Minimizing irrigation water demand: An evaluation of shifting planting dates in Sri Lanka

Climate change coupled with increasing demands for water necessitates an improved understanding of the water–food nexus at a scale local enough to inform farmer adaptations. Such assessments are particularly important for nations with significant small-scale farming and high spatial variability in climate, such as Sri Lanka. By comparing historical patterns of irrigation water requirements (IWRs) to rice planting records, we estimate that shifting rice planting dates to earlier in the season could yield water savings of up to 6%. Our findings demonstrate the potential of low-cost adaptation strategies to help meet crop production demands in water-scarce environments. This local-scale assessment of IWRs in Sri Lanka highlights the value of using historical data to inform agricultural management of water resources when high-skilled forecasts are not available. Given national policies prioritizing in-country production and farmers’ sensitivities to water stress, decision-makers should consider local degrees of climate variability in institutional design of irrigation management structures.     

Effect of surface coatings, grain size, and ionic strength on the maximum attainable coverage of bacteria on sand surfaces

The injection of bacteria in the subsurface has been identified as a potential method for in situ cleanup of contaminated aquifers. For high bacterial loadings, the presence of previously deposited bacteria can result in decreased deposition rates--a phenomenon known as blocking. Miscible displacement experiments were performed on short sand columns (approximately 5 cm) to determine how bacterial deposition on positively charged metal-oxyhydroxide-coated sands is affected by the presence of previously deposited bacteria. Approximately 8 pore volumes of a radiolabeled bacterial suspension at a concentration of approximately 1 x 10(9) cells ml-1 were introduced into the columns followed by a 2-pore-volume flush of cell-free buffer. It was found that the presence of Al- and Fe-coated sand increased both deposition rates and maximum fractional surface coverage of bacteria on the sediment surfaces. The effect of grain size on maximum bacterial retention capacity, however, was not significant. Decreasing ionic strength from 10(-1) to 10(-2) M KCl resulted in noticeable decreases in sticking efficiency (alpha) and maximum surface coverage (thetamax) for clean silica sand--results consistent with DLVO theory. In columns containing positively charged Al- and Fe-coated sands, however, changes in alpha and thetamax due to decreasing ionic strength were minimal. These findings demonstrate the importance of geochemical controls on the maximum bacterial retention capacity of sands.     

Using triple bottom line metrics and multi-criteria methodology in corporate settings

With the growing importance of environmental sustainability in the corporate sector, businesses are compelled to progress from assessing and benchmarking their environmental impact to making decisions on how to prioritize impact reduction alternatives. Most often, business decisions are driven by financial metrics, but with sustainability improvements becoming a business goal, it is also important to assess metrics from environmental and social spheres; nevertheless, practically and systematically performing such an assessment is challenging. We present an application of a multi-criteria decision analysis (MCDA) method that addresses the aforementioned challenges in a corporate setting. Our case study company – one of the largest inland marine freight carriers in the United States – promotes a business culture focused on financially viable, yet socially and environmentally responsible solutions. Thus, we combine life cycle analysis (LCA), financial calculation methods, and corporate surveys to quantify environmental, economic, and social performance measures, respectively. Multiattribute utility theory is integrated with analytic hierarchy processes (AHPs) and fuzzy analysis to create a carefully designed framework for corporations with diverse groups of stakeholders. With company leadership, implementation is feasible and successful at prioritizing alternatives among diverse stakeholders. The process provides a platform for negotiation and promotes discussions on decision drivers. The use of MCDA methodologies promoted the inclusion of a suite of metrics that aligned with the company's sense of social and environmental responsibility, generating an in-depth analysis of the alternatives that factored in other things besides economics. Return-on-investments (ROI) calculations, the typical approach used in the corporate setting, would have required significantly less time and effort from the company, but the results of our MCDA application indicated that inclusion of triple bottom line metrics delve deeper into stakeholder preferences. Thus, our case study company gained a holistic view of the candidate alternatives, in addition to creating a platform for structured discussions about company goals and priorities.     

Measuring Urban Water Conservation Policies: Toward a Comprehensive Index

This article (1) discusses existing efforts to measure water conservation policies (WCPs) in the United States (U.S.); (2) suggests general methodological guidelines for creating robust water conservation indices (WCIs); (3) presents a comprehensive template for coding WCPs; (4) introduces a summary index, the Vanderbilt Water Conservation Index (VWCI), which is derived from 79 WCP observations for 197 cities for the year 2015; and (5) compares the VWCI to WCP data extracted from the 2010 American Water Works Association (AWWA) Water and Wastewater Rates survey. Existing approaches to measuring urban WCPs in U.S. cities are limited because they consider only a portion of WCPs or they are restricted geographically. The VWCI consists of a more comprehensive set of 79 observations classified as residential, commercial/industrial, billing structure, drought plan, or general. Our comparison of the VWCI and AWWA survey responses indicate reasonable agreement (ρ = 0.76) between the two WCIs for 98 cities where the data overlap. The correlation suggests the AWWA survey responses can provide fairly robust longitudinal WCP information, but we argue the measurement of WCPs is still in its infancy, and our approach suggests strategies for improving existing methods.     

A Review of the United States' Past and Projected Water Use

Good information and data on water demands are needed to perform good analyses, yet collecting and compiling spatially and temporally consistent water demand data are challenges. The objective of our work was to understand the limitations associated with water‐use estimates and projections. We performed a comprehensive literature review of national and regional United States (U.S.) water‐use estimates and projections. We explored trends in past regional projections of freshwater withdrawals and compared these values to regional estimates of freshwater withdrawals made by the U.S. Geological Survey. Our results suggest a suite of limitations exist that have the potential for influencing analyses aiming to extract explanatory variables from the data or using the data to make projections and forecasts. As we explored regional projections, we paid special attention to the two largest water demand‐side sectors — thermoelectric energy and irrigation — and found thermoelectric projections are more spread out than irrigation projections. All data related to water use have limitations, and there is no alternative to making the best use that we can of the available data; our article provides a comprehensive review of these limitations so that water managers can be more informed.     

Simulation of solute transport across low-permeability barrier walls

Low-permeability, non-reactive barrier walls are often used to contain contaminants in an aquifer. Rates of solute transport through such barriers are typically many orders of magnitude slower than rates through the aquifer. Nevertheless, the success of remedial actions may be sensitive to these low rates of transport. Two numerical simulation methods for representing low-permeability barriers in a finite-difference groundwater-flow and transport model were tested. In the first method, the hydraulic properties of the barrier were represented directly on grid cells and in the second method, the intercell hydraulic-conductance values were adjusted to approximate the reduction in horizontal flow, allowing use of a coarser and computationally efficient grid. The alternative methods were tested and evaluated on the basis of hypothetical test problems and a field case involving tetrachloroethylene (PCE) contamination at a Superfund site in New Hampshire. For all cases, advective transport across the barrier was negligible, but preexisting numerical approaches to calculate dispersion yielded dispersive fluxes that were greater than expected. A transport model (MODFLOW-GWT) was modified to (1) allow different dispersive and diffusive properties to be assigned to the barrier than the adjacent aquifer and (2) more accurately calculate dispersion from concentration gradients and solute fluxes near barriers. The new approach yields reasonable and accurate concentrations for the test cases.     

Migration of Cs through quartz sand: experimental results and modeling approaches

We present results from experiments on the migration of ¹³⁷Cs through columns containing quartz sand. Times for ¹³⁷Cs movement through these columns and the quantity of ¹³⁷Cs adsorbed by the sand decreased as the ionic strength of the pore water increased from 0.002 to 0.1 m. The breakthrough curves were characterized by a slow approach towards steady-state concentrations as well as by long tails, indicating that ¹³⁷Cs adsorption to the sand grains was, at least in part, controlled by rate-limited reactions. Various formulations for solute mass transfer were tested for their ability to fit the experimental breakthrough curves. Based on a statistical analysis, a nonlinear, two-site model was identified as the most appropriate for describing the suite of experimental data. Variation in the model parameter that describes the rate of ¹³⁷Cs adsorption to the sand showed no consistent pattern with changes in ionic strength. In contrast, model parameters describing the sorption capacity of the sand grains and the fraction of kinetic sorption sites on the sand decreased with increasing ionic strength. The parameter describing the rate of ¹³⁷Cs desorption varied directly with changes in ionic strength.