Luana Gallo

Environmental analysis of a regulated Mediterranean stream based on epilithic diatom communities – the Crati River case (southern Italy)

A regulated Mediterranean watercourse, the Crati River (Calabria, southern Italy) was studied during two different seasons. Benthic diatom samples were collected from eight stations. The environmental analysis of the Crati River was carried out using two diatom indices, one designed for the evaluation of water quality (EPI-D: Eutrophication Pollution Index – Diatom based), the other aimed at assessing physical disturbance on the basis of the proportion of motile species in the community, the Quantitative Navicula Nitzschia Surirella (QNNS) index. Within this group of algae the ratio between abundances of heterotrophs and autotrophs (NH:NA(NNS)) was also calculated as an estimate of water column turbidity. The biological quality of the river was assessed by comparing the EPI-D results with those of an assessment method based on macroinvertebrates (EBI: Extended Biotic Index). Chemical monitoring was adopted to evaluate both environmental quality and the sinking effect due to the Tarsia reservoir. The results suggest that both diatom and macro-invertebrate indices show a progressive increase of environmental impairment along the river, but EPI-D detects the strongest alterations, presumably due to an appreciable enrichment in nutrient concentrations and a moderate increase in organic load. The abatement of suspended solids and nutrient concentrations downstream from the Tarsia reservoir in July and their successive increase in November, when the barrage is opened, was registered mainly by variations of the QNNS and EPI-D and, secondarily, by a change in the NH:NA(NNS) ratio.