Water-Quality Data-Assessment of Long-Term Time Trends, Weser River Basin, Germany – a Case Study
Water-Quality Data-Assessment of Long-Term Time Trends, Weser River Basin, Germany – A Case Study
Timothy D. Steele 1, Simon Henneberg 2, and Houshang Behrawan 3 Department of Geoinformatics, Hydrogeology, and Modelling
1President, TDS Consulting Inc., Denver, CO, United States and Alexander von Humboldt- Foundation Guest Research Scholar, Friedrich-Schiller-Universität-Jena, Germany; 2Executive Secretary, Weser River Basin Commission, Hildesheim, Germany, and 3Ph.D. Graduate Student, Friedrich-Schiller-Universität-Jena, Germany
ABSTRACT
The 1979-2008 period of record for the four Weser River basin monitoring sites was used for demonstrating several data-assessment techniques and evaluation of time trends. Statistical and graphical analyses were conducted, and anomalous or possible erroneous data values were highlighted, modified, and/or deleted as a key part of the quality-assurance/quality- control (QA/QC) process. An overview of results is as follows: • For major salt-ions as a function of specific conductance (SC), bivariate plots were made. Relative good regression functions resulted for magnesium (Mg), sulphate (SO4), and especially for chloride (Cl). Such functions can be used to fill in missing data values or gaps in the record. • Time series plots indicated no time trends in streamflows but rather distinct periods of anthropogenic impacts and post-remediation trends for many of the variables. Seasonality was apparent for water temperature, dissolved-oxygen concentrations, and SC (for this variable, especially in the early part of the period of record (POR)). • Nitrate-N exhibited a slight downward time trend, especially during the recent period. • During the data assessment, several anomalous data values and other errors in data entry were apparent. These were changed or otherwise noted in the modified dataset file for further consideration.
The long-term time trends and bivariate relationships provide useful information regarding this monitoring program as well as benefits attained through mining-related remedial actions, especially in the upper part of the basin, changes in agricultural-fertilizer application, and wastewater-treatment plant improvements. Decreased concentrations (hence, loads) of major ions are primarily a result of control of salt point sources and of nitrate as well as a result of controls of application of fertilizers to agricultural lands.
It is recommended that similar data-assessment methods be applied for other monitoring sites having long-term water-quality data. Additional information will be discussed in the presentation, extracted from the river-basin management plan prepared for the Weser River Basin Commission, in accordance with the EU Water Framework Directive (WFD).
INTRODUCTION AND BACKGROUND
As part of ongoing applied research at the Friedrich-Schiller-Universität Jena’s (FSU-Jena’s) Department of Geoinformatics, Hydrology, and Modelling, this water-quality data assessment for the Weser River basin was conducted in order to evaluate the information content of selected available long-term monitoring data.
The Weser River basin has a total catchment area of 49,000 km2 (Figure 1). The primary land uses include agricultural lands and grasslands. The catchment’s total population is 9.34 million inhabitants (FGG-Weser, 2008; 2009). The principal water-quality issue (‘pressure’) involves diffuse pollution from agriculture. In addition, historically, salt discharges were made into this catchment from adjacent areas, contributing to major ionic loads and higher concentrations historically. In conducting a data search on the Flussgebietsgemeinschaft Weser (undated) (www.fgg-weser.de) website, it was found that long-term water-quality data were tabulated in a series of annual data files for the period-of-record (POR) 1979-through- 2008. For this case study, selected data for four of the 15 long-term monitoring sites were used to demonstrate various data-assessment methods as well as to evaluate both natural and anthropogenic effects over this 30-year period.
Figure 1 – Weser River Basin, Showing Locations of Water-Quality Monitoring Sites
Approaches
Key water-quality monitoring sites throughout the Weser River basin are indicated on Figure 1. For this case study, four monitoring sites were selected to demonstrate several data- analysis procedures and QA/QC protocols. The period of record at each site was used for this purpose. During the course of this assessment, statistical and graphical analyses were conducted, and anomalous or possible erroneous data values were highlighted, modified, and/or deleted as a key part of the QA/QC process.
An important role of any data assessment is to derive information from the basic data (Ward, 2002). Data without analysis and evaluation have minimum value; only when data are subject to graphical and statistical analyses and/or inputs into empirical or process models or summarized in other forms for interpretative-report documents, is value added for specific uses of the data.
Relatively simplistic but useful data-assessments tools applied to this case study consist of graphical analyses (bivariate-regression or time-series plots), and period-of-record or sub- period statistics. These methods are patterned after previously-developed methods (Steele, 1972; 1973) and applications (Steele and others, 1974; Steele, 1980; Bongartz and others, 2007). The overall objective in this application of these tools is to derive information from the basic data, in terms of long-term time variability and changes in streamflows and several water-quality variables and in assessing conditions responding to various impacts occurring in this river basin, either through natural processes or various anthropological impacts (human- related economic activities). For the statistical summary, nondetects were set to ½ the detection limit. This data assessment demonstrates preliminary analyses and findings and is not intended to be all-inclusive. Additional, more-detailed and really-extensive, analyses are recommended.
RESULTS
A variety of river-basin conditions and human-related activities affect the water-quality conditions at the monitoring sites selected for this case study. Examples include the extensive agricultural areas throughout the basin and industrial and mining impacts. These latter effects were in particular noted for pre-unification times when effluents from such activities adversely impacted water quality of this stream. Descriptions of causal effects are aided upon the cited literature (Cherlet, 2007) as well as understanding of the basin’s conditions provided by this paper’s second author.
Graphical analyses (Weser-Hemelingen as an example)
Figure 2a exhibits the commonly observed inverse relationship between specific conductance (SC) and streamflow. SC variability is significantly greater at the low end of the range of streamflows. As will be noted later, most of the higher SC values occurred prior to 1991, when high-salinity effluents were curtained in the river basin.
Figure 2a -- Weser-Hemelingen, Specific Conductance vs Streamflow
870 770 670 570 470 uS/cm 370 270
Specific Conductance (SC), 170 70 60 260 460 660 860 1060 1260 1460 1660 1860 2060 Streamflow (Q), m3/s
Figure 2b gives the stream time-series, using values associated with biweekly sampling surveys over the period of record. Seasonal and year-to-year variations are apparent; however, and this and other monitoring sites in this case study, no streamflow time trend was apparent from the various data series.
Figure 2b -- Weser-Hemelingen, Streamflow Time Series, 1979-2008 (POR)
1600
1200
800
Abfluß, m3/s Abfluß, 400
0
9 0 4 0 1 3 5 7 3 4 6 /7 /8 /86 /9 /9 9 /9 /01 0 /0 008 /4 4 0 /1 9 0 6 /7/0 6 1 /27/8 3 4/7/88 2 /21/9 /3 5/4/99 3/ 1 /2 .2 9/27/82 7 5/ 8 6 9 7 11/2 12/1 10/18/ 11/23/ .0 1 2 Date
The possibility for bivariate regression functions with SC as the independent variable were analyzed for calcium (Ca), magnesium (Mg), sulphate (SO4) and chloride (Cl) (Steele and Houshang, 2009). The Cl-SC plot (Figure 3) gives the best correlation (r2 = 0.93), indicating the quite good bivariate regression function for these variables. This type of plots indicates the inherent interdependence of major ions with SC; this often can be used as an independent variable to estimate ion concentrations as a function of SC when fewer or no data are available (Steele, 1972).
Figure 3 -- Weser-Hemelingen, Chloride vs. Specific Conductance
3560
3060
2560
2060
1560 y = 3,632x - 193,4 1060 R² = 0,93 Chloride (Cl), mg/L 560
60 80 180 280 380 480 580 680 780 880 SC, uS/cm
The time-series plot for streamflows (Figure 2b) exhibits naturally occurring seasonal variations but no distinctive time trend. This condition confirms that water-quality time trends for the major ions most likely are caused by anthropogenic effects rather than multiyear variations or trends in flows at this Weser River monitoring site downstream in the basin.
Figure 4 provides a time-series plots for SC for the entire (30-year) period of available record. This time-series plot exhibits seasonality (high flows/low SCs vs. low flows/high SCs) and the relative greater SCs occurring in the late 1980s and early 1990s. This pattern confirms similar time trends apparent for the major ions (Steele and Houshang, 2009). Beginning in 1992, SCs were consistently lower and exhibited a slight decreasing time trend. Shorter-term time-series SC plots exhibited decreasing trends, possibly indicating continuing improvements in curtailing salinity sources to this mainstem river.
Figure 4 -- Weser-Hemelingen, Specific Conductance Time Series, 1979-2008 (POR)
850 750 650 y = -0,2662x + 310,99 550 R² = 0,33 450 350 SC, uS/cm SC, 250 150 50
9 0 7 8 88 90 99 01 03 9 991 993 004 008 1984 1986 19 19 19 20 20 2 7/ 0/ 7/ 1/ /6/ 7/ 1/4/19 4/ 2/ 5/4/ 3 1/ 23/ /26/2006 9/27/1982 7/2 5/3 8/21/1995 6/30/1997 1/ 9 11/24/1 12/19/1 10/18/1 1 21.07.2 Date
The nitrate (NO3-N) time series exhibited seasonality over time and only a slight time trend over the entire 1979-2008 POR (Figure 5a). However, this downward trend was more apparent when considering only the more recent (1991-2008) period, as given in Figure 5b.
Figure 5a -- Weser-Hemelingen, Nitrate Time Series, 1979-2008 (POR)
11.0
9.0
7.0
5.0 NO3-N, mg/L NO3-N, 3.0
1.0
8 6 80 91 04 08 9 /1997 /4/1979 7/1982 7/1984 0/1986 0 6/200 1 /24/19 4/7/198 2/1/1990 5/4/1999 3/6/2001 1/7/2003 .07.20 9/2 7/2 5/3 8/21/1995 6/3 9/2 11 12/19/1 10/18/1993 11/23/20 21 Date
Figure 5b -- Weser-Hemelingen, Nitrate Time Series, 1991-2008 (Post-Unification) 9.0 y = -0,0039x + 5,1432 R² = 0,20 7.0
5.0
NO3-N, mg/L NO3-N, 3.0
1.0
96 99 02 05 07 08
1/4/1991 7/7/1992 /13/1996 9/8/19976/2/1998 2/5/2002 8/5/2003 25/20 10/9/1991 3/31/1993 9/18/19946/19/19953 2/23/19991/30/19 8/22/20005/15/2001 4/27/20041/18/2005 7/18/20064/15/2007 12/18/19 1 11/12/20 10/ 24.12.2029.09.20 Date
Water temperature time-series plots exhibit a typically consistent seasonal pattern with no time trend. This seasonal pattern can be accurately characterized by a simple-harmonic function (Steele, 1974). Although function coefficients often can be regionalized (as a function of elevation and/or latitude), this aspects is left as a recommended future study effort for a more extensive data assessment for all monitoring sites.
Dissolved-oxygen concentrations indicate some seasonality (Figure 6), although this pattern is not as consistent as for water temperature (Steele and Houshang, 2009). However, on a seasonal basis, the inverse relationship between water temperature and dissolved-oxygen concentrations is apparent (high T/low DO during summer vs. low T/high DO during winter), a pattern consistent in many streams in the northern hemisphere.
Figure 6 -- Weser-Hemelingen, Dissolved-Oxygen Time Series, 1979-2008
14.0
12.0
10.0
8.0 DO, mg/L
6.0 y = 0.0012x + 8.8205 R2 = 0.0212 4.0
9 8 0 1 3 5 7 6 8 7 8 9 9 9 9 9 0 9 980 9 9 9 9 1 /1984 /1986 19 19 /1 /1 /1 /1 /1999 /2001 /2003 /20 /4/1 4/ 7 0 /7/ /1/ 9 8 1 4 6 7 1 2 /2 /3 4 2 /1 /1 /2 /30 5/ 3/ 1/ /26 1/ 9/27/1982 7 5 2 0 8 6 9 1 1 1 11/23/2004 21.07.200 Date
The pH time-series plots (Steele and Houshang, 2009) also indicate some seasonality. During 2004, unexplained increases in pH values (highest for the POR) were noted.
For assessing trace-metals (TMs) data, three species were selected for this assessment (Steele and Houshang, 2009). TMs were analyzed in water only through 2000, 6-to-8 times per year from 1979 through 1985 and then biweekly from 1986 through 2000. Beginning in 2001, these metals were analyzed in sediments approximately monthly at this downstream monitoring site. Relevant details are provided in the companion data-assessment report (Steele and Houshang, 2009). Only a few anomalously high concentrations occurred randomly in each time-series. In the case of TMs analyzed on sediments, some variability was exhibited; however, no time trend or seasonal variability was apparent.
Statistical summary and time trends (Weser River at Hemlingen monitoring site)
Both POR (Table 1a) and recent-period (Table 1b) basic statistics were calculated for the variables discussed above through the graphical analyses. These results are useful to confirm findings from the graphical analyses as well as some quantification of noteworthy time trends. It is useful (and recommended) and the sample sizes (that is, numbers of values for each variable) be noted in the summaries. These statistical-summary results are tabulated below:
Table 1a – Statistical Summary, Selected Variables over Entire Period of Record Variable Units Average # Values Maximum Minimum 1979-2008 POR Streamflow M3/s 340 782 1888.7 65.1 Specific Conductance mS/m 202 765 831 70 Calcium mg/L 81 735 110 53 Magnesium mg/L 56 710 190 13 Sulfate mg/L 155 774 380 53 Chloride mg/L 544 766 3000 65 Nitrate (as Nitrogen) mg/L 4.6 775 25 1.3 pH S.U. 7.8 760 9.0 6.7 Water Temperature deg C 12.1 775 25.5 0.4 Dissolved Oxygen mg/L 9.3 777 15.5 2.9 1979-2000 POR Chromium in Water ug/L 2.9 430 25.4 1 Zinc in Water ug/L 31.2 430 460 3 Manganese in Water ug/L 146 427 1500 25 Source: Excel file WeserRWQPlotsStatsR2.xls
Table 1b – Statistical Summary, Selected Variables over Recent Period of Record Variable Units Average # Values Maximum Minimum 1990-2008 Years Streamflow m/s 336 469 1591.21 88.6 Specific Conductance mS/m 145 463 350 70 Calcium mg/L 78 431 110 53 Magnesium mg/L 39 404 100 13 Sulfate mg/L 132 469 240 61 Chloride mg/L 306 461 1100 65 Nitrate (as Nitrogen) mg/L 4.4 469 8.6 1.3 pH S.U. 7.8 453 9.0 6.7 Water Temperature deg C 12.5 465 25.5 0.4 Dissolved Oxygen mg/L 9.6 465 15.5 4.3 1990-2000 Years Chromium in Water ug/L 1.7 261 8.4 1 Zinc in Water ug/L 23.8 261 83 9 Manganese in Water ug/L 115 261 890 41 2001-2008 Years Chromium in Sediments ug/kg 53.7 99 80 27 Zinc in Sediments ug/kg 749 99 1200 310 Manganese in Sediments ug/kg 3170 99 6200 1500 Source: Excel file WeserRWQPlotsStatsR2.xls
These statistical results further support the time trends exhibited in the various time-series plots and discussed in the previous section. Specifically, although streamflows between the POR and recent period were nearly the same (within 2 percent), SC values for the recent period were nearly 30 percent lower, and the major-ion concentrations lower in the range of four to 55 percent (Ca and Cl, respectively).
Selected data-assessment highlights for three more monitoring sites (see Figure 1)
Fulda-Wahnhausen.— For this upstream site in the Fulda River basin on a major tributary, water-quality conditions are quite good relative to characteristics indicated further downstream (described previously). SC vs. streamflow indicates a typical hyperbolic relationship, with lower SCs at higher flows. Although considerable scatter is shown, bivariate plots of major ions versus SC indicate general trends of the interrelationships between these variables. Time-series plots of flow and water quality indicate mixed patterns and vary, in part, with the time period considered. For the 30-year available period, Ca, Mg, and Cl indicate no time trend (for example, Figures 7 for Cl), SC gives a slightly increasing trend over time, and SO4 and NO3-N (Figure 8) show a decreasing time trend. For the shorter time period since unification of Germany, SC indicates a slight upward trend over time at this upstream tributary site (Figure 9a). Information was not sufficient for this part of the Weser River basin to evaluate possible causes of the SC time-series nor the decreasing time trends in SO4 and NO3-N at this upstream location.
Figure 7 -- Fulda-Wahnhausen, Chloride Time Series, 1979-2008
125
y = 0.0039x + 47.443 100 R2 = 0.0044
75
Cl, mg/L 50
25
0
9 1 3 1 4 4 6 90 9 96 98 02 08 97 982 984 9 992 993 000 001 00 986 1 2 /198 1 1 1 /199 1 /07/ /19 /19 2 20 /200 0 8 /7/ /7 8 /5/ 6 1/1/1 3 /20/198 9/9/1985/20/ 2/5/1 /1 6 18 /2 3 7/5/2 2 /29/2007.06.20 2/20/19803/ 5/10/ 6 7/30/ 3 4/27/ 8/28/199510 1/25/ 4/15/ 5/26/2003 8/15/20059/ 3 10 11/30/1987 11/17/199712 10 2 Date
Figure 8 -- Fulda-Wahnhausen, Nitrate Time Series, 1991-2008 (Interim/Post-Unification)
6.0 y = -0,0034x + 4,5165 5.0 R² = 0,24 4.0
3.0 NO3-N, mg/L NO3-N, 2.0
1.0
1 2 2 3 3 4 4 5 6 9 0 2 4 6 7 9 9 9 9 9 9 9 9 9 98 9 0 00 01 0 0 0 0 08 08 9 9 9 9 9 / 9 9 9 9 0 0 0 0 0 005 0 0 0 0 1 1 1 /1 1 /02 /08/ /1998 /1 1 /2 /2 2 2 /2006 2 .2 .2008 /7/ /4 /1/ 4 9 7/1 1/1995 3/1 8/1997 6 /1/ /2 /9/2 0/2003 3 8/2 /8/ 1 /20/ 8 2 /17/ 1 2 /2 1 /2 1 4/ /19 1 5 /13/2 /26 2 1 /21/ 7/4/ 1/ /1 1 .01 .04.2 11 7/23/19911 8 2 9/ 3/11/19969 3/ 10/6/1997 0 4/19/19991 1 5/15/20011 5/27/20021 6/ 6 7 7/23/20075 8 1 1 1 12/15/2003 1 2 29.07.200803. Date
Figure 9a -- Fulda-Wahnhausen, Specific Conductance Time Series, 1992-2008 (Interim/Post Remediation)
75 y = 0,009x + 44,17 R² = 0,026 60
45
SC, uS/cm 30
15
2 3 4 4 5 6 8 0 2 3 5 6 7 9 08 993 99 99 997 999 00 004 00 005 199 /1 /1 /03/ 199 /1 1 /199 1 /2000 200 /2 2 200 20 /6/ 5 8/ /4/1995 7 7 /3/ 5 6/ 1 8/4/19921 28 24/10/95/ 28/ 2/9/19989/ /18/19995/2/200/2 2 9/1/20031 /11/2004 /21/ 6/ 7/9/200.01.2008.05.2008 .12. 2/ 9/13 12 6/17 7/ 3/22/ 0 6/11/2001 7/22/2 3/ 0 4/25/2 1 11 1 11 15 09 12.08.200802 Date
Weser-Hemeln and Weser-Hessisch Oldendorf sites.— For these sites in the middle part of the basin, water-quality conditions increased relative to characteristics described upstream for the Fulda River tributary. Streamflows nearly double those for the monitoring site at Wahnhausen further upstream (average Qs of 123 vs. 67.3 m3/s). SC over the entire period of record increases at Hemeln by almost an order of magnitude (412 uS/cm v. 44.0 uS/cm upstream); however, a substantial decrease has occurred after unification (Figure 9b).
Figure 9b -- Weser-Hemeln, Specific Conductance Time Series, 1992-2004 (Interim Remediation)
550 500 450 y = -0,559x + 338,45 400 R² = 0,33 350 300 250 uS/cm 200 150 100 50
Specific Conductance (SC), (SC), Conductance Specific 0
0 1 94 992 993 9 995 996 997 998 999 00 00 004 1 1 1 1 1 1 1 2 6/ 6/ 6/ 1/ 1/ 1/6/1 1/6/ 1/6/ 1/6/ 1/6/ 1/ 1/6/2 1/6/2 1/6/2002 1/6/2003 1/6/
Date
For the Weser-Hessisch Oldendorf downstream (Figure 1), water-quality conditions were higher than at Wahnhausen furthest upstream in the Fulda River tributary but less than average values upstream at the Hemeln site. Average streamflow increases about 40 percent more than that for the second monitoring site at Hemeln upstream (average Qs of 177 vs. 123 m3/s). SC over the entire period of record some decreases at this site compared to the upstream site at Hemeln (320 uS/cm vs. 412 uS/cm upstream); however, again at Hessisch Oldendorf a substantial SC decrease has occurred after unification (Figure 9c).
Figure 9c -- Weser-Hessisch Oldendorf, Specific Conductance Time Series, 1992-2004 (Interim Remediation) 450 400 y = -0,0239x + 1047,9 350 R² = 0,26 300 250 200 uS/cm 150 100 50
Specific Conductance (SC), (SC), Conductance Specific 0
1 98 995 /1992 /2002 /6 /6/1993 /6/1994 /6/1 /6/1996 /6/1997 /6/19 /6/1999 /6/2000 /6/200 /6 /6/2003 /6/2004 1 1 1 1 1 1 1 1 1 1 1 1 1
Date
SC vs. streamflow again shows a typical hyperbolic relationship at these two mid-basin locations; however, shifts in SC-Q patterns for Weser-Hemeln result from upstream remediation efforts, causing a distinct separation over time (Figure 10a). This SC-Q shift is observed downstream at Weser-Hessisch Odendorf (Figure 10b) as well. This pattern is in contrast with that observed at the furthest downstream monitoring site (Weser-Hemlingen, see Figure 2a above).
Figure 10a -- Weser-Hemeln, Specific Conductance vs. Streamflow
1200
1000
800
600 SC, uS/cm 400
200
0 0 50 100 150 200 250 300 350 400 450 500 550 600 650 Streamflow, m3/s
Figure 10b -- Weser-Hessisch Oldendorf, Specific Conductance vs. Streamflow
960 860 760 Note shift downward in SC-Q patterns 660 1stFlush? over time. Feb 1980 560 460 SC, uS/cm 360 260 160 60 50 150 250 350 450 550 650 750 850 Streamflow, m3/s
Although considerable scatter is shown, bivariate plots of major ions versus SC indicate general correlation patterns of the interrelationships between these variable pairs. However, in the case of SO4, a few anomalously high values were noted (Steele and Houshang, 2009). However, SC and major-ion concentrations at this location indicate decreasing values over time. For the 30-year available period, NO3-N shows a seasonally variable pattern but not a time trend until recent years. For the shorter time period since unification of Germany, SC indicates a downward time trend; however, SC data are lacking at this since 2004 (Steele and Houshang, 2009). At present, definitive information is not available to explain possible causes of the SC time-series patterns nor the decreasing time trends in all major and a recent downward time trend in NO3-N at these two monitoring-site locations (Figures 11a and 11b).
Figure 11a -- Weser-Hemeln, Nitrate Time Series, 1991-2008 (Post-Unification)
7.5 y = -0,002x + 4,6885 6.5 R² = 0,10 5.5
4.5
3.5 NO3-N, mg/L NO3-N, 2.5 1.5
1 5 6 0 1 4 5 92 93 97 98 02 06 99 9 9 99 9 9 00 00 0 00 00 0 1 /1 /1 /1994 1 /1 /1 /2 /2 /2 2 /2 /2 /2007 /7/ /7/199 /7/ /7 /7 /7/ /7/2008 1 1/7 1/7 1/7 1 1 1/7 1/7 1/7/1999 1 1 1/7 1/7/2003 1 1/7 1/7 1/7 1
Date
Figure 11b -- Weser-Hessisch Oldendorf, Nitrate Time Series, 1991-2008 (Post-Unification) 6.9 y = -1E-04x + 7,8251 R² = 0,030 5.9
4.9
3.9 NO3-N, mg/L NO3-N, 2.9
1.9
1 2 6 7 2 3 6 7 9 95 9 99 0 0 994 9 99 00 005 / 00 1 2 /19 /199 /1993 /19 /20 /2 /2004 /07 /7 0/1 9/1 /8 /4 7 0/2 0.2008 1 5/9/ /2 /2 9 2 6/6/ 1 /2 .1 2/17 3/29 6 7 3/18 4/26 8 3 10/19/1998 11/29/19 1 Date
For the Weser’s Hemeln and Hessisch Oldendorf sites, SC as well as major-ion and NO3-N concentrations all indicate decreasing values over time. For a shorter time period since unification of Germany, SC indicates a downward shift and continuing decreasing time trend.
Monitoring-Sites Comparisons.— As was highlighted above for this fourth site located furthest downstream (Steele and Houshang, 2009), water-quality conditions continue to decrease slightly relative to characteristics indicated further downstream. The average streamflow increase at Hemelingen is nearly double compared to the third monitoring site at Hessisch Oldendorf upstream (average Qs of 340 vs. 177 m3/s). SC over the entire period of record indicates some decrease at Hemelingen compared to the upstream sites (202 uS/cm vs. 320 uS/cm at Hessisch Oldendorf and 412 uS/cm at Hemeln upstream). Again, a substantial SC decrease has continued to occur at this downstream site after unification. SC vs. streamflow again shows a typical hyperbolic relationship; however, the shift in SC-Q patterns indicated at the two sites upstream (indicating impacts of reductions in salt-mining sources upstream) are less distinctive at this furthest downstream site (Figure D-1). Although considerable scatter is shown, bivariate plots of major ions versus SC indicate general correlation patterns of the interrelationships between these variable pairs; however, the bivariate Ca-SC plots are relatively nonlinear compared to other major ions at all sites. Time- series plots of streamflow for all four sites indicate no trend. However, SC as well as major- ion concentrations all indicate decreasing values over time. For the shorter time period since unification of Germany, SC and NO3-N concentrations indicate downward shifts and continuing decreasing time trend. At present, information is limited to evaluate possible causes of the SC time-series patterns and the decreasing time trends in all major ions and NO3-N at this monitoring-site location. Useful information within the Weser River basin management plan (FGG-Weser, 2009) provides insight as to the economic activities in the river basin as well as beneficial improvements in point-source wastewater treatment plant discharges, agricultural applications of fertilizers, and other remediation actions.
DISCUSSION
The principal anthropogenic impacts affecting water quality in the Weser River basin are described in the river-basin management plan by the Flussgebietsgemeinschaft Weser (FGG- Weser, 2007b), along with associated remedial actions to control these adverse impacts. Key activities involve closing of salt mines, along with point-source controls of high-salinity flows and reductions of nutrients through better use and management of detergents and fertilizer applications on agricultural lands.
Further evaluation should be made of possible streamflow effects, resulting in decreased constituent values with higher flows through dilution. Such effects were noted in the dataset. For certain periods at each site, streamflows, SC values, or water-quality variable concentrations were missing for parts of a given year or an entire year within the period of record. Additional observations and notes regarding water-quality conditions and areal/temporal patterns using data for the four selected monitoring sites in the basin are given in a separate, more detailed report (Steele and Houshang, 2009.
CONCLUSIONS AND RECOMMENDATIONS
The dataset selected for this case study provided useful information. Relatively greater focus was made on time variability for streamflows as well as the various water-quality variables – seasonality and multi-year time trends – for the Weser River monitoring site located at Hemelingen. Possible bivariate-regression functions enable possible data fill-in and/or extrapolation to be made for some lacking data values. Time-trend analyses in several instances indicate effects of changes in human activity impacting water-quality conditions.
This data assessment should be extended to other monitoring sites in the Weser River basin. Priority might be given to those sites having streamflows concurrent with water-quality sample/measurement results. In addition, quantification of seasonal patterns for water temperature should be made using a simple-harmonic function (Steele, 1974). Resultant harmonic coefficients then can be regionalized or otherwise used to assess changes from natural seasonal variability (such as below spill structures or dams).
Further evaluation is recommended regarding the overall water policy and associated components and milestones of the European Union’s Water Framework Directive (Steele and Bongartz, 2006; Steele and others, 2008; Steele, 2009), within the context of management planning for large river basins in Europe. This water policy incorporates in a formalized structure all of the components of watershed plans as promulgated by U.S. Environmental Protection Agency guidance documents. Distinctive positive aspects of the WFD include the integration of different water bodies (groundwater, surface waters, and coastal areas), linkage of biological and ecological characterizations with water quality, and formalized inputs and information transfer with stakeholders and the general public through meetings and outreach.
ACKNOWLEDGMENTS
Support of the Alexander-von-Humboldt Foundation, Bonn, Germany, for the principal author in conducting this applied research is gratefully acknowledged. Also, the technical assistance and logistical support of the Friedrich-Schiller-University of Jena, Department of Geoinformatics, Hydrology, and Modelling, Germany, and of the Weser River Basin Commission, Hildesheim, Germany, were useful in the preparation of this data-assessment case-study presentation and overview of river-basin conditions.
REFERENCES
Bongartz, Klaus, Steele, T.D., and Lindenschmidt, Karl-Erich, 2004, Water-Quality Data Assessment, Saale River Basin, Germany: National Water Quality Monitoring Council (NWQMC), 4th National Monitoring Conference on Building and Sustaining Successful Monitoring Programs, Chattanooga, TN, May 19, Abstract #97 published in Conference Program, p. 139.
Bongartz, Klaus, Steele, T.D., Martina Barborowski, and Lindenschmidt, Karl-Erich, 2007, Monitoring, Assessment, and Modelling Using Water-Quality Data in the Saale River Basin, Germany: Environmental Monitoring and Assessment, DOI 10.107/s10661- 007-9645-y, Springer Heidelberg, Germany, 14 p.
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