Engineering Bulletins: Aids to the Development of Remedial Alternatives

An overview of activities of the Risk Reduction Engineering Laboratory in response to the Environmental Protection Agency’s Treatability Initiative are described and a summary of the information in the first ten Engineering Bulletins, which are a component of the initiative, is provided.     

Do we need “more research” or better implementation through knowledge brokering?

“More research is needed” is an iconic catchphrase used by scientists worldwide. Yet policy and management decisions are continually being made with variable levels of reliance on scientific knowledge. Funding agencies have provided incentives for knowledge exchange at the interfaces between science and policy or practice, yet it remains the exception rather than the rule within academic institutions. An important step forward would be the establishment and professionalization of knowledge brokering (i.e., as a complement to existing technology transfer and communications departments). This would require an explicit commitment of resources by both funding agencies and institutions. Many academic scientists are genuinely interested in the applications of their research. This interest could be stimulated by providing support for the process of knowledge brokering and by integrating the natural, social, and engineering sciences to address broad policy- and practice-relevant questions.     

Modeling instability development in layered systems

This study investigates patterns of finger development and propagation in layered porous media. Fingers are created with interfacial perturbations, formed by adding a thin zone of regularly varying hydraulic conductivity along the layer. Simulation results agree qualitatively with those observed in two-dimensional laboratory experiments. In all cases, the formation of instabilities requires seeding of perturbations, even if the system is unstably stratified. A series of simulations show how the shapes of the instabilities differ according to where along the unstable interface the instabilities form and the layer in which they develop. Pathline analyses indicate how the patterns of flow in the domain can be exceedingly complex. Concentration distributions are influenced by movements of water between layers and the formation of a large convection cell in the lowermost layer. These numerical investigations reinforce inferences from the experimental studies that classical stability theory is less useful in determining whether instabilities will form and what their shape will be. Even with the relatively simple layering, patterns of flow and resulting concentrations are complex.     

Nitrogen and phosphorus runoff losses from variable and constant intensity rainfall simulations on loamy sand under conventional and strip tillage systems

Further studies on the quality of runoff from tillage and cropping systems in the southeastern USA are needed to refine current risk assessment tools for nutrient contamination. Our objective was to quantify and compare effects of constant (Ic) and variable (Iv) rainfall intensity patterns on inorganic nitrogen (N) and phosphorus (P) losses from a Tifton loamy sand (Plinthic Kandiudult) cropped to cotton (Gossypium hirsutum L.) and managed under conventional (CT) or strip-till (ST) systems. We simulated rainfall at a constant intensity and a variable intensity pattern (57 mm h(-1)) and collected runoff continuously at 5-min intervals for 70 min. For cumulative runoff at 50 min, the Iv pattern lost significantly greater amounts (p < 0.05) of total Kjeldahl N (TKN) and P (TKP) (849 g N ha(-1) and 266 g P ha(-1) for Iv; 623 g N ha(-1) and 192 g P ha(-1) for Ic) than did the Ic pattern. However, at 70 min, no significant differences in total losses were evident for TKN or TKP from either rainfall intensity pattern. In contrast, total cumulative losses of dissolved reactive P (DRP) and NO3-N were greatest for ST-Ic, followed by ST-Iv, CT-Ic, and CT-Iv in diminishing order (69 g DRP ha(-1) and 361 g NO3-N ha(-1); 37 g DRP ha(-1) and 133 g NO3-N ha(-1); 3 g DRP ha(-1) and 58 g NO3-N ha(-1); 1 g DRP ha(-1) and 49 g NO3-N ha(-1)). Results indicate that constant-rate rainfall simulations may overestimate the amount of dissolved nutrients lost to the environment in overland flow from cropping systems in loamy sand soils. We also found that CT treatments lost significantly greater amounts of TKN and TKP than ST treatments and in contrast, ST treatments lost significantly greater amounts of DRP and NO3-N than CT treatments. These results indicate that ST systems may be losing more soluble fractions than CT systems, but only a fraction the total N (33%) and total P (11%) lost through overland flow from CT systems.     

Relations between Conspecific Density and Effects of Ultraviolet‐B Radiation on Tadpole Size in the Striped Marsh Frog

Global increases in ultraviolet‐B radiation (UVBR) associated with stratospheric ozone depletion are potentially contributing to the decline of numerous amphibian species around the world. Exposure to UVBR alone reduces survival and induces a range of sublethal effects in embryonic and larval amphibians. When additional environmental stressors are present, UVBR can have compounding negative effects. Thus, examination of the effects of UVBR in the absence of other stressors may substantially underestimate its potential to affect amphibians in natural habitats. We examined the independent and interactive effects of increased UVBR and high conspecific density would have embryonic and larval striped marsh frogs (Limnodynastes peronii). We exposed individuals to a factorial combination of low and high UVBR levels and low, medium, and high densities of striped marsh frog tadpoles. The response variables were time to hatching, hatching success, posthatch survival, burst‐swimming performance of tadpoles (maximum instantaneous swim speed following an escape response), and size and morphology of tadpoles. Consistent with results of previous studies, we found that exposure to UVBR alone increased the time to hatching of embryos and reduced the burst‐swimming performance and size of tadpoles. Similarly, increasing conspecific density increased the time to hatching of embryos and reduced the size of tadpoles, but had no effect on burst‐swimming performance. The negative effect of UVBR on tadpole size was not apparent at high densities of tadpoles. This result suggests that tadpoles living at higher densities may invest relatively less energy in growth and thus have more energy to repair UVBR‐induced damage. Lower densities of conspecifics increased the negative effects of UVBR on developing amphibians. Thus, low‐density populations, which may include declining populations, may be particularly susceptible to the detrimental effects of increased UVBR and thus may be driven toward extinction faster than might be expected on the basis of results from single‐factor studies. Relaciones entre la Densidad Conespecífica y los Efectos de la Radiación Ultravioleta‐B sobre el Tamaño de Renacuajos de Limnodynastes peronei     

Effects of irrigation on the environment of selected areas of the Western United States and implications to world population growth and food production

Studies of irrigation drainage in the Western United States have documented some of the effects of irrigating land without first understanding and then considering implications from the interdependent relationships of hydrology, geology, geochemistry, biology, climatology, land use and socio-economic issues. In studies completed in 26 areas, selenium is the trace element found most often at elevated concentrations in water, bottom material and biota. Boron, arsenic, mercury and pesticide residues have also been found at elevated levels in some areas. Bioaccumulation of constituents associated with irrigation drainage is common. As the world experiences an explosive population growth, particularly in poorer countries, demands for food production from marginal, submarginal and newly irrigated soils are likely to cause severe adverse environmental impacts from allocation of limited water resources and contamination from irrigation drainwater. Cultivated marginal land is highly susceptible to degradation from soil erosion, salinization and waterlogging, not withstanding release of contaminants from application of irrigation water.