Intermountain basins use in subtropical regions and their influences on benthic fauna

Conversion of high mountain forests into pastures or croplands and changes in land uses have produced changes in hydrology, vegetation cover and terrestrial aquatic linkages, resulting in increased nutrient loads on water bodies. The developing countries today need to obtain an indicator response signature under multiple stressor scenario, to identify causes of water bodies impairment. Intermountain land use impact on a Subtropical Andean River was studied in Tucumán province, Northwestern Argentina. Benthic macroinvertebrates were used as indicators of diffuse alterations produced by anthropic activities on a small valley at ca. 1000 m.a.s.l. The objectives were: (a) test the effect of land use on macroinvertebrate assemblages; (b) test the response of benthic fauna to diffuse organic pollution and (c) test the accuracy of the current biological water quality indices. Nutrient levels were higher than international standards. First axis in multivariate analysis shows an important upstream–downstream gradient meanwhile the second axis shows seasonal effects. These effects are specially produced by monsoonal regime of rainfall (ca. 80% in summer). No effect of the land use or diffuse pollution was detected on the macroinvertebrate assemblage structure, probably due to the good oxygen availability. Of the several biotic indices (BI) and metrics tested, only one worked on acceptable levels being ‘affected’ by small oxygen variations. Dry winter, dry and warm spring with high sunlight exposure plus high levels of nutrients could be an undesirable combination for standing waters of a reservoir projected in this watershed. A correct monitoring of water quality and alternatives as management of reforested margins is the right beginning. These actions and more studies represent interesting alternatives for poor regions of undeveloped countries. Copyright © 2008 John Wiley & Sons, Ltd.