Spatio-temporal dynamics of surface water quality of two large reservoirs of Brazilian hydroelectric plants

ABSTRACT The use of water resources for energy generation, generally, involves the design of artificial dams and reservoirs. The construction of reservoirs may be associated with socio-environmental impacts. The use of statistical techniques and indexes to assess surface water quality data has been an efficient tool for understanding the spatial dynamics of these environments. The work aimed to evaluate the water quality in two large reservoirs and their main tributaries, the Emborcação and Nova Ponte hydroelectric power plants in Minas Gerais. Secondary data were evaluated using the Multivariate Statistical Technique of Cluster Analysis (CA), followed by non-parametric tests, also the Environment Water Quality Index (WQI) and the Trophic State Index (TSI). To support the discussion of the results, the types of land use and occupation in the study area were also analyzed. The results of the CA indicated the separation of the monitoring sites of each reservoir into groups, according to their locations and the type of environment in which they are inserted. The results of the statistical tests suggested a better water quality in the groups formed by stations located in the reservoir and close to it, which have been confirmed by WQI. The results of the WQI indicated the adequacy of the quality of these waters, in relation to the proposed uses for class 2 framing. About the TSI, there was the presence of intermediate primary productivity at acceptable levels. The predominance of land use for agriculture can partially justify the degradation conditions of the water quality watercourses’, especially about the parameters associated with solids and nutrients.

摘要 水资源用于发电领域时，通常涉及人工拦河坝与水库的设计营建。水库建设往往伴随一系列社会与环境影响。借助统计技术与指标评估地表水水质数据，已成为解析此类水环境空间动态特征的高效手段。本研究旨在评估米纳斯吉拉斯州恩博尔卡桑水电站与新蓬特水电站配套的两座大型水库及其主要支流的水质状况。本研究采用聚类分析（Cluster Analysis, CA）这一多变量统计技术对二手数据进行分析，后续辅以非参数检验，同时运用水环境质量指数（Environment Water Quality Index, WQI）与营养状态指数（Trophic State Index, TSI）开展评估。为辅助结果讨论，本研究同时对研究区域内的土地利用与覆被类型进行了分析。聚类分析结果显示，两座水库的监测点位可依据其所处地理位置与嵌入的环境类型划分为不同群组。统计检验结果表明，位于水库库区及紧邻库区的监测站点所构成的群组水质更佳，这一结论得到了水环境质量指数评估结果的验证。水环境质量指数评估结果显示，上述水体的水质满足二类水体的预设使用功能要求。营养状态指数结果表明，研究区域水体处于中等初级生产力水平，且处于可接受范围之内。研究区域内农业用地占主导的土地利用格局，可部分解释河道水质出现退化的原因，尤其是与固体悬浮物及营养盐相关的水质参数出现异常。