DOI: 10.5061/dryad.02v6wwqh9
title: <em>Avicennia germinans</em> and <em>Spartina alterniflora</em> soil shear strength and belowground biomass data near Port Fourchon, LA

description: Subtropical black mangrove (Avicennia germinans) is expanding into higher
 latitudes and encroaching on existing temperate salt marshes with the
 potential to alter a variety of ecological processes. In the Mississippi
 River Delta (Louisiana, USA), wave-driven marsh edge erosion is on the
 order of meters per year and accounts for half of the total sizable marsh
 loss. Here, we show that edge erosion is reduced by 40-60% when colonized
 by Avicennia as compared to salt marsh dominated by Spartina alterniflora.
 The lower erosion rate in sites dominated by Avicennia is associated with
 a greater soil shear strength, more live belowground biomass, and deeper
 roots. Furthermore, Avicennia reduces edge erosion only when there are
 dense, well-established stands. Marshes with sparse Avicennia cover had
 similar edge erosion rates to those with Spartina, likely due to lower and
 more shallow root biomass. Avicennia at 10 m inland also had similar soil
 shear strength and live belowground biomass as those at the marsh edge,
 suggesting that as the marsh erodes, newly exposed Avicennia will be
 better able to withstand wave action as compared to Spartina. Overall,
 climate-driven Avicennia expansion will not prevent marsh edge erosion,
 but it will significantly slow it down. Avicennia germinans could be used
 for restoration and a nature-based solution to reduce edge erosion, with
 efforts that allow Avicennia ~5 years to mature before being exposed along
 the marsh edge.
description: # *Avicennia germinans* and *Spartina alterniflora* soil shear strength
 and belowground biomass data near Port Fourchon, LA Dataset DOI:
 [10.5061/dryad.02v6wwqh9](https://doi.org/10.5061/dryad.02v6wwqh9) ##
 Description of the data and file structure This dataset contains soil
 shear strength (kPa) and belowground biomass (g) data collected near Port
 Fourchon, LA (USA). Study sites were selected using aerial imagery and
 ground reconnaissance based on the abundance of *Avicennia*, *Spartina*,
 and their location relative to wave action. Sites were classified as
 either Dense *Avicennia*, i.e., 100% *Avicennia* cover, Sparse
 *Avicennia*, i.e., 50% *Avicennia* cover and 50% *Spartina* cover, or
 Dense *Spartina*, i.e,. 75 – 100% *Spartina* cover.  Field measurements of
 soil shear strength, live and dead belowground biomass, bulk density, and
 % organic matter were taken at two Dense *Avicennia* sites, two Sparse
 *Avicennia* sites, and two Dense *Spartina* sites. At each study site,
 three transects were established approximately 5-10 m apart. Along each
 transect, elevation was measured at 2 m intervals from the marsh edge to
 25 m inland using a Leica GS14 GNSS Receiver (Leica v. 7.03). Soil shear
 strength was measured at distances of 2, 10, and 20 m along one of the
 three transects at each site using a Humboldt Shear Vane. Eight replicate
 measurements were taken at each distance at depths of 5, 15, 25, 35, 45,
 55, and 65 cm. Belowground biomass was collected at 2 and 20 m distances,
 using a sharpened PVC soil core (15.2 cm diameter x 45 cm depth). Bulk
 density and % organic matter were sampled using a russian peat core to a
 depth of 65 cm (5 cm diameter). Soil cores were cut into 5 cm depth
 sections and brought back to the laboratory, where they were stored cold
 before analysis. Belowground biomass cores were cut into 5 cm depth
 sections and rinsed through a 1 mm sieve. Roots and rhizomes were then
 separated by species, live/dead, and dried at 60°C to a constant weight.
 Soil bulk density was determined for each of the 5 cm depth sections
 following drying at 60°C to a constant weight and calculation of dry mass
 over volume. Soil samples were then ashed in a muffle furnace at 550°C for
 five hours, and the % organic matter was calculated as the percent dry
 mass loss. ### Files and variables #### File:
 Manuscript_ScientificReports_data_1.12.26.xlsx **Description:** Soil shear
 strength, belowground biomass, bulk density, and % organic matter from
 sites with dense *Avicennia germinans*, Sparse *Avicennia germinans*, and
 Dense *Spartina alterniflora* sites near Port Fourchon, LA (USA) #####
 Variables (Headers) * Article_Name: Site name used in the manuscript
 '*Avicennia germinans* and *Spartina alterniflora* soil shear
 strength and belowground biomass data near Port Fourchon, LA * Site: Site
 name (number) used during data collection and analysis * Site.txt: Site
 name (letter) used during data collection and analysis  * Species: Species
 name (*S. alterniflora* = *Spartina alterniflora*, and *A. germinans* =
 *Avicennia germinans*) * Distance (m): Distance from the edge of the marsh
 * Depth (cm): Depth from the marsh surface * Shear_Strength: Soil Shear
 Strength (kPa) * Sample: Sample number (number) used during data analysis
 * Sample_txt: Sample number (letter) used during data analysis * Live_BB:
 Live Belowground Biomass (g) * Dead_BB: Dead Belowground Biomass (g) *
 Total_BB: Total Belowground Biomass (g) * Bulk Density (g/cm^3^) * Organic
 Matter (%) * Layer: Upper (0-20cm) and Lower (20-65 cm) * Location: Site
 located near Fourchon or Grand Isle