Quantifying Benthic Nitrogen Fluxes in Puget Sound, Washington—A Review of Available Data

In Puget Sound, Washington, underrepresenting or neglecting benthic flux as a source of nitrogen to marine waters can result in ineffective management actions and can lead to chronic water-quality problems, such as hypoxia, in sensitive areas. Shallow areas near the shores of Puget Sound are most likely to experience low levels of dissolved oxygen because of the combination of relatively low circulation, warm summer water temperatures, and proximity to watershed nutrient contributions. In these shallow areas, benthic nutrient fluxes may be the dominant local source of nitrogen. Studies of benthic fluxes of nutrients have been quantified in very few areas in the Puget Sound and more sediment flux data, as well as detailed information about controls on benthic fluxes, are needed. To address this data gap, we conducted an extensive search of the literature for data related to benthic nitrogen fluxes in Puget Sound. A total of 138 individual flux chamber measurements and 38 sets of diffusive fluxes were compiled. Of the diffusive fluxes, 35 new datasets were located, and new flux calculations are presented. In total, 65 new diffusive flux calculations are provided across all nitrogen species (ammonium, nitrate, and nitrite). Data analysis of this newly compiled benthic flux dataset showed that deep (greater than 50 meters) water tended to have lower flux values than shallow (less than 50 meters) depths. Additionally, variability in flux at the shallow depths was greater, possibly indicating a more dynamic interaction between the benthic and pelagic environments. The overall range of bottom temperatures from studies in the Puget Sound area was small (5–16 degrees Celsius) and only ammonium flux showed any pattern with temperature with increased variability at temperatures greater than 12 degrees Celsius. We identify several areas needed for future research from this newly compiled data set. As more is learned about the role of benthic nitrogen fluxes in Puget Sound, this information can be incorporated into coupled sediment and biogeochemical models to better capture nutrient and oxygen dynamics, and to provide improved information for managers of Puget Sound resources