Program
 
General Session 2: Marine & estuarine biogeochemistry
 
 
 
Poster
Exploring biogeochemical generations of DIC/DIN in the North Branch of inner Changjiang Estuary: Controls and environmental effects in dry seasons
GS2-61
Weidong Zhai* , Institute of Marine Science and Technology, Shandong University, Jinan 250100, China
Xiuli Yan, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China
Di Qi, Third Institute of Oceanography, SOA, Xiamen 361005, China
Presenter Email: wdzhai@126.com
To understand biogeochemical controls of unique dissolved inorganic nitrogen/carbon distributions in the North Branch of inner Changjiang (Yangtze River) Estuary, and to evaluate effects of saltwater spillover from the North Branch on dry-season export fluxes of biogenic elements to the adjacent East China Sea, we investigated a surveying data set of surface water carbonate system, nutrients, and relevant hydrochemical parameters obtained shortly after spring-tide periods in spring 2010, a relatively dry season, covering the channel-like South Branch and the freshwater-blocked North Branch. In the North Branch with a water residence time of approximately 1 month, biogeochemical additions of ammonium (7.4 to 65.7 micro-mol/kg) and alkalinity (196 to 695 micro-mol/kg) along with high salinity of 4.5 to 17.4 were detected. The North Branch partial pressure of CO2 (pCO2) was measured from 930 to 1518 μatm at the salinity range between 4 and 16, which was substantially higher than the South Branch pCO2 of 700 to 1100 micro-atm. Based on field data analyses and simplified stoichiometric equations, we suggest that the estuarine additions of dissolved inorganic nitrogen/carbon in the North Branch were quantified by biogeochemical processes combining biogenic organic matter decomposition, ammonia oxidation, CaCO3 dissolution, and CO2 degassing. In the South Branch upper reach, remarkable salinity values of 0.20 to 0.88 were detected, indicating saltwater spillover from the North Branch. It enhances springtime export fluxes of nutrients, dissolved inorganic carbon, and alkalinity from Changjiang. Also it lowers water-to-air CO2 flux in the South Branch.