Macroinvertebrados da lavoura de arroz irrigado tratada com os agrotóxicos Carbofuran e Penoxsulam

Abstract

The rice cultivation (Oryza sativa) has been target of speculations because of its effects in the environment. The intensive pesticides uses in the ricefields have contributed in a meaningful manner to many things related to this crop. The purpose of this study was to compare the benthic macroinvertebrates community in an irrigated rice farm treated with pesticides Carbofuran (insecticide) and Penoxsulam (herbicide) comparing to a control farm. The experiment was accomplished in an experimental lowland area, from the Crop Science Departament of the Universidade Federal de Santa Maria, during the harvest 2008/2009. To a benthic fauna sampling, it was used a Corer sampler. It was accomplished five benthic macroinvertebrates sampling during the study, the delimitation was in blocks divided, by chance, with three repetitions, and the sampling happened in 3rd, 14th, 28th and 56th day after the water entrance in the system. Besides, it was accomplished the following determination: pH, temperature, dissolved oxygen and the pesticides persistence in the water. The analysed pesticides, the Penoxsulam herbicide showed the biggest water persistence, that was detected until the sampling day (56th day), without much oscillation in its concentration according to the studied period. Among the sampling organisms, Chironomidae was the dominant group in the three treatments. This way, the total individuals abundance in this study was confirmed by this family organisms, which didn t suffer a variation among the treatments during the sampling days (twoway- ANOVA). The analyses variance, which evaluated the total macroinvertebrates abundance and the taxon richness, detected interactions between the day sampling factors and the (two-way- ANOVA) treatments. The posterior test (Tukey HSD) showed the abundance in the community in the 8th day the sampling was different in parcels treated with Penoxsulam and Carbofuran. However, on the other samplings, the organisms total abundance was similar in the two treatments (Carbofuran, Penoxsulam and Control). The posterior taxons richness comparison showed that just in the 56th sampling day the macroinvertebrates richness in the controlled parcels was superior than in the parcels treated with Carbofuran insecticide. The Diversity Shannon level varied during the sampling days, but there wasn t a meaningful difference in the (two-way-ANOVA) treatment. The results indicated that the macroinvertebrates colonization process in the control areas didn t have a meaningful variation related to the areas treated with Penoxsulam Carbofuran, showing that the tested pesticides didn t affected the benthic fauna colonization, in the ricefields. On the other hand, it was verified a subtle diversity along to the successional process evaluated in this study (from the 3rd to the 56th day).