Abstract. Globally, reservoirs are a significant source of atmospheric CO2. However, precise quantification of greenhouse gas emissions from drinking water reservoirs on the regional or national scale is still challenging. We calculated CO2 fluxes for 39 German drinking water reservoirs during a period of 22 years (1991–2013) using routine monitoring data in order to quantify total emission of CO2 from drinking water reservoirs in Germany. All reservoirs were small net CO2 sources with a median flux of 167 g C m–2 y–1, which makes gaseous emissions a relevant process for the reservoirs carbon budgets. In total, German drinking reservoirs emit 44000 t of CO2 annually, which makes them a negligible CO2 source in Germany. Fluxes varied seasonally with median fluxes of 30, 11, and 46 mmol m–2 d–1 in spring, summer, and autumn respectively. Differences between reservoirs appeared to be primarily caused by the concentration of CO2 in the surface water rather than by the physical gas transfer coefficient. Consideration of short term fluctuations of the gas transfer coefficient due to variable wind had only a minor effect on the annual budgets. High CO2 emission only occurred in reservoirs with pH < 7 and total alkalinity < 0.2 mEq l–1. Annual CO2 emission correlated exponentially with pH, making pH a suitable proxy for CO emission from German drinking water reservoirs.
Review of ‘CO2 emissions from German drinking water reservoirs estimated from routine monitoring data’ by Saidi and Koschorreck
