The Impact of Herbicides on Benthic Organisms in Flooded Ricefields in Southern Brazil

Abstract

Agricultural production is always directly associated with the use of agrochemicals to control the harmful organisms that attack the crops and reduce the harvest. In spite of their benefits, the use of agrochemicals usually causes great problems, considering that these often-toxic chemicals are used in large quantities over large areas, and generally persist in the environment for some time (Prime et al., 2005). As a consequence of agrochemical application, water quality and aquatic biodiversity have been compromised due to the destructuring of the physical and chemical environment and alteration of the natural dynamics of the biological communities (Goulart & Callisto, 2003). According to Biggs et al. (2007), it is highly important to regulate the use of an agrochemical and its action against non-target organisms in the aquatic environment. However, specific data on the occurrence and population dynamics of aquatic organisms in agricultural areas are very limited. Studies by Mesleard et al. (2005) indicate that the use of herbicides, insecticides, and fertilizers can modify the feeding pattern and alter the development of animal communities present in rice fields, especially the invertebrates. Because they are sedentary organisms and have relatively short life cycles (compared to fish), benthic macroinvertebrates are considered good indicators of water quality. Due to their short life cycles, they express more rapidly the changes in the environment through changes in structure of their populations and communities (Rosemberg & Resh, 1993). Because they also have great biological diversity, they tend to exhibit a greater variability of responses to different kinds of environmental impacts (Rosemberg & Resh, 1993). Another aspect refers to adaptive strategies to environmental instabilities of the environment, in general, resilience and persistence. A resilient biota can rapidly recolonize areas disturbed by flooding; and a persistent biota demonstrates a good capacity to resist disturbances (Winterbotton et al., 1997). The use of herbicides can indirectly influence the zoobenthic community, since, as seen in experiments carried out by Moreby & Southway (1999), the use of selective herbicides against a species of weed is essential to conserve the invertebrates that feed on plants. The use of broad-spectrum herbicides risks negative effects on the food chain of these herbivores and thus causing an imbalance in the community.