Hydrodynamic Modeling as A Tool for Ecologists on the Mississippi River

Computer generated hydrodynamic models are important tools in bridging the gap between ecologists and engineers.  Hydrodynamic models can provide essential data to ecologists on parameters such as: discharge, velocity, residence time, bed shear stress, Froude number, and water depth (to name a few) which are the primary parameters of hydrodynamics.  These models provide the necessary frame work to understand processes within hydraulics and how these may affect ecosystems.  Hydrodynamic models also guide us in making comparisons to real world events, which can tell us if the model results or field data (or both) are in error. In addition, hydrodynamic models are tools that allow biologists and river managers to simulate a range of scenarios in which they can better understand the flow regimes of the river, along with spatial and temporal distribution of the hydrodynamic properties which effect biota. In particular, collaborative work by the U.S. Geological Survey Upper Midwest Environmental Sciences Center, U.S. Army Corps of Engineers, and the University of Iowa, Lucille A. Carver Mississippi Riverside Environmental Research Station (LACMRERS) are testing new models in Pool 8 and Round Lake near LaCrosse, Wisconsin. Recent research is working on coupling water-quality parameters (such as nitrate) with hydrodynamic equations. Our current understanding of nutrient dynamics – nitrogen in particular – is based entirely on a large set of static snap-shots of concentrations and biogeochemical analyses that rather poorly describe the highly variable nature of discharge-based delivery and movement of these bio-active compounds (e.g., nitrate and soluble phosphorus).  Management of water quality in the Upper Mississippi River (UMR) and ultimately the Gulf of Mexico requires a much better understanding hydrologic delivery of these elements to off-channel regions of rivers (particularly floodplain lakes and backwaters) to predict rates of removal or biological uptake.  We know that floods deliver solutes to off-channel areas and that some of these solutes are potent affecters of changes in rates and sources of primary productivity, causing eutrophication and excess algal growth.  We also know that flood-induced changes in backwater loading of nitrate stimulates nitrate removal via denitrification while also increasing sedimentation and backwater filling.