title: CO2emissions from German drinking water reservoirs.
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 CO2fluxes for 39 German drinking water reservoirs during a period of 22years (1991-2013) using routine monitoring data in order to quantify total emission of CO2from drinking water reservoirs in Germany and to identify major drivers. All reservoirs were a net CO2source with a median flux of 167gCm-2y-1, which makes gaseous emissions a relevant process for the carbon budget of each reservoir. Fluxes varied seasonally with median fluxes of 13, 48, and 201gCm-2y-1in spring, summer, and autumn respectively. Differences between reservoirs appeared to be primarily caused by the concentration of CO2in the surface water rather than by the physical gas transfer coefficient. Consideration of short term fluctuations of the gas transfer coefficient due to varying wind speed had only a minor effect on the annual budgets. High CO2emissions only occurred in reservoirs with pH<7 and total alkalinity <0.2mEql-1. Annual CO2emissions correlated exponentially with pH but not with dissolved organic carbon (DOC). There was significant correlation between land use in the catchment and CO2emissions. In total, German drinking water reservoirs emit 44000t of CO2annually, which makes them a negligible CO2source (<0.005% of national CO2emissions) in Germany.
authors.affiliation: National Research Council, Institute of Ecosystem Study, Largo Tonolli 50, 28922 Verbania Pallanza, Italy. Electronic address: h.saidi@ise.cnr.it.
authors.forename: Helmi
authors.initials: H
authors.lastname: Saidi
authors.affiliation: UFZ - Helmholtz Centre for Environmental Research, Department of Lake Research, Brückstr. 3a, D-39114 Magdeburg, Germany. Electronic address: matthias.koschorreck@ufz.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Koschorreck
keywords: Carbon dioxide flux; Gas transfer coefficient; Greenhouse gases; Wind; pCO(2); pH