A description of historical and ambient water quality conditions is often required as part of navigational studies. This paper describes a series of tools developed by the USGS that can aid navigation managers in developing water quality assessments. The tools use R, a statistical software program, and provide methods to retrieve historical streamflow and water quality data, summarize observations, model concentrations and fluxes, and estimate seasonal, annual, and decadal trends. The utility of these tools is demonstrated by providing an analysis of the seasonal variability and long-term trends of nitrate plus nitrite, orthophosphate, and suspended sediment concentrations and fluxes at nine sites in the Mississippi River Basin. Trends in annual mean concentration and flux showed fairly stable nitrate plus nitrite at most of the nine sites, with increases in the Upper Mississippi and Missouri Rivers and decreases on the Illinois River over a 40-year period beginning in 1980. Orthophosphate concentration or flux increased at almost all sites over a similar time period. Conversely, a concurrent steady decline in suspended sediment concentrations and fluxes was noted at sites throughout the basin.
A phased study of the dike fields within the Vicksburg and Memphis Districts of the US Army Corps of Engineers was conducted to document the channel morphology trends since dike construction on the Lower Mississippi River (LMR). This included the development of the hydrographic survey database and methodology utilized to identify changes in channel geometry in response to dike construction. A subsequent report will provide further refinements to the approach and results of the comprehensive assessment. Recent Mississippi River Geomorphology and Potamology program efforts have employed the database developed by Mr. Steve Cobb to assess the geomorphic changes in 21 dike systems along the LMR. Previous studies using this database have indicated that the dike fields have not caused a loss of channel capacity. Furthermore, these efforts suggested that the trends in the dike fields are closely related to the long-term geomorphic trends along the LMR. Previous efforts using the Cobb database provided considerable insight into the dike effects on the LMR, but they were limited spatially and temporally. In this study, a database and protocols were developed to allow for a more robust assessment of dike field impacts and to extend the spatial and temporal extents of the analysis.
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