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Abstract

1. The Cerrado, a seasonal savanna vegetation, is one of the largest biomes in the Neotropics. Conversion of Cerrado into agroecosystems has caused severe alterations in the species composition, functioning and habitat structure of streams and rivers. 2. As a case study for the Cerrado, the environmental quality of stream-valley systems was investigated in the catchment of the Tenente Amaral River near the city of Jaciara, Mato Grosso, Brazil. 3. Interpreting a Landsat-7 image of the area, and using a rapid assessment protocol with airborne and field observations, 481 first-order streams were identified in the catchment area (875.36 km2), equivalent to an average of 0.55 springs per square kilometre. The total stream density was 0.83 km km-2. 4. Only the uppermost headwater zones of the streams were unimpaired (8.5% of the stream channels). The largest part of the studied stream sectors were moderately (59.3%) or strongly (32.2%) impaired. 5. The greatest impact was caused by erosion. Sediments released by gully erosion alone were calculated as 2.6 × 106 m3 of sediments in the upper zone of one tributary of the Tenente Amaral River. The sediments had deleterious effects on fauna and flora. 6. The highly erosion-prone stream valleys in the Cerrado require full protection. In the transition area between agroecosystems and hillslopes, buffer zones consisting of a replanted interfluvial Cerrado tree vegetation and a vegetated buffer strip should be planted. Apart from erosion protection, these strips can provide valuable income for the farmers through selling non-wood products. 7. The legal situation providing the baseline for the protection of the Cerrado streams is reviewed, including the efforts of the Brazilian states and collaboration of UNESCO. 8. We suggest that it is possible to transfer this management strategy to similar biomes in the seasonal tropics provided that the tree species lists are carefully adapted to the regional flora.