Agricultural Pesticide Use Decreases Species Richness in Stream Invertebrates

Despite years of scientific studies to guide regulation efforts, it is unknown to what degree agricultural pesticides cause species losses and thus a decrease in total biodiversity. To examine this relationship, Beketov et al. (2013) analyzed the effects of pesticides on taxa richness of stream invertebrates, using additional analyses to discriminate the possible confounding factors from the effects of pesticides. In all study sites it was shown that pesticide use caused a loss in species and family richness, indicating that pesticide use should be considered a main driver of regional biodiversity loss. —Kahea Kanuha
Beketov, M., Kefford, B., Schafer, R., Liess, M., 2013. Pesticides reduce regional biodiversity of stream invertebrates. Proceedings of the National Academy of Sciences 110, 11039—11043.

                  Beketov et al. applied the contaminant category richness to study the impacts of pesticide use on freshwater stream invertebrates. Contaminant category richness describes the taxa richness of stream invertebrates particular to different water contaminant levels, quantified by the relationship between the number of individuals and the number of taxa recorded. Data were used from Europe (33 sites) and Australia (18 sites) and included pesticide exposure assessment, stream invertebrate records, and data on environmental factors that may compound the effects of pesticides.
                  Study sites were assigned a contamination category based on toxic units (TUs) computed from the maximum pesticide concentrations at peak water runoff events. The contamination categories were then compared to the species and family richness of each respective study site. The Chao 2 richness estimator used the collected data to predict the species richness for an infinite number of samples taken at each site. Results show significant differences in taxonomic richness among all contamination categories. The percentage decrease in taxonomic richness between the uncontaminated and highly contaminated sites ranged from 27%, from the Australian family-level data, to 42%, for the European species-level data. Such an extensive decline is comparable to the effects of other known drivers of biodiversity loss. This indicates that for the goal of slowing biodiversity loss, safer standards should be set for pesticide use, methods, and mitigation practices.
                  Two methods were used to discern the possible effects of confounding factors from the effects of pesticide use. In the first, the SPEAR approach was used to identify the taxa that are particularly vulnerable to pesticides. After these taxa were identified, the data were checked to see whether the overall declines in taxa richness were based on the losses of taxa particularly vulnerable to pesticide use. As expected, it was found that pesticide contamination was associated with a decrease in the number of pesticide-vulnerable taxa. Secondly, available water quality and habitat variables were analyzed to see if any of them would explain the differences between contamination categories. The only significant difference found was in electrical conductivity between the slightly and heavily contaminated sites in Australia, but it was not a consistent linear trend and thus it is unlikely to be a major driver of the observed diversity patterns.

                  The effects of pesticide use on the taxa richness in Europe were identified in the contaminant concentration level that is considered to be protective by current European agricultural pesticides regulation. This indicates that current standards are not high enough to protect stream biodiversity. Agricultural pesticide use is predicted to increase in the coming decades due to the effects of climate change, and without more stringent regulation it may become an even more important driver of biodiversity loss in the future.

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