A MODEL TO ENHANCE WETLAND DESIGN AND OPTIMIZE NONPOINT SOURCE POLLUTION CONTROL1

ABSTRACT: A dynamic, compartmental, simulation model (WETLAND) was developed for the design and evaluation of constructed wetlands to optimize nonpoint source (NPS) pollution control. The model simulates the hydrologic, nitrogen, carbon, dissolved oxygen (DO), bacteria, vegetative, phosphorous, and sediment cycles of a wetland system. Written in Fortran 77, the WETLAND models both free‐water surface (FWS) and subsurface flow (SSF) wetlands, and is designed in a modular manner that gives the user the flexibility to decide which cycles and processes to model. WETLAND differs from many existing wetland models in that the interactions between the different nutrient cycles are modeled, minimizing the number of assumptions concerning wetland processes. It also directly links microbial growth and death to the consumption and transformations of nutrients in the wetland system. The WETLAND model is intended to be utilized with an existing NPS hydro‐logic simulation model, such as ANSWERS or BASINS, but also may be used in situations where measured input data to the wetland are available. The model was calibrated and validated using limited data from a FWS wetland located at Benton, Kentucky. The WETLAND predictions were not statistically different from measured values for of five‐day biochemical oxygen demand (BOD₅), suspended sediment, nitrogen, and phosphorous. Effluent DO predictions were not always consistent with measured concentrations. A sensitivity analysis indicated the most significant input parameters to the model were those that directly affected bacterial growth and DO uptake and movement. The model was used to design a hypothetical constructed wetland in a subwatershed of the Nomini Creek watershed, located in Virginia. Two‐year simulations were completed for five separate wetland designs. Predicted percent reductions in BOD₅ (4 to 45 percent), total suspended solids (85 to 100 percent), total nitrogen (42 to 56 percent), and total phosphorous (38 to 57 percent) were similar to levels reported by previous research.     

THE EFFECTS OF VEGETATION AND SOIL TYPE ON STREAMBANK EROSION,SOUTHWESTERN VIRGINIA,USA1

The goal of this research was to evaluate the relative effects of root density, freeze/thaw cycling, and soil properties on the erodibility and critical shear stress of streambanks. The erodibility and critical shear stress of rooted bank soils were measured in situ at 25 field sites using a submerged jet test device; several soil, vegetation, and stream chemistry characteristics shown to influence soil erosion were also assessed. Multiple linear regression analysis was conducted to determine those factors that most influenced streambank erodibility and the relative impact of riparian vegetation. Study results indicated that soil erosion is a complex phenomenon that depends primarily on soil bulk density. Freeze/thaw cycling, soil antecedent moisture content, the density of roots with diameters of 2 to 20 mm, soil texture, and the interaction of soil pore water and stream water had a significant impact on soil erodibility and critical shear stress, depending on soil type. Riparian vegetation had multiple significant effects on soil erodibility. In addition to reducing soil erodibility through root reinforcement, the streamside vegetation affected soil moisture and altered the local microclimate, which in turn affected freeze/thaw cycling (FTC). This study represents the first in situ testing of the erodibility of vegetated streambanks and provides a quantitative analysis on the effects of vegetation on streambank erosion, relative to other soil physical and chemical parameters.     

Transpiration and Root Development of Urban Trees in Structural Soil Stormwater Reservoirs

Stormwater management that relies on ecosystem processes, such as tree canopy interception and rhizosphere biology, can be difficult to achieve in built environments because urban land is costly and urban soil inhospitable to vegetation. Yet such systems offer a potentially valuable tool for achieving both sustainable urban forests and stormwater management. We evaluated tree water uptake and root distribution in a novel stormwater mitigation facility that integrates trees directly into detention reservoirs under pavement. The system relies on structural soils: highly porous engineered mixes designed to support tree root growth and pavement. To evaluate tree performance under the peculiar conditions of such a stormwater detention reservoir (i.e., periodically inundated), we grew green ash (Fraxinus pennsylvanica Marsh.) and swamp white oak (Quercus bicolor Willd.) in either CUSoil or a Carolina Stalite-based mix subjected to three simulated below-system infiltration rates for two growing seasons. Infiltration rate affected both transpiration and rooting depth. In a factorial experiment with ash, rooting depth always increased with infiltration rate for Stalite, but this relation was less consistent for CUSoil. Slow-drainage rates reduced transpiration and restricted rooting depth for both species and soils, and trunk growth was restricted for oak, which grew the most in moderate infiltration. Transpiration rates under slow infiltration were 55% (oak) and 70% (ash) of the most rapidly transpiring treatment (moderate for oak and rapid for ash). We conclude this system is feasible and provides another tool to address runoff that integrates the function of urban green spaces with other urban needs.     

OPTIMAL ALLOCATION OF WATER QUALITY CONTROLS IN URBANIZING RIVER BASINS1

ABSTRACT: Urbanizing river basins in the west are encountering serious water quality degradation resulting from the expanded water utilization. In order to avoid aggravating such conditions, water quality controls need to be implemented. The important questions are, therefore, where and how to impose such constraints on the urban and agricultural sectors to achieve the desired level of pollution control. An application of the model developed to address such questions is made in the Utah Lake drainage area of Central Utah as a test of the model's utility. The region is subdivided into five major sub-basins containing both municipal and agricultural water demands. A submodel of each sub-basin is developed which optimizes the water quality control strategies by linking the urban to the agricultural uses and then evaluating the levels of control for each sector. From these results, a cost-effectiveness function for each sub-basin is generated. By jointly considering the cost-effectiveness relationship for each sub-basin, an optimum policy for the entire basin is determined.     

An assessment of adherence to basic ecological principles by payments for ecosystem service projects

Programs and projects employing payments for ecosystem service (PES) interventions achieve their objectives by linking buyers and sellers of ecosystem services. Although PES projects are popular conservation and development interventions, little is known about their adherence to basic ecological principles. We conducted a quantitative assessment of the degree to which a global set of PES projects adhered to four ecological principles that are basic scientific considerations for any project focused on ecosystem management: collection of baseline data, identification of threats to an ecosystem service, monitoring, and attention to ecosystem dynamics or the formation of an adaptive management plan. We evaluated 118 PES projects in three markets—biodiversity, carbon, and water—compiled using websites of major conservation organizations; ecology, economic, and climate‐change databases; and three scholarly databases (ISI Web of Knowledge, Web of Science, and Google Scholar). To assess adherence to ecological principles, we constructed two scientific indices (one additive [ASI] and one multiplicative [MSI]) based on our four ecological criteria and analyzed index scores by relevant project characteristics (e.g., sector, buyer, seller). Carbon‐sector projects had higher ASI values (P < 0.05) than water‐sector projects and marginally higher ASI scores (P < 0.1) than biodiversity‐sector projects, demonstrating their greater adherence to ecological principles. Projects financed by public–private partnerships had significantly higher ASI values than projects financed by governments (P < 0.05) and marginally higher ASI values than those funded by private entities (P < 0.1). We did not detect differences in adherence to ecological principles based on the inclusion of cobenefits, the spatial extent of a project, or the size of a project's budget. These findings suggest, at this critical phase in the rapid growth of PES projects, that fundamental ecological principles should be considered more carefully in PES project design and implementation in an effort to ensure PES project viability and sustainability.     

Performance of single-gene noninvasive prenatal testing for autosomal recessive conditions in a general population setting

Objective

Carrier screening with reflex to single-gene noninvasive prenatal testing (sgNIPT) is an alternative approach for identifying pregnancies at risk for inherited autosomal recessive conditions without the need for a sample from the reproductive partner. This study is the largest clinical validation of this approach in a general population setting.

Methods

The clinical performance of carrier screening with reflex to sgNIPT for cystic fibrosis, spinal muscular atrophy, alpha thalassemias, and beta hemoglobinopathies was assessed by collecting pregnancy outcome data on patients who underwent this testing and comparing the neonatal outcome to the assay-predicted fetal risk.

Results

Of 42,067 pregnant individuals who underwent screening, 7538 carriers (17.9%) had reflex sgNIPT, and neonatal or fetal outcomes were obtained for 528 cases, including 25 affected pregnancies. Outcomes demonstrated high concordance with sgNIPT, for example, all pregnancies with 9 in 10 personalized fetal risk results were affected (positive predictive value (PPV) of 100% for the sub-group) and the sgNIPT assay showed a sensitivity of 96.0% (95% CI: 79.65%–99.90%), specificity of 95.2% (95% CI: 92.98%–96.92%), average PPV of 50.0% (95% CI: 35.23%–64.77%), and negative predictive value (NPV) of 99.8% (95% CI: 98.84%–99.99%). The end-to-end performance of carrier screening with reflex to sgNIPT was calculated to have a sensitivity of 92.4% and specificity of 99.9%, which are unaffected by partner carrier screening or misattributed paternity unlike a traditional carrier screening workflow, which has a 35% sensitivity and a maximum of 25% PPV (1 in 4) in a real-life setting.

Conclusion

This study builds upon earlier findings to confirm that carrier testing with reflex to sgNIPT is highly accurate for general population screening. Given this high accuracy and an NPV of 99.8%, this workflow should be considered as an option for most of the general pregnant population. When the biological partner sample is unavailable, this workflow should be recommended as the first-line approach.     

WATER SUPPLY,TREATMENT, DISTRUBTION,AND REUSE OPTIMIZATION IN ARID URBAN AREAS1

ABSTRACT: A Management level model has been formulated in which a system analysis format is employed to answer some of the basic questions regarding urban water management strategies The model incorporates a multilevel optimization scheme to coordinate urban water supply, distribution, and wastewater management. A test of the model's utility is made in an application to the water management problems of the Denver, Colorado metropolitan area. Denver has utilized both agricultural transfers and transmountain diversions to supplement the natural stream resources of the South Platte River. Although plans are being made to increase the capacity of these sources, increasingly stringent standards on the area's effluents are enhancing the feasibility of reclaiming and recycling a portion of the wastewater. The urban model used in this study indicates the decision points at which respective strategies are introduced. However, by formulating the model from a planner's viewpoint, the most important results gained from the analysis are the costs of various institutional constraints which may restrict the decision maker's ability to implement optimal policies.     

PCE solubilization and mobilization by commercial humic acid

In this paper, comparison is made of terms describing solubilization of hydrophobic organic compounds (HOC) by dissolved humic substances (DHS) and commercial non-ionic surfactants. This paper examines the ability of a commercial humic acid (Aldrich humic acid) to solubilize and mobilize tetrachlorothene (PCE) residual in porous media. The constant for solubilization of PCE by Aldrich humic acid is shown to be a factor of two to thirty times less than that published for dodecyl alcohol ethoxylate surfactants, showing that Aldrich humic acid is less capable than some non-ionic surfactants at solubilizing residual PCE. The depression of PCE–water interfacial tension in the presence of DHS is shown to be significantly less than published values for a non-ionic surfactant, and surfactant mixtures, indicating that the DHS used in this study is less prone to cause mobilization of non-aqueous phase liquids relative to surfactants. Several possible advantages of DHS use in the remediation of subsurface media contaminated with HOC are described, including the ability of DHS to solubilize HOC irrespective of the DHS concentration, and potential lesser tendency of DHS to depress the interfacial tension between non-aqueous phases and water relative to surfactants (an advantage when mobilization is undesired).