Distributions of colored dissolved organic matter and dissolved organic carbon in the Pearl River Estuary, China

Abstract

The distributions of colored dissolved organic matter (CDOM) and of dissolved organic carbon (DOC) were studied in the Pearl River Estuary from 18 to 26 July 1999 (during the wet season). The highest level of CDOM was found in the fresh water, and lowest in the sea water, indicating the river water is a main source of CDOM in this estuary and may has impact on the optical properties of the South China Sea. However, the CDOM concentration is relatively low compared to the reports from other estuaries in the world. CDOM also did not show a conservative mixing behavior in the Pearl River Estuary. This non-conservative behavior may not be due to removal processes (such as flocculation and photodegradation), but is probably the result of different water mass sources having distinct CDOM composition and optical properties. DOC concentration, contrary to CDOM, varied little with the salinity gradient, leading to a different distribution between CDOM and DOC in the Pearl River Estuary. The absence of a co-variation between CODM with DOC suggests that the contribution of CDOM to DOC is variable and it is probably not feasible to estimate DOC by the remote sensing of CDOM in the Pearl River Estuary.