天目湖沙河水库水生态安全状况长期变化及影响因素

为构建更为合理的个性化水库水生态安全评价指标体系，以我国东南低山丘陵地区水源地型水库天目湖沙河水库为例，基于2010~2020年逐月水生态监测数据，分析了水库水生态安全状况长期变化特征及影响因素，提出了以满足沙河水库水生态服务功能为目标的生态安全评价方法.结果表明，季节上，夏秋季SD相对较低，而总磷（TP）、浮游植物叶绿素a（Chl-a）、高锰酸盐指数和蓝藻生物量（BM_c）相对较高；空间上，不同区域的水体透明度（SD）存在显著差异（P<0.05），多年均值呈现河流区 < 过渡区 < 湖泊区的现象，其他指标均呈现出河流区较过渡区和湖泊区高的现象；垂向上，5~9月随热分层出现，许多指标出现分层，其中异味物质2-甲基异莰醇（MIB）和Chl-a在水深4 m处出现最大值，硅藻生物量（BM_b）和BM_c最大值分别在水深2 m和0.5 m处出现.基于水生态指标的变化特征认识，应充分考虑水库水生态安全的时空差异性，将水生态安全风险较高的春夏季作为评价期，以Chl-a为核心指标，结合SD和MIB等指标，通过建立关键指标与其他指标的相关关系，构建了沙河水库水生态安全评价体系；评价结果表明，沙河水库10年来水生态安全状况整体优良，但年际波动较大，不同区域的得分差异大，对于存在热分层的区域应采取季节性分3层采样调查数据进行评估.本研究表明在湖库水生态安全管理中选取个性化方案监测评估的必要性；总磷偏高和藻类疯长引发的水体透明度下降和异味物质含量升高是影响亚热带地区水库生态服务功能的主要因素，年际间较大尺度的水文气象条件变化给水库水生态安全带来较大不确定性.

Long-term Changes and Drivers of Ecological Security in Shahe Reservoir, China

Monthly datasets of ecological indicators from 2010 to 2020 in Shahe Reservoir, Tianmuhu, China, were examined to reveal the long-term variations in water ecological security and its driving factors. The results of Secchi disk depth(SD) measurements revealed significantly spatial variation(P<0.05) within the reservoir. The highest SD was recorded in the downstream-linked reservoir, and the lowest SD was recorded in the upstream tributaries. In contrast, the values of other water ecological indicators were higher in the upstream tributaries than in the transition region and the downstream-linked reservoir area. In summer and autumn, the SD was low, while the concentrations of total phosphorous(TP), chlorophyll a(Chl-a), the permanganate index, and cyanobacterial biomass(BM_c) were high. During the thermal stratification period from May to September, the concentrations of 2-methylisoborneol(MIB) and Chl-a were highest at a depth of 4 m, while diatom biomass(BM_b) and BM_c reached their maximum at depths of 2 m and 0.5 m, respectively. Therefore, spatial and temporal variations should be fully considered when evaluating aquatic ecological security. Focusing on spring and summer, when the risk of water ecological security was high, Chl-a combined with SD and MIB along with their correlation with other water quality indexes, was used to evaluate and optimize the ecological security of Shahe Reservoir. The evaluation results showed that the aquatic ecological security of the reservoir was excellent over the last 10 years; however, annual fluctuations have been large and the evaluation scores were spatially variable. While seasonal sampling strategies focusing on three layers depths are economical and reliable for lake regions with thermal stratification, our results indicate that tailored monitoring may be required to determine the aquatic ecological security of lakes and reservoirs. In Shahe Reservoir, the decrease in the SD and the increase in MIB caused by high TP and algal blooms were the most important drivers of ecological service function in the reservoir. Furthermore, hydrometeorological factors may also play important roles in the aquatic ecological security of reservoirs.