Engineering ecosystems: An ecosystem function - ecosystem service model for the analysis of private sector development opportunities

A market-based operational definition for sustainable development is proposed and illustrated. The method explicitly recognizes the possibility of incremental improvements toward the overall goal of sustainability. The definition: "Development at any scale is sustainable when investment in preservation or enhancement of natural resource functions has a positive rate of return." This definition solves a persistent problem: no method exists by which private, market-based development projects can be measured and graded with respect to independent criteria of sustainability. The market basis for sustainable development relies on the observation that many ecosystem functions provide direct "services" or values to human economic endeavors and that these ecosystem services can be explicitly included in a pro forma evaluation of proposed development projects. "Sustainability" in this definition is therefore linked to description and measurement of these ecosystem functions and their services. Two real-world examples show how measurement of ecosystem services might be practically achieved. In the first example, area-normalized rates of denitrification (g N m-2 day-1) in wastewater treatment plants and natural systems are calculated and compared. In the second example, attenuation of flood peak discharges (m3 sec-1 hectare-1) by wetlands and two types of retention ponds is modeled in the context of a housing development. In both examples, comparisons show engineered replacements of ecosystem services to be at least an order of magnitude more land-efficient than the original, intact ecosystems in providing the specific services. In private sector development, investment in the engineered equivalent of an ecosystem service which is otherwise provided "for free" by intact ecosystems results in the ability to use land for other development activities; in essence, a land-for-service exchange. Considering that intact natural ecosystems obviously provided the "replaced" service as just one of many such services, the order of magnitude differences in service rates found in this study appear to offer sufficient margin for meeting the sustainability criterion for investment in ecosystem services. Finally, the benefits and limitations underlying this approach are discussed, and the policy implications are explored with respect to their impact on science and engineering.