Publications [#225260] of Emily S. Bernhardt

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Papers Published

  1. Helton, AM; Bernhardt, ES; Fedders, A, Biogeochemical regime shifts in coastal landscapes: the contrasting effects of saltwater incursion and agricultural pollution on greenhouse gas emissions from a freshwater wetland, Biogeochemistry, vol. 120 no. 1-3 (August, 2014), pp. 133-147 [doi] .
    (last updated on 2019/04/19)

    Many coastal plain wetlands receive nutrient pollution from agricultural fields and are particularly vulnerable to saltwater incursion. Although wetlands are a major source of the greenhouse gases methane (CH₄) and nitrous oxide (N₂O), the consequences of salinization for greenhouse gas emissions from wetlands with high agricultural pollution loads is rarely considered. Here, we asked how saltwater exposure alters greenhouse gas emissions from a restored freshwater wetland that receives nutrient loading from upstream farms. During March to November 2012, we measured greenhouse gases along a ~2� km inundated portion of the wetland. Sampling locations spanned a wide chemical gradient from sites receiving seasonal fertilizer nitrogen and sulfate (SO₄ ²⁻) loads to sites receiving seasonal increases in marine salts. Concentrations and fluxes of CH₄ were low (<100� µg� L⁻¹ and <10� mg� m⁻²� h⁻¹) for all sites and sampling dates when SO₄ ²⁻ was high (>10� mg� L⁻¹), regardless of whether the SO₄ ²⁻ source was agriculture or saltwater. Elevated CH₄ (as high as 1,500� µg� L⁻¹ and 45� mg� m⁻²� h⁻¹) was only observed on dates when air temperatures were >27� °C and SO₄ ²⁻ was <10� mg� L⁻¹. Despite elevated ammonium (NH₄ ⁺) for saltwater exposed sites, concentrations of N₂O remained low (<5� µg� L⁻¹ and <10� µg� m⁻²� h⁻¹), except when fertilizer derived nitrate (NO₃ ⁻) concentrations were high and N₂O increased as high as 156� µg� L⁻¹. Our results suggest that although both saltwater and agriculture derived SO₄ ²⁻ may suppress CH₄, increases in N₂O associated with fertilizer derived NO₃ ⁻ may offset that reduction in wetlands exposed to both agricultural runoff and saltwater incursion.