Do Riparian Buffers Protect Stream Invertebrate Communities in South American Atlantic Forest Agricultural Areas?

Abstract

We investigated the influence and relative importance of insecticides and other agricultural stressors in determining variability in invertebrate communities in small streams in intensive soy-production regions of Brazil and Paraguay. In Paraguay we sampled 17 sites on tributaries of the Pirapó River in the state of Itapúa and in Brazil we sampled 18 sites on tributaries of the San Francisco River in the state of Paraná. The riparian buffer zones generally contained native Atlantic forest remnants and/or introduced tree species at various stages of growth. In Brazil the stream buffer width was negatively correlated with sediment insecticide concentrations and buffer width was found to have moderate importance in mitigating effects on some sensitive taxa such as mayflies. However, in both regions insecticides had low relative importance in explaining variability in invertebrate communities, while various habitat parameters were more important. In Brazil, the percent coverage of soft depositional sediment in streams was the most important agriculture-related explanatory variable, and the overall stream-habitat score was the most important variable in Paraguay streams. Paraguay and Brazil both have laws requiring forested riparian buffers. The ample forested riparian buffer zones typical of streams in these regions are likely to have mitigated the effects of pesticides on stream invertebrate communities. This study provides evidence that riparian buffer regulations in the Atlantic Forest region are protecting stream ecosystems from pesticides and other agricultural stressors. Further studies are needed to determine the minimum buffer widths necessary to achieve optimal protection.

The Biological Assessment and Rehabilitation of the World’s Rivers: An Overview

“…Nevertheless, in the last 20 years a considerable amount of information has been produced in South and Central America on the ecology, biodiversity and response of organisms to environmental stressors in rivers [ 108 ] such as in: Uruguay [ 109 ]; Paraguay [ 110 ]; Bolivia [ 111 ]; Chile [ 112 ]; Colombia [ 113 ]; Peru [ 114 ]; Ecuador [ 115 ]; Guiana Francesa [ 116 ]; Venezuela [ 117 ]; Brazil [ 118 , 119 ]. Most studies were conducted based on a single or few temporal samplings with some exceptions covering multiple years, such as in studies of the Rio das Velhas basin, Minas Gerais, Brazil [ 120 , 121 ].…”

Ecological Integrity Impairment and Habitat Fragmentation for Neotropical Macroinvertebrate Communities in an Agricultural Stream

“…Alternative to the construction of denitrification systems, the reduction in applied fertilizers in the crop fields, as well as restoration of previously existing lagoons and the riparian habitats alongside the watercourses, may serve the purpose of buffer zones, temperature control, sediment and nutrient retention, and food source and habitat diversification for the biota [ 4 , 56 , 72 , 73 ]. Therefore, the protection of the riparian vegetation may sensibly improve the habitat conditions for all aquatic organisms, and at the same time diminish the effects of agricultural activities, as has been confirmed by [ 74 ] for Brazilian and Paraguayan streams. This measure also favors connectivity by means of riverine biological corridors.…”

Pesticides Burden in Neotropical Rivers: Costa Rica as a Case Study

“…We believe that greater efforts must be made by the government agencies and the farmers in the Neotropical region, in order to guarantee that toxic substances applied to the crops for pest control do not reach natural superficial waters in concentrations that pose unacceptable risks. The protection of the riparian vegetation is key to this purpose since it helps mitigate the effects of pesticides and excess nutrients to aquatic biota [ 53 ] and also provides habitat for refuge and later recolonization of organisms into the streams [ 54 ].…”