Long-term Monitoring Shows How Highly Modified Rivers Respond to Additional Drivers of Change

Large rivers are among the most-regulated and highly modified ecosystems, globally. More than 65% of the world’s large rivers are fragmented by dams, experience hydrological regulation, and are controlled for navigation purposes. Large rivers are increasingly modified by multiple drivers that cumulatively influence these ecosystems. However, few studies explicitly explore the effects of, or responses to, multiple drivers. Furthermore, our understanding of how system-wide drivers overlap in space or time and interact with each other is lacking. The question remains: do highly modified large-river systems maintain the ability to respond to additional cumulative anthropogenic drivers in a significant and substantial way, and if so, how are these responses manifested? To improve our knowledge of the influence of anthropogenic drivers in large rivers, we need to investigate ecosystem response at broad spatial and temporal scales, whereas most studies focus on single drivers and small scales. This study utilizes a 60-year, river-wide dataset to determine if fish community diversity in the Illinois River changed in response to two major, system-wide anthropogenic drivers: the Clean Water Act (1972) and the Asian carp invasion (2000). We analyzed diversity changes for the entire river system, between distinct geomorphic zones, and among functional feeding guilds.