Climate change represents one of the major challenges of our century with great potential to alter water quality, and hence, find suitable solutions becomes a must. Stanca–Costesti reservoir is one of the most important in Romania and one of the most affected by the hydrologic variability. The studies regarding the trophic state of this reservoir are few, even if there are some environmental issues in its hydrological basin that could be further investigated. According to the National Administration “Apele Romane” (ANAR) yearly reports, the Stanca–Costesti reservoir is, from the trophic state point of view, an oligotrophic lake. The current research is based on chemical and some biological data collected over 10 years (ANAR) for the trophic state of the Stanca–Costesti reservoir, using the Carlson index. The research investigates the hydrological data and spans over 10 years that were classified into three categories, namely: wet year, normal year, and dry year and the influences generated by the contrasting weather (flow and temperature changes) on the trophic state of the lake. The research findings show that the trophic state of the lake is directly influenced by the hydrological variability, namely evolving to a hypertrophic status due to concentrations of nutrients. Moreover, over the years, according to ANAR data, the water quality in the reservoir alternated. Hence, at times, the quality of the water was poor, with possible negative influences on water usage. As a consequence, we proposed that the water quality be verified monthly, and this should be done by means of a more reliable method, such as a multiparameter index or multicriteria analysis.

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Global existence of a large percentage of lakes with eutrophication problems (54% in Romania) demands a predictive tool for the quality of these ecosystems. In this context, this paper proposes an eutrophication model that describes the thermal and biochemical behaviour of an eutrophic reservoir. This model was used to study an artificial lake (Goleşti reservoir) located in Romania. The conceptual model concerns a lake, which is considered as a closed aquatic system, and analyze a simply food web (nutrients, primary producers and secondary consumers). The model, calibrated and validated using the data collected over the two years (2008 and 2009), reproduces spatial and temporal concentration distribution of water quality constituents.

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In this paper, for 24 SHPPs with significant installed capacity, between 676 and 6430 kW, totalizing almost 76 MW, with installed flows between 1.3 and 80 m3/s, the energy production is evaluated without and with an ecological flow representing 35 to 4.6 % from the mean flow in SHPP intake cross section. The energy loss is evaluated and there are presented some conclusions and assumptions regarding the way to impose an increased ecological flow without affecting too much the green energy produced in SHPPs.