4. Impact of Human Activities on Water Status

4. Impact of human activities on water status

4.1 Groundwater

This section examines the environmental effects 4.1.2 Groundwater chemical status that are apparent in aquifer 8 as a result of the environmental pressures described in Section 3.4.1. In order to be able to closely assess the chemi- The subdivision of aquifer 8 into groundwater cal status of the groundwater in the individual bodies 8-1 to 8-6 has been dealt with in Section groundwater bodies the following three ground- 1.7.2. This subdivision was made on the basis of water chemistry parameters have been exam- the same chemical substances as are examined ined: here. • 2,6-dichlorbenzamid (BAM) • Nitrate 4.1.1 Abstraction of groundwater • Conductivity.

Based on large series of soundings, attempts have The method chosen is that recommended been made to identify changes in the groundwa- and described in the Guidance Document on ter potential caused by human activities. Useful groundwater (GD2.8), with the groundwater data are hard to come by as soundings have usu- chemical status being described on the basis of ally been made in the waterworks abstraction the arithmetic mean of the content in the indi- wells. This can lead to pronounced local lower- vidual groundwater bodies together with the ing of the water table, which is not representative respective conﬁ dence intervals. The status for of changes in the general water table. Moreover, 2,6-dichlorbenzamid, nitrate and conductivity there are problems with determining the refer- is shown in Table 4.1.1. The arithmetic mean ence level by the sounding such that systematic and CL(AM) is shown for each component in errors arise. groundwater body 8-1 to 8-6. CL(AM) is the sum Changes in water level have been detected in of the arithmetic mean and the 95% conﬁ dence some wells. These changes can be attributed to interval. Assuming that the data are normally variation in the climate, including the precipi- distributed, 95% of the measured values will thus tation. In connection with the present work it lie below the CL(AM). has not been possible to identify changes in the The data for BAM show that subdivision of groundwater potential that are attributable to aquifer 8 into several groundwater bodies was human activities. Neither has it been possible to the right thing to do in that the average concen- identify an increasing water table despite the fact tration in groundwater body 8-3 is considerably that groundwater abstraction by waterworks has higher than in the other groundwater bodies. If decreased by 30% over the past 10 years, the whole aquifer had been considered to be a

2,6-dichlorbenzamide Nitrate Conductivity Table 4.1.1 (µg/l) (mg/l) (µS/cm) Groundwater status with respect to 2,6- Groundwater body Arithmetic mean CL( ) Arithmetic mean CL( ) Arithmetic mean CL( ) AM AM AM dichlorbenzamid, ni- 8-1 No data 78.5 1 650 trate and conductivity for each of the ground- 8-2 0.02 0.04 5.85 11.73 752.07 823.17 water bodies of aquifer 8. Both the mean and 8-3 0.68 1.83 1.54 3.4 756.55 1 149.08 the CL(AM) (mean + 95% conﬁ dence inter- 8-4 0.04 0.08 8.89 14.55 610.53 667.95 val) are given. 8-5 0.01 0.01 0.32 0.47 697.76 760.53

8-6 0.02 0.04 9.79 24.22 692.79 774.29

Odense PRB Odense Pilot River Basin 97 4.1 Groundwater

single groundwater body this would have been detected in groundwater body 8-5, and it has masked, and the BAM concentration would have not been analysed for in groundwater body 8- been high for the whole aquifer. The same applies 1. 2,6-dichlorbenzamid has been detected in an for nitrate, where the concentration is higher in aquifer beneath groundwater body 8-1, though. groundwater bodies 8-2, 8-4 and 8-6 than in the It is therefore concluded that despite the fact that other groundwater bodies. With conductivity, groundwater body 8-1 has not been analysed for only groundwater bodies 8-1 and 8-3 differ from 2,6-dichlorbenzamid, it does not meet the objec- the remaining bodies in aquifer 8. tive for this substance. It transpires that the groundwater bodies The extent of 2,6-dichlorbenzamid contamina- that have been identifi ed on the basis of a raised tion is expected to increase in future as the sub- conductivity (Table 1.7.10) also do have a higher surface groundwater gradually moves deeper. It conductivity (Table 4.1.1). The same applies for is thus expected that the groundwater bodies will BAM and especially for nitrate. Based on the not be able to meet the objectives with respect to groundwater chemical status of the individual pesticides and their metabolites in 2015. Neither groundwater bodies it can be concluded that the is it expected that it will be possible to meet this description of status is in agreement with the sub- environmental objective with the technological division of aquifer 8 into groundwater bodies. solutions currently available. In view of land use and the natural protection above the groundwa- Chemical stratifi cation of the groundwater ter bodies, moreover, it is concluded that ground- bodies water body 8-5 will not become contaminated From the available chemical data it is not possi- with 2,6-dichlorbenzamid. ble to identify any chemical stratifi cation of the groundwater bodies. The reason for this is partly the relatively fl imsy data material, and partly that the groundwater bodies are restricted with respect to their vertical distribution. 4.2 Watercourses Trend in groundwater chemical status Based on the nitrate data, attempts have been 4.2.1 Physical pressures made to identify any trend in groundwater chemical status. It has not been possible to identify any Anthropogenic pressure on the watercourses trend, again due to the fl imsy data material, in- in Fyn County really started around 5 000 cluding the lack of large unbroken time series. years ago with the clearing of the woodland for agricultural use, thereby rendering many of the watercourses unshaded. Moreover, from around the 13th Century some of the watercourses were 4.1.3 Objective compliance and risk dammed for mill operation. This – together with of future lack of compliance the establishment of dams for meadow irrigation in the 19th Century – disrupted the continuity The current objectives for the two selected sub- of the watercourses, thereby hindering fi sh such stances, 2,6-dichlorbenzamid and nitrate, are as trout and eel from their natural migration be- described in Section 1.7.3. tween fresh water and sea water. In newer times The characterization of the chemical status other obstructions have arisen too, for example shows that with respect to nitrate, all the ground- culverts under roads. water bodies meet the objective. With groundwa- The appearance of the watercourses has also ter bodies 8-2, 8-4 and especially 8-6, however, been changed through other forms of regulation. there is the future risk that they will not meet the Many naturally meandering or sinuous water- current objective for nitrate (maximum 25 mg/l) courses have been straightened and the beds ex- if the concentration increases. From the existing cavated, and in places the slope has been neutral- data there is presently no evidence to indicate ized by the construction of falls. These activities that the nitrate concentration is increasing in really started in the 18th Century and accelerated these three groundwater bodies, though. up through the 19th Century until the last major As far as concerns 2,6-dichlorbenzamid, the regulation project in 1960, which encompassed a characterization shows that groundwater bod- considerable part of the River Odense (Riis et al., ies 8-2, 8-3, 8-4 and 8-6 do not meet the current 1999). The aim of such regulation was to ensure objectives. No 2,6-dichlorbenzamid has been improved drainage and thereby to increase the

Odense 98 PRB Odense Pilot River Basin 4.2 Watercourses

possibilities to use the adjoining land for agri- Figure 4.2.1 Relative impact (in cultural production. At the same time, rapid re- N %) of groundwater moval of the water was further ensured in many abstraction on median places through intensive maintenance in the form minimum water fl ow of clearance of all aquatic vegetation as well as in the various catch- vegetation along the banks and borders of the wa- ments within Odense tercourses and dredging of the bed substratum. River Basin. The rela- The regulation, the changed physical condi- tive impact of ground- tions (with soft, unstable bed and rapid drain- water abstraction is ing away of the water), the restricted hydraulic calculated as the total abstraction multiplied interaction with the immediate surroundings by 0.6, which is the (see Section 4.4) and the continued disturbances factor whereby abstrac- contributed – together with pollution – to the tion is expected to af- disappearance of many sensitive plant and animal fect groundwater input species from the watercourses. A few species have to the watercourses. not just disappeared locally, but are no longer Median minimum wa- found in Fyn County at all (see for example Riis ter fl ow is without any et al., 1999). input of wastewater Even though numerous improvements have from treatment plants and is reported as been made to the physical conditions over the “output” from a given past 15 years, including actual restoration and catchment. the introduction of more environment-friendly >50 maintenance, there is no doubt that the physical 0 5 10 km 25-50 conditions are often a hindrance to attainment of 15-25 good watercourse ecological status. 0-15 Water fl ow in the watercourses of Fyn County supply Odense City is abstracted from wells at No data generally varies relatively much during the Borreby in the catchment of Holmehave Brook. course of the year in that only a small part of the This water is discharged as treated wastewater water derives from deep groundwater. By far the in the lower part of the River Odense. As a majority of the discharge is accounted for by sub- consequence, parts of the Holmehave Brook surface groundwater, drainage water or surface system lose a large proportion of their natural runoff (see Section 1.3). Both plants and animals water fl ow, which in summer can result in some are affected by – but adapted to – these natural reaches drying out completely. The Stavis and fl uctuations in water fl ow. This applies not least Lunde watercourse systems also “lose” water to those species associated with regularly sum- due to groundwater abstraction, albeit that this mer-dry watercourses. Human intervention in is partly compensated for in the Lunde Stream the natural water cycle causes further stress to through the input of treated wastewater from the the organisms, however. catchment of Stavis Stream. Each year in Fyn County, approx. 38 million Despite the major impact that it still has, to- m3 of groundwater are abstracted for the drink- tal abstraction of groundwater in Fyn County ing water supply. In addition, approx. 11 million has generally fallen by approx. 35% since 1979, m3 are abstracted for industrial purposes, crop among other reasons due to the introduction irrigation, etc. (see also Section 4.1). The amount of green taxes. In several cases, groundwater of water abstracted corresponds to approx. 25% abstraction has nevertheless led to the loss of of the mean summer runoff in the watercourses species (macroinvertebrates) from watercourses of Fyn County, or more than half of the amount in Fyn County, especially in the upper ends of of water that fl ows in the watercourses in dry the watercourses. summers. A considerable part of the abstracted The lowermost reaches of the River Odense drinking water is “returned” to the watercourses are subject to a rather special form of physical in the form of treated wastewater, but not neces- pressure, namely large amounts of saline cool- sarily in the area from where it was abstracted. ing water discharges from the combined heat Large amounts of groundwater are abstracted and power plant Fynsværket. The cooling water within Odense River Basin (Figure 4.2.1), in is abstracted from Odense Canal, which is in some catchments amounting to over 50% of direct contact with Odense Fjord. The cooling the median minimum water fl ow in the associ- water discharge is so considerable that much of ated watercourses. For example, groundwater to the warm, salty water penetrates like a “wedge”

Odense PRB Odense Pilot River Basin 99 4.2 Watercourses

at least 2.5 km upstream from the outlet of the input. Until just about 15 years ago, moreover, river. The salt water lies at the bottom such that highly polluting discharges of silage juice, liquid the fresh water ﬂ ows over it. As a consequence, manure and manure seepage from agricultural the river bed is devoid of any actual watercourse holdings were common. As a result of these dis- fauna. However, watercourse fauna exists in the charges the ﬂ ora and macroinvertebrate fauna subsurface vegetation along the banks of the became highly impoverished, and the natural watercourse, except downstream of the cooling trout population disappeared from the majority water outlet, where the salinity is too great. of watercourses. Since the end of the 1980s, the environmental state of watercourses in Fyn County (including those in Odense River Basin) has improved con- 4.2.2 Impact of pollutant loading siderably, however, especially that of the major watercourses (Figure 4.2.2). Human activities, especially during the past 100 Today the main sources of readily degradable

years, have caused pollution of the watercourses organic matter pollution (measured as BOD5) are in Fyn County. These conditions are described wastewater from public wastewater treatment in detail and documented in Fyn County (2001a). plants and stormwater outfalls in the towns and The present section therefore only briefl y exam- wastewater from sparsely built-up areas. Ap- ines the main factors that have been and are of prox. 85% of the population in the region – and greatest signifi cance for watercourse environ- somewhat more in Odense River Basin – inhabit mental state. towns. Wastewater treatment has been highly Until just over 40 years ago, badly treated centralized over the past 25 years, however, and wastewater from dairies, abattoirs, towns, etc. the wastewater treatment plants have been mod- comprised a major source of organic matter ernized (over 99% of the wastewater is treated biologically) in order to effectively remove both the organic matter and the nitrogen/phosphorus Municipal/private watercourses compounds. Thus over 95% of the organic mat- Environmental status 1984-2002 100 ter and phosphorus is removed, while the treat- Figure 4.2.2 ment effi ciency for nitrogen is over 85%. As a Environmental sta- consequence, especially the main watercourses tus assessed from the 80 macroinvertebrate that receive urban wastewater have become much cleaner. The BOD content of these watercourses fauna in major (coun- 60 5 ty) and minor (mu- has thus decreased to an average of approx. 2 nicipal and private) mg/l within the past 20 years. The minor wa- 40 watercourses in Fyn tercourses in Odense River Basin are affected by County in the period poorly treated wastewater from a large propor- 1984–2002. 20 tion of the approx. 6 900 properties located in P: Pesticide-affected; Apportioned by fauna class (%) class by fauna Apportioned the sparsely built-up areas. The BOD content of FC: Fauna class. 5 0 lllllllllllllllllllllllllllll these watercourses is therefore somewhat higher 84 86 88 90 92 94 96 98 00 02 Other (desiccation etc.) than in the larger watercourses. The macroinver- Year P tebrate fauna in the minor watercourses is mark- FC 1-3 edly affected by the enhanced organic matter FC 4 County watercourses content (see Fyn County, 2001c). FC 5 Environmental status 1984-2002 Ammonium-(and ammonia-)nitrogen and 100 FC 6-7 phos phorus also largely derive from wastewater.

As with BOD5, however, the concentration of 80 these two substances in the larger watercourses has decreased markedly over the past 20 years. 60 The present phosphorus content is not solely attributable to discharges from urban wastewater 40 treatment plants and sparsely built up areas, but also to input from arable land. Thus despite the 20 above-mentioned considerable reduction, the phosphorus concentration is considerably higher Apportioned by fauna class (%) class by fauna Apportioned than the natural concentration in watercourses 0 lllllllllllllllllllllllllllll 84 86 88 90 92 94 96 98 00 02 in Fyn County (and Denmark). Year With ammonium-(and ammonia-)nitrogen in contrast, the concentrations reached nowadays

Odense 100 PRB Odense Pilot River Basin 4.2 Watercourses

are only very rarely critical for fi sh, and are of charge of wastewater. From the environmental no signifi cance to the macroinvertebrates. The point of view, the fi rst two sources are undoubt- phosphorus content is of no signifi cance to the edly the most important. macroinvertebrates and fi sh either, and is un- Wastewater is an important source of other likely to be of any signifi cance to higher plants, hazardous substances present in the watercourses which obtain a considerable proportion of their even though they are removed to some extent be- nutrients from the watercourse sediment. In con- fore reaching the watercourses, all depending on trast, the presence of large amounts of fi lamen- their biodegradability and the type of treatment tous green algae (especially Cladophora), which plant. Another major source of these substances can be harmful to other watercourse organisms, is stormwater outfalls. A large number of differ- is primarily determined by the raised concen- ent substances have been detected, among other trations of dissolved phosphorus (Fyn County, places in the lower part of the River Odense. The 1997). Such blooms of fi lamentous algae are often levels are not very high, though, and only PAH hindered by the macroinvertebrates grazing the compounds occur in slightly elevated concentra- algae while these are still “small”, however. tions relative to the national criteria. Investiga- The nitrate-nitrogen concentration is mark- tions of the River Odense do not indicate that edly enhanced compared with the natural level PAH compounds, for example, have any sig- in streams in Fyn County (and Denmark). This nifi cant effect on macroinvertebrates. However, is primarily attributable to leaching from arable there is the risk of reproductive disturbances in land. The nitrate-nitrogen concentration has fi sh caused by hazardous substances with endo- decreased by approx. 20–25% over the past 15 crine disrupting properties, although this has not years or so, however. Despite the enhanced lev- been investigated in the River Odense. els, nitrate-nitrogen probably has no signifi cant impact on the occurrence and amount of plants, macroinvertebrates and fi sh in the watercourses. 4.2.3 Objective compliance and risk A large number of different pesticides have of future lack of compliance been detected in the watercourses in Fyn County, including the River Odense. As many as 40% of the 100 or so substances that have been This section describes the present state of com- analysed for have thus been detected with vary- pliance with the objectives stipulated in the Re- ing frequency and in concentrations of up to 11 gional Plan 2001–2013 and Action Plan on the µg/l. The greatest proportion of the pesticides Aquatic Environment II, and assesses the risk detected are herbicides, which also comprises the of failure to meet the provisional objectives es- largest group of pesticides. Given the relatively tablished pursuant to the WFD by the year 2015 low concentrations in which they are present, with the measures hitherto adopted. the substances detected are unlikely to pose a In 2002, the current objectives have been met major threat to life in the watercourses. For ex- at approx. 50% of the monitoring stations in ample, aquatic plants are unlikely to be harmed. Odense River Basin and in the watercourses of The opposite is the case, though, with a number Fyn County as a whole (the criteria are apparent of pyrethroid insecticides that have not been from Table 1.4.9). This is also the case for the analysed for because they are expected to occur open parts of the watercourses assigned a quality in concentrations considerably below the detec- objective in the two test areas, the main course tion limit with normal analyses. In a number of of the River Odense and the Ryds Stream catch- documented cases, these substances have caused ment (see Section 1.4). The degree of compliance considerable mortality among insects and crus- with the objectives roughly corresponds to the taceans in particular, and in some cases also fi sh. average situation in Denmark (Skriver, 2002). If The assessment is that over the past 10 years, instead one applies the criterion that the objec- these substances have caused considerable dam- tive has to be met for fi ve consecutive years (see age to the macroinvertebrate fauna in up to 14% the grounds for this in Section 1.4), the percent- of the watercourses in Fyn County. The acute age of watercourse stations in Fyn County that effects have reduced considerably in recent years, meet the objectives stipulated in the Regional though, among other reasons due to a campaign Plan is much smaller – only 25%. Irrespective focused on the users of the pesticides. The input of the choice of assessment period, the degree of of pesticides primarily occurs via runoff from lo- objective compliance is greatest for watercourses cations used to fi ll and clean spraying equipment assigned quality objective A and least for water- in agriculture, via runoff from market gardens, courses assigned quality objective B3 (see Table through leaching from fi elds in surface runoff or 1.4.9, where these codes are explained). That so drainage water, and to some extent via the dis- few watercourses assigned quality objective B3

Odense PRB Odense Pilot River Basin 101 4.2 Watercourses

Table 4.2.1 Overview of water WB No. Type Provi- Ref. Current status Provis. ecol. status Current Provis. Expected bodies in the main sional status (FC) (FC/Phys.index) objective objective provis. com- course of the River HM (FC) (WFD) pliance Odense and Ryds (WWT/IPC)

Stream catchment in- O1 1 + 7 4 M / P B1/B2 H * + / - dicating typology (pro- O2 1 - 7 7 H / H B1/B2 H * + / + visional system), heavy O3 1 + 7 Unknown ? / ?M B1/B2 H * + / - modiﬁ cation (HM, pro- (O4) (Lake) - - - (B) (A1) (H) * (- / ) visional designation), O5 2 + 7 3 - 4 P - M / P - B B1/B2 - B3 G * - / - reference conditions O6 2 - 7 5 - 6 G - H / P - G B1/B2 H * + / - assessed from the mac- O7 3 - 7 5 - 6 G - H / M - B (pre) B1/B2 H * + / + (Rest.) roinvertebrates (fauna O8 3 + 7 Unknown ? / ?P B1/B2 G * + / - class, FC; provisional O9 3 - 7 5 - 7 G - H / G B1/B2 H * + / + classiﬁ cation), current O10 3 - 7 5 - 7 (G - H / M - P) B1/B2 H * + / - status assessed from the O11 3 - 7 5 - 7 G - H / G - H B1/B2 H * + / + macroinvertebrates O12 3 + 7 3 - 4 P - M / ?P B1/B2 G * - / - (FC), ecological status O13 3 - 7 5 - 6 G - H / G B1/B2 H * - / - O14 3 + 7 3 - 5 P - G / ?P - M B /B G * - / - assessed from the mac- 1 2 O15 3 - 7 4 - 6 M - H / M - G B H - / - roinvertebrates and 3 O16 3 + 7 4 M / ?P B G - / - physical conditions 3

(provisional, based R1 1 + 7 4 + rør M / M + pipe B1/B2 G + / - on FC and modiﬁ ed R2 1 + 7 5 + rør G / P - ?G + pipe A H + / -

Aarhus Index), current R3 1 + 5 Unknown + pipe ? / ?P + pipe B3 G - / - objective pursuant to R4 1 + 7 Piped Piped = B - G - / - the Regional Plan cur- R5 1 + 7 Piped Piped = B - G - / - rently in force, future R6 1 + 7 4 - 5 + pipe M - G / M - B + pipe B1/B2 G + / - objective (provisional R7 1 - 7 4 - 6 + pipe M - H / M - G + pipe B3 H + / - assessment) pursuant to R8 1 + 7 4 - 5 + pipe M - G / M - ?G + pipe B1/B2 ** G - / - the Water Framework R9 1 + 7 Unknown + pipe ? / ?P + pipe B3 G - / -

Directive (WFD), and R10 1 - 7 5 G / M - G B1/B2 H + / - expected compliance R11 2 - 7 5 - 7 G - H / M - G B1/B2 H + / - with the objective R12 2 - 7 6 - 7 H / M - G B1/B2 H + / - (provisional assess- R13 2 + 7 4 M / P B1/B2 G - / - ment ) in 2015. The WFD objectives are abbreviated H: High; comply with the objective is sometimes due to the fauna class) may not deteriorate. Moreover, G: Good; M: Moderate; the fact that the physical conditions are so bad the objective has been set to high ecological P: Poor and B: Bad. as to preclude attainment of fauna class 5, even status in the whole of Rislebækken Brook out * Indicates that the though the watercourse water is clean. Moreover, of consideration for Lake Arreskov, which is reach is encompassed objective compliance is clearly greatest for the presently assigned the highest quality objective by the Habitats Direc- large watercourses, corresponding to the median A1 (see Section 4.3). The possibilities for meeting tive, such that special fauna class being one grade higher than in the the WFD’s objectives within the specifi ed time requirements can be smaller watercourses. The difference is greatest if frame have been assessed on the basis of the plans expected concerning one examines objective compliance over a period hitherto adopted and in force and assuming that safeguarding certain species or habitats. ** of fi ve years. The degree of objective compliance the environmental measures (improved wastewa- Indicates that the objec- has increased over the past 15–20 years, not least ter treatment) in the sparsely built-up areas are tive for the watercourse since 2000. implemented as planned. It is apparent that with was fi rst set during an The future environmental objective pursu- the present initiatives, only 4 out of 28 water- inspection in spring ant to the WFD is that all watercourses should course reaches (14%) will fully comply with the 2003. Expected compli- achieve good (or better) ecological status by 2015 provisional objectives established pursuant to the ance with the objec- at the latest. Moreover, the Directive stipulates WFD, and that it is particularly the poor physi- tive has been assessed that the present status must not be allowed to cal conditions and discharges of wastewater from with respect to both deteriorate. Based on present knowledge of the stormwater outfalls that limit the possibilities for improved water quality in connection with biological and physical conditions (see Section compliance with the objectives for watercourses planned wastewater 1.4) a provisional assessment has been given of (assessment of the signifi cance of watercourse treatment in sparsely the ecological status of the watercourse reaches water for lakes and coastal waters is not encom- built-up areas (WWT) in the two test areas (Table 4.2.1), as well as an as- passed here; see Sections 4.3 and 4.5). It should and improved physi- sessment of the possibilities for complying with be noted, moreover, that it can take up to 5–10 cal conditions (IPC). the WFD environmental objectives by 2015 (Ta- years before the effect of the implemented envi- Expected compliance ble 4.2.1). The objectives have been established ronmental improvements have a serious impact is indicated by +, and on the basis of the criteria in Table 1.4.10 and the on the biological conditions in the watercourses. non-compliance by –. condition that the existing state (assessed from

Odense 102 PRB Odense Pilot River Basin 4.3 Lakes

4.3 Lakes

4.3.1 Physical pressures 4.3.2 Impact of pollutant loading

Over the years, many lakes have been exposed to Nutrients various physical pressures in the form of water Over the years, the majority of the lakes have level regulation, reclamation etc. In some places, been subjected to extremely high nutrient load- moreover, water abstraction has reduced water ing. Some of the lakes served as recipients for fl ow to the lakes. Conversely, new lakes have poorly treated urban wastewater, and many are arisen through damming and excavation. affected by nutrient loading from agricultural sources and wastewater from sparsely built-up Water level regulation areas. This has led to a marked increase in algal The water level in most lakes can be regulated by growth, blooms of potentially toxic blue-green a retaining weir in the outlet. The impact of this algae, the shading-out of submerged macro- on lake ecological state is so small that it is not phytes, and the impoverishment of the lake fauna considered to have any signifi cant impact, how- (macroinvertebrates, fi sh and birds). ever. In certain cases, water level regulation can Within the past six years, investigations en- be used to improve the state of the lake through compassing fi sh, submerged macrophytes, phy- enhanced wash-out of phosphorus during the toplankton, zooplankton and physico-chemical summer period. variables have been carried out in six major lakes (15–317 ha) (see Table 4.3.1). The lakes are all of Water abstraction the type “alkaline, clearwater, shallow freshwa- Pursuant to the Regional Plan, water abstraction ter lakes”, except Lake Søby, the mean depth interests are prioritized as follows: 1) The public of which is 3.6 m, and which must therefore be water supply, 2) Maintenance of environmentally considered as deep, cf. Section 1.5.3. acceptable water fl ow in watercourses and water The investigations show that the lakes have exchange in lakes, and 3) Other purposes such large algal populations, often dominated by as abstraction for industrial, agricultural and blue-green algae, absent or poorly developed recreational use. submerged macrophyte vegetation, high nutri- Abstraction of surface water is thus severely ent concentrations and poor Secchi depth. In restricted, and to the greatest extent possible addition, the fi sh populations are generally too groundwater abstraction must not have negative dominated by roach and bream, with too few effects on watercourses and lakes. piscivores such as perch and pike. The overall assessment is that groundwater Based on the provisional proposals for a lake abstraction does not presently have any serious typology (National Environmental Research impact on the lakes’ water balance. Current Institute, in prep.) all the lakes will belong to work with integrated models for groundwater the class “poor ecological status” cf. Section 1.5. and surface water will be able to shed more light The chief determinant of lake state is the phos- on this issue. phorus availability, and based on the phosphorus concentration alone the classifi cation of some of Reclamation the lakes is a little better, namely “moderate” to Many water bodies – especially the smaller ones “poor” ecological status. One of the reasons for – have disappeared since the end of the 19th Cen- this might be that following a reduction in nutri- tury as a result of drainage and lowering of the ent loading, the state of some of the lakes is just water level. In the catchment of Lake Arreskov, slowly improving, and that some of the biological for example, the number of lakes decreased by conditions – for example the distribution of sub- 76% from 276 in 1890 to 65 in 1992. merged macrophyte vegetation – lag behind. An- Larger lakes have also disappeared, for example other problem is that the nitrogen concentration Lake Næsbyhoved, which was drained and par- in the lakes is typically too high. None of the six tially excavated as a harbour in Odense in 1863. lakes are presently able to meet the criteria for See also Section 1.1. good ecological status. The former – and now reclaimed – lakes are Less comprehensive investigations have also not included in this report unless they still exist been made of 30 minor lakes. Nutrient con- as wetlands. centrations were enhanced and the submerged

Odense PRB Odense Pilot River Basin 103 4.3 Lakes

macrophyte vegetation was markedly reduced in received wastewater containing heavy metals, nearly all of these lakes (90%). cf. Danish Environmental Protection Agency Based on the above-mentioned investigations it (1983a). The sediment content of chromium is must be concluded that by far the majority of the markedly raised in Lake Brahetrolleborg Slotssø, lakes in Odense River Basin are affected by nu- though, as this lake formerly received wastewater trients to such a degree that they do not meet the from a tannery. objective of a natural and diverse ﬂ ora and fauna The moderate heavy metal concentrations or the criteria for good ecological status. detected in the water phase and sediment of the lakes reﬂ ect the fact that, apart from Lake Heavy metals Brahetrolleborg Slotssø, they do not or have not Water phase received wastewater containing high levels of In 1998 and 2001, the surface water concentra- heavy metals. tions of seven heavy metals were analysed in Lake Arreskov. All concentrations were below Pesticides the limit levels for surface waters, cf. Ministry of In 2001, water from Lake Arreskov was analysed Environment and Energy (1996). for 47 pesticides/pesticide residues. Four pesticides and four pesticide residues were detected. Sediment The substance most frequently detected was 2,6- The content of heavy metals in the surface sedi- dichlorbenzamid (BAM), which was detected in ment of the lakes is moderate, and in most of the all samples. The following substances were also eight lakes investigated in Odense River Basin detected: Hydroxyatrazine, AMPA, hydroxysi- within the normal range for lakes that have not mazine, glyphosat, TCA (trichloro acetic acid),

Table 4.3.1 Biological and physi- Lake: Arreskov Dallund Langesø Nørresø Nr. Søby Søbo cal conditions in six lakes i Odense River Year of investigation 2002 1998 1997 2001 2001 1998 Basin (1997–2002). Area (ha) 317 15 18 69 18 21 The plankton values are means for the sum- Mean depth (m) 1.9 1.9 3.1 2.3 0.5 3.6 mer period. The water chemistry values are Fish CPUE No. 236 98 275 474 266 300 medians for the same CPUE Wt (kg) 4.709 4.606 4.914 5.566 12.442 4.032 period. The ecological class determined Vegetation Number of species 11 3 0 2 0 0 according to the Na- tional Environmental Coverage (%) 11.4 <1 0 <1 0 <1 Research Institute (in Phytoplankton Chlorophyll a (µg/l) 35.8 30 70 55 239 29.7 prep.) is also indicated. Blue-green algal biomass 3 34.1 2.73 7.59 2.82 3.26 0.058 (mm /l) Zooplankton Biomass (mm3/l) 7.5 5.75 5.79 3.53 17.18 3.75

Zooplankton:phytoplankton ratio 0.21 1.27 0.34 0.57 0.63 0.74

Water chemistry Total P (mg/l) 0,15 0.07 0.174 0.075 0.28 0.074

Total N (mg/l) 1.586 0.997 2.21 1.33 3.47 1.19

SS (mg/l) 13.21 11.87 12.7 7.29 61.15 5.67

pH 8.63 8.05 8.74 8.48 9.53 8.25

Secchi depth (m) 1.10 1.00 0.94 0.78 0.24 1.55

Ecological status:

Based on phosphorus content Poor Moderate Poor Moderate Bad Poor

With inclusion of biological parameters Bad Bad Bad Bad Bad Bad

Odense 104 PRB Odense Pilot River Basin 4.3 Lakes

Lake Type Reference status Current ecological Current Provisional future objective Expected Reason for cf. Table status objective compliance failure to 1.5.5 with provi- meet objec- sional future tive objective Total P Chl. a Total P Chl. a Total P Chl. a (mg/l) (µg/l) (mg/l) (µg/l) <(mg/l) <(µg/l) Arreskov 12 0.044 5) 39 6) 0.189 100 A1 High 0,050? 42? 6) No a, b Brændegård 12 0.015 1) 4 1) 1.816 45 A1 High ? 3) ? 3) ? a, b Sortesø 11 0.015 1) 4 1) 0.164 210 A1 High 0,025 4) 7 4) No b St. Øresø 12 0.0151) 4 1) 0.043 8 A1 High 0,025 4) 7 4) No a, c Nørresø 12 0.030 2) ? 0.073 60 A1 High 0,040? 10? No a, b Fjordmarken ? 0.015? 1) 4 1) - - A1 High 0,025? 7? ? ? Søbo 13 0.008 1) 4 1) 0.087 58 B Good 0,013 4) 7 4) No a, b Langesø 12 0.135? 2) ? 0.172 119 B Good 0,135? ? No a, b Nr. Søby 12 0.015 1) 4 1) 0.283 237 B Good 0,050 4) 13 4) No a, b Dallund 12 0.020 2) ? 0.059 34 B Good 0,050 4) 13 4) Perhaps a, b Fjellerup 12 0.015 1) 4 1) 0.208 109 B Good 0,050 4) 13 4) No a, b Brahetrolleborg Slotssø 12 0.015 1) 4 1) 0.868 94 B Good ? 3) ? 3) ? a, b

Notes: Table 4.3.2 1) Cf. Table 1.5.6 2) Assessed on the basis of paleolimnological studies Overview of lake type, 3) P content and algal biomass naturally elevated due to the presence of a cormorant colony in Lake Brændegård expected concentra- 4) Cf. National Environmental Research Institute (in prep.) tion of phosphorus and 5) Model calculations, cf. Fyn County (2003a) chlorophyll a in the 6) Model calculations based on total P, cf. Jensen et al. (1997) surface water in reference conditions (mean Reason for failure to meet objective: a) N and P loading from agriculture for the summer period b) P release from sediment 1.5–30.9), current con- c) Wastewater from sparsely built-up areas centration of phosphorus and chlorophyll a in the surface water (summer mean), cur- terbutylazin and simazine. The concentrations in to the WFD. In addition, a number of the clean- rent objective, provi- which the substances were detected were all low, est gravel quarry lakes will probably be able to sional future objective and none exceeded the limit value for drinking meet the current objective, and perhaps also the with proposed require- water of 0.1 µg/l. criteria for good ecological status/good ecologi- ments as to phosphorus cal potential. and chlorophyll a Other hazardous substances The remaining lakes are all to some extent af- concentrations in the In autumn 2002, the surface sediment of three fected by former and present-day nutrient load- surface water (summer lakes (Arreskov, Langesø and Store Øresø) was ing, and therefore do not meet their current ob- mean), expected compliance with objective investigated for the following groups of com- jective. Some as yet uninvestigated isolated lakes and reason for failure pounds: PAHs, PCBs, chlorinated pesticides, may exist that meet the objective, however. to meet the objective chlorobenzenes, chlorophenols, plasticizes, P- The state of those lakes that were previously for 12 lakes in Odense triesters, nonlyphenols, bisphenol-A, LAS, phe- polluted by large amounts of urban wastewater River Basin. nols, and brominated fl ame retardants. is slowly improving. Thus the submerged macro- Although the results have not yet been as- phyte vegetation has returned in some of these sessed, it does not seem that the sediment content – but is only widespread in Lake Arreskov. of these substances is high. A precondition for improvement in lake state is that nitrogen and phosphorus loading from agricultural sources and wastewater from sparsely built-up areas are adequately reduced. During the 4.3.3 Objective compliance and risk coming years, phosphorus loading from waste- of future lack of compliance water can be expected to decrease considerably in line with the introduction of requirements for The present assessment is that only one lake, improved phosphorus removal from wastewater Lake Store Øresø, currently meets the objective from properties in the catchments of the larger of a natural and diverse fl ora and fauna. It has a lakes. This is hardly likely to be suffi cient to low phosphorus concentration, a low algal abun- ensure that the lakes will meet the objective, dance and a widespread submerged macrophyte though, and it will therefore be necessary to also vegetation. It is uncertain, though, whether this take action to reduce phosphorus and nitrogen lake will be able to meet the more specifi c provi- loading from agricultural sources. The trend in sional criteria for good ecological status pursuant the lakes will depend on the measures imple-

Odense PRB Odense Pilot River Basin 105 4.4 Wetlands

mented in this area. 4.4 Wetlands Another factor is that lakes react very slowly to reductions in loading, among other reasons 4.4.1 Physical pressures due to nutrients accumulated in the sediment. It is therefore hardly likely that more than just The physical pressures on the wetlands in the a few of the lakes can meet the objective of good form of regulation of watercourses, drainage/ ecological status by 2015. ditching of wetlands and the nearby surround- By way of example, on the basis of current ings, abstraction of groundwater, fi lling-in and knowledge about the lakes and measures already peat mining have had a considerable impact on planned an assessment has been made of the the function of the wetlands as nutrient sinks and extent to which 12 of the large lakes in Odense on their natural state. River Basin will meet the provisional future ob- From the second half of the 19th Century, a jectives by 2015 (Table 4.3.2). The planned meas- pronounced desire arose from agriculture and so- ures are fi rst and foremost improved treatment ciety in general for better drainage of the fi elds. of the wastewater from sparsely built-up areas. Minor regulations of the River Odense and its It is apparent that the majority of lakes cannot tributaries were carried out on several occasions be expected to meet the objective with the during that period. With adoption of the Land hitherto adopted measures. Only a single lake Reclamation Act in 1940, major regulation of might possibly meet the objective. With regard watercourses was initiated. As a consequence, to the WFD’s general objective of at least good many wetlands have partially or completely ecological status by 2015, there are possibly two disappeared. An example is the regulation of the out of the 12 lakes that can comply. As regards River Odense, which took place over the period the remaining lakes in Odense River Basin, it is 1941–1960. This resulted in the cultivation of the hardly likely that more than just a very few of lowland areas along the watercourses. It has not them can meet the objective of good ecological been possible to maintain this cultivation on all status by 2015. of this land right up to the present time, however. For example, large areas around Ulvebækken White water-lily Brook are presently meadow and mire. A subsid- ( Nymphaea alba) ence survey (Nielsen, 2002) has shown that large . parts of the lowland areas have subsided by up to 1 m, while those alongside Ulvebækken Brook has subsided by up to 3 m. The rule of thumb is 1 cm per year. There are several reasons for the subsidence. When the water level is lowered in peaty soils these dry out, thereby enabling consolidation to take place. At the same time the peat becomes oxidized due to drainage, whereaf- ter decomposition increases. The new water table in re-created wetlands will therefore have to be adapted to the subsidence that has taken place; otherwise, very large lakes will form in the watercourse systems themselves, which is undesir- able from the point of view of fi sh passage. Since 1890, the area of extensively farmed lowland has decreased by 45% in Odense River Basin. This reduction is typically attributable to drainage and ditching of meadows/wetlands, straightening and deepening of watercourses and the pumping of water away from wetlands. Watercourse maintenance has also infl uenced the water level in the adjoining wetlands. Prior to adoption of the new Watercourse Act in 1983, the watercourses were maintained frequently, and in a hard-handed manner. With the new Wa- tercourse Act the purpose was changed such that drainage has to be ensured while concomitantly

Photo: Bjarne Andresen, Fyn County

Odense 106 PRB Odense Pilot River Basin 4.4 Wetlands

1930s Figure 4.4.1 Consequences of drainage for the river valley along the River Odense/Tørringe Brook. Scenarios for the drainage level in the 1930s, 1960s and in between, which are used when re-creating new wetland in 2003. Lake Swamp Wet meadow Dry meadow

2003

Open water 0 5 10 km Swamp Wet meadow Humid meadow Dry meadow

1960s

Swamp

Wet meadow Dry meadow

Odense PRB Odense Pilot River Basin 107 4.4 Wetlands

taking into consideration the environmental re- will also be indirectly affected if the vegetation quirements to watercourse quality. changes. Abstraction of groundwater for drinking wa- The waterborne loading primarily derives from ter, industry and irrigation also infl uences the agriculture and has its greatest effect on those water level in wetlands. This is particularly the wetland areas located closest to the source of case for wetlands located in upwelling areas. A pollution. Nitrogen compounds are transformed, lower water table will also diminish water fl ow especially nitrate, which is reduced to gaseous ni- in the watercourses, however, which will have a trogen under anaerobic conditions, such that the more general effect on all the wetlands along the load decreases with increasing distance from the watercourses and hence have a great impact. source. The extent to which the fl ora and fauna The fi lling-in of wetlands and peat mining in will be affected depends on the magnitude of wetlands naturally have very direct consequenc- loading and the type of wetland. es for wetlands. Filling-in leads to the disappear- Certain pesticides will also be degraded in ance of the wet low-lying parts through covering wetlands, but the fl ora and fauna will be affected of the peat layer, usually with other soil types. depending on the type of pesticide. As regards Conversely, peat mining entails removal of the phosphorus, heavy metals and hazardous sub- peat layer, whereby valuable plant communities stances, these can sediment, bind or be released disappear and are replaced by water-fi lled peat depending on the redox state and biological mines. Peat mining has now ceased in Fyn Coun- processes. Transport of particulate matter out of ty, and the fi lling-in of wetlands has reduced wetlands, typically during major runoff events, considerably in recent years. can result in the release from wetlands to down- An example of a wetland that has been drained, stream water bodies. but which is now being re-established under Ac- The airborne pollution distributes over the tion Plan on the Aquatic Environment II, is the whole surface of the wetlands, although in such a reach of the River Odense upstream of Tørringe manner that loading is highest in the parts closest Brook. This reach was regulated during the peri- to the source. The deposition encompasses nitro- od 1944–1950. Scenarios for the consequences of gen, primarily in the form of ammonia, phos- drainage of the fl oodplain have been established phorus, heavy metals and hazardous substances, for the 1930s, the 1960s and for drainage state in including pesticides. between. These are being used in connection Nutrient loading of wetlands favours the nu- with the re-establishment of a new wetland in trient-tolerant plant species, resulting in loss of 2003 (See Figure 4.4.1). vegetation diversity and an increase in the rate at which the wetlands become overgrown. Thus it is already necessary to take steps to conserve the rare natural habitat types in the open coun- 4.4.2 Impact of pollutant loading tryside. Internationally agreed critical loads have been Pollutant loading is described in Section 3. As established indicating how much nitrogen load- regards the wetlands, this encompasses both ing the various habitat types can tolerate if they waterborne and airborne pollution in the form are to be conserved as characteristic and varied of the nutrients nitrogen and phosphorus, or- habitat types in the long term. For the naturally ganic matter, heavy metals and hazardous sub- nutrient-poor habitat types such as raised bogs, stances. The loading derives from waterborne poor fens, rich fens, heaths and some dry grass- and airborne discharges and emissions from the lands, the lowest critical load is 5–20 kg N/ha/yr. agricultural sector, sewage and rain water from The critical load for the naturally more nutrient- sparsely built-up areas, emissions from industry, rich habitat types such as freshwater meadows, power stations, traffi c, etc. Sewage from waste- certain types of mire and dry grasslands is of the water treatment plants is no longer discharged to order of 20–35 kg N/ha/yr. The critical load for wetlands and lakes. All discharges from wastewa- woodland varies between 7 and 30 kg N/ha/yr ter treatment plants are now led solely to water- depending on the soil conditions and type of courses and coastal waters. woodland (Bak, 2001). Nutrient loading of wetlands infl uences their The average background loading with airborne natural state, especially the vegetation, but also nitrogen in Fyn County is approx. 20 kg N/ha/ the aquatic animals and birds. Other animals yr (Bak, 2001). Due to livestock production, associated with wetlands due to the presence though, the total nitrogen loading from the air of a particular type of vegetation, e.g. insects, can be much higher than 20 kg N/ha/yr locally.

Odense 108 PRB Odense Pilot River Basin 4.4 Wetlands

The critical load for natural and woodland habi- With regard to the wetlands being re-estab- tats in Fyn County will therefore be exceeded in lished under Action Plan on the Aquatic Envi- many places. For example, the critical load for ronment II, the aim is to denitrify as much nitro- the majority of the mires in Fyn County that gen as possible and retain as much phosphorus have been assigned a high quality objective in the as possible while concomitantly re-creating some Regional Plan 2001–2013 (quality objective A or natural habitats with natural hydrology as an B) is of the order 5–20 kg N/ha/yr. alternative to cultivated ﬁ elds. Nitrogen reten- Investigation of the nature quality of mires tion amounts to 200–350 kg N/ha/yr for the 21 in Fyn County has shown that Red List plant wetlands in Fyn County. The range is based on species associated with nitrogen-poor soils are the experiences from monitored re-established at signiﬁ cantly greater risk of becoming extinct wetlands and from investigated wetlands with than Red List plant species that are able to grow calculated nitrogen transformation rates. Six of on more nitrogen-rich soils (Vinther & Tran- these 21 wetlands are located in Odense River berg, 2002). At the same time, the majority of the Basin, corresponding to approx. 570 ha. Of this, Danish Red List plant species are associated with approx. 220 ha of wetland will have been estab- nutrient-poor habitats (Ejrnæs, 2000). Corre- lished by the end of 2003. This corresponds to sponding critical loads have not been established a nitrogen reduction of approx. 114–200 tonnes for phosphorus. N/yr in Odense River Basin.

Re-established wetland at Karlsmosen 2002.

Photo: Lars Bangsgaard, Fyn County

Odense PRB Odense Pilot River Basin 109 4.5 Coastal waters

4.5 Coastal waters

4.5.1 Physical pressures fairway considerably deeper than the surround- ing natural fjord bottom entails the risk of intru- The physical pressures on Odense Fjord are sion of hypoxic bottom water from the border described in Section 1.8.4, and physically modi- zone (which is frequently subject to oxygen defi - fi ed areas are identifi ed in Figure 1.8.7. The main cit) via the fairway to the outer parts of Odense physical pressures on the fjord are dyking and Fjord (“imported oxygen defi cit”), as well as reclamation of former areas of fjord, construc- the development of local oxygen defi cit in the tion of harbours, excavation of shipping fairways stagnant bottom water in the fairway. Sediment and changes in the fjord’s water exchange, salin- dispersal during excavation of the fairway will ity and temperature as a result of the intake and reduce the transparency of the fjord water and discharge of cooling water by Fynsværket com- result in enhanced release of otherwise sediment- bined heat and power (CHP) plant. bound organic matter, nutrients and hazardous substances, both during and following the exca- Dyking and land reclamation vation work. Habitat conditions for the fl ora and The extensive dyking and reclamation of former fauna will thus deteriorate, among other reasons segments of the fjord have considerably reduced due to diminished light penetration of the water the capacity of the fjord and associated wetlands column, enhanced sedimentation, enhanced to retain and reduce nutrients from the surround- oxygen consumption in the water column due ing arable land. Nutrient loading will therefore to turnover of organic matter, and enhanced be refl ected by raised nutrient concentrations in concentrations of nutrients and hazardous sub- the fjord to a greater extent than previously. stances. The methods selected to maintain the fairway and dispose of the removed substrate, Shipping fairways – excavation and clearance the duration of the clearance work and the in- The establishment and clearance of a shipping terval between fairway maintenance operations will signifi cantly affect the resultant pressure on the fjord. 50 2.5 Figure 4.5.1 Total N in Odense Fjord (mg N/l) Trend in source-appor- Wastewater (kg N/ha/yr) Cooling water tioned annual nitrogen 40 * Diffuse loading (kg N/ha/yr) 2.0 The circulation of cooling water through Fyns- and phosphorus load- værket CHP plant negatively affects the Odense ing from land-based 30 1.5 Fjord system through mortality of the organisms sources together with that are sucked into the cooling water system, the annual mean concentration in the 20 1.0 through the effects of warm, saline water on surface water at station the River Odense, through obstruction of the N load (kg N/ha/yr) ODF17 in the outer 10 0.5 upstream migration of eel and sea trout in the part of Odense Fjord. River Odense and Stavis Stream, through the Total water N in surface (mg N/l) effects of heat on the inner fjord and through 0 lllllllllllllllllllllll0.0 86/87 89/90 92/93 95/96 98/99 01/02 enhanced growth of sea lettuce in the inner *inclusive wastewater from sparsely built-up areas fjord. The raised temperature generally increases phytoplankton and macrophyte production in the area, and in warm summer periods there is 3.5 0.35 Total P in Odense Fjord (mg P/l) an enhanced risk of heat stress and hence of in- 3.0 Wastewater (kg P/ha/yr) 0.30 creased mortality among the seagrasses, etc. Ac- * Diffuse loading (kg P/ha/yr) cording to model calculations, the cooling water 2.5 0.25 circulation can also be interpreted as having posi- 2.0 0.20 tive effects on the fjord in that water exchange in the inner fjord is increased, thereby entailing 1.5 0.15 lower nutrient concentrations. Furthermore, 1.0 0.10 the growth of seagrasses is stimulated, and the P load (kg P/ha/yr) phytoplankton production reduced. The latter 0.5 0.05 is relatively low already, though, and in terms of Total water P in surface (mg P/l) eutrophication is of lesser importance compared 0.0 lllllllllllllllllllllll0.00 86/87 89/90 92/93 95/96 98/99 01/02 with the growth of eutrophication-dependent *inclusive wastewater from sparsely built-up areas macroalgae. Through modelling it has been

Odense 110 PRB Odense Pilot River Basin 4.5 Coastal waters

µg/l possible to quantify certain of the effects with a Chlorophyll a Figure 4.5.2 ±SD 6910008 Trend in annual mean satisfactory degree of certainty, while determina- 25 Annual mean concentration of chlo- tions of the effects of greatest signiﬁ cance for the 20 rophyll a in the inner fjord, namely those on biological conditions, are part of Odense Fjord less certain. 15 (Seden Strand).

Fishery 10 Trawling for mussels constitutes a major pressure on the areas where fi shery is carried out, 5 among other reasons because of damage infl icted upon the eelgrass vegetation and the benthic in- 0 vertebrates. At present, the use of mussels from Odense Fjord for human consumption is pro- 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 hibited, cf. Section 4.5.2. If the consumption of mussels from the fjord is permitted once again, however, resumed fi shery will place such great reduced phosphorus loading of the fjord, and physical pressure on the fjord as to impede the in summer also nitrogen loading. Nevertheless, attainment of good ecological status. considerable nutrient loading, especially with Fishery in the fjord is presently carried out nitrogen, still takes place from the cultivated with passive gear. Restrictions are in force in catchment (Figure 4.5.1). parts of the fjord (see Section 2, Figure 2.7), Correcting for the interannual variation in pre- among other reasons to ensure the free migra- cipitation and riverine runoff leads to the conclu- tion of salmonids to the River Odense and Stavis sion that riverine nutrient loading of the coastal Stream. The effects of fi shery on the fi sh stock in waters around Fyn has decreased by 25–35% for the fjord have not yet been determined. nitrogen and approx. 75% for phosphorus relative to the period prior to adoption of the fi rst Action Plan on the Aquatic Environment in 1987; corresponding reductions have been obtained with 4.5.2 Impact of pollutant loading respect to loading of Odense Fjord. Diffuse loading accounts for more than 80% of Odense Fjord receives nutrients and hazardous the nitrogen input to Odense Fjord and 75% of substances from wastewater treatment plants and the phosphorus input; most of the remainder de- individual industrial discharges, as well as from rives from point sources, and a minor part from diffuse loading, primarily from agriculture, from the atmosphere (see also Section 3.4). During the its approx. 1 060 km2 catchment, which corre- summer period, though, nitrogen loading from sponds to just under one third of Fyn. wastewater is of the same magnitude as diffuse Since the beginning of the 1990s, 99.8% of all loading and signifi cantly affects the environ- household wastewater from the sewerage catch- mental state of especially the inner fjord (Seden ment is effectively treated. This has considerably Strand).

Figure 4.5.3 Seden Strand Seden Strand 30-31 August 1982 2000-2001 Distribution of macro- Sea lettuce Sea lettuce phytes (Sea lettuce, 76-100% 76-100% Ulva lactuca; Widg- 51-75% 51-75% 26-50% 26-50% eon grass, Ruppia Vigelsø 1-25% 1-25% Vigelsø maritima; Eelgrass, Widgeon grass Distribution of 51-100% Zostera marina; widgeon grass Scattered <50% Bladder wrack, Fucus 51-100% Tornø Eelgrass Tornø vesiculosus Scattered ) and ﬁ la- Filamentous algae mentous algae (mainly Ecto- Bladder wrack the brown alga

ø N ø N carpus siliculosus and e e g i t g i Clado- t the green algae S S phora sp.) in the inner 0 1 km 0 1 km fjord (Seden Strand) in 1982 and 2000–2001.

Odense PRB Odense Pilot River Basin 111 4.5 Coastal waters

Figure 4.5.4 N conditions and pH in the water, both on a daily Distribution of fi lter basis and over longer periods during the summer. feeders (soft clams, Mya arenaria, and the When the sea lettuce biomass decomposed, this polychaete, Nereis di- OTTERUP was frequently accompanied by oxygen defi cit versicolor) in Odense and the release of hydrogen sulphide. The de- Odense Fjord. Fjord creasing sea lettuce biomass due to the falling st.3 nutrient concentrations has resulted in more sta- Soft clams st.1st.2 >60 ind/m² ble oxygen conditions in the inner fjord. Oxygen <60 ind/m² defi cit and release of hydrogen sulphide are now MUNKEBO <10 ind/m² Seden KERTEMINDE relatively rare in this area. Strand Polychaetes The outer fjord still experiences occasional oxy- >2 000 ind/m² gen defi cit, primarily as a result of the intrusion <2 000 ind/m² of hypoxic bottom water from the area outside the fjord via the excavated fairway, as mentioned above. The risk of such “imported oxygen defi -

ODENSE 0 1 2 3 km cit” occurring largely depends on the frequency and duration of oxygen defi cit in the border zone outside the fjord, and hence on the general oxygen conditions in the coastal waters of Fyn. Nutrients The lower level of phosphorus loading is re- Phytoplankton fl ected in a signifi cant decrease in the phospho- Phytoplankton biomass in Odense Fjord ex- rus concentration in the fjord water. Moreover, pressed in terms of the chlorophyll a concentra- the trend in nitrogen concentration is towards tion has remained largely unchanged over the decreasing concentrations in the summer. The past 25 years (Figure 4.5.2), despite the fact that nitrogen concentration in the fjord is closely nutrient concentrations can now be so low in related to nitrogen input. In years when river- periods as to limit phytoplankton growth (see ine runoff is high, the nitrogen concentration is Section 1.8). Phytoplankton biomass in the fjord relatively higher in the fjord water than in years is somewhat low relative to the nutrient load and when riverine runoff is low, for example as in compared with other fjords in Denmark; blooms 1996–97 (Figure 4.5.1). still occur frequently, however. Despite a signifi cant reduction in nutrient dis- One of the reasons for the low phytoplankton charge, especially of phosphorus, input of both biomass is that Odense Fjord is a very shallow nitrogen and phosphorus is still great. Together fjord with an unusually high content of poly- with a considerable discharge of hazardous sub- chaetes and mussels, which fi lter the phytoplank- stances this makes environmental conditions in ton out of the water column. These have the po- the fjord very unstable, as is refl ected in the fjord tential to fi lter the water in the inner fjord several fl ora and fauna. times daily. Other contributory factors are the relatively short residence time (couple of weeks), Oxygen conditions the use of fjord water for cooling by Fynsværket In the shallow inner part of the fjord, Seden CHP plant with the resultant enhanced mortal- Strand, the formerly very high sea lettuce ity of both phytoplankton and zooplankton, and biomass caused large fl uctuations in oxygen nutrient uptake by macrophytes.

Vegetation Figure 4.5.5 % Odense Fjord Intersex Sexual transformation St.1 As a result of the reduction in nutrient loading (intersex) in the female 80 St.2 of the fjord, the former mass occurrences of sea common periwinkle St.3 lettuce have diminished, and the rooted macro- ( Littorina littorea) in 60 phyte vegetation has gained ground in the inner Odense Fjord in the fjord (Figure 4.5.3). Widgeon grass – and to some period 1998–2002. extent eelgrass – have recolonized in the inner 40 fjord, and a more diverse macroalgal community has established in the outer fjord, including a 20 large proportion of the slowly growing brown algal species bladder wrack. Nevertheless, nutri- 0 1998 1999 2000 2001 2002 ent loading remains so high that for long periods

Odense 112 PRB Odense Pilot River Basin 4.5 Coastal waters

of the growth season the inner fjord is still domi- polychaetes and molluscs. The same species are nated by rapidly growing ephemeral macroalgae, found in both the inner and outer fjord, but the especially sea lettuce and fi lamentous algae, and density of both individuals and biomass is far major blooms of fi lamentous algae are a recur- greater in the inner fjord than in the outer fjord. ring problem in the outer fjord. Moreover, the abundance of fi lter feeders is by far The distribution of the freely fl oating ephem- the greatest in the inner fjord (Figure 4.5.4). eral macroalgae varies considerably from year The fauna in Odense Fjord is severely affected to year. These shade out the submerged macro- by hazardous substances. The content of TBT, phytes, thus making it diffi cult to establish and PAHs and PCBs (polychlorinated biphenyls) maintain a stable rooted macrophyte vegeta- in common mussels is so great that limit values tion. Eelgrass coverage exhibits large temporal recommended in the international conventions variation relative to other areas, and at present are exceeded. The Danish Veterinary and Foods is generally less than 7% in the eelgrass-vegetated Administration advises against consuming mus- depth intervals in the fjord. This is very low com- sels from Odense Fjord and has prohibited compared to other shallow areas, such as in the South mercial mussel fi shery in the fjord. The TBT Fyn Archipelago (coverage >60%), and to the content in the fjord sediment is also so high as estimated reference situation for Odense Fjord, to cause sexual and reproductive changes in the where the criterion for eelgrass coverage is >80% common periwinkle (Littorina littorea). The main the macrophyte-vegetated depth intervals (see jority of the females closest to the source of TBT section 1.8.5). have become masculinized, and many of the An impact of hazardous substances on the oc- male periwinkles have a reduced number of penis currence and distribution of the vegetation can- glands, possibly diminishing their reproductive not be excluded. Preliminary studies in Odense capacity (Figure 4.5.5). Fjord have demonstrated effects on eelgrass and widgeon grass of such substances as TBT (tri- butyl tin), PAHs (polyaromatic hydrocarbons), 4.5.3 Objective compliance and risk and other as yet unidentifi ed substances in the of future lack of compliance sediment.

Benthic invertebrates Pursuant to the WFD, the Article 5 characteriza- Odense Fjord has a diverse benthic inverte- tion and analysis has to contain an assessment of brate fauna consisting of polychaetes, molluscs, the likelihood that with the measures hitherto echinoderms and crustaceans. In terms of both adopted the water bodies will fail to meet the ob- number of individuals and biomass, the commu- jective of at least good ecological status by 2015 nity is dominated by eutrophication-dependent at the latest.

Expected Reason Table 4.5.1 Provisional Water body Type compliance with for non- Overview of the ﬁ ve objective objective compliance marine water bodies encompassed by Inner fjord (Seden Strand) 1 G No N, P, HS Odense River Basin: ODF NW 2 H No N, P, HS Type, provisional objective, expected com- Outer fjord ODF NE 2 G No N, P, HS pliance with objective and reason for failure ODF Mid 2 G No N, P, HS to meet the objective. Boundary zone 3 G No N, P

Type 1: Inner fjord, salinity <18 PSU Type 2: Fjord, salinity 7–18 PSU, mean depth 0–3 m Type 3: Inner marine waters between Djursland/Sjællands Odde and Fyns Hoved/Røsnæs, salinity 15–20 PSU, depth <15 m

N: Nitrogen P: Phosphorus HS: Hazardous substances

H: High ecological status G: Good ecological status

Odense PRB Odense Pilot River Basin 113 4.5 Coastal waters

Due to the unstable nature of the biological 2003b). structure of the fjord and the impact of hazard- Model calculations show that the measures ous substances on the fjord fl ora and fauna, the hitherto implemented and adopted pursuant to current quality objective for the whole fjord is Action Plans on the Aquatic Environment I+II not met. Provisional objectives pursuant to the together with the measures directed at wastewa- WFD are presented for Odense Fjord in Section ter from sparsely built-up areas, etc. will reduce 1.8.6. According to these proposals, the parts of loading of the fjord to approx. 1 900 tonnes N/yr the fjord that have been assigned the highest qual- and 65 tonnes P/yr assuming the same mete- ity objective in the Regional Plan have to meet orological conditions as in 1998 (Nielsen et al., the environmental objective “High ecological 2003b). These provisional calculations thus show status”, while the remainder of the fjord and the that there is the likelihood that the WFD objec- border zone have to attain “Good ecological sta- tive of good ecological status will not be met tus” (see also Table 1.8.2, as well as Section 1.8.6 with the measures hitherto adopted. for a discussion of the establishment of the objec- As far as concerns hazardous substances and tives for the areas encompassed by international heavy metals, the WFD requires the concentra- protection). A precondition for meeting the ob- tions, in the reference conditions/high ecological jective is the establishment and maintenance of status to be close to zero for hazardous substances a stable biological structure; in areas with high and not above background level for heavy metals. ecological status this may show “no, or only With good ecological status, the concentrations very minor, evidence of distortion” relative to may not exceed standards set on the basis of tox- undisturbed conditions, while in areas with good icity tests etc. (cf. WFD, Annex V). These crite- ecological status it may “deviate only slightly” ria are not presently met. The overall magnitude undisturbed conditions (WFD, Annex V). of hazardous substance and heavy metal loading These status criteria are not presently met in of the fjord is not presently known (cf. Section the fjord (Table 4.5.1). 3.6). Analyses of the sediment have revealed very Attainment of the assigned ecological status high concentrations, though, and marked effects will among other things require that nutrient on the fauna and possibly also the fl ora have been loading is reduced to a level where climate-re- demonstrated. The attainment of good ecological lated interannual variation in riverine nutrient status will require a considerable reduction in the loading has no signifi cant effect on the biological present concentration levels in the fjord. structure of the fjord. Provisional scenario calcu- In connection with review of Fynsværket lations made by dynamic modelling of the fjord CHP plant’s discharge permit it was concluded have shown that assuming a macrophyte crite- that the physical pressures on the fjord associated rion of max. 50% deviation from the reference with the intake and discharge of cooling water conditions as to macrophyte biomass, it will not by the plant could be one reason why it may be be possible to attain good ecological status until diffi cult to meet the objective in a future loading nutrient loading has been reduced to less than ap- situation. prox. 800 tonnes N/yr and 30 tonnes P/yr. This The effects of fi shery, including possible future means that the current level of nitrogen loading trawling for mussels, could also impede attain- will have to be reduced by somewhere in the ment of good ecological status in the fjord and order of 1 200 tonnes N/yr, and the phosphorus the border zone outside the fjord. loading by approx. 43 tonnes P/yr (Nielsen et al.,

Sea lettuce ( Ulva lactuca) on the fjord bottom..

Photo: Nanna Rask, Fyn County

Odense 114 PRB Odense Pilot River Basin