Spatiotemporal variations in euphotic depth and their correlation with influencing factors in a tributary of the Three Gorges Reservoir

After the initial impoundment of the Three Gorges Reservoir (TGR), most of its tributaries have been influenced because of the backwater and the input of nutrients. The spatiotemporal variability in euphotic depth and its major influencing factors were investigated in the Xiaojiang River Basin of the TGR to reveal this change. Analyses were based on the photosynthetically active radiation (PAR) and water quality indices in five sampling sites of the Xiaojiang River from May 2007 to April 2009. Results showed only slight spatial variation in the average euphotic depth while significant temporal variation was taken place. Moreover, correlation analysis indicated that the diffuse attenuation coefficients for PAR (K-d(PAR)) was significantly correlated to the total suspended solids (TSS) (R-2 = 0.6794), but not to chlorophyll-a (Chl-a) (R-2 = 0.045). The unique hydrological conditions of the TGR might be the determinants of the spatiotemporal variability.