Nitrogen isotopes reveal a particulate-matter-driven biogeochemical reactor in a temperate estuary

Abstract. Estuaries and rivers are important biogeochemical reactors that act to modify the loads composition of nutrients in coastal zone. In a case study during July 2013, we sampled an 80 km transect along Elbe Estuary under low-oxygen conditions. To better elucidate specific mechanisms estuarine nitrogen processing, tracked evolution stable isotopic nitrate, nitrite, particulate matter, ammonium through water column. This approach allowed assessment situ isotope effects nitrite oxidation remineralization at reach scale. The were consistent with pure-culture assessments. We found budget is governed by settling, resuspension, further used our data evaluate sources sinks via mass-balance approach. find reactivity its estuary, main control on dynamics inorganic species. Moreover, while underscoring this role matter delivery reactivity, mass balance also indicated additional reactive nitrogen, such as possible denitrification column nitrate intensively dredged deep Hamburg Harbor region.