Food web characteristics of fish communities across degraded lakes provide insights for management in multi-stressor environments

Interactions between multiple stressors can result in unexpected ecological outcomes, especially in lowland lakes. Degraded shallow lakes typically occur in populated areas and are therefore subject to the combined effects of increased nutrient and sediment loading, and species invasions. This presents challenges for meeting ecological restoration objectives measured using traditional indicators of lake enrichment. Here we use stable isotope analyses from six shallow lakes in a highly modified agricultural landscape to explore how well fish community-level trophic metrics reflect individual and combined anthropogenic stressors. Community trophic metrics differed within a single basin and in similarly degraded shallow lakes, and appeared to reflect subtly different relative strengths of anthropogenic stressors within particular systems. Even allowing for the comparatively narrow range of lake and catchment conditions investigated here, our results support other studies indicating that food web metrics are sensitive to both the effects of eutrophication and invasive species in shallow lakes. Trophic responses to multiple stressors highlight the complexities of determining cause and effect relationships for prioritising stressor specific management actions, and subsequent measurement of ecosystem response. Notwithstanding these complexities, food web metrics derived from stable isotope analyses hold potential value for detecting complex responses to shallow lake management and restoration efforts.