der to develop “lessons learned” that can be applied in future ecosystem valuation activities. Chapter 6 assesses judgment and uncertainty associated with ecosystem valuation and suggests how analysts and decision-makers can and should respond. Lastly, Chapter 7 synthesizes the current knowledge regarding ecosystem services valuation and builds on the preceding chapters in order to provide guidelines for policymakers and planners concerned with the management, protection, and restoration of aquatic ecosystems. It also identifies what the committee feels are overarching recommendations for improving the valuation of ecosystem services and related research needs.

Some believe that environmental amenities and services lie outside the scope of economic analyses, arguing that the need to protect environmental assets is self-evident and not properly the subject of economic analyses (see Chapter 2 for further discussion). However, wherever there is scarcity and the need to choose between alternatives, the question of relative values is unavoidable. It may be costly to protect, conserve, and restore aquatic ecosystems, and the costs are borne by giving up benefits in other parts of the economy, now or in the future. When ecosystem protection projects and policies are proposed, it is appropriate to ask whether they achieve the stated goals in a cost-effective and efficient manner, whether the costs are commensurate with the benefits received, what society’s costs are if protection is not provided, and whether costs and benefits are properly allocated across the present population and across generations.

Economic valuation requires that ecosystems be described in terms of the goods and services they provide to humans or other beneficiaries. Goods and services, in turn, must be quantified and measured on a common (though not necessarily monetary) scale if improvements to one ecosystem are to be compared to improvements to another. Although the issues that this raises apply to all types of ecosystems, the use of such information has started to come into particularly sharp focus for aquatic ecosystems and especially for wetlands (NRC, 2001).

Studying ecosystem services presents several challenges that are discussed throughout this report. The most fundamental challenge lies in providing an explicit description of the links between the structure and function of natural systems and the benefits (i.e., goods and services) derived by humanity. This problem is complicated by the fact that humans are an integral part of the system; by incomplete knowledge of how ecosystems function; and by the fact that ecosystem services tend to be specific to locations and situations, thus making it difficult to develop generic principles or identify generic characteristics.

The challenges to both ecologists and economists implicit in valuing ecosystem services are summarized in Figure 1-3. Human actions affect the structure, functions, and goods and services of ecosystems. Ecosystem conditions are