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Biogeochemistry of organic matter and associated elements along the river-estuary-ocean continuum
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Low molecular organic acids--distributions, spatio-temporal variations,and their effects on carbon dioxide system of seawater in coastal area
Wednesday 9th @ 1450-1510, Conference Hall
Haibing Ding* , Ocean University of China
Presenter Email: dinghb@ouc.edu.cn |
| Low molecular weight organic acids (LMWOAs) are important metabolites or intermediates in biochemical processes and widely observed in different environments. In China coastal area, three LMWOAs -- formic acid, acetic acid and lactic acid were identified in seawater. Their distributions and spatio-temproal variations were investigated. In general, their concentrations showed decreased trend from inshore to offshore area. In seawater, their contribution to DOC was up to about 20%. Many factors, including microbial activities, algal release, riverine input, human activities and etc. affect their spatio-temporal variations significantly. According to the formic-to-acetic acid ratio, the key factors controlling distributions patterns of the LMWOAs were attributed to active human activities around coastal area. High concentration of LMWOAs account for a large fraction of organic alkalinity (Org-Alk) in seawater. Considering the effect of LMWOAs on pH value of seawater, a new software Org TCO2TA was developed to calculated the pH value of coastal seawater based on alkalinity equation by separating Org-Alk into LMWOA Alk (LMWOA-Alk) and humic acid Alk (HA-Alk). In the calculations, all dissociation constants of organic acids were from previous literature. Our results showed that pH values obtained from the Org TCO2TA software were closer to the pH values from spectrophotometric measurement than those from the traditional CO2SYS program, indicating pH values of seawater can be influenced by high concentrations of LMWOAs. The Org TCO2TA software can calculate the pH values of coastal seawater more accurately by considering the effects of LMWOAs.
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