Analyzing the spectral response of submerged aquatic vegetation in a eutrophic lake, Shanghai, China

Re-establishment of submerged aquatic vegetation (SAV) has been recognized as a valuable approach to ecological engineering for the restoration of eutrophicated lakes. Remote sensing technology can be used to monitor the distribution and abundance of SAV through time on a large scale. However, the radiation reflected from SAV must cross the air-water interface and certain optically active components in the water column, such as the depth from the water surface to the plant canopy (WDC), the algal chlorophyll content (Chla), the suspended content (SC) and the water transparency (WT), may alter the spectral signal of the SAV, resulting in inaccuracies in the interpretation of the related remote sensing images. In this study, the spectral characteristics of the SAV plant species Potamogeton crispus, Myriophyllum spicatum and Potamogeton malaianus with varied coverage and water conditions were measured in situ using a spectroradiometer in a eutrophic lake near Shanghai, China. The results showed that the spectral reflectance for varying coverages of SAV appeared mainly within the wavebands 700-900. nm. Canonical correspondence analysis (CCA) ordination based on the reflectance data within the 700-900. nm wavelength bands for 261 quadrats of P. crispus, M. spicatum and P. malaianus together with the variables of coverage, WDC, Chla, SC and WT indicated that the coverage of SAV and WDC were the most important factors affecting the spectral characteristics of SAV. The first derivative curves showed the differences in the position of the peak and valley of spectral reflectance among SAV species. Based on the results from this study, a two-independent variable regression model was established, which predicted the coverage of SAV effectively in the field, in conjunction with variations in water conditions. The implications of these results, in terms of the ability of relevant remote sensing to estimate and monitor the distribution and dynamics of submerged aquatic vegetation on a large scale, are discussed.