Atmospheric Stilling Promotes Summer Algal Growth in Eutrophic Shallow Lakes.

Algal blooms are environmental challenges confronting lakes worldwide and are significantly influenced by chlorophyll a yields per unit phosphorus (Chl a /TP), or nitrogen (Chl a /TN). Here, the influence of inter-annual hydrometeorological variations on Chl a /TP and Chl a /TN were evaluated in eutrophic shallow Lake Taihu, China. Our results demonstrated significant increases ( p < 0.001) in both Chl a /TN and Chl a /TP from 2005 to 2017, and increased Chl a yields during the winter months were mainly correlated with higher water temperature and longer sunshine hours, which may cause severer blooms in winter and spring. In remaining months from 2005 to 2017, typical associations between atmospheric stilling (or water level elevation) and higher Chl a yields were observed. The results also indicate that atmospheric stilling and water level elevation significantly ( p < 0.001) decreased background turbidity and promoted buoyant cyanobacterial biomass, alleviating phytoplankton light limitation. Given the subtropical location, eutrophic status, and high background turbidity of Lake Taihu, light may be the critical limiting factor for summer phytoplankton growth; thus, improved light availability would promote Chl a yields until self-shading caused further light limitations. If the mechanism is general, promoting the effect of atmospheric stilling on annual peak Chl a in shallow lakes may be greatly underestimated, and our finding will affect future bloom mitigation efforts in such systems.