WATER QUALITY DURING TWO HIGH-FLOW YEARS ON THE LOWER MISSOURI RIVER: THE EFFECTS OF RESERVOIR AND TRIBUTARY CONTRIBUTIONS

Complex socioeconomic and ecological issues, ranging from impaired streams to Gulf of Mexico hypoxia, have made nutrient management an increasingly important issue across the USA. High flows during 2010 and 2011 provided a unique opportunity to investigate trends in discharge, total nitrogen, nitrate/nitrite, total phosphorus, orthophosphorus, suspended sediment and total suspended solids during two distinct high-flow years on the Missouri River. We compared collections taken during 2010 and 2011 at 12 lower Missouri River locations (river kilometers 1212 to 71) and 22 Missouri River tributary locations. During 2011, average concentrations for all sampled parameters were significantly lower, despite significantly higher total discharge, than 2010 concentrations. Differences in water chemistry between years are likely attributed to the primary source of water. Tributary inflow created high flows during 2010, whereas record releases from Gavin’s Point Dam created high flows during 2011. Analysis of flow estimated the contribution of these releases at each site and revealed strong positive relationships between the percentage of estimated tributary flow at each site and the concentrations of total nitrogen, total phosphorus and total suspended solids. These monitoring efforts underline the contrasting impacts that tributary streams and reservoir releases have on nutrient export of the Missouri River during high-flow events and reveal a larger trend of increased nutrient concentrations as the proportion of Missouri River tributary flow increased

WATER QUALITY DURING TWO HIGH-FLOW YEARS ON THE LOWER MISSOURI RIVER: THE EFFECTS OF RESERVOIR AND TRIBUTARY CONTRIBUTIONS

Complex socioeconomic and ecological issues, ranging from impaired streams to Gulf of Mexico hypoxia, have made nutrient management an increasingly important issue across the USA. High flows during 2010 and 2011 provided a unique opportunity to investigate trends in discharge, total nitrogen, nitrate/nitrite, total phosphorus, orthophosphorus, suspended sediment and total suspended solids during two distinct high-flow years on the Missouri River. We compared collections taken during 2010 and 2011 at 12 lower Missouri River locations (river kilometers 1212 to 71) and 22 Missouri River tributary locations. During 2011, average concentrations for all sampled parameters were significantly lower, despite significantly higher total discharge, than 2010 concentrations. Differences in water chemistry between years are likely attributed to the primary source of water. Tributary inflow created high flows during 2010, whereas record releases from Gavin’s Point Dam created high flows during 2011. Analysis of flow estimated the contribution of these releases at each site and revealed strong positive relationships between the percentage of estimated tributary flow at each site and the concentrations of total nitrogen, total phosphorus and total suspended solids. These monitoring efforts underline the contrasting impacts that tributary streams and reservoir releases have on nutrient export of the Missouri River during high-flow events and reveal a larger trend of increased nutrient concentrations as the proportion of Missouri River tributary flow increased

IS SHALLOW WATER A SUITABLE SURROGATE FOR ASSESSING EFFORTS TO ADDRESS PALLID STURGEON POPULATION DECLINES?

It is hypothesized that slow, shallow water habitats benefit larval pallid sturgeon Scaphirhynchus albus; however, testing this hypothesis is difficult, given the low number of larval pallid sturgeon present in large rivers. In contrast, relatively large numbers of age-0 shovelnose sturgeon Scaphirhynchus platorynchus have been sampled, providing a potentially useful baseline to assess the importance of slow, shallow water to age-0 sturgeon of both species (hereafter age-0 sturgeon) in the lower Missouri River. Thus, we investigated the potential relationships between the prevalence of shallow water \u3c1.5m and the age-0 sturgeon catch rates at multiple scales. Age-0 sturgeon were usually sampled in water \u3e1.5 m, and catch rates were usually highest in the upper half [i.e. river kilometer (RKM) 400 to 800] of the lower Missouri River study area, whereas the availability of water \u3c1.5m was usually highest in the lower half (i.e. RKM 0 to 400). Similarly, there was no relationship between age-0 sturgeon mean catch-per-unit effort and ha/km of water \u3c1.5m at any studied scale. Our results may suggest that shallow water, as currently defined, may not be a suitable surrogate for assessing efforts to address pallid sturgeon population declines. However, it is still unknown if lack of appropriate habitat is currently limiting pallid sturgeon