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Annual mass load estimators are evaluated for application to a range of tributary types including highly responsive systems. Evaluations are performed by conducting retrospective studies with comprehensive sets of field data for total phosphorus concentration and discharge. Four estimators from three broad categories are selected for study based on their performance in previous research. Extimators are evaluated using Monte Carlo sampling studies in which load estimates made from random subsamples are compared to true loads calculated from a complete loading record. The performance of the estimators differs strongly among the tributary test cases. Hydrograph characteristics and/or concentration/discharge relationships appear to play a strong role in the precision of all of the estimators and in the bias of averaging and regression estimators. Beale's ratio estimator is the only estimator to provide unbiased estimates for both stable and responsive systems, although stratification is necessary under event sampling. Consistent accuracy of the ratio estimator is valuable because it will allow the design of future sampling programs and accurate estimation of confidence intervals from collected sample data.

Transport studies were conducted to assess ocean disposal of soil contaminated with low-level natural radioisotopes. The experimental approach involved characterization of the soil for parameters affecting transport and fate of radionuclides. Radioactivity was associated with discrete soil particles up to 6,000 [Mu]m. Gross and most individual isotope and element activities were more concentrated on smaller particles. The median size based on gross radio-activity was 125 [Mu]m, while the median size based on dry mass was 350 [Mu]m. Particle-settling velocities measured in a 1 m settling column ranged up to 8.2 cm/s (median 2.1 cm/s). Large-scale mixed water column experiments (5 m) confirmed that settling would be the dominant verticle transport mechanism for the soil particles. Experimental results were used to calibrate a convective-diffusive transport model, which was applied to a hypothetical ocean disposal site in 4,000 m of water. The model indicated that 95% of the soil and associated radionuclides would impact the bottom sediment within five days and up to 40 km from the disposal point, along the mean current flow., The viability of ocean disposal for radioactive soil is studied. The soil transportation model used for ocean disposal considers factors such as time of arrival at the bottom, together with the horizontal and vertical distance travelled caused by current. Results show that 95% of soil will land in about five days within 0.5-40 kilometers from the disposal site. Middlesex soil was used for testing, but characteristics would differ depending on the kind of soil that was used.

Cyanobacterial harmful algal blooms (CyanoHABs) have serious adverse effects on human and environmental health. Herein, we developed a modeling framework that predicts the effect of climate change on cyanobacteria concentrations in large reservoirs in the contiguous U.S. The framework, which uses climate change projections from five global circulation models, two greenhouse gas emission scenarios, and two cyanobacterial growth scenarios, is unique in coupling climate projections with a hydrologic/water quality network model of the contiguous United States. Thus, it generates both regional and nationwide projections useful as a screening-level assessment of climate impacts on CyanoHAB prevalence as well as potential lost recreation days and associated economic value. Our projections indicate that CyanoHAB concentrations are likely to increase primarily due to water temperature increases tempered by increased nutrient levels resulting from changing demographics and climatic impacts on hydrology that drive nutrient transport. The combination of these factors results in the mean number of days of CyanoHAB occurrence ranging from about 7 days per year per waterbody under current conditions, to 16-23 days in 2050 and 18-39 days in 2090. From a regional perspective, we find the largest increases in CyanoHAB occurrence in the Northeast U.S., while the greatest impacts to recreation, in terms of costs, are in the Southeast.