Lago Bidighinzu - Italy

Bidighinzu Lake is a warm monomitic and hypereutrophic reservoir located in northwestern Sardinia at 334 m a.s.l. Built in 1956, it is mainly used for drinking water for a population of about 160,000 users. Bidighinzu Lake covers a surface area of 1.7 × 10⁶ m² and has a maximum volume of 12.2×10⁶ m³ and a mean depth of 7.3 m. According to ECOSTAT, it belongs to the LM7 category (altitudes <800 m a.s.l., mean depths >15 m, conductivity <2.5 mS cm−1). Its watershed has a surface area of 52 km² with a geological substrate consisting of basalt, limestone, and shale. The supplies of water from the catchment to the lake are insufficient to make up for the losses and human demands. Consequently, the lake receives additional water from Temo Lake and Rio Mannu-Su Tulis river lock, localized in different watersheds. Problems of potabilization have arisen since the early years of the reservoir’s use, particularly in summer-autumn, because of hypolimnic deoxygenation and the excessive presence of algae in the epilimnion. To face this situation, different restoration actions were carried out in Bidighinzu Lake. Among the most important: the installation in 1966 of an aeration system in the area around the water intake tower and in 1987 the reduction of nutrient loads from the watershed by the diversion of civil and industrial wastewater downstream of the dam. A comparison among data collected from just before to about 10 years after this last action the site did not show any improvement in the trophic status. Since 2006, the lake is managed by the Sardinia Water Authority (ENAS) and is part of LTER-Italy. The site has real-time remote monitoring station equipped with a multiparameter probe housed on floating platform. The main scientific purposes at present concern the relationships between trophic status, abundance of cyanobacteria and the presence of toxins; the assessment of climate change and local factors on the phytoplankton dynamics; the development of territorial indicators related to the trophic conditions based on the land cover and use of catchment areas. Recently in Lake Bidighinzu it was conducted an experimental activity, with an aeration system with micro-bubbles. The aim was to maintain sufficient oxygen in the hypolimnetic waters, especially in the summer months, in order to improve the purification process, prevent phosphorus release from sediments and mitigate eutrophication. Available data sets include information on phytoplankton and limnological variables since the last 70.