scholarly journals Biophysical controls of marsh soil shear strength along an estuarine salinity gradient

2021 ◽  
Vol 9 (3) ◽  
pp. 413-421
Author(s):  
Megan N. Gillen ◽  
Tyler C. Messerschmidt ◽  
Matthew L. Kirwan
Keyword(s):  
Shear Strength ◽  
Salt Marshes ◽  
Salinity Gradient ◽  
River Estuary ◽  
Belowground Biomass ◽  
York River ◽  
Marsh Soil ◽  
Freshwater Marshes ◽  
Soil Shear Strength ◽  
Wave Erosion

Abstract. Sea-level rise, saltwater intrusion, and wave erosion threaten coastal marshes, but the influence of salinity on marsh erodibility remains poorly understood. We measured the shear strength of marsh soils along a salinity and biodiversity gradient in the York River estuary in Virginia to assess the direct and indirect impacts of salinity on potential marsh erodibility. We found that soil shear strength was higher in monospecific salt marshes (5–36 kPa) than in biodiverse freshwater marshes (4–8 kPa), likely driven by differences in belowground biomass. However, we also found that shear strength at the marsh edge was controlled by sediment characteristics, rather than vegetation or salinity, suggesting that inherent relationships may be obscured in more dynamic environments. Our results indicate that York River freshwater marsh soils are weaker than salt marsh soils, and suggest that salinization of these freshwater marshes may lead to simultaneous losses in biodiversity and erodibility.

scholarly journals Biophysical controls of marsh soil shear strength along an estuarine salinity gradient

2020 ◽  
Author(s):  
Megan N. Gillen ◽  
Tyler C. Messerschmidt ◽  
Matthew L. Kirwan
Keyword(s):  
Shear Strength ◽  
Salt Marshes ◽  
Salinity Gradient ◽  
River Estuary ◽  
Belowground Biomass ◽  
Marsh Soil ◽  
Freshwater Marshes ◽  
Soil Shear Strength ◽  
Indirect Impacts ◽  
Wave Erosion

Abstract. Sea-level rise, saltwater intrusion, and wave erosion threaten coastal marshes, but the influence of salinity on marsh erodibility remains poorly understood. We measured the shear strength of marsh soils along a salinity and biodiversity gradient in the York River estuary in Virginia to assess the direct and indirect impacts of salinity on marsh erodibility. We found that soil shear strength was higher in monospecific salt marshes (5–36 kPa) than biodiverse freshwater marshes (4–8 kPa), driven by differences in belowground biomass and rooting structure. However, we also found that shear strength at the marsh edge was controlled by sediment characteristics, rather than vegetation or salinity, suggesting that inherent relationships may be obscured in more dynamic environments. Our results indicate that freshwater marsh soils are weaker than salt marsh soils, and suggest that salinization of freshwater marshes may lead to simultaneous losses in biodiversity and erodibility.

scholarly journals Controls on soil organic carbon stocks in tidal marshes along an estuarine salinity gradient

2016 ◽  
Vol 13 (24) ◽  
pp. 6611-6624 ◽  
Author(s):  
Marijn Van de Broek ◽  
Stijn Temmerman ◽  
Roel Merckx ◽  
Gerard Govers
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Salt Marshes ◽  
Salinity Gradient ◽  
Tidal Marshes ◽  
Freshwater Marshes ◽  
Marsh Sediments ◽  
Maximum Turbidity Zone ◽  
Maximum Turbidity ◽  
Soc Stocks

Abstract. Tidal marshes are sedimentary environments and are among the most productive ecosystems on Earth. As a consequence they have the potential to reduce atmospheric greenhouse gas concentrations by sequestering organic carbon (OC). In the past decades, most research on soil organic carbon (SOC) storage in marsh environments has focused on salt marshes, leaving carbon dynamics in brackish and freshwater marshes largely understudied and neglecting the diversity among tidal marshes. We therefore conducted an extensive sampling campaign to quantify and characterize SOC stock in marshes along a salinity gradient in the Scheldt estuary (Belgium and the Netherlands). We find that SOC stocks vary significantly along the estuary, from 46 in freshwater marshes to 10 kg OC m−2 in salt marshes. Our data also show that most existing studies underestimate total SOC stocks due to shallow soil sampling, which also influences reported patterns in OC storage along estuaries. In all sampled tidal marsh sediments the SOC concentration is more or less constant from a certain depth downward. However, this concentration decreases with increasing salinity, indicating that the amount of stable SOC decreases from the upper estuary towards the coast. Although the net primary production of macrophytes differs along the estuary, our data suggest that the differences in OC storage are caused mainly by variations in suspended sediment concentration and stable particulate OC (POC) content in the water along the estuary. The fraction of terrestrial suspended sediments and POC that is transported downstream of the maximum turbidity zone is very limited, contributing to smaller amounts of long-term OC sequestration in brackish and salt marsh sediments. In addition, high rates of sediment deposition on freshwater tidal marshes in the maximum turbidity zone promote efficient burial of OC in these marsh sediments.

scholarly journals The importance of an estuarine salinity gradient on soil organic carbon stocks of tidal marshes

2016 ◽  
Author(s):  
Marijn Van de Broek ◽  
Stijn Temmerman ◽  
Roel Merckx ◽  
Gerard Govers
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Salt Marshes ◽  
Net Primary Production ◽  
Salinity Gradient ◽  
Tidal Marshes ◽  
Freshwater Marshes ◽  
Marsh Sediments ◽  
Maximum Turbidity Zone ◽  
Maximum Turbidity

Abstract. Tidal marshes are sedimentary environments that are among the most productive ecosystems on earth. As a consequence tidal marshes, and vegetated coastal ecosystems in general, have the potential to reduce atmospheric greenhouse gas concentrations as they efficiently sequester soil organic carbon (SOC). In the past decades, most research has focused on salt marshes, leaving carbon dynamics in brackish- and freshwater marshes largely understudied and neglecting the diversity among tidal marshes. Moreover, most existing studies underestimate total organic carbon (OC) stocks due to shallow soil sampling, which also influences reported patterns in OC storage along estuaries. We find that SOC stocks vary significantly along the salinity gradient of a temperate estuary (Scheldt estuary, Belgium and The Netherlands), from 46 kg OC m−2 in freshwater marshes to 10 kg OC m−2 in saltmarshes. In all tidal marsh sediments the OC concentration has a constant value from a certain depth below the surface downward. However, this concentration decreases with increasing salinity, indicating that the amount of stabile SOC decreases from the upper estuary towards the coast. Although net primary production of macrophytes differs along the estuary, our data suggest that these differences in OC storage are caused mainly by variations in suspended sediment concentration and stable particulate OC (POC) content in the water along the estuary. The fraction of suspended sediments and POC that is transported downstream the maximum turbidity zone is very limited, contributing to smaller amounts of long term OC sequestration in brackish- and saltmarsh sediments. In addition, high rates of sediment deposition on freshwater tidal marshes in the maximum turbidity zone promote efficient burial of OC in these marsh sediments.

Finite Element Modeling of a Mechanically Stabilized Earth Trial Wall

2021 ◽  
pp. 036119812110164
Author(s):  
Andrew Lees ◽  
Michael Dobie
Keyword(s):  
Finite Element ◽  
Shear Strength ◽  
Retaining Wall ◽  
Back Analysis ◽  
Soil Parameters ◽  
Failure Behavior ◽  
Valuable Insight ◽  
Deformation And Failure ◽  
First Case ◽  
Soil Shear Strength

Polymer geogrid reinforced soil retaining walls have become commonplace, with routine design generally carried out by limiting equilibrium methods. Finite element analysis (FEA) is becoming more widely used to assess the likely deformation behavior of these structures, although in many cases such analyses over-predict deformation compared with monitored structures. Back-analysis of unit tests and instrumented walls improves the techniques and models used in FEA to represent the soil fill, reinforcement and composite behavior caused by the stabilization effect of the geogrid apertures on the soil particles. This composite behavior is most representatively modeled as enhanced soil shear strength. The back-analysis of two test cases provides valuable insight into the benefits of this approach. In the first case, a unit cell was set up such that one side could yield thereby reaching the active earth pressure state. Using FEA a test without geogrid was modeled to help establish appropriate soil parameters. These parameters were then used to back-analyze a test with geogrid present. Simply using the tensile properties of the geogrid over-predicted the yield pressure but using an enhanced soil shear strength gave a satisfactory comparison with the measured result. In the second case a trial retaining wall was back-analyzed to investigate both deformation and failure, the failure induced by cutting the geogrid after construction using heated wires. The closest fit to the actual deformation and failure behavior was provided by using enhanced fill shear strength.

Shear Strength Monitoring System Based on Measurement of Shear Wave Velocity and Moisture Content

2014 ◽  
Vol 635-637 ◽  
pp. 750-754
Author(s):  
Peng Hu ◽  
Qing Li ◽  
Yi Wei Xu ◽  
Nan Ying Shentu ◽  
Quan Yuan Peng
Keyword(s):  
Shear Strength ◽  
Moisture Content ◽  
Shear Wave ◽  
Monitoring System ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Bender Elements ◽  
Strength Measurement ◽  
Soil Shear Strength ◽  
The Relationship

Expound the importance of soil shear strength measurement at mudslide hidden point to release the loss caused by the disaster, explain the relationship between shear wave velocity, moisture content and shear strength, design the shear strength monitoring system combining the shear wave velocity measured by Piezoelectric bender elements and moisture content.

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