Abstract:

We sought to assess the extent of oil distribution in Alabama coastal salt marshes from the Deepwater Horizon oil spill, and determine the effects of that oil on vegetation and soil conditions. Baseline soil and vegetation data were collected from ten plots in each of thirteen wetlands in May 2010 in Baldwin County, AL. Follow up data were collected from the same sites in May and September 2011. The data we collected included number of species in each wetland, percent coverage by each species in each plot, maximum height of dominant species, as well as soil and vegetation tissue samples. These vegetation and tissue samples were then frozen prior to processing. Soil samples were dried and analyzed for total petroleum hydrocarbon (TPS) concentration (mg TPH/ Kg soil) and for carbon, nitrogen, and sulfur (CNS) makeup.

Suggested Citation:

Anderson, Chris. 2015. The distribution of residual oil in Alabama coastal marshes and its impact on marsh vegetation from May 2010 - September 2011.. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N74Q7RXR

Purpose:

The goals of this project were to 1) examine the distribution of residual oil within and among coastal Alabama marshes and 2) determine the effect of residual oil on marsh structure (plant height, cover, density, and biomass). Objectives of this study were to 1) determine if tidal marsh exposure to residual oil is highest at wetlands closest to the Gulf of Mexico of Mobile Bay, 2) within each wetland, determine where the highest concentrations of residual oil, and possibly the greatest impact to plants, occur (at the edge or interior of the marsh), and 3) determine if residual oil exposure has caused a change in marsh structure/biomass (above ground biomass, stem height, covert) and if there is a relationship between residual oil exposure and changes in plant structure/biomass.

Data Parameters and Units:

Vegetation : Site Number, Data Collection Date (MM/DD/YYYY), Latitude (decimal degrees), Longitude (decimal degrees), General Location [Perdido Pass, Bon Secour Bay, Magnolia River, Oyster Bay, Little Lagoon, Wolf Bay, Point Pleasure Road], Mean Total Plant Cover (%), Mean Juncus roemerianus Cover (%), Mean Maximum Plant Height (meters), Wetland species richness. Soil: Site Number, Middle or edge plot, Soil Carbon (%), Soil Nitrogen (%), Soil Sulfur (%), May 2010 TPH Total Petroleum Hydrocarbons (mg/Kg), September 2011 TPH (mg/Kg).

Instruments:

Thirteen wetlands were sampled for this project. At each wetland, one transect was taken perpendicular from the water’s edge to the land’s edge, along which ten 1 m^2 plots were evenly. Plot 1 was the closest to the water, and plot 10 was closest to the upland shore. Baseline vegetation (2010 only): In each plot, vegetation was surveyed for species richness, total cover per species, and average maximum height of the dominant vegetation. Soils: Two samples were collected at each wetland, one at the water’ s edge (Plot 1, edge) and one at the middle of the transect (Plot 5, ‘middle’). At each plot, a soil corer was used to extract two cores and cut two 10 cm soil cores from each wetland. Samples were stored in glass canisters and placed in a cooler for transport to the lab. The Florida residual petroleum organic method (FL-PRO) was used to determine total petroleum hydrocarbons (TPH), and a LECO CNS 2000 was used to determine percent soil composition.

Error Analysis:

Samples were taken over three 3-day periods: one in May 2010, one in September 2011. Transects varied in length depending on the width of the wetland, but plot size was constant (ten plots, each 1 m^2). All wetlands sampled were in Baldwin County, AL. Some were immediately on the Gulf coast, some were in bays and inlets, and some were upstream in coastal creeks.

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