Hydrologic Conditions Control the Seasonal Changes in Dissolved Organic Matter Delivery to the Lower Pearl River Estuarine Waters
Singh, S., Dash, P., Silwal, S., Sasidharan, S. M., Moorhead, R. J., Sheng, P., & Lu, Y. (2016). Hydrologic Conditions Control the Seasonal Changes in Dissolved Organic Matter Delivery to the Lower Pearl River Estuarine Waters. Bays and Bayous Symposium 2016. Biloxi, MS.
The quality and quantity of riverine discharge of dissolved organic matter (DOM) represents the linkages between the terrestrial ecosystem and receiving aquatic ecosystems. DOM quantity, quality, transport and fate can be modified through complex interactions of various biogeochemical, physical, and hydrological processes such as photo- and bio-degradation, climate, and hydrological discharge. In this study, we examined the seasonal variability of DOM amount and quality in the lower Pearl River estuary. Surface water samples were collected during four field campaigns, each spanning over a week, conducted in December, 2014, and in March, May, and August, 2015. DOM composition was determined using a suite of spectrofluorometric indices and a site-specific parallel factor analysis model, and dissolved organic carbon (DOC) and total nitrogen (TN) concentrations were measured in the laboratory. Terrestrially derived humic-like DOM, fluorescence and biological indices, and DOC were sensitive to higher river discharge during spring (March and May), whereas labile DOM compositions and a250:a365 ratio corresponded to low river discharge and possibly to increased photo- and bio-degradation and autochthonous production during summer (August) and winter (December). A non-conservative relationship of terrestrially and microbially derived humic-like DOM was observed with salinity, which could potentially be due to flocculation, sorption, autochthonous production, and photo- and bio-degradation. Thus, seasonal variability in discharge, temperature, and photo- and bio-degradation processes mainly controlled the DOM character in the lower Pearl River estuarine waters. This study furthers our understanding of seasonal variability of DOM with hydrological changes and changes in other physicochemical controls in estuarine environments.