Sulphate reduction and anaerobic methane oxidation in sediments of Lake Grevelingen

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In seasonally stratified and hypoxic coastal saline Lake Grevelingen anthropogenically enhanced nutrient input has supported a high primary production already for several decades. This has resulted in the accumulation of large amounts of organic matter in the sediments. Because most oxygen is already lost in the upper millimetres of the sediment, most of this organic matter is currently degraded under anoxic conditions by sulphate reduction (SR) and methanogenesis. Sulphate reduction also plays a key role in removing upward diffusing methane through anaerobic oxidation in the sulphate-methane-transition zone (SMTZ). Incomplete oxidation of methane leads to an upward tailing of the methane profile and a broadening of the SMTZ with both sulphate and methane being present over a wide depth interval. The processes responsible for such a broad SMTZ, which is also observed in sediments of other systems, are still incompletely understood. Here, we will expand the existing pore water data set on sulphate and methane dynamics in sediments of Lake Grevelingen with rate measurements of SR and anerobic oxidation of methane (AOM) to obtain further insight into the distribution and extent of both processes in the SMTZ. Furthermore, the sedimentary dynamics of iron, manganese and phosphorus and the impact of AOM on their source and sink behaviour will be studied. This study will contribute to a better understanding of the processes leading to anaerobic oxidation of methane in marine sediments and the impact on other biogeochemical cycles.