Description
Summary:Water samples were taken at the surface and the bottom in transects crossing the lake or coastal site from locations with observed erosion to presumably undisturbed locations. The water sampler (1.5 L Uwitec, Austria) was attached to a graduated rope, lowered by hand and filled twice. Combined water samples were transferred to 2 L Nalgene bottles, filled to the top and subsampled at the field station for further analysis. pH, dissolved oxygen concentration and electrical conductivity: pH, dissolved oxygen concentration and electrical conductivity were measured in the laboratory with a WTW 340i Multiprobe. Before each measurement the sensor was calibrated for oxygen and pH. Dissolved methane: At the coastal sites, 120 ml glass bottles were filled without bubbles and capped with butyl septa and aluminum crimps. After adding 10 ml of synthetic air (Alphagaz 1), we added 0.2 ml of 8 N NaOH. For the lakes, 60 ml syringes were filled with 40 ml of water and 20 ml of air. After shaking for 2 minutes, 10 ml of the headspace (containing the methane) was transferred into 20-ml vials, which had been filled completely with saturated NaCl solution. Methane concentrations in the headspace were measured with a Shimadzu GC 2014, a Rt Alumina Bond column and at 50° for 2 min in the laboratory in Germany. Further calculations of the amount of dissolved methane were performed according to Magen et al. (2014). Dissolved inorganic carbon and total alkalinity: Water samples for dissolved inorganic carbon and total alkalinitiy (DIC and TA) were filtered through a pre-rinsed Pall AcroPak 1000 Supor Membrane 0.8/0.2 μm filter. The filtered water sample was filled into 250 ml Pyrex borosilicate glass bottles. One end of silicone tubing from the filter was placed at the bottom of the glass bottle and the bottle was rotated while filling to ensure no bubbles accumulated inside. Overflowing was allowed to avoid the persistence of any minute bubbles. Samples were preserved by adding 100 μl of 50% saturated HgCl2 solution after removing 2.5 ...