Abstract:
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 (
TurbTot) may enhance the understanding on these processes. This study investigated algal turbidity (
TurbAlg), non-algal turbidity (
TurbNonAlg), and their contribution to
TurbTot in percentage (
TurbAlg%,
TurbNonAlg%) 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
TurbAlg and
TurbNonAlg, and when TP exceeded 100 μg/L,
TurbAlg and
TurbAlg% showed accelerated increases while
TurbNonAlg% showed a decreasing trend.
TurbAlg,
TurbAlg% and
TurbNonAlg were significantly lower in macrophyte-present lakes than in macrophyte-absent lakes, while
TurbNonAlg% was not significantly different between lakes.
TurbNonAlg and
TurbNonAlg% increased significantly with decreased biomass of submersed macrophytes (
BMac), while
TurbAlg and
TurbAlg% showed no significant varying trend. In summary,
TurbAlg was determined mainly by TP, while
TurbNonAlg was greatly determined by
ZM, TP, and submersed macrophytes. The fact of continuously increasing
TurbAlg and
TurbNonAlg 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.