Assessing the feasibility of reestablishing ecosystem processes

1. Assessing the feasibility of reestablishing ecosystem processes on the Mississippi River in the Twin Cities, Minnesota Christian Lenhart1, John L. Nieber1and Lucius Jonett2 1Bioproducts and Biosystems Engineering Department, University of Minnesota 2Department of Landscape Architecture, University of Minnesota Feasibility assessment Project Background and Purpose The Twin Cities reach of the Mississippi River was historically industrially dominated. Yet with increasing recreational usage an evolving economics of the Twin Cities there is growing interest in recreational, aesthetic and ecological uses of the river. The City of Minneapolis has proposed to close its upper harbor to barge traffic, creating opportunity for restoration of ecological, historic, aesthetic and recreational features. This study will provide a synthesis of existing and past work on restoration and management activities within the river (not watershed management) between Coon Rapids Dam and St. Paul (above Pool 1, within Pool 1 and upper Pool 2). Gaps and opportunities for restoration of ecological, socio-economic and aesthetic services have been identified. A preliminary assessment of the feasibility of these actions will be provided. Promising strategies wil be identified for more detailed analysis and implementation. • The assessment of feasibility of rehabilitation and management actions was based on 3 aspects: • Physical constraints – hydrology, geomorphology, permanent alterations to river • Ecological issues – ecosystems processes; fish and mussel habitat; connectivity longitudinally and laterally • Socio-Economic constraints – industrial and energy uses; river recreation; tourism; aesthetics Review and synthesis of existing restoration and management work dfdf • Gaps analysis of existing study • Lack of in-river work in Pool 1 and above to Coon Rapids Dam • Improvement of fish and mussel passage to Pool 1 • Structural focus over process • Ecological restoration and watershed management has been done outside of the floodprone area. Reichardt 1857 Ecological processes Physical processes Fish and mussel dispersal and passage Hydrologic processes: water level drawdown Prior to construction of the Ford and Lower St. Anthony Falls dams, water levels varied greatly on the Mississippi River. Seasonal drawdown could promote wetland revegetation in certain reaches and whitewater recreation in the spring below St. Anthony Falls. Photo by Minnesota Historical Society (1890s prior to lock and dam projects) Processes of island formation were halted in Pool 1 via inundation and dredging for maintain the 9 foot channel for barge traffic Fish passage improvements at Ford Dam would allow Lake Sturgeon and other gravel-spawning fishes to access one of the largest cobble/boulder beds on the Mississippi below St. Anthony Falls The Mississippi River below St. Anthony Falls (above) was a unique high gradient, boulder/cobble habitat providing excellent habitat for fish and mussels. It was one of Minnesota’s major tourist site in the 1800s. The falls and rapids were modified for hydropower and milling in the late 1800s and for barge traffic in the 1960s. Aesthetic improvements could enhance the area today, still a major destination for local residents and tourists. Pool 1 has excellent mussel habitat and is located next to the St. Croix river, a mussel biodiversity hotspot. The edangered Higgins Eye mussle recently re-establishing in Pool 1 1895 2009 Processes of island formation could be re-stablished in some locations above and below Pool 1. Within Pool 1, island re-establishment would be more challenging, though a large sediment supply exists for use in island seeding. Large river restoration and management issues Most direct stream restoration work has been on small streams, < 1000km2 in drainage area. Large scale rivers have different ecological, geomorphic, and socioeconomic processes at work Requires focus on process over structures Channel-floodplain processes are important for ecological connectivity and sediment deposition Ecological: big rivers such as the Mississippi are often regional centers for aquatic biodiversity of fish and mussels Socio-Economic: large rivers are often hubs of commerce and tend to have much historic and cultural importance Social, economic and aesthetic Social processes – re-establish gathering points, points of access along river. Many local government and non-profit organizations, including the National Park Service’s, Mississippi National River Recration Ara Aesthetics- management for aesthetic concerns rather than industrial/ economic only Economic – changing economics of cities; true cost-benefit analysis Sediment Transport was altered by the dams, creating large deposit of sediment behind Ford Dam, in Pool 1. Sediment inhibits habitat restoration options though combinations of dredging and water level variation could remove some of the sediment wedge. Dredged materials could be used to re-establish islands under appropriate physical and socio-economic situations. Project Examples Recreation – seasonal whitewater run in April-May Aesthetics – Use visual assessment procedure (Mullan 2009) , St. Anthony Falls Economic – changing economics of cities; true cost-benefit analysis Water quality and TMDLs Total Maximum Daily Load studies have created the necessity of reducing sediment and nutrient loads and baccteria levels. Lake Pepin, a dowsntream natural “lake” on the Mississippi is imparied for turbidity while many reaches in and near the metro area are listed for bacteria. TMDLs may drive water quality improvemetns within the study area of Pool 1 and 2. Streamflow has changed over time, making more water available for hydropower