The Response of Fish Diversity in a Highly Modified Large River System to Multiple Anthropogenic Stressors

Abstract

Large riverine landscapes are among the most productive ecosystems on earth, and the most affected by humans. Few studies explicitly explore the effects of, or responses to, multiple stressors in highly modified large river systems. Changes in fish assemblages in response to multiple anthropogenic stressors were explored from a 60-year data set for the Illinois River (Illinois, USA). Despite a legacy of stressors, the highly modified Illinois River responded to additional multiple stressors, especially four distinct stressor phases, which included two policies to improve water quality and bigheaded carp invasion. The response in fish diversity (Shannon H′) was complex in terms of the number of thresholds in the pattern of fish diversity, the rate and direction of change between thresholds, and the variance of response at two spatial scales and two ecological levels of organization. Overall, nine response trajectories were observed. Changes in fish diversity in the Illinois River since 1959 do not conform to current ecosystem response models. Without long-term and broad-scale data, elucidating complex responses in large river ecosystems is unlikely. Expanding the spatial and temporal scale of investigation in modified large rivers will increase our ability to understand how these ecosystems respond to multiple stressors.

Riverine landscapes, water resource development and management: A view from downunder

“…Establishing the “state” of riverine landscapes within the Anthropocene is essential for the study and management of contemporary riverine landscapes. Recent research by DeBoer, Thoms, Casper, and Delong (2019); DeBoer, Thoms, and Delong (2020) showed the Illinois River ecosystem (Illinois) once degraded by pollution from the Chicago metropolis did not recover to its Pre‐Settlement state following major system wide restoration efforts. Rather the Illinois River showed “novel” unexpected responses some of which suggest a reduction in its capacity to absorb future disturbances.…”

Large rivers as complex adaptive ecosystems

“…Thus, many large rivers are reflective of an Anthropocene landscape, with few pristine riverine landscapes remaining (cf. DeBoer, Thoms, Casper, & Delong, 2019). This legacy of modification represents a challenge for the current management of these landscapes.…”

Numerical Modelling as a Support Tool for River Habitat Studies

“…The response of fluvial ecosystems to external and internal drivers is a matter of study since more than a century [1,2], and involved scientists having very different backgrounds and applying manifold techniques. Research on the responses of river systems to external forcing has considered the influence of single [3], sequential [4] and multiple [5] stressors, showing that the cumulative effect produced by the latter is far for being completely understood, especially in large rivers.…”

“…Given that large watercourses are among the most productive ecosystems worldwide [6], they are also highly affected by anthropogenic activities such as dredging, bank stabilization or dam construction [2,[7][8][9], involving significant morphological modifications or species invasions [10,11]. Nowadays, the use of numerical models for evaluating the effects of multiple natural and anthropogenic stressors in impacted ecosystems is becoming paramount thanks to the improvements in computational capacity.…”

“…Nowadays, the use of numerical models for evaluating the effects of multiple natural and anthropogenic stressors in impacted ecosystems is becoming paramount thanks to the improvements in computational capacity. In fact, several modelling tools are available to evaluate the dynamics of river ecosystems at appropriate spatial and temporal scales [2,3,12].…”