Absorption and fluorescence of chromophoric dissolved organic matter in the Pearl River Estuary, South China

Abstract

The Pearl River is a complex river network under the influence of heavy urbanization and industrialization. The Pearl River Estuary receives freshwater from eight major sources, each containing various pollutants. The spectral absorption and fluorescence properties of chromophoric dissolved organic matter (CDOM) in the Pearl River Estuary were studied during November 2002, a low flow (dry) season. Over a salinity range of 33–0, CDOM absorption coefficients at 355 nm ( a(355)) ranged from 0.24 to 1.93 m − 1 , lower than several other American and European estuaries. In contrast to the wet season, conservative mixing was evidenced by a linear, inverse relationship between a(355) and salinity. CDOM, primarily of terrestrial origin, contained more anthropogenic organic matter than natural plant decay matter: tryptophan-like fluorophore T had the strongest signal among all fluorophores for the entire study region. The absorption spectral slope ( S), determined between 300 and 500 nm, ranged between 0.0138 and 0.0184 nm − 1 and did not show distinguishable patterns except in the transition zone between the estuary and the South China Sea. The relative composition of fluorophores was found to vary among different sources. This result demonstrated the potential for using fluorophores to characterize the composition of CDOM and trace pollutants to their various freshwater sources.