Fertilizer legacies meet saltwater incursion: challenges and constraints for coastal plain wetland restoration

Ardon, M., et al., 2017. Elementa-Science of the Anthropocene

Original research (primary data)
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Coastal wetland restoration is an important tool for climate change adaptation and excess nutrient runoff mitigation. However, the capacity of restored coastal wetlands to provide multiple ecosystem services is limited by stressors, such as excess nutrients from upstream agricultural fields, high nutrient legacies on-site, and rising salinities downstream. The effects of these stressors are exacerbated by an accelerating hydrologic cycle, expected to cause longer droughts punctuated by more severe storms. We used seven years of surface water and six years of soil solution water chemistry from a large (440 ha) restored wetland to examine how fertilizer legacy, changes in hydrology, and drought-induced salinization affect dissolved nutrient and carbon concentrations. To better understand the recovery trajectory of the restored wetland, we also sampled an active agricultural field and two mature forested wetlands. Our results show that nitrogen (N) and phosphorus (P) concentrations in soil solution were 2-10 times higher in the restored wetland compared to two mature forested wetlands, presumably due to legacy fertilizer mobilized by reflooding. Despite elevated nutrient concentrations relative to reference wetlands, the restored wetland consistently attenuated N and P pulses delivered from an upstream farm. Even with continued loading, N and P concentrations in surface water throughout the restored wetland have decreased since the initial flooding. Our results suggest that high nutrient concentrations and export from wetlands restored on agricultural lands may be a severe but temporary problem. If field to wetland conversion is to become a more widespread method for ameliorating nutrient runoff and adapting coastal plain ecosystems to climate change, we should adopt new methods for minimizing the initial export phase of wetland restoration efforts.

Case studies

Basic information

  • Case ID: INT-035-1
  • Intervention type: Restoration
  • Intervention description:

    large scale restored wetland in the coastal plain; 440 ha of former agricultural fields undergoing stream and wetland restoration

  • Landscape/sea scape ecosystem management: Yes
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Reduced water quality  Positive N and P concentrations in surface water and soil solution
  • Approach implemented in the field: Yes
  • Specific location:

    Timberlake Observatory for Wetland Restoration (TOWeR) is located in Tyrell County (35° 54′22′′N, 76° 09′25′′W,), North Carolina

  • Country: United States of America
  • Habitat/Biome type: Streams, rivers, riparian | Wetlands |
  • Issue specific term: Not applicable


  • Notes on intervention effectivness: water quality here is relevant, linked to climate impacts because authors suggest that a changing climate and sea level rise (along with agricultural activities) have caused novel biogeochemical regimes [impacting nutrient pollution in water resources] for water quality impact, effectiveness is compared to baseline nutrient concentrations and assess how they change over time for drought impacts, there is no control or relevant baseline to compare to. looks at response of the intervention to an isolated drought event.
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Not applicable
  • Compare effectivness?: No
  • Compared to the non-NBS approach: Not applicable
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: No
  • Impacts for the ecosystem: Not reported
  • Ecosystem measures: n/a
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures: n/a
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: No
  • Experimental evalution done: Not applicable
  • Non-experimental evalution done: Empirical case study
  • Study is systematic: