Soil Shear Strength Losses in Two Fresh Marshes with Variable Increases in N and P Loading

R Eugene Turner,James E Bodker,Christopher Swarzenski

doi:10.1007/s13157-020-01265-w

R Eugene Turner, James E Bodker + Show 1 more

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https://doi.org/10.1007/s13157-020-01265-w

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Abstract

We measured soil shear strength (SSS) from 2009 to 2018 in two hydrologically distinct freshwater marshes dominated by Panicum hemitomon after nitrogen (N) and phosphorous (P) were applied to the surface in spring. The SSS averaged over 100-cm depth in the floating and anchored marshes declined up to 30% throughout the profiles and with no apparent differences in the effects of the low, medium, and high N + P dosing. Plots with only N or P additions exhibited significant changes in SSS at individual depths below 40 cm for the anchored marsh, but not the floating marsh. The average SSS for the anchored marsh over the entire 100 cm profile declined when N and P were added separately or together. At the floating marsh, however, the SSS decreased when N and P were added in combination, or P alone, but not for the N addition. Increasing nutrient availability to these freshwater marsh soils makes them weaker, and perhaps lost if eroded or uplifted by buoyant forces during storms. These results are consistent with results from multi-year experiments demonstrating higher decomposition rates, greenhouse gas emissions, and carbon losses in wetlands following increased nutrient availability.

Highlights

The rising concentrations of nitrogen, phosphorus and sulfur in air, streams, and other waterbodies over the last 100 years (Meybeck 2003; Holtgrieve et al 2011; Greaver et al 2012; Stets et al 2015) are in intimate contact with wetlands whose global extent is approximately 0.43 million km2 in the Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.2 U.S Geological Survey, Lower Mississippi-Gulf Water Science Center, 3535 S
The results from the few multi-year field experiments in tundra and coastal wetland ecosystems demonstrated that increased nutrient availability may cause a decline in live below-ground biomass, weaken soils, enhance greenhouse gas emissions, and decrease resilience to hurricanes (Mack et al 2004; Bragazza et al 2006; Darby and Turner 2008a, b; Deegan et al 2012; Feller et al 2015; Hollis and Turner 2018)
We sampled two freshwater marshes dominated by Panicum hemitomon in the Mississippi River Delta

Summary

Introduction

The remaining wetland area in 2000 was 6–7% of the global land mass (Melton et al 2013) and holds a disproportionately larger portion of the terrestrial carbon storage, which is one-fifth of the world’s soil carbon (Post et al 1982). The results from the few multi-year field experiments in tundra and coastal wetland ecosystems demonstrated that increased nutrient availability may cause a decline in live below-ground biomass, weaken soils, enhance greenhouse gas emissions, and decrease resilience to hurricanes (Mack et al 2004; Bragazza et al 2006; Darby and Turner 2008a, b; Deegan et al 2012; Feller et al 2015; Hollis and Turner 2018)

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