Calculation and retrieval of euphotic depth of Lake Taihu by remote sensing

Abstract

The euphotic zone is defined as the layer where net phytoplankton production is positive. Therefore, determination of the euphotic depth is useful for estimating primary production. The TM data on 2007-01-07 and 2006-08-01, accompanied by real-time water quality parameters including concentrations of tripton and chlorophyll-a (Chl.a) in Lake Taihu, were used to develop quantitative retrieval models of tripton and Chl.a. Euphotic depth was calculated using the model developed in Lake Taihu based on the concentrations of tripton and Chl.a. The euphotic depth ranged from 0.27 to 2.28m (mean 0.56±0.22m) in winter depth from 0.21 to 2.03m (mean 0.98±0.24m) in the summer. In the winter, the euphotic depths showed spatial distributions which were ordered as : the south of Lake Taihu the west coast of Lake Taihu the lake center Xukou Bay Gonghu Bay Meiliang Bay East Lake Taihu Zhushan Bay. In summer, the order changed as follows: the west coast of Lake Taihu Meiliang Bay East Lake Taihu the lake center Gonghu Bay Zhushan Bay the south of Lake Taihu. Seasonally, the euphotic depth was significantly shallower in summer than in winter; however, seasonal variation differed among areas of the lake. Euphotic depths in Meiliang Bay, Gonghu Bay, the west coast of Lake Taihu, the lake center, Xukou Bay and the south of Lake Taihu were higher in the summer than in the winter, but no marked seasonal variations were found in Zhushan Bay and East Lake Taihu.