There are several general premises that the committee feels accurately reflect the current state of knowledge about the value and valuation of aquatic ecosystem services. These premises frame the more detailed discussion of major conclusions that follows. The key links embodied in these premises are illustrated in Figure 7-1, which is a more detailed version of Figure 1-3.

  1. Ecosystem structure along with regulatory and habitat/production functions produce ecosystem goods and services that are valued by humans. Examples include production of consumable resources (e.g., water, food, medicine, timber), provision of habitat for plants and animals, regulation of the environment (e.g., hydrologic and nutrient cycles, climate stabilization, waste accumulation), and support for nonconsumptive uses (e.g., recreation, aesthetics).

  2. In addition, many people value the existence of aquatic ecosystems for their own sake, or for the role they play in ensuring the preservation of plant and animal species whose existence is important to them. This value can stem from a belief that these species or ecosystems have intrinsic value or from the benefits that humans get from their existence, even when that existence is not directly providing goods or services used by human populations. In some cases, this “nonuse” value may be the primary source of an ecosystem’s value to humans.

  3. The total economic value of ecosystem services is the sum of the use values derived directly from use of the ecosystem and the nonuse value derived from its existence. Use value can be decomposed further into consumptive uses (e.g., fish harvests) and nonconsumptive uses (e.g., recreation).

  4. Human actions affect the structure, functions, and goods and services of ecosystems. These impacts can occur not only from the direct, intentional use of the ecosystem (e.g., for harvesting resources), but also from the unintentional, indirect impacts of other activities (e.g., upstream agriculture). Human actions are, in turn, directly affected by public policy and resource management decisions.

  5. Understanding the links between human systems and ecosystems requires the integration of economics and ecology. Economics can be used to better understand the human behavior that impacts ecosystems, while ecology aids in understanding the physical system that is both impacted and valued by humans.

  6. Nearly all policy and management decisions imply changes relative to some baseline and most changes imply trade-offs (i.e., more of one good or service but less of another). Protection of an ecosystem through a ban on or reduction of a certain type of activity implies an increase in ecosystem services but a reduction in other services provided by the restricted activity. Likewise, allowing an activity that is deemed detrimental implies a reduction in some ecosystem services but an increase in the services generated by the allowed activity.

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