Land-use and hydroperiod affect kettle hole sediment carbon and nitrogen biogeochemistry

• Published in: The Science of the total environment 2017-01, Vol.574, p.46-56
• Main Authors: Nitzsche, Kai Nils, Kalettka, Thomas, Premke, Katrin, Lischeid, Gunnar, Gessler, Arthur, Kayler, Zachary Eric
• Format: Article
• Language: English
• Subjects: Biogeochemical transformations; Depressional wetlands; Evaporation; Landscape functioning; Stable isotopes; Wet-dry cycles
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2016.09.003

Kettle holes are glaciofluvially created depressional wetlands that collect organic matter (OM) and nutrients from their surrounding catchment. Kettle holes mostly undergo pronounced wet-dry cycles. Fluctuations in water table, land-use, and management can affect sediment biogeochemical transformations and perhaps threaten the carbon stocks of these unique ecosystems. We investigated sediment and water of 51 kettle holes in NE Germany that differ in hydroperiod (i.e. the duration of the wet period of a kettle hole) and land-use. Our objectives were 1) to test if hydroperiod and land management were imprinted on the isotopic values (δ13C, δ15N) and C:N ratios of the sediment OM, and 2) to characterize water loss dynamics and kettle hole-groundwater connectivity by measuring the stable δ18O and δD isotope values of kettle hole water over several years. We found the uppermost sediment layer reflected recent OM inputs and short-term processes in the catchment, including land-use and management effects. Deeper sediments recorded the degree to which OM is processed within the kettle hole related to the hydroperiod. We see clear indications for the effects of wet-dry cycles for all kettle holes, which can lead to the encroachment of terrestrial plants. We found that the magnitude of evaporation depended on the year, season, and land-use type, that kettle holes are temporarily coupled to shallow ground water, and, as such, kettle holes are described best as partially-closed to open systems. [Display omitted] •Kettle holes lie on the boundary of the aquatic and terrestrial domains.•Surface sediments reflect surrounding land-use and management.•Deeper sediments reflect past organic matter sources and the hydroperiod.•The onset of evaporation and lateral flow partly determine kettle hole hydroperiod.•Strong links between land use and hydroperiod drive kettle hole biogeochemistry.