Spatiotemporal dynamics of coupled dissolved silica and bicarbonate in a dam-induced urban lake system in the Three Gorges Reservoir Area

Abstract

Dissolved silica (DSi) and bicarbonate (HCO3–) stoichiometric coupling is collectively regulated by chemical weathering and algal activity, and potentially indicates the aquatic silicon retention and carbon emission in aquatic systems. Damming markedly remodels the hydrological conditions and aquatic biological activity, however, its effects on the spatiotemporal dynamics of coupled DSi and HCO3– remain poorly understood. Here we deciphered a 2-year hydrological and water quality dataset collected at multiple sites within an urban lake, namely Hanfeng Lake, the largest pre-dam of the Three Gorges Reservoir, to unravel the spatiotemporal dynamics of DSi and HCO3– and selected hydrological and water quality variables using cluster analysis, and to explore the best predictors for DSi:HCO3– using partial least squares regression. The changes of DSi, HCO3– and selected water variables could be characterized by spatial east and west zones, and further by temporal periods 1, 2 and 3 corresponding respectively to fluctuation stage, fluvial stage and lacustrine stage in each zone based on the hydrographic features of Hanfeng Lake. Wet season presented higher flow velocity, permanganate index, concentrations of DSi, HCO3–, nitrate-nitrogen and total suspended solids, and lower water level, secchi depth and chlorophyll-a, but equal DSi:HCO3– relative to dry season. DSi was overall negatively correlated with HCO3–, highlighting the dominant role of chemical weathering rather algal activity. DSi:HCO3– exhibited significant relationships with various variables, but was the best predictable using water level, permanganate index and nitrogen-based variables, suggesting the strong effects of water level fluctuation and pollution discharge on the coupling of silicon and carbon. Our results have great significance for understanding and modeling the biogeochemical cycles of silicon and carbon in the dam-induced lake ecosystems worldwide.