Abstract
Important land‐use changes and intense human impacts often accompany economic development. In many Mediterranean countries, especially in the coastal areas, tourist activities have taken the place of forestry and agriculture. Population pressure has increased and with it problems of fresh‐water availability and waste disposal have arisen. Streams draining the Catalan Coastal Ranges illustrate the impacts of these changing land uses on water quality in formerly rural areas.
Research was undertaken on the downstream changes in surface‐water quality in the Ridaura basin, a typical Mediterranean coastal torrent. The data show a clear downstream increase of suspended and solute loads related to land uses. The middle and lower reaches under agricultural and urban land uses exhibited a marked increase in nearly all chemical components, mainly calcium, chlorides, sulfates and calcium carbonate, and an increase in suspended sediment. The impact of heavy anthropogenic influences was also apparent. In the upper reaches, a waste disposal site strongly influences the dissolved load, although downstream dilution mitigates its effect. In the lower reaches which are under urban influence, there is a notable increase in conductivity, especially downstream of a water treatment plant, where values of more than 1000 μS cm^−1^ were observed (above the maximum allowed), together with a decrease in dissolved oxygen (often less than the recommended limits). Ammonia, phosphates, sulphates chlorides and nitrates increase their value downstream, and sometimes reach levels surpassing the recommended maxima. It is interesting to note that, for the local people, superficial pollution by rubbish from a waste dump was felt to be more important than serious chemical pollution from the sewage treatment plant effluent. The subterranean flux was also sampled in several wells, and the chemical composition of their waters also show higher concentrations of solutes downstream with values of the limit of the maximum accepted levels. Copyright © 2004 John Wiley & Sons, Ltd.