Hydrogeochemistry of the River Rhine: Long term and seasonal variability, elemental budgets, base levels and pollution

Abstract The long-term and seasonal variations in the composition of water and suspended matter in the River Rhine are discussed. The study is based on the analysis of 240 water samples and of 79 suspended matter samples collected during a 10-year period from 1975 to 1984. The discharge is dominated by two hydrological regimes, namely a winter flow derived mainly from surface flow and groundwater flow in the German/French part of the drainage basin, and by a summer flow derived mainly from snowmelt and precipitation in the Alps. Principle components analysis of the data for the dissolved constituents reveals three factors: (1) heavy metals, (2) major ions, and (3) nutrients. Time series analysis of these factors demonstrates a perfect seasonality for the nutrients, a reduction of the loads of heavy metals and a more complicated pattern for the major dissolved ions. The latter pattern is due to pollution. Principle components analysis of the data for suspended matter reveals four factors: (1) heavy metals, (2) clays, (3) calcium carbonate, and (4) manganese oxides. In time series analysis the scores on the first factor decrease in the period considered, those on the second factor correlate positively with the discharge regime, and those on the third and fourth factor are at their highest during summer flow due to a combination of source area, biological activity and temperature. On the basis of recent and historical data on the chemistry of the Rhine, one can estimate the natural levels of the major element load of the river. This natural load is derived from denudation of various rock types in the drainage basin. A simple steady-state model is used to estimate the contributions of aluminosilicate rocks and of limestones to the total denudation. Data for trace element contents of common rocks are available in geochemical tables. This then allows one to estimate the base levels of the heavy element load of the river. Comparison of the actual level loads with the base level loads makes it possible to calculate a pollution factor for each of the heavy metals. The following factors (measured levels/base levels) were calculated for the pollution of the Rhine between Basel and the German-Dutch border: Cr (5), Co (

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