A national critical loads framework for atmospheric deposition effects assessment: IV. Model selection,applications, and critical loads mapping

The critical loads approach is emerging as an attractive means for evaluating the effects of atmospheric deposition on sensitive terrestrial and aquatic ecosystems. Various approaches are available for modeling ecosystem responses to deposition and for estimating critical load values. These approaches include empirical and statistical relationships, steady-state and simple process models, and integrated-effects models. For any given ecosystem, the most technically sophisticated approach will not necessarily be the most appropriate for all applications; identification of the most useful approach depends upon the degree of accuracy needed and upon data and computational requirements, biogeochemical processes being modeled, approaches used for representing model results on regional bases, and desired degree of spatial and temporal resolution. Different approaches are characterized by different levels of uncertainty. If the limitations of individual approaches are known, the user can determine whether an approach provides a reasonable basis for decision making. Several options, including point maps, grid maps, and ecoregional maps, are available for presenting model results in a regional context. These are discussed using hypothetical examples for choosing populations and damage limits. 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. 3904. 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.     

A national critical loads framework for atmospheric deposition effects assessment: II. Defining assessment end points,indicators, and functional subregions

The United States Environmental Protection Agency, with support from the US Department of Energy and the National Oceanographic and Atmospheric Administration, has been evaluating the feasibility of an effects-based (critical loads) approach to atmospheric pollutant regulation and abatement. The rationale used to develop three of the six steps in a flexible assessment framework (Strickland and others, 1992) is presented along with a discussion of a variety of implementation approaches and their ramifications. The rationale proposes that it is necessary to provide an explicit statement of the condition of the resource that is considered valuable (assessment end point) because: (1) individual ecosystem components may be more or less sensitive to deposition, (2) it is necessary to select indicators of ecosystem condition that can be objectively measured and that reflect changes in the quality of the assessment end point, and (3) acceptable status (i.e., value of indicator and quality of assessment end point at critical load) must be defined. The rationale also stresses the importance of defining the assessment regions and subregions to improve the analysis and understanding of the indicator response to deposition. Subregional definition can be based on a variety of criteria, including informed judgment or quantitative procedures. It also depends on the geographic scale at which exposure and effects models are accurate and on data availability, resolution, and quality. 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 US 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. 3903. 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.     

COORDINATION OF PUBLIC AND PRIVATE AC A CASE STUDY OF LAKE RESTORATION1

ABSTRACT: The potential for joint public and private action for lake restoration is examined using Lake Apopka, Florida, as a case study. Initial calculations indicate that private incentives alone are inadequate to attract investment in a facility to grow and harvest water hyacinths for conversion to methane gas. However, the private externality of water quality improvement associated with harvesting water hyacinths provides a key linkage between the public's water quality objectives and the private gas producer's actions. In order to establish the potential basis for negotiation, the public's willingness-to-pay for environmental services associated with improved water quality is estimated and compared with the estimated subsidy required to induce private action. A conceptual framework is then presented for coordinating actions between private firms and public water management agencies in order to internalize the private externality of water quality improvement while simultaneously achieving the public and private objectives. Results indicate that the subsidization of water hyacinth production and harvesting compares favorably with alternative means of enhancing the water quality of Lake Apopka.     

Interactions of risk analysis and contingency planning in risk management

Risk management entails knowledge of the risk and how best to reduce it; its objective is to minimize losses arising from existing or potential risk. With effective contingency planning, risk analysis and its corollary, consequence analysis, can contribute synergistically to improved risk management. Until recently, risk analysis and contingency or emergency response planning were considered distinct disciplines with little interactive potential. Fortunately, industry now recognizes that linking the two can help ensure public safety as well as preserve the financial integrity of plant owners. Both areas are receiving increased and well-deserved attention; several incidents in recent years have demonstrated that losses could have been greatly reduced if better precautions and procedures had been in place as a result of risk analysis and contingency planning.     

Assessing the construct validity and utility of two new influence tactics

Progress in developing theories of interpersonal influence depends on the identification of meaningful and measurable constructs for classifying influence behavior. We assessed the construct validity and relative effectiveness of two new influence tactics with a field survey study, an incident study, and a laboratory experiment. The confirmatory factor analysis of data from the survey study indicated that collaboration and apprising were distinct from nine proactive tactics identified in earlier research. Additional evidence for construct validity was provided by a comparison of tactics in terms of expected differences in influence outcomes, frequency of use, and differential use with subordinates and peers. Managers who understand the differences among the tactics will be more effective in influencing people in organizations. Copyright © 2005 John Wiley & Sons, Ltd.     

Arsenic remobilization in a shallow lake: the role of sediment resuspension

Oxic resuspension occurs regularly in shallow lakes, yet its role as a mechanism for contaminant remobilization remains ill defined. This study investigated contaminant remobilization during sediment resuspension and determined whether changes in contaminant sediment partitioning reflected the mechanisms controlling remobilization. Arsenic-contaminated sediment from a shallow wetland was subjected to simulated resuspension under a range of differing initial pH conditions. The effect of resuspension on As partitioning was evaluated using a fractionation scheme targeting the dissolved, ion exchangeable, carbonate, organic, amorphous iron oxide, crystalline iron oxide, and apatite fractions. Rate investigations demonstrated that arsenic remobilization occurred on timescales similar to resuspension events, with concentrations reaching steady state within 24 h. The sediment also buffered slurry pH to 8.3 in experiments where the initial pH was between 4 and 10. This pH regulation was attributed to carbonate dissolution or acid-base equilibria of surface base functional groups, although iron oxide and organic matter dissolution did occur in experiments with an initial pH outside this range. Remobilization caused losses in arsenic associated with the ion exchangeable, organic, and amorphous iron fractions but changes in initial pH have a negligible effect on arsenic remobilization or partitioning within the well-buffered region. Resuspension released approximately 20% of the total sediment arsenic, although calculations indicated that a single resuspension event would not significantly change water column arsenic concentrations. While not conclusively proving the mechanisms of remobilization, fractionation gave valuable insight into the effect of sediment resuspension on contaminant remobilization.     

Temporal and spatial variation in the δ<Superscript>15</Superscript>N and δ<Superscript>13</Superscript>C values of fish and squid from Alaskan waters

To test the hypothesis that stable isotope ratios from marine organisms vary, the δ¹⁵N and δ¹³C values from fish and squid collected in Alaskan waters were measured across years (1997, 2000, and 2005), seasons, geographic locations, and different size/age classes, and between muscle tissue and whole animals. Temporal, geographic, and ontogenetic differences in stable isotope ratios ranged from 0.5–2.5‰ (δ¹⁵N) to 0.5–2.0‰ (δ¹³C). Twenty-one comparisons of stable isotope values between whole organisms and muscle tissue revealed only four small differences each for δ¹⁵N and δ¹³C, making costly and space prohibitive collection of whole animals unnecessary. The data from this study indicate that significant variations of stable isotope values from animals in marine systems necessitates collection of prey and predator tissues from the same time and place for best interpretation of stable isotope analysis in foraging ecology studies.