Citation:

Clark, C., M. Bell, J. Boyd, J. Compton, E. Davidson, C. Davis, M. Fenn, L. Geiser, L. Jones, AND T. Blett. Nitrogen-induced terrestrial eutrophication: cascading effects and impacts on ecosystem services. Ecosphere. ESA Journals, 8(7):e01877, (2017). https://doi.org/10.1002/ecs2.1877

Impact/Purpose:

Here, we show that terrestrial eutrophication is a widespread phenomenon across the continental United States and demonstrate the variety of ecosystem services and people affected by this environmental stressor. Because our work did not involve social evaluation of eutrophication-driven FEGS changes, we cannot yet say how large those impacts are in economic or other terms. However, the activity does suggest numerous causal pathways between eutrophication and ecological outcomes that could be economically and socially important. Our assessment is not comprehensive, and thus represents a summary of major impacts considered by experts in the field, and most certainly is an underestimate of the total number of impact pathways nationally. Nevertheless, our assessment was thorough and found that exceedances of 21 N critical loads in five ecoregions affected 582 unique pathways. These exceedances ultimately affected 66 FEGS across a range of categories (21 categories) and 198 regional and FEGS-specific human beneficiaries of various types (16 types). The exact narrative varied widely from place to place, but the general pattern was similar: Species of interest are lost, community composition changes, and secondary effects occur, including changes in fire regimes, runoff and aquifer recharge, carbon sequestration, and habitat of high-value species. These findings underscore the national extent of impacts from terrestrial eutrophication and suggest areas for future research to better enable society to quantify and evaluate the impacts to society from this environmental stressor.

Description:

Human activity has significantly increased the deposition of nitrogen (N) on terrestrial ecosystems over pre-industrial levels leading to a multitude of effects including losses of biodiversity, changes in ecosystem functioning, and impacts on human well-being. It is challenging to explicitly link the level of deposition on an ecosystem to the cascade of ecological effects triggered and ecosystem services affected, because of the multitude of possible pathways in the N cascade. To address this challenge, we report on the activities of an expert workshop to synthesize information on N-induced terrestrial eutrophication from the published literature and to link critical load exceedances with human beneficiaries by using the STressor–Ecological Production function–final ecosystem Services Framework and the Final Ecosystem Goods and Services Classification System (FEGS-CS). We found 21 N critical loads were triggered by N deposition (ranging from 2 to 39 kg N·ha−1·yr−1), which cascaded to distinct beneficiary types through 582 individual pathways in the five ecoregions examined (Eastern Temperate Forests, Marine West Coast Forests, Northwestern Forested Mountains, North American Deserts, Mediterranean California). These exceedances ultimately affected 66 FEGS across a range of final ecosystem service categories (21 categories, e.g., changes in timber production, fire regimes, and native plant and animal communities) and 198 regional human beneficiaries of different types. Several different biological indicators were triggered in different ecosystems, including grasses and/or forbs (33% of all pathways), mycorrhizal communities (22%), tree species (21%), and lichen biodiversity (11%). Ecoregions with higher deposition rates for longer periods tended to have more numerous and varied ecological impacts (e.g., Eastern Temperate Forests, eight biological indicators) as opposed to other ecoregions (e.g., North American Deserts and Marine West Coast Forests each with one biological indicator). Nonetheless, although ecoregions differed by ecological effects from terrestrial eutrophication, the number of FEGS and beneficiaries impacted was similar across ecoregions. We found that terrestrial eutrophication affected all ecosystems examined, demonstrating the widespread nature of terrestrial eutrophication nationally. These results highlight which people and ecosystems are most affected according to present knowledge, and identify key uncertainties and knowledge gaps to be filled by future research.

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