The effect of intense hydrodynamic disturbance on chromophoric dissolved organic matter in a shallow eutrophic lake

Abstract

Chromophoric dissolved organic matter (CDOM) is an important component of aquatic ecosystems and its movement is a complicated process. To investigate the effect of strong wind-induced sediment suspension on CDOM concentration, we carried out an in situ observation in a large, shallow lake, which is seriously affected by eutrophication and cyanobacterial blooms, using a finely stratified sampling device and several automatic monitoring instruments. During the observation, a typhoon-induced strong wind with a mean wind speed of 6.6 m/s swept the Lake Taihu basin. The strong wind-induced hydrodynamic disturbance caused explosive sediment suspension. During the strong winds, the maximum turbidity in the overlying waters reached 175.4 NTU, which was 12.2 times the background value recorded before the strong winds. Sediment suspension resulted in the release of CDOM from within the sediment. The CDOM absorption coefficient a(355) in the overlying water showed that there was no significant difference between any two water layers for all time points during the observation (13 July to 16 July). The CDOM concentration was fully mixed along the water depth. However, the mean a(355) values recorded in all time points during the wind were higher than that before the wind (p < 0.001). The maximum value during the wind event was 2.524 ± 0.097 m−1, which was 1.4 times that of the value before the disturbance. CDOM concentrations were significantly correlated with hourly mean wind speed (p < 0.05) and turbidity (p < 0.01). Because Lake Taihu is frequently affected by strong wind processes, CDOM concentration changes caused by intense hydrodynamic disturbance are important for quantitative remote sensing of water quality and primary productivity.