A national critical loads framework for atmospheric deposition effects assessment: I. Method summary

The United States Environmental Protection Agency (EPA), with the assistance of the US Department of Energy (DOE) and the National Oceanographic and Atmospheric Administration (NOAA) is examining the utility of a critical loads approach for evaluating atmospheric pollutant effects on sensitive ecosystems. A critical load has been defined as, “a quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge.” Working in cooperation with the United Nations Economic Community for Europe’s (UN-ECE) Long Range Transboundary Air Pollution (LRTAP) Convention, the EPA has developed a flexible, six-step approach for setting critical loads for a range of ecosystem types. The framework is based on regional population characteristics of the ecosystem(s) of concern. The six steps of the approach are: (1) selection of ecosystem components, indicators, and characterization of the resource; (2) definition of functional subregions; (3) characterization of deposition within each of the subregions; (4) definition of an assessment end point; (5) selection and application of models; and (6) mapping projected ecosystem responses. The approach allows for variable ecosystem characteristics and data availability. Specific recognition of data and model uncertainties is an integral part of the process, and the use of multiple models to obtain ranges of critical loads estimates for each ecosystem component in a region is encouraged. Through this intercomparison process uncertainties in critical loads projections can be estimated. The research described in this article has been funded by the US Environmental Protection Agency. This document has been prepared at the EPA Environmental Research Laboratory in Corvallis, Oregon, through contract #68-C8-0006 with Man Tech Environmental Technology, Inc. It has been subjected to the agency’s peer and administrative review and approved for publication. Mention of trade names or commercial products does not constitute endorse ment or recommendation for use.     

SUMMARY OF MODIFICATIONS OF THE U.S. GEOLOGICAL SURVEY MODULAR,FINITE-DIFFERENCE,GROUND-WATER FLOW MODEL TO READ AND WRITE GEOGRAPHIC INFORMATION SYSTEM FILES1

ABSTRACT: The U.S. Geological Survey modular, three-dimensional, finite-difference, ground-water flow model, commonly called MODFLOW, has been modified so that it can read and write files used by a geographic information system (GIS). The modified model program is called MODFLOWARC. The design of MODFLOWARC parallels the design of the ground-water flow model program MODFLOW. The names of the variables, modules, and submodules used to explain the operations of MODFLOWARC were derived from the names used in MODFLOW. During the data input phase, MODFLOWARC reads array control records similar to the original control records of MODFLOW, except an additional variable is added. This additional variable is the name of the computer files containing array data in GIS format. Data output is achieved by setting record/input flags and by supplying a variable that is the name of the directory where the output data will be recorded. The modifications to MODFLOW were minimized so that MODFLOWARC will operate on an existing ground-water flow model without modifying array control records.     

POTENTIAL EFFECTS OF CLIMATE CHANGE ON SURFACE‐WATER QUALITY IN NORTH AMERICA1

ABSTRACT: Data from long‐term ecosystem monitoring and research stations in North America and results of simulations made with interpretive models indicate that changes in climate (precipitation and temperature) can have a significant effect on the quality of surface waters. Changes in water quality during storms, snowmelt, and periods of elevated air temperature or drought can cause conditions that exceed thresholds of ecosystem tolerance and, thus, lead to water‐quality degradation. If warming and changes in available moisture occur, water‐quality changes will likely first occur during episodes of climate‐induced stress, and in ecosystems where the factors controlling water quality are sensitive to climate variability. Continued climate stress would increase the frequency with which ecosystem thresholds are exceeded and thus lead to chronic water‐quality changes. Management strategies in a warmer climate will therefore be needed that are based on local ecological thresholds rather than annual median condition. Changes in land use alter biological, physical, and chemical processes in watersheds and thus significantly alter the quality of adjacent surface waters; these direct human‐caused changes complicate the interpretation of water‐quality changes resulting from changes in climate, and can be both mitigated and exacerbated by climate change. A rigorous strategy for integrated, long‐term monitoring of the ecological and human factors that control water quality is necessary to differentiate between actual and perceived climate effects, and to track the effectiveness of our environmental policies.     

Volunteer monitoring of E. coli in streams of the upper Midwestern United States: a comparison of methods

Fecal contamination of water is a public health concern for those using the water for drinking or recreation. The EPA recommends using Escherichia coli to evaluate recreational freshwaters for fecal contamination. With limited resources available, states have recently focused on training volunteers to expand data collection and resource assessment. Several bacteria testing methods are available for use by the public; however, few studies have comprehensively evaluated their use by volunteers. This study evaluated two E. coli monitoring methods used by volunteers: Coliscan Easygel® and 3M^TM Petrifilm^TM, incubated for 24 and 48 hours. The methods were assessed to determine how closely each matched results with EPA-approved laboratory analyses. Analysis of covariance results indicated that when used by volunteers to monitor surface water, 3M^TM Petrifilm^TM results were more similar to laboratory analyses than Coliscan Easygel®. Both test methods had similar overall accuracy of predicting if a sample exceeded or fell below the 235 cfu/100 mL EPA body contact standard for recreational surface waters. Two-thirds of volunteers preferred 3M^TM Petrifilm^TM.     

A national critical loads framework for atmospheric deposition effects assessment: III. Deposition characterization

Methods are discussed for describing patterns of current wet and dry deposition under various scenarios. It is proposed that total deposition data across an area of interest are the most relevant in the context of critical loads of acidic deposition, and that the total (i.e., wet plus dry) deposition will vary greatly with the location, the season, and the characteristics of individual subregions. Wet and dry deposition are proposed to differ in such fundamental ways that they must be considered separately. Both wet and dry deposition rates are controlled by the presence of the chemical species in question in the air (at altitudes of typically several kilometers in the case of wet deposition, and in air near the surface for dry). The great differences in the processes involved lead to the conclusion that it is better to measure wet and dry deposition separately and combine these quantifications to produce “total deposition” estimates than to attempt to derive total deposition directly. A number of options for making estimates of total deposition to be used in critical loads assessment scenarios are discussed for wet deposition (buckets and source receptor models) and for dry deposition (throughfall, micrometeorology, surrogate surfaces and collection vessels, inference from concentrations, dry-wet ratios, and source-receptor models). The research described in this article has been funded by the US Environmental Protection Agency. This document has been prepared at the EPA Environmental Research Laboratory in Corvallis, Oregon, through contract #68-C8-0006 with ManTech Environmental Technology, Inc., and Interagency Agreement #1824-B014-A7 with the U.S. Department of Energy and at Oak Ridge National Laboratory managed by Martin Marietta Energy Systems, Inc., under Contract DE-AC05-84OR21400 with the US Department of Energy. Environmental Sciences Division Publication No. 3905. It has been subjected to the Agency’s peer and administrative review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.     

Evaluation of alternative landfill cover soils for attenuating hydrogen sulfide from construction and demolition (C&D) debris landfills

Hydrogen sulfide (H(2)S) generated from C&D debris landfills has emerged as a major environmental concern due to odor problems and possible health impacts to landfill employees and surrounding residents. Research was performed to evaluate the performance of various cover materials as control measures for H(2)S emissions from C&D debris landfills. Twelve laboratory-scale simulated landfill columns containing gypsum drywall were operated under anaerobic conditions to promote H(2)S production. Five different cover materials were placed on top of the waste inside duplicate columns: (1) sandy soil, (2) sandy soil amended with lime, (3) clayey soil, (4) fine concrete (particle size less than 2.5 cm), and (5) coarse concrete (particle size greater than 2.5 cm). No cover was placed on two of the columns, which were used as controls. H(2)S concentrations measured from the middle of the waste layer ranged from 50,000 to 150,000 ppm. The different cover materials demonstrated varying H(2)S removal efficiencies. The sandy soil amended with lime and the fine concrete were the most effective for the control of H(2)S emissions. Both materials exhibited reduction efficiencies greater than 99%. The clayey and sandy soils exhibited lower reduction efficiencies, with average removal efficiencies of 65% and 30%, respectively. The coarse concrete was found to be the least efficient material as a result of its large particle size.     

Transport and fate of nitrate in a glacial outwash aquifer in relation to ground water age,land use practices,and redox processes

A combination of ground water modeling, chemical and dissolved gas analyses, and chlorofluorocarbon age dating of water was used to determine the relation between changes in agricultural practices, and NO3- concentrations in ground water of a glacial outwash aquifer in west-central Minnesota. The results revealed a redox zonation throughout the saturated zone with oxygen reduction occurring near the water table, NO3- reduction immediately below it, and then a large zone of ferric iron reduction, with a small area of sulfate (SO4(2-)) reduction and methanogenesis (CH4) near the end of the transsect. Analytical and NETPATH modeling results supported the hypothesis that organic carbon served as the electron donor for the redox reactions. Denitrification rates were quite small, 0.005 to 0.047 mmol NO3- yr(-1), and were limited by the small amounts of organic carbon, 0.01 to 1.45%. In spite of the organic carbon limitation, denitrification was virtually complete because residence time is sufficient to allow even slow processes to reach completion. Ground water sample ages showed that maximum residence times were on the order of 50 to 70 yr. Reconstructed NO3- concentrations, estimated from measured NO3- and dissolved N gas showed that NO3- concentrations have been increasing in the aquifer since the 1940s, and have been above the 714 micromol L(-1) maximum contaminant level at most sites since the mid- to late-1960s. This increase in NO3- has been accompanied by a corresponding increase in agricultural use of fertilizer, identified as the major source of NO3- to the aquifer.