North Rhine-Westphalia, the most industrialized and densely populated
state of Germany, is drained by six major tributaries of the Rhine: th
e Sieg, Wupper, Ruhr, Erft, Emscher, and Lippe. The first four drain p
redominantly catchments with Phanerozoic siliciclastic rocks, while th
e latter two dewater Cretaceous carbonate basins. Together, the rivers
account for similar to 11 percent of the Rhine water, and they reflec
t various stages of pollution, from a moderately polluted Sieg and Ruh
r 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 m
ain source of water in these rivers. Down-stream, the water becomes en
riched in O-18, by similar to 2 permil, due to low altitude precipitat
ion and because of evaporation, particularly in artificial lakes. Howe
ver thermal fractionation, when water is utilized for cooling in power
stations and smelters, also contributes to this trend. State-wide, an
d down-stream within rivers, the increasing pollution levels are chara
cterized by rising salt concentrations (from normal riverine values up
to a third of seawater), by up to two orders of magnitude CO2 overpre
ssures, oxygen depletion, and enhanced nutrient concentrations. The de
lta(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. Evas
ion of gaseous CO2 into the atmosphere and microbial nitrification are
the most important processes for the riverine aquatic cycles of carbo
n 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.