Testing diagnostic bioindicators in prairie streams: are biological traits and delta 15N of aquatic insects able to detect agricultural impacts?

Abstract

Agricultural activities in the Red River watershed of Manitoba, Canada, can be significant sources of excess nutrients, sediments and pesticides leading to ecological effects in streams and downstream Lake Winnipeg. In such multiple stressor environments, it is difficult to identify, separate and diagnose the cause of environmental impacts from different agricultural activities using traditional methods (e.g., taxa assemblage). However, ecological function indicators (e.g., functional feeding groups) have potential as diagnostic indicators because they lead to the identification of ecological change pathways. This study evaluated the efficacy of two indicators of ecological function: biological traits and nitrogen isotopic signatures (δ15[15 superscript]N) of benthic macroinvertebrate. Indicator sensitivity was evaluated by their association with human activity gradients that define the type and intensity of human activities (i.e., livestock, wastewater lagoon discharge, crop production). Results indicated that biological traits and δ15[15 superscript]N of BMI were effective diagnostic bioindicators for small scale impacts (e.g., riparian condition) and point sources of stressors (e.g., wastewater discharge). However, catchment scale agricultural activities were not associated with the bioindicators likely because of hydrological factors affecting the timing of stressor transportation in these prairie catchments. This study also demonstrated the importance of testing pathways of human impacts based on conceptual models including the type and magnitude of exposure to human activities and natural gradients.