Publication Abstract

Carbon and nitrogen flow through pelagic and benthic food webs in the North Sea - susceptibility to environmental change and human impacts

Carbon and nitrogen flow through pelagic and benthic food webs in the North Sea - susceptibility to environmental change and human impacts

Suzanne Painting*, Ruth Parker*, John Aldridge*, Naomi Greenwood* & Rodney Forster*

Carbon and nitrogen flows through pelagic and benthic food webs in the central and southern North Sea are being investigated using a combination of fieldwork and modelling studies. The underlying hypotheses include (1) that enhanced benthic-pelagic coupling increases the diversity and productivity of UK shelf seas; (2) that benthic-pelagic coupling is weakened by direct human impacts (e.g. removal of benthos due to trawling) and environmental change (e.g. enhanced stratification due to climate change).

Observational data show spatio-temporal variability in food web structure and function. Coupled physical-biological models provide detailed data on C and N budgets, and are used to test the importance of benthic-pelagic coupling on productivity. Preliminary results for the seasonally stratified Oyster Ground site (45m depth) using a 1-D version of ERSEM are presented here. Functional groups within the biological compartments have been summed to yield aggregated phytoplankton, zooplankton and benthic biomass and fluxes.

To assess the importance of benthic-pelagic coupling, chemical and biological processes in the seabed were ‘switched off’, making the bed a passive sink for pelagic detrital material, with no return of nutrients to the pelagic system. This had a clear effect on primary and secondary production, with reduced biomass throughout the summer, and a weaker autumn bloom. The annual decrease in available carbon, considering both the microbial loop and primary production, was around 15%. The same simulations for a mixed water column showed an almost identical relative decrease in available carbon in the absence of the benthic recycling of nutrients.  In a shallower water column (35m) impacts were greater.

Reference

Suzanne Painting*, Ruth Parker*, John Aldridge*, Naomi Greenwood* & Rodney Forster* (2007) Carbon and nitrogen flow through pelagic and benthic food webs in the North Sea - susceptibility to environmental change and human impacts. Conference on Aquatic Change, Plymouth 2007

Suzanne Painting*, Ruth Parker*, John Aldridge*, Naomi Greenwood* & Rodney Forster*

Conference on Aquatic Change, Plymouth 2007