Horst Behrendt

Retention of nutrients in river systems: dependence on specific runoff and hydraulic load

The total nutrient inputs (emissions) from point and diffuse sources into 100 different river basins in Europe are compared with the measured load (transport). The catchment areas range between 121 and 194 000 km2. Other characteristic parameters of the basins, including specific runoff, surface water area and the nutrient concentration show large differences. Independent of the different methods applied for estimating nutrient emissions, these are in general higher than the actual transport. The ratio of the transport to the emission was used to exclude the effects of basin size and to facilitate comparisons between river basins. A statistical model of the retention, including net sedimentation and denitrification, is derived for the description of the discrepancy between the measured transport and the estimated total emission of nutrients, which is assumed to reflect retention of nutrients in a river system. It was found that the load-weighted retention of phosphorus is controlled practically only by the specific runoff of the basin. The load- weighted retention of nitrogen is further dependent on the proportion of the basin area occupied by surface water, the basin size itself and the mean annual nitrogen concentration at a specific monitoring station. Application of the statistical model reduces the mean deviation between the calculated emissions and the values given by different authors from about 40% to 20%.

Development of the heavy metal pollution trends in several European rivers: an analysis of point and diffuse sources

A comparison has been made between the metal pollution in several European rivers in various stages of clean-up and management for the period of 1980-1996. The investigated rivers were Rhine, Meuse, Scheldt, Weser and Elbe. The results from this comparison showed that the simple statement that characterizes the river Elbe as ‘the most polluted river in Europe’ is a simplification. Three independent methods are presented to estimate point and diffuse source contributions in emissions and riverine transports. All methods were applied to the Elbe and Rhine rivers to estimate the contribution of point and diffuse sources for six heavy metals. The results of the source apportionment estimates show that there are temporal differences in source strength and source origin. A dramatic drop in industrial inputs and inputs from waste water treatment plants can be observed. The comparison of all methods shows some differences, which might be caused by retention processes (such as sedimentation) in the river system.

Influence of small-scale turbulence and large-scale mixing on phytoplankton primary production

To test the hypotheses that as well small scale turbulence as large scale vertical mixing cannot be neglected when quantifying primary production especially in shallow polymictic lakes, experiments were run on three different scales. (1) To achieve more natural conditions in bottles used for in situ incubation measurements of primary production, bottle stirrers were designed and tested in situ. The operation of the bottle stirrers guaranteed a homogeneous distribution of seston in the samples during incubation. Stirring increased primary production of plankton from a eutrophic lake significantly only when buoyant cyanobacteria were dominant. (2) To investigate the influence of turbulent mixing on primary production under controlled conditions, a circulating water column was maintained in large mesocosms. The comparison of static and dynamic in situmeasurements of primary production revealed a distinct increase of production by mixing. (3) To find out the importance of mixing form, primary production was measured in the shallow, eutrophic, polymictic lake Muggelsee by moving water samples up and down with bottle lifts in two different ways. The two simulated motions (linear and circular) result in a different integral light supply of the enclosed phytoplankton. The higher light supply during circular movement in comparison to linear movement resulted in higher primary production in the circulating bottles compared to the bottles that were moved in a linear fashion.

Changes of the nutrient loads of the Odra River during the last century - their causes and consequences

Changes of the nutrient loads of the Odra River during the last century - their causes and consequences Nutrient emissions by point and diffuse sources and their loads were estimated for the Odra catchment over the time period of the last 50 years by means of the model MONERIS. For nitrogen a change of the total emissions from 38 kt·a−1 N in the mid of 1950s a maximum of 105 kt·a−1 N in the early 1980s and a recent value of about 84 kt·a−1 N were estimated for the total Odra Basin. The share of the point source discharges on the total N emissions varied between 24% (1955) and 35% (1995). The emissions from groundwater and tile drained areas represent the dominant pathway (37-56% of total N emissions) during all investigated time periods. Emissions from tile drained areas increased from the mid of 1950s to end of 1980s by a factor of 20 and reached in this period the same amount as emissions by groundwater. For phosphorus the emissions changed from 4 kt·a−1 P in 1955 to 14 kt·a−1 P in 1990 and a recent level of 7 kt·a−1 P. Point source discharges caused between 36 to 66% of total P emissions and represent the dominant pathway for all investigated time periods. Erosion and discharges from paved urban areas and sewer systems was the dominant diffuse pathway of the total P emissions into the river system. The comparison of calculated and observed nutrient loads for the main monitoring stations along the Odra River shows that the average deviation is 12% for total phosphorus (1980-2000) and 15% for dissolved inorganic nitrogen (1960-2000). From the analysis it can be concluded that the present load of dissolved inorganic nitrogen (DIN) and total nitrogen (TN) of the Odra into the Baltic Sea is about 2.3 times higher than in the mid of 1960s. The maximum DIN load (1980s) was more than 3 times higher than in the 1960s. The change of the total phosphorus (TP) load is characterized by an increase from the 1955s to 1980 from 2 to 7 kt·a−1 P (factor 2.6). Around 2000 the TP load was 4 kt·a−1 which is only the double of the level of the 1955s. Zmiany ładunków biogenów w Odrze w ciągu ostatniego wieku — przyczyny i skutki Emisja składników biogennych ze źródeł punktowych i rozproszonych oraz ich ładunki w zlewni Odry zostały obliczone dla 50 ostatnich lat z wykorzystaniem modelu MONERIS. Emisja związków azotu w zlewni Odry zmieniała się od 38 kt·r−1 N w połowie lat 50. XX w. do maksymalnie 105 kt·r−1 N we wczesnych latach 80. Udział zrzutów ze źródeł punktowych w całkowitej emisji azotu zmieniał się między 24% (1955 r.) a 35% (1995 r.). Emisja z wód gruntowych i obszarów zdrenowanych jest czynnikiem dominującym i stanowi 37-56% całkowitej emisji azotu w analizowanym okresie. Emisja z obszarów zdrenowanych zwiększa się od połowy lat 50. do końca lat 80. 20 razy, osiągając taką samą wielkość jak emisja z wód gruntowych. Emisja związków fosforu zmieniła się od 4 kt·r−1 P w 1955 r. do 14 kt·r−1 P w 1990 r., a ostatnio osiągnęła 7 kt·r−1 P. Zrzuty ze źródeł punktowych stanowią od 36 do 66% całkowitej emisji fosforu i są dominującym czynnikiem w całym badanym okresie. Erozja oraz zrzuty zanieczyszczeń z obszarów miejskich to najważniejsze drogi dopływu związków fosforu ze źródeł obszarowych do rzeki. Porównanie obliczonych oraz obserwowanych ładunków składników biogennych w głównych stanowiskach monitoringowych zlokalizowanych wzdłuż Odry, wskazuje, że średnie odchylenie wynosiło 12% w przypadku fosforu całkowitego (1980-2000) i 15% - azotu mineralnego (1960-2000). Po przeanalizowaniu wyników można wysnuć wniosek, że aktualny ładunek azotu mineralnego (DIN) i azotu całkowitego (TN) wnoszony z Odry do Morza Bałtyckiego jest około 2,3 razy większy niż w połowie lat 60. Maksymalny ładunek DIN (1980 r.) był ponad 3 razy większy od tego z lat 60. Zmiany ładunku fosforu całkowitego (TP) są charakteryzowane zwiększeniem wartości z 2 kt·r−1 P (1955 r.) do 7 kt·r−1 P (1980). Około 2000 r. ładunek TP wynosił 4 kt·r−1, co jest wartością tylko dwukrotnie większą od stwierdzonej w 1955 r.

The N and P budget of the shallow, flushed lake Müggelsee: retention, external and internal load

The shallow (mean depth 4.9 m), polymictic and eutrophic lake Muggelsee was highly loaded with phosphorus (6 gP m−2 a−1) and nitrogen (170 gN m−2 a−1) by the river Spree up to the end of the 1980s. Annual load declined by 40–50% during the last years (1991–97). Phosphorus retention fluctuated strongly during the seasonal cycle between −200 and +100 kgP d−1 and from year to year between −44% and + 26% of the P import. At the end of the eighties, the P retention capacity of the sediment was exceeded and Muggelsee became a source of phosphorus. The lake regained its ability to retain P in the sediments after external load reduction in the 1990s. However, the internal load of P reached the level of the external one. The release of P during summer was strongly related to the import of nitrate. On long-term average (1979–1997), less than 1% of the P input was retained in Muggelsee. About 24% of the nitrogen load were removed in the lake on annual mean. This rate decreased during the last years.

Vulnerable areas of phosphorus leaching - detection by GIS-analysis and measurements of phosphorus sorption capacity

A model is presented to detect vulnerable areas of phosphorus leaching combing GIS-modeling and measurements on phosphorus sorption capacity of different soil types. The GIS-model uses spatial information on the topology, land use, soil types, water tables and climatic water balance. The phosphorus surplus of the agricultural topsoil is estimated based on the average of fertilizer use and the uptake by crops over a long period of time and, additionally, the application rates of manure around cowshed and pigsties. The model is applied to the catchment area of Lake Schwielochsee, a hypertrophic shallow lake situated about 100 km south-east of German capital, Berlin. The phosphorus content and the phosphorus sorption capacity were measured at several sides with differing soil types. Parameters of the GIS-model are deduced from the results of these measurements.

Modelling nutrient emissions and the impact of nutrient reduction measures in the Weser river basin, Germany

To implement the European Water Framework Directive (WFD) into German law, measures have to be taken to reduce the unacceptably high nutrient input into rivers. To identify the most effective measures, the sources and pathways of nutrient emissions into rivers have to be quantified. Therefore, the MONERIS model is applied, which quantifies nutrients emissions into river basins, via various point and diffuse pathways, as well as nutrient load in rivers. Most nitrogen emissions come from groundwater flow (43%), tile drainages (30%), and point sources (12%), whereas most phosphorus emissions come from groundwater flow (31%), point sources (23%), erosion (13%) and overland flow (12%). Because of their great distance from the river basin outlet, the southern sub-basins Werra and Fulda-Diemel have an 8% reduction in their nitrogen loads and a 15% and 16% reduction in their phosphorus loads, respectively. This reduction is due to retention in the main part of the river Weser. For the choice of the most effective measures, the different retention in the river is relevant.

Aspects of Decision Support in Water Management: Data based evaluation compared with expectations

In the cities of Berlin and Potsdam nine water management strategies (scenarios) were evaluated with respect to their ecological effects to the system of surface water. Scenarios were generated by combining different water management measures such as wastewater and storm water treatment. Indicators were qualitatively modelled as well as quantitatively evaluated by experts’ knowledge. For decision support Hasse Diagram Technique (HDT) was used. The scenario modular structure increases the transparency of the evaluation process and brought up the question whether time and work consuming calculation of data by mathematical models is needed or experts’ knowledge is sufficient for evaluation. To clarify this question, the results of two evaluation examples were compared: (a) data based and (b) experts expectations. Beyond the concept of antagonistic indicators the similarity-profile is introduces as a new tool to compare HDT evaluation results. Our study revealed that in the present investigation evaluation by expert knowledge is not satisfactory. The shift in the type of indicators from state to pressure and the effect of up scaling from local to regional may be the reason.

Schwermetallbilanzierung für die Elbe und für ihre Teileinzugsgebiete

Die Schwermetallbelastung der Flusse wird durch punktformige und diffuse Eintragsquellen verursacht. Fur weiterer Masnahmen zur Reduzierung der Schwermetallbelastung sollen verschiedene Methoden (Immissions- und Emissionsschatzung) fur die Feststellung der Anteile der punktformigen und diffusen Eintrage an der gesamten Gewasserbelastung eines Flusgebietes z.B. der Elbe angewandt werden. Beide Schatzmethoden wurden bisher fur verschiedene Regionen in Deutschland bzw. fur verschiedene Flusgebiete angewandt (Behrendt 1993), wobei die Methoden generell analog zu denen sind, die fur die Quantifizierung der Nahrstoffbelastung angewandt wurden (Werner und Wodsack 1994, Behrendt 1993).