Anatomy of pollution: Rivers of north Rhine-Westphalia, Germany

North Rhine-Westphalia, the most industrialized and densely populated state of Germany, is drained by six major tributaries of the Rhine: the Sieg, Wupper, Ruhr, Erft, Emscher, and Lippe. The first four drain predominantly catchments with Phanerozoic siliciclastic rocks, while the latter two dewater Cretaceous carbonate basins. Together, the rivers account for similar to 11 percent of the Rhine water, and they reflect various stages of pollution, from a moderately polluted Sieg and Ruhr to the heavily damaged Emscher. The delta(18)O(H2O) of -8.5 +/- 1.5 permil SMOW suggests that summer recharge into local aquifers is the main source of water in these rivers. Down-stream, the water becomes enriched in O-18, by similar to 2 permil, due to low altitude precipitation and because of evaporation, particularly in artificial lakes. However thermal fractionation, when water is utilized for cooling in power stations and smelters, also contributes to this trend. State-wide, and down-stream within rivers, the increasing pollution levels are characterized by rising salt concentrations (from normal riverine values up to a third of seawater), by up to two orders of magnitude CO2 overpressures, oxygen depletion, and enhanced nutrient concentrations. The delta(13)C(DIC) demonstrate that microbial respiration of C-org in soil/groundwater systems accounts for about 50 to 100 percent of the entire DIG, with the higher values typical of more polluted ecosystems. Evasion of gaseous CO2 into the atmosphere and microbial nitrification are the most important processes for the riverine aquatic cycles of carbon and nitrogen, resulting in more advanced dissipation of CO2 and NH4+ in the less polluted ecosystems. Denitrification may fuel generation of some ''excess'' CO2 only in the highly polluted ecosystems, such as the Emscher.