Germanium in Lake Geneva (Switzerland/France) along the spring productivity period

Abstract

In this study we present, for the first time, profiles of germanium and its species (inorganic, monomethyl and dimethyl germanium) in a lake: Lake Geneva (Switzerland/France). The period studied covers the spring productivity phase, from January to June 2021, through monthly sampling campaigns in a location where the lake is about 70 m deep (Petit Lac). They have been complemented with samplings in April and June in the lake's deepest point (Grand Lac) and in the main river tributaries. The concentrations of the different species have been measured by a hydride generation – cryotrapping – inductively coupled plasma mass spectrometry (HG-CT-ICP MS/MS) method. Particular attention has been paid to the reliability of the analytical data. When the lake was well mixed, inorganic germanium concentrations were 1.4 ng L−1. Concentration profiles evolved over the season, progressively displaying a typical nutrient-type behaviour, which exactly followed those of silica. Methyl germanium showed conservative behaviour over the entire season with an average concentration of about 0.1 ng L−1. Dimethyl germanium could be detected in some cases but not quantified. Our observations confirm previous studies in oceans but with the difference that, contrary to oceans, inorganic germanium concentrations in the lake largely exceed the concentration of organic species.