SELF-PURIFICATION PROCESSES ALONG A MEDIUM-SIZED STREAM

Water quality levels and loads of nutrients transported by the Aguera stream (northern Spain) were studied for a year to assess the self-pur ification capacity of this system, The main villages produce an increa se of nutrient concentrations and a degradation of water quality. Neve rtheless, the high retention capacity, especially for phosphate, allow s the stream to recover its previous levels of quality after a short r each. The retention of nutrients depends on a complex combination of t he flow level, hydrologic stability and the development of periphytic communities.