Nature 448, 180-182 (12 July 2007) | doi:10.1038/nature05963; Received 26 December 2006; Accepted 25 May 2007

Reversal of the net dinitrogen gas flux in coastal marine sediments

R. W. Fulweiler1, S. W. Nixon1, B. A. Buckley1 & S. L. Granger1

  1. Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882-1197, USA

Correspondence to: R. W. Fulweiler1 Correspondence and requests for materials should be addressed to R.W.F. (Email: wally@gso.uri.edu).

The flux of nitrogen from land and atmosphere to estuaries and the coastal ocean has increased substantially in recent decades. The observed increase in nitrogen loading is caused by population growth, urbanization, expanding water and sewer infrastructure, fossil fuel combustion and synthetic fertilizer consumption1, 2. Most of the nitrogen is removed by denitrification in the sediments of estuaries and the continental shelf, leading to a reduction in both cultural eutrophication and nitrogen pollution of the open ocean3, 4. Nitrogen fixation, however, is thought to be a negligible process in sub-tidal heterotrophic marine systems5. Here we report sediment core data from Narragansett Bay, USA, which demonstrate that heterotrophic marine sediments can switch from being a net sink to being a net source of nitrogen. Mesocosm and core incubation experiments, together with a historic data set of mean annual chlorophyll production6, 7, support the idea that a climate-induced decrease in primary production has led to a decrease in organic matter deposition to the benthos and the observed reversal of the net sediment nitrogen flux. Our results suggest that some estuaries may no longer remove nitrogen from the water column. Instead, nitrogen could be exported to the continental shelf and the open ocean and could shift the effect of anthropogenic nitrogen loading beyond the immediate coastal zone.

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