Quantitative description of respiration processes in meso-eutrophic and eutrophic freshwater environments

We propose a modification of measurement methodology allowing the overall respiration rate (V_Resp) close to the in situ conditions; size of the labile, respirable organic matter pool (OM_Resp); and its turnover time (Tt) to be calculated. In addition to the respiration of dissolved substrates by free-living bacteria, the respiration of attached bacteria and other planktonic organisms is also taken into account. In case study we evaluated the modified, quantitative description of respiration processes in surface waters of lakes of different trophic status: mezzo-eutrophic and eutrophic. In both types of studied environments, V_Resp oscillated between 1.0 μmol C l^-1 h^-1 and 3.0 μmol C l^-1 h^-1, and the size of the OM_Resp pool varied from 39.3 μM C to 828.7 μM C. Despite of higher OM_Resp concentrations in eutrophic lakes, we found a lower susceptibility of OM to respiration processes in eutrophic than in meso-eutrophic lakes but similar V_Resp in both types of lakes. We conclude that the proposed method allows a fast quantitative description of labile organic matter utilization by aerobic aquatic microorganisms.