Comparison of Multiple Water Quality Parameters During Two High Flow Years on the Lower Missouri River

High flows on the Missouri River in 2010 and 2011 presented a unique opportunity for water quality monitoring efforts. Trends in discharge (617 – 8552 m³ s^-1), total nitrogen (0.40 – 8.93 mg L^-1), nitrite/nitrate (0.02 – 3.90 mg L^-1), total phosphorus (50 – 2000 µg L^-1), orthophosphorus (20 - 490 µg L^-1), suspended sediment (13 – 3180 mg L^-1), and total suspended solids (17 – 2393 mg L^-1) were compared from collections taken in 2010 and 2011 at thirteen Missouri River locations (River Miles 774 to 48). In 2011, average concentrations for all sampled parameters were significantly lower than those in 2010 while total discharge was significantly higher. Differences in water chemistry between years are likely attributed to the primary source of water.  2010 flows can be credited to high tributary flows while 2011 discharges can be tied to high releases from the Gavins Point Dam. Analysis of flow was done to estimate the contribution of these releases at each site. This revealed strong positive relationships between the percent of estimated tributary flow at each site and the concentrations of TN, TP, and TSS. These monitoring efforts underline the contrasting impacts that tributary streams and reservoir releases have on nutrient export to the Missouri River during high flow events and reveal a larger trend of nutrient concentrations increasing as the proportion of tributary flow on the Missouri River increases.