Persistence of a Chemical Gradient in the Lower Platte River, Nebraska

During a 1986-87 study of microhabitat utilization by Platte River fauna we noted a persistent difference in conductance between north and south banks. A series of transects across the river, measured on 11 August 1987, between River Miles 78-59, demonstrated that the conductivity gradient persisted throughout the 32 km study segment. Typical readings were 315 umhos cm-1 for the north side and 550 umhos cm-1 for the south side. Additional upstream measurements showed that the gradient originates at the confluence of the Platte River and the Loup River Power Canal (RM 101). Upstream, the Platte River mean monthly conductivity is 922 umhos cm-1 while the Canal is 283 umhos cm-1 . Correlation analysis of the relative contribution of the Canal to total downstream discharge shows a significant negative correlation (r= -0.60; P=.0001) to the conductivity levels of the Platte River below the confluence. Occurrence of this conductivity gradient may indicate a lack of mixing of other chemical constituents in the water including pollutants