Abstract
AbstractThe contribution of sediments to nutrient cycling of the coastal North Sea is strongly controlled by the intensity of fluxes across the sediment water interface. Pore‐water advection is one major exchange mechanism that is well described by models, as it is determined by physical parameters. In contrast, biotransport (i.e., bioirrigation, bioturbation) as the other major transport mechanism is much more complex. Observational data reflecting biotransport, from the German Bight for example, is scarce. We sampled the major sediment provinces of the German Bight repeatedly over the years from 2013 to 2019. By employing ex situ whole core incubations, we established the seasonal and spatial variability of macrofauna‐sustained benthic fluxes of oxygen and nutrients. A multivariate, partial least squares analysis identified faunal activity, in specifically bioturbation and bioirrigation, alongside temperature, as the most important drivers of oxygen and nutrient fluxes. Their combined effect explained 63% of the observed variability in oxygen fluxes, and 36–48% of variability in nutrient fluxes. Additional 10% of the observed variability of fluxes were explained by sediment type and the availability of plankton biomass. Based on our extrapolation by sediment provinces, we conclude that pore‐water advection and macrofaunal activity contributed equally to the total benthic oxygen uptake in the German Bight.
Highlights
Recent studies demonstrated that the bioturbation potential correlated with total organic carbon (TOC) content, chlorophyll concentration, oxygenation depth, sediment oxygen consumption, ammonium efflux, and denitrification (Solan et al 2004, Braeckman et al 2014; Gogina et al 2020)
We focus on general trends and present results to highlight the interplay of benthic fluxes and independent site characteristics such as sediment type, benthic community, and temperature
The bottom water chlorophyll concentration had a clear maximum during the spring bloom in May (Fig. 3B), which was more pronounced at the coastal stations (A–E) than at the distal stations (F–I)
Summary
It is difficult to predict the magnitude of biogeochemical processes in systems with high biodiversity and high abundance of macrofauna Descriptive nonquantitative indices such as the community bioturbation potential (Solan et al 2004) and the community bioirrigation potential (Renz et al 2018; Wrede et al 2018), aim to simplify complex community effects on exchange processes. Due to their nonquantitative nature, these biotransport proxies do not give absolute values for sediment reworking, bioirrigation, or biogeochemical cycling. It is justified to apply these biotransport indices to estimate macrofaunal impact on biogeochemical processes
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