| 作者： |
Li, Yan; Ma, Yu; Wang, Haijun; Wang, Hongzhu; Cui, Yongde; Bian, Shijun; Zhang, Miao; Liu, Mengmei; Yu, Yexin; Schallenberg, Marc |
| 论文摘要： |
Regime shifts from submersed macrophyte dominance to phytoplankton dominance have been widely reported in small- to medium-sized shallow lakes. However, alternative stable states in large shallow lakes (surface area >500 km(2)) remain unconfirmed. To understand the alternative stable states and the main influencing factors of submersed macrophytes in large lakes, the ecosystem states from monitoring data from 1959 to 2019 in large shallow Taihu Lake (2 338 km(2) in average depth of 2.12 m) in China were examined. Changes in submersed macrophyte coverage (C-Mac) and phytoplankton chlorophyll a (Chl a) in the time series and their relationships with environmental factors were analyzed. During the field investigation from August 2018 to May 2019, nutrients and Chl a showed obvious heterogeneity across the lake, being generally higher in the western and northern areas and lower in the southeast area, while C-Mac was only observed in the eastern areas, e.g., East Taihu Lake, Xukou Bay, and Gonghu Bay. During the long-term monitoring from 1959 to 2019 in the Central Region, Meiliang Bay, and East Taihu Lake, Chl a increased significantly in the time series. C-Mac varied slightly among different subareas, always at low levels (<10%) in the Central Region and Meiliang Bay but at relatively high levels in East Taihu Lake (10%-90%). Frequency distributions of response variables had no multimodality except for C-Mac in East Taihu Lake, with two peaks between 15% and 20% and between 55% and 60%. A dual relationship was found between Chl a and total phosphorus (TP) in the areas with and without macrophytes, while C-Mac showed no relationship with TP, and submersed macrophytes did not flourish in the Central Region and Meiliang Bay even when TP was at very low levels (approximate to 10 mg/m(3)). Taihu Lake had similar algal turbidity (Turb(Alg)) as small- to medium-sized lakes but generally presented with higher values of nonalgal turbidity (Turb(NonAlg)), as did their contribution to total turbidity as a percentage. This study suggested that large shallow Taihu Lake may have no alternative stable states, but more evidence is needed for East Taihu Lake, which was dominated by macrophytes, as it remains unknown whether hysteresis occurs between the processes of eutrophication and oligotrophication. Unfavorable conditions caused by wind might be the main reason due to the absence of submersed macrophytes in Taihu Lake. These results demonstrate that stricter nutrient control is needed to maintain a healthy state or to recover from a decayed state for large lakes. |
