Journal of Environmental Science for Sustainable Society, Vol. 1, 39-46, March 2007 GEOCHEMISTRY OF THE RIVER RHINE AND THE UPPER DANUBE: RECENT TRENDS AND LITHOLOGICAL INFLUENCE ON BASELINES Jens HARTMANN 1, Nils JANSEN 2, Stephan KEMPE 3, Hans H. DÜRR 4 1 Postdoctoral Researcher, Institute of Applied Geoscience, Darmstadt University of Technology (Schnittspahnstrasse 9, D-64287 Darmstadt, Germany) E-mail: [email protected] 2 Ph.D.-Student, Institute of Applied Geoscience, Darmstadt University of Technology (Schnittspahnstrasse 9, D-64287 Darmstadt, Germany) E-mail: [email protected] 3 Professor, Institute of Applied Geoscience, Darmstadt University of Technology (Schnittspahnstrasse 9, D-64287 Darmstadt, Germany) E-mail: [email protected] 4 Postdoctoral Researcher, Faculty of Geosciences, Utrecht University (Heidelberglaan 2, 3508 TC Utrecht, The Netherlands) E-mail: [email protected] Human pressure is now severe on most of the rivers worldwide. The long term fluxes of dissolved geogenic and biogenic matter are changing dramatically, causing notable changes in aquatic bioactivity. Typical patterns of anthropogenic pressure that influence eutrophication, salinization and chemical contamination are discussed. The heavily influenced rivers Rhine and upper Danube will be used as examples, also considering their geological settings. In the past decade sewage treatment reduced nitrate and orthophosphate loads in both basins. This influenced bioactivity in the rivers, causing less silica depletion due to diatom blooms in the Rhine. Therefore a notable increase in minima concentrations of dissolved silica can be observed. In the upper Danube, however, an increase in orthophosphate concentration since 2003 is noticeable; breaking the former decreasing trend, despite treatment efforts. The hydrochemistry of major ions in both basins is strongly influenced by the ratios of carbonate, siliciclastic sediment and igneous or metamorphic rock outcrops. In addition Mesozoic evaporites and salt mining were responsible for extremely high levels of Cl, Na and SO4 in the Rhine, peaking in the 70s and 80s at concentrations of 350, 180 and 140 mg/l, respectively. Water basin management efforts cut former high levels to less than a half. Heavy metals and persistent organic pollutant concentrations are declining in the Rhine as well. A combination of climate change and anthropogenic water inputs resulted in an increase of water temperature of the Rhine by 3.5 °C during the past 50 years. In the upper Danube such a trend in water temperature can not be observed. Key Words : Danube, Rhine, lithology, baseline, trend analysis, nutrients, silica, temperature, evaporite, salinization, water temperature 1. INTRODUCTION and aquatic biotope progressively used and transformed by humans. Human pressures influence Continental aquatic systems can be observed many basins in a way that the continental aquatic from two perspectives1): a) as a major link between system no longer can be considered as being atmosphere, biosphere, pedosphere, geosphere and controlled only by Earth system processes1)2)3). This oceans within the Earth system and b) as water source study reviews geochemical baselines and recent 39 Jens HARTMANN et al. trends for some major elements in the Rhine and station Jochenstein cover the period from 1982 till upper Danube. Due to recent progress in water basin 2005. However, only some parameters were management, anthropogenic pressures like measured during the entire period. In addition, data salinization and eutrophication are decreasing, from a detailed study on the Danube’s geochemical causing changes in annual baselines of element background levels for the years 1991/92 were used4). concentrations1). Examples of the influence of To evaluate the influence of lithology on the lithology on hydrochemical composition in the hydrochemical composition of the river Rhine and Danube are presented. In addition, a possible the upper Danube the distribution of 15 lithological influence of climatic change on water temperature is types was calculated6). For this a global lithological discussed. map was used, which was specifically conceived for analyzing the relationship between hydrochemical composition of rivers and lithology on large scales6). 2. HYDROLOGY In addition, the German Geological Map was used to significantly improve the resolution of lithological Detailed descriptions of the hydrological regime units for catchment areas located in Germany 7). of the Rhine and the upper Danube can be found Using this information, it was possible to identify elsewhere3)4)5). The Rhine basin has a size of 185,300 lithological units containing significant amounts of km2 and the main stem of the river is 1320 km long. evaporites. Those units are known to contribute to At station Bimmen/Lobith, close to the salinization. German-Dutch border, the Rhine has a tributary area of 159,500 km2 delivering a discharge of 2200 m3/s on long term average. The Alpine Rhine (upstream of 4. NUTRIENTS N, P AND SI Lake Constance) constitutes only 19 % of the catchment area, but delivers nearly half of the Dominating nitrogen (N)- and phosphorus discharge on average. The flow regime of the river (P)-species in both rivers are nitrate and Rhine is dominated by melt water and precipitation orthophosphate, representing a large proportion of runoff from the Alps in summer and by precipitation the total N- and P-load (Fig. 1 and 2). runoff from the mid-basin uplands in winter. Major Both basins are heavily influenced by agriculture. winter tributaries are Mosel, Main and Neckar. Below Lake Constance, the Rhine is additionally The Danube is the second largest river in Europe. influenced by large urban areas concentrating around Its upper course runs for 587 km through southern Stuttgart, the Area at the Rhine- Main- junction Germany. At station Jochenstein (close to Passau at (Frankfurt) and in North-Rhine-Westphalia the German-Austrian border) the catchment has a (Ruhrgebiet). During the 1970s and 80s the river size of 77,050 km2 with an average discharge of Rhine was one of the most heavily polluted rivers in 1,440 m3/s. The upper Danube flows through the world, carrying sometimes more than 800 mg/l of agricultural areas of the northern Alpine foreland. Its total dissolved matter. The upper Danube was not Hydrology is controlled to a large extent by alpine affected by such high pollution levels, because the runoff, provided mostly by Isar and Inn. Their catchment contains less urban areas and lacks salt discharge peaks during summer season4). Other mining industry. important tributaries are the rivers Iller, Regen and Since the 1970s efforts increased to reduce Lech. nutrient emissions by installing sewage treatment plants8). This resulted in a recovery since the 1990s with respect to orthophosphate (Fig. 1) and 3. DATA particulate P (not shown here) as both were emitted mainly from point sources. However, for the upper Data used in this study were provided by the Danube a recent increase in orthophosphate since German Federal Institute of Hydrology (BfG) and the 2003 can be observed (Fig. 2). Nevertheless Bavarian Administration for Environment. The concentrations are still below those of the Rhine Rhine is intensively monitored since the 1950s. River. Available data for station Bimmen/Lobith cover the Nitrate, which is also emitted by diffuse sources, period from 1954 to 2001. Monitoring is coordinated did not decrease as much as orthophosphate. Recent by the ICPR (International Commission for the annual averages (since 2000) are 2.7 mg/l nitrate-N Protection of the Rhine). Data for the Danube at (Rhine) and 2 mg/l nitrate-N (upper Danube). 40 GEOCHEMISTRY OF THE RIVER RHINE AND THE UPPER DANUBE - - NO3 -N concentration, Bimmen/Lobith, Rhine NO3 -N concentration, Jochenstein, Danube 6 4.5 4.0 5 3.5 4 3.0 3 2.5 mg/l mg/l 2.0 2 1.5 1 1.0 0.5 0 1982 1984 1987 1990 1993 1995 1998 2001 2004 2006 1949 1954 1960 1965 1971 1976 1982 1987 1993 1998 2004 3- PO4 -P concentration, Jochenstein, Danube 3- PO4 -P concentration, Bimmen/Lobith, Rhine 0.30 0.8 0.7 0.25 0.6 0.20 0.5 0.15 0.4 mg/l mg/l 0.10 0.3 0.2 0.05 0.1 0.00 1982 1984 1987 1990 1993 1995 1998 2001 2004 2006 0.0 1949 1954 1960 1965 1971 1976 1982 1987 1993 1998 2004 Fig.2 Nitrate and orthophosphate concentration in the Si-concentration, Bimmen/Lobith, Rhine upper Danube at station Jochenstein, close to the border between Germany and Austria. 4 2) 3 dissolved silica concentrations . A similar effect can be observed for the Rhine 2 (Fig. 1). In the 80s nitrate and orthophosphate mg Si /l Si mg concentrations peaked. During this time dissolved 1 silica concentrations reached a minimum (Fig. 1). Since the beginning of the 90s an increasing trend 0 can be observed, mainly due to an increase in annual 1976 1979 1982 1985 1988 1991 1994 1997 2000 minima. Recent average concentrations of dissolved Fig.1 Nitrate, orthophosphate and dissolved silica silica in the Rhine at Bimmen/Lobith are around 2.5 concentrations in the river Rhine at monitoring station mg Si /l. Silica is mainly derived from weathering of Bimmen/Lobith. (For dissolved silica trends before and after silicates and an important nutrient for aquatic January 1990 are given. The annual average increase for ecosystems. The observed correlation of dissolved silica since 1990 is 0.07 mg Si /l a.) eutrophication and silica depletion due to bioactivity pH, Bimmen/Lobith, Rhine Treatment efforts resulted in a noticeable decrease of N and P inputs that had an effect on the carbon 8.5 dynamics in the aquatic system. In the Neckar river-system (an important tributary of the Rhine), N 8.0 and P-concentration decreases are correlated with a sharp decrease in the partial pressure of CO2 and an pH increase in pH, indicating changes in the 7.5 relationships between photosynthesis and respiration processes2)9).