title: Stable isotope mass balances versus concentration differences of dissolved inorganic carbon - implications for tracing carbon turnover in reservoirs.
abstract: The aim of this study was to identify sources of carbon turnover using stable isotope mass balances. For this purpose, two pre-reservoirs in the Harz Mountains (Germany) were investigated for their dissolved and particulate carbon contents (dissolved inorganic carbon (DIC), dissolved organic carbon, particulate organic carbon) together with their stable carbon isotope ratios. DIC concentration depth profiles from March 2012 had an average of 0.33 mmol L-1. Increases in DIC concentrations later on in the year often corresponded with decreases in its carbon isotope composition (δ13CDIC) with the most negative value of -18.4 ‰ in September. This led to a carbon isotope mass balance with carbon isotope inputs of -28.5 ‰ from DOC and -23.4, -31.8 and -30.7 ‰ from algae, terrestrial and sedimentary matter, respectively. Best matches between calculated and measured DIC gains were achieved when using the isotope composition of algae. This shows that this type of organic material is most likely responsible for carbon additions to the DIC pool when its concentrations and δ13CDICvalues correlate negatively. The presented isotope mass balance is transferable to other surface water and groundwater systems for quantification of organic matter turnover.
authors.affiliation: a Department of Geography and Geosciences, GeoZentrum Nordbayern , Friedrich-Alexander University Erlangen-Nuremberg (FAU) , Erlangen , Germany.
authors.forename: Johannes A C
authors.initials: JAC
authors.lastname: Barth
authors.affiliation: a Department of Geography and Geosciences, GeoZentrum Nordbayern , Friedrich-Alexander University Erlangen-Nuremberg (FAU) , Erlangen , Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Mader
authors.affiliation: b Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster , Münster , Germany.
authors.forename: Franziska
authors.initials: F
authors.lastname: Nenning
authors.affiliation: a Department of Geography and Geosciences, GeoZentrum Nordbayern , Friedrich-Alexander University Erlangen-Nuremberg (FAU) , Erlangen , Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: van Geldern
authors.affiliation: c UFZ - Helmholtz Centre for Environmental Research , Magdeburg , Germany.
authors.forename: Kurt
authors.initials: K
authors.lastname: Friese
mesh_terms: D000531:Altitude; D017554:Carbon Compounds, Inorganic / Q000032:analysis* / Q000737:chemistry; D002247:Carbon Isotopes / Q000032:analysis*; D011232:Chemical Precipitation; D004784:Environmental Monitoring; D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments / Q000032:analysis*; D005858:Germany; D060587:Groundwater / Q000032:analysis / Q000737:chemistry; D011891:Rain / Q000737:chemistry; D012995:Solubility; D013696:Temperature
chemical_list: D017554:Carbon Compounds, Inorganic; D002247:Carbon Isotopes
keywords: Algae; DIC; DOC; POC; aquatic carbon species; carbon cycle; carbon-13; carbon turnover; isotope geochemistry; lakes; reservoirs