全球变暖对青藏高原不同补给类型湖泊生产力的影响

Impact of global warming on lake productivity in different lakes on the Qinghai-Xizang Plateau

研究以青藏高原阿翁错和托素湖湖泊沉积物为研究对象,通过多指标(总有机碳含量、有机碳同位素和有机碳埋藏速率等)综合分析,重建不同补给类型湖泊的生产力变化及碳循环过程。结果显示:全球变暖对不同类型湖泊的生产力的影响存在显著差异。在以降水和冰川融水为主要补给源的阿翁错,全球变暖造成冰川融水补给增加。当指示冰川融水补给量变化的δ^(18)O_(carb)值逐渐偏负时,湖泊沉积物TOC含量逐渐升高;指示冰川融水输入造成湖泊面积持续扩张,营养物质增加,湖泊生产力提高;当湖泊面积扩张较快,即冰川融水在短时间内快速输入时,TOC含量下降,可能是由于当冰川融水输入过多,造成湖水温度下降过快时,底栖藻类生产力下降,进而湖泊固碳能力下降。对于受人类活动影响的托素湖,全球变暖对湖泊水文过程及生产力的影响较小,δ^(18)O_(carb)值变化主要受控于农业灌溉活动引起的湖泊补给水量的变化。当δ^(18)O_(carb)值升高时,TOC含量增加;推测是由于农业灌溉耗水量增加导致湖泊补给水量减少,湖泊水位下降,湖泊底部接收到更多光照,湖泊生产力上升,固碳能力随之上升。

Understanding the relationship between climate change and the lake ecosystem variations is crucial for studying the impact of global warming on the lake carbon cycling process.However,less is known of how lake ecosystem variations responding to the global warming in different lakes on the Qinghai-Xizang Plateau(TP)where thousands of lakes distributed.Here we present comparison researches from Aweng Co(81°37′48″E~81°48′00″E,32°42′00″N~32°48′36″N,4430 m a.s.l.)and Toson Lake(96°50′00″E~97°03′00″E,37°04′00″N~37°13′00″N,2808 m),they are closed lakes with different hydrological process.Aweng Co(pH is 9.2,salinity is 29.5 g/L)is mainly supplied by glacier melt water via groundwater and precipitation.And Toson Lake(pH is 8.4,salinity is 35.7 g/L)is at the end of Bayin River drainage basin,and it is fed by precipitation and the flowing from Herleg Lake.There are villages and farmland in the upstream of the Toson Lake.Two sediment cores were drilled from the lake center in Aweng Co and Toson Lake,they were AWC2015(445 cm)and TSL17G(55 cm),respectively.The top sediment of AWC2015 and TSL17G were measured by 210Pb and 137Cs.We focused on the lake carbon cycling process in the two lakes in recent 100 years.Multi-proxy including organic carbon isotope,total organic carbon content and organic carbon accumulation rate were measured to reconstruct the lake productivities and carbon burial rates in two lakes.Results showed that global warming had different impacts on the photosynthetic process in different lakes depending on the lake level,actual temperature and sunlight at the lake bottom.In Aweng Co,when the values ofδ^(18)O_(carb) tended to be negative,and TOC content increased,indicating that more glacier melt water supplied the lake,resulting in expanding of the lake area,more nutrient supplying the lake,and improving of the lake productivity consequently.However,when plenty of glacier melt water flowed into the lake in short time and the water temperature decreased rapidly,slowing down the photosynthetic process and resulting in decreased carbon burial rate consequently.In the human-disturbed lake,the variations ofδ^(18)O_(carb) and TOC content indicated that human activity played more important roles in driving aquatic biomass by influencing sunlight at the lake bottom via lake level change.With the increasing of water consumption for agriculture,the water that finally supplied the lake would decrease,and resulted in lower lake level and more light reaching the lake bottom,favoring the growth of the benthic algae,and the organic carbon burial rate increased finally,and vice versa.Therefore,global warming had different impacts on the carbon cycling process in lakes with different hydrological process.