Spatiotemporal characteristics of layered chlorophyll-<i>a</i> concentration and influencing factors in Danjiangkou Reservoir

Abstract

2017年5月-2019年10月，对南水北调中线水源水库——丹江口水库库区水体7个监测位点、0~20 m间4个水层的垂向叶绿素a（Chl.a）浓度与水质因子进行了季度性调查，以期了解不同位点、不同水层Chl.a分布的主要驱动因子.结果表明，丹江口水库各位点营养状态指数（TSI）均为中营养化状态.水体Chl.a浓度具有逐年增加的趋势，且极高值有逐渐增加的趋势.营养盐和Chl.a浓度均存在较大的空间异质性，入库区具有较高的总磷和氨氮浓度，汉江库区具有最高的Chl.a浓度，源头污染源控制和监测仍然是丹江口水库管理的重中之重.不同位点Chl.a浓度的驱动因子存在较大差异，汉江入库和大坝区Chl.a浓度分别受到硝态氮和pH的影响，而出水口大坝位点主要受到了水深、水温和氨氮的影响.丹江入库区Chl.a浓度受到了水深、氨氮、总磷和水温的影响，但丹江库区表现出了与其他生态区较大的区别，其Chl.a浓度主要受到水深和有机质输入的影响.因此，对丹江口水库各位点的管理，应该分不同生态区采取针对性的管理措施.本研究旨在为南水北调中线工程可持续的生态调度提供基础生态数据支持，为完善水库水源地的有效管理提供理论支撑.;The study was carried out at 4 vertical water layers among the 0-20 m water layer of 7 horizontal monitoring stations seasonally during May 2017-October 2019 in Danjiangkou Reservoir of the Middle Route Project of South to North Water Diversion in China, and explored the key drivers of the changes in chlorophyll-a (Chl.a) along with different water layers of different sampling stations. Based on the trophic state index (TSI), we found that all sites in the Danjiangkou Reservoir were mesotrophic water bodies. We found a trend of increase in Chl.a concentration in the Danjiangkou Reservoir, and the extreme concentrations were likely increasing yearly. The nutrient and Chl.a concentration showed temporal and spatial changes in the Danjiangkou Reservoir. The upstream of the reservoir area has higher total phosphorus and ammonia nitrogen concentrations, the Hanjiang Reservoir has the highest Chl.a concentration. Therefore, source pollution control and monitoring are still the top priority of Danjiangkou Reservoir management. The important drivers of Chl.a concentration varied among different sites. The Chl.a concentration in the upstream of Hanjiang River and the dam area are affected by nitrate nitrogen and pH, respectively, while the dam site of the outlet is mainly affected by water depth, water temperature and ammonia nitrogen. The Chl.a concentration in the upstream of Danjiang Reservoir is affected by water depth, nitrogen nutrients, total phosphorus and water temperature, but the Chl.a concentration in the Danjiangkou Reservoir was mainly affected by water depth and organic matter input. Therefore, the management of each site of the Danjiangkou Reservoir should be divided into different ecological zones and adopt the right management measurements. This study aims to provide basic ecological data for the sustainable ecological scheduling of the South-to-North Water Diversion Middle Route Project and provide a theory for improving the management of reservoirs.