Characteristics of chromophoric dissolved organic matter in the nearshore waters of the western Taiwan Strait

Absorption and fluorescence of chromophoric dissolved organic matter (CDOM) in the nearshore waters of the western Taiwan Strait were examined in April and October of 2008. CDOM absorption coefficient at 412 nm (ag(412) in m−1) showed an inversed linear relationship with salinity, indicating conservative mixing between freshwater and seawater, although the relationship changed with seasons and locations. On average, except in the vicinity of two major rivers (Minjiang River and Jiulongjiang River), ag(412) was higher in October (dry season) (0.173 ± 0.036 m−1) than in April (wet season) (0.123 ± 0.059 m−1). This observation is counter intuitive but consistent with those derived from MODIS satellite measurements. Combined with the CDOM EEM spectra (fluorescence excitation–emission matrix), the results suggest that 1) Minjiang River and Jiulongjiang River were the primary land-based CDOM sources; 2) The marine end-members were controlled by the South China Sea Warm Current in April and the Zhe-Min Coastal Water in October; 3) The land-based CDOM was more from sewage than from soil leaching; and 4) Light absorption in the blue wavelengths was dominated by CDOM and detritus.