Research ArticleENVIRONMENTAL STUDIES

The social costs of nitrogen

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Science Advances  05 Oct 2016:
Vol. 2, no. 10, e1600219
DOI: 10.1126/sciadv.1600219
  • Fig. 1 The marginal and total social costs of N fertilizer applied in each county in Minnesota.

    Damages from NO3 represent the sum of costs in each county in Minnesota due to groundwater contamination of private domestic wells and public water suppliers. Damages from ammonia (NH3) and N oxides (NOx) are related to premature deaths from N fertilizer emissions that contribute to the formation and associated impacts of PM2.5 and include regional damages within and beyond the borders of Minnesota. Damages from N2O are estimates of the costs due to global climate change converted into CO2 equivalents and valued using the SCC. Total costs are average annual values based on reported on-farm N fertilizer inputs assuming a 20-year time horizon and a 3% rate of discount (59). Marginal costs are estimated as dollars per kilogram of N fertilizer.

  • Fig. 2 Spatial heterogeneity in N-related damages.

    Damages are associated with groundwater NO3 contamination where the risk of damages is estimated as the sum of NO3 threats, vulnerability, and exposure. Threat is represented here as the risk of row crop expansion, calculated as the percent change in fertilized acres of cropland between 2007 and 2012 (60). Vulnerability is estimated from soil and geologic characteristics that facilitate the transport of NO3-enriched runoff and increase the susceptibility of aquifers to contamination (51). Exposure is quantified as the number of households in each county that rely on self-supplied groundwater, normalized by county area and log-transformed (48). All indices were normalized on a 0-to-1 scale.

  • Table 1 Comparing the SCC and the SCN.
    SCCSCN
    Assumes uniform spatial distribution of atmospheric C, regardless of spatial location of emissionsThe location where N enters the system needs to be known to
    route N to end points of interest where damages may occur.
    Costs only associated with C in atmospheric poolCosts associated with N in atmospheric, surface water, groundwater, and coastal pools
    All forms of greenhouse gases can be aggregated into a single equivalent form (CO2).Different forms of N must be accounted for separately based on their differential impacts.
    Damages are spatially explicit; populations vary in their exposure to climate risks and vulnerability to impacts.Damages are spatially explicit; populations vary in their exposure to N-related risks and vulnerability to impacts.
    Climate impacts are experienced globally. The most-damaging impacts are in the distant future.N impacts are local to regional to global and occur over shorter and longer time scales; long-term impacts are poorly characterized.
    Damage functions driven by a single proxy variable (changes in temperature)Multiple damage functions driven by changes in multiple forms of N in different locations
    Uncertainty driven by climate sensitivity, expected damages, and discountingUncertainty driven by location of emissions, flow, routing, expected damages of N in different pools, and discounting

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/10/e1600219/DC1

    table S1. Average and total social costs of N from fertilizer application in each Minnesota county (in 2010 dollars).

    table S2. Parameter estimates and significance tests for the logistic regression model used to predict well nitrate contamination among a larger data set of wells with known locations and unknown nitrate concentrations.

    table S3. Costs (in 2010 dollars) associated with nitrate treatment for public water suppliers in Minnesota.

  • Supplementary Materials

    This PDF file includes:

    • table S1. Average and total social costs of N from fertilizer application in each Minnesota county (in 2010 dollars).
    • table S2. Parameter estimates and significance tests for the logistic regression model used to predict well nitrate contamination among a larger data set of wells with known locations and unknown nitrate concentrations.
    • table S3. Costs (in 2010 dollars) associated with nitrate treatment for public water suppliers in Minnesota.

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