Chapter 36 - Nitrogen Fluxes from Rivers to the Coastal Oceans

Abstract

This chapter reviews information from previous studies regarding nitrogen inputs to landscapes and the associated delivery of nitrogen to coastal waters around the world. It specifically focuses on fluxes of total nitrogen rather than dissolved inorganic nitrogen (DIN, typically including nitrate, nitrite, and ammonium), since most of the organic nitrogen added to the oceans in rivers is likely converted to DIN on ecologically meaningful time scales; that is, terrestrially derived organic nitrogen in marine sediments is only a very small proportion of the inputs (probably < 6%) assuming that all nitrogen in deltaic sediments represents terrestrially derived organic nitrogen. Several models have been developed to estimate nitrate fluxes to the global ocean; these generally yield estimates of nitrate fluxes that are one-third to one-half of global estimates for total nitrogen fluxes in rivers. However, in considering the role of human activities, it is important to note that the nitrate fluxes represent a much higher proportion of the anthropogenically increased nitrogen fluxes. Though ammonium fluxes are generally much lower than nitrate fluxes in streams and rivers, they also may represent a substantial proportion of the increased fluxes resulting from anthropogenic activities, such as in some urban areas with inputs of wastewater.