Incorporating Water Quality Analysis into Navigation Assessments as Demonstrated in the Mississippi River Basin

Abstract

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.

Differing field methods and site conditions lead to varying bias in suspended sediment concentrations in the Lower Mississippi and Atchafalaya Rivers

“…SS has declined in the Mississippi River for many decades. The largest decreases in SS occurred prior to or around the 1980s in the Lower Mississippi and Atchafalaya Rivers (Meade & Moody, 2010 ; Mize et al, 2018 ) yet leveled off over the last decade (Kleiss et al, 2021 ).…”

“…Ultimately, we want to determine the usability of SS data records that were collected using multiple field methods to help resource managers, scientists, and engineers working in large river systems better understand and model SS from these complex records. In the Lower Mississippi and Atchafalaya Rivers, like in many large coastal river systems, SS concentrations are used to determine SS fluxes (e.g., Allison et al, 2012 ) and trends (e.g., Kleiss et al, 2021 ; Mize et al, 2018 ), and accurate estimation of these values are important for maintaining adequate channel depths for navigation and for planning and implementing coastal restoration activities.…”

Ten years of Gulf Coast ecosystem restoration projects since the Deepwater Horizon oil spill

“…It is evident from this example that nowhere near enough reduction of nitrogen loss has been made to expect detectable ecosystem responses in the GoM. To achieve desired benefit–cost ratios from investments in water quality and other post-DWH improvements on the GoM ( 13 ) it is important to appropriately scale expectations for the effects of restoration using suitable statistical tools ( 14 ).…”