Podem as lavouras de arroz auxiliarem na conservação de macroinvertebrados aquáticos do sul do Brasil? : unindo o sistema produtivo com conservação da biodiversidade

Abstract

Wetlands are prioritary ecosystems for conservation due to their vast biological diversity and productivity, besides their many functions and value. In southern Brazil conservative data show that about 90% of the original wetlands are already destroyed due to agricultural expansion, mainly the irrigated rice fields. On the other hand, rice is the most important cereal grown in developing countries, being the main food source for more than half of the world population. Also, a high diversity of plants and animals has been found in these agricultural areas. The main goal of this study was to assess the structure and diversity of macroinvertebrates in rice fields with different rice cultivation systems (organic and conventional) and ages (3, 10 and 20 years) over the different hydrological phases of the cultivation cycle in an important rice cultivation area in Rio Grande do Sul to preserve the biota in these agroecosystems. Sampling was conducted over two cultivation cycles (August 2010 to June 2012) in 17 rice fields and eight natural wetlands in the coastal plain of Rio Grande do Sul. Qualitative samples were obtained using a dip net. The samples were collected by kicking up the substrate and then sweeping above the disturbed area to capture dislodged or escaping macroinvertebrates. Five random sweeps of 1 m each were performed in each area. The main results were: sampling resulted in a total of 37,035 individuals in 82 taxa of macroinvertebrates collected in rice fields and natural wetlands; organic agriculture negatively affects aquatic macroinvertebrate community as much as conventional, even in functional terms and the first years of cultivation of rice crops are the most impactful for the community of aquatic macroinvertebrates. These results can be used in management plans which aim at reconciling agricultural production and biodiversity conservation in Rio Grande do Sul.