El Nihuil Reservoir: Hydrochemical characteristics, aquatic macro and microflora and trophic state

Abstract

Both the physical chemical quality of the water and the primary plankton productivity and the presence of macrophytes are analyzed to assess the trophic status of the reservoir throughout its length and at different times of the year. To do this, electrical conductivity, total solids, anions and cations, among others, have been measured through quarterly sampling, as well as the content of chlorophyll a, phosphorus, nitrogen and Secchi transparency, all as established by the Standard Methods for the Examination of Water and Wastewater. Qualitative and quantitative analysis of phytoplankton has also been carried out, including biodiversity calculations and the estimation of the surface area occupied by macrophytes, as well as present submerged and aerial species. The results indicate calcium sulphated waters, with an average value of total solids around 1 g/L, with very low phytoplankton productivity in which diatoms predominate and a TN:TP ratio < 9, resulting in nitrogen limiting algal development. The trophic state indices (TSI) show a lake with oligotrophic waters in all its extension, even when the great development of macrophytes requires adequate measures for their control and better use of the lake for various purposes.