![]() For example, the continental shelf off the Gironde, which flows into the Bay of Biscay, had not yet been studied from this perspective although recent simulations suggested that this area should already have experienced deoxygenations in recent decades. Given the global observations of eroding intertidal areas and rising sea levels, we suggest that the predicted habitat loss may cause significant changes for coastal biogeochemistry and should be investigated further to understand its potential consequencesĪlthough not systematically considered as oxygen minimum zones, River-dominated Ocean Margins are sensitive to oxygen depletions. With this assumption, we estimate 11% and 8% reductions for respective nitrogen and phosphorus removal in the entire ES by 2060. As an upscaling exercise, we estimate potential erosion induced changes if the ES stations are representative for the system. ![]() The calculated removal of total DIN and DIP from the water column was 34–38% higher in intertidal compared to subtidal samples suggesting stronger denitrification and phosphorus adsorption to solid particles from intertidal sediments. Subtidal sediments exhibited an average efflux of nitrates (0.28 mmol m−2 d−1) and phosphates (0.09 mmol m−2 d−1) into the water column, while intertidal areas displayed average influxes (nitrates = −1.2 mmol m−2 d−1, phosphates = −0.03 mmol m−2 d−1) directed into the sediment. Compared to subtidal stations, OM was significantly more reactive in intertidal samples and exhibited 37% higher O2 fluxes, suggesting a strong influence from microphytobenthos. Monthly fluxes and porewater concentrations of dissolved inorganic nitrogen (DIN), phosphorous (DIP), silica (DSi), carbon (DIC) and oxygen (O2) as well as organic matter (OM) characteristics were measured from intertidal and subtidal sediments from June 2016–December 2017. This study investigates differences between biogeochemical fluxes of intertidal and subtidal sediments of the ES and assesses how ongoing erosion may modify the sedimentary ecosystem functioning of this coastal bay in the coming decades. The Dutch Eastern Scheldt (ES) has been predicted to lose around 35% of intertidal areas by 2060. Coastal areas are subjected to several anthropogenic stressors with much of the world's intertidal areas receding due to human activities, coastal erosion and sea level rise.
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