Diatom communities as indicators of environmental stress in the Guadiamar River, S-W. Spain, following a major mine tailings spill

An accident in a mine tailings dam caused the outflow of mud and water rich in heavy metals in April 1998 that flooded the Guadiamar River and its floodplain, in the vicinity of Donana National Park. The impact on the periphytic communities was evaluated by analyzing the evolution of the diatom communities after seven (November 1998) and fourteen months (June 1999) of the accident. The comparison between the reference and affected sites showed a shift from a diatom community dominated by Fragilaria construens, Achnanthes minutisssima and Amphora pediculus to another dominated by Nitzschia palea and Gomphonema parvulum. The values for Shannon-Wiener diversity strongly decreased in the affected area; changes between survey periods failed to show a marked recovery. However, evenness was slightly higher for the June 1999 period, suggesting a slight improvement in the diatom community. Diatom indices (IPS-IDG, Descy, CEE, Lange-Bertalot) were applied to the data. Values for these also showed a marked decrease in water quality at sites closest to the mine tailings spill, as well as a progressive recovery downstream. Correlation analyses between the diatom descriptors and the environmental variables confirmed that heavy metals in the water and sediment had a marked and lasting effect on the diatom communities of the Guadiamar. Other pollution events (e.g. 'alpechin' sewage) probably hindered recovery of the periphytic communities.