Temporal Variations Of Chromophoric Dissolved Organic Matter In Different Waters

4This study focused on the temporal pattern of Chromophoric Dissolved Organic Matter (CDOM) in different waters,which is a topic rarely reported in the literature.The content and the variation of CDOM in Furong pool, Qingren pool and the Taiwan Strait were investigated.From May to December 2006, CDOM absorption coefficients at 355 nm ( a g(355)) ranged from 1.91 to 3.50 m-1 in Furong Pool (2.88 m-1 on average), and from 3.95 to 9.85 m-1 in Qingren Pool (5.35 m-1 on average). The spectral slope (Sg) (300～500 nm) in both waters ranged from 0.016 to 0.019 nm-1. These two pools had totally different surrounding, leading to different temporal patterns of CDOM. Qingren pool is surrounded by forests. Peaks of CDOM occured following precipitation induced by typhoon. It meant that terrestrial input from surrounding forests by massive rainfall was the primary factor controlling the variation of CDOM in Qingren pool. By contrast,Furong pool is on the main campus of Xiamen University, surrounded by architecture. It was found that ag(355) was significantly correlated with aph(675) during May to July in 2006 (R2=0.66,n=12;R2=0.87,n=12). While the contribution from phytoplankton might be dominant during most of the observing period, it was noticed that storm events (e.g. precipitation >150 mm) could result in high values of ag(355).a g(355) was low in the southern Taiwan Strait in summer, 2005 and 2006. It ranged between 0.01 to 0.36 m-1, similar to those observed in the open ocean. In 2005, a g(355) showed a linear, inverse relationship with salinity in the surface water near Dongshan Island. However, for most of the samples with salinity higher than 32, a g(355) was highly correlated with chlorophyll a (Chla) (R2=0.53,n=53), indicating CDOM was mainly from local production rather than terrestrial input in 2005. In 2006, a g(355) showed a weakly inverse relationship with salinity and a weakly positive relationship with Chla. It was thus suggested that CDOM was influenced by both terrestrial input and local production during the survey. A continuous bloom was observed triggered by coastal upwelling during both cruises. a g(355) ranged from 0.01 to 0.36 m-1 ,while Chla changed from 0.29 to 15.38μg/L. However, neither a consistent day-to-day CDOM variation nor CDOM -Chla coupling.In addition, a linear relationship between a g(355) and the fluorescence intensity of CDOM was only found in three short periods in the two pools. Absorption peaks in the UV-B bands (300～350 nm) were observed in the Southern Taiwan Strait in 2005, which were probably associated with mycosporine-like amino acids (MAAs) released by planktons.