洞庭湖出口径流变化及对生态系统的影响

为了阐明洞庭湖出口径流变化及生态效应，根据城陵矶1960~2016年的日径流量数据，采用生态盈余和生态赤字两个生态径流指标，分别从年和季节尺度分析了洞庭湖出口径流变化，并讨论了其对洞庭湖生态系统的影响。研究结果表明：年生态盈余和年生态赤字的变化范围分别为0~0.39和0~0.47，且年生态赤字比年生态盈余的波动更加剧烈和频繁；季节生态径流指标差异较大，春季和冬季生态盈余波动比较频繁，夏季和秋季生态盈余变化不大；除冬季外，春季、夏季和秋季生态赤字在水文变异后呈明显上升趋势，且高于生态盈余；季节生态变化总值整体呈上升趋势，且在水文变异后更加离散，表明生态系统受到了较大的扰动。气候变化和人类活动是导致径流变异的主要影响因素。降水对生态赤字的影响较大；人类活动导致了高流量减少、低流量增加，使季节生态径流指标发生较大改变。径流变化与生态系统关系的基本准则表明，洞庭湖出口径流与生态系统具有紧密的联系，且径流改变对生态系统产生了负面影响。

Changes in Streamflow at the Outlet of Dongting Lake and Their Impacts on Ecosystems

Based on the daily streamflow data of Chenglingji station from 1960 to 2016, two eco-flow metrics, ecosurplus and ecodeficit, were used to evaluate the changes in streamflow and their related ecological effects at the outlet of Dongting Lake. Both annual and seasonal eco-flow metrics were analyzed and the ecosystem influences were also discussed. The results indicated that the average annual ecosurplus and ecodeficit fell in the range of 0-0.39 and 0-0.47, respectively, and the annual ecodeficit had a more frequent fluctuation than the annual ecosurplus. Changes of seasonal eco-flow metrics differed greatly. Ecosurplus had frequent fluctuations in spring and winter, while had no significant fluctuations in summer and autumn. Seasonal ecodeficit showed an increased trend in all seasons except for winter, and were higher than the values of seasonal ecosurplus. The total seasonal ecochange increased during the whole period, and became more discrete during the post-impact period, which indicated a severely disturbance on the ecosystem. Climate change and human activities are two main factors of the eco-flow alteration at the outlet of Dongting Lake. Furthermore, precipitation had greater impact on ecodeficit. Human activities may lead to a large alteration of seasonal eco-flow metrics, through reducing high flow and increasing low flow. According to the four basic principles of flow regimes and ecosystems, Streamflow of Dongting Lake outlet had a close relationship with the ecosystems, and streamflow alteration had negative impacts on the ecosystems.