Porewater and sediment geochemistry of five temperate Swiss lakes

We sampled sediments from three water depths in five lakes in central Switzerland: Lake Lucerne, Lake Zurich, Lake Zug, Lake Baldegg, and Lake Greifen. All took place in June and July of 2016. Three sublittoral stations differing in water depth and bottom water O2 concentrations were sampled. Per each lake station, one 60-mm diameter and 3–4 150-mm diameter gravity cores (UWITEC, AT) were taken from boats or motorized platforms. The thin cores were used for analyses of radionuclides, X-ray fluorescence, grain size, and archiving (one-half). Wide cores were used as follows: the core with the least disturbed sediment surface was used for microsensor measurements (O2, pH). Sediment porewater samples were obtained by rhizons (0.2 μm pore size, Rhizosphere) from a designated core with pre-drilled holes that were taped during coring for analyses of dissolved anions and cations including redox sensitive elements. Sediment samples for cell counts, methane concentration analyses, and physical property determinations (porosity, bulk density, dry density, water content) were taken from a third core using sterile cut-off syringes. Samples for solid-phase carbon analyses (TOC, total inorganic carbon (TIC)) were also taken from this core.