WILLOW POSTS BANK STABILIZATION1

ABSTRACT: Harland Creek, in east-central Mississippi, is a rapidly migrating, meandering stream that is experiencing severe bank erosion. More than 9,000 willow (Salix nigra) posts were emplaced in February 1994 by the U.S. Army, Corps of Engineers in an effort to stabilize eroding stream banks using an experimental bioengi-neering technique. Monitoring of this stream reach and the willow post bank stabilization has resulted in a data base to assess willow mortality as related to bank aspect, post diameter, cover, and base elevation above low water. Monitoring has also resulted in the development of revised construction guidelines. Survivability of the posts, a necessary condition for long-term success, was found to average 81 percent in May 1994, 43 percent in October 1994, and 41 percent in August 1995. Even with survivability as low as 29 percent to 34 percent at specific bend reaches, willow posts are documented to be successful in bank stabilization for the period of monitoring, in comparison with more traditional riprap stabilization methods. Guidelines for improved survivability and recommended site selection are presented. Cost of willow post bank stabilization is less than traditional riprap, and willow posts can be emplaced using readily available equipment and materials.     

FLUME CONDITION ASSESSMENT IN COLORADO1

ABSTRACT: A study was conducted in which 66 Parshall flumes used for agricultural flow measurement were assessed for physical integrity, settlement, and submergence. A total of 292 physical defects was documented. A flow measurement error analysis was performed indicating that 52 percent of the flumes measured flow beyond ±3 percent of the correct value and 41 percent of the flumes measured flow beyond ±5 percent. The findings indicate that the infrastructure is aging. The flow measurement system comprised of flumes no longer provide an accurate accounting of water through the distribution network.     

WATERSHED RESPONSES TO CLIMATE CHANGE AT GLACIER NATIONAL PARK1

ABSTRACT: We have developed an approach which examines ecosystem function and the potential effects of climatic shifts. The Lake McDonald watershed of Glacier National Park was the focus for two linked research activities: acquisition of baseline data on hydrologic, chemical and aquatic organism attributes that characterize this pristine northern rocky mountain watershed, and further developing the Regional Hydro-Ecosystem Simulation System (RHESSys), a collection of integrated models which collectively provide spatially explicit, mechanistically-derived outputs of ecosystem processes, including hydrologic outflow, soil moisture, and snow-pack water equivalence. In this unique setting field validation of RHESSys, outputs demonstrated that reasonable estimates of SWE and streamflow are being produced. RHESSys was used to predict annual stream discharge and temperature. The predictions, in conjunction with the field data, indicated that aquatic resources of the park may be significantly affected. Utilizing RHESSys to predict potential climate scenarios and response of other key ecosystem components can provide scientific insights as well as proactive guidelines for national park management.     

Towards a better understanding of tetrachloroethene entry pressure in the matrix of Permo-Triassic sandstones

The pressure required for a chlorinated solvent to enter a geological medium can be calculated given knowledge of the characteristic pore size of the medium and the interfacial tension (IFT) and contact angle of the solvent-water-rock system. Using a centrifuge-based method, capillary pressure-saturation curves have been determined for 30 water-saturated samples of Permo-Triassic sandstones for the solvent tetrachloroethene (PCE). These curves have been successfully fitted using the van Genuchten function to determine PCE entry pressure for each of the sandstone samples. A plot of PCE entry pressures against average pore diameter shows a linear relationship in log-log space; however, observed values for PCE entry pressure are significantly lower than would be expected theoretically for a sandstone-PCE-water system. This may be explained either by a decrease in the IFT or an increase in the contact angle. The IFT may decrease during contact with sandstones due to hysteresis effects during imbibition and drainage of fluids, but this is unlikely to be sufficient to account for the low entry pressures observed. Therefore, it is inferred that the low observed PCE entry pressures are due to higher than expected PCE contact angles, and that the average pore-throat surface of the sandstones is more solvent wetting than would be expected. A weak acid extraction indicates the presence of calcite and dolomite in the sandstone cores, and a correlation is observed between carbonate content per unit porosity and a reduction in PCE entry pressure. It is suggested that these mineral phases are responsible for observed wettability changes and a conceptual model is proposed. One consequence of the lower observed entry pressures is that solvents are likely to penetrate deeper into the matrix of water-saturated sandstones than previously expected.     

Real-world vehicle emissions: a summary of the Eleventh Coordinating Research Council On-Road Vehicle Emissions Workshop

The Coordinating Research Council (CRC) held its eleventh workshop in March 2001, focusing on results from the most recent real-world vehicle emissions research. We summarize the presentations from researchers engaged in improving our understanding of the contribution of mobile sources to ambient air quality and emission inventories. Participants in the workshop discussed efforts to improve mobile source emission models and emission inventories, the role of on-board diagnostic (OBD) systems in inspection and maintenance (I/M) programs, particulate matter (PM) emissions, contributions of diesel vehicles to the emission inventory, on-road emissions measurements, fuel effects, unregulated emissions, and microscale and modal emission models, as well as topics for future research.     

Determination of acute exposure guideline levels in a dispersion model

The U.S. Environmental Protection Agency (EPA) is in the process of establishing acute exposure guideline levels (AEGLs) for a number of toxic chemicals. These guidelines represent predictable human consequences from measured exposures of selected toxic chemicals over time. They are intended for emergency planning and regulatory purposes. This paper presents a method that can be used by atmospheric dispersion models to compute AEGL values and graphically display the regions exposed to each guideline level on area maps. EPA currently defines three levels of AEGLs corresponding to increasingly severe symptoms, ranging from notable discomfort (AEGL-1) to serious adverse health effects (AEGL-2) to life-threatening effects or death (AEGL-3). For each chemical's three AEGL levels, guideline concentrations are defined for five exposure durations: 10 min, 30 min, 1 hr, 4 hr, and 8 hr. Dispersion models can compute a chemical dosage (time-integrated concentration) and a peak concentration throughout the area exposed to the plume. The AEGL then can be computed by finding the effective duration of the plume at each location, computing the AEGL-equivalent dosages for these durations, and comparing the dosage at each point with the AEGL-equivalent dosages. AEGL contours then can be plotted and readily interpreted in terms of expected toxicity levels for each level of health impact.     

Case study II: application of the divalent cation bridging theory to improve biofloc properties and industrial activated sludge system performance-using alternatives to sodium-based chemicals.

The objective of this study was to investigate the application of the divalent cation bridging theory (DCBT) as a tool in the chemical selection process at an activated sludge plant to improve settling, dewatering, and effluent quality. According to the DCBT, to achieve improvements, the goal of chemical selection should be to reduce the ratio of monovalent-to-divalent (M/D) cations. A study was conducted to determine the effect of using magnesium hydroxide [Mg(OH)2] as an alternative to sodium hydroxide (NaOH) at a full-scale industrial wastewater treatment plant. Floc properties and treatment plant performance were measured for approximately one year during two periods of NaOH addition and Mg(OH)2 addition. A cost analysis of plant operation during NaOH and Mg(OH)2 use was also performed. During NaOH addition, the M/D ratio was 48, while, during Mg(OH)2 addition, this ratio was reduced to an average of approximately 0.1. During the Mg(OH)2 addition period, the sludge volume index, effluent total suspended solids, and effluent chemical oxygen demand were reduced by approximately 63, 31, and 50%, respectively, compared to the NaOH addition period. The alum and polymer dose used for clarification was reduced by approximately 50 and 60%, respectively, during Mg(OH)2 addition. The dewatering properties of the activated sludge improved dewatering as measured by decreased capillary suction time and specific resistance to filtration (SRF), along with an increase in cake solids from the SRF test. This corresponded to a reduction in the volume of solids thickened by centrifuges at the treatment plant, which reduced the disposal costs of solids. Considering the costs for chemicals and solids disposal, the annual cost of using Mg(OH)2 was approximately 30,000 dollars to 115,000 dollars less than using NaOH, depending on the pricing of NaOH. The results of this study confirm that the DCBT is a useful tool for assessing chemical-addition strategies and their potential effect on activated sludge performance.     

Isotopic evidence for niche partitioning and the influence of anthropogenic disturbance on endemic and introduced rodents in central Madagascar

We applied a multi-isotope approach to examine aspects of niche partitioning, competition, and mobility for rodents in the Central Highlands of Madagascar. Specifically, we used carbon (δ¹³C), nitrogen (δ¹⁵N), and strontium (⁸⁷Sr/⁸⁶Sr) isotope ratios in bone to investigate diet and mobility for endemic tufted tail rats (Eliurus spp.), and introduced black rats (Rattus rattus) and house mice (Mus musculus) within and outside a fragment of montane humid forest in the Ambohitantely Special Reserve. There was a clear spatial segregation in trapping success for different species: Eliurus was only in the forest interior and edge, Mus only outside of the fragment in a marsh and park housing complex, and Rattus in all habitats except the housing complex. We find only moderate support for mobility of rodents among habitats. Mus may routinely move between the marsh and housing complex. However, regular movement between the forest edge and interior, or between the forest fragment and surrounding grassland is not supported. Taxa appear to target different foods: Rattus tends to feed at a higher trophic level than Eliurus, and Mus consumes some C₄ resources. To date, strontium isotopes have been underutilized in ecological research. Here, we show that they are highly complementary to carbon and nitrogen isotope data. Even in localities with relatively uniform underlying geology, it may be possible to distinguish individuals that regularly forage in different habitats.