Mass balance modelling of contaminants in river basins: a flexible matrix approach

A novel and flexible approach is described for simulating the behaviour of chemicals in river basins. A number (n) of river reaches are defined and their connectivity is described by entries in an n x n matrix. Changes in segmentation can be readily accommodated by altering the matrix entries, without the need for model revision. Two models are described. The simpler QMX-R model only considers advection and an overall loss due to the combined processes of volatilization, net transfer to sediment and degradation. The rate constant for the overall loss is derived from fugacity calculations for a single segment system. The more rigorous QMX-F model performs fugacity calculations for each segment and explicitly includes the processes of advection, evaporation, water-sediment exchange and degradation in both water and sediment. In this way chemical exposure in all compartments (including equilibrium concentrations in biota) can be estimated. Both models are designed to serve as intermediate-complexity exposure assessment tools for river basins with relatively low data requirements. By considering the spatially explicit nature of emission sources and the changes in concentration which occur with transport in the channel system, the approach offers significant advantages over simple one-segment simulations while being more readily applicable than more sophisticated, highly segmented, GIS-based models.     

Modeling inorganic aerosols and their response to changes in precursor concentration in Mexico City

Based on data from the 1997 Investigación sobre Materia Particulada y Deterioro Atmosférico-Aerosol and Visibility Evaluation Research (IMADA-EVER) campaign and the inorganic aerosol model ISORROPIA, the response of inorganic aerosols to changes in precursor concentrations was calculated. The aerosol behavior is dominated by the abundance of ammonia and thus, changes in ammonia concentration are expected to have a small effect on particle concentrations. Changes in sulfate and nitrate are expected to lead to proportional reductions in inorganic fine particulate matter (PM2.5). Comparing the predictions of ISORROPIA with the observations, the lowest bias and error are achieved when the aerosols are assumed to be in the efflorescence branch. Including crustal species reduces the bias and error for nitrate but does not improve overall model performance. The estimated response of inorganic PM2.5 to changes in precursor concentrations is affected by the inclusion of crustal species in some cases, although average responses are comparable with and without crustal species. Observed concentrations of particle chloride suggest that gas phase concentrations of hydrogen chloride may not be negligible, and future measurement campaigns should include observations to test this hypothesis. Our ability to model aerosol behavior in Mexico City and, thus, design control strategies, is constrained primarily by a lack of observations of gas phase precursors. Future campaigns should focus in particular on better understanding the temporal and spatial distribution of ammonia concentrations. In addition, gas phase observations of nitric acid are needed, and a measure of particle water content will allow stable versus metastable aerosol behavior to be distinguished.     

Multi‐Criteria Decision Support Systems for Flood Hazard Mitigation and Emergency Response in Urban Watersheds1

Abstract: Flood management problems are inherently complex, time‐bound and multi‐faceted, involving many decision makers (with conflicting priorities and dynamic preferences), high decision stakes, limited technical information (both in terms of quality and quantity), and difficult tradeoffs. Multi‐Criteria Decision Support Systems (MCDSS) can help to manage this complexity and decision load by combining value judgments and technical information in a structured decision framework. A brief overview of MCDSS is presented, an original MCDSS architecture is put forth, and future research directions are discussed, including extensions to Multi‐Criteria Spatial Decision Support Systems and group MCDSS (as flood management involves shared resources and broad constituencies). With application to the September 11‐12, 2000 Tokai floods in Japan, the proposed multi‐criteria decision support instruments enhance communication among stakeholders and improve emergency management resource allocation. In summary, by making the links among flood knowledge, assumptions and choices more explicit, MCDSS increases stakeholder satisfaction, saves lives, and reduces flood management costs, thereby increasing decision‐making effectiveness, efficiency and transparency.     

Leading indicators of safety in virtual organizations

A primary purpose in measuring safety is to develop intervention strategies to avoid future accidents. Recognizing signals before an accident occurs offers the potential for improving safety, and many organizations have sought to develop programs to identify and benefit from alerts, signals and prior indicators. In this paper, we address the challenge of identifying and evaluating leading indicators of safety in virtual organizations–organizations comprised of multiple, distributed members, temporarily linked together for competitive advantage, that share common value chains and business processes supported by distributed information technology. We begin by discussing risk propensity in virtual organizations and leading indicators of safety. We then describe a pilot study to identify leading indicators for one safety-critical system, and use the results of that study and the literature just described to propose an approach to developing leading indicators in virtual organizations.     

Groundwater quality surrounding Lake Texoma during short-term drought conditions

Water quality data from 55 monitoring wells during drought conditions surrounding Lake Texoma, located on the border of Oklahoma and Texas, was compared to assess the influence of drought on groundwater quality. During the drought month of October, water table levels were three feet (0.9 m) lower compared with several months earlier under predrought climate conditions. Detection frequencies of nitrate (> 0.1 mg/l), orthophosphates (> 0.1 mg/l), chlorides (> MCL), and sulfates (> MCL) all increased during drought. Orthophosphate level was higher during drought. Largest increases in concentration were nitrate under both agriculture lands and in septic tank areas. An increase in ammonium-nitrogen was only detected in the septic tank area. The study showed that stressors such as nitrate and total salts could potentially become a health or environmental problem during drought.     

COMPARATIVE EVALUATION OF LAND COVER DATA SOURCES FOR EROSION PREDICTION1

ABSTRACT: A fundamental problem in protecting surface drinking water supplies is the identification of sites highly susceptible to soil erosion and other forms of nonpoint source (NPS) pollution. The New York City Department of Environmental Protection is trying to identify erodible sites as part of a program aimed at avoiding costly filtration. New York City's 2,000 square mile watershed system is well suited for analysis with geographic information systems (GIS); an increasingly important tool to determine the spatial distribution of sensitive NPS pollution areas. This study used a GIS to compare three land cover sources for input into the Modified Universal Soil Loss Equation (MUSLE), a model estimating soil loss from rangeland and forests, for a tributary watershed within New York City's water supply system. Sources included both conventional data (aerial photography) and Landsat data (MSS and TM images). Although land cover classifications varied significantly across these sources, location-specific and aggregate watershed predictions of the MUSLE were very similar. We conclude that using Landsat TM imagery with a hybrid classification algorithm provides a rapid, objective means of developing large area land cover databases for use in the MUSLE, thus presenting an attractive alternative to photo interpretation.     

Integrated Assessment of Abatement Strategies to Improve Air Quality in Urban Environments, the USIAM Model

Planning effective strategies to combat air pollution in amajor city such as London requires integration ofinformation on atmospheric concentrations and where theyexceed prescribed air quality standards, detailed data onemissions and potential measures to reduce them includingcosts, and a good understanding of the relativecontributions of different emission sources to pollutantconcentrations plus the remaining background. The UrbanScale Integrated Assessment Model (USIAM) is designed as atool to integrate such information, and to explore andassess a variety of potential strategies for improving airquality. It is based on the same principles as theAbatement Strategies Assessment Model (ASAM) that has beenused in the UN Economic Commission for Europe. To startwith the USIAM model is being developed with respect to theparticulate PM₁₀ only, and in particular the primaryparticulate contribution. The secondary particulate istreated as part of the background superimposed on theprimary particulate concentrations; this may need to betreated more specifically at a later stage, particularlywith respect to nitrate formation over the city. The USIAMmodel therefore sets out to examine a selection of severeepisode conditions as well as long-term annual averageconcentrations, and aims to find strategies that aresuccessful in eliminating exceedance of the prescribedtarget concentrations. By ranking different options forabatement of emissions, for example in terms of cost orease of implementation, the USIAM model can also select andprioritise different potential strategies.     

WATER MANAGEMENT ISSUES FOR THE NINETIES1

ABSTRACT: This paper summarizes contemporary water management issues as recognized by 19 U.S. organizations. Only the issues are identified herein. Individual organization stands are not presented. Most suggestions for action are those of the author. Addresses of all organizations whose documents were reviewed are included in the Reference section so that those desiring to learn more about an organization's stand can readily make contact.     

Salt marsh vegetation change in response to tidal restriction

Vegetation change in response to restriction of the normal tidal prism of six Connecticut salt marshes is documented. Tidal flow at the study sites was restricted with tide gates and associated causeways and dikes for purposes of flood protection, mosquito control, and/or salt hay farming. One study site has been under a regime of reduced tidal flow since colonial times, while the duration of restriction at the other sites ranges from less than ten years to several decades. The data indicate that with tidal restriction there is a substantial reduction in soil water salinity, lowering of the water table level, as well as a relative drop in the marsh surface elevation. These factors are considered to favor the establishment and spread ofPhragmites australis (common reed grass) and other less salt-tolerant species, with an attendant loss ofSpartina-dominated marsh. Based on detailed vegetation mapping of the study sites, a generalized scheme is presented to describe the sequence of vegetation change from typicalSpartina- toPhragmites-dominated marshes. The restoration of thesePhragmites systems is feasible following the reintroduction of tidal flow. At several sites dominated byPhragmites, tidal flow was reintroduced after two decades of continuous restriction, resulting in a marked reduction inPhragmites height and the reestablishment of typical salt marsh vegetation along creekbanks. It is suggested that large-scale restoration efforts be initiated in order that these degraded systems once again assume their roles within the salt marsh-estuarine ecosystem.