Diatom records and environmental changes over the past 200 years at Zhenbu Co Lake,southeastern Tibetan Plateau
Currently,most studies on the response of lake ecosystems on the Tibetan Plateau to climate warming over the past 200 years have focused on deep lakes,whereas studies on ecosystems characterized by many shallow lakes are scarce.In this paper,we selected the shallow lake Zhenbu Co on the southeastern Tibetan Plateau as the research object.Based on 210Pb and 137Cs dating of sediments and high-resolution diatom identification,the changes in the diatom assemblage over the past 200 years were reconstructed.Combined with total organic carbon(TOC),total nitrogen(TN)and carbon-nitrogen ratio(C/N)of the sediments,the response of the lake ecosystem to climate change was explored.The results showed that during 1820-1950 AD,the content of Encyonema lange-bertalotii in sediment was high,indicating the abundant aquatic plants and high lake-water transparency in Zhenbu Co.Since 1950 AD,the diatom assemblages shifted,decreasing rapidly in Encyonema lange-bertalotii content and increasing in small Fragilaria content,which indicated a decline of aquatic plants and decreased lake-water transparency.Meanwhile,the contents of TOC and TN increased,and the C/N decreased,which indicated that the productivity and nutrient level of the lake increased,and the percentage of algae in the lake organic matter increased.Rapidly rising temperature,increased precipitation(i.e.,more nutrients entering into the lake),and enhanced human activities(i.e.,the appearance of new temples in the watershed)may have jointly led to higher lake productivity and algal bloom content,as well as lower aquatic plant content and decreased water clarity.Eventually,the diatom assemblages abruptly shifted.Based on our results,shallow lakes may face ecosystem shifts in the context of climate warming and humidification on the Tibetan Plateau,and the monitoring and protection of such lakes should be strengthened in the future.The timeline of the abrupt shift of the plateau shallow lake ecosystem in this paper is basically consistent with that in China and other parts of the world,which also provides new evidence for determining the stratigraphic marker of the Anthropocene.Thus,the lakes of the Tibetan Plateau can serve as natural laboratories for studying the Anthropocene.
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