Stream habitat structure influences macroinvertebrate response to pesticides

Agricultural pesticides continue to impair surface water ecosystems, although there are few assessments of interactions with other modifications such as fine sediment and physical alteration for flood drainage. We, therefore, surveyed pesticide contamination and macroinvertebrates in 14 streams along a gradient of expected pesticide exposure using a paired-reach approach to differentiate effects between physically modified and less modified sites. Apparent pesticides effects on the relative abundance of SPEcies At Risk (SPEAR) were increased at sites with degraded habitats primarily due to the absence of species with specific preferences for hard substrates. Our findings highlight the importance of physical habitat degradation in the assessment and mitigation of pesticide risk in agricultural streams.

► %SPEAR abundance significantly decreased with increasing TU (D. magna).
► %SPEAR abundance was significantly lower when soft sediment was dominant.
► Species specific habitat preferences influenced the total effect of pesticides.
► This study has strong implications for future stream management and risk assessment.