Long-term and inter-monthly dynamics of aquatic vegetation and its relation with environmental factors in Taihu Lake, China.

This paper discussed the long-term and inter-monthly variation in the distribution area of aquatic macrophytes in Taihu Lake, as well as the relationship between these variations and environmental factors. The findings were of great significance to the protection and environmental remediation of lake ecosystems. This paper presented data from 92 periods during 1980 to 2017 on the distribution area of aquatic macrophytes (including submerged macrophytes and floating-leaved macrophytes, but excluding emergent macrophytes) in Taihu Lake. Data were acquired by remote-sensing and subsequent image interpretation. The analysis of the inter-monthly variation indicated that the area occupied by aquatic macrophytes first increased and then decreased from January to December. Specifically, the distribution area was very small from January to March, began to increase gradually from April to August, reached its maximum in September, and decreased gradually from October to December. The analysis of the long-term variation showed that the distribution and area of aquatic macrophytes experienced two stages during the years 1980 to 2017: 1) gradual increase, 2) sharp decrease. In the first stage (1980 to 2014), the area occupied by aquatic macrophytes increased by 9 times, the maximum distribution area was 206.27 km (in May), 307.92 km (in September) and 277.33 km (in October). In the second stage (2015 to 2017), the distribution area of aquatic macrophytes decreased sharply to 50 km or less. The distribution area of aquatic macrophytes during the months of January to December had a significant positive correlation with monthly average temperature, COD value, secchi disk depth(SDD), area of cyanobacteria and chlorophyll-a (Chl-a) concentration, a significant negative correlation with water quality indices such as dissolved oxygen (DO) value and NH-N concentration, but no significant correlation with water quality indices such as pH values and total suspended matter (TSM) concentration. The distribution area of aquatic macrophytes from 1980 to 2017 had a significant positive correlation with annual average temperature, annual minimum water level, pH value, SDD, area of cyanobacteria and Chl-a concentration, but no significant correlation with water quality indices such as DO value, COD value, NH-N concentration and TSM concentration. The sharp decrease in the distribution area of aquatic macrophytes in 2015 and subsequent years was primarily due to the mechanized salvage of aquatic plants.