Citation:

Wigand, C., E. Watson, R. Martin, E. Davey, Roxannel Johnson, Alana Hanson, D. Johnson, S. Warren, AND L. Deegan. Marsh soil responses to tidal water nitrogen additions contribute to creek bank fracturing and slumping. Coastal and Estuarine Research Federation (CERF) 24th Biennial International Meeting, Providence, RI, November 05 - 09, 2017.

Impact/Purpose:

Coastal eutrophication is a worldwide problem and in this long-term ecosystem experiment, the soil marsh responses to dissolved nitrogen enrichment were examined. Large-scale dissolved nutrient enrichment caused a reduction in belowground biomass, increased water content of soils, and increased microbial decomposition, which is linked with slumping of low marsh Spartina vegetation into creeks, and ultimately marsh loss. In this study, we reported significantly increased soil % organic matter, root % nitrogen, and soil respiration from the enriched creeks. The continuity in horizontal soil shear strength, measured across the adjacent low and high marsh in the enriched Sweeney Creek, was significantly reduced compared with the reference West Creek. We identified the reduced continuity of soil shear strength across the marsh landscape as a possible mechanism contributing to the reported fracturing and creek-bank collapse in the enriched creek systems. Understanding the role coastal eutrophication plays in marsh loss will assist land managers, restoration specialists, and decision-makers in developing science-based management and restoration plans.

Description:

Large-scale dissolved nutrient enrichment can cause a reduction in belowground biomass, increased water content of soils, and increased microbial decomposition, which has been linked with slumping of low marsh Spartina vegetation into creeks, and ultimately marsh loss. Our study was part of a whole-ecosystem, nutrient-enrichment experiment which was conducted in four first-order tidal creeks (reference creeks: West and Nelson; fertilized creeks: Sweeney and Clubhead) in the Plum Island Sound Estuary (MA) in the northeast USA. We report significantly increased soil % organic matter (P reference creeks). The fertilized organic soils had noticeably more benthic algae and appeared more decomposed and watery. The continuity in horizontal soil shear strength, measured across the adjacent low and high marsh in the fertilized Sweeney, was significantly reduced (P < 0.0001) compared with the reference creek. We identified the reduced continuity of soil shear strength across the marsh landscape as a possible mechanism contributing to the reported fracturing and creek-bank collapse in the fertilized creek systems. In addition, in the face of accelerated sea level rise in recent years in the northeast USA, an increase in flooding exposure by low marsh vegetation apparently caused increases in soil wet bulk density, reductions in Spartina belowground biomass, and increases in Distichlis spicata cover among both reference and nitrogen enriched creeks, which may exacerbate marsh responses (e.g., creek-bank fracturing and slumping) to coastal eutrophication.

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