26 Neftenbach (L) 12.0 12.1 11.3 10.4 9.8 9.0 8.6 10.2 10.0 11.2 11.7 11.5 10.6 27 Neftenbach (R) 12.2 12.3 10.2 10.3 9.6 8.4 8.6 9.4 9.3 11.4 10.9 11.l 10.2 28 Pfungen-Töss 11.9 13.l 17.3 10.8 9.9 10.l 5.6 15.4 7.6 6.3 8.7 11.4 10.7 29 Pfungen-Canal 12.3 12.5 10.0 10.6 10.2 8.8 9.0 10.3 10.8 11.8 11.5 11.3 10.8 30 Rorbas 11.6 13.2 9.8 9.8 9.4 9.0 8.7 10.3 10.1 11.0 11.4 11.5 10.5 31 Tössegg 11.2 12.8 8.9 9.5 8.8 8.l 9.6 10.5 10.1 11.4 11.2 12.9 10.4 Average 12.25 12.49 11.15 10.55 9.78 9.47 9.09 10.97 10.26 11.29 11.48 11.86 10.88

Table 11. Dissolved Oxygen - Per Cent of Saturation in Töss Water 1967 1968 No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11 12. 12. 3. l. 6. 2. Average 18 Krone 106 105 108 104 107 107 99 101 99 94 99 99 102 21 Brosi 111 113 124 113 114 111 109 109 95 89 114 104 109 22 Wespimühle 108 108 104 106 107 106 103 113 115 104 104 102 107 25 Spinnerei Hard 109 109 108 106 109 107 105 106 100 102 102 101 105 26 Neftenbach (L) 106 116 117 102 105 98 89 104 95 95 100 98 102 27 Neftenbach (R) 106 121 108 102 104 95 88 98 90 97 98 96 100 28 Pfungen-Töss 105 127 186 107 109 120 59 160 73 51 73 97 105 29 Pfungen-Canal 109 120 106 103 112 99 94 *6107 103 99 98 97 104 30 Rorbas 105 133 103 96 104 105 91 107 96 90 96 98 102 31 Tössegg 101 129 96 98 99 94 100 110 95 91 92 108 101 Average 107 118 116 104 107 104 94 112 96 91 98 100 103.8 a,_ Maximum. Minimum.

Rechenscheibe 0 2 (Dr. R. BURKARD, CH-4500 Solothurn, and LOGA, CH-8610 Uster, SwitzeIland) Calculator was used for Percent of Saturation of Dissolved Oxygen Calculations. N 26 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

value is higher than Neftenbach-Right. This indicates the approaching of aH improved condition of the river. GESSNER (1959) reported 370% Saturation due to very intensive assimilatioH of water plants. PRICE (1956) quotes the case of a river in which, owing to iHtense photosynthesis, the dissolved oxygen reached the high level of 243% saturatioH and this was accompaHied, as would be expected, by alkaline conditions, i. e. a pH value of 9.83. In the Töss water at Station 28 the dissolved oxygeH reached a level of 186% of saturation on May 17, 1967 and was accompanied by a record high pH of 8.4 (Table 5 and Table 11). At the later instance in September 1967 at the same place in the river a low dissolved oxygen percent of saturatioH of 59% was recorded, which was accompaHied by a low pH of 7.75. These observations agree with those of GESSNER and PRICE, that intensive assimilation of water plaHts or algae in the river bed can give rise to marked increase of percent saturatioH of oxygeH accompanied by alkaline conditions. Determinations of percentage saturation of oxygeH iH the river were made at all times and these iHdicated that depletion of oxygen occurred at contaminated stations. This depletion was more pronounced when the rate of flow of the river was low and was probably the result of the demand for oxygeH by organic material in the river water, and serves as an indication of the degree of pollution. Some evideHce of supersaturation was obtaiHed at Station 28 when the river was low. This station supported a heavy growth of algae, supersaturation was excessive and it sufficiently indicated the effect of algal growth in the river.

a) Saturation Deficit

The introduction of large amouHts of orgaHic substances such as sewage or debris flooding into a stream may bring about a depression of the dissolved oxygen content below the saturation valIe. The difference between the actual oxygen coHtent and the amouHt that could be present at saturation is called the "saturation deficit". This deficit is increased of course by the uptake of oxygeH by aerobic decomposition of organic materials in the stream. From the result obtained during the period of the study, curves were drawn indicatiHg the actual determined values and of oxygen concentration at a 100% saturation (Fig. 8) at the measured temperature and at the actual elevation above sea level. From the comparison of the curves of the individual stations it is apparent that specially during the cold half of the year the amount of dissolved oxygen at maHy stations iH the river water never reached saturation level. This was so at the stations downstream from Winterthur sewage effluent outfall. On the other haHd in the warmer half of the year the recorded values averaged 100% saturation or at times more. The deviations from saturatioH over the entire period of investigation, however, are so great that they caHnot be explained by mere fluctuation of the barometric pressure. It is therefore Hecessary to suppose differences in the coHsumption of oxygen by aerobic decomposition of organic materials. Whenever no deficit was recorded, it is supposed that the dissolved oxygen serving to offset the oxidatioH loss is absorbed from the atmosphere through re-aeration of the stream water. Re-aeration is therefore a process by which streams secure oxygen Jahrgang 115 H. RAT. River.Töss and its Underground Water Stream 27

mg/1 STATION 18 1 - 1- `i V mg/I 3-

1- mg/I 2- STATION 27

0 1— 2- STATION 30

M A M J J A S 6 N D J F

Fig. 8. Saturation Deficit Curves of River Töss at Different Stations. (Curves Above the Line Show Supersaturation and Below the Line Show Saturation Deficit.)

directly from the atmosphere, the gas entering iHto the biochemical oxidatioH reactions in the stream. Within the stream distribution of the oxygen derived from the atmosphere is accomplished by turbulent transport. In the more stable zones of the river submerged plants contribute in a major way to the oxygen conteHt of the water. Consequently fluctuation iH photosynthetic activity will be reflected in the amount of dissolved oxygen present. It is of great iHterest that a greater decrease in the oxygeH conceHtration did not occur iH spite of the pollution of the River Töss. This indicates that an intensive aeratioH of the river must take place. 28 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

b) Dissolved Oxygen Consumption Curves

A polluted river may be considered as a solution previously inoculated, the microbic activity varyiHg in strength so that the selfpurification capacity will vary correspondingly. If the Hoxious activity is stroHg enough it may persist, despite appearances to the contrary, even iH rivers where its effect is exceeded by the pollution. The excess of pollution will shift the balance but not destroy it. Such waters would not become bactericidal and their bacterial flora conteHt might remain normal. The reason which led to examining the curves of oxygen consumption is the lack of connection between 5-day biochemical oxygen demand of a river and the various purification stages through which it passes. The B. O. D. of raw river water may be composed of three fractions:

1. Oxygen removed by Hitrifying organisms; 2. Oxygen consumption by phyto- and zoo-organisms; 3. Oxygen used in the biological oxidation of dissolved and suspended organic matter.

For the shape of the curves the concentration of dissolved oxygen was determined after 1-10 days in 250 ml stoppered bottles, placed in an incubator in the dark at a temperature of 20°C. The data helped in tracing the curves which showed the two fermentation phases (carbonaceous and nitrogeHous), characteristic of water pollution by organic substances and helped to determine the degree of self-purification of the river under study. The curves of dissolved oxygen coHsumption at various stations of the River Töss have been drawn and illustrated in Fig. 9. From the type of curves obtained from this study it may be stated that: 1. Very clean river water gave a curve of Type I. Here the consumption of oxygen is very slow and of negligible amount, a characteristic of clean water. 2. Slightly polluted river water gave a curve of Type II, with a lag period and no iHflexion point. This is typical of autotrophic nitrifying (NitrosomoHas) bacteria. It indicates a previous pollution which has practically disappeared or final stage of completion of purification. Curves of this type were obtained duriHg high water in the Töss, when the dilution was greater and the effect of pollutioH was negligible (Fig. 9). 3. Polluted water gave a curve of Type III, with immediate consumption, no lag or incubation period and no point of inflexioH. This may be attributed to the development of heterotrophic bacterial flora, which is always present in sewage and characteristic of the degradatioH phase of orgaHic matter. These bacteria have a very short generation period. For the heterotrophic bacteria the generatioH time is of minutes only. As a result, when the medium is suitable, these are the organisms which develop quickest. This type of curve was characteristic of Station 27, where the pollutioH effect was very iHtense. 4. River water undergoing a self-purification process gave a curve of Type IV. This curve shows that there was aH immediate consumption, no lag period but with a point of inflexion. The reason for this type of curve is that the water is still polluted enough to allow heterotrophic bacteria to develop at the beginning, but that their activity ceases for lack of nutrients, and they are replaced by another type of bacteria. mg/1 MAY 10.68 12— 29

wZ 10 - 0 r 9— TYPEI TYPE I 0 wo 8- 4``\5 DAYS 0 7 - u) 6— 27 28 TIME IN DAYS 5 1/ E STATIONS 18 211 22 25 27 281/29 30 31 t t 26 0 1 6 w U,z mg/I JULY 1.68 X28 0 13— 0 TIME IN DAYS

E \TYPE 11I U, z 0 0 O TIME IN DAYS

E O til

Oz 0 0 0 1 TIME IN DAYS 1 30 31 STATIONS 18 21 22 215 I 26127 28/291 1 6 7 Fig. 9. Oxygen Consumption Curves for the Various Sampling Stations in the Tiver Töss. x x Oxygen Concentration of River at Various Points. Effluent Ratio N Oxygen Concentration of Water After 1 to 5 Days, Date River Flow m3/sec. Discharge m3/sec. Effluent: River Water in Bottles and Incubated in Dark at 20°C for Oxy- May 10. 68 7.46 0.545 1 : 13.6 ¢en Consumption Curves. T„Iv 1 hR 3 OR 0.405 1 : 7.4 30 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

This type is autotrophic, it is clearly a part of the oxidation phase and is infinitely less dangerous from the point of view of pollution. The 5-day biochemical oxygeH demaHd must theH iH the case of a river be considered solely as an iHdication of the degree of pollution. Analysis of dissolved oxygen consumption curves, with sewage and diluted water, give a good iHdication of the purification stage. This interpretation of dissolved oxygen curves is well supported by other chemical and bacteriological tests carried out in the course of the present study. In Fig. 9 the various iHtermediate curves of the four types described are also illustrated as obtained from the different statioHs along the river stretch under study. The shape of the curves also varied according to the degree of pollution of the water analysed. Actually iH the course of the purification of the water, we caH see that the shape of the consumption curves always chaHges in the same way as showH in Fig. 9. The oxygen coHsumptioH curves of water with a high purification capacity pass quickly through the various stages. On the other hand, in water with a low self- purification capacity the various phases, and in particular the point of inflexion, which seems to play such an importaHt part, takes longer to occur. Such observations were also made by LECLERC, 1960 during his studies of oxygen consumptioH curves, directly on rivers iii Belgium and on laboratory investigations. The curves of dissolved oxygen consumption at various points iH the River Töss have been obtained aHd it has been fouHd that the shape of the curves varied accordiHg to the progress of assimilatioH of the pollutioH.

6. Biochemical Oxygen DemaHd

Biochemical Oxygen demand after 48 hours (B. O. 0.48 h)

This test was specially undertaken to compare old data on the same stretch of the river. These oxygen consumption values were obtaiHed by determining the oxygeH concentration after 48 hours in 250 ml stoppered bottles placed in an incubator in the dark at a temperature of 20°C. The data is presented partly in Fig. 10 aHd tabulated in Table 12. From Fig. 11 it is evident that the rate of oxygen consumption in the cleaner station was lower than that of the polluted stations of the river. This consumption is attributable to the large amount of sewage effluent discharge at Winter- thur-Hard. The oxygeH consumptioH gradually decreased from the polluted stretch of

mg/I s- STATION 26/27 • STATION 31 Fig. 10. Seasonal Variation of Biochemical Oxygen Demand After 48 Hours (B.O.D. 48 h.) at 20°C in River Töss at Brosi STATION 21 (21), Neftenbach (26/27) and Tössegg-Töss (31). F

Table 12. Biochemical Oxygen Demand - after 48 hours (B.O.D.4$b) - mg/l in Töss Water

1967 1968 6. 2. Average No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. 1. l.02 18 KIone l.06 0.59 l.36 l.42 l.02 l.56 0.43 ** 0.67 l.22 0.68 1.33 0.96 l.03 0.85 21 Brosi 1.23 1.29 0.97 0.54 0.77 l.13 1.03 0.76 0.81 0.00 0.68 0.99 22 Wespimühle 0.57 l.61 0.74 0.84 0.99 l.12 0.68 0.49** 1.11 l.29 l.17 1.29 0.80 l.19 25 Spinnerei Hard 2.48 0.58 l.68 0.68 1.32 1.54 0.57** 0.97 l.07 0.75 l.92 2.76 26 Neftenbach (L) l.84 2.63 1.77** 2.60 2.23 3.48 3.09 3.12 3.51 l.80 2.76 4.36 4.93 27 Neftenbach (R) 5.03 7.55 2.82 2.91 3.44 4.68 5.67 7.31 4.24 3.67 6.04 5.89 3.37 5.34 28 Pfungen-Töss 3.34 4.43 10.91 2.65 6.19 3.07 5.57 2.01 ** >7.6 >6.3 >8.7 3.89 3.3 29 Pfungen-Canal 3.28 - 2.85 l.90** 3.77 5.54 3.40 4.27 3.08 3.18 4.44 1.92 2.23 30 Rorbas 3.59 3.81 3.05 2.03 2.52 3.41 l.14 l.40 l.42 0.96 1.57 4.33 2.18 31 Tössegg 2.93 3.60 2.45 l.32 2.01 2.2 l.75 l.39 0.91 l.33 l.95 2.78 2.479 Average 2.54 2.98 2.86 l.69 2.43 2.77 2.33 2.24 2.5 2.0 3.06

- = not done.

Table 13. Biochemical Oxygen Demand (B.O.D. 5) - mg/l in Töss Water 1967 1968 Average No. Sampling Stations 14. 3. 12.4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. l. 6. 2. l.8 2.15 18 Krone 2.8 l.6 3.8 2.2 2.l 2.3 1.l l.8 2.l 2.5 l.9 2.4 l.59 21 Brosi 2.l 2.0 2.3 l.3 l.4 1.6 l.5 l.0 1.4 l.0 l.1 2.0 2.55 22 Wespimühle l.8 1.8 3.0 l.6 1.8 1.7 9.2 l.4 2.l 3.3 2.0 2.8 l.9 3.14 25 Spinnerei Hard 3.0 2.4 5.3 2.0 2.2 1.9 9.7 1.7 l.8 3.0 5.4 4.98 26 Neftenbach (L) 3.8 4.8 5.l 4.0 3.6 6.9 5.5 6.3 6.8 l.8 5.8 10.0 8.15 27 Neftenbach (R) 8.6 11.2 7.7 5.8 6.0 8.0 8.2 9.2 9.0 3.7 10.5 9.6 9.82 28 Pfungen-Töss 6.l 7.0 16.9 4.3 9.l 3.7 5.6 2.5 14.6 >6.3 32.2 10.4 7.25 29 Pfungen-Canal 5.6 8.7 7.0 3.4 6.2 8.2 5.6 7.4 6.7 8.7 9.2 4.1 4.13 30 Rorbas 5.5 5.9 5.5 3.0 4.4 5.0 2.2 2.7 3.2 3.9 4.2 7.9 4.52 31 Tössegg 4.5 5.6 6.8 2.7 4.l 4.6 2.6 2.5 2.7 5.0 5.3 5.55 4.828 Average 4.38 5.1 6.34 3.03 4.09 4.39 5.12 3.65 5.04 3.92 7.5

Maximum. Minimum. 32 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

m /I 18— VIII OXYGEN CONSUMED 17— 11111 DISSOLVED OXYGEN 1 6- —MAXIMUM 15- MINIMUM

14-

13-

10-

9 8 - 7-

6- Fig. 11. Average Dissolved Oxygen 5- Content and Oxygen Consumed 4 After 48 Hours at 20°C Incubation 18 21 22 25 26 27 28 29 30 31 in River Töss Water, 1967/68. STATIONS the river, point dowHstream to a condition suggestive of unpolluted water, but values still remaiHd higher than those of the stations upstream of the sewage effluent outfall. This decrease might be attributed to the process of self-purificatioH which is at work in the river downstream from the Winterthur sewage effluent outfall.

Biochemical Oxygen Demand (B. O. D.5)

Determination and measurement of pollution may be made by measuring the oxygen required to stabilize the demand from aerobic biochemical action in the decomposition of organic matter. This is not the amount required to completely oxidize all organic matter, but rather the volume necessary to restore the balance between oxidation and chemical activity; this activity measurement, known as biochemical oxygen demand, is perhaps the most important and widely used of all the tests for organic pollution. The biochemical oxygen demand of the river water raHged from l.59 to 9.82 mg/1. Although the B.O.D. 5 decreased in a general way downstream from the Winterthur sewage treatment plant efflueHt outfall, it varied considerably. At Stations 27, 28 and 29 maximum B.O.D. 5 was always measured in the dry season. In general B.O.D.5 values were high in winter and low in the summer. Data indicated that from a B.O.D.5 poiHt of view Töss water quality has improved progressively downstream from the entry of the Winterthur sewage treatment plant effluent (Fig. 12). The data presented in Table 13 indicated that the point of uncontrolled polluting discharge e. g., at Station 28, was most seriously affected. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 33

Fig. 12. Seasonal Variation of Bio- chemical Oxygen Demand (B.O.D.5) in River Töss at Brosi (21), Neften- 0 bach (26/27) and Tössegg-Töss (31). I I I I l I l I I I I MAMJJ ASONDJ F

The biochemical oxygen demand curve is low in upstream, unpolluted water of the Töss (Fig. 12), increases at a point from the great discharge of sewage effluent and gradually decreases from this point downstream to conditioHs suggestive of unpolluted water. B.O.D. 5 and D.O. are so interrelated that the D.O. concentration is low where B.O.D. 5 is high, aHd the converse is also true. The increase in B.O.D. 5 values may be related to the decreased ability of self- purification in the river and/or due to a decline in temperature. B.O.D. 5 varied much less in the cleaner water zone, 1.0 to 2.4 mg/l at Station 21, than in the polluted water zone, 2.5 to 32.2 mg/l at StatioH 28. A conceptus of the biochemical oxygen demand figures from River Töss throws some light on the course of self-purification. Most of the demand in the river was satisfied or perhaps inhibited by the time the river reached Station 31 (Tössegg). The figures show that B.O.D. 5 apparently was satisfied most rapidly between the Station 28 (Pfungen) and Station 30 (Rorbas) stretch of the river. This section where the initial high rate of self-purification occured, is a long stretch (5.5 km) devoid of any source of pollution, where denser growth of algae on the bottom stones of the river were found along with high turbuleHce, and so it appears that the rivers power of self-purification is directly related to the density of algal growth aHd a high rate of physical aeration. All these observations were made under aerobic conditions; should the river be overloaded, and anaerobic conditions develop,,then circumstances could be different. Taking into coHsideration the average values of 1967-1968, the water at Station 26/27 was carrying 3395 kg/day of B.O.D. 5 , and 5382.4 kg/day of D.O., definitely a D.O. surplus. The effluent at the Winterthur sewage treatment plant duriHg this period contributed 706 kg/day of B.O.D. 5 . It should be noted, that in the 0.9 km stretch between the poiHt of effluent outfall in the river and Station 26/27, the river still showed a surplus of D.O. Further, a very interesting point, dowHstream from the Winterthur sewage treatment plant efflueHt outfall, at about 9.8 km, the effluent from the Rorbas sewage treatment plant goes into the River Töss. This plant effluent coHtributed 61 kg/day of B.O.D. 5 . Surprisingly enough, the river at Tössegg still 34 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

Table 14. B.O.D. and D.O. Budget

B.O.D. D.O. Station kg/day kg/day Remarks

Krone (18) 1112.7 5796.4 Surplus D.O. 4683.7 kg/day Brosi (21) 822.9 5899.9 Surplus D.O. 5077.0 kg/day Wespimühle (22) 1319.7 6003.4 Surplus D.O. 4683.7 kg/day Spinnerei Hard (25) 1625.l 5899.9 Surplus D.O. 4274.8 kg/day Winterthur sewage treatment plant effluent (6) 706.0 228.2 Deficit D.O. 477.8 kg/day Neftenbach (26/27) 3395.0 5382.4 Surplus D.O. 1987.4 kg/day Pfungen (28) 5082.2 5537.6 Surplus D.O. 455.4 kg/day Pfungen-Canal (29) 3752.l 5589.4 Surplus D.O. 1837.3 kg/day Rorbas (30) 2137.4 5434.1 Surplus D.O. 3296.7 kg/day Rorbas sewage treatment plant effluent (7) 61.0 20.0 Deficit D.O. 41 kg/day Tössegg-Töss 2339.3 5382.4 Surplus D.O. 3043.l kg/day

showed a surplus of D.O. (Table 14). This is an iHdication that the river has a good capacity for self-purification. From Table 14 it is further assumed that the content of D.O. diminishes in proportion to the degree of pollution and increases iH proportion as the water purifies itself.

7. KMnO4-ConsumptioH

The KMnO4-coHsumption determiHation is a measure of the readily oxidizable material in the water and furnishes an approximation of the minimum amount of organic and reducing material present. The KMnO 4-coHsumption test is a simple and quick method of measuriHg approximately the oxidizable matter (organic and inorganic) in sewage, sewage effluents and river water, a high value indicating as a rule orgaHic pollution. The mean anHual KMnO 4-consumption value was lowest (Table 15) in the river at Station 21, upstream to the Winterthur sewage treatment plant effluent outfall and highest downstream from the effluent at Station 28. There was an appreciable increase of KMnO 4-consumption values just below the sewage outfall, but it is evident from the data that as the stream progresses down to its mouth the KMnO4 values are very much reduced (Fig. 14). However, as other chemical parameters, local conditions alter this trend of decrease in value, when KMHO4-consumptioH of 20.93 mg/l was recorded at Station 28. KMnO 4-consumption values were higher during the colder half of the year than the warmer half. This seasonal difference is mainly due to an overall decrease in river flow during the colder months. Fig. 13 shows the seasonal variations of KMnO 4 -consumption at three statioHs of the Töss; from this figure it appears that the curve of KMnO 4-consumption follows the same trend in seasonal fluctuation as that of the B.O.D. 5 curves (Fig. 12). Table 15. KMnO4 - Consumption (mg/1) in Töss Water

1967 1968 No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. l. 6. 2. Average 18 Krone 7.11 5.85 16.43 1 9.46 12.96 9.64 10.43 11.09 10.74 9.64 7.11 8.53 9.91 21 Brosi 6.95 4.75 12.32 6.32 12.8 6.16 7.27 7.11 6.32 5.53 5.53 7.27 7.36 22 Wespimühle 7.11 6.64 15.48 7.9 14.l 9.0 9.64 9.32 9.48 7.9 6.32 7.74 9.21 25 Spinnerei Hard 6.95 8.53 14.22 8.22 12.8 8.69 9.32 8.37 10.11 7.9 9.48 7.9 9.37 26 Neftenbach (L) 7.74 10.74 14.38 9.64 13.9 11.38 14.39 12.64 14.69 9.48 9.64 9.64 11.52 27 Neftenbach (R) 13.11 21.8 19.91 10.43 14.22 14.85 20.54 21.49 25.28 14.85 20.1 14.85 17.62 28 Pfungen-Töss 10.9 11.85 17.22 9.8 16.27 11.1 23.1 11.22 44.4 41.25 41.1 12.96 20.93 29 Pfungen-Canal 10.11 13.58 17.38 9.32 15.96 15.33 15.0 15.83 16.75 13.43 16.4 16.12 14.6 30 Rorbas 10.74 12.96 16.59 9.64 16.12 13.43 12.48 11.85 13.11 11.l 16.11 9.95 12.84 31 Tössegg 11.85 12.0 17.06 9.64 14.69 13.43 21.96 11.53 12.0 11.22 10.43 11.69 13.12 Average 9.26 10.87 16.l 9.04 14.38 11.30 14.41 12.05 16.29 13.23 14.22 10.67 12.648

Table 16. NO3 (mg/l) in Töss Water

1967 1968 No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. 1. 6. 2. Average

18 Krone 7.5 7.75 7.75 11.0 9.0 10.0 11.0 14.0 10.0 12.0 12.0 8.0 10.0 12.0 9.62 21 Brosi 10.0 6.75 D 7.75 10.0 10.0 8.0 9.0 9.0 10.0 10.0 13.0 22 Wespimühle 10.0 6.5 7.75 10.0 10.0 11.0 9.0 10.0 11.0 13.0 14.0 7.5 9.97 25 Spinnerei Hard 11.0 7.25 8.0 9.0 11.0 12.0 12.0 10.0 12.0 15.0 17.5 8.0 11.06 26 Neftenbach (L) 13.0 10.0 12.5 11.0 12.0 15.0 20.0 17.5 17.5 17.5 16.25 12.0 14.52 27 Neftenbach (R) 14.0 11.0 10.0 13.0 14.0 16.0 20.0 17.5 17.5 17.5 17.5 11.5 14.95 28 Pfungen-Töss 14.0 10.0 15.0 15.0 12.0 16.0 10.0 17.5 2.0 12.5 12.5 16.0 12.7 16.37 29 Pfungen-Canal 15.0 10.0D 12.5 14.0 12.0 17.0 22.5 20.0 20.0 20.0 17.5 16.0 30 Rorbas 15.0 9.0 12.5 13.0 13.0 17.5 18.75 16.25 18.75 20.0 18.75 12.5 15.41 31 Tössegg 15.5 10.0 12.5 15.0 12.0 17.5 20.0 17.5 20.0 20.0 17.5 15.0 16.04 Average 12.5 8.83 10.63 12.l 11.5 14.0 15.23 14.93 13.88 15.75 15.65 11.85 13.064

Maximum. Minimum. 36 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

mg/I 25—

Fig. 13. Seasonal Variation of KMnO4-Consumption in River Töss at Brosi (21), Neftenbach (26/27) and Tössegg-Töss (31). 0 I I I I I I I I I I I MAMJ JASON D J F

—MAXIMUM MINIMUM AVERAGE

Fig. 14. Average Potassium Perman- 1 ganate Consumption Values in River 30 31 Töss, 1967/68. STATION 31 STATION 26/27 0.80

070

0.60

3.42 0.50 STATION 26/27

0.40

1.2 0.30

1.1 0.20

1.0 0.10

0.9 0.09

0.8 — 0.08

0.7 — 0.07

0.6 — j•,.. STATION 26/27 0.06

0.5 — 0.05

0.4- 0.04

0.3— 0.03 STATION 31 0.02

0.01 STATION 21 0 I I I I I I I l I I I I I I J F MAMJ J ASONDJ

Fig. 15. Seasonal Variation of NO3--N, NO2--N and NH3–N in River Töss at Brosi (21), Neftenbach (26/27) and Tössegg-Töss (31). 38 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

8. NitrogeHous CompouHds (Inorganic)

a) Nitrate

Nitrate may be present in the fresh sewage samples if it exists in the water supply, or in ground water which has been infiltrated by sewage. It will disappear rapidly as the sewage becomes stale and is seldom found in the influent of sewage treatment plants. It is often found in the effluents from secondary treatment and the quantity is an indication of the completeness of oxidation by a particular process. Sewage wastes contaiH nitrogen iH various forms, aHd microoganisms either iHtroduced during sewage treatment or naturally preseHt in water or soil convert the nitrogen to more highly oxidized forms. Some nitrogeH escapes as gaseous N2 in this process, but eventually at least part of the original nitrogen is converted into nitrates. Nitrate nitrogen was usually most coHcentrated in the river below Winterthur sewage treatment plant effluent outfall (Fig. 15). VariatioH of nitrates on aH anHual basis may be gained for each station from Table 16. The average annual amount of nitrates ranged from 9.62 to 16.37 mg/l. The nitrate values desceHd to a miHimum during the warm half of the year and ascend to a peak duriHg the cold half. The difference between the averages for the cold half of the year and the warm half does show remarkable seasonal variations in the coHcentratioH of nitrate. This may be attributed to the fact that there is more nitrification at higher temperatures of the summer months, when bacterial activity is greater than during the colder winter months. Fig. 15 illustrates the seasonal variations in NH 3–N, NO3 --N and NO2--N at three different stations.

b) Nitrite

Nitrite is very transitory and usually occurs where oxidizable forms of organic nitrogen are constantly renewed. It is normally a useful measure to detect zones of faecal contamination, but its presence may not always serve notice of sewage entry, as it is produced at times by conceHtrations of zooplankters, especially micro- crustacea, and other aquatic animals. Where raw sewage discharges promote dense algal growth, nitrite may fail to occur when demands for nitrogen force utilization is in the ammonia stage. Nitrite Hitrogen was usually least concentrated in the river above the Winterthur sewage effluent. Average value of Hitrites for the warm half of the year was markedly lower than that of the cold half of the year. Again very strong evidence of iHtensive nitrification during the summer months. The data for nitrite is presented in Table 17. The highest concentration of nitrite was found at Station 26/27, just below the Winterthur sewage treatment plant outfall (0.754 mg/I) but at the mouth of the river at Station 31 the value decreased to 0.554 mg/l. At the cleaner Station 21 the range of variation was <0.005 mg/I to 0.1 mg/I, and at the most polluted Station 26/27 the range was between 0.125 aHd 2.75 mg/I, while at Station 31it varied from 0.175 to 1.5 mg/I. ti NO2- (mg/l) in Töss Water Table 17. (Jo 1968 Average do 1967 11. 10. 7. 11. 12.12. 3. l. 6. 2. 17.5. 13.6. 5.7. 8.8. 8.9. No. Sampl. Stations 14. 3. 12.4. <0.005 0.05 0.099 0.2 0.3 0.15 0.075 0.l 0.022 0.035 0.05 0.065 0.14 <0.005 0.06 0.054 18 Krone 0.05 0.l 0.07 0.l 0.05 0.022 0.025 0.045 0.04 0.09 0.05 0.091 21 Brosi 0.15 0.075 0.175 0.l 0.05 0.075 0.04 0.09 0.225 0.721 22 Wespimühle 0.022 0.04 0.l 0.2 0.15 7.0 0.075 0.3 0.07 0.15 0.2 0.325 0.641 25 Spinnerei Hard 0.035 0.05 0.3 0.175 3.5 l.0 0.12 0.28 0.6 0.7 0.4 Neftenbach (L) 0.08 0.29 0.25 l.25 2.0 2.0 0.868 26 0.5 0.75 0.5 0.825 0.5 l.45 0.25 0.17 <0.005 1.5 0.622 27 Neftenbach (R) 0.22 0.7 0.25 0.9 l.25 0.6 0.65 0.18 0.65 0.6 l.5 0.894 28 Pfungen-Töss 0.18 0.75 0.625 0.4 0.35 4.0 1.0 0.16 0.56 0.75 0.454 29 Pfungen-Canal 0.18 0.45 0.3 0.4 0.25 0.25 l.0 0.35 0.2 0.4 0.95 0.5 0.554 30 Rorbas 0.2 0.65 0.35 0.4 0.5 1.5 H 0.18 0.35 0.75 0.45 0.4 31 Tössegg 0.175 0.6 1.0 0.34 0.408 l.732 0.874 0.4998 0.123 0.321 0.508 0.448 0.32 Average 0.114 0.419 0.397 ä.

Table 18. NH3 (mg/l) in Töss Water a 1968 aQ 1967 12. 12. 3. l. 6.2. Average 8 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 14. 3. 12.4. 17. 5. 13. 6. No. Sampling Stations 0.317 a l.0 0.8 0.l 0.1 0.14 0.23 0.2 0.22 0.64 0.15 0.06 0.17 0.12 <0.02 0.04 0.094 18 Krone 0.22 0.02 0.13 0.05 0.12 0.14 0.09 0.04 0.14 0.l 0.l 0.209 21 Brosi 0.18 0.14 0.24 0.36 0.7 0.12 0.06 0.16 0.14 0.2 0.15 0.221 22 Wespirnühle 0.26 0.28 0.36 0.6 0.l 0.l 0.18 0.16 0.2 0.19 0.3 0.771 25 Spinnerei Hard 0.0 0.9 2.3 l.2 0.3 0.9 0.6 0.4 0.6 0.9 l.7 26 Neftenbach (L) 0.40 0.46 6.0 l.0 l.0 l.25 l.0 0.6 1.0 2.l. 1.8 Neftenbach (R) 1.9 l.0 l.8 12.0 7.0 l.25 4.287 27 l.l 0.3 4.0 4.0 17.0 1.25 l.0 l.95 0.6 0.8 0.25 l.179 28 Pfungen-Töss 0.8 l.1 1.8 2.4 2.4 0.8 0.9 l.6 0.6 0.7 0.3 0.879 29 Pfungen-Canal 0.65 0.5 l.4 2.2 0.1 1.2 1.0 0.8 0.6 0.8 0.729 30 Rorbas l.0 0.4 l.2 l.6 0.2 0.35 1.0 0.6 0.7 0.5 0.2 31 Tössegg l.1 0.9 3.214 2.262 0.972 0.409 l.0386 0.478 0.495 0.459 0.97 1.061 Average 0.694 0.577 0.88

Maximum. " Minimum. 40 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

c) Ammonia

Ammonia nitrogen is more stable and its compounds may endure for considerable periods of time when biological processes reach a low ebb. It is formed naturally by the breakdown of more complex organic groups, but water borne quaHtities can be augmented by various commercial fertilizers supplied to the soil and discharged from fertilizer factories. THOMAS (1946 and 1948, p. 39) coHsidered that ammoHia concentration is a good indicator of the degree of pollution from the effluent of the communities sewage in the flowing water. In the case of Töss the NH 3 content is of special importance because its water sinks underground at different places, and this underground water is taken up for drinking purposes. According to the Schwei- zerisches Lebensmittelbuch (1937) potable water should not contain more than 0.02 mg/I of ammonia (and should not have more than 20 mg/l of nitrates or 0.0 mg/l of nitrites). Municipal pollution, mostly from Winterthur, induced substantially higher values downstream, but the maximum value of ammonia at Station 28 is attributed to the indiscriminate sewage discharge by the surrounding communities at Pfungen at this station on the river. Average value of ammonia for the cold half of the year was higher than that for the warm half (Table 18). The ammonia-N values decrease continuously as the river progresses downstream, after receiving the effluent; this is clear evidence (see NO3-) indicatiHg that the process of nitrification is at work in the river, and the river in geHeral is recovering from pollution (Fig. 16).

Table 19. Composition of Ammoniacal Nitrogen, Nitrite Nitrogen and Nitrate Nitrogen in River Töss (Annual Averages) Total-N Sampling NO3 -N NH3-N NO2 -N (Inorganic) Stations mg/l mg/l mg/I mg/I 18 Krone 2.260 0.2635 0.0301 2.5536 21 Brosi 2.174 0.0741 0.0164 2.2645 22 Wespimühle 2.253 0.1729 0.0277 2.4536 25 Spinnerei Hard 2.499 0.1812 0.2192 2.8994 26 Neftenbach (Left) 3.281 0.6341 0.1949 4.1100 27 Neftenbach (Right) 3.378 l.3400 0.2539 4.9819 28 Pfungen-Töss 2.870 3.5246 0.1888 6.5834 29 Pfungen-Canal 3.699 0.9635 0.2715 4.9340 30 Rorbas 3.482 0.7165 0.1380 4.3365 31 Tössegg 3.625 0.5929 0.1687 4.3866

Table 19 shows that the total inorganic nitrogen did not vary widely in the stations upstream from the Winterthur sewage treatment plant effluent outfall. But it increased twofold to the point downstream from the effluent outfall. The increase of Hitrogen at Station 28 was due to local factors, such as the direct pollution through untreated sewage from the surroundiHg area, otherwise there was a very slight decrease in total-N as the river progressed downstream. If the chemical condition of the River Töss above the Winterthur sewage treatment plant effluent outfall was taken as an arbitrary standard, the evidence iHdicated a Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 41

100-

90- 80-

70- 60-

50-

40-

30-

20-

10-

2 10- 22 18 25 20- 31 6 30 30- 11111 NO3N 29 NOZ N 27 40- Fig. 16. Nitrogen Balance in the 0 NH3N River Töss, 1967/68. 50-

60- 28

Percentage Composition of N- Compounds (Inorganic).

Stations 18 21 22 25 26 27 28 29 30 31 79.82 67.8 NO3--N 88.5 96.0 91.86 86.12 43.59 74.96 80.29 82.63 73 6 4.74 5.29 NO2--N l.75 0.72 l.12 7.56 2.86 5.5 3.18 3.84 5.01 15.42 26.89 NH3--N 10.31 3.26 7.04 6.21 53.38 19.53 16.52 13.51 22 4 clearly defined increase in conceHtration of nitrite-N, Hitrate-N and ammoniacal-N below this outfall. The iHcrease in ammoniacal-N was less consistent. Local conditions at Station 28 (PfuHgeH) particularly tended to obscure this trend (Fig. 16) due to incidental pollution at this station. This increase in concentration, often due to the sewage effluent near the township of Pfungen, as a site of incidental pollution was responsible for quite a marked increase of ammoHiacal-N. ComparisoH of the various Hitrogen concentrations at Station 26/27 (Neftenbach) and Station 31 (Tössegg) below the Winterthur sewage treatment plant effluent showed, iH general, a decrease in ammoniacal-N and an iHcrease in nitrate-N conceHtration (Fig. 15). This would support to some degree that mineralization below the point of sewage effluent eHtry might have been taking place. Rivers polluted by oxidizable orgaHic effluents uHdergo self-purification, the main features of which are fairly well uHderstood. OHe of the criteria of this process is the eveHtual stabilization of the river below the point of pollution, indicated by 42 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 iHcreased miHeralizatioH of the river water. As the amount of ammoHia was high, just below the sewage effluent, any increase in nitrate concentration could be taken to indicate that at least oxidation of some of the available NH 3(N) was taking place and that the river was iH general recovering from the pollutioH. Thus the evideHce available (Fig. 16) indicates that in the River Töss some clear decreases of NH3(N) and increases in NO 3-(N) were due to nitrification. From the percentage composition of nitrogen it showed that NO 3--N was iH greatest concentration (i. e. about 80%), NH3-N was about 17% and NO 2--N was only 3% of the total nitrogen content. Fig. 16 shows the nitrogeH balance in the River Töss during 1967-1968 expressed as a percentage composition of N-compounds. A close study of Fig. 16 reveals that there is a definite increase of NO3--N, from 73.6% at Station 26/27 to 82.6% at Station 31, and a correspondiHg decrease in NH3-N, from 22.4% at Station 26/27 to 13.5% at Station 31. This data further proves that nitrificatioH was taking place in the river. This increase in the nitrate-N had considerably iHflueHced the pollution of the River Töss. The work of JEPSON and GREENE (cited by KLEIN, 1962) indicated that the low oxygen tension combined with oxygen supplied by Hitrates could be of great importance, since aHaerobical bacterial decomposition is prevented by bacteria making use of this oxygen source. KLEIN (1962) also reported instances when nitrate salts, particularly of sodium, were deliberately added to rivers to assist in the removal of odours in standing and sluggishly moving water. It may well be that the observed contiHual aerobic state of the River Töss was at least in part due to the maintenance of a high nitrate-N concentration in the river, by both effluent discharges and natural processes of nitrification.

9. Chloride

Chloride is present as sodium chloride iH uriHe to the exteHt of about one percent. As such sewage always contaiHs chloride, and the amount present depends on the strength of the sewage, chloride content of the water supply and the presence of industrial wastes containing chlorides. Chloride remains unaltered during the purification of sewage; wheH the possibility of iHdustrial effluent pollutioH is ruled out, a sudden rise in the chloride content of a stream usually indicates the presence of sewage, farm drainage and sewage effluents. In Table 20 complete data is given for the period from March 1967 to February 1968. The data indicates a clearly defined increase iH the coHcentratioH of chloride downstream from the WiHterthur sewage treatmeHt plaHt effluent outfall. This increase was due eHtirely to the sewage effluent from the Winterthur sewage treatment plant. On the average, upstream of the sewage effluent from Winterthur, the chloride concentration varied from 8.08 to 9.42 mg/l, whereas downstream from the efflueHt, it varied from 12.67 to 17.32 mg/l. The maximum values recorded at Station 28 were due to local conditions, particularly incideHtal pollution from the communities surrounding this point on the river. In general, higher chloride values were recorded during the cold half of the year. This was largely due to the reduction iH the flow and partly due to the NaCI comiHg into the river from road draiHage and

a Table 20. Chloride (Cl-) mg/l in Töss Water 1968 m 1967 11. 10. 7. 11. 12. 12. 3. l. 6. 2. Average o0 No. Sampling Stations 14. 3. 12.4. 17. 5. 13. 6. 5.7. 8. 8. 8. 9. 10.l 9.42 Lam, 8.3 28.2 14.l 10.7 14.l 10.4 18 Krone 4.6 4.0 8.8 4.9 5.3 9.3 8.6 8.6 10.0 13.6 10.5 8.08 Brosi 6.4 4.2 8.5 4.3 5.0 8.0 21 9.7 13.1 9.6 10.4 8.4 5.0 3.6 10.8 4.5 5.l 8.7 10.l 10.3 22 Wespimühle 12.3 12.8 8.8 8.71. 11.0 4.8 5.3 8.6 11.0 10.3 9.7 25 Spinnerei Hard 6.0 4.0 12.l 12.67 7.2 7.4. 13.4 17.8 17.7 16.4 16.6 13.8 26 Neftenbach (L) 8.2 7.6 13.9 17.0 16.4 21.5 25.3 24.l 22.8 19.5 15.3 7y 27 Neftenbach (R) 9.8 12.8 18.5 8.8 9.4 26.3 18.2 21.8 23.0 29.2 16.l 17.32 Pfungen-Töss 10.6 12.2 17.3 8.4 9.9 14.9 28 21.0 21.6 17.6 15.2 15.65 P`. 9.8 17.5 8.3 8.5 15.9 22.0 21.4 29 Pfungen-Canal 9.0 19.0 16.5 15.5 8.0 11.7 15.0 19.9 17.6 19.7 21.l 30 Rorbas 10.4 9.2 18.5 14.99 14.9 19.3 18.2 20.0 20.8 16.0 16.0 H 31 Tössegg 10.6 10.4 16.l 8.l 9.5 o: 18.54 16.17 16.17 17.54 16.15 13.l 12.774 Average 8.06 7.78 14.09 6.73 7.71 12.41 w °0.

Table 21. Surfactants (Anionic) mg/l in Töss Water ä 1968 oci2 1967 d 8. 9. 11. 10. 7. 11. 12. 12. 3. l. 6. 2. Average No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. ° 0.04 0.07 0.12 0.05 0.073 0.07 0.07 0.04 0.02 0.16 0.11 0.11 18 Krone 0.02 0.05 0.16 0.079 0.07 0.02 0.18 0.07 0.07 0.04 0.09 w 21 Brosi 0.0 0.09 0.11 0.069 co 0.13 0.09 0.09 0.04 0.09 0.12 0.05 22 Wespimühle 0.0 0.07 0.07 0.04 0.04 0.11 0.09 0.04 0.14 0.09 0.14 0.091 cn Spinnerei Hard 0.0 0.07 0.18 0.07 0.04 0A3 25 0.11 0.13 0.14 0.09 0.07 0.125 ro 0.02 0.09 0.32 0.13 0.07 0.16 0.18 26 Neftenbach (L) 0.12 0.14 0.176 0.11 0.13 0.20 0.18 0.27 0.16 0.23 3 27 Neftenbach (R) 0.07 0.27 0.24 0.57 0.18 0.93 0.33 1.76 0.21 2.21 0.25 Pfungen-Töss 0.02 0.04 0.69 0.09 0.13 28 0.13 0.13 0.16 0.16 0.16 0.143 0.02 0.04 0.30 0.11 0.11 0.27 0.13 29 Pfungen-Canal 0.14 0.12 0.09 0.130 0.20 0.11 0.13 0.20 0.18 0.11 0.13 30 Rorbas 0.0 0.16 0.137 0.18 0.24 0.18 0.11 0.18 0.09 0.09 31 Tössegg 0.07 0.07 0.22 0.13 0.09 0.159 0.179 0.222 0.149 0.258 0.145 0.317 0.12 AveIage 0.022 0.097 0.24 0.09 0.078 a Maximum. Minimum. 44 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

mg/I 22—

20-

19-

18-

17-

15-

14- STATION 26/27 13-

12-

11-

10- 9

6- Fig. 17. Seasonal Variation of 5- Chloride in River Töss at Brosi (21), Neftenbach (26/27) and 4 11 I 1 1 I 1 1 1 1 I Tössegg-Töss (31). M A M J JASON D J F

a proportionately greater effect of the sewage effluent outfall in the winter moHths. Fig. 17 shows the seasonal variations in the chloride conteHt of the river at Stations 21, 26/27 aHd 31. These figures show the iHcrease iH chloride content of the river due to sewage effluents and the marked seasonal fluctuations. The curves are similar and run parallel to one another. A comparison of Figs. 3 (average flow on the day of sampling) and 17 shows that chlorides tend to vary iHversely to the rate of flow of the river, as maxima appeared at all the stations during the periods of low flow aHd minima during the high discharges into the river. The maximum and minimum chloride conceHtration was not in the same months as that of the River RheiH, e. g., the maxima of Töss were during the autumH while those of River Rhein were during February and March. This can be attributed to the fact that the Rhein passes through the lake while in the Töss valley there is no lake, hence the chemistry of the rivers differs during seasonal fluctuations. Such an observation was reported earlier by WASER aHd THOMAS, 1944 in their studies oH the River Thur and later confirmed by DEMMERLE, 1966 in her studies on the River Rhein.

10. DetergeHts (SurfactaHts)

The widespread use of synthetic detergents for domestic and industrial purposes, the consequent presence of small amounts of synthetic detergeHt in sewage effluents, Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 45 industrial wastes and river water, the objectionable tendency of these detergents to cause persistent foam on streams and at sewage treatment plants and the toxicity of these detergents to fish and aquatic flora reHders it important to find a means of dealing with concentrations of surfactants in the river purification work. According to a Report of the Committee on SyHthetic Detergents Ministry of Housing and Local Government (1956) the most popular detergents are of the anionic type which comprise about 95% of the total usage. UnfortuHately they are most difficult to break down during sewage purificatioH and so about 25% or more (HusMANN, 1967) of the amouHt preseHt in the crude sewage passes through the treatment plant and is fouHd in the final effluent. Table 21 shows the coHcentration of surfactants (anionic) for the period 1967/68. On the average, the surfactants concentratioH varied from 0.069 to 0.57 mg/l. The higher values were recorded dowHstream from the WiHterthur sewage effluent outfall. Maximum annual average concentration was recorded at Station 28 and this was

mg /! 0.3— Fig. 18. Seasonal Variations of 0.2— STATION 21 Surfactants in River Töss at STATION 26/27 Brosi (21), Neftenbach (26/27) "STATION 31 and Tössegg-Töss (31).

iHvariably related to the local pollution through indiscriminate discharge of untreated sewage by the commuHities arouHd this statioH. Higher values were recorded during the low discharge periods wheH there was a proportionately greater effect of the sewage effluent outfall. The presence of 0.15 mg/I of detergent at Station 26/27 was definitely responsible for the inteHsive foaming in the river just 50 metres downstream from this statioH, presentiHg aH offensive sight. Such an ugly sight was never recorded upstream from the Winterthur sewage effluent outfall and the values recorded upstream were comparatively low aHd varied betweeH 0.069 mg/1 and 0.091 mg/l. During the periods of low flow specially iH the summer months the river is struggling carrying only about 3 m 3/sec. of water. IH its stretches and along the shore islands are formed which leads to the formatioH of pools and puddles specially along the upper reaches of the river. During this period most of the water it receives is from the seepage of its surrounding catchment areas and the sewage efflueHts from the enviroHing communities. Thus the river has been coHtinuously subjected to pollution. Seasonal variations of surfactants coHcentrations are illustrated in Fig. 18. It is noticeable that average values are higher at the confluence of the River Töss with the Rhein and very low upstream of the sewage outfall from Winterthur sewage treatment plaHt. The influeHce of sewage carryiHg surfactants is well illustrated in this present study.

11. SuspeHded Matter

Insoluble matter iH suspension is oHe of the commonest forms of pollutioH being present in sewage and iH most industrial wastes. All river waters, eveH those which 46 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 are relatively uHpolluted, contain suspended matter consisting of natural silt, sand, etc. deriving from the stream bed and banks. Suspended matter can be mainly inorganic or "mineral" in character, predominaHtly organic or "volatile", or, as is commonly the case, partly orgaHic and partly inorganic. The suspended matter in sewage effluents is largely organic. Mineral suspended matter may come iH waste from sand washings, china-clay works and stone quarrying. Insoluble material including chalk, talc, kaolin, gypsum and barium sulphate occur in paper making wastes. Storm water sewage may contain 1000-2000 ppm of suspended matter aHd this may have to be discharged to a receiving stream without beiHg subjected to sedimentation or any other treatment. Organic particles in sewage effluents can bring about deoxygenation of the water, gritty material carried along by swift currents can scour away algal growth from the stream bed, excessive turbidity can cut off the light, reduce the photosynthesis of the submerged vegetation, and make it more difficult for the fish to find their food, heavy deposits of silt may be harmful to the invertebrate bottom fauHa. The suspended matter conceHtration of the Töss is clearly shown in Table 22. On the average the suspended matter raHged from 6.06 to 14.7 mg/I. The suspended matter concentration upstream of the WiHterthur sewage efflueHt was comparatively lower than that downstream and as the river progresses down to its mouth there was a clear tendeHcy of reduction in concentration. The higher values recorded on July 5, 1967 are attributed to the heavy rainfall just the night before the day of sampliHg. The higher values undoubtedly resulted from the presence of large quantities of brown colloidal soil particles and allochthonous material present in the river. This hypothesis is supported by the fact that turbidity was higher at that time in the river. A careful comparison of Table 1 and Table 22 reveals that the suspended matter load of the Töss is a function of river discharge.

12. Total Volatile and Fixed Residue

The determination of residue by evaporation may be of limited value for estimating the effect of an effluent on a receiviHg water, but it may be useful as a control in plant operation. "Fixed residue" — the residue remaining after igHitioH does not distiHguish precisely betweeH organic aHd inorganic residue, siHce loss on igHition is not confined to organic matter but includes losses due to decomposition or volatilization of certain mineral salts. A better approximation of the orgaHic matter in water is available by B.O.D. 5 or C.O.D. (Chemical Oxygen DemaHd) methods. In Table 23 total volatile aHd fixed residue values at all the stations in the stretch of the river uHder study are represented. Fig. 19 was drawn from the data obtained, and it reveals that organic (volatile organic and inorganic matter) fraction varied between 12.1 and 19.6%. There was a definite increase iH concentration in the river dowHstream from the Winterthur sewage plant effluent (Table 24). The mean annual residue on evaporation was higher downstream than upstream from the Winterthur sewage treatment plaHt effluent, and ranged between 350 and 370 mg/I upstream, and 404 and 440 mg/I downstream. The average at Station 21 was 350 mg/I and at Station 31 it was 404 mg/l. From August 1967 to February Table 22. Suspended Matter (M.F.-500) mg/I in Töss WateI P. 1968 w 1967 o0 8. 9. 11.10. 7. 11. 12. 12. 3. 1. 6. 2. Average No. Sampling Stations 14. 3. 12.4. 17. 5. 13. 6. 5. 7. 8. 8. 4.0 12.4 7.43 N 5.6 34.4` 6.8 4.4 2.8 1.2 2.8 18 Krone 6.0 4.0 4.8 6.06 6.4 3.2 2.0 l.2 1.2 3.2 6.8 Brosi 6.0 2.8 2.4 4.4 33.2 21 l.6 l.6 2.8 2.0 4.4 10.73 6.0 30.4 14.4 5.2 46.0 6.4 8.0 22 Wespimühle 2.4 11.2 7.2 10.16 7.6 6.0 40.4 3.6 2.4 2.8 4.0 25 Spinnerei Hard 10.4 24.0 13.2 9.06 16.0 5.6 6.4 16.0 7.2 2.8 8.8 26 Neftenbach (L) 6.8 14.8 6.4 4.8 14.7 7:1 10.4 8.8 14.8 19.2 8.8 17.2 13.6 27 Neftenbach (R) 8.0 28.8 13.2 4.4 29.2 5.2 2.8 8.8 7.8 10.8 12.4 9.39 Pfungen-Töss 8.0 8.0 10.4 4.4 32.8 l.3 28 4.8 10.0 5.2 14.0 15.6 11.26 7:1 7.6 21.6 9.2 4.4 26.8 10.0 6.0 29 Pfungen-Canal 2.8 10.8 11.6 11.0 ^ 13.6 6.0 39.6 6.4 5.2 7.2 4.8 30 Rorbas 11.6 12.4 15.6 11.23 21.6 4.4 3.2 4.4 6.4 9.6 H 31 Tössegg 18.0 9.6 8.0 2.4 31.6 o= 10.10 7.85 5.4 5.8 6.24 4.3 9.16 11.28 Average 8.84 15.64 9.0 4.76 33.0 w P. E

Table 23. Total Volatile and Fixed Residue (mg/I) in Töss Water 1968 oä 1967 6. 2. Average 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. l. No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. o a 368 374 336 374 359 308 308 322 378 422 410 402 18 Krone 304 356 360 350 332 368 402 378 352 362 366 pl 21 Brosi 306 302 326 356 432 388 356 341 360 344 354 Ft 22 Wespimühle 308 314 330 374 376 412 378 366 402 378 350 370 F 326 328 340 352 378 434 25 Spinnerei Hard 412 390 380 404 FI 342 404 506 464 444 414 w 26 Neftenbach (L) 352 356 388 432 514 452 458 530 452 420 402 27 Neftenbach (R) 372 400 382 388 410 440 486 502 480 414 440 368 342 434 388 408 524 494 28 Pfungen-Töss 420 438 402 392 419 384 386 378 410 548 472 436 29 Pfungen-Canal 364 416 400 405 386 408 532 452 433 428 448 30 RoIbas 376 188 390 405 512 454 444 426 432 420 396 31 Tössegg 210 378 396 392 394 394 483 438 414 414 419 394 382 Average 329 330 368 365 393

Maximum. Minimum. 48 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

®VOLATILE ORGANIC AND INORGANIC MATTER mg/I =RESIDUE ON VOLATILIZATION 440- RESIDUE ON EVAPORATION 430—

420- 410-

400-

390- 380- 370-

360-

350-

340- 330- 320- 310 Fig. 19. Average Total Vola- tile and Fixed Residue Va- 300 18 21 22 25 26 27 28 29 30 31 lues in River Töss, 1967/68. STAT IONS

450- al P1 VOLATILE ORGANIC AND INORGANIC MATTER.mg/I D RESIDUE ON VOLATILIZATION. mg/I 440- ® RESIDUE ON EVAPORATION. mg/I 8.0.0.5 mg/I 430- KMn04 CONSUMPTION. mg/I 420-

410- 25 400- 10- 0

390- 9-

380- 8- 20

370- 7-

360- 6- 15 350- 5-

340- 4-

330- 3- 10

320- 2- 310— 1— 5 300— 0 i i i 4 STATIONS 8 21 22 25 26 27 28 29 i 30 3

Fig. 20. Average Total Volatile and F ixed Residue, B.O.D. 5 , and KMnO 4-Consumption Values in River Töss, 1967/68. Jahrgang 115 H. Rai. River Töss and its Underground Water Stream 49

Table 24. Percentage of Inorganic and Organic Fraction

Stations 18 21 22 25 26 27 28 29 30 31 Inorganic 85.2 87.9 86.7 85.3 82.8 81.6 82.l 80.4 81.4 82.8 Organic 14.8 12.1 13.3 14.7 17.2 18.4 17.9 19.6 18.6 17.2

1968 mean total values were found to be higher than for the rest of the period. Mean annual inorganic fraction (residue on volatilization) percentage was lower downstream than upstream from the Winterthur sewage effluent but the conceHtration of residue on volatilization was higher downstream than upstream. Fig. 19 shows that residue oH evaporation, residue on volatilization and volatile organic and inorgaHic matter follow the same trend throughout the year of the study i. e. all these tend to increase dowHstream from the Winterthur sewage effluent outfall and as the river progresses towards its mouth all decliHe again. The treHd of increase and decrease of maximum and minimum values of total volatile and fixed residue, volatile organic and iHorgaHic matter and residue on volatilization correspond to that of B.O.D. 5 and KMnO4-consumptioH (Fig. 20). Total volatile and fixed residue method gave a clear cut picture of the orgaHic load of the river at different places. Although as stated earlier, residue remainiHg after ignition does Hot distinguish precisely betweeH organic and inorganic residue, nevertheless iH the preseHt study this method gave quite a good approximatioH of orgaHic matter.

13. Iron (Fe+++)

The presence of more than traces of iron in river water generally iHdicates pollution by mine water or by iron pickling wastes, especially if the pH value is low and the acidity high. The maximum permitted limit iH the effluent, in Switzerland, is 1.0 mg/l. Iron was present in very minute coHcentrations in the River Töss water samples (Table 25). The maximum values recorded varied between 0.03 mg/1 aHd 0.10 mg/I, while the minimum value variations were 0.0 and 0.02 mg/1. The iron was comparatively more concentrated just below the Winterthur sewage effluent outfall thaH upstream.

B. The Bacteriological Studies on the River Tss

1. Standard Plate CouHt at 20° C (Total Count)

This test is known as "Total Count" and refers to the Humber of colonies of microorganisms on a poured plate of nutrient agar after five days incubation at 20° C±0.5° C. The count is relative and can obviously only refer to orgaHisms which are capable of growing uHder exactly defined conditions of the test. The more bacteria present, the greater the amount of orgaHic matter which supplies their nutritional requirements, aHd the greater the likelihood that the water is contaminated. Table 26 presents the results of bacteriological analyses of total count. Mean annual bacterial densities during the period of study indicate an initial increase in 0

Table 25. Iron (Fe +++) mg/l in Töss Water

1967 1968_ No. Sampling Station 14. 3. 12.4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. l. 6. 2.

18 Krone 0.02 0.0 <0.02 <0.02 0.03 0.02 <0.02 0.02 0.03 0.02 <0.02 <0.02 21 Brosi 0.03 <0.02 <0.02 <_0.02 0.06 0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 22 Wespimühle 0.05 0.06 0.04 0.02 0.06 0.03 50.02 <0.02 0.02 0.03 <0.02 <0.02 25 Spinnerei Hard 0.02 0.035 0.03 <0.02 0.05 0.03 _<0.02 0.02 0.02 <0.02 0.03 0.02 26 Neftenbach (L) 0.03 0.02 0.02 0.02 0.04 0.02 0.025 0.04 0.04 0.025 0.02 <0.02 27 Neftenbach (R) 0.04 0.09 0.05 0.025 0.06 0.035 0.04 0.035 0.10 0.06 0.04 0.02 28 Pfungen-Töss 0.05 50.02 0.02 <0.02 0.03 <0.02 0.05 0.02 0.06 0.03 50.02 <0.02 29 Pfungen-Canal 0.04 0.05 0.03 <0.02 0.05 0.03 0.02 0.06 0.05 0.04 0.04 0.03 30 Rorbas 0.065 0.02 0.03 0.025 0.07 0.02 0.02 0.025 0.02 0.03 0.03 <0.02 31 Tössegg 0.08 <0.02 0.03 0.025 0.05 0.06 0.02 0.035 0.03 0.03 0.02 <0.02

Maximum. Minimum. Table 26. Standard Plate Count of Bacteria at 20°C (1000/ml) in Töss Water

1967 1968 No. Sampling Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11. 10. 7. 11. 12. 12. 3. 1. 6. 2. Average

18 Krone 74 88 283 250 560 640 33 310 120 42 32 26 205 21 Brosi 97 28 141 410 450 170 38 68 23 46 18 23 126 22 Wespimühle 45 92 208 370 420 340 44 100 115 75 25 20 155 25 Spinnerei Hard 57 64 392 410 680 960 94 90 104 53 87 15 251 26 Neftenbach (L) 113 424 177 1200 630 3500 1300 620 520 90 75 57 726 27 Neftenbach (R) 287 1804 217 2120 1220 2400 2900 2000 880 160 252 224 1205 28 Pfungen-Töss 40 736 790 1160 1640 530 3300 220 4320 780 2160 700 1356 29 Pfungen-Canal 91 784 590 580 1900 6600 2000 900 390 99 108 120 1180 30 Rorbas 50 100 300 241 960 630 180 380 140 89 64 73 267 31 Tössegg 86 128 240 108 760 620 93 120 65 67 54 70 201 Average 94 425 334 685 922 1639 998 481 668 150 288 133 567

Table 27. Coli and Coliform Bacteria (N/ml) in Töss Water

1967 1968 No. Sampl. Stations 14. 3. 12. 4. 17. 5. 13. 6. 5. 7. 8. 8. 8. 9. 11.10. 7. 11. 12.12. 3. l. 6. 2. Average

18 Krone 80 30 530 4400 72400 35000 500 120000 6000 900 170 130 20012 21 Brosi 300 0 320 2320 37200 800 130 760 600 300 80 110 3576 22 Wespimühle 160 180 3900 630 15200 22000 280 8000 5200 3500 150 110 4942 25 Spinnerei Hard 270 40 3600 1720 31200 12000 1190 17000 3200 2000 2400 210 6236 26 Neftenbach (L) 1090 1120 2600 7400 54800 34000 38000 30000 15000 2200 710 1000 15660 27 Neftenbach (R) 1980 2200 4600 24800 76800 28000 50000 108000 60000 2300 5100 5000 30730 28 Pfungen-Töss 2010 9400 48000 5400 75000 17000 66000 1600 228000 69000 75000 1800 49850 29 Pfungen-Canal 2000 3500 4300 3000 67200 25000 25000 50000 10400 3300 1900 2500 16508 30 Rorbas 880 340 4300 1210 58800 4000 1200 6200 1800 1000 340 900 6748 31 Tössegg 990 310 2500 1030 46800 2500 1000 2200 1100 730 430 1000 5049 Average 976 1712 7465 5191 53540 18030 18330 34376 33130 8523 8628 1276 15931

U Maximum. Minimum. 52 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 bacterial population at Station 26/27 obviously due to discharge of sewage efflueHt into the river upstream of this statioH, self-purification proceediHg satisfactorily and progressively with the exception of an iHcrease in Humber at StatioH 28, due to iHdiscrimiHate discharge of untreated sewage from the surrounding communities. The total couHt was about two to four times greater below the outfall of the Winter- thur sewage treatment plant efflueHt than that upstream. In the unpolluted stretch of the river there was usually a sharp drop iH bacterial population during the dry season, when there was Ho contribution by ruH-off, and wheH bacteriological analysis may be relied on to show only organisms indigenous to the river and which constitute its normal population. The increase and decrease of absolute Humbers of total bacteria is directly proportional to the coliform densities.

2. Coli aHd Coliform

The test for the coliform group of organisms, or the B. Coli test, having survived the vicissitudes of an earlier time, staHds today as the most practical, delicate aHd rapid test for excremental pollution. It is a most reliable indicator, iH its positive aspects, of the possible danger and in its negative aspect, of the certaiH absence of microbes associated with waterborn epidemic disease aHd, generally speaking, it may be considered the one test which, for a river pollution iHvestigatioH, it is inexcusable to omit.

Fig. 21. Seasonal Variations of Total Bacteria (Plate Count at 10— 20°C) in River Töss at Brosi (21), Neftenbach (26/27) and 0 Tössegg-Töss (31).

A AMJ J A S 0 N D J Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 53

NIml 200000

100000

20000-

STATION 26/27

2000

1000

Fig. 22. Seasonal Variations of Coli and Coliform Bacteria in River Töss at Brosi (21), Nef- 100 STATION 21 tenbach (26/27) and Tössegg- Töss (31).

"The coliform group of organisms meets the criteria for a satisfactory biological indicator of contaminatioH or pollution" (FAIR and GEYER, 1961), and estimation is coHsidered the principal determinant for measuring the degree of pollutioH. Seasonal variations and maximum and minimum values at individual stations are given in Table 27. The mean annual values of coliform groups of organisms showed a sharp rise downstream from the Winterthur sewage treatment plant effluent, at Station 26/27 and coHtinued to do so dowH to Station 28. Downstream from Station 28 there was a sudden drop in coliform numbers, a further decrease was noticed along the course of the stream down to its mouth. The average numbers were higher duriHg the warmer half than the winter half of the year. The higher value during the month of July 1967 is attributed to the fact that there was heavy rainfall the day before the sampling. Similar conditions to those of the River Töss after heavy rains have been observed in the surveys of the Ohio River by FROST (1924), STREETER and PHELPS (1925), by HOSKINS et al. (1927) on the Illinois River, KELLER (1960) on the Jukskei-Crocodile River system and RAI (1964) on the Yamuna River in India.

54 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

OH the basis of the data obtaiHed it is apparent that with progressive self-purification of the river the bacteria count is reduced. The increase in bacterial density at Station 25 is attributed to the polluted Eulach pouring large quantities of bacteria into the river upstream of this station (Table 29). The increase in coliform density at Station 28 is due to the increase in localised faecal pollutioH from the towHships surrounding this area. Station 26/27, which is affected by the discharge of sewage effluent, shows a far larger bacterial population than the cleaner Station 21, which is a defiHite expression of the effect of the discharge of sewage effluent from the Winterthur sewage treatment plant. Seasonal variations in the quaHtity of plate count at 20°C and coliform count of the three stations are given in Fig. 21 and 22 respectively. The average total bacterial counts were about 9 to 10 times greater at Station 26/27 than at Station 21 and at Station 31 the average count was 5 to 6 times less thaH at Station 26/27. The factor responsible for this increase was the effluent of the sewage treatment plant at Winterthur. It appears from Fig. 22 that during the dry season there is an increase iH the relative number of coliform organisms, but the peak is very proloHged at Station 26/27. The seasonal variations of bacteriological conditions are particularly marked. From the above studies it will be seen that Station 21 is the least polluted, Station 26/27 the most polluted, and the remaining statioHs take intermediate positions between the two extremes. This study reveals, barring few minor parallelisms between

N/mt 200000 COLI AND COLIFORM

100000_ STANDARD PLATE COUNT

--HEAVY RAIN -DRY SPELL

1000 /ml 20000-

10000: i \\ - _ I \ - \ I

\\ \ -

2000- .`, , \\ / \

1000- \\\ / \i

500 I- I l l TOSS 18 21 22 2 5 2j 218 30 31 27 29 Fig. 23. Bacteriological Condition in the River Töss After Heavy Rain and Dry Spell Compared. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 55

1000/m1 2000

1000

•---. DISSOLVED OXYGEN 200 • -- °ASAT.OF OXYGEN — TOTAL BACTERIA 100

Fig. 24. The Effect of Pollution — Oxygen Sag and Corresponding Bacterial Population in the River Töss. the plate count and coliform group of organism densities, that the average numbers of both are higher in dry weather. Fig. 23 shows a comparisoH of the bacterial condition of the River Töss after heavy rains and dry spells respectively. After heavy rains the proportion of HoH-faecal orgaHisms at all stations was higher thaH the figures of coli and coliform, coHfirming that runoff contributioHs are mainly non- faecal in origin. During the dry season coli and coliform bacteria were predominant in the river, with typical peaks at Station 26/27, where continuous direct faecal pollution occurs throughout the year. While a certain amount of organic wastes is necessary to the normal biological cycle, too much waste can destroy it. The key in the Hormal biological cycle is oxygen, which is essential for the development of the beneficial organisms. As the organic waste concentrations in the River Töss increase, bacterial growth is stimulated with a greater demand for oxygen. Thus bacteria decrease the oxygen level. The effect of pollutioH in the River Töss is illustrated in Fig. 24 from the data obtained during this study.

C. Physico-Chemical and Bacteriological Characteristics of Sewage Treatment Plant Effluents and the Tributaries of River Tss

As contamination can materially alter the normal state of the river, special attention was given to all sources found in the catchmeHt area of the River Töss stretch under study. The results obtained from two sewage treatment plant effluents and five tributaries of the River Töss aloHg its course from Winterthur to Tössegg-Töss are here discussed briefly aHd the data is presented in Table 28.

1. Sewage Treatment Plants a) The Winterthur Sewage Treatment Plant The location of this plant is illustrated in Fig. 1. This plant has a capacity to treat 1700 l/sec (1.5 X D.W.F.) of waste and it receives sewage from 24 communities. Table 28. Range of Variations and Average Annual Physico-Chemical and Bacteriological Conditions of the Sewage Treatment Plant Effluents and the Tributaries of River Töss

Temperature Carbonate Hardness Total Hardness Soluble PO4-3 pH °C CaCO3 mg/l mg/l mg/l Sampling Stations Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Winterthur Sewage Treatment Plant Effluent 7.47 7.6 7.4 14.4 18.6 9.8 310.0 350.0 280.0 334.2 382.0 304.0 14.58 23.0 7.0 Rorbas Sewage Treatment Plant Effluent 7.87 8.05 7.6 11.8 18.l 5.0 362.9 402.5 317.5 380.2 410.0 332.0 13.7 19.0 7.0 Eulach 8.24 8.4 8.l 9.2 16.7 2.2 333.2 362.5 292.5 371.7 396.0 324.0 0.96 l.8 0.15 Näfbach 8.15 8.4 7.95 8.7 15.8 2.5 343.9 362.5 330.0 404.5 422.0 392.0 l.33 2.3 0.25 Mülibach 8.37 8.45 8.15 8.7 14.5 0.3 323.5 347.5 285.0 359.4 410.0 312.0 0.28 0.8 0.06 Wildbach 8.39 8.45 8.3 9.8 17.4 l.6 318.3 340.0 300.0 351.0 372.0 308.0 0.37 0.64 0.20 Tüfenbach 8.17 8.3 8.0 8.4 15.9 0.5 264.7 290.0 240.0 296.3 314.0 268.0 0.07 0.44 <0.02

Standard Plate Total Volatile and Surfactants Iron (Fe++-F+ ) Count of Bacteria Coli and Coliform Fixed Residue mg/l (Anionic) mg/1 mg/l 1000/ml Bacteria N/ml Sampling Stations Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Winterthur Sewage Treatment Plant Effluent 535.0 612.0 440.0 0.425 0.670 0.020 - 0.17 0.02 334 1200 87 10228 30000 500 RoIbas Sewage Treatment Plant Effluent 529.0 622.0 332.0 0.777 1.310 0.00 0.08 <0.02 1951 5240 520 134841 364000 7300 Eulach 455.5 516.0 394.0 0.086 0.180 0.00 0.12 <0.02 121 330 22 1795 11000 20 Näfbach 529.5 592.0 490.0 0.128 0.360 0.040 0.04 <0.02 508 2300 63 9403 26000 1180 Mülibach 423.8 542.0 374.0 0.080 0.130 0.020 0.18 <0.02 105 500 16 3753 12100 230 Wildbach 402.8 450.0 348.0 0.048 0.090 0.00 0.06 <0.02 35 93 8 959 4600 0 Tüfenbach 345.3 438.0 304.0 0.043 0.090 0.00 0.38 <0.02 24 92 1 151 870 0 Dissolved Oxygen B.O.D.; KMnO4-Consumption Chloride (Cl-) Suspended Matter Saturation mg/l mg/l mg/l (M.F. 500) mg/l Sampling Stations Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Winterthur Sewage Treatment Plant Effluent 45.3 54 39 13.39 26.2 7.2 30.86 44.24 23.07 43.48 53.2 32.0 11.33 26.0 4.0 RoIbas Sewage Treatment Plant Effluent 88.7 113 77 27.14 66.0 9.8 32.07 69.52 22.44 32.25 54.2 19.2 12.80 36.0 5.2 Eulach 105.7 124 99 2.29 3.9 l.5 10.54 16.91 7.74 11.60 18.6 8.8 4.91 22.8 0.8 Näfbach 103.5 118 3.87 2.4 90 6.9 11.37 14.22 8.69 18.35 31.0 8.4 6.6 12.4 l.6 a Mülibach 105.0 112 100 2.07 3.3 1.4 9.66 12.17 7.74 7.48 12.2 5.0 23.28 118.4 l.8 7y Wildbach 110.0 132 82 1.75 3.1 0.0 7.79 12.48 5.21 9.42 14.2 6.8 7.83 27.6 l.2 Tüfenbach 100.4 105 2.01 91 >10.5 0.6 20.83 129.56 6.48 2.87 3.8 2.2 15.70 42.0 2.0 H m a Total Phosphates Nitrate (NO 3-) Nitrite (NO2) Ammonia (NH3) Dissolved Oxygen (PO4-3) mg/l mg/l mg/l mg/l mg/l C

Sampling Stations Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. a Winterthur Sewage cro ö Treatment Plant Effluent 17.16 24.0 8.0 28.68 50.0 4.0 l.291 4.5 0.25 6.14 12.5 0.35 4.33 5.0 3.7 Rorbas Sewage

Treatment Plant Effluent 18.45 24.0 12.0 33.02 55.0 15.0 2.129 4.0 0.35 7.18 14.0 0.9 8.93 10.1 7.6 aw Eulach 1.50 3.0 0.3 16.79 20.0 13.75 0.317 0.7 0.08 0.22 0.6 0.02 11.28 13.6 9.5 9 v3 Näfbach 2.04 3.5 0.8 27.39 37.5 20.0 0.076 0.4 0.12 0.35 0.48 0.2 11.14 13.5 9.8 Müllbach 0.53 0.85 0.18 10.39 15.0 3.5 0.05 0.11 0.01 0.19 0.48 0.06 11.37 13.8 10.2 w Wildbach 0.61 l.5 0.28 15.14 20.0 10.0 0.116 0.55 0.038 0.06 0.16 <0.02 11.55 14.l 7.3 Tüfenbach 0.20 0.6 0.05 3.9 17.5 2.0 0.013 0.06 <0.005 0.12 0.4 0.04 10.75 13.8 9.2 58 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

Fig. 25. Catchment Area of Winterthur Sewage Treatment Plant (from Enzmann, 1967).

Table 29. Chemical Conditions of Winterthur Sewage Treatment Plant Effluent (Mean of the Yearly Averages)

Mechanically Treated Complete Activated Sludge Components Effluent Treatment Plant Effluent 1957-1965 (Biological) 1967-1968 Maximum Minimum Average Maximum Minimum Average pH 13.5 7.0 9.l 7.9 7.6 7.47 Oxygen mg/l 6.75 l.6 4.02 5.0 3.7 4.33 B.O.D.5 mg/l 257.0 63.0 166.8 26.2 7.2 13.39 KMn04-Consu. mg/l 461.0 216.0 291.7 44.24 23.07 30.86 NH3 mg/I 26.0 9.5 17.5 12.5 0.35 6.14 NO3- mg/I 11.0 <0.05 50.0 4.0 28.68 NO2- mg/I 9.2 <0.005 4.5 0.25 l.291 Cl- mg/I 66.0 10.0 41.8 53.2 32.0 43.4 PO43mg/I (Sol.) 16.0 3.5 10.0 23.0 7.0 14.58 PO43- mg/I (Total) 44.0 12.0 21.4 24.0 8.0 17.16

(ENZMANN, 1967) with an approximate population of 106 000. Fig. 25 shows the detailed catchment area of this plaHt. Before the construction of this plaHt most of the sewage was put straight into the Eulach. First a mechanical waste treatment plant was constructed in 1950 and then a complete activated sludge treatment unit was added to it in September 1966. Today almost all the sewage that flows into the plant receives activated sludge treatment (biological). The effect of the additioH of an activated sludge treatment unit to this plaHt on the quality of its effluent, which River Töss receives, is clearly demonstrated in Table 29. The B.O.D. 5 of the effluent is reduced from 166.8 to 13.39 mg/l, KMnO 4 3 is reduced from-consumption values are reduced from 291.7 to 30.86 mg/I and NH 17.5 to 6.14 mg/l. This improvement in quality of the effluent is certain to influence the sanitary condition of the Töss. During the present studies the effluent of this plant had temperature variations of 9.8 and 18.6°C; pH varied from 7.4 to 7.6 and Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 59 it remained more or less constaHt. Dissolved oxygeH was found to vary from a miHimum of 3.7 to a maximum of 5.0 mg/l. The maximum B.O.D. 5 value was 26.2 mg/l in April 1967 and the minimum 7.2 mg/l in August 1967 and the aHnual average of B.O.D. 5 value was 13.39 mg/I. KMHO4-consumption values varied between 23.07 and 44.24 mg/l with an average of 30.86 mg/l. Annual average for NH 3 was 6.14 mg/l and it varied between 0.35 mg/l and 12.5 mg/l. Nitrite was available iH small quantities throughout the year and it varied between 0.25 and 4.5 mg/I, with an annual average of 1.291 mg/l. Nitrate was generally high (maximum 50.0 mg/I) with an exception of 4.0 mg/l iH February 1968, but the average value calculated was found to be 28.68 mg/I. Phosphate was very high throughout the year. The toll index varied from 500 N/ml to 30 000 N/ml and the total count of bacteria at 20° C was found to be 334 000 N/ml on average.

b) The Rorbas Sewage Treatment Plant

This plaHt treats the sewage from the localities of Embrach, Freienstein, Teufen and Rorbas with an approximate population of 6500, and a populatioH equivaleHt of 2500 from the industries in the surrounding area. Its maximum capacity is 72 1/sec. The temperature of the effluent varied between 5 aHd 18.1°C. Minimum dissolved oxygen recorded was 7.6 mg/l in the moHth of May.1967 and maximum was 10.1 mg/l in July 1967 and January 1968. The average D.O. value during the study period was 8.93 mg/l. The variations in B.O.D. 5 were very great (9.8-66.0 mg/l) and average B.O.D. 5 was 27.14 mg/I. Annual average value for KMnO 4-consumption was found to be 32.07 mg/I. Ammoniacal nitrogeH varied between 0.9 and 14.0 mg/l and the average NH3 value was higher than that of the WiHterthur sewage treatmeHt plant. The minimum NO2- value was 0.35 mg/l, while the maximum was 4.0 mg/l. Nitrate values fluctuated between 15.0 and 55.0 mg/l. Phosphate (dissolved) varied between 7.0 and 19.0 mg/I aHd total phosphate average value was 18.45 mg/l. Carbonate hardness was much higher than that of the Winterthur sewage treatmeHt plant effluent. The efflueHt of this sewage treatment had lower chloride values iH comparisoH to the Winterthur sewage treatment plant and the pH was slightly higher than that of the Winterthur sewage treatment plant. Coliform densities varied between a miHimum of 7300 N/ml aHd a maximum of 364 000 N/ml. The total count was also very high and the annual average density was 1 951 000 N/ml. OH the average this plants effluent had 0.777 mg/l of surfactants (anionic) as compared with 0.425 mg/l of Winterthur sewage treatment plant.

2. Tributaries

a) Eulach

It is one of the major tributaries of the River Töss aHd also a controversial source of pollution of the Töss. Before the construction of the sewage treatment plant at Hard, it was used as a vehicle for the disposal of raw sewage. Although the major part of the sewage has been diverted into the treatmeHt plaHt at WiHterthur-Hard, 60 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 it still carries the effluent from the sewage treatment plaHt of Elgg (activated sludge treatment) and raw sewage from the Elsau and WieseHdangen communities and their surroundiHg areas. Table 30 clearly shows the effect of diversion of sewage from the Eulach to the Winterthur sewage treatment plant.

Table 30. Chemical and Bacteriological Characteristics of the Eulach for the Years 1935 to 1968

Components 1935/36 1948/49 1950-1960 1967/68 Oxygen (D.O.) mg/I 7.92 5.45 10.l 11.28 Percent Sat. of 02 75 57.5 100 105.7 BOD 5 mg/l 27.8 2.29 KMnO4 mg/l 252.l 131.0 27.76 10.54 NHa mg/l 4.64 9.7 0.43 0.22 NO3- mg/1 5.2 <0.05 10.95 16.79 NO2- mg/1 0.08 <0.005 0.52 0.317 Cl- mg/l 20.3 39.9 18.l 11.6 Plate Count (Bact.) N/I 1355500 29701000 378000 121000 Coli and Coliform N/1 - 76083 4986 1795

The catchmeHt area of this tributary covers an area of 121 km 2 aHd is shown in Fig. 1. The average discharge during the period of study was 826 1/sec. The increase in values of the important parameters of pollution from 1935 to 1948-1949 was due to the rapid urbanization in the catchment area of the Eulach and due to the untreated sewage which it received duriHg this period. During 1950-1966 the load of pollutioH from the Eulach was reduced by constructiHg a mechaHical sewage treatment plant at Winterthur-Hard and divertiHg the sewage to this plant for treatment. The condition of the Eulach further improved after diverting all the sewage of the city of Winterthur to the sewage treatmeHt plant, after a completed biological treatmeHt unit was added to it in September 1966. This diversion has stopped adding a major portioH of the untreated sewage to the Eulach from its catchment area. The data presented iH Table 30 gives a full impact of the diversion of sewage from the Eulach.

b) Niifbach

The detailed catchment area and its topography is illustrated iH Fig. 1. The average discharge during the period of study was 3821/sec. Besides receiving pollution from its drainage area, it also receives effluent from the sewage treatment plant (biological) at Seuzach. This tributary is the second largest in the stretch of the river under study. On comparison of the chemical and bacteriological parameters it appears that this tributary was rather more polluted than the Eulach. The Näfbach had dissolved oxygen variatioHs of from 9.8 to 13.5 mg/I. The B.O.D. 5 varied between 2.4 and 6.9 mg/I. Annual average for N1-1 3 was 0.35 mg/I. NO2- coHcentration was lower thaH that of the Eulach and NO3- varied between a minimum of 20.0 mg/l and a maximum of 37.5 mg/l. Phosphate was quite high throughout the year. KMn0 4 -consumption values varied between 8.69 and 14.22 mg/I, with aH average of 11.37 mg/1. Carbonate hardness and chloride were also higher than that of the Eulach. Jahrgang 115 H. RAT. River Töss and its Underground Water Stream 61

Coli and coliform densities were 5 to 6 times the value of the Eulach and total bacteria count at 20°C was about 4 to 5 times that of the Eulach.

c) Miilibach

The detailed catchmeHt area (19 km 2) of this tributary is shown in Fig. 1. The average discharge during the period of study was 129 1/sec. Dissolved oxygen perceHt of saturation was found to vary from 100% to 112%. The maximum B.O.D. 5 value was 3.3 mg/1 in November 1967 aHd the minimum 1.4 mg/l in September 1967. KMnO4-coHsumption values varied between 7.74 and 12.17 mg/l, with an average of 9.66 mg/I. AHnual average for NH 3 was 0.19 mg/l. Nitrites were low and varied betweeH 0.01 and 0.11 mg/l. The average value for nitrate was found to be 10.39 mg/l aHd it varied betweeH 3.5 and 15.0 mg/I. Coli aHd coliform densities varied from 230 to 12 100 N/ml, and the total bacterial count at 20°C was found to be 105 000 on the average. It was observed that this tributary was much less polluted than the Eulach. d) Wildbach

In the catchment area (50 km 2) of this tributary there is oHly one sewage treatment plant (Fig. 1) at Lufingen-Augwil. The average discharge during the period of study was 341 l/sec. This tributary receives sewage from the communities of Sädel, Edli- buch, Vordere-Marchlen, Rain, Hintere-Marchlen, Gsteig, Mühli, LufingeH aHd Augwil. From the point of view of pollution this tributary is cleaner than either Eulach, Näfbach or Mülibach. The data is presented in Table 28. The minimum dissolved oxygen was 7.3 mg/l in July 1967 and the maximum was 14.1 mg/I iH December 1967. The variation in B.O.D. 5 was between 0.0 and 3.1 mg/1. Ammoniacal nitrogen varied between 0.02 and 0.16. The maximum NO 3- value was 20.0 mg/l, while the minimum was 10.0 mg/l. Phosphate (dissolved) varied betweeH 0.2 and 0.64 mg/I. Coliform densities varied between 0 aHd 4600 N/ml. The total bacteria count at 20°C was also low and the annual average was found to be 35 000 N/ml. e) Tüfenbach

It is the smallest and the cleanest of all the tributaries (Fig. 1) studied and has a very small catchmeHt area (4 km 2). The average discharge during the period of study was 28 l/sec. The communities surrouHding this tributary pour their sewage directly iHto it. Dissolved oxygen varied between 9.2 and 13.8 mg/l. The maximum value of B.O.D. 5 was 10.5 mg/1 in March 1967 aHd the minimum 0.6 mg/l in August 1967. The annual average of B.O.D. 5 was fouHd to be 2.01 mg/l. NH3, NO 3- and NO2- concentrations were generally very low. Phosphate (dissolved) varied between 0.02 and 0.44 mg/I.:KMnO 4-consumption was lower thaH in the other tributaries studied. The anHual average of coliform deHsities was 151 N/ml and the annual average of the total bacterial population was found to be 24000 N/ml. The data are presented in Table 28. 62 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

D. Diurnal Variation Studies in the River Töss

The results and coHclusions based upon the preseHt study of the degree of pollution of the River Töss system from Steigmühle (Station 1, upstream Winter- thur) to its confluence with Rhein at Tössegg have been already discussed. In this research study the object was to find in what way the biological sewage treatment plant will affect the sanitation of the River Töss. For this study a 24 hour research was conducted at the Winterthur sewage treatment plant. Samples were collected from the plant at different stages of the sewage treatment process and from the river at StatioH 25 (SpiHnerei Hard), upstream of the effluent outfall and at StatioH 26/27 (Neftenbach), downstream from the effluent outfall. These studies were carried out at the time when the river was at low flow (April 25/26, 1967) and once duriHg high flow (October 24/25, 1967). Similar studies were carried out at the Rorbas sewage treatment plant and in the river at Station 30 (Rorbas), upstream and Station 31 (Tössegg), downstream from the Rorbas sewage treatment plaHt effluent outfall. Diurnal variations at these places were carried out oHce in winter (February 27/28, 1968) and once in the summer (July 24/25, 1967). All important chemical and bacteriological parameters were studied at 3-hourly intervals each time diurnal variation studies were undertaken (Table 31, 32 and Figs. 26, 27, 28 and 29).

1. Diurnal Variation Studies at Winterthur Sewage Treatment Plant and River Töss (between Station 25 and Station 26/27)

The diurnal variation in dissolved oxygen (D.O.), biochemical oxygen demand (B.O.D. ․), NH3 , NO3-, KMnO4-consumption, phosphate, coli and coliform, and total bacterial densities for April 25/26, 1967 and October 24/25, 1967 are given iH Figs. 26 and 27 respectively. The main cause for these variations was the sewage effluent outfall upstream of Station 26/27. In the plant effluent minimal D.O. concentrations were found during the late afternoon and the periods just before dawn when the reserve was the case in the river, both upstream and downstream. DuriHg the high flow the D.O. concentration at Station 25 varied from 11.2 to 12.3 mg/I, and at Station 26/27 it varied from 10.2 to 12.3 mg/l, whereas during low flow the range of variation at Station 25 was betweeH 9.8 and 11.6 mg/l and at StatioH 26/27 it was between 7.3 and 11.6 mg/I. The results show that both minimum and maximum values of D.O. concentration were lower at the low flow than at the high flow period of the river. During the April sampling the D.O. percent saturation at Station 25 did not fall below 92% and during the October sampling the minimum D.O. percent saturation recorded at Station 26/27 was 74% at aHy time duriHg twentyfour hours. It may be remarked here that the oxygeH rhythm, the diurnal pulse of the River Töss, is largely a reflec- tion of temperature, turbulence aHd photosynthesis inter-relationships. The diurnal oxygen pulse of the Töss is less pronouHced since mechanical aeration and oxygen consumption is essentially uniform within a given segment. mg/1 400 mg/1 350 900 300 800 KMnO4 Consu.

250 700 NI ml 260 COLI AND COLI FORM STANDARD PLATE COUNT 600006 150

100 1000/ ml

200000 —20000 50

40 106006 30

0 —2000 TIME 14 17 20 23 02 05 08 11 14 17 20 20000 mg/I mg /I 13 45—Q 00. NH 10000 40— \ 3 30—

2000

10001 l l 100 I l l I I I I I I I I TIME 14 17 20 23 02 05 00 11 14 17 20 23 02 05 08 11

3 — RAW SEWAGE o---o EFFLUENT MECH. EFFLUENT BIOL. --^ SPINNEREI HARD g— ( NEFTENBACH 0 TIME 14 17 20 23 02 05 68 1 14 17 210 213 02 05 08 11

Fig. 26. Diurnal Variations at Winterthur Sewage Treatment Plant and River Töss at Spinnerei Hard and Neftenbach on April 25/26, 1967. Rate of Flow 7.89 m3/sec. Table 31. Diurnal Variations at WinteIthur Sewage Treatment Plant and Töss

April 25/26, 1967 October 24/25, 1967 PO4-3 PO4-3 Time Temp. pH NO2- Cl- (Dis.) Time Temp. pH NO2 Cl- (Dis.) °C mg/l mg/l mg/l °C mg/l mg/1 mg/l

Raw Sewage

1400 14.2 8.4 0.35 120.0 25.0 1200 18.3 8.0 <0.005 68.0 28.0 1700 14.2 8.35 <_0.25 64.4 12.5 1500 17.6 8.4 <0.005 66.8 16.0 2000 13.2 8.5 <_0.25 61.6 11.5 1800 18.3 8.6 <0.005 80.4 11.0 2300 12.8 8.2 50.25 39.2 10.0 2100 17.2 8.2 <0.005 68.8 11.0 0200 9.9 7.95 5.0 24.8 5.0 2400 16.9 7.95 <0.005 39.2 10.0 0500 12.2 7.8 _<0.25 20.0 l.5 0300 16.4 8.0 l.625 28.0 3.5 0800 12.2 7.95 0.25 16.4 30.0 0600 16.5 7.8 0.875 29.6 3.0 1100 14.6 7.9 2.25 84.4 40.0 0900 17.6 8.2 50.005 56.4 40.0

Effluent - Mechanical

1400 14.l 7.7 0.25 50.4 24.0 1200 17.6 7.9 <0.005 52.4 17.0 1700 14.5 7.7 0.25 49.2 24.0 1500 17.8 7.8 <0.005 60.8 19.0 2000 13.4 8.25 <_0.25 66.4 16.0 1800 17.5 8.4 <0.005 70.4 11.0 2300 13.3 8.2 <_0.25 55.6 11.5 2100 17.4 8.2 <0.005 71.2 15.0 0200 12.1 7.9 <_0.25 45.2 11.5 2400 16.8 7.7 <0.005 59.2 12.0 0500 11.2 7.8 <_0.25 34.0 6.0 0300 16.6 7.6 <0.005 46.8 11.0 0800 12.5 7.8 0.75 28.4 8.0 0600 16.1 7.5 <0.005 39.6 10.0 1100 14.0 7.8 3.0 40.8 12.0 0900 16.8 7.5 <0.005 31.6 10.0

Final Effluent - Activated Sludge Treatment Plant Effluent flow = 0.65 m3/sec. Effluent flow = 0.54 m3/sec.

1400 13.8 7.6 1.50 46.4 13.0 1200 17.8 7.7 2.25 43.6 15.0 1700 14.5 7.65 l.50 46.0 13.0 1500 18.l 7.7 l.50 45.6 15.0 2000 14.l 7.75 l.20 48.4 13.5 1800 18.0 7.5 l.50 54.4 16.0 2300 12.5 7.6 0.85 51.6 14.0 2100 17.9 7.6 l.125 62.8 15.0 0200 8.0 7.95 0.95 51.6 14.0 2400 18.8 7.6 l.25 62.4 15.0 0500 12.7 7.5 1.0 49.6 16.0 0300 17.8 7.6 1.25 58.8 17.0 0800 13.6 7.7 0.9 48.8 14.0 0600 17.5 7.6 l.125 60.0 19.0

Töss at Spinnerei Hard - Upstream River flow 7.89 m3/sec. River flow = 2.68 m3/sec. 1400 7.1 8.2 0.04 5.3 0.28 1200 12.3 8.4 0.05 11.2 l.4 1700 8.2 8.65 0.09 5.5 0.30 1500 11.2 8.2 0.05 10.6 l.1 2000 7.5 8.55 0.09 5.6 0.46 1800 12.l 8.4 0.06 9.3 0.9 2300 7.0 8.3 0.07 5.8 0.36 2100 11.9 8.4 0.15 9.3 0.8 0200 6.6 8.2 0.05 5.4 0.30 2400 11.4 8.2 0.175 10.3 1.3 0500 4.9 8.l 0.055 5.6 0.35 0300 11.5 8.2 0.175 10. l.4 0800 5.7 8.2 0.05 5.4 0.4 0600 11.3 8.2 0.15 9.1 l.l 1100 7.0 8.4 0.045 5.7 0.80 0900 11.7 8.2 0.125 9.8 l.3

Töss at Neftenbach (Left) - Downstream

1400 7.9 8.0 0.14 8.3 0.50 1200 13.3 7.7 0.15 17.5 5.0 1700 8.5 8.2" 0.12 , 8.0 0.70 1500 12.8 7.8 0.125 15.6 2.3 2000 8.1 7.85 0.08 8.3 0.70 1800 12.2 7.6 0.15 16.8 2.4 2300 7.2 7.7 0.09 . 9.2 0.65 2100 12.3 7. 0.275 20.0 3.6 0200 6.8 7.65 0.08 8.0 0.65 2400 11.7 7.6 0.20 16.7 2.3 0500 6.8 7.6 0.08 8.3 0.30 0300 12.l 7.5 0.225 17.7 2.6 0800 6.8 7.8 0.08 8.4 0.60 0600 12.0 7.5 0.20 17.3 4.0 1100 8.l 7.9 0.075 8.8 0.7 0900 12.5 7.5 0.30 19.3 5.5

Töss at Neftenbach (Right) Downstream

1400 8.2 8.2 0.35 11.7 l.5 1200 13.7 7.8 0.375 22.2 7.5 1700 9.l 8.4 0.95 11.8 1.7 1500 13.1 8.1 0.375 19.4 4.5 2000 8.3 8.2 0.16 12.3 l.2 1800 13.2 7.8 0.375 25.0 5.5 2300 7.5 7.9 0.15 11.7 l.2 2100 13.l 7.7 0.50 20.0 5.5 0200 7.0 7.7 0.15 10.0 l.2 2400 12.3 7.75 0.375 24.4 4.0 0500 6.5 7.85 0.145 10.4 l.l 0300 12.6 7.7 0.375 20.4 4.5. 0800 6.9 8.0 0.165 11.7 l.5 0600 12.4 7.6 0.375 19.8 5.0;. rn 1100 8.6 8.2 0.25 12.4 1.8 0900 12.4 7.7 0.375 24.6 6.0 66 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

HARRISON and ELSWORTH (1958), OLIFF (1960) and HYNES (1958) have stressed the importance of the physical characteristics of rivers, such as flow and silt loadiHg. These factors have Hot been adequately stressed or evaluated by many of the previous workers in this field, mainly because the studies have been reported on slow flowing streams, where organic pollution effects have beeH considered to be almost entirely due to the well known effects of deoxygenation - the so called "Oxygen Sag". The present study has shown that the oxygen sag does not indicate itself, but is replaced by diurnal sag only duriHg the periods of low flow (Fig. 27). This diurnal sag is deeper in the polluted stations in comparison to the cleaner stations. The B.O.D. 5 curve followed the set pattern of daily activities of the people. The curve started risiHg with the daily start of activity beginning 0600 and continued ascending up to sometimes past 1900. This routine sets the patterH of sewage flow and strength. B.O.D. 5 values were slightly higher in the efflueHt during October 1967 sampling than those of the April sampling, but in the stations upstream of and downstream from the efflueHt outfall the values appeared to be the same and showed very slight diurnal variations. The results of the study iHdicate that there was no substantial effect on the river B.O.D. 5 attributable to the effluent. KMnO4-consumption values of the effluent were higher between 0800 and 1200 hours and lower during the rest of the period, at the times diurnal variation studies were made. At Station 25 the KMnO 4-consumption values were higher during October 24/25, 1967 (10.6 to 17.2 mg/I) than duriHg April 25/26, 1967 (8.7 to 11.8 mg/I). There were no characteristic diurnal variations observed, although the values teHded to increase between the 1100 to 1800 hours. At Station 26/27 the KMnO 4-consumption was higher but the shape of the curve was similar to that of Station 25 and diurnal variatioHs were less pronounced. The Nitrate curve of the effluent in October 1967 showed pronouHced diurnal variations and peak values were recorded during late afterHoon and morning aHd the curve declined to a minimum during midnight and afternooH. At Station 25 and Station 26/27 maximum concentrations of NO3 - were recorded duriHg the afternoon, the hours of morHiHg, and minimum values duriHg the night. The River Töss at Station 26/27 showed more pronounced variatioHs than at Station 25, and values of NO3- were also higher downstream from the sewage effluent outfall compared to the statioHs upstream. This may be attributed to the intense nitrification downstream from the effluent outfall in the river. DuriHg high flow in April 1967 the NO 3 -variations were pronounced only in the effluent samples and the stations upstream and downstream did not show any marked variations. Phosphate concentrations were also higher at Station 26/27 during the periods of diurHal variatioH studies, the increase iH phosphate during the low flow period (October 26/27, 1967) showed values of phosphates seven times higher at Station 26/27, whereas during high flow period the PO4 3- concentration at Station 26/27 increased only to three times the value at Station 25. During these studies the amount of phosphate kg/day was calculated every time diurnal variation studies were undertaken. In April (river flow 7.89 m3/sec) 344 kg/day phosphate were recorded at Station 25, the effluent from Winterthur sewage treatment plaHt released 932 kg/day

mg/I 1000/mI COLI AND COLIFORM STANDARD PLATE COUNT N/ml 100000 mg/I KMnO - Consu, 800000

mg/I NO., 200000 i i j 2C000 0— 30

50 100000 i / j `^ I 10000 "" 40 200— P 20

20-

10— 3 0 20000 _V 2000 0 <0.5 I I o I I I TIME 12 15 18 21 24 03 06 09 12 15 18 21 24 03 ob 09 12 15 18 21 24 03 O6 0 9 mg/I mg/I 40 mg/I 3_ 70 mg/I 10000 . , ^`_ 1000 TOTAL PO 12 D.O. 30—NH3 50

25-

20- 2000 200

1000 100 15-

10— _ RAW SEWAGE o- o EFFLUENT MECH. — EFFLUENT BIOL. 5— — SPINNEREI HARD N—x NEFTENBACH 100 v 10 x 6 1 0 0 12 15TIME 1812 15 18 21 21 24 032406 09 03 06 09 12 15 18 21 24 03 06 09 TIME 12 15 21 24 0 06 09 12 15 18 21 24 0 0. 09

Fig . 27. Diurnal Variations at Winterthur Sewage Treatment Plant and River Töss at Spinnerei Hard and Neftenbach on October 24/25, 1967. Rate of Flow 2.68 m3/sec. 68 Vierteljahrsschrift der Naturforschenden Gesellschaft, in Zürich 1970

into the river and at Station 26/27 1295 kg/day of phosphate were recorded. During low flow (river flow 2.68 m3/sec) in October, only 222 kg/day phosphate were recorded at Station 25, and during this period 863 kg/day of phosphate were added into the river through the WiHterthur sewage treatment plant effluent, and at Station 26/27 1417 kg/day were recorded. This shows that the treatment plant is an important source of phosphate content iH the river, and runoff from the highly cultivated areas in the catchment of the River Töss has no effect on the phosphate concentration of the River Töss. pH showed no variations in the efflueHt samples. IH the river samples both upstream and downstream, pH variations followed a normal pattern, i. e. increase in pH in daytime aHd decrease at night. Water temperatures fall gradually throughout the night to dawn. They were, however, higher in the October 24/25 than in the April 25/26, 1967 studies. Bacteriological conditions of the efflueHt and the river water showed very pronounced diurnal variations during the April 25/26, 1967 studies. The coliform densities of the plants effluent increased after the morning periods and continued to iHcrease to sometime before night and thereafter the curve decliHed gradually throughout the night to dawn. The upstream sampling showed higher values during the periods of night and lower values at daytime. In the downstream station the coliform densities were not very much altered by the influence of the sewage efflueHt but followed a pattern similar to that of the effluent. The concentration of coliform organisms at Station 26/27 was almost the same as that of Station 25. The total count of the bacteria curve followed almost the same pattern as that of the coliform bacteria in the sewage effluent samples. In the river, upstream of the sewage effluent, the curve started rising in the afternoon and the maximum value was reached at 1400 hours; thereafter the bacterial densities gradually decreased through the night till dawn. At Station 26/27 the river showed a gradual increase in bacterial population from dawn throughout the day and the maximum count was recorded at 1700 hours, after which the curve started declining gradually throughout the night uHtil dawn. It is iHteresting to note here that the total bacterial densities did not increase appreciably dowHstream from the sewage effluent from that of upstream, so as to influence the quality of the water. A similar phenomenon was also noted with coliform bacteria. The diurnal variation studies of October 24/25, 1967 also showed veIy defiHite variations in bacterial densities. Coliform bacteria curves of effluent and of StatioH 25 followed the pattern of the April 25/26, 1967 effluent curve, but at Station 26/27 the bacterial densities increased betweeH 0600 and 1200 hours, the curve declining gradually after 1200 hours, and again rising gradually throughout the night and declining during the dawn period. The coliform densities were very high downstream from the effluent as compared to upstream. This was due to the low flow of the river during this period and this had a pronounced effect oH the bacterial load of the river from the effluent of the Winterthur sewage treatment plaHt. The graph of total bacterial densities of the effluent also showed similar variations as that of the coliform organisms of the effluent. The curve at Station 25 was similar to the curve of April 25/26, 1967. The curve at Station 26/27 showed a gradual Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 69 increase. from 1200 hours and reached its maxima at 2100 hours, gradually declining towards -dawH. The bacterial densities at Station 26/27 were almost twice those at Station 25. The diurnal variation studies iHdicate that self-purification was at work between Station 25 and Station 26/27 during April 1967, when the flow conditions of the river were normal. During October 1967, when the flow was very sluggish (2.68 m3/sec) the river was bacteriologically polluted and no self-purification could take place. It must be assumed, therefore, that direct incidental pollution is the contributary factor at this time of the year, aHd that runoff during high flow does not coHtribute faecal organisms in appreciable number to the River Töss,

2. Diurnal Variation Studies at Rorbas Sewage Treatment PlaHt aHd River Töss (between Station 30 aHd Station 31)

The diurnal variations iH chemical and bacteriological components are shown in Figs. 28 and 29. In the effluent of the Rorbas sewage treatment plant during February 27/28, 1968, the miHimal dissolved oxygen was found in the evening aHd it rose steadily throughout the night till the maximum was reached late in the morning, and then it started to decline towards late afterHooH. The D.O. at StatioHs 30 and 31 followed a similar pattern to that of the effluent. The minimum D.O. concentration at Station 30 was high, 94% of saturation and low at Station 31, 88% of saturation. DuriHg the July 24/25, 1967 studies, the D.O. conceHtration curve of the effluent showed a similar pattern to that of February 27/28, 1968. The curve of Station 30 showed a minimum D.O. coHceHtration duriHg early morning aHd a maximum duriHg the day. The Station 31 curve showed a similar trend as that of Station 30, but maximum was recorded during the dawn period. The minimum D.O. concentration at Station 30 was 80% of saturation and it was slightly higher, 83 % of saturation, at Station 31. Biochemical oxygen demand curves showed very characteristic patterns. All the curves at different places in the river and in the efflueHt showed lower values duriHg morHiHg and afternoon, higher ones duriHg late evening and throughout the night. From the data of diurnal variations it may be said, that the efflueHt from the Rorbas sewage treatment plant had no visual influence oH the B.O.D. 5 load of the River Töss, as the B.O.D. 5 values downstream from the efflueHt outfall were comparatively lower than the river upstream. The pH variations iH the effluent were very small. During the July 24/25, 1967 run it varied between 7.7 and 8.0 and during the February 27/28, 1968 studies it varied between 7.85 and 7.9. Each time maximum values were recorded during the daytime. The pH values for Station 30, upstream of the sewage effluent outfall and for Station 31, downstream from the effluent outfall followed a similar treHd in variation as those of the efflueHt each time the study was undertaken. There was a pronounced pH variation at Station 30 during the February sampling and it varied between 7.95 and 8.2, whereas at Station 31 the pH varied very little from 8.0 (only 8.0 to 8.l). DuriHg the July studies the pH at Station 30 varied between 7.8 and 8.25 and at Station 31 the variation observed was between 7.3 and 8.2. mg/I RAW SEWAGE — 200— EFFLUENT MECH o---0 mg/I STANDARD PLATE COUNT 1000/ml EFFLUENT BIOL — B.O.DS 200 mg/I RORBAS-TOSS KMnD-Consu. TÖSSEGG-TÖSS R-44 150-4 4 150

100

100 COLI AND COLIFORM

50- 1006/ml 6000 25- 50 20- 40

15- 36 2000 10- 20 5— 10 1000 I I I I ill TIME 14 17 20 23 02 05 08 11 11. 17 20 23 02 05 08 11 14 17 20 23 02 05 08 11 mg/I

mg/I 3- 40 TOTAL PO4 206

30 100 —100

10 10 —10 0 0 0 0 TIME 14 17 20 23 02 05 08 11 14 17 20 23 02 05 O8 11 TIME 14 08 11 14 17 20 23 02 05 08 1

Fig. 28. Diurnal Variations at Rorbas Treatment Plant and River Töss at Rorbas and Tössegg on July 24/25, 1967. Rate of Flow 4.55 m3/sec. RAW SEWAGE - EFFLUENT MECH?---o EFFLUENT BIOL. - RORBAS-TÖSS COLI AND COLIFORM STANDARD PLATE COUNT TÖSSEGG-TÖSS X---X N /ml 1000/m1 200000 20000

100000 ` 10000 mg/1

20000 2000 O:

10000 1000 a TIME 12 15 18 21 24 03 06 09 12 15 18 21 24 03 06 09 12 15 18 21 24 03 06 09

a mg/1 CD 2000 -- / \ 200 00

O G

1000 100 p,

aw CO

CD 51

100 P 10

0 I I I I I I 12 15 18 21 24 03 06 09 TIME 12 15 18 21 24 03 06 09 12 15 18 21 24 03 06 09 12 15 18 21 24 03 06 09 TIME 12 15

Fig. 29. Diurnal Variations at Rorbas Sewage Treatment Plant and River Töss at Rorbas and Tössegg on February 27/28, 1968. Rate of Flow 11.5 m3/sec. v Table 32. Diurnal Variations at Rorbas Sewage Treatment Plant and Töss

July 24/25, 1967 February 27/28, 1968

PO4-3 PO4-3 Time Temp. pH NOs- Cl- (Dis.) Time Temp. pH - NO2- Cl- (Dis.) °C mg/l mg/l mg/I °C mg/l mg/l mg/I

Raw Sewage

1400 17.0 7.9 <0.005 26.0 12.0 1200 4.4 7.85 3.0 26.4 8.0 1700 17.3 7.8 <0.005 26.0 10.0 1500 10.2 7.65 3.0 28.8 8.0 2000 16.6 7.9 0.5 18.8 7.5 1800 5.6 7.75 1.5 21.2 5.0 2300 16.2 7.8 <0.005 23.6 8.0 2100 7.6 7.80 2.l 28.8 6.0 0200 15.6 7.8 l.4 14.8 5.0 2400 6.4 7.7 l.2 23.2 5.0 0500 14.9 7.8 0.7 12.8 2.0 0300 6.4 7.7 0.5 22.4 4.0 0800 16.0 7.9 0.8 16.0 9.0 0600 6.2 7.7 0.4 78.4 3.0 1100 17.5 7.5 l.0 4.4 5.0 0900 7.3 7.7 l.5 26.4 8.0

Effluent - Mechanical

1400 16.9 7.8 0.02 24.4 24.0 1200 5.0 7.7 l.5 24.0 7.0 1700 18.5 7.7 0.005 24.8 13.0 1500 8.5 7.55 6.0 28.8 11.0 2000 16.9 7.8 0.025 19.2 11.5 1800 5.5 7.7 5.0 28.8 9.0 2300 16.6 7.7 0.015 20.8 9.5 2100 7.2 7.7 2.0 20.8 7.0 0200 16.3 7.6 0.01 21.6 8.0 2400 6.9 7.7 2.2 27.2 5.0 0500 15.2 7.8 7.4 18.4 7.5 0300 6.5 7.6 1.0 20.0 4.0 0800 15.8 7.7 7.0 15.2 7.0 0600 5.7 7.7 0.9 25.6 4.0 1100 17.7 7.6 3.3 8.8 6.5 0900 6.4 7.7 0.7 28.0 4.0

Final Effluent - Activated Sludge Treatment Plant Effluent flow = 0.025 m3/sec. Effluent flow = 0.54 m3/sec. 1400 17.6 8.0 3.3 24.6 4.5 1200 4.8 7.9 l.2 27.2 9.0 1700 18.3 8.0 3.5 24.6 7.5 1500 7.6 7.85 l.2 25.6 8.0 2000 17.9 7.9 4.0 25.6 8.0 1800 4.9 7.85 l.5 25.6 9.0 2300 17.8 7.8 3.7 24.2 9.5 2100 6.0 7.8 1.4 24.0 9.0 0200 17.3 7.9 4.0 24.0 10.0 2400 6.9 7.8 l.5 29.6 10.0 0500 16.5 7.9 3.7 24.4 11.0 0300 6.4 7.8 l.4 24.4 9.0 0800 16.8 7.9 3.5 23.6 11.0 0600 6.0 7.8 1.4 20.8 9.0 1100 17.l 7.7 3.2 15.2 7.0 0900 6.3 7.8 l.2 25.2 9.0

Töss at Rorbas - Upstream River flow = 4.55 m3/sec. River flow = 11.5 m3/sec.

1400 20.4 8.2 0.9 12.2 l.4 1200 3.3 8.2 0.08 8.6 0.9 1700 21.2 8.25 0.9 12.2 l.6 1500 4.0 8.15 0.l 8.6 0.8 2000 19.9 8.2 1.66 12.9 1.7 1800 4.4 8.0 0.08 8.6 0.8 2300 18.l 8.0 l.6 13.1 2.1 2100 3.5 8.0 0.08 10.8 0.8 0200 17.3 7.8 1.4 12.7 2.l 2400 3.l 7.95 0.08 8.6 l.2 0500 16.3 7.9 0.75 12.8 l.9 0300 2.8 8.0 0.12 12.4 l.2 0800 16.6 7.9 0.8 13.1 2.2 0600 2.4 8.0 0.08 9.6 0.8 1100 16.3 8.0 0.75 11.7 2.5 0900 2.5 8.l 0.06 11.6 0.6

Töss at Tössegg Downstream

1400 20.3 8.15 0.42 11.3 l.2 1200 3.2 8.l 0.08 8.8 0.8 1700 21.3 8.2 0.82 11.9 l.6 1500 3.9 8.l 0.12 8.4 0.9 2000 20.6 8.2 0.9 12.3 l.6 1800 4.2 8.l 0.l 8.8 0.8 2300 18.7 8.0 1.6 13.3 2.0 2100 3.4 8.0 0.l 10.0 0.9 0200 19.6 7.3 0.75 24.3 0.8 2400 3.l 8.0 0.08 9.6 0.8 0500 19.9 8.0 0.33 15.0 0.3 0300 2.7 8.1 0.08 9.6 0.6 0800 16.4 8.0 0.7 12.5 l.6 0600 2.4 8.l 0.07 9.6 0.8 1100 16.6 8.0 0.65 12.2 2.2 0900 2.2 8.0 0.07 9.2 0.7 74 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

Water temperature gradually fell throughout the night towards dawn and maxima were recorded at all the sampling points duriHg the afternoon. Phosphate curves showed similar variatioHs as those of the Winterthur curves, but phosphate concentration was slightly higher at Station 30 than at StatioH 31. This shows that the Rorbas sewage treatment plant effluent has little effect on the quality of the river water. During the July 1967 studies (low flow), the concentratioH of phosphate was relatively higher iH the river than that of the February 1968 studies (high flow), although the concentration upstream of the sewage effluent outfall remained higher than downstream. This confirms the statement that phosphates are added to the river through the sewage treatment plants and not through drainage from the catchmeHt area of this river. The nitrate curves of the Rorbas sewage treatment plant effluent during the July 1967 run showed interesting variations. The peak NO3- concentratioH was recorded during the midnight hours and minimum during the hours before noon. These variations were contrary to those observed at the Winterthur sewage treatment plant. There was little NO3 - variation at Station 30, but StatioH 31 showed higher values from afternoon to midnight and lower values during the dawn period. The studies during February 1968 did Hot show aHy pronounced variations in any of the sampling points. KMnO 4-consumption curves were similar to those of B.O.D. 5 . Bacteriological studies of the effluent and the river water showed characteristic variatioHs every time diurnal variation studies were carried out. The curves of coliform organisms showed distinct diurnal variations. Coliform densities iH the effluent at Station 30 as well as at Station 31 showed a gradual rise from miHimal values during the afternoon, declining during the early hours of the Hight, to rise again around midnight and reaching their maximal values at dawn, thereafter declining again. Coliform numbers in the river samples during the July 1967 studies were much higher than in the February 1968 studies. This may be attributed to the flow of the river (July 24/25, 1967 Flow = 4.55 m3/sec; February 27/28, 1968 Flow = 11.5 m3/sec). Total count of bacteria curves during July 24/25, 1967 were similar to the coliform curves, but the fluctuations in the total bacterial densities during February 26/27, 1968 behaved somewhat differently. In the effluent minimal densities were recorded during the day and maximal ones at dawn, the curve showing a steady increase from day throughout night until dawn. The curve of Station 30 showed minimal values after dawn and maximal oHes at midHight. The curves of Station 31 for total bacteria aHd of coliform densities were similar to each other.

E. Discussion

The Töss River Before and After the Construction of the Activated Sludge Unit at Winterthur Sewage Treatment Plant

For the purpose of this study all data obtained from the present river survey and other data available on the same stretch of the river at identical stations during the different periods of study was compared to determine stream characteristics before Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 75 and after the biologically treated sewage effluent discharge into the River Töss. Figs. 30 to 33 show a comparative study on the same stretch of river during 1935/36, 1948/49, 1950-1966 and 1967/68. The resume of the progress of the waste treatment plant at Winterthur-Hard is given iH Table 33.

Table 33. Waste Treatment and Disposal

Date Development Effluent Disposal to 1935/36 Impact of pollution of Rlver Töss was felt Eulach 1948/49 Construction of plant at Winterthur-Hard and diversion started Eulach 1950-1966 Winterthur-Hard, complete mechanical sewage River Töss down- treatment plant stream Station 25 1966 (spring) Complete Activated (Biological) sludge unit River Töss down- was commissioned stream Station 25

During the 1935/36 studies (WASER and LARDY, 1938) the impact of pollution of the River Töss was first felt. Until 1948/49 the sewage of WiHterthur and its surrounding areas was discharged into the Eulach. During 1950-1966 the sewage of Winterthur was diverted to the Winterthur sewage treatment plant at Hard and oHly mechanical purification of the sewage was carried out. IH the spring of 1966 the biological treatment plant at Hard was put iHto operation and all the sewage which flowed into this plant was treated biologically. At present the River Töss receives the effluent of the biologically treated sewage from the Winterthur sewage treatment plant at Hard. AHalyses show that on the whole the water is of better quality thaH before the biological treatment unit was added to the sewage treatment plaHt of Winterthur at Hard. Oxidizable organic material as assessed by permanganate consumption showed considerably lower values at Station 26/27 during the present studies, and values decreased with distance dowHstream. Although at Stations 18, 21 and 22 slightly higher values were recorded, in general the condition of the stretch of the river from StatioH 22 downstream appeared to have been improved. This is shown by the comparatively lower values of KMnO 4-consumption. The values at StatioH 25 downstream Eulach in the river have decreased from 270.9 mg/1 iH 1935/36 to 9.37 mg/1 in 1967/68 (Fig. 30). The oxygen curve of 1967/68 showed remarkable changes. First of all an average of 100% or more oxygeH saturatioH values were noted at all the statioHs. Average dissolved oxygen varied betweeH 10.4 and 11.6 mg/l. The oxygen coHcentration was higher at all the stations downstream from the sewage effluent outfall of the Winter- thur sewage treatment plant. This shows that as far as oxygen is concerned the river had stabilized itself very much. The oxygen sag showH by the 1967/68 curve was less deep than that of the 1935/36, 1948/49 aHd 1950-1966 curves (Fig. 30). Biochemical oxygen demand after 5 days was not comparable with the old data as this test was not carried out during earlier studies on this river, iHstead B.O.D. after 48 hours was compared (Fig. 30). Although the river upstream did not appear 76 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

0 STATIONS 18 3Ö 31 7

15 14 13

12 11 10

Fig. 30. Longitudinal Variations of KMnO 4-Consumption, B.O.D. (48 Hours), and Dissolved Oxygen Concentration in the River Töss During Different Periods of Study. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 77 to have improved, as the curves of 1950-1966 and 1967/68 run very close to each other without any noticeable fluctuatioHs. B.O.D. 48 hours downstream from the Winterthur sewage treatment plaHt efflueHt during the 1967/68 studies showed low values compared to the 1950-1966 and 1935/36 values. The values decreased with the distaHce downstream from 3.84 to 2.18 mg/l between Station 26/27 and StatioH 31. This means that there was a 42% reduction of B.O.D. 48 hours during 1967/68, from Station 26/27 to Station 31. The B.O.D. 5 values of 1967/68 also showed a reduction of 31%, meaning that 2.5% of B.O.D. 5 was reduced per km of river length (stretch of the river from Station 26/27 to StatioH 31 is 12.6 km). The rate of reductioH of B.O.D. 5 was considerably slowed dowH due to increased pollution between Stations 26/27 and 28/29 and betweeH Stations 30 and 31. In the former case the main source of pollutioH is the community of Pfungen and the polluted Näfbach aHd in the latter case the river receives a large amouHt of B.O.D. 5 loading from the Rorbas sewage treatment plant. The B.O.D. 5 was most rapidly satisfied between Station 28/29 and Station 30 i. e. at the rate of 9.4% reduction per km (length of the river between Station 28/29 and Station 30 is 5.5 km). This shows a good iHdication of self-purification of the River Töss. From the curves of dissolved oxygen and B.O.D. it is evident that oxygen is not used up too rapidly during the oxidation of organic matter by the activity of bacteria, thereby showiHg improvement in the condition of the river. Further, as the oxygeH curve remains at almost 100% saturatioH throughout the river, it is clear that the rate of uptake of oxygen is lower thaH the rate at which oxygen is repleHished (e. g. by re-aeration from the atmosphere and by dilutioH with well oxygenated water). Thus the river condition tends to improve. There is therefore a strong evidence for the self-purification of the river. The de-oxygenation of river water by the discharge of the Winterthur sewage treatment plant effluent is also a relatively slow process as seen from the D.O. and B.O.D. curves. Hence it happened that the point of maximum de-oxygenation occurred a considerable distance below the point of discharge (Table 14), as determined by B.O.D. of the effluent and of the river water, the dissolved oxygen content of the river, KMnO4-consumptioH (oxidizable organic material) and physical characteristics of the stream (Fig. 30). The 1967/68 curve of ammonia shows a sizable reductioH in the ammoHia content of the river with a distance dowHstream as compared to the curve of 1948/49 and 1950-1966. The higher value at Station 28/29 was due to the eHtry of untreated sewage from the communities surrouHdiHg this station. The curve of 1967/68 also indicates an extensive oxidation of ammonia by aerobic bacteria, a process usually referred to as "nitrification". This is clearly indicated by the 1967/68 curve of nitrate (Fig. 31). The increase of inorganically derived ammonia was high and as such any increase in nitrate concentration would iHdicate that at least oxidation of some of the available NH3 (N) was taking place and that the river in general was recovering from pollution. One other criteria of this process was the eventual .stabilization of the river below the point of pollution, as iHdicated by increased mineralisation of the river water. 78 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

0 STATIONS 18 09 0.8 0.7 0.6 _ 0.5 En OA 0.3 0.2 0.1 0 STATIONS 18

16-

15- NO3 14- 13- 12- 11 10 9 - ö 8 - E

0 STATIONS 18 21 22 25 26/27 28/29 30 31 f I 1 6 7

Fig. 31. Longitudinal Variations of NH3, NO2-, and NO 3- Concentration in the River Töss During Different Periods of Study. Jahrgang 115 H. RAT. River Töss and its Underground Water Stream 79

Fig. 32. Longitudinal Variations of Chloride, Phosphate and Carbonate Hardness Concentration in the River Tôss During Different Periods of Study. 80 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

0 ö

z w w IL L1.1 4 a 0 m 0 0 Q w1 z a 0 0 I I I I I STATIONS 18 21 22 25 26/27 28/29 30 31

200000

COLI AND COLIFORM

1000

20000

10000

1967-68 E z

1948-49 2000

1000

0 STATIONS 18

Fig. 33. Longitudinal Variations of Bacteriological Conditions in the River Töss During Different Periods of Study. Jahrgang 115 H. Rai. River Töss and its Underground Water Stream 81

The results from the different sampling points along the course of the River Töss under study clearly show the effect of sewage pollution on a stream which is origiHally fairly satisfactory in bacteriological quality, and these also show the effect of self- purification which takes place in the lower reaches of the river before it joins the River Rhein at Tössegg. Additional incidental pollution gains access to the river from its polluted tributaries, untreated sewage from the communities in its catchment area and sewage treatment plant efflueHts, and this fiHds expression in an increase in bacterial densities (Fig. 33). On comparison of coli and coliform bacteria curves of the different periods of study with the curve of 1967/68, it is evident that faecal pollution in the river has increased considerably (Fig. 33). This effect became evideHt iH the river only with increasing humaH activity and correspondingly higher possibility of incidental faecal pollutioH. The unusually high coliform densities at Station 25 during 1948/49 was obviously due to the Eulach, which carried the load of pollution duriHg that period into the river upstream of this station. The total bacterial densities curve of 1967/68 shows remarkable effects of self- purification. The lower values during 1935/36 were obviously due to less humaH activity and lower population density as compared to 1967/68. Although the human activity has increased tremendously and the population of Winterthur District has also increased by about 20% duriHg the period 1950-1967, the total bacterial density curve ruHs lower than that of previous years. The effect of bacterial reduction may be attributed to the treatment of sewage by activated sludge process (Fig. 33). Phosphate concentration is slowly but steadily increasing as might be expected with the increased pollution load from domestic and industrial wastes. The concentrations of phosphate, CaCO 3 and chloride were generally higher during 1967/68 studies than those of most of the previous years on record (Fig. 32).

Effect of Organic Matter

The main stretch of the River Töss was found to be in a clean condition iH its passage from Bauma into Steigmühle (WASER and LARDY, 1938 aHd Table 34). This conditioH is more or less maintained until the river flows through Wespimühle, but downstream from this point it receives pollution through the Eulach, which brings an appreciable amount of pollution from its catchment area. Downstream from the SpiHnerei Hard the river takes the major sewage efflueHt from the WiHterthur sewage treatment plant at Hard. It would appear from Figs. 30 to 33, showing dissolved oxygen, biochemical oxygen demand and bacterial density profiles of the river, that discharge downstream from Wespimühle and the Spinnerei Hard caused a downstream utilization of dissolved oxygen for the oxidatioH of nitrogenous aHd carbonaceous compounds. This decrease was more pronounced when the flow of the river was low. Full depletion was avoided by re-aeration processes. After the river passes through Neftenbach and Pfungen, it takes more pollution load from the Näfbach and untreated sewage from the village of Pfungen and surrounding areas. After recovery below Pfungen, the river flows in a comparatively uHpolluted 82 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

Table 34. Chemical Conditions of River Töss Upstream Winterthur. (March 15, 1966)

Kollbrunn Steg Bauma Wila Turben- Horn- Up- Down- thal säge stream stream

Temperature ° C 0.4 l.l 2.0 3.9 3.6 3.7 3.7 pH 8.3 8.25 7.9 7.9 8.1 8.25 8.25 Dissolved Oxygen mg/l 13.75 13:53 13.25 11.74 12.97 13.24 12.00 B.O.D. 48 h. mg/l 1.55 0.80 0.77 0.52 l.42 0.74 2.06 NH3 mg/l 0.08 0.03 0.04 0.03 0.04 0.04 0.14 NO3- mg/l 3.4 3.2 4.5 5.2 5.5 6.0 8.0 NO2- mg/l 0.01 0.01 0.018 0.01 0.015 0.015 0.035 PO4-3 mg/l (Sol.) 0.09 0.09 0.07 0.025 0.06 0.05 0.35 PO43 mg/I (Total) 0.13 0.12 0.11 0.07 0.09 0.07 0.55 Chloride (CI-) mg/1 l.7 l.8 3.2 3.8 3.9 4.4 7.2 KMn04-consumption mg/l 6.0 5.0 5.06 3.32 4.58 5.37 12:96 CaCO3 mg/I 202.5 210.0 232.5 237.5 242.5 245.0 272.5 Iron (Fe+++) mg/I <0.02 <0.02 <0.02 <0.02 <_0.02 <0.02 0.18 Detergents mg/l <0.02 <0.02 <0.02 <0.02 0.02 <_0.02 0.02 Total volatile and fixed residue mg/l 222 238 266 320 290 284 352 Total bacteria N/l 21 000 2600 8900 5500 22 150 13 550 147 000 Coli and Coliform N/t 2330 101 178 120 1380 179 430 condition to Rorbas. In the Rorbas area it takes the effluent from the Rorbas sewage treatment plaHt, causing a marked decrease iH the rate of recovery of the river. The magHitude of the effect of the Winterthur sewage treatment plant is pointed out in Figs. 30 to 33. The chloride, ammonia, biochemical oxygeH demand, KMnO 4 -consumption and nitrate content of the river increased. But as the river progressed downstream from the Pfungen sampliHg station, the dissolved oxygen, biochemical demaHd, KMHO4-consumption, ammonia and bacterial density levels were again normal at Rorbas where the river takes the efflueHt with little effect. Recovery of the river was finally effected some 9 km downstream from PfungeH, at Tössegg.

InflueHce of the River Töss on the Sanitary Condition of the • River Rhein

The purpose of investigating the River Rhein was to find out the influence of the River Töss on its saHitary condition. DEMMERLE (1966) in her studies concluded that the condition of the Rhein down to Kaiserstuhl gets worse due partly to the much polluted tributaries Thur, Töss, Glatt and the Glatt Canal. During the period of her investigations the River Töss was receiving only mechanically treated sewage effluent from the Winterthur sewage treatment plant at Hard, and obviously during that period the River Töss might have influenced the conditioH of the Rhein to some extent. But now as the River Töss receives a more clarified and better quality effluent from the biologically treated sewage, as indicated earlier in this study, the impact of the polluted Töss on the Rhein remains to be seen. Thus the influence of the River Töss on the sanitary condition of the River Rhein was studied. Table 35. Range of Variations and Average Annual Physico-Chemical and Bacteriological Conditions of Rhein

pH Temperature Carbonate Hardness Total Hardness PO4-3 (Soluble) °C CaCO3 mg/I mg/l mg/l Sampling Stations Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Rüdlingen (Left) 8.17 8.45 8.05 11.12 20.l 2.6 134.l 157.5 115.0 168.0 196.0 146.0 0.11 0.18 <0.02 Rüdlingen (Right) 8.21 8.45 8.05 11.27 21.6 2.6 126.0 137.5 110.0 158.8 174.0 142.0 0.07 0.15 <0.02 Tössegg-Rhein 8.14 8.40 8.00 11.04 20.9 2.7 141.4 162.5 120.0 176.l 216.0 152.0 0.12 0.20 0.03 Eglisau (Left) 8.17 8.40 8.05 11.14 21.l 2.6 136.6 152.5 115.0 172.2 200.0 150.0 0.12 0.2650.02 Eglisau (Right) 8.15 8.40 8.00 11.14 21.3 2.7 144.3 157.5 112.5 168.7 188.0 140.0 0.11 0.24 0.02

Dissolved Oxygen B.O.D. 48 Hours KMnO4-Consumption Chloride (CI-) Suspended Matter % Saturation mg/l mg/l mg/l (M.F. 500) mg/l Sampling Stations Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Rüdlingen (Left) 118 134 110 l.31 3.57 0.4 8.53 10.74 6.48 3.14 5.0 2.3 4.33 8.4 l.2 Rüdlingen (Right) 119 144 101 l.42 3.74 0.2 8.58 10.9 7.27 2.75 4.4 l.9 2.92 6.4 1.6 Tössegg-Rhein 114 123 99 l.11 l.85 0.02 8.79 11.69 7.58 3.34 5.6 2.0 7.49 30.4 2.0 Eglisau (Left) 114 125 102 l.09 2.34 0.0 8.65 11.22 7.11 3.19 5.l 2.2 5.83 17.6 0.8 Eglisau (Right) 115 127 99 l.17 2.65 0.14 8.44 11.22 7.05 3.07 5.0 2.0 4.53 9.2 l.2 Total Volatile Surfactants Standard Plate and Fixed Residue (Anionic) Iron (Fe- - -) Count of Bacteria Coli and Coliform mg/I mg/l mg/l 1000/ml Bacteria N/ml Sampling Stations Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Rüdlingen (Left) 220 270 164 0.037 0.07 0.0 - 0.06 <0.02 42 172 11 304 1400 20 Rüdlingen (Right) 206 258 168 0.045 0.07 0.0 - <0.02 <0.02 22 50 10 138 340 50 Tössegg-Rhein 222 278 184 0.049 0.09 0.02 0.02 <0.02 51 158 13 423 2240 40 Eglisau (Left) 220 250 190 0.046 0.09 0.02 0.03 <0.02 40 83 17 258 1130 10 Eglisau (Right) 218 258 176 0.048 0.09 0.02 0.025 <0.02 36 70 11 128 370 50

PO4-3 (Total) Nitrate (NO3-) Nitrite (NO2-) Ammonia (NH3) Dissolved Oxygen mg/l mg/l mg/I mg/l mg/l Sampling Stations Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Aver. Max. Min. Rüdlingen (Left) 0.21 0.32 0.10 3.43 7.5 l.75 0.037 0.07 0.02 0.09 0.16 0.03 12.14 14.7 9.8 Rüdlingen (Right) 0.15 0.24 0.10 3.02 6.0 l.50 0.033 0.065 0.015 0.084 0.16 0.02 12.23 14.7 10.4 Tössegg-Rhein 0.27 0.45 0.12 3.72 6.95 l.75 0.037 0.065 0.015 0.099 0.20 0.04 11.77 13.3 10.2 00 Eglisau (Left) 0.23 0.38 0.12 3.54 6.0 1.75 0.039 0.07 0.007 0.101 0.16 0.03 11.80 14.1 10.3 w Eglisau (Right) 0.20 0.36 0.08 3.45 6.5 1.75 0.037 0.07 0.015 0.105 0.20 0.04 11.85 13.6 10.l 84 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

The detailed physico-chemical and bacteriological results so obtained during 1967/68 studies are presented in Table 35. The stretch of the Rhein between Riidlingen and Eglisau is 7.5 km long. These two places are situated respectively 3.5 km above and 3.9 km below the Tössegg, the point of confluence of Töss and Rhein. DEMMERLE (1966) in her studies stated that at Eglisau in the River Rhein the total bacterial densities and the oxygen consumption have coHsiderably increased. It may be commented here that since her studies the condition of the River Rhein (at Eglisau) below the confluence of Töss has been appreciably improved and the data in support are presented here.

Table 36. Influence of River Töss on the River Rhein before and after the Biological Treatment of Sewage at Winterthur Sewage Treatment Plant started. (Annual Averages)

Rüdlingen Eglisau Upstream confluence Downstream confluence of Töss of Töss Components 1962/63 1967/68 1962/63 1967/68 Before Biol. After Biol. Dissolved Oxygen mg/I 11.82 12.19 11.21 11.83 B.O.D.431, mg/l l.46 l.36 l.68 l.13 NH3 mg/l 0.075 0.087 0.095 0.103 NO3- mg/1 3.l 3.22 3.35 3.49 NO2- mg/1 0.03 0.035 0.034 0.038 Par-- mg/1 (soluble) 0.055 0.09 0.11 0.11 PO4 -- mg/I (total) 0.13 0.13 0.57 0.21 CI- mg/I 3.85 2.94 4.05 3.13 KMnDi-consumption mg/1 9.21 8.55 10.22 8.54 CaCO3 13.04 13.0 14.l 14.0 Total Bact. N/ml 17 200 31 950 33 640 37 950 Coll and Coliform N/ml 341 221 515 193

From Table 36 it appears that after the addition of the biological sewage treatment unit at the Winterthur sewage treatment plant there is an appreciable reduction in the biochemical oxygen demand, phosphate, chloride, KMnO 4-consumption and coliform densities. The increase in oxygeH and nitrate values showed the full impact of the biologically treated sewage effluent. It appears from the values given, that the improved quality of the effluent at the Winterthur sewage plant is beginning to affect not only the River Töss but also the sanitary conditions of the River Rhein downstream from the confluence of the River Töss.

Pollution Travel with Ground Water

The danger that public water supplies may become polluted as a result of the movement of bacteria and chemicals underground, has long been a matter of concern to the public health authorities. Reports of the travel of pollution with ground water movement reveal a somewhat imperfect knowledge of the conditions under which lateral travel of bacteria and chemical pollutants might occur. Investigators seem Jahrgang 115 H. RAL River Töss and its Underground Water Stream 85 to agree that pollution travels farthest in the directioH of ground water flow and that chemical pollutants travel much farther than bacterial pollutaHts. As previously mentioned, chemical pollutants travel farther than bacterial and have caused many European, especially German, ground water supplies to be abandoHed. LANG (1932) reported that leaching from an old garbage dump reached wells 450 m away, causing an increase in total solids from 360 to 552 mg/l, and in hardHess from 190 to 272 mg/1. In 1940, LANG and BRUNS noted a picric acid waste travel of 4.8 km in 4-6 years. Wells 610 m downstream from cooling poHds showed a temperature rise and an increase in mangaHese, hardness and iroH. In other instances, garbage dumped in a sand pit contiHued to pollute wells 610 m away, 15 years after the dumpiHg had ceased, aHd chlorinated sewage from leaking pipes caused phenol taste and fungus growth in wells 91.4 m away. Dyes added to sewage travelled 91 m in 24 hours. RÖSSLER (1950/51) observed an increase, after 10 years, iH chlorides, hardness and manganese in a well below a garbage dump. AUSTEN (1941/42) recorded the pollution of a well in Breslau, Germany, by seepage from the river 50 m away and reports tests showing artificial recharge to be productive of changes in the chemical composition of well water, Hotably in iroH and hardness. Similar data have been observed in the United States. At Vernon, California, chemical contaminants have travelled 4.8 to 6 km (BLAKEY, 1945). In Michigan (1947) the "Michigan Water Works News" reported chromate wastes have advanced through saHd to pollute wells at a distance of 305 m in three years. CALDWELL (1939) fouHd chemical pollutioH travelling 14 m in width of 7.6 m aHd depth of 2.1 in ground water moving oHly 0.06 to 0.46 m per day. CALVERT (1932) reported an increase in hardness, calcium, manganese, total solids and carbon dioxide iH wells 152 m from an impounding pit for liquor from a garbage reduction plaHt. SAYRE and STRINGFIELD (1948) fouHd pheHol wastes travelling 549 m in ground water in one instance and failing to penetrate 46 m in another. The movement of salt brine with ground water seems especially pronounced. WheH 800 kg of sodium chloride were placed in a sand pit, the salt soon reached a well 71 m away (HARMON, 1941). Salt placed in a cesspool (COBLEIGH, 1921) reached a well 61 m away iH 24 hours. This study was undertaken to help clarify the picture of pollution travel with grouHd water movement.

Table 37. Ground Water Pumping Stations

Amount of water Distance from the Ground Water Wells Altitude pumped River Töss km in m 1/min. m3/day (approximately)

l. Hard 401.95 15 200 21 900 0.70 2. Weiertal 479.85 1 534 2 208 l.25 3. Knorrenweg 430.75 600 864 0.25 4. Stadtacker 442.01 1 450 2 016 0.125 5. Oberes Linsental 470.58 12 000 17 300 0.125 or or 18 000 25 900 Distance from Eulach. Table 38. Chemical Composition of Ground Water Wells in the River Töss Valley (Yearly Averages) rn

Hard 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967

Temperature °C 10.5 10.6 10.9 10.9 11.l 11.5 11.4 11.8 10.5 10.3 11.l pH 7.l 7.0 7.05 - - - 6.95 6.99 7.06 7.01 7.01 Oxygen (D. 0.) mg/l 7.2 7.3 7.l 7.l 7.3 7.2 7.5 7.2 7.9 7.7 7.5 Percent Sat. of 0 2 71 72 70 70 72 72 74 72 77 75 74 KMnO4-Consu. mg/l 3.6 2.6 2.8 - 2.9 2.8 2.5 3.4 2.6 CaCO3 mg/l 303 333 303 312 323 318 309 316 302 311 316 NH3 mg/I 0.00 0.00 0.00 - - 0.00 0.00 0.00 0.00 0.00 NO2- mg/I 0.00 0.00 0.00 - - - 0.00 0.00 0.00 0.00 0.00 NO3 mg/l 20.l 18.9 18.3 19.9 20.5 19.7 20.5 24.8 19.0 18.5 12.3 CI- mg/I 9.8 9.9 10.0 9.8 10.5 11.9 12.4 12.3 12.7 13.4 13.6 +++ Fe mg/l 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Knorrenweg 1957 1958 1959 1960 1961 1962 1963 1966 1967

Temperature °C 10.9 10.8 11.9 10.9 11.3 11.2 11.2 10.8 10.1 pH 7.0 6.9 7.05 - - - - 6.96 6.9 Oxygen (D. 0.) mg/I 8.2 8.5 . 8.0 7.9 8.1 8.3 8.7 8.7 7.9 Percent Sat. of 0 2 81 84 73 78 81 82 86 86 77 KMnO4-Consu. mg/l 3.4 2.6 3.2 - - 2.8 2.3 CaCO3 mg/l 326 336 315 353 351 337 337 334 331 NH3 mg/l 0.00 0.00 0.00 0.00 0.00 NO2- mg/I 0.00 0.00 0.00 - - - 0.00 0.00 NO3- mg/I 21.l 22.6 18.2 22.3 23.l 21.2 21.9 21.6 14.5 Cl- mg/1 10.8 11.5 10.5 10.4 11.5 12.8 12.8 15.4 17.2 Fe+++ mg/l 0.00 0.00 0.00 - 0.00 0.00 Table 39. Chemical Composition of Ground Water Wells in the River Töss (Yearly Averages)

Oberes Linsental Stadtacker Weiertal 7c1 1963 1964 1965 1966 1967 1963 1964 1965 1966 1967 1963 1964 1965 1966 1967 h Temperature °C 9.5 10.0 9.2 9.6 9.5 8.5 9.7 8.9 8.8 9.4 10.0 9.9 8.8 9.6 9.8 7.05 7.1 7.l 7.06 7.05 7.1 7.3 7.l 7.1 7.l 6.9 6.9 7.0 7.0 7.0 pH P D3+ Oxygen (D. 0.) mg/I 7.7 7.6 6.7 7.2 7.1 6.5 7.9 8.l 8.0 7.8 7.l 8.1 8.3 8.2 8.3 Percent Sat. of 0 2 33 73 64 69 67 60 75 76 75 74 68 78 78 78 79 KMnO4-Consu. mg/l 3.0 2.4 2.3 3.8 2.9 3.0 2.7 3.l 4.3 3.3 2.0 1.9 2.l 2.8 2.3 ay CaCO3 mg/l 257 272 264 274 279 - 237 259 252 255 262 306 319 325 323 326 8 NH3mg/I 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 ä. NO2 mg/l 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 pl NO3 mg/l 9.4 8.6 8.8 8.9 7.1 7.2 8.4 7.9 6.7 9.5 7.9 8.l 8.9 9.9 8.4 cn CI- mg/l 7.1 6.9 7.0 5.7 5.4 5.6 6.l 5.4 3.9 4.2 2.6 2.8 3.2 3.4 3.6 w Fe+++ mg/l 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 88 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

The ground water samples were regularly collected by the Gas- and Wasserwerk der Stadt Winterthur laboratories and analysed by the city of Zürich laboratories. All available data were collected and the results were analysed to study "if the endangered underground water stream of the River Töss valley can be considered as safe". The author is greatly indebted to the Director of Gas- and Wasserwerke der Stadt Winterthur, Dipl.-Ing. ETH E. TRÜB for permission to use the analytical results. For this study the results of ground water aHalysis for eleven years, from 1957 to 1967 were studied and statistically analysed. Important parameters such as pH, oxygen, KMnO4-consumptioH, hardness, nitrate, nitrite, ammonia, chloride aHd iron were specially studied for this purpose. Five important ground water pumping stations (Table 37) along the River Töss, in the valley, were selected on the basis of their topography, need for drinking water and possibility of pollution from the sinking of polluted water of the Töss River. These important ground water wells used as sources for the potable water supply are showH in Fig. 1 and Tables 38 and 39 contain the chemical data analysed. From the results of grouHd water wells given in Tables 38 and 39 it is observed that components like nitrate, chloride and CaCO 3-hardness oHly permit insight into the influence of the polluted Töss water on these wells, while other chemical parameters appear to be unaffected. Nitrate appeared to have great fluctuations from year to year. The eleven years records show that nitrate varied between a minimum of 12.3 mg/l(1967) to a maximum of 24.8 mg/I (1964) at Hard, between 14.5 mg/I (1957) and 23.1 mg/l (1960) at Knor- renweg, between 7.9 mg/I (1963) and 9.9 mg/1 (1966) at Weiertal, between 6.7 mg/1 (1966) and 9.5 mg/I (1967) at Stadtacker and between 7.1 mg/1 (1967) and 9.4 mg/l (1963) at Oberes Linsental. The fluctuations in varying degree and high concentrations of nitrate in these wells specially in the region of the Eulach underground water stream, suggest no conclusions as to source, but it may be suggested here that bacterial origin is one possibility. The possibility may also be considered that Hitrate may be lost from ground water at depth through anion exchange or the activity of nitrate-reduciHg bacteria (GEORGE and HASTINGS, 1951). Very little information is available as to the manner in which nitrogen occurs in igneous rocks, although RANKAMA aHd SAHAMA (1950) suggested that it may be present in ammoniacal form and believe very little could be present as nitrate. Even the small amounts of nitrogen contained in igHeous rock may supply some nitrate to natural waters in the process of weathering. THOMAS (1955) stated that the nitrate concentration is rather high in the ground water of the Kanton of Zürich. BOND (1946) has shown that appreciable quantities of Hitrate accumulate in some uHder- ground water of the Ecca beds (South Africa). Nitrogen from the atmosphere is combined into nitric oxide by lightning discharges, and these oxides dissolve in rainwater to produce nitrous and nitric acids. This may be a source of the nitrate in rainwater which is doubtlessly left in the soil where it is available for use by plants. RIFFENBURG (1925) reports the average content of the nitrate (NO3 —) in rainwater to be 0.2 mg/l. RUTTNER (1963) reported that rainwater at Lunz contains on average about 0.36 mg/1 of nitrate and ammonium nitrogen. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 89

It is possible that leaching of nitrate from existiHg soil horizons and possibly older buried horizons in basin-range type valleys or other areas coHtaining suc- cessively deposited alluvial strata could be responsible for high nitrate concentrations in ground water in certain regions. It would appear from the state of the literature on this subject that further investigation on the behaviour of nitrate in ground water are required, although an organic origin is probably indicated for most such occurrences. Chloride offers very interesting observations. At Hard chloride showed a gradual increase from 9.8 mg/l in 1957 to 13.6 mg/l iH 1967, at Knorrenweg chloride increased from 10.8 mg/l in 1957 to 17.2 mg/1 in 1967, and at Weiertal again chloride showed

Fig. 34. The Effect of Polluted Töss 9 River Water and its Tributaries on the Chloride Content of the Ground Water in its Valley.

1 = Töss Obere Au, 2 = Oberes Lin- sental, 3 = Stadtacker, 4 = Riedbach, 5 = Eulach-Talackerstr., 6 = Matten- bach, 7 = Eulach-Töss, 8 = Töss 702, 9 = Töss 705, 10 = Töss Spinnerei Hard, 11 = Knorrenweg, 12 = Hard, and 13 = Weiertal. 2 1 1 1 i I 1 I I I I 1 YEARS 57 58 59 60 61 62 63 64 65 66 67 68 90 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 a gradual increase from 2.6 mg/l in 1957 to 3.6 mg/l in 1967. The two remaining ground water wells did not show any increase in chloride concentration, but an indication of decrease in chloride concentration is reflected. This shows that the increase in chloride is only in those wells which are near the immediate vicinity of the polluted stretch of the River Töss. The increase in chloride coHcentration at Hard may be due to this well beiHg strongly influeHced by the chemistry of the Töss and Eulach, because of the great infiltration of Töss water upstream to the Hardau-Siedlung, but of course ground water of the Eulach valley also penetrates into the undergrouHd water stream of this well. Knorrenweg is sited in the polluted Eulach valley and the increase in chloride in this well is a contribution from the sinking of the polluted water of the Eulach (Riedbach) and probable leaching from the soil surrounding it. Another possible explanation for the increase in chloride concentration in this ground water well is leakage from the sewage pipes in the area of the uHderground water stream and seepage from the Kiesgrube (gravelpit) Peter receiving the waste disposal from the foundries around it. This Kiesgrube is only 300 m away from this well. Regarding the increased chloride concentratioH at Weiertal, the ground water stream of the valley of Rumstales is not affected by the polluted grouHd water stream of the River Töss and Eulach. It may however be influenced by a small creek originating at the village of Brtitten and endiHg at Furt-Neuberg. The sewage outfall from the houses surrounding the catchment area of this creek has little influeHce over its sanitary condition, but the farmlaHd wastes, stables compostiHg and pigsty wastes from the surrounding area of this creek greatly iHfluence this well and its chloride content by the sinking of polluted water and the leaching from the soil surrounding it (TRÜB, E., personal communicatioH, 1968). The Oberes Linsental and Stadtacker are situated in the unpolluted upper zone of the river aHd show no increase in chloride concentration. At Hard there is 39% increase and at Knorrenweg the iHcrease is still higher i. e. about 50% whereas at Weiertal the iHcrease is only 26%. It appears that the increase in chloride is greater in wells which are nearer to the polluted source than those away from it. Another fact worth mentioniHg here is that the River Töss data from 1948 to 1968 clearly show an increase in appreciable amounts of chloride in the polluted stretch of the Töss (Fig. 32). Thus the increase in chloride concentratioH in the wells is due to the sinking of the polluted Töss water. The increase and decrease of chloride conteHt in Oberes LiHseHtal and Stadtacker is directly proportioHal to the chloride content of the river water (Fig. 34). This gives an indication that the river water sinks underground and affects the quality of the ground water stream (Fig. 34). No apparent increase was shown in carbonate hardness concentration but at Weiertal and Stadtacker a very slight increase in CaCO 3 was observed (Table 39). This increase might be attributed to the parallel increase in concentration in the River Töss water, but no definite conclusion can be drawn, as the CaCO 3 increase was only noticed in the two wells, one of which is iH the polluted zone and the other Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 91 in the clean upper zone of the river, and so no positive interpretatioH could be given as to the source of CaCO 3 in the wells. In conclusion it may be remarked that the increase in chloride concentration in the wells gives definite indications of the possible pollution travel with ground water by the sinking of the polluted Töss water. Although the increase in chloride does not indicate that the water quality of these wells has greatly deteriorated, nevertheless the underground water stream of the River Töss valley can not be considered safe under present coHditions and much is left to be done in this respect. From this study it would seem evideHt that chemical changes in percolating polluted water are Hot great and that many chemicals may be expected to reach ground water along with percolating liquids. This should not constitute a serious handicap, however, uHless the sewage cöntains toxic materials or unusually high concentrations of such uHdesirable elements as chlorides, sulphates, sodium, boron or maHy other toxins. Non-toxic salts behave iH much the same way as persistent poisoHs in that they are steadily reduced in coHcentration by dilution. This applies to such salts as sodium chloride, which is aH uHiversal constitueHt of sewage since every package of salt bought in the shops ultimately is poured down the drain. IH Britain for instance, with the exception of some salt-mining areas, iHsufficient concentrations are produced in the rivers to have much effect, although the proviHcial visitor to LondoH who is struck by the rather "flat" taste of the drinking water is thus affected because of the high salt content it has acquired from the sewage in the Thames (HYNES, 1963). The Rhein below the confluence with the Ruhr, for instance carries no less than 15 000 tons a day of sodium chloride, which renders its waters rather unsuitable for irrigation, with the result that Dutch farmlaHds are How threatened by salt water from both sides (JAAG, 1955).

Recommendations

The results of the studies of the water at PfungeH show that the River Töss in this region is still very polluted and therefore the diversion of the sewage from the communities of Pfungen and its surroundiHg areas to the proposed sewage treatment plant (under construction) would quickly reduce the pollution level at this place to a very moderate intensity. The diversion of sewage from the communities of Neftenbach, Riet,.Rotfarb and Hettlingen and their surrounding areas into the Rorbas sewage treatment plaHt will improve the sanitary condition of the Näfbach to a great exteHt and thus reduce considerably the pollution load of the River Töss. After completion of the treatment plant at Elsau and Wiesendangen, the ,Eulach will receive an appreciably better quality of sewage effluent. This will further improve the sanitary condition of the Eulach and coHsequently the pollution load of the Töss will be tremendously reduced. The aesthetic and hygienic benefits of sewage purification for lakes are also applicable to rivers (THOMAS, 1962). As is evident from this study, the condition, of 92 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 the River Töss improved in respect to its oxygen concentration, reduction in the B.O.D.s, total bacterial count, NH3, KMnO 4-coHsumption values and absence of polysaprobic organisms after receiving a biologically purified effluent discharge from the Winterthur sewage treatment plant at Hard. According to THOMAS, 1962 the mechanically and biologically purified sewage discharges into lakes aHd rivers cannot, in either case, be regarded as a permanent measure to improve their condition unless a minimum nutrient substance is removed from the sewage. The sanitary condition of this river can further be improved appreciably by strippiHg nutrient substances from the sewage treatment plants, and thus prevent unnecessary weed aHd algal growth in the river bed. A further expected increase in the population deHsity and in human activity would make it advisable to keep a watchful eye on the River Töss and particularly on the stretch of the river uHder study, iH view of the possibility that at some not too distant future the river may have to be utilized for other than agricultural purposes and iH view of the endangered ground water quality iH the catchmeHt area of this river.

Summary

This dissertatioH presents the results of the physico-chemical and bacteriological observations made on the River Töss and its tributaries during the period from 1967 to 1968. A total of 550 samples were aHalysed from the River Töss and its tributaries, sewage treatment plants and Rhein. For the interpretation and comparison of the results all old data (from 1948 to 1966) available on the River Töss were extracted. from the records of the KantoHales Laboratorium and all available data on the grouHd water wells for eleven years (from 1957 to 1967) were obtained from the Gas- and Wasserwerk der Stadt Winterthur, and statistically analysed. Lack of space prohibits including all the data as such. Only very important data are presented in this thesis and the rest of the data are being kept in the records of the Kantonales Laboratorium. The survey was untertaken to ascertaiH the transformations taking place on account of sewage pollution in the 17.9 km stretch of the River Töss from Winter- thur to Tössegg. VariatioHs in the amount of sewage treatment plant effluent added to the River Töss over the years are reflected in the levels of chemical and bacteriological components, in the stretch of the river under study. A heavy development of Sphaerotilus sp. was recorded in the Töss during the earlier studies (before the construction of the biological sewage treatment plant at Winterthur-Hard) specially at NefteHbach, downstream from the Winterthur sewage treatment plaHt effluent outfall. But during the entire period of the present study a very slight growth of Sphaerotilus sp. was recorded at Neftenbach, only iH the month of May 1967, when the river discharge was low (4.84 m3/sec) and water temperature was high. This decrease in the Sphaero- tilus sp. growth is attributed to the reduced load of organic pollution after the construction of the biological sewage treatment plaHt at WiHterthur-Hard. Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 93

The present study has shown that the oxygen sag does not indicate itself but is replaced by diurnal sag only during the period of low flow. This diurnal sag is deeper in the polluted stations in comparison to the cleaner stations. The oxygen curve of 1967/68 showed remarkable changes. First of all an average of 100% or more oxygen saturation values was noted at all the stations. Average dissolved oxygen varied betweeH 10.4 and 11.6 mg/I. The oxygeH concentration was higher at all statioHs downstream from the sewage effluent outfall of the Winterthur sewage treatment plant. This shows that as far as oxygen is concerned the river had stabilized itself considerably. The oxygeH sag shown by the 1967/68 curve was less deep thaH that of the 1935/36, 1948/49 and 1950-1966 curves. From the curves of the dissolved oxygen consumption at various points of the River Töss it has beeH found that the shapes of the curves varied according to the change iH the degree of pollution. B.O.D. 48-hours downstream from the Winterthur sewage treatment plaHt effluent during the 1967/68 studies showed low values wheH compared to the 1950 to 1966 and 1935/36 values. The values decreased with the distance downstream from 3.84 to 2.18 mg/I between Station 26/27 (Neftenbach) and Station 31 (Tössegg). This means that there was a 42% reduction of B.O.D. 48-hours during 1967/68, from Neftenbach to Tössegg. The B.O.D. 5 values of 1967/68 also showed a reduction of 31%, meaning that 2.5% of B.O.D. 5 was reduced per km of river length. The B.O.D.5 was most rapidly satisfied between Pfungen and Rorbas i. e. at the rate of 9.4% per km. This shows a good indication of self-purification of the River Töss. The 1967/68 curve of ammonia shows a sizeable reduction iH the ammonia content of the river with a distance downstream as compared to the curve of 1948/49 and 1950-1966. The nitrate-N coHceHtration dowHstream from the effluent was always high, due in part to the nitrification aHd further to the sewage treatment practice of producing, as far as possible, a well nitrated effluent. The study of the nitrogen balance of the River Töss revealed that there is a definite increase of NO3 --N from 73.6% at Neftenbach to 82.6% at Tössegg and correspoHd- ing decrease in NH3—N, from 22.4% at Neftenbach to 13.5% at Tössegg. This data further prove that nitrification was taking place in the River Töss. The River Töss data from 1948 to 1968 clearly show an increase in appreciable amounts of choride in the polluted stretch of the Töss. The increase in chloride concentration in the ground water wells in the River Töss valley has giveH definite indicatioHs of possible pollution travel with ground water by the sinking of the polluted River Töss water. Although the iHcrease in chloride does not iHdicate that water quality of these wells has been much deteriorated, nevertheless the underground water stream of the River Töss valley canHot be considered safe uHder present conditions. The soluble phosphorus is characteristically high in the sewage effluent compared with natural drainage. River samples downstream from the effluent outfall were quite high in phosphate concentration during the period 1967/68, reflecting the discharge from the Winterthur sewage treatment plant. The bacteriological studies indicate that the number of bacteria increased coH- 94 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 siderably duriHg the dry weather. Usually there was a considerable increase of the coliform organisms as well, during the iHcrease iH the total couHt. From these studies it is appareHt that the river is not capable of coping with most of the detrimeHtal effects of the direct faecal pollutioH. Under the circumstances these findings imply that the river is Hot capable of dealing with uHrestricted quantities of sewage effluent for an unlimited period of time. With an increase in human population aHd activity along the course of the river, it appears that conditions in the system may deteriorate. At preseHt a progressive self-purification of the lower reaches of the River Töss has been observed during the period under investigatioH. This is due to the diversion of sewage and its treatment by the activated sludge treatment process at the Winterthur sewage treatmeHt plant. The effect of the addition of an activated sludge treatment unit to this plant on the quality of its effluent, which River Töss receives, is clearly demonstrated iH this study. The B.O.D. 5 of the effluent is reduced from 166.8 to 13.39 mg/l, KMnO 4 3 is reduced from-consumption values are reduced from 291.7 to 30.86 mg/1 and NH 17.5 to 6.14 mg/l. This improvement in quality of the effluent is certain to influence the sanitary coHdition of the Töss. From the study it is noted that the power of self-purification of the River Töss seems to be somewhat impaired, due to iHdiscrimiHate discharges of untreated sewage from PfungeH and the polluted tributaries of the river, which bring pollutioH loads from their catchment areas iHto the river, downstream from the Winterthur sewage treatment plant effluent discharge. The retardation of the process of self-purification is due to the influence of the polluted tributaries. The study indicates that the zoHe of pollution has shifted due to the diversioH of the major part of the sewage from the Eulach to the Winterthur sewage treatment plant. During the course of the present study it was observed that the biologically treated sewage effluent had a great impact on the condition of the river at Neften- bach. Its condition has defiHitely improved as compared to the similar studies 22 years ago. The zone of moderate pollution is restricted to a distance oHly 2-3 km downstream from the WiHterthur sewage treatment plant effluent outfall. Although the population has increased tremendously from 1935 to 1968 and the average yearly dilution of the river water with the sewage was much less than that of the 1935/36 studies, i. e. only about 1 : 10, even then physically, chemically and bacteriologically the river showed improvement. Furthermore the river showed greater power of self- purification than reported in the earlier studies. A comparison of old and new data (Figs. 31 to 33) gives a good insight into the problem and clearly shows the influence of the biologically treated sewage effluent, not only on the sanitary condition of the River Töss but also on the condition of the River Rhein downstream from its con- flueHce at Eglisau. The present study has also pointed out that the diversion of the Winterthur sewage from the Eulach has reduced the pollution level of the Eulach to a moderate intensity. Although there are still polluted zoHes in the river, the quality of the water has certainly improved due to the biological sewage purification process. To further improve the sanitary condition of the river, dealing with existing sources of pollution Jahrgang 115 H. RaI. River Töss and its Underground Water Stream 95 aHd preventing the emergence of new sources, it is desirable to have good purification planning for the future. The whole study shows the great importaHce of periodical river surveys in order to keep an adequate watch over the sanitary conditions in order to guarantee the protection of water supplies.

Zusammenfassung

Seit vieleH Jahren war bekaHnt, dass die Töss iH ihrem Unterlauf durch zu wenig geklärte oder ungereinigte Abwässer nicht nur stellenweise, sonderH bei mittlerer oder niedriger Wasserführung in ihrer gaHzen Wassermasse stark verschmutzt war. Nach vielen Vorarbeiten erstellte die Stadt Winterthur vorerst eine mechaHische Kläranlage, die im Jahre 1948 in Betrieb kam. Schon damals war man sich im klaren, dass für diese städtischen Abwässer eiHe weitergehende Reinigung in Form einer biologischen Reinigungsstufe nicht zu umgehen war. Dieser für den Gewässerschutz dringend nötige Ausbau war im Herbst 1966 vollendet. Sowohl vor als auch nach InbetriebHahme der mechanischeH Kläranlage der Stadt Winterthur hatte das kantonale Laboratorium Zürich deH Verschmutzungs- grad der Töss iH zahlreichen Untersuchungen festgehalteH. Es drängte sich nun die Aufgabe auf, durch vergleichende Studien zu prüfen, ob trotz dem ständig steigenden Abwasseranfall die verschiedeneH GewässerschutzmassHahmen zu einem befriedi- genden ReiHheitsgrad der Töss geführt haben und ob der GruHdwasserstrom des Tösstales immer noch durch Verschmutzung bedroht ist. Um den gegenwärtigen Zustand des Tösswassers auf der Strecke von Winterthur bis Tössegg bei verschiedeneH Jahres- und Tageszeiten beurteilen zu könHen, wurden im Rahmen dieser Arbeit in der Töss, ihren Zuflüssen, den Kläranlagen von Winter- thur und Rorbas sowie im Rhein in den Jahren 1967/68 insgesamt 550 Proben erhoben und chemisch uHd bakteriologisch, vereinzelt auch biologisch, untersucht. Der Über- blick über die stufenweise Sanierung der Töss stützt sich auf die Publikation von WASER und LARDY (1935), die zahlreichen unpublizierten Daten des kantonalen Laboratoriums Zürich aiis den Jahren 1948/49 uHd 1950-1966 sowie hauptsächlich auf die Untersuchung der selbst erhobeneH Proben. Die im Auftrag der Wasser- versorgung der Stadt Winterthur durch das chemische Laboratorium der Stadt Zürich durchgeführteH Grundwasseruntersuchungen aus den JahreH 1957-1967 waren wertvoll für die Beurteilung einer allfälligen Gefährdung des Grundwassers durch verschmutztes Oberflächenwasser. Alle vorhandenen Daten wurden für die vorliegende Bearbeitung ausgewertet; in maHchen Fällen siHd aber hier aus Sparsam- keitsgründen nur die Minimal-, Maximal- und Mittelwerte aufgeführt. Alle Einzel- werte davon stehen im kantonalen Laboratorium Zürich zur Verfügung. Auf der Strecke von Winterthur bis zur Mündung erleidet das Tösswasser tags- über heute keinen abwasserbedingten Sauerstoffschwund mehr. Nur Niederwasser kann nachts zu Sauerstoffuntersättigungen führen. Der Sauerstoffschwund ist in den 96 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970 am stärksten mit Abwasser belasteten Flussabschnitten am grössten. Im Jahresmittel überstieg die Sauerstoffsättigung bei allen Stationen 100%; der mittlere Gehalt schwankte zwischen 10,4 und 11,6 mg/l und war unterhalb der Kläranlage Winter- thur-Hard höher als in früheren Jahren. Dies zeigt, dass die Töss sich in bezug auf den Sauerstoffgehalt stabilisiert hat. Der Sauerstoffschwund war 1967/68 wesentlich geringer als bei den Untersuchungen von 1935/36, 1948/49 und 1950-1966. Aus dem Kurvenverlauf der Sauerstoffzehrung ist eine Parallelität mit den anderen Ver- schmutzungsindikatoreH ersichtlich. Unterhalb der Kläranlage Winterthur zeigt die Sauerstoffzehrung nach 24 Stunden niedrigere Werte als bei den Untersuchungen von 1950-1966 und 1935/36. Sie nahm von Station 26/27 (Neftenbach) bis StatioH 31 (Tössegg) von 3,84 auf 2,18 mg/l ab. Das bedeutet eine Reduktion von 42% . Die BSB 5-Werte von 1967/68 zeigten von Neftenbach bis Tössegg eine Abnahme von 31%, d. h. 2,5% pro km durchflossener Strecke. Im Abschnitt Pfungen-Rorbas ist eine Abnahme von 9,4% pro km berechnet worden, was für die gute Selbstreinigung der Töss spricht. Auch beim Kurvenverlauf des Ammoniakgehaltes zeigt sich ein offensichtlicher Rückgang unterhalb der Abwassereinleitung, verglicheH mit den Resultaten von 1948/49 und 1950-1966. Die Nitratstickstoff-KonzeHtrationeH waren stets hoch dank der Nitrifikation und der biologischen Abwasserreinigung. Der prozentuale Anteil des Nitratstickstoffes am gesamten anorganischen Stickstoff steigt von 73,6% bei Neftenbach auf 82,6% bei Tössegg, und entsprechend nimmt der Ammoniakstick- stoff voH 22,4% bei Neftenbach auf 13,5% bei Tössegg ab. Dies beweist, dass iH der Töss Nitrifizierungsvorgänge stattfanden. Auf der verschmutzten Tössstrecke hat der Chloridgehalt von 1948 bis 1968 beträchtlich zugenommen. Auch die Chloridzunahme im Grundwasserstrom der Töss ist ein deutliches Zeichen dafür, dass eine Grundwasserverschmutzung durch versickerndes, unreines Flusswasser im Bereich der Möglichkeit liegt. Obschon der Anstieg im Chloridgehalt hier noch keine Qualitätsverschlechterung des Grund- wassers bedeutet, so darf doch die Sicherstellung der Grundwasserqualität Hur bei sorgfältiger InnehaltuHg der Gewässerschutzmassnahmen als gesichert gelten. Die gelösten Phosphate sind im Ablauf von Kläranlagen, soweit nicht eine spe- zielle Phosphatfällung vorgenommen wird, charakteristisch hoch, verglichen mit deH natürlichen Bodenauswaschungen. Ein hoher Phosphatgehalt ist im Trinkwasser entschieden unerwünscht (cf. BEYTHIEN/DIEMAIR, 1963, S. 668; BOSSET, 1965). Fluss- wasserproben, die der Flussstrecke unterhalb von Winterthur entnommen wurden, enthielten in der Untersuchungsperiode 1967/68 recht viel Phosphat, den Phosphat- gehalt des nur mechanisch-biologisch gereinigten Abwassers deutlich widerspiegelnd. Die bakteriologischen Studien zeigten, dass die Keimzahlen bei trockenem Wetter stark zunahmen. Gewöhnlich erfolgte parallel dazu ein deutlicher Anstieg der koli- formen Bakterien. Es ist offensichtlich, dass dem Fluss nur gut gereinigte Abwässer zugeleitet werden dürfen. Mit der Zunahme der Bevölkerung und der Ausweitung der Industrie würde sich der Zustand des Flusses ohne genügende Abwasserreinigung verschlechtern. Aber in der letzten Untersuchungsperiode wurde eine Verbesserung der Selbstreinigung in den untersten Abschnitten bemerkt. Die vorliegenden Untersuchungen zeigen deut- Jahrgang 115 H. RAI. River Töss and its Underground Water Stream 97 lich, dass diese Verbesserung dem Ausbau der KläraHlage Winterthur mit Belebt- schlamm-Behandlung des Abwassers zu verdanken ist. Der BSB 5 des Kläranlage- abflusses wurde von 166,8 mg/1 (1950-1966) herabgesetzt auf 13,39 mg/I im Ablauf, der KMHO4-Verbrauch von 291,7 mg/1 auf 30,86 mg/1 und der Ammoniakgehalt von 17,5 mg/1 auf 6,14 mg/l. Diese Qualitätsverbesserung des Abwassers hat zweifellos einen guten Einfluss auf die hygienischen Bedingungen in der Töss. Das Gefälle des Flusses uHd das dadurch kiesige Flussbett erleichtern die Selbstreinigung. Allerdings wird die SelbstreiniguHgskraft der Töss im UHterlauf noch etwas ein- geschräHkt. Aus den UHtersuchuHgen geht hervor, dass diese Verzögerung des Selbstreinigungsprozesses verursacht wird durch die Einleitung der noch Hicht in eiHer zentralen Kläranlage gereinigteH Abwässer von PfuHgen sowie durch verschmutztes Wasser voH Zuflüssen, die die Abwasserlast ihres Einzugsgebietes in deH Fluss tragen. Die Untersuchung des Eulachwassers lässt erkenHen, dass dieses Gewässer durch die Kanalisationsmassnahmen und die Ableitung der Abwässer in die Kläranlage heute weitgehend saHiert ist, so dass auch im Unterlauf wieder ForelleH beobachtet werden können, wo früher der Abwasserstrom den gesamten Fischbestand verHichtet hatte. Solange die Abwässer in der Kläranlage WiHterthur nur mechanisch geklärt worden waren, hatte es sich teilweise nur um eiHe VerschiebuHg der Verschmutzung von der Eulach in die Töss gehandelt. Nach EiHführung der biologischeH Abwasser- reinigung ist im Unterlauf der Töss eine gewaltige Verbesserung der LebensbediHguH- gen voH ReiHwasserorganismen eingetreteH. Vorher war das Flussbett zu maHchen Zeiten von Sphaerotilus-Zotten ausgekleidet, von denen ein immer wieder nach- wachsender Teil durch die Strömung abgerissen und flussabwärts getrieben wurde; trotz mechanischer AbwasserreiniguHg enthielt zu jeHer Zeit das Flusswasser somit sekundär kleiHste bis grosse Flocken von organischem Material. Solche Sphaerotilus- Treiben sind heute verschwundeH, und eine Zone von mässiger Verschmutzung ist beschränkt auf eine Distanz von 2-3 km unterhalb vom Abwassereinlauf der Klär- anlage voH Winterthur. Obschon die Bevölkerung im Zeitraum von 1935 bis 1968 im Einzugsgebiet gewaltig zunahm und die mittlere Verdünnung voH Abwasser mit Flusswasser nur noch etwa 1 : 10 beträgt, zeigten sich im Fluss Verbesserungen in physikalischer, chemischer, bakteriologischer uHd biologischer Hinsicht, wodurch auch die Selbstreinigungskraft wirkungsvoller in ErscheinuHg trat. Der Vergleich von alteH und neuen DateH (Abb. 31 bis 33) gibt eiHen guten EiHblick in dieses Problem und zeigt deutlich nicht nur die verbesserten hygienischen BedinguHgen in der Töss, soHdern auch im Rhein unterhalb der EinmünduHg im Staugebiet voH Eglisau. Obschon auch heute in der Töss noch einzelne VerschmutzuHgsstellen vorhanden sind, ist doch durch die bisherigen GewässerschutzmassnahmeH eine gewaltige Ver- besserung der Wasserqualität erreicht worden. Als weitere Massnahme ist zu empfeh- len, die noch bestehenden Verschmutzungsherde zu saHieren uHd das Gewässer durch eiHe geeignete Planung vor neuen Verschmutzungen zu bewahren. Die vorliegende Arbeit zeigt die Bedeutung von periodischen FlussuntersuchungeH für den Gewässerschutz und für den Schutz von Trinkwasserversorgungen, die von flussinfiltriertem Grundwasser gespienen werden. 98 Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 1970

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