Transport Characteristics of Phosphorus Sources at the Multi-scale Watershed and the Associated Ecological Effects on Poyang Lake

Abstract

In this study, a cascaded watershed system in the Poyang Lake area was selected as the study site, which ranged from the primary tributaries to the lake area (Xiangxi River→Jiazhu River→Ganjiang River→Poyang Lake). The aims of the study were to monitor the P wet deposition and runoff process in the Poyang Lake area and discuss the P transport characteristics at the multi-scale watershed and its impact on phytoplankton community structure in the Poyang Lake. The results showed that the P concentration in the Poyang Lake area exhibited significant seasonal changes. Apart from the Xiangxi River watershed, the concentrations of total phosphorus (TP), dissolved total phosphorus (DTP), and orthophosphate(PO43-) were higher in the low flow period than in the high flow period at other watersheds. There was a significant correlation between TP concentration and diatom density during the high flow period, and between TP concentration and cryptophyta during the low flow period. The order of the amounts of TP and PO43- transport by runoff under different rain intensities is as follows:light rain > moderate rain > heavy rain. There is a significant difference in the deposition flux between the wet season and the dry season with seasonal change, in which the flux during the wet years was about 2.8 times higher than in the dry years. The export flux of P was also shown to be higher in the high flow than in the low flow period. As watershed size increased, the contribution rate of P export did not increase, indicating that P transported at different scales was not the main source of P in each watershed.