Consensus Report

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Nutrient recycling, habitat for plants and animals, flood control, and water supply are among the many beneficial services provided by aquatic ecosystems. In making decisions about human activities, such as draining a wetland for a housing development, it is essential to consider both the value of the development and the value of the ecosystem services that could be lost. Despite a growing recognition of the importance of ecosystem services, their value is often overlooked in environmental decision-making. This report identifies methods for assigning economic value to ecosystem services\u0097even intangible ones\u0097and calls for greater collaboration between ecologists and economists in such efforts.

Key Messages

  • Although valuation of multiple ecosystem services is more difficult than valuation of a single ecosystem service, interconnections among services may make it necessary to expand the scope of the analysis.
  • Aquatic ecosystems generally have some capacity to provide consumable resources (e.g., water, food); habitat for plants and animals; regulation of the environment (e.g., hydrologic cycles, nutrient cycles, climate, waste accumulation); and support for nonconsumptive uses (e.g., recreation, aesthetics, research). Considerable work remains to be done in documentation of the potential that various aquatic ecosystems have for contribution in each of these broad areas.
  • Because ecosystem changes are likely to have long-term impacts, some accounting of the timing of impacts is necessary.
  • Complex ecosystem dynamics and incomplete knowledge of ecosystems will have to be resolved before comprehensive valuation of ecosystems is tractable, but comprehensive ecosystem valuation is not generally essential to inform many management decisions.
  • Considering the best available and most reliable information about the benefits of improvements in ecosystem services or the costs of ecosystem degradation will lead to improved environmental decision-making. This information is likely to be only one of many possible considerations that influence policy choice.
  • Ecologists have qualitatively described the structure and function of most types of aquatic ecosystems. However, the complexity of ecosystems remains a barrier to quantification of these features, particularly their interrelationships.
  • Ecologists understand the uncertainties in ecosystem analysis and accept them as inherent caveats in all discussions of system performance.
  • Ecosystem processes are often spatially linked, especially in aquatic ecosystems. Full accounting of the consequences of actions on the value of ecosystem services requires understanding these spatial links and undertaking integrated studies at suitably large spatial scales to fully cover important effects
  • Even when the goal of a valuation exercise is focused on a single ecosystem service, a workable understanding of the functioning of large parts or possibly the entire ecosystem may be required.
  • From an ecological perspective, the value of specific ecosystem functions/services is entirely relative. The spatial and temporal scales of analysis are critical determinants of potential value.
  • Further integration of the sciences of economics and ecology at both intellectual and practical scales will improve ecologists´┐Ż ability to provide useful information for assessing and valuing aquatic ecosystems.
  • General concepts regarding the linkages between ecosystem function and services have been developed. Although precise quantification of these relationships remains elusive, the general concepts seem to offer sufficient guidance for valuation to proceed with careful attention to the limitations of any ecosystem assessment.
  • Investigation of the spatial and temporal thresholds of significance for various ecosystem services is necessary to inform valuation efforts.
  • It is clear that economists and ecologists should work together to develop valid estimates of the values of various aquatic ecosystem services that are useful to inform policy decision-making.
  • Many, but not all, of the goods and services provided by aquatic ecosystems are recognized by both ecologists and economists. These goods and services can be classified according to their spatial and temporal importance.
  • Natural systems are dynamic and frequently exhibit nonlinear behavior. For this reason, caution should be used in extrapolation of measurements in both space and time. Although it is not possible to avoid all mistakes in extrapolation, the uncertainty warrants explicit acknowledgment.
  • Potentially useful classification and inventories of aquatic ecosystems as well as their functional condition exist at both regional and national levels, though the relevance of these classification and inventory systems to assessing and valuing aquatic ecosystems is not always clear.
  • Related in some ways to the precautionary principle is the concept of a safe minimum standard, which introduces a class of choices in which decision-makers seek to maintain population or ecosystem levels sufficient for survival
  • Studies that focus on valuing a single ecosystem service show promise of delivering results that can inform important policy decisions. In no instance, however, should the value of a single ecosystem service be confused with the value of the entire ecosystem, which has far more than a single dimension.
  • The benefit and cost estimates that emerge from an economic valuation exercise will be influenced by the way in which the valuation question is framed. In particular, the estimates will depend on the delineation of the changes in ecosystem goods or services to be valued, the scope of the analysis (in terms of both the geographical boundaries and the inclusion of relevant stakeholders), and the temporal scale.
  • The problems of developing an interdisciplinary terminology and/or a universally applicable protocol for valuing aquatic ecosystems were illuminated, but ultimately identified as unnecessary objectives.
  • The valuation of aquatic and related terrestrial ecosystem services inevitably involves investigator judgments and some amount of uncertainty. Although unavoidable, uncertainty and the need to exercise professional judgment are not debilitating to ecosystem valuation.
  • The value of ecosystem services depends on underlying conditions. Ecosystem valuation studies should clearly present assumptions about underlying ecosystem and market conditions and how estimates of value could change with changes in these underlying conditions.
  • There is a variety of nonmarket valuation methods that are available and have been presented in this chapter. However, no single method can be considered the best at all times and for all types of aquatic ecosystem valuation applications.