Proxies, drivers, and impact of macrofaunal transport in sediment of the southern North Sea.

Coastal sediments play an important role in the nutrient cycling, and the intensities of exchange processes between bottom water and pore water control the balance between sequestration and recycling of nutrients. Pore water advection as one major exchange mechanism is determined by physical parameters and thus well describable with models. By contrast, biotransport (bioirrigation, bioturbation) as the other major transport mechanism is much more complex and observational data are often scarce to quantify these processes.

We present ex-situ observations of oxygen and nutrient fluxes, sediment characteristics, and fauna composition over the past six years from all benthic provinces of the German Bight, which enable us to describe the spatial and seasonal variability of the benthic- pelagic coupling. We employ this dataset to detect environmental drivers of the observed variability and to test several proxies of faunal activity.

Our results show that abiotic parameters (sediment type, local primary production) explain the spatial variability while the dynamics of temperature and faunal activity explain the temporal variability. Effects of the complex benthic communities on benthic exchange rates can be parameterized by surprisingly simple proxies, which may help to improve benthic exchange models. By comparing in-situ measurements of pore water advection with ex situ observations, we conclude that biotransport approximately doubles the benthic- pelagic exchange rates in the German Bight.