内蒙古黄旗海近1600年来生态系统演化及驱动机制OA

Located in the arid-semi-arid transition zone on the margin of the East Asian monsoon region,Lake Huangqihai consti-tutes a typical lake ecosystem highly sensitive to both climate change and human activities.Disentangling the differences between climate-driven natural processes and anthropogenic ecological alterations represents a key scientific challenge in understanding the response mechanisms of lake ecosystems in this area.This study reconstructed the historical evolution of phytoplankton primary pro-ductivity and trophic state over the past approximately 1600 years in Lake Huangqihai using visible reflectance spectroscopy(VRS)-inferred sediment chlorophyll-a(Chl.a)concentrations and visible-near-infrared spectroscopy(VNIR)-inferred lake wa-ter total organic carbon(TOC)concentrations.These proxies were integrated with analyses of sediment TOC,total nitrogen,total phosphorus,grain size,magnetic susceptibility,and geochemical elements to systematically investigate ecosystem dynamics and their drivers.The results indicate that before about 820 AD,although the climate was humid and the East Asian summer monsoon intensified,runoff from the watershed reduced light penetration in the lake,suppressing primary productivity.From 820 to 1500 AD,warm and humid conditions promoted watershed vegetation development,increasing nutrient inputs to the lake.This nutrient enrichment likely exceeded ecological thresholds,substantially elevating phytoplankton productivity and lake water TOC concentra-tions,and driving significant shifts in ecosystem structure.After 1500 AD,despite a transition to cooler and drier conditions,in-tensified agricultural activities resulted in enhanced soil erosion and nutrient fluxes,sustaining relatively stable algal productivity.During the 20th century,a combination of climatic warming,increased evaporation,and heightened anthropogenic disturbances-including groundwater over-extraction and exploitation of lake resources-led to considerable lake level decline and reduced algal productivity,signaling ecosystem degradation.This study reveals a nonlinear and phased ecosystem evolution in Lake Huangqihai under the combined influences of climate change and human activities,underscoring the critical role of land use,groundwater man-agement,and hydrological processes in regulating the stability of lake ecosystems in arid and semi-arid regions.These insights offer a scientific foundation for ecosystem restoration and adaptive water resource management in similar environments.