Effects of land use on water chemistry and macroinvertebrates rates in twostreams of the Piracicaba river basin, south-east Brazil

1. Several studies have shown that land use has a strong influence on river chemistry and its biotic components. Most of these studies focused on nitr ogen in temperate American and European catchments. Much less is known abou t the relationship between stream conditions and land use in tropical areas of developing countries. 2. Besides climate, there are three important differences between attribute s of temperate and tropical catchments: non-point sources are the dominant contributor of pollution in USA, whereas point source pollution is the most important in our study; use of fertilizer is much smaller in developing co untries, and the type of agriculture and management practices are distinct. 3. We test whether the chemical composition of streams and their macroinver tebrate communities can be related to land use. Accordingly, we compared th e variability of chemical composition and macroinvertebrate communities in the streams of two catchments (Pisca and Cabras) belonging to the same ecor egion, but having different types of land use. 4. The main land use in the Pisca catchment in 1993 was sugar cane (62%), f ollowed by pasture (22%) and urban centres (10%). In contrast, the main lan d use in the Cabras catchment was pasture (60%), followed by annual crops ( 13%) and forest (10%); urban centres occupied only 2% of the catchment. 5. In the Cabras catchment, most of the parameters correlated with a land u se index (LUI) (Fig. 2). However, only conductivity, major cations and majo r anions (with exception of sulfate) had a statistically significant correl ation coefficient. More than 90% of the variance was explained for these pa rameters. DIC, NO3 and richness of invertebrates (RI) also strongly correla ted with LUI (R-2 = 0.75), although these correlation coefficients were not significant. Total suspended solids (TSS) had a significant correlation wi th LUI (R-2 = 0.98), but, the correlation was inverse. In the Pisca catchme nt, conductivity, major cations (with exception of potassium), major anions , and DIC, DO, and DOC had a strong and statistically significant correlati on with LUI. Correlation coefficients were also high for respiration rate, although the correlation was not statistically significant.