Abstract
Despite a large variety of processes that can control Mo and its potential to become an environmental tracer of euxinic environment, this element is not often studied in lakes. The aim of this paper is to identify main seasonal biogeochemical processes that involve Mo in a well constrained freshwater system (Lake Pavin water-column) in order to evaluate their respective importance. In Lake Pavin, 4 main processes have been identified: 1) the transitional process represented by Mo assimilation of by phytoplankton in the epilimnion (nitrogen biological fixation and nitrate assimilation); 2) transient process represented by dissolved Mo adsorption onto Fe and Mn metal oxides at oxic/anoxic interface (depth 50 - 60 m); 3) Mo precipitation where apparent sulfide production rate is maximum, and from 80 m depths; 4) release of dissolved Mo due to Mo benthic flux or input from a deep source.
Highlights
Mo is a trace element which interests both geochemists and biochemists because it plays an important role in natural biogeochemical cycles of elements such as nitrogen and sulphur cycle where they are bound to molybdenum by specific enzymes [1] [2]
Mo is considered in marine sediment records as a proxy of anoxic paleo-environments where sulphide builds up and precipitate molybdenum [3]-[7]
Following the possible transformation of molybdate to thiomolybdates (Equations (1) to (5), molybdenum can co-precipitate with iron sulfides and organic molecules-rich sulphide participating in the capture and long term sequestration of molybdenum [27] [40] [41]
Summary
Mo is a trace element which interests both geochemists and biochemists because it plays an important role in natural biogeochemical cycles of elements such as nitrogen and sulphur cycle where they are bound to molybdenum by specific enzymes [1] [2]. In spite of molybdenum biological properties and potential reactivity in aquatic systems, there are very few works on lake ecosystem. There is a lack of publications that compare to different biogeochemical processes [8]. The aim of this research is to identify processes that involve Mo in a well constrained freshwater system in order to evaluate their respective importance. Lake Pavin is the perfect natural laboratory to study dynamic behaviour of Mo in presence both of microalgaes, manganese and iron oxides productive layers and sulphidic layers
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