Testing Biological Pesticide Indices for Danish Streams


This project focused on quantifying ecological effects of pesticides in Danish streams and was primarily based on the German SPEAR index. The project was subdivided into three phases that was based on existing data, an experimental mesocosm study, and comprehensive field work, respectively. In phases 1 and 2 we found that SPEAR was significantly affected by insecticide concentrations but also physical habitat quality, and that the primary responses of macroinvertebrates towards insecticides was determined by their surface area:volume ratio and voltinism with small size and slow reproduction being characteristic of higher sensitivity. In Phase 3 we showed that the SPEAR index was significantly correlated to pesticide concentrations expressed as Toxic Units (TU), whereas the Danish Stream Fauna Index (DSFI) showed weak to no correlation to TU. Increasing number of rain events leading to TU > 0.001 in water samples in May-July significantly decreased SPEAR index values with > 2 such pollution episodes reducing SPEAR up to 60% compared to SPEAR values in early May (before the primary season for agricultural insecticide application). Ecosystem primary production was positively correlated with insecticide concentrations. This indicates that macroinvertebrate grazers were impacted by insecticides indirectly allowing higher algae biomass accrual in the streams. Based on the high complexity of pesticide mixtures in space and time we conclude that intensive sampling efforts, especially targeting increased stream discharge during rain events, are needed to link pesticide occurrence to ecological effects. Stressor specific ecological indices are probably not able to correctly diagnose specific causes of ecological impairment.

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