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Streambed vertical hydraulic conductivity (Kv) plays an important role in understanding and quantifying the stream–aquifer interactions. While several researchers have discussed the spatial variability of streambed horizontal hydraulic conductivity or Kv at one or several close-located sites in a river, they did not develop any statistical distribution analysis of streambed Kv at distant sites along a large river. In this paper, the statistical distribution and spatial variation of streambed Kv at 18 test sites in a 300-km reach of the Platte River in Nebraska are presented. Insitu permeameter tests using the falling-head method were carried out to calculate the streambed Kv values. Fine-grained sediments transported by two tributaries, the Loup River and the Elkhorn River, to the Platte River appear to result in lower streambed Kv values downstream of the confluences between the Platte River and the tributaries. The streambed Kv values were found to be normally distributed at nearly each test site. When the correlated Kv values were eliminated from the grid sampling plots, the remaining independent sub-datasets of streambed Kv values were still in normal distribution at each test site. Furthermore, the combined streambed Kv values upstream of the first confluence between the Platte River and the Loup River was normally distributed, which may be due to the lack of tributaries in-between and thus streambed sediments were well distributed in this reach and belonged to a single population of hydraulic conductivity values. In contrast, the combined dataset of all measurements conducted downstream of this confluence was no longer in normal distribution, presumably as a result of the mixing of different sediment sources.

Most sturgeon species worldwide have been in steep decline since the 1900s. This research evaluated shovelnose sturgeon health, reproduction, and exposure to environmental contamination in the lower Platte River. Shovelnose sturgeon served as a surrogate species for the endangered pallid sturgeon and their health was assessed by incorporating measurements of general health with hepatic, immune, and reproductive system biomarkers. Environmental contaminants were measured in water, potential pallid sturgeon food items (cyprinid minnows), and shovelnose sturgeon digesta, liver, and blood plasma. Contaminants detected in shovelnose sturgeon at concentrations of concern included PCBs, selenium, and atrazine. Total PCBs in carcasses (n = 8) averaged 0.32 μg/g ww. Selenium averaged 4.8 μg/g dw in carcasses (n = 30) and 80 percent of individuals sampled were within the 4 to 6 μg/g threshold range for reproductive impairment in sensitive fish species. Pallid sturgeon food items had significantly (p < 0.05) greater concentrations of Hg, Se, and Zn than shovelnose sturgeon digesta. Atrazine was detected in all blood plasma samples analyzed (n = 50) at concentrations from 0.24 to 28 μg/L, but was not detected in liver (n = 19). Although the effects of atrazine exposure to shovelnose sturgeon are unknown, results of this study and previous work by others indicate that it may be disrupting steroidogeneisis. Gross observations and condition indices seem to indicate that shovelnose sturgeon from the lower Platte River are healthy; however, reproductive biomarkers and histological examination of gonads indicate potential reproductive impairment as indicated by ovicular atresia, abnormal estrogen to testosterone ratios, and high concentrations of vitellogenin in males. Pallid sturgeon may be especially at risk to contaminants in the lower Platte River that bioaccumulate and cause reproductive impairment because they have a more piscivourus diet, greater maximum life-span, and a longe

The central Platte River Valley provides crucial staging habitat for the endangered whooping crane (Grus americana) and the mid-continent population of sandhill cranes (Grus canadensis). Platte River flow depletions and the conversion of native wet meadows for agriculture and other purposes has decreased the cranes natural habitat in the central Platte River Valley, and waste corn now makes up most of the cranes diet while they are in the Valley. The purpose of this research was to measure organochlorine, elemental contaminant, and pesticide exposure to sandhill cranes from the central Platte River Valley, and to evaluate their reproductive condition. Pesticides and organochlorines were measured in soil and waste corn samples collected from cornfields where sandhill cranes foraged. Elemental and/or organochlorine contaminants were measured in sandhill crane carcass, liver, brain, muscle, and kidney tissues. Reproduction in sandhill cranes was evaluated by measuring sex steroids in blood plasma and by histological examination of gonads. Sandhill cranes collected from the central Platte River Valley in 1999 and 2001 appeared to be in normal reproductive condition and concentrations of organochlorines in their tissues were not at levels considered harmful. In addition, pesticides in corn and soil from cornfields were all below detection. Elemental contaminants measured in crane tissues also were generally low, with the exception of boron. Concentrations of boron in sandhill crane livers (n = 7) averaged 43.60 ± 3.59 mg/kg dw and exceeded reproductive toxicity thresholds established for mallards. Boron concentrations also were detected at higher concentrations than previously reported in sandhill crane livers analyzed ten years earlier in the same study area. More research is needed to identify sources of boron in the area and further evaluate whether boron exposure to sandhill cranes may be adversely affecting their reproductive potential.

Habitat fragmentation has been implicated as a major cause of population decline in grassland birds. We tested the hypothesis that a combination of area and shape determines the use of grassland patches by breeding birds. We compared both species richness and individual species presence in 45 wet meadow grasslands in the floodplain of the central Platte River, Nebraska. Bird data were collected through the use of belt transects and supplemented by walking and listening outside transects. Our data supported our primary hypothesis that perimeter–area ratio, which reflects both the area and shape of a patch, is the strongest predictor of both individual species presence and overall species richness. The probability of occurrence for all six common species (Grasshopper Sparrows, Bobolinks, Upland Sandpipers, Western Meadowlarks, Dickcissels, and Red-winged Blackbirds) was significantly inversely correlated with perimeter–area ratio. The probability of occurrence of Grasshopper Sparrows, Bobolinks, Upland Sandpipers, and Western Meadowlarks was also correlated with area. We conclude that species richness is maximized when patches are large (>50 ha) and shaped so that they provide abundant interior areas, free from the impacts of edges.

An extended Kalman filter was developed to automate the real-time projection of ice-affected streamflow, based on routine measurements of stage and air temperature and the relation between stage and flow during open-water conditions. The form accommodates three dynamic modes of ice effects: sudden formation-ablation, stable ice conditions, and final elimination. The filter was applied to historical data from two long-term stream-flow-gaging stations. They were stable and parameters converged for both stations, producing estimates that were highly correlated with and linearly related to published streamflow values in a log-transformed metric. At St. John River at Dickey, Maine, logarithms of projected streamflow values were within 8% of the logarithms of published values 87.2% of the time and within 15% of published values 96.6% of the time during periods of ice effects. At Platte River at North Bend, Nebraska, logarithms of projected streamflow values were within 8% of the logarithms of published daily values 90.7% of the time and within 15%, 97.7% of the time during ice-affected conditions. This extended Kalman filter allows estimation of ice-affected streamflow at other gaging stations by adjusting filter parameters to site-specific conditions.

The Standard Penetration Test (SPT) is critically examined with respect to its ability to estimate relative density in situ. Six test specimens, 4 ft in diameter by 6 ft high, were constructed using Platte River sand and Standard Concrete sand. SPT's were performed, using field drilling equipment, on specimens under three overburden pressures and constructed to three relative densities. The results are presented as a family of curves correlating relative density with SPT N-values at the three overburden pressures. This research is an extension of a previous test series on Reid Bedford Model sand and Ottawa sand. The results from tests of the four sands are compared, and a statistical analysis is presented which produced an empirical equation relating relative density to overburden pressure, SPT N-value, and coefficient of uniformity. Comparisons are also made between this work and that of Gibbs and Holtz at the Bureau of Reclamation and Bazaraa at the University of Illinois. Conclusions are presented based on both series of tests. (Author), See also rept. no. 3, AD-A037 192.