The macroinvertebrates have been used as indicators of environmental quality. The objective of this study was to compare the quality of water which drains from the rice flooded crop (drainage water) with the irrigation water, sourced from Gravataí River, near the Porto Alegre City, using benthonic macroinvertebrate community as bioindicator. This study was carryout at the Rice Experiment Station of IRGA, in Cachoeirinha (RS), during the 2006/2007 harvest. A layer of 5cm soil, containing benthonic macroinvertebrate was sampled, using a Corer (78.54cm²), at the irrigation source (Gravatai River and Irrigation Channel) and at the effluents receptor (Drainage Channel). Oxygen dissolved (O2) in water also was registered in each point. The sampled material was filtered in a mesh sieve with f 0.5mm and fixed. The macroinvertebrates were identified and the ecologic parameters as abundance, richness, diversity and evenness were evaluated and compared among the sample points. Such ecologic parameters showed a more complex and structured community at the drainage channel, than at irrigation channel, and at Gravatai River, indicating that the environmental features is better in the point which received the water that pass through the crop, than at the irrigation points. Therefore, the benthic macroinvertebrate community in this study suggests that effects generated by cities and industries of Porto Alegre region are more aggressive to aquatic environments than that promoted by rice crop managed according to the technical guidelines.
rice flooded crop; urbanization; environmental impact; bio-monitoring; benthic macroinvertebrates