Development of a multimetric index based on aquatic macroinvertebrate communities to assess water quality of rice fields in southern Brazil

In the last decade, dozens of indices based on macroinvertebrates were developed to evaluate lotic ecosystems. In contrast, very few of these indices have been applied in lentic ecosystems. Natural wetlands in southern Brazil are increasingly threatened by the expansion of irrigated rice. The main objective of this study was to develop a multimetric index based on macroinvertebrates to evaluate the water quality of natural wetlands and rice fields in southern Brazil. Three samplings were carried out over the rice growth cycle in four conventional and four biodynamic rice fields, and four natural wetlands. The wetlands were considered as reference sites, and the conventional and biodynamic rice crops were considered as manipulated sites at different levels of degradation. Seven metrics were included in the final index after passing though sensitivity and correlation tests. The results indicated that our index has a power to detect a gradient of variation in water quality. Natural wetlands had the best water quality, biodynamic crops had intermediate water quality, and the conventional crops had the lowest water quality. We believe that development of this macroinvertebrate-based multimetric index of water quality could be an important tool for monitoring natural wetlands and rice crops in southern Brazil.