Sedimentary mud and phaeophytin-a are reliable predictors of oxygen consumption and nitrogen turnover in the southern North Sea

Coastal systems are exposed to variable human uses and anthropogenic pressures, yet they provide valuable ecosystem services. Understanding the benthic processes in these systems is crucial for their effective management and conservation. This study investigates sediment characteristics as proxies for oxygen and nitrogen turnover in coastal, sandy, permeable sediments. We incubated sediment samples to quantify the turnover of ammonium and nitrate and analyzed various sediment properties to determine the most suitable predictors of sediment reactivity. Oxygen consumption rates and rates of ammonium and nitrate turnover strongly correlate with mud content and phaeophytin-a, which are identified as the best proxies for sediment reactivity. Ultimately, our data show that sediment nutrient recycling and turnover is intimately linked to spring primary production in the water column. In order to deduce reaction rates of oxygen, ammonium and nitrate from sediment properties, we provide linear regression coefficients and their uncertainties, enabling access to previous observations that would otherwise remain inaccessible due to missing data. This study provides insights for the development of benthic models that ultimately can be used to assess the impact of anthropogenic pressures on coastal systems. The findings have implications for nutrient management and monitoring in the German Bight, as an improved understanding of sediment reactivity allows for more appropriate and sustainable management and monitoring policies to be implemented.