Variance analysis and comparison of trophic state indexes: Rio Bonito and Suíça power plants reservoirs

ABSTRACT Reservoirs have been built worldwide to regularize flows for improvement of watersheds water resources use conditions for different purposes, such as human and industrial supply, irrigation and power generation. Waters of rivers and streams that carry excessive nutrients from sewage and fertilizers, when dammed, may be subject to significant qualitative changes resulting from eutrophication processes. Several indexes have been created by researchers for trophic state classification of water bodies. In this study three trophic state indexes (TSIs), developed by Carlson (1977), Lamparelli (2004) and Cunha, Calijuri and Lamparelli (2013), were analyzed and compared, through the application to two power plant reservoirs, denominated Rio Bonito and Suíça, located in the Santa Maria da Vitoria river watershed, Espírito Santo state, Brazil. Results from 20 water quality monitoring campaigns were considered, conducted between October 2008 and July 2014. The reservoirs receive nutrient loads originated from domestic sewage, agricultural crops and chicken farms. It was concluded that application of different models may result in very different trophic state class definition. The application of the Carlson model (1977), developed for temperate climate reservoirs, resulted into higher eutrophic class level, classifying the reservoirs mainly as eutrophic and mesotrophic. Lamparelli (2004) and Cunha, Calijuri and Lamparelli (2013) models, developed for tropical/subtropical climate reservoirs, presented closer results, classifying the reservoirs mostly as oligotrophic. It was also concluded that seasonality and rainfall in reservoirs catchment areas may influence very significantly the reservoirs water quality parameters and trophic state classification. The wide variety of trophic classes chosen for the reservoirs, in this work, indicates the importance of the proper choice of models and indexes, according to the prevailing conditions in the water bodies of interest.

摘要 全球范围内已兴建水库以调节径流，优化流域水资源的多用途利用条件，涵盖生活与工业供水、农业灌溉及水力发电等场景。携带生活污水与化肥中过量营养物质的河川径流，在被大坝截留后，可能因富营养化过程发生显著的水质变化。研究者已开发出多种用于水体营养状态分类的指标。本研究针对由Carlson（1977）、Lamparelli（2004）以及Cunha、Calijuri与Lamparelli（2013）提出的3种营养状态指数（Trophic State Indexes, TSIs）展开分析与对比，将其应用于巴西圣埃斯皮里图州圣玛丽亚达维多利亚河流域内的两座水电站水库——里约博尼图（Rio Bonito）与苏伊萨（Suíça）水库。本研究采用了2008年10月至2014年7月期间开展的20次水质监测作业数据。上述两座水库承接源自生活污水、农作物种植与养鸡场的营养盐负荷。研究结果表明，采用不同模型可能得到差异显著的营养状态等级划分结果。针对温带气候水库开发的Carlson（1977）模型，其应用结果指向更高的富营养化等级，主要将两座水库归类为富营养型与中营养型。针对热带/亚热带气候水库开发的Lamparelli（2004）与Cunha、Calijuri及Lamparelli（2013）模型，所得结果更为接近，主要将水库归类为贫营养型。此外研究还发现，水库汇水区的季节变化与降雨条件，可对水库水质参数及营养状态分类产生极为显著的影响。本研究中针对两座水库得到的营养等级划分差异显著，这表明需根据目标水体的实际环境特征，合理选择对应的模型与指标。