Mineralization of autochthonous particulate organic carbon is a fast channel of organic matter turnover in Germany's largest drinking water reservoir

[摘要] Turnover of organic matter (OM) is an essential ecologicalfunction in inland water bodies and relevant for water quality. This isespecially important for the potential of dissolved organic carbon (DOC)removal as well as for emissions of CO 2 . In this study, we investigatedvarious phases of OM including DOC, autochthonous particulate organic carbon(auto-POC), allochthonous particulate organic carbon (allo-POC), andsedimentary matter (SED) in a temperate drinking water reservoir (RappbodeReservoir, Germany) by means of dissolved inorganic carbon (DIC)concentrations and carbon stable isotope ratios. In order to best outlinecarbon turnover, we focused on the metalimnion and the hypolimnion of thereservoir, where respiration is expected to be dominant and hardly disturbedby atmospheric exchange or photosynthesis. DIC concentrations ranged between0.30 and 0.53 mmol L −1 , while δ 13 C DIC values rangedbetween − 15.1 ‰ and − 7.2 ‰ versus the VPDB (Vienna PeeDeeBelemnite) standard. Values of δ 13 C DOC and δ 13 C auto-POC ranged between − 28.8 ‰ and − 27.6 ‰and between − 35.2 ‰ and − 26.8 ‰, respectively. Isotopecompositions of sedimentary material and allochthonous POC were inferredfrom the literature and from measurements from previous studies with δ 13 C SED = - 31.1  ‰ and δ 13 C allo-POC ranging from − 31.8 ‰ to − 28.6 ‰. Comparison of DIC concentration gains and stableisotope mass balances showed that auto-POC from primary producers was themain contributor to increases in the DIC pool. Calculated OM turnover rates(0.01 to 1.3  µ mol L −1  d −1 ) were within the range foroligotrophic water bodies. Some higher values in the metalimnion are likelydue to increased availability of settling auto-POC from the photic zone.Samples from a metalimnetic oxygen minimum (MOM) also showed dominance ofrespiration over photosynthesis. Our work shows that respiration intemperate lentic water bodies largely depends on auto-POC production as amajor carbon source. Such dependencies can influence the vulnerabilities ofthese aqueous systems.

[学科分类] 大气科学