VARIATIONS OF ALGAL AND NON-ALGAL TURBIDITY AMONG THE YANGTZE SUBTROPICAL SHALLOW LAKES

Increasing turbidity is the main cause for the disappearance of submersed macrophytes and regime shift from clear-water to turbid-water states along the eutrophication of lakes. Quantitative discrimination on the contribution of algal and non-algal particles to total turbidity (Turb_Tot) may enhance the understanding on these processes. This study investigated algal turbidity (Turb_Alg), non-algal turbidity (Turb_NonAlg), and their contribution to Turb_Tot in percentage (Turb_Alg%, Turb_NonAlg%) using data from Yangtze shallow lakes. The results showed that both absolute and percentage non-algal turbidity (averaged 0.96/m and 71.0%) were much higher than those of algal turbidity (averaged 0.19/m and 11.0%). Total phosphorus (TP) positively impact Turb_Alg and Turb_NonAlg, and when TP exceeded 100 μg/L, Turb_Alg and Turb_Alg% showed accelerated increases while Turb_NonAlg% showed a decreasing trend. Turb_Alg, Turb_Alg% and Turb_NonAlg were significantly lower in macrophyte-present lakes than in macrophyte-absent lakes, while Turb_NonAlg% was not significantly different between lakes. Turb_NonAlg and Turb_NonAlg% increased significantly with decreased biomass of submersed macrophytes (B_Mac), while Turb_Alg and Turb_Alg% showed no significant varying trend. In summary, Turb_Alg was determined mainly by TP, while Turb_NonAlg was greatly determined by Z_M, TP, and submersed macrophytes. The fact of continuously increasing Turb_Alg and Turb_NonAlg along with increasing TP and degrading macrophytes demonstrates that nutrient control and macrophyte maintenance are practically important during the whole process of eutrophication, although there exists a threshold for clear-to-turbid regime shifts.