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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 consumption. 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 ocean. Nitrogen fixation, however, is thought to be a negligible process in sub-tidal heterotrophic marine systems. 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 production, 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.

The successful implementation of the nitrogen-vacancy (NV) center in diamond as a qubit has spawned a great deal of interest in this defect. In principle, similar defects suitable for quantum computing should exist in other material systems; however, very little work has been done on identifying NV-like centers in other materials. We discuss the key properties of the NV center in diamond in the context of uncovering similar defects in other materials, with the specific example of SiC. Using first-principles calculations, we compare the properties of the NV center in diamond to the analogous defect in 4H-SiC. We also compare the properties of the bare vacancies. We calculate defect formation energies and charge-state transition levels to determine which defects are likely to form. Then, by analyzing the defect-induced electronic states, we determine whether stable defects in 4H-SiC may have properties similar to those of the NV center in diamond. [ABSTRACT FROM AUTHOR]