External loading reduction has been implemented to improve water quality in China since the 2000s. To evaluate the effects of nutrient reduction on phytoplankton, long-term monitoring data for Lake Wuli from 1998 to 2017 were analyzed. After the restoration since 2003, nitrogen decreased significantly from 8 to 2 mg/l until 2008 and then remained stable until 2017, while total phosphorus declined progressively from 0.2 mg/l to approximately 0.08 mg/l during 2003 and 2017. Biological data indicated that phytoplankton biovolume decreased after restoration until 2010 and then increased slightly from 2010 to 2017, mainly due to increasing of cyanobacterial biovolume. The dominant taxa shifted from cryptophyta to cyanobacteria since 2009. The results of both nonmetric multidimensional scaling and random forest regression showed that changes in nutrients, especially decreases in nitrogen, were the main drivers for phytoplankton community variation and increasing of cyanobacterial biovolume to the total phytoplankton biovolume ratio in summer and autumn. In addition to nutrients reduction, climatic variables such as wind speed decrease also played vital roles in increasing of cyanobacterial dominance in Lake Wuli. Our study confirmed that phytoplankton community respond strongly to nitrogen reduction in the subtropics and that climate change mediates the response.
HYDROBIOLOGIA 卷: 847 期: 13 页: 2963-2975 出版年: 2020