Historical trophic evolution resulting from changes in climate and ecosystem in Lake Taihu and seven other lakes, China

Abstract

Under natural conditions, the evolution of lake trophic status is not only influenced by climatic and hydrological factors but also by the biological interactions and feedbacks occurring within the lake ecosystem. To envision long-term changes of lake trophic status in several shallow lakes from the Yangtze River basin, we focused on variations in nutrient level and attempted to use both hydrologic- and ecodynamic-based physical models. One was an equivalent-hydrology model with external driving forces from catchment climate and hydrology changes (Model 1), the other was a dynamic model with internal driving forces from the biological interactions within the lake ecosystem (Model 2). Two models were employed in order to distinguish the effects of climate change (by Model 1) from ecosystem feedbacks (by Model 2) on the long-term lake nutrients changes and to further determine which driver was the primary cause for the changes. Variations in lake producer biomass and total phosphorus (TP) were simulated for a historic 200-yr period (1640–1840 AD) in Lake Taihu and seven other similar lakes from the Yangtze River basin after calibration and validation of the control runs (1950–2000 AD). Results showed that (1) TP simulations by Model 1 and Model 2 were mostly consistent with the reconstructed nutrient records from lake sediment cores; (2) the long-term variations of lake nutrients were primarily affected by precipitation under the influence of climate change and the decreases in lake nutrients were more likely to respond to the dry climate; and (3) approximately 49% of the variability in nutrient concentrations were contributed by the feedback of biological interactions in the lake ecosystem. The study results provide a scientific basis for long-term control of nutrients in lakes along the middle–lower reaches of the Yangtze River.