Nitrogen cycling in coastal permeable sediments from eutrophied regions

Abstract

Coastal seas buffer the ocean from anthropogenic pollution such as fixed nitrogen. Much of the coastal zones are comprised of sandy sediments, which are permeable. The interaction between sediment topography and bottom water movement causes advective flow of porewater in the sediment. This enhanced porewater supply leads to intense biogeochemical activity, removing nitrate and reducing it to inert N2. Therefore this work focuses on nitrogen cycling in coastal sands. It was possible to follow the fate of nitrate within the sediment, revealing the surprising importance of eukaryotes to N-loss. Furthermore, in subtidal sediments high rates of nitrification were identified, which coupled to high denitrification rates suggests that sandy sediments play an important role in mediating N-turnover in this region. The fluctuating oxygen and nutrient concentrations lead to an environment, which stimulates the occurrence of aerobic denitrification and allows for high nitrous oxide production, much of which is emitted to the atmosphere.