VARIATIONS OF ALGAL AND NON-ALGAL TURBIDITY IN A LARGE SHALLOW LAKE——TAIHU LAKE

With the eutrophication of lakes, phytoplankton blooms, resulting in the loss of submersed macrophytes and the decline of biodiversity and ecosystem services. The deficiency of underwater light caused by high turbidity was considered to be the primary reason. Up to now, the researches about the relationship between submersed macrophytes and turbidity have been mainly concentrated in small- and medium-sized lakes, but there is limited understanding of such relationship in large shallow lakes, considering probability because the limited macrophytes coverage and larger influence of wind. In order to explore the inhibition effect of submersed macrophytes on turbidity in large shallow lakes, a large shallow lake——Taihu Lake was investigated to explore the variations of algal and non-algal turbidity and analyzed their contribution to total turbidity in the areas with and without submersed macrophytes. The results showed that: (1) Non-algal turbidity (Turb_NonAlg) (mean value=2.45/m) was the dominant turbidity contributor in Taihu Lake, counting 83% of the total turbidity (2.88/m), and even reaching 89% in spring; (2) The difference of Turb_NonAlg between the areas with (2.52/m) and without submersed macrophytes (2.37/m) was not significant (P>0.05); (3) Under the similar levels of total phosphorus concentration (TP), Turb_Alg in the areas with submersed macrophytes (0.21/m) was not significantly different from the areas without (0.32/m) (P>0.05), the former was even higher than the latter in summer. The results suggested that in such large shallow lakes, submersed macrophytes cannot inhibit the turbidity effectively in both Turb_Alg and Turb_NonAlg. Therefore, the large shallow lakes tend to shift from clear to turbid state easier than the small- and medium-sized lakes under similar nutrient level, and the back forward shift might be more difficult. The results suggest that there is little benefit from planting submersed plants in large shallow lakes to reduce turbidity.