OPTIMIZATION PROCEDURE FOR COST EFFECTIVE BMP PLACEMENT AT A WATERSHED SCALE1

ABSTRACT: A combinatorial optimization procedure for best management practice (BMP) placement at the watershed level facilitates selection of cost effective BMP scenarios to control non point source (NFS) pollution. A genetic algorithm (GA) was selected from among several optimization heuristics. The GA combines an optimization component written in the C++ language with spatially variable NFS pollution prediction and economic analysis components written within the Arc View geographic information system. The procedure is modular in design, allowing for component modifications while maintaining the basic conceptual framework. An objective function was developed to lexicographically optimize pollution reduction followed by cost increase. Scenario cost effectiveness is then calculated for scenario comparisons. The NPS pollutant fitness score allows for evaluation of multiple pollutants, based on prioritization of each pollutant. The economic component considers farm level public and private costs, cost distribution, and land area requirements. Development of a sediment transport function, used with the Universal Soil Loss Equation, allows the optimization procedure to run within a reasonable timeframe. The procedure identifies multiple near optimal solutions, providing an indication of which fields have a more critical impact on overall cost effectiveness and flexibility in the final solution selected for implementation. The procedure was demonstrated for a 1,014‐ha watershed in the Ridge and Valley physiographic region of Virginia.     

Water scarcity: An alternative view and its implications for policy and capacity building

This article focuses on the somewhat ambiguous concept of scarce water, or, more accurately stated, on the rather more ambiguous concept of scarcity. Still today, water scarcity in a region is defined largely in physical terms, typically gallons or cubic metres per capita if a stock or per capita-year if a flow. However useful purely physical measures may be for broad comparisons, they cannot adequately reflect the variety of ways in which human beings use water — neither to their wastefulness when water is perceived as abundant nor to their ingenuity when it is not. This article argues that water scarcity should be defined according to three orders of scarcity that require, respectively, physical, economic and social adaptations. It goes on to demonstrate that perceiving scarcity mainly in physical terms limits opportunities for policy-making and approaches for capacity building.     

Selection of Bioindicators of Pollution for Marine Monitoring Programmes

The ultimate management concerns related to toxic chemicals in the marine environment are for the magnitude and extent of biological effects, including those on human health, that may result. Over the past several years, the National Status and Trends (NS&T) Program of the US National Oceanic and Atmospheric Administration (NOAA) has supported the development and application of a number of bioeffects measurements, including biochemical indicators of contaminant exposure and of reproductive status in fish, prevalence of histopathological lesions, toxicity bioassays of sediments and water, and benthic community structural features. Some of these measurements have been applied as part of regular sampling at the nationwide network of NS&T sites, while others have been assessed in more intensive, regional studies. Our experience with different indicators is summarized and discussed in relation to a set of monitoring objectives and evaluation criteria. Current conclusions are: (a) iterative application of controlled laboratory experiments and field validation tests are required to verify causality and mechanisms of biological responses to contaminants; (b) contaminant concentrations, indicator species, and local conditions vary considerably in different areas and at different times, requiring the use of different effects measurements oriented toward specific objectives and hypotheses; and (c) tiered, sequential application of a mix of indicators, including direct measurements on indigenous organisms and indirect bioassay approaches, is useful and effective for estimating the magnitude and spatial extent of contaminant bioeffects.     

Chemistry of methylmercurials in aqueous solution

The kinetics of acid cleavage of dimethylmercury (DMM) was studied in aqueous solution. At 25°C and pH 5, DMM has an acidolysis half-life of about 33 years. Cleavage of dimethylmercury by mercuric species is pH-dependent and is slow at the concentrations of mercuric species in solution in the aquatic environment. Dimethylmercury and methylmercuric ion do not undergo sunlight photodegradation. The evaporative loss of dimethylmercury from water can be compared with oxygen diffusion based on the ratio of transfer constants.