Epsilon Open Archive

Abstract

The main objective of this thesis was to examine pesticide mixture toxicity and its effects on aquatic biota in agricultural streams. This was accomplished by (1) calculating the ΣTUs for algae and Daphnia magna and a pesticide toxicity index (PTI) based on water quality standards (WQS) for long-term monitoring data (2002-2010), (2) by performing algal inhibition tests with Pseudokirchneriella subcapitata, using both collected in situ water samples and reconstituted water spiked with field-observed pesticide mixtures, and (3) by studying seasonal changes in macroinvertebrate and diatom communities during 2008 in four agricultural streams and determine a set of community-based metrics such as species richness, diversity, ASPT, SPEAR and IPS. Partial Least Squares (PLS) regression was used to analyse community changes.

Long-term data showed that collected stream water samples had peaks of estimated pesticide toxicity, mainly due to herbicides though insecticides and fungicides also contributed. ∑TUalgae, based on weekly average concentrations, exceeded 0.1 on 28 out of 902 occasions, and 8 of these were higher than 0.2. Only one or a few pesticides contributed to a major part of estimated mixture toxicity in the streams.

The algal growth inhibition studies in spiked water showed negative effects at pesticide concentrations corresponding to those found in stream water samples, indicating that pesticide effects on algae occur under in situ conditions. The field study also showed effects of pesticides, suggesting diatom diversity as a sensitive indicator of pesticide effects. Macroinvertebrate community changes were primarily explained by physiochemical conditions, though some non-insect invertebrates decreased (Asellus aquaticus) or increased (Oligochaeta) with pesticide exposure. Somewhat surprisingly, the SPEARpesticides index, specifically developed to detect pesticide effects of macro-invertebrate communities in streams, was not related to pesticide toxicity. The SPEAR index may need to be modified to better fit to Swedish conditions.

A combination of chemical and biological monitoring is needed to increase our understanding of the relationship between pesticide stress and the biological diversity of agricultural streams. Specific endpoints and analysis methods are also needed to separate effects of pesticides from effects of other stressors.