富营养化驱动下西凉湖百年来生态系统演化轨迹

长江中下游浅水湖泊是区域社会可持续发展的重要自然资源,富营养化问题致使该地区湖泊发生草-藻转换,限制了湖泊生态系统服务的供给.湖泊环境问题是生态系统受外力长期胁迫的结果,湖泊生态治理与保护须充分了解系统的演化规律,但是相关认识受限于长期监测资料的缺失.为了厘清长江中下游地区典型草型湖泊生态系统演化轨迹,更有效管理受损湖泊,选择西凉湖为研究对象,利用沉积记录代用指标粒度、元素和硅藻等,在高分辨率放射性核素定年的基础上,分析了近150年来西凉湖生态系统的演变规律.结果表明,西凉湖在20世纪40年代之前水体清澈,营养水平较低,沉水植物相对较少;而20世纪40年代以后,人类活动逐渐增强导致湖泊营养水平升高,水生植被增多;硅藻群落结构逐渐由浮游硅藻组合向底栖和附生硅藻组合演替,同时沉积物营养不断增加,表明以流域土地利用方式改变、围垦和渔业养殖等为代表的人类活动深刻改变了湖泊生态系统结构.研究认为虽然湖泊营养在20世纪70代之后一直维持在较高水平,达到富营养化标准,但沉水植被的生长限制了湖泊藻类浓度,西凉湖并未藻类暴发.同时也发现外源营养的增加通过湖泊初级生产者深刻影响了湖泊的地球化学循环,造成了...

Ecosystem Evolutionary Trajectory of Lake Xiliang over the Past Century Driven by Eutrophication

Shallow lakes in the middle and lower reaches of the Yangtze River are important natural resources for the regional sustainability. Eutrophication has transformed many lakes in this region from a clear macrophyte-dominated state to a turbid phytoplankton-dominated state, limiting the supply of lake ecosystem services. Environmental deterioration of these lake ecosystems was the result of long-term pressures from external forces. A full understanding of the lake evolution is the prerequisite for ecological management and protection, but the relevant understanding is limited by the lack of long-term monitoring data. Lake Xiliang was thus selected to clarify the evolutionary trajectory of typical macrophyte-dominated lake ecosystems in the middle and lower reaches of the Yangtze River and better govern lakes in this region. Based on high-resolution radionuclide dating, the evolutionary patterns over the past 150 years of Lake Xiliang were analyzed using sedimentary proxies such as grain size, chemical elements, and diatoms. The results showed that before the 1940s, Lake Xiliang was clear with a low nutrient level and relatively fewer submerged plants. Conversely, after the 1940s, human activities gradually increased and led to the higher nutrient level and higher coverage of macrophytes; the diatom composition gradually evolved from planktonic-dominated assemblages to benthic- and epiphytic-dominated ones, and the nutrient level of sediment also kept increasing, indicating that human activities represented by land use changes in the watershed, polder, and fish farming have profoundly changed the ecosystem structure of the lake. The study showed that although lake nutrients have been maintained at a high level after the 1970s and became eutrophic, the growth of submerged vegetation limited the concentration of algae in the lake and prevented an algae outbreak in Lake Xiliang. It was also found that the increase in exogenous nutrients profoundly affected the geochemical cycle of the lake through primary producers, causing the accumulation of sediment calcium carbonate. This process showed that the succession of submerged plants driven by eutrophication affected the nutrient geochemical cycle of Lake Xiliang, which may increase the risk of endogenous release. The evolutionary processes of a typical macrophyte-dominated lake in the middle and lower reaches of the Yangtze River was thus clarified, and the ecological risks faced by this type of lake under long-term human activities and climate change were also assessed, providing a scientific basis for the management of regional lakes.