Vertical distribution of optically active water components and its influence on remote sensing reflectance in a eutrophic water

The vertical distribution of optically active water substances ( chlorophyll a,suspended solids and CDOM) is important to control underwater light climate in eutrophic waters,which fundamentally affects the estimation of water color variables from remote sensing.Using vertical bio⁃optical dataset in August and November,2011 from Taihu Lake, analyses of vertical variation of optically active water components and its influencing factors were performed.Furthermore,the effect of the vertical profiles of water components present on remote sensing reflectance was also examined. The results 环 境 科 学 学 报 36 卷 demonstrated that wind speed was an extremely important factor influencing the vertical distribution of optically active water components in eutrophic lakes. Under conditions when low wind speeds (< 3.0 m·s-1) or no wind occurred,chlorophyll a concentrations rapidly increased in surface water,leading to algae blooms.At high wind velocities (> 5.0 m·s-1),vertically mixing occurred and chlorophyll a moved downwards with a maximum in the bottom water. Under other wind speeds conditions,chlorophyll a concentration had a maximum value at a water depth in Taihu Lake.The suspended solids and CDOM were quasi⁃uniformly distributed in the vertical profiles on condition that the wind speed was less than 5.0 m·s-1 .However,resuspension processes were important in controlling the sources of suspended solids and CDOM when wind velocity was higher than 5.0 m·s-1 .The average chlorophyll a concentrations at 0~ 0.5 m water depth was significantly related to the band⁃ratio(Rrs(709) / Rrs(681)) with the correlation coefficient r = 0.86,which showed its relatively high impact on the remote sensing reflectance when no algae blooms appeared,however,for shallow waters,the surface suspended substance showed an important influence on remote sensing reflectance of water.These results will be benefit for providing methodology for better estimates of water color variables in inland waters.