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A series of locks and dams were constructed and put into operation on the Upper Mississippi River in the 1930s to facilitate commercial navigation. As a result, historical floodplain landscapes were altered. For example, islands characterized by floodplain forests experienced prolonged unfavourable hydrologic conditions and were eliminated from many areas of the river. The distribution and extent of other large river habitat types (e.g., wetlands, secondary channels) were also impacted. In addition, large areas of open water habitat were created through the impoundment of the river. Proposed management plans for the Upper Mississippi River include (1) modernization of the locks and dams to improve navigation efficiency, and (2) ecological restoration to conditions more characteristic of pre-impoundment. The purpose of the work reported here is to describe and apply a spatially explicit comprehensive aquatic systems model (SECASM). The SECASM is offered as one approach for evaluating the anticipated outcomes of alternative management and restoration actions (e.g., island creation, floodplain forest restoration, water level management). The model simulates spatial-temporal changes in the distribution and extent of five land-use types representative of the Upper Mississippi River floodplain: prairie, marsh, upland woody vegetation, surface water, and combined urban/agricultural areas. The SECASM has a spatial resolution defined by 100 x 100-meter grid elements (i.e., 1 ha) and operates using a daily time step for simulated durations up to 100 years. Transitions of habitat types within each grid element are determined by a combination of rule-based algorithms and ecological process equations. The model outputs are amenable to the production of landscape maps and the calculation of landscape metrics (e.g., lacunarity index) that usefully summarize landscape patterns. The ability of the SECASM to realistically describe alterations in Upper Mississippi River floodplain landscapes was evaluated by using Pool 5 land-use patterns reported for 1890 as an initial condition, simulating 100-y of landscape change (including impoundment), and comparing model results with reported conditions for 1989. The SECASM was subsequently used to examine several hypotheses concerning landscape impacts of impoundment, outcomes of alternative restoration actions, and the potential effects of nutrient enrichment.
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