A framework to quantify the strength of ecological links between critical loads of atmospheric deposition and final ecosystem services

Michael Bell1, Jennifer Phelan2 and Tamara Blett3

Anthropogenic deposition of nitrogen and sulfur can lead to the acidification and eutrophication of ecosystems. Scientists generally rely on biological indicators of deposition to signal when ecosystem conditions have been altered beyond an acceptable amount and label this value the critical load. However, these biological indicators are not always capable of being directly related to ecosystem services (ecosystem components that provide benefits to humans). Therefore, we developed the STEPS (STressor – Ecological Production function – Final Ecosystem Services) Framework to link changes in a biological indicator of a critical load to a final ecosystem service. The STEPS framework produces “chains” of ecological components that explore the breath of impacts in the change due to exceedance of a critical load. Chains are comprised of the biological indicator, the ecological production function (EPF) which uses ecological components to link the biological indicator to an ecological endpoint that is a final ecosystem service, as well as the user group who directly uses, appreciates, or values the component. The framework uses a qualitative score (High, Medium, Low) for the Strength of Science (SOS) for the relationship between each of the components in the EPF to identify research gaps and prioritize decision making based on what research has been completed.

We tested the STEPS Framework within a workshop setting using the Final Ecosystem Goods and Services Classification System (FEGS-CS) to describe final ecosystem services. We identified chains for four modes of ecological response to deposition: aquatic acidification, aquatic eutrophication, terrestrial acidification, and terrestrial eutrophication. The workshop participants identified 169 unique EPFs linking a change in a biological indicator to a FEGS. After accounting for the multiple beneficiaries of each FEGS, we ended with a total of 1073 chains. The SOS scores allow managers and policy makers may use this information to understand uncertainty imbedded in responses to critical loads, or select chains with strong scientific foundations for quantitative assessment and subsequent valuation. The chains are also being used to tell compelling stories to translate the impacts of air pollution to a beneficiary-specific audience by using the ecological component that the group values and linking it back to the exceedance of a critical load via the EPFs. The results of the analysis can be transferred to the social science community enabling them to apply valuation measures to multiple or selected chains, providing a more comprehensive analysis of the effects of anthropogenic stressors  on measures of human well-being.


1National Park Service, michael_d_bell@nps.gov
2RTI International, jenphelan.contractor@rti.org
3National Park Service, tamara_blett@nps.gov