Defining ecosystem restoration potential using a multiple reference condition approach: Upper Mississippi River System, USA

Abstract

Large scale ecosystem restoration is an important societal issue because significant risks, costs, and benefits can accrue on large landscapes. It is important to understand baseline ecosystem conditions, existing condition, and to the extent possible estimate ecosystem response to alternative management scenarios. Incorporating sound ecological theory for ecosystem process and function into restoration planning and implementation is critical to make restoration sustainable. The Upper Mississippi River System is an excellent case study for such issues because it is an important, multiple-use ecosystem with significant ongoing investment in ecosystem, agri-system, and navigation system management.

I compared large-scale geomorphology, hydrology, and land cover information among presettlement, contemporary, and potential future reference conditions to examine ecosystem state and evaluate mechanisms responsible for ecosystem condition. Ecologically relevant geomorphic classes were devised from existing data and evaluated by river reach to characterize presettlement geomorphology. I superimposed dams and levees onto the geomorphic landscape to reflect the altered hydrogeomorphology of the contemporary ecosystem. I also analyzed pre- and post-impact river stages and aquatic habitat class distribution. My floodplain inundation simulation analysis provided new information on the potential spatial distribution of frequent floods. Land cover data available for presettlement and modern reference periods were compared at several spatial scales. I used multivariate analyses to evaluate land cover characteristics among geomorphic reaches, as well as to assess the influence of hydrogeomorphic drivers on land cover for presettlement and contemporary reference periods.

The hydrogeomorphic response to development was clear with impoundment altering the 2-yr flood distribution in the north and levees altering it in the south. The hydrogeomorphic response to development indicates several restoration objectives that are appropriate system-wide and others that are best suited to specific river reaches.

I was also able to test several hypotheses related to large river ecology. The Upper Mississippi River System does have distinct reaches that are formed by ancient glacial influences and tributary influences during the last 10,000 years. Tributaries delivering sediment as alluvial fans create diverse floodplain topography which supports diverse plant communities. Tributaries appear to diversify floodplain habitats in many ways.