Sinks of the anthropogenically enhanced carbon cycle in surface fresh waters

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Abstract
The carbon chemistry of rivers and lakes has been severely affected by man's activities. This is evident from the data base of the SCOPE/UNEP project, Carbon Transport in Major World Rivers. Increase of erosion following deforestation and agriculture removes carbon from the biosphere into inland deposition centers, lakes, and reservoirs and causes the organic carbon load of rivers to increase. Organic sewage and eroded soil carbon fuel respiration in rivers thus increases the CO2 pressure and diminishes the O2 and NO3 loads in relation to the total organic content. Nutrient release causes eutrophication of lakes and coastal seas, resulting in enhanced primary productivity and CO2 sequestering. Loss of CaCO3 in upstream lakes and boosting PCO2 cause increasing undersaturation of streams with respect to carbonate minerals. In estuaries this undersaturation leads to the corrosion of marine carbonate, as is experimentally shown for the River Elbe, fixing riverine free CO2 as bicarbonate permanently. All sinks combined, up to 1015 g C per year can additionally be sequestered from the anthropogenically enhanced carbon cycle.