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Holistic approaches to assessing stressors and managing aquatic ecosystems should be the rule; instead, they are the exception. Disjointed, overlapping, and competing environmental regulatory actions—all with the noble mission of protecting and restoring the environment—can no longer be justified.
For at least 60 years, environmental regulatory programs in the United States, Europe, and other developed countries have relied heavily on various forms of assessing chemical risk to manage and protect ecosystems. Water quality, primarily focused on chemical regulation, emerged from the need to control water pollution problems caused by poor or nonexistent wastewater treatment. The result has been largely a single-chemical approach to environmental management and regulatory programs. To protect aquatic life uses for example, many countries developed water quality criteria for selected priority compounds. Legally enforcing these criteria (such as the Clean Water Act in the U.S.) has undoubtedly reduced chemical pollution, and many aquatic systems have benefited. Abundant information demonstrates, however, that single-chemical standards are just one approach to assess, manage, and regulate aquatic systems. For example, toxicity testing (e.g., the U.S. Environmental Protection Agency's [U.S. EPA] whole effluent toxicity program [WET]) has been used successfully to help assess effects of chemical interactions and the effects of unknown chemicals that may be present. Such testing, however, addresses only direct toxicity effects. Many aquatic systems are impaired by non-chemical stressors, including invasive species, habitat degradation from agriculture and urbanization, and flow modifications or are influenced by complex interactions among chemicals and other stressors (e.g., nutrients) that are not addressed using either a single-chemical approach or mixture toxicity testing.
The Current Conundrum
Using a suite of indicators that address many types of stressors or sources of ecological impairment is critical for improving environmental management. Approaches that integrate information obtained from different indicators that lead to a sensible and efficient plan resulting in improved environmental conditions are needed. Numerous weight-of-evidence (WoE) approaches have been suggested but rarely are these used consistently in regulatory programs. For example, the U.S. EPA's Causal Analysis/Diagnosis Decision Information System (CADDIS) approach provides a framework for linking stressors with observed biological impairment (www.epa.gov/caddis). Environment Canada's Environmental Effects Monitoring Program also considers multiple stressors using several types of endpoints. The European Union's Water Framework Directive (WFD) describes an integrative approach that considers other stressors and legislation, yet new directives and regulatory enforcements still focus on a single-chemical approach. Recently, the U.S. EPA released a draft document—“Identifying and Protecting Healthy Watersheds: Concepts, Assessments, and Management Approaches” (www.epa.gov/healthywatersheds)—to address the need for integrative efforts. This is a step forward, but reinforces that wide-ranging approaches to holistic management have not significantly impacted the regulatory process—at least to date. The norm across North America and Europe remains a single-chemical approach to regulate aquatic ecosystems. Indeed, the National Association of Clean Water Agencies (NACWA) noted that a “meaningful, functional watershed approach remains elusive” and identified several obstacles to implementing such an approach, including addressing agricultural nonpoint sources, adaptive management based on science, and breaking down programmatic regulatory and enforcement silos 1. In general, the U.S. EPA and individual states have implemented Independent Application, which requires that each of the three measures of integrity—chemical criteria, WET, and biocriteria—be evaluated separately. Each of these measures alone, however, fails to answer questions about biological health effectively.
By combining physical habitat, chemical conditions, WET, and biological assessment data, a more realistic assessment of biological community health and impacts will result. This integrated, multiple-stressor approach could help ensure that resources are directed toward mitigating the most limiting stressors, whether they are physical or chemical, to improve biological communities.
Several environmental lawyers were surveyed in preparing this article. All agreed that water quality regulatory programs are driven by broad-based comparisons of chemical concentrations with established water quality standards. Further, regulations tend to emphasize assessing and controlling point source discharges and disregard other stressors in bodies of water being examined (G.A. Burton, University of Michigan, unpublished data). Such a policy approach raises a crucial question: Are our regulations effective at managing ecosystems exposed to mixtures of chemicals, let alone a wide range of chemical, physical, and biological stressors? In our view, focusing on chemical water quality, based on complying with single-chemical standards, results in oversimplifying complex factors that cause undesirable ecological conditions. What results is a distorted view of the importance of point sources and chemical factors.
Examples abound in which regulatory management actions have been driven based solely on numeric chemical thresholds being exceeded. These actions result in questionable environmental protection or limited restoration success. Certain risk-driven criteria based on single-species tests, for example, may be much lower than natural background concentrations, such as for naturally enriched constituents such as aluminum, copper, and other metals. According to risk-based criteria principles, this could lead to policies designed to reduce national emissions, and, indeed, this has been the case. An alternative would be to elevate the standards so they do not fall below background concentrations and not use risk-based criteria for the aforementioned constituents. For example, the Alaska Department of Environmental Conservation has developed an approach to address certain naturally elevated metals. The Louisiana Department of Environmental Quality has developed a similar approach to address naturally depressed dissolved oxygen regimes in habitats such as bayous. From a broader perspective, using additional regional ecological information regarding the origins of certain compounds (an approach used to develop nutrient criteria or thresholds in some U.S. ecoregions, for example) would be a more realistic risk management approach that considers local natural background concentrations. Solely using a risk-based method, applied nationwide, would not help reach environmental goals in these cases.
Another example is the U.S. water quality assessments such as the National Water Quality Inventory Report to Congress, which characterizes information as reported by each state, routinely includes more stream miles impaired by sedimentation and other habitat-related stressors than any other cause, including chemicals. The causes of increased sedimentation include changes in hydrology, increased impervious surfaces, improper storm water management, and farming practices that promote excessive erosion. A single-stressor focus to regulating aquatic ecosystems (i.e., a chemical standards focus) undermines introducing approaches that would prioritize stressors or considering cause-effect relationships. As a result, the bureaucratic process—such as measuring which chemical standards are exceeded—drives aquatic ecosystem management and restoration rather than ecological and toxicological principles. Yet doesn't it make sense to consider an integrated policy cycle for water management that takes into account diverse factors that affect ecosystem quality? Might this be more effective than continuing to regulate and manage ecosystems via separate programs? If so, what would be needed?
Our Solution: Ecosystem Reality Checks
Ecosystem Reality Checks (ERC) should be a required step between assessing risk (the science) and management actions (society). They should be holistic, as promoted in CADDIS and other eco-epidemiological approaches that rely on WoE. This means they should address ecological status (endpoints) relevant to the sources of stress and incorporate outcomes that propose alternative, iterative management options.
A generalized framework for an ERC process is shown in Figure 1. From the center to the end, the color ramp represents an increase in scientific inquiry, regulations, and intra- and interagency involvement to confirm ecosystem diagnostics, that is, the ERC. The beginning, at the center of the cycle, is a single regulatory program with the goal of reducing risks to a single chemical. To begin the process, fate and toxicity data are prepared to predict risks in the field. A retrospective comparison with field data yields knowledge gaps that lead to more effective predictive models, such as refinements in exposure (e.g., equilibrium partitioning, bioavailability predictors) and risk. A more holistic analysis may indicate that simply understanding one chemical may be insufficient to account for, predict, or achieve a desired ecological status. Hence, in an ERC, mixtures of chemicals are considered, which requires temporally and spatially explicit exposure assessments that can be overlaid with information on species presence based on known behaviors, typically requiring tools such as geographic information systems. A result of these analyses can be the probabilistic assessment of a suite of chemicals within a specific geographical space and time. When compared with appropriate biomonitoring data, these data determine the coherence of the “prospective” tools. It is at this point where agencies focused on chemical regulations must partner with agencies responsible for factors important for ecological status. Multiple nonchemical stressors and their relationship to species exposures and responses are integrated into the chemical risk predictions. This then allows us to determine the relative risk or hazard of each stressor in terms of their contribution to ecological impairment. Through interagency cooperation, each stressor is managed appropriately, which leads to achieving the desired ecological status and in essence confirming the diagnosis. This process represents an Ecological Reality Check.
The Single-Chemical Versus a Multi-Stressor Approach
The importance of a multiple-stressor perspective (the Environmental Reality Check [ERC]) in assessing and managing watersheds is apparent in a case study performed for the Hocking River watershed (Ohio, USA). A general description of the Ohio data sources and the statistical method used for the second and third approaches can be found in Kapo et al. 11.
Using several environmental data resources, three different approaches were applied to identify sites in the Hocking River watershed at risk for impacts to their fish communities based on the environmental conditions present. The results of each approach were compared with real-world observations (sites with known biological impact) to determine how well each approach captured ecosystem reality (Fig. 2).
2. A weight-of-evidence based geographical information system evaluation demonstrates how different lines of evidence yield different conclusions regarding which waters are impaired. The combination of habitat, water chemistry, and landscape yield more realistic assessments of stressor-response relationships 11.
The presence of ecological impacts was based on biomonitoring surveys in the watershed conducted by the Ohio Environmental Protection Agency. Three approaches were applied to predict the real-world distribution of ecological impacts in the watershed as a function of cumulative risks. First, the traditional single-chemical approach identified sites having one or more water quality criteria exceedances for metals. This approach demonstrated the weakest agreement with ecosystem reality, because the vast majority of real-world impacted sites were left unaccounted for. Second, a biomonitoring and mixture toxicity approach, which incorporated cumulative metals (mixture) toxicity, fared significantly better at identifying impacted sites than the single-chemical approach, in part because it incorporated cumulative risks (here modeled by an ecotoxicological response addition model, applied to all metals present at the sites). This approach incorporated a retrospective component by using statistical relationships statewide between bio-monitoring data and mixture toxicity to identify sites where ecological impact was likely to occur. Third, the most successful identification of impacted sites was achieved using a multi-stressor approach in which a variety of stressor variables in addition to cumulative metals toxicity were evaluated. Significantly, the multi-stressor approach demonstrated that the specific influence of metals toxicity across the impacted sites was greatly outweighed by other sources of potential stress, such as aspects of general physical and chemical factors in the watershed.
The three assessment approaches correspond to potentially very different management strategies. Two of the approaches (the single- and refined-chemical approaches) focus only on reducing metal emissions and exposures for a limited number of sites with observed impacts. These two approaches are characterized by incomplete recovery as a result of neglected stressors and neglected sites. One of the approaches—the multi-stressor approach—evaluates the ecosystem from a wider perspective to identify the most important stressors and handle them accordingly. This approach to assessing stressors best reflects ecosystem reality and offers the most practical guidance for subsequent management actions.
Implementing a system of ERCs could condense disparate schemes from different regulatory fields, with the potential to grow it into an overarching regulatory paradigm. Such a system could explicitly consider the role of chemical contamination in light of multiple stressors in human-altered aquatic systems. An ERC is necessary because chemicals, whether singly or in mixtures, are just one class of stressors that affect aquatic biota and, in many cases, are no longer the chief cause of ecosystem impairments.
Complementary Approaches to Evaluating Stressors
Currently, protecting our waterways largely follows a chemical-specific approach (see sidebars, Single-Chemical Versus a Multi-Stressor Approach and Tidal Surface Waters in The Netherlands: Masking Nonchemical Stressors). Typically, water and sediment quality assessments are conducted in response to a regulatory directive, rely heavily on chemical benchmarks, and use standardized toxicity and bioaccumulation tests 2. It is also well recognized, however, that assessing ecosystem and sediment quality that integrates multiple methods into a WoE-based approach can be more accurate and more useful from a resource management perspective. Even these multiple-stressor approaches, however, are often conducted in a disjointed or inconsistent manner, such that they may fail to establish stressor causality 3. For example, site characterizations of the quality of physical and chemical factors (e.g., suspended solids, sedimentation, nutrients, toxicity), and biological status (structure, function) may change throughout the year. Sampling for each of these factors, though, may be relegated to convenient sampling periods (summer and fall, lower flows) and locations (e.g., bridges) that are not necessarily relevant to the spatial and temporal dynamics of each factor. Hence, protecting biotic communities may be unsuccessful because decisions and actions have been based on data collected in time and space that do not coincide with actual stressor events, whether they are single or multiple. Obviously, this has marked repercussions on how to improve, restore, or remediate the ecosystem.
While the single-chemical management approach has resulted in many success stories since the 1970s, continued successes appear to be partial and less common today; indeed, they are perhaps more coincidental than intentional. Still, chemical pollution has been tagged recently as one of nine major drivers of global concern in an exploration of safe planetary boundaries of major stressors 4. Methods are lacking, however, regarding how to determine the reality of these drivers' significance alone or specifically when considered in conjunction with the planetary boundary on biodiversity loss 5. In other words, a chemical focus is insufficient because other factors need to be considered to manage ecological status.
Tidal Surface Waters in The Netherlands: Masking Nonchemical Stressors
The importance of a multiple-stressor data analyses in assessing and managing national assessments is apparent in an assessment of chemical risk of Dutch sediments.
A biomonitoring dataset was collected for sediments in Dutch surface waters. The acute toxicity of the local chemical mixtures ranged from very low to 40% exceedence of species' EC50 values. It was expected, therefore, that toxic effects would be visible when samples were ranked according to increasing toxicity.
To reveal these expected impacts, simple product-moment correlations were derived between mixture toxic pressures in sediments and taxa abundance, for nearly 100 sediment taxa (per taxon). Thereafter, these correlation values were rank ordered, starting with taxon with the most negative correlation to those with the most positive correlation. A significant correlation was found only for a low fraction of taxa (Fig. 3A). As expected, some impacts were negative (chemical loads reduced abundance of these taxa, left), whereas some were positive (abundance increase at increased chemical loads, right). It could be (wrongly) concluded that no mixture impact was present for the remaining taxa (middle). Yet just the opposite is true. A statistical model (generalized linear model) that describes a taxon's abundance data in relation to a suite of potentially relevant abiotic habitat characteristics (including the toxic pressure of mixtures) indicated that the field abundance of 74% of the species appeared to be significantly influenced by chemical mixtures. Again, both increasing and decreasing impacts were found, as well as “optimum” abundance trends (bell-shaped abundance change with increased chemical loads). The combination of generalized linear models with Monte Carlo simulation showed the sensitive, opportunistic, and optimum species (Fig. 3B).
3. (A) Rank-ordered correlation between toxic pressure of mixtures (msPAF-EC50) and taxon abundance for 103 taxa (279 sites) showed an indifferent response for most taxa (blue). (B) Field-based exposure-abundance patterns for a random subset of taxa derived from generalized linear models + Monte Carlo simulation showed that 74% of all taxa exhibit significant sensitive (negative), optimum, or opportunistic (positive) abundance changes with increased toxic pressure.
The implication is that a predicted toxic pressure of 40% (for 40% of species the EC50 would be exceeded) apparently does not show up as clear abundance reduction for an equivalent percentage of species through simple correlation techniques; indeed, they remained masked by other stressors' effects. The ERC that was applied—through the generalized linear models and the further data analyses—showed that systematic abundance changes associated with chemical mixtures occurred in most species and were thus apparently masked by other stressors. The example suggests a high association between predicted and observed fractions of species that were negatively affected (nearly 1:1), followed by major opportunist responses. The Ecosystem Reality Check conducted here has policy relevance, such as via the European Water Framework Directive. In that directive, the policy aims are to reach Good Chemical Status as well as Good Ecological Status. Deviations from Good Ecological Status ask for evaluating the possible impacts of mixtures of chemicals on local species assemblages. In the context of ERC, an approach such as a validated toxic pressure approach can be applied as a lower-tier approach to quantify the fraction of species affected by a local mixture, which expands the classical approach of evaluations via Water Quality Criteria.
What Is Blocking the ERC Process?
In ecosystems for which environmental management decisions have been made to remediate and restore waterways, it is both surprising and disconcerting that few cases have demonstrated improvements in ecosystem quality in recent years. Most stream restoration or remediation efforts in urban-dominated watersheds have been unsuccessful because important stressors have not been removed or inadequate refugia exist 6. Indeed, 80% of benthic taxa decline in a wide range of watersheds when impervious areas are only 0.5 to 2% of the area 7. Routine monitoring of chemical standard exceedances does little to account for impairments due to urban runoff. In addition, chemical standards may be attained, but without source populations available, restoration efforts fail. Current management efforts are often focused on restoring physical habitats or removing contaminated sediment mass and fail to take a holistic approach to restoring the biological integrity of our waterways. If an ERC approach had been established to assess both baseline conditions and the role of other stressors and their sources, then corrective actions could have facilitated successful (and measurable) remedies and restorations 5. So why don't we apply ERCs yet? Is there a block in science, in policy, or both?
Crossing the Rubicon: The Stepping Stones
Before attempting to solve a problem, risk assessors commonly frame the problem. A key issue is this: What are the current regulations on which to establish an ERC? What stepping stones are in place to support or launch the ERC as a mindset or method?
In addition to chemical-oriented policies, such as the Toxic Substance Control Act (TSCA) and Federal Insecticide Fungicide and Rotenticide Act (FIFRA), the U.S. EPA has divisions devoted to the safety of environmental compartments or species groups of concern, such as surface waters, ground water, and terrestrial organisms (for example, the Office of Water, Office of Solid Waste and Emergency Response, and the Office of Research and Development). Their efforts are often relatively uncoordinated, and thereby unable to iteratively assess the aggregate and potentially cumulative effects of multiple chemicals, let alone other stressors. Although the U.S. EPA's CADDIS methodology is highly flexible and has, as mentioned, the potential to affect corrective management, its connection to chemical and other regulatory environmental policies and, more specifically, water regulatory programs in the United States, has not been delineated clearly. Thus far, CADDIS has been used mostly in special cases within a regulatory or management context, for example, certain Total Maximum Daily Loads [TMDLs]). While the U.S. EPA has jurisdiction over most chemical management policies in the United States, other agencies manage other stressors, such as the U.S. Department of Agriculture (soil till management, forest management), the U.S. Food and Drug Administration (pharmaceuticals), and National Oceanic and Atmospheric Administration (marine ecological status). In essence, there is no coherent coordination in the United States—let alone among regional, state, and local agencies—to avoid pitfalls and holistically manage relevant stressors that contribute to ecological status.
The situation in Europe is similar. The European Union has enacted a suite of regulations, much like those in the United States, but there is room for improvement. A recent illustration of this is provided in a cross-regulations evaluation of how chemical mixtures are handled in risk assessment and management 8. Many regulations handle mixtures differently and are based on different underlying scientific views and arguments. Sometimes, a regulation looks at single compounds only because scientific methods for handling mixtures were deemed absent at the time the regulation was enacted. In other cases, subgroups of compounds are considered on the basis of assumed similar mechanisms of action, which is then taken as justification for partial mixture modeling and risk assessment. This evaluation concluded that for Europe, “There is sufficient know-how [in terms of dealing with mixtures, yet]…the question as to how this scientific knowledge might be best transferred into appropriate regulatory approaches is, however, not at all trivial…”. This evaluation stipulated that “…consistent and clear [policy] mandates are needed to take mixture toxicity into account in the numerous pieces of legislation that contribute to the protection of…the environment from chemical risks…” 8. These statements refer to 21 relevant EU substance- or product-oriented pieces of legislation. The picture in Europe thus becomes more entangled when one looks at overarching regulations such as the Water Framework Directive, the Marine Strategy Directive, and the proposed Soil Directive. The Kortenkamp et al. report 8 suggested focusing on receptors experiencing multi-exposures rather than focusing on sources. Not all chemicals co-occur in the field, however. Using an ERC approach, mixture risk assessments are needed only for those compounds that are likely to co-occur in realistic field settings. Notably, a similar conclusion was drawn more or less independently in the recent EU project named NoMiracle (http://nomiracle.jrc.ec.europa.eu/default.aspx), a project designed to increase knowledge on the transfer of pollutants between different environmental compartments and on the impact of cumulative stressors, including chemical mixtures. In short, regulatory action—at least in the United States and Europe—is triggered along separate regulatory lines, in which scientific foundations vary and are not viewed in the broader context. Nevertheless, there is a way forward by using a growing focus on the final policy target: The overall impacts in aquatic systems.
This more holistic approach to environmental regulation is possible through Registration, Evaluation, Authorisation, and Restriction of Chemical substances (REACH), the EU's chemical-focused regulation. REACH starts from the chemical perspective, whereas the Water Framework Directive (WFD) focuses on the water body. REACH aims to prevent and limit the emissions of the most toxic compounds. It refers to possible accumulation of compounds that are produced and used, such as specific mixtures that accumulate at downstream locations. The regulation allows for the idea of addressing such sites of concern and specifically mentions a link to the WFD. Hence, the crucial regulatory mandate is a very short portion of the law, but it is there to act as stepping stone. The WFD adds to REACH through the Good Chemical Status approach, which identifies selected priority and basin-specific compounds for phase out and the integral focus on the net effects of all stressors. Water authorities are required to act, for example, through River Basin Management Plans, to reach the holistic goal of “Good Ecological Status.” What can and cannot be prevented in source-oriented policies is captured by the compartment-oriented policies, which are cross-linked.
Even so, mandating stepping stones in current regulations has not yet brought about adopted methods for ERCs. Although crucial policy mandates do indeed exist, the regulatory need has not yet been translated into validated, operational, and adopted methods of practice. Currently, we have simply a library of methods—but they are ready to be used in ERCs. Unfortunately, how and when to implement such method is unclear as yet.
Defining the Ecosystem Reality Check
We thus begin here to define the concept of routinely implemented ERCs, which we propose must be:
Targeted. An ERC is meant to manage natural resources efficiently and effectively, thus minimizing costs and provide the greatest benefits.
A process. An ERC encompasses an iterative evaluation of risk assessment results and alternative risk management options.
Holistic. An ERC considers the dominant physical, chemical, and biological stressors and their links to ecosystem impairments.
Scientific. An ERC considers all issues along relevant hypothesized cause-to-effect chains, avoiding bias to either sources or receptor.
Pragmatic and practical. An ERC can consist of using existing, pragmatic, and practical approaches from various scientific disciplines and is as simple or as complex as needed in the context of a defined problem.
Possible. ERCs are mandated by current regulations, but not everywhere. Using the ERC productively is possible immediately by shifting the mindset of environmental assessors and managers.
An ERC framework, illustrated in Figure 2, incorporates the complementary benefits of traditional preventative approaches. Typically, these approaches are used by linking what are now often disjointed, overlapping, or competing regulatory programs, all of which are concerned with protecting and restoring aquatic systems. Notably, our focus here has been on aquatic systems, but with the abundance of regulatory mechanisms and drivers, the ERC principles can and should also be applied to terrestrial systems.
ERC Flexibility: Does One Size Fit All?
The short answer is “no.” Commonly, various risk assessment schemes are conducted according to a tiered scheme. Simple and conservative methods are used initially with more complex and realistic methods employed as needed in higher tiers. Chemical water quality criteria can be characterized, for example, as a lower-tier approach, with refinements possible in the United States only on a site-specific basis for the most part, because criteria are designed to protect aquatic ecosystems in general. Considering mixtures, assessment approaches have appeared at various tiers of the science, from the simplest to the most complex. For example, a simple approach to assess chemical mixtures is to employ a Safety Factor (e.g., 1/10th of a risk assessment-derived level to account for uncertainties, including mixtures). More complex approaches consider the additivity of chemicals within a mechanism of action (e.g., Toxic Equivalence Factors for dioxin) or across mechanisms via mixed-model approaches. The risk assessment problem defines the level of specificity and complexity needed. Food web models, for example, represent a more complex, higher-tier approach. Recently, a suite of existing risk assessment methods have been compared and combined in tiered frameworks 9. The examples provided in this paper support our initial answer: An ERC is not a one-size-fits-all approach even when considering chemical risks.
Examples in an ERC Context
Multi-stress conditions change chemical sensitivity
Stress conditions for individuals and populations often increase their sensitivity to toxicants. The environmental context determines the causal link between the stressor and the biological community. How universal are chemical criteria for stressed environments? Are they sufficiently protective? Can chemicals be the focus in environs where physical (habitat alteration) and biological stressors (invasive species) predominate? Do the stressors interact?
In this case, the ecological impact of an old waste site releasing heavy metal contamination into Antarctic costal waters was assessed. Researchers identified that the ultraviolet (UV) radiation present in Antarctica increased sensitivity of local invertebrates living in shoreline waters by more than an order of magnitude. This relationship has been identified in the field and validated with in-situ and laboratory investigations 10.
Implications for the ERC concept
In the case presented, the source of contamination, a waste site was removed. Hence, assessing the combined action of chemical and a ubiquitous environmental stressor (UV radiation) triggered a management action. Future human activities in areas with high UV radiation may be affected by these results. The increase of organism sensitivity due to UV is just a single example of a wide range of stressors that increase mortality due to toxicants, including temperature, nutrients, siltation, oxygen, competition, predation and parasites 2.
The Clinch River: Managing multiple stressors
The Clinch River in southwest Virginia (USA) has one of the most diverse assemblages of freshwater mussels and native fish in the United States, both of which have been imperiled, although the cause of species declines has been elusive thus far. Many stressors have been implicated, most of which fall outside the realm of current regulations (e.g., habitat impairment). The current regulatory approach identified that fecal coliform bacteria and sediment were impairing water quality in a small part of the watershed based on state standards and visual inspections (Fig. 4). This approach identified an important stressor (and its major sources), but it addressed only a small part of the watershed and ignored other well-documented biological information available. Appropriate management actions were left vague and little connection was made to an actual restoration strategy. The process that was initiated failed to result in restoration decisions and actions.
A watershed ecological risk assessment was conducted with multiple stakeholders involved (including a non-regulatory office of the state [Virginia] and the U.S. EPA), using GIS and multivariate analyses. The assessment identified not only sediment from agricultural sources as an important factor, but also coal fine sedimentation from leaking coal slurry impoundments, toxic chemicals from recurring transportation and industrial spills toxics, biochemical oxygen demand from urban runoff and Combined Sewer Overflows, and channel alterations from riparian corridor degradation as important stressors (Fig. 4).
Implications for the ERC concept
Using a multiple-stressor framework, risk analyses demonstrated that proximity to several sources of stressors and multiple stressors were highly related to the biological conditions. A single-stressor approach could not provide the information needed to protect or restore the valued aquatic resources in this system successfully, because the cumulative mixture of stressors is a critical factor (Fig. 2). Using an ERC approach led to useful management strategies in this watershed.
Great Lakes: Interactions of multiple, non-toxic stressors
The Great Lakes (USA) have been undergoing dramatic changes in the past 20 years, with changes becoming more dramatic during the past two years. This ecosystem contains 21% of the world's freshwater and 84% of the supply for the United States. As such, the scope and magnitude of the ecosystem services the Great Lakes provide are likely unmatched by any other freshwater system. Nevertheless, the salmonid fishery is collapsing in Lake Huron. Several invertebrate and fish species are at or near extinction in some of the lakes, including the amphipod Diporeia (a keystone species) and Daphnia sp. The southern basin of Lake Michigan and much of Lake Huron are now more oligotrophic than Lake Superior.
These dramatic food web changes can be linked to the complex interactions of multiple stressors. Several recent papers (see Supplemental Data: Suggested Reading) have shown key stressor connections between species loss; increased and selective filtering by invasive species (the notorious zebra and quagga mussels); increasing harmful algal blooms; increasing hypoxia; increasing benthic algae (Cladophora); and subsequent beach “muck” and closures due to pathogens, in addition to excessive phosphorous runoff.
Implications for the ERC concept
Although the U.S. Clean Water Act has focused on maintaining the physical, chemical, and biological integrity of the Great Lakes via chemical regulations, it has done little to manage the combination of these broad-scale and dominant stressors. Our examples have shown where an ERC approach would be useful. While these are good examples, we need a deliberate path forward.
The Path Forward
Science has matured sufficiently to provide regulators with methods to develop and implement ERCs. As discussed, chemical-centric regulatory schemes have had a positive impact; however, they are limited in scope and cannot account for myriad other factors that may impair ecosystems. Because the science is ready and intentional regulatory systems will be needed to maintain or improve the ecological status of human-affected systems, the time is right to develop a path forward. We recommend that an Ecosystem Reality Check framework be developed and adopted, building on existing regulatory programs when needed.
The evidence and thoughts presented here should result in a changed mindset for all those involved in assessing risk and managing environmental issues. Furthermore, the ERC mindset will reduce the negative connotations associated with being the messengers of bad news (“The risk is…” or “We didn't consider this…”). Risk assessors with an ERC mindset will instead opt for solutions (“Alternative management strategies are…”).
In the long term, the ERC concept will require further steps. The Society of Environmental Toxicology and Chemistry has conducted several “Pellston” workshops with the goal of providing integrated approaches (Fig. 2) to assess and then develop prospective tools to positively affect ecological change. It appears, however, that resource and regulatory agencies have paid little attention to many of these tools. The result is the continued disuse of holistic approaches that could lead to improved or restored ecological status. Just as there are internationally approved methods for testing physical, chemical, and biological (e.g., biodegradation, toxicity) attributes to provide suitable data to assess the potential risks of chemicals in the environment, it is time to elevate current methods used for assessing non-chemical stressors and holistic integration systems via an international effort with the goal of developing and promoting ERCs. The step to be made would be to establish consensus on ERC via international, multi-stakeholder workshops. The output of these steps should be practical ERC approaches for which it is clear that the benefits of managing resources effectively outweigh the costs mandating this new paradigm.
Call to Action
Make ERCs the status quo
Regulatory approaches to assessing and managing the quality of ecosystems have tended to focus on a single stressor-centric approach and fail to “see the forest for the trees.” While this has been and can be effective in rather simplistic systems in which one stressor source dominates, it may be very ineffective in complex, human-affected systems in which multiple stressors and sources occur. The examples we have presented illuminate our arguments. For our world's increasingly more complex and at-risk environments, we need Ecosystem Reality Checks to be the status quo. Indeed, using several complimentary indicators simultaneously to address the numerous stressors and sources of ecological impairment is critical if we ever hope to improve environmental management.
We recognize that it can be challenging to determine ERCs in complex systems, because this requires knowledge of diverse issues such as selecting appropriate reference conditions, defining multiple spatial-exposure relationships, and assessing dominant versus cumulative stressors. Separate regulatory approaches have identified and managed stressors, but have not linked approaches to manage multiple stressors effectively in their appropriate contexts. Nevertheless, it is in human-affected systems that billions are being spent on remediation. An ERC would provide a predictive evaluation of success. Despite the wide array of environmental disciplines and agencies that may be needed to determine an ERC, the reality will be a more efficient use of scientific, regulatory, and financial resources to protect, conserve, or restore ecological status. Hence, we believe that the ERC mindset is productive and can be adopted here and now.
The status quo of environmental regulatory actions executed via disjointed, overlapping, and competing programs, all with the noble mission of protecting and restoring the environment, can no longer be justified. It is time for Ecological Reality Checks to be a routine procedure in all management frameworks.
D. De Zwart and L. Posthuma received financial support from the Dutch National Institute for Public Health and the Environment (RIVM) Strategic Research Program (project S/607001), “Environmental Impact Assessment,” under the auspices of CEO-RIVM and RIVM's scientific Advisory Board.