Ecosystem Response Through a Resilience Lens: Do Differences in the Illinois River Over 150 Y Indicate Regime Shifts?

Most of the world's large river ecosystems are subject to multiple anthropogenic stressors including climate change, disconnection between the main river channel and floodplain, flow regulation, and land-use modification. Viewed through a resilience lens, these ecosystems are potentially in a new regime, exhibiting a different structure, function, and set of feedbacks. We investigated the trophic status and food web character response to anthropogenic stressors over 150 years in the Illinois River. Differences in stable isotope ratios, community niche space, basal resource contribution to higher levels in the food web, mean trophic position of fish functional feeding guilds, and food chain length among four stressor phases suggest changes in ecosystem function in the Illinois River. Moreover, the river did not return to pre-stressor conditions following watershed-wide restoration efforts. Differences in trophic status and food web character also varied between the upper- and lower-river zones of the Illinois River over time. This spatial divergence further highlights the complexity of responses to multiple stressors in this ecosystem. Overall, differences in trophic status and food web character suggest a shift to a new regime-an Anthropocene regime-and one that has a reduced capacity to absorb additional disturbances. Given human pressures are a global issue, our results based on a 150 years data set, could assist in the management of riverine landscapes that face regime shifts due to human stressors.