Biogeochemical cycles in sediment and water column of the Wadden Sea: The example Spiekeroog Island in a regional context

Tidal flats like the Wadden Sea are areas of high primary production and organic matter remineralization rates. This paper provides an overview of benthic remineralization pathways and the recycling of various metabolic products, exemplified by interdisciplinary studies around Spiekeroog Island (Germany). Organic matter produced in the Wadden Sea area as well as material imported from the North Sea is remineralized in tidal flat sediments. Wadden Sea sediments may thus be regarded as biogeochemical reactors promoting or accelerating organic matter remineralization. Due to advective flow, which is of special importance in permeable sandy sediments, pore waters enriched in remineralized nutrients and methane are actively released from sediments into the overlying water column. This biogeochemical recycling forms the prerequisite for continuously high primary production in the Wadden Sea, and proves a tight coupling between benthic and pelagic dynamics. Additionally, the export of excess nutrients from the Wadden Sea further offshore may trigger biological activity in coastal waters of the North Sea. In this contribution, we will also summarize open questions which need to be answered for a thorough understanding, management and protection of the unique Wadden Sea ecosystem. In particular, the currently understudied, but potentially significant effects of climate change (e.g., rising sea level and increase in storm surge extremes) on biogeochemical cycles in sediments and open waters of the Wadden Sea are discussed.