INTEGRATING UNDERWATER LIGHT CONDITION AND SEED BANK TO INDICATE SUBMERSED MACROPHYTE RESTORATION ZONE: LAKE JINHU AS A CASE

Submersed macrophytes play an important role in maintaining lake ecosystem health and supporting fishery sustainability. The restoration of submersed macrophytes is an effective measure of ecological reconstruction in shallow lakes. However, assessment of the restorable zone of macrophytes is usually neglected in practical ecological restoration, resulting in low survival rates of introduced submersed macrophytes. In this study, Lake Jinhu (with two subareas, Donghu and Liujiahu), Zhijiang, Hubei Province, was studied as a case with the purpose of developing a method to assess the restoration zone of submersed macrophytes by integrating the underwater light climate and seed bank of submersed macrophytes. Two comprehensive surveys were carried out in June and December 2018. The seed bank of submersed macrophytes was analyzed in June. The ratio of Secchi depth to water depth and the seed bank distribution of submersed macrophytes were selected as the key factors to assess the restoration zones. The results suggested a serious eutrophication of Lake Jinhu. In June, the ratio of Secchi depth to water depth ranged from 0.13 to 0.25, with an average of 0.17, all much lower than the required thresholds for the regrowth of submersed macrophytes. In December, the ratio of Secchi depth to water depth ranged from 0.18 to 0.95, with an average of 0.44, mostly meeting the requirement for macrophyte growth. The density of the submersed macrophyte seeds ranged from 0 to 200 ind./m², with an average of 24 ind./m². Based on the underwater light climate and the spatial distribution of the seed bank, combined with the topography of the lake bottom, we suggest that the water level be lowered in winter and spring. The southeastern part of Lake Donghu, the western bank of Lake Donghu, and the eastern bank and the western part of Lake Liujiahu are zones suitable for the restoration of submersed macrophytes. The relevant findings are expected to benefit lake management in restoring submersed macrophytes by improving the efficiency of ecological restoration while lowering the cost of management.