RedoxPhos: How do physical and biogeochemical conditions in pelagic boundaries control vertical transport and generation of phosphorus species?

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Scenarios of climate change emanate, that the duration and stability of thermal stratification will increase. Previous studies on the consequences for the productivity of lakes reported contradicting results. It is often assumed that anaerobic processes will lead to an enhanced release of phosphorus (P) from the sediments. New results from marine research show that pelagic redoxclines act as P traps due to the formation of mineral phases. Our project aims at the observation of transformation of organic and inorganic P species and their transport towards the sediment using geochemically quite different lakes with distinct pelagic redoxclines. Thereby the temporal and spatial changes of biogenic phosphorus are considered in close connection with the iron-sulfurand manganese cycle. The hypothesis will be verified whether a prolonged stratification can additionally remove phosphorus from the water body via the formation of solid phases. For this purpose, using cylindrical sedimentation traps above and below of natural redoxclines, settling matter will be sampled and structurally analyzed. In a long-term in situ experiment, exposing ’meromixis columns’, the complete mixing will be suppressed and strong gradients will be induced in the water body above the sediment. By means of chemical analyses, modern physical structure determination and thermodynamic calculations the influence of pelagic boundaries onto the sink function of sediments for phosphorus will be quantified.