Summary

The Gulf of Mexico (GoM) has a combination of ecological richness, economic value, and physical location that makes it unique among seas. Its habitats and ecosystems include oyster reefs, salt marshes, seagrass beds, mangrove forests, estuaries, barrier islands, coral reefs, and sandy beaches, as well as the water column and bottom habitats of the Gulf itself. The 21st-century GoM is also vulnerable to ecosystem pressures and stressors, such as altered freshwater flows, coastal development, pollution, overfishing, and landscape alterations. It is further susceptible to the effects of fundamental natural and anthropogenic driving forces, such as climate change.

When the Deepwater Horizon (DWH) platform explosion and resulting oil spill occurred in April 2010, it resulted in yet another substantial impact to Gulf ecosystems from Texas to Florida, which were already experiencing many anthropogenic stressors. The resulting civil and criminal claims, fines, and penalties from the spill included approximately $16.7 billion for economic and environmental restoration activities.

Now, nearly a decade into these restoration efforts, there is a need to assess the impacts of these activities and to lay a foundation for restoration efforts that will continue beyond the allocation of DWH funds. The need for this effort was identified through discussions with stakeholders and representatives from several DWH funding entities,¹ and from information in publications from Gulf-based entities, nongovernmental organizations, and the National Academies of Sciences, Engineering, and Medicine.

The Gulf Research Program (GRP) at the National Academies initiated this report, with a committee of volunteer experts, to assess the cumulative effects of multiple restoration projects along the U.S. Gulf of Mexico coast in the context of long-term environmental trends; to consider effects of acute events and long-term environmental changes; to discuss synergistic and antagonistic effects of multidecadal restoration activities; and to recommend adaptive management strategies to address these factors. In addition, the committee was asked to assess the relevant existing resources, including the available data, for informing decision making and to consider what additional efforts are needed (see Box 1.1 in Chapter 1 for the full Statement of Task). The geographic scope of restoration efforts considered by this report looks beyond the project scale to the estuary/watershed scales (i.e., coastal areas connected by characteristics of their hydrology) and even larger scales (e.g., regional or Gulf-wide scale).

___________________

¹ When used in this report, the “DWH funding entities” are defined as the following: the RESTORE (Resources and Ecosystems Sustainability, Tourist Opportunities, and Revived Economies) Council state and federal members (states of Alabama, Florida, Louisiana, Mississippi, and Texas; U.S. Department of Commerce; U.S. Department of the Interior (DOI); U.S. Environmental Protection Agency (EPA); U.S. Department of Agriculture (USDA); U.S. Coast Guard; and U.S. Department of the Army); the DWH NRDA (Natural Resource Damage Assessment) Trustees (National Oceanic and Atmospheric Administration [NOAA], EPA, DOI, USDA, and the five Gulf states); the National Fish and Wildlife Foundation Gulf Environmental Benefit Fund; the U.S. Fish and Wildlife Service North American Wetlands Conservation Fund; the Centers of Excellence; the NOAA RESTORE Science Program; and the Gulf Research Program.

LONG-TERM ENVIRONMENTAL TRENDS AFFECTING RESTORATION EFFORTS

Large-scale and long-term changes in hydrology, geomorphology, biogeochemistry, trophic status, and species range distributions have been occurring within the GoM in response to both natural and anthropogenic forces. Further, these forces are themselves impacted by system-wide stressors, such as those associated with the DWH oil spill, and their rate of change is accelerating as a result of climate change. Assessment of long-term environmental trends that describe the changing conditions of an ecosystem are essential for providing decision makers and restoration practitioners with useful insight in their assessment of cumulative effects of multiple restoration actions.

The changing climate is a major stressor in the GoM, and some of its associated stressors, such as relative sea level rise, can reflect both natural and anthropogenic forces. Overall, long-term trends show that relative sea level is rising, that intense hurricanes are increasing in frequency, that sea surface temperature is gradually increasing, that subsurface waters are acidifying at a rate that is higher than the global surface ocean rate, and that more tropical species (including mangroves and fish species) have been observed year-round in the northern GoM. Inputs of freshwater, dissolved and particulate nutrients, and suspended sediments act to influence salinity regimes, water residence times and other features of physical circulation, trophic status and keystone habitats, and water clarity and sediment accretion rates. And over previous decades, changes in land uses and human activities have modified the annual patterns and magnitude of these inputs. Current and projected climate change effects will further influence these trends.

Better understanding and assessment of long-term environmental trends is critical from a restoration planning perspective. Although some parameters needed to assess environmental trends in the GoM are well monitored, data collection and analysis for many aspects are limited. The Gulf Coast of today is unlikely to look like the Gulf Coast of the future; these changes are likely to influence the success or failure of ongoing and future GoM restoration projects.

ASSESSING THE CUMULATIVE EFFECTS OF RESTORATION: CURRENT AND EMERGING APPROACHES

Estuary- and watershed-scale restorations in the GoM are involved undertakings. Measurable changes as a result of restoration actions are often confounded by the effects of multiple interacting stressors, including long-term environmental trends. Several approaches can be used to consider and address these challenges.

Defining Cumulative Effects of Restoration The cumulative effects of restoration refer to the collective additive, synergistic, and antagonistic effects of all restoration activities that occur within a setting defined by common or connected characteristics of hydrology, geomorphology, ecology, ecological function, and/or biodiversity. Assessment of the cumulative effects of restoration may occur at various geographic landscape scales, such as a marsh complex, bay, estuary, watershed, or the Gulf Coast itself. The scale of assessment may also be defined by specific interests in the outcomes, such as ecosystem processes (e.g., sedimentation), biodiversity or specific organisms (e.g., oysters), performance targets (e.g., water quality), type of restored system (e.g., wetland restoration), political boundaries (e.g., state boundaries), or type of restoration method (e.g., living shorelines).

Antagonism and Synergism in Restoration Efforts Diverse pressures in estuarine and coastal waters, both natural and anthropogenic, generate multiple stresses on ecosystem structure and function. The effect of those multiple stressors can be additive (equal to the sum of their individual effects), synergistic (greater than the sum of their individual effects), or antagonistic (less than the sum of their individual effects); they may also be judged either beneficial or detrimental relative to program goals and objectives. The cumulative effects of restoration efforts in a given estuary or watershed may also be additive, synergistic, or antagonis-

tic and similarly judged beneficial or detrimental. Exploring how to make use of ecological synergies and avoid antagonistic interactions could improve benefits of multi-project restoration efforts.

Conceptual Models and Hypothesis Development Conceptual models—graphical representations of interrelationships between drivers, pressures and stressors, restoration actions, and ecosystem response, based on one or more hypotheses—are often used to represent understanding of the current and future states of the ecosystem. They are crucial for determining restoration project priorities and assessing future projections. Preparing a conceptual model can enhance understanding of the current state of an ecosystem and raise informative questions about underlying assumptions. Their applicability to the evaluation of cumulative effects of large-scale restoration bears emphasis. For example, a conceptual model can capture the potential synergistic and antagonistic effects that occur as a result of interactions among habitats being restored, knowledge that may be tested by future studies and assessment of the effectiveness of actions over time.

Multiple Lines of Evidence—An Approach for Assessing Cumulative Effects Evaluating the effects of a restoration effort often involves an individual body of water or watershed and is therefore unreplicable. This means that the usual experimental design with which most ecologists and environmental scientists are familiar, with randomly allocated treatments and replication, is not possible. However, this does not mean that rigorous analysis of system-wide restoration projects cannot be done, only that strict assignment of cause and effect cannot be made via standard methods of statistical analysis alone. An evidence-based evaluation methodology that utilizes multiple lines of evidence and causal criteria can compensate for the inability to use traditional experimental designs, the lack of reference conditions, the lack of replication, the difficulties in establishing causality, and the likely shortage of appropriate data.

Tools for gathering multiple lines of evidence include:

• research on critical ecological uncertainties, which is important for avoiding unexpected outcomes;
• evidence-based review of the literature, which is a systematic approach to assessing environmental cause and effect via information synthesized from multiple publications;
• physics-based and ecosystem models, which encompass both the flow of materials and energy in addition to capturing complex interactions among ecosystem components, processes, and services;
• meta-analysis of restoration action effectiveness, which includes the assessment of interim reports and data in lieu of published scientific literature when the timing of publication in scientific literature is inadequate for decision making;
• analysis of data and modeling of target species—for example, population models that predict or simulate population dynamics of species within an ecosystem due to changes in habitat characteristics from a set of pressures and stressors;
• models for cumulative net ecosystem improvement, which are methods for estimating whether and to what degree an ecosystem may or may not have improved as a result of an intervention such as restoration; and
• change analysis on the landscape setting, using a suite of tools that rely on data-driven models and that can be quite effective in teasing apart complex relationships among ecosystem stressors and responses.

APPLICATIONS OF SYNTHESIS AND CUMULATIVE EFFECTS ASSESSMENT IN THE GULF OF MEXICO

The projects supported by the legal settlements of the 2010 DWH oil spill represent an opportunity and a challenge for assessment and learning because of the unprecedented number and diversity of projects and organizations involved and the 5–30-year time frame of payments from the settlements. Individual project monitoring can help ensure that what is learned from initial projects benefits successive projects. The ongoing, large-scale, long-term restoration is also an opportunity to assess cumulative impacts of multiple projects on estuary/watershed and larger scales.

Prior Assessments Quantitative analyses of the effectiveness of different types of restoration, such as the effects of seagrass or oyster reef restoration on a local-bay or statewide basis, remain uncommon in the GoM. The committee was unsuccessful in obtaining enough information to quantitatively demonstrate the feasibility of synthesizing DWH-funded project-level monitoring data and information for the assessment of cumulative effects and achievement of restoration objectives. Despite numerous calls from various committees and organizations for consistent and transparent monitoring and assessment since the DWH oil spill, barriers exist for the collation of monitoring and assessment of successes or failures of restoration projects. These barriers include varied or nonexistent monitoring requirements, depending on funding stream, and a lack of publicly available final reports and/or monitoring data. In addition, examples of syntheses in the GoM that have attempted to detect beneficial cumulative effects of multiple restoration efforts at the estuary/watershed- and Gulf-wide scales are very limited.

Several long-term, science-based resource management programs located in GoM estuaries offer examples of the application of multiple lines of evidence to assess cumulative effects of the many restoration actions implemented in each area over the last three decades. Although not designed to assess cumulative effects, the Tampa Bay Estuary Program and its partners, the Galveston Bay National Estuary Program in partnership with the Galveston Bay Foundation, and the Comprehensive Everglades Restoration Plan each utilized tools and techniques similar to the theoretical approaches outlined above. In addition, each program developed and now applies program-specific approaches to assessing cumulative effects of restoration efforts within their study areas.

MOVING FORWARD

Because GoM ecosystems cross many political boundaries, coordination across geographic and jurisdictional lines is also needed. There are several actions to consider that would contribute to supporting the scientific efforts (e.g., monitoring, modeling, and research) needed for effective adaptive management and, in turn, assessment of cumulative effects of restoration efforts Gulf-wide.

Data Resources Long-term environmental trends for some parameters and species are now available at local and regional scales, but data collection, analysis, and reporting are often inconsistent, and existing efforts are not adequate to detect all important Gulf-wide trends. Possessing baseline and trend data for important environmental variables when evaluating restoration efforts provides fundamental support for the synthesis activities needed to inform cumulative effects assessment and adaptive management actions. Building on existing monitoring efforts, filling in known data gaps, and moving toward a Gulf-wide ecosystem monitoring network could help practitioners move forward. State and federal resource agencies also collect long-term environmental monitoring data specific to their agency and state missions, and this information can be useful for assessing the cumulative impact of multiple restoration projects at estuarine or larger scales.

However, such efforts are hampered by the lack of a unifying GoM analysis and synthesis activity for many key stressors. No one entity has the resources and the explicit responsibility to accomplish this objective. Thus, this type of analysis and synthesis activity, so essential for accurate assessments of cumulative effects of large-scale restoration activities, remains to be undertaken.

Finally, it is important that all data and information regarding restoration be available to all users, regardless of where data are deposited. FAIR principles (Findable, Accessible, Interoperable, Reusable; e.g., Wilkinson et al., 2016) are widely accepted and can provide guidance for data management and stewardship.

Emerging Technologies Recent advancements in data-driven techniques, such as artificial intelligence (AI), machine learning, deep learning, and cloud and edge computing, are expected to fundamentally transform many domains of human endeavor, including post-restoration monitoring. Traditional remote sensing, combined with new sensing technologies and AI-driven techniques, can generate high-quality, long-term monitoring data across terrestrial and coastal ecosystems. Although some large-scale remote sensing studies to monitor GoM-wide water quality and wetland habitats have been conducted in the past, the committee could not identify any integrated remote sensing and emerging-technology-driven monitoring studies adopted for Gulf restoration projects. These newer data-driven frameworks are not expected to replace traditional restoration science–driven ecosystem monitoring, but they can complement and strengthen them.

Program-Level Adaptive Management Strategies Environmental background trends, especially those associated with climate change, are exhibiting higher variability over time; in turn, restoration practices that have been successful in the past may no longer be adequate to compensate for the effects of anticipated changes in background trends. Adaptive management techniques can provide restoration program managers with the ability to revisit and update large-scale restoration strategies, based on periodic review of monitoring data and progress toward programmatic goals. However, successful implementation of adaptive management in Gulf restoration has been limited; this lack of success is not isolated to the region, but there are examples of successful implementation elsewhere.

The Importance of Data Synthesis Synthesis efforts are needed to determine how much the many localized restoration efforts, collectively, have resulted in measurably improved coastal and estuarine ecosystems across the GoM region. In addition, such analyses provide a mechanism for adjusting efforts to produce better restoration outcomes. A synthesis framework makes it possible to address difficult and exceedingly complex environmental questions and provide answers that lead to increased understanding of coastal and estuarine system dynamics and, ultimately, better management decisions. Synthesis at scales relevant to management groups is also particularly needed in the Gulf because of strong and concerning trends in both chronic (e.g., sea level rise, tropicalization) and acute (e.g., hurricanes, floods) stressors that can, directly and indirectly, strongly influence the success of restoration projects at all scales.

A comprehensive monitoring database is needed for any synthesis activities, yet current data collection in the GoM is often inadequate for regional or Gulf-wide synthesis, and there are considerable inconsistencies in the types of variables and techniques used in monitoring programs across the Gulf. There is a lack of centralized data management, storage, and access across the many restoration projects. Funding for long-term monitoring efforts is difficult to obtain. Without serious synthesis efforts, it seems unlikely that it can be quantitatively determined whether and to what degree GoM habitats and ecosystems have improved.

Steps Needed to Assess Cumulative Effects Figure S.1 summarizes the key components needed for assessing cumulative effects of multiple restoration efforts. It includes the development of conceptual models, assessment of data needs and acquisition of additional data (if needed), implementation of the multiple lines of evidence approach, and data synthesis. The cycle can be repeated as part of adaptive management and related decision-making efforts.

The assessment of the largest ecological restoration investment in history is an unprecedented challenge and opportunity. Significant funds have been expended or committed to date on DWH-funded projects, with valuable progress having been made in advancing monitoring and modeling capabilities. The restoration community has made much progress on recovery and restoration efforts related to the DWH oil spill and from the impacts of hurricanes and other climatic events. Learning achieved through the remainder of

the settlement period will be the foundation for the next generation of managers, who inherit the responsibility for GoM ecosystems and communities. An underlying theme of this report is the need for integration of science and management of restoration activities. It is envisioned that each DWH funding entity, within its programmatic authority, can work cooperatively with others to realize this integration.

CONCLUSIONS AND RECOMMENDATIONS

Conclusion 1: Adequate scientific evidence needed to evaluate cumulative effects of restoration on a regional scale in the Gulf of Mexico is currently not available and, to date, no entity has been tasked to develop and implement a strategy to assess cumulative effects of environmental restoration efforts. Environmental benefits associated with multiple restoration projects have been observed within some Gulf of Mexico estuaries and watersheds, although not at larger scales. Without a focused effort and strategy, rigorous synthesis of the effects of multiple restoration projects at a regional or Gulf-wide scale cannot be conducted.

Conclusion 2: Because environmental changes can influence the success or failure of restoration efforts and can hinder the ability to detect potential cumulative effects of multiple restoration efforts, a thorough understanding of long-term environmental trends is essential for decision makers and restoration practitioners. Advanced monitoring techniques and approaches, including satellite remote sensing, connected sensor networks, and automation, can greatly assist in determining long-term environmental trends and assessing acute events. In addition, long-term environmental trends derived from targeted monitoring efforts can inform a range of analytical tools. The output from these tools can support the development of adaptive management actions that will subsequently improve restoration success and protect existing investments. Significant spatial and temporal gaps in monitoring Gulf of Mexico-wide

environmental indicators and data collection and dissemination efforts limit development of this important and valuable capability. Specifically:

• Long-term environmental trends across the Gulf Coast states are monitored by a patchwork of government agencies, nonprofit organizations, and industries for a variety of reasons (e.g., regulatory, environmental tracking, performance evaluation). Study designs, data collection methods, analyses, and data availability vary and are often not comparable, making synthesis very difficult.
• One-time Gulf-wide monitoring studies are useful, but without periodic updates, do not generate enough information to determine long-term background trends needed for cumulative effects assessments.
• Key metrics to assess landscape-scale changes and support adaptive management include those necessary to estimate environmental trends associated with climate change; freshwater, nutrient, and sediment loading to coastal waters; land use/land cover; ambient water quality; status and trends of finfish and shellfish species, marine mammals, turtles, and birds; and primary and secondary production. For example, enhanced efforts and standardization of methods are needed for:
  • ambient water quality, the measurement of which can be enhanced by using high-spatiotemporal-resolution satellite data on chlorophyll a, suspended sediments, colored organic matter, and harmful algae;
  • tide gage data and subsidence measurements to estimate local, relative sea level rise;
  • estimating the extent and effects of ocean and coastal acidification, information essential for successful restoration and maintenance of commercially important shellfish and in the selection of materials for restoration efforts (e.g., oyster shells, limestone);
  • tracking, targeting needed research, and managing the effects of tropicalization on fishery species, other species, and habitats; and
  • estimating the ecological functioning of restored habitats, something not often measured even though the spatial extent of restored habitats is usually monitored and reported.

Conclusion 3: The Gulf Coast environmental restoration community (federal agencies, states, nongovernmental organizations, and local public and private entities) has an opportunity to incorporate what has been learned from past and ongoing ecosystem restoration to inform future projects and programs supported by the remaining DWH funds. However, unless data and information from existing projects are made accessible and identification of information needed to assess cumulative effects of restoration efforts is undertaken more expeditiously, opportunities to improve the likelihood of success in the many projects remaining to be implemented will be greatly reduced or even permanently lost. Although it may be too early to fully assess cumulative effects of DWH-funded restoration efforts because of lag times between implementation and detection of effects, applying “lessons learned” from existing restoration efforts can help mitigate future risks of failure and ensure that DWH funds are invested wisely to increase the likelihood of meaningful and long-term Gulf of Mexico recovery and resilience.

Conclusion 4: Natural and anthropogenic drivers create multiple ecosystem pressures and stressors that act on restoration efforts over broad spatial scales, ranging from individual projects to entire ecosystems. The cumulative impacts of these pressures and stressors are often complex, resulting in synergistic and antagonistic effects of ecological significance. However, synergistic and antagonistic effects of large-scale restoration efforts in the Gulf of Mexico have not been assessed to date, and results from a limited number of assessments are mixed.

Conclusion 5: The use of multiple lines of evidence to develop a framework to help assess cumulative effects for large-scale restoration efforts in the Gulf of Mexico has been proposed and, in some cases, applied. Assessment of cumulative effects of large-scale restoration is a recent research area and work on applying this research to restoration implementation is needed.

Conclusion 6: Opportunities exist now to prepare for the assessment of cumulative effects and restoration success from existing regional or large-scale restoration efforts in the Gulf of Mexico. These include:

• applying methods to assess functional equivalency between restored and natural sites;
• assessing the degree of environmental stress from natural and anthropogenic sources;
• applying a multiple-lines-of-evidence approach to assess cumulative effects at the estuary or watershed scale in preparation for Gulf-wide efforts;
• undertaking comparative analysis of estuaries or watersheds across the Gulf of Mexico to develop a greater understanding of similarities and differences among these systems; and
• evaluating expected benefits of a restoration effort as compared to a future condition without the effort.

These opportunities will involve consideration of changing environmental trends and a commitment to monitor, analyze, synthesize, and report results.

This page intentionally left blank.