Environmental evolution and driving factors of Woniu Lake in the Da Hinggan Mountains in 1848-2019
Over the past 2 centuries,the lakes of the Northeast Plain and mountainous regions have been sub-jected to the dual impacts of climate change and human activities,leading to a series of ecological degradation issues.Understanding the historical evolution and driving mechanisms of lake ecological environments is cru-cial for the restoration of lake ecosystems in the future.However,there is a research gap in the reconstruction of the ecological environment of modem lakes in Northeast China.To address this,we utilize sediment n-al-kanes,grain size,total organic carbon(TOC),total nitrogen(TN),and carbon-to-nitrogen ratio(C/N)to invest-igate the evolutionary patterns of Woniu Lake over the past 200 years based on 210Pb and 137Cs dating.By integ-rating modem monitoring data and historical records of the basin,we further evaluate the driving factors be-hind various environmental pressures on the lake's evolution.The results showed that the environmental evolu-tion of Woniu Lake is broadly consistent with regional socio-economic transitions.Prior the 1940s,Woniu Lake was in a natural evolutionary phase with low and stable productivity,and its organic matter was primarily derived from external sources.Aquatic plant biomass was low,and the lake was in a relatively weak hydro-dynamic conditions.The watershed environment was stable,with forest coverage dominant and minimal hu-man impact.However,from the 1940s to the 1990s,human activities such as agricultural irrigation and defor-estation exacerbated the decline in lake water levels and the input of external nutrients,resulting in elevated primary productivity and enhanced contributions from autochthonous organic matter,with organic matter in-puts mainly from large aquatic plants.This led to a degradation of the lake's ecological environment,but without any significant state changes.After the 1990s,the algal productivity indicated by short-chain n-alkanes of Woniu Lake sharply increased due to the rapid development of modem industry and urbanization in the basin,leading to a transition to eutrophication.Redundancy analysis and variation partitioning analyses showed that nutrient factors played a key role in influencing the ecological evolution of Woniu Lake,independently ac-counting for 30.3％of the variance,alongside climate factors and watershed erosion from the 1950s to the 2020s.Since the 1990s,human activity factors became predominant over natural environmental factors and,in interaction with nutrient factors,became the main control of the short-term organic matter sources in Woniu Lake.The significant enhancement of human interference has led to the lake's transition to eutrophication un-der the combined stress of multiple pressures.
Aershan Areathe Da Hinggan Mountainslake ecological environment evolutionn-alkanesNortheast ChinaWoniu Lake
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