Nitrate sources and dynamics in a salinized river and estuary – a δsup15/supN–NOsub3/subsup−/sup and δsup18/supO–NOsub3/subsup−/sup isotope approach

摘要

To trace NO₃− sources and assess NO₃− dynamics insalinized rivers and estuaries, three rivers (Haihe River: HH River, Chaobaixin River: CB River and Jiyun River: JYRiver) and two estuaries (HH Estuary and CJ Estuary) along the Bohai Bay(China) have been selected to determine dissolved inorganic nitrogen (DIN: NH₄+, NO₂− and NO₃−. Upstream of the HH River, NO₃−was removed 30.9 ± 22.1% by denitrification, resulting from effectsof the floodgate: limiting water exchange with downstream and prolongingwater residence time to remove NO₃−. Downstream of the HH RiverNO₃− was removed 2.5 ± 13.3% by NO₃− turnoverprocesses. Conversely, NO₃− was increased 36.6 ± 25.2% byexternal N source addition in the CB River and 34.6 ± 35.1% byin-stream nitrification in the JY River. The HH and CYEstuaries behaved mostly conservatively excluding the sewage input in the CJEstuary. Hydrodynamics in estuaries has been changed by the ongoing reclamationprojects, aggravating the loss of the attenuation function ofNO₃− in the estuary.