Abstract:

We investigated potential and actual rates of marsh soil nitrogen cycling seasonally (April, July, and October 2014) in 6 Terrebonne Bay marsh sites. In this study, we chose three regions where we could find oiled and unoiled pairs of marshes located within close proximity to each other. Potential rates of N-cycling (15N-labelled NO3 soil incubations) and denitrification enzyme activity (DEA) were measured at 2 locations (1 and 10m from the marsh edge) at all six sites. Actual N cycling rates were conducted using 15N-labelled flooded 4cm diameter sediment cores collected 10m from the marsh edge at each site. 5 replicate cores were collected from each of two sites per date and destructively sampled during the linear portion of DO decline in the overlying water. Additionally, we measured a series of basic site characterizations, soil properties, assessed oil status, and characterized the dissolved inorganic nutrient concentrations in overlying water and adjacent bay water samples.

Suggested Citation:

Roberts, Brian. 2016. Potential and actual rates of nitrogen cycling in salt marsh soils, Terrebonne Bay (LA), 2014. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7V985ZX

Purpose:

This dataset was developed as part of a research project investigating the effects of the Deepwater Horizon oil spill on salt marsh biogeochemistry. This component of the CWC research effort focused on examining temporal and spatial patterns in salt marsh soil N cycling rates and whether these rates demonstrated impacts from the Deepwater Horizon oil spill 4 years post-spill.

Data Parameters and Units:

Date--Dates that the field sampling was initiated Site-Site identifier Latitude (decimal degrees)-part of site location Longitude (decimal degrees)--part of site location Oil status--indicates whether the site received oil exposure (Oiled) following the Deepwater Horizon oil spill or not (Unoiled) Location--indicates whether the sampling location was at the "edge" or "interior" of the site Distance from marsh edge (m)--location relative to marsh edge Plot--indicates whether the sample refers to plot "A" or "B"; “Mean” values represent the “mean” of the values for “A” and “B” or if there is only a single value for a location it is recorded in this row. Incubation salinity (psu)--salinity that DEA slurries were incubated at potential denitrification rate:DEA--rate of potential denitrification rate generated from DEA slurries; units of micromoles N per gram dry weight of sediment per day Incubation salinity (psu)--salinity that 15N potential slurries were incubated at potential denitrification:15N potentials--rate of potential denitrification generated from 15N potential slurries; units of micromoles N per gram dry weight of sediment per day potential annamox:15N potentials--rate of potential annamox generated from 15 potential slurries; units of micromoles N per gram dry weight of sediment per day Incubation temp--temperature that whole cores were incubated at; units of degrees celsius Incubation salinity (psu)--salinity that whole cores were incubated at In situ (actual) denitrification (D14)--actual rates of denitrification generated from whole core incubations; units of micromoles N per meter squared per day whole core potential denitrification (D15)--potential rates of denitrification based on the total rate of denitrification of labeled 15N during the whole core incubations; units of micromoles N per meter squared per day whole core potential denitrification (Dtotal)--potential rates of denitrification based on D14 + D15 generated from the whole core incubations; units of micromoles N per meter squared per day nirS--denitrifier abundances based on the gene copies of nirS per gram dry weight of sediment water temp (°C)--temperature of baywater adjacent to site Salinity (psu)--salinity of baywater adjacent to site specific conductance (mS)--specific conducatance of baywater adjacent to site NO3 + NO2 (micromol L-1)--concentration of dissolved nitrate + nitrite in baywater adjacent to site NH4 (mmol L-1)--concentration of dissolved ammonium in baywater adjacent to site PO4 (mmol L-1)--concentration of dissolved orthophosphate in baywater adjacent to site SiO2 (mmol L-1)--concentration of dissolved silicate in baywater adjacent to site Height (cm)--height of overlying water at the plot water temp (°C)--temperature of overlying water at plot Salinity (psu)--salinity of overlying water at plot specific conductance (mS)--specific conducatance of overlying water at plot NO3 + NO2 (micromol L-1)--concentration of dissolved nitrate + nitrite in overlying water at plot NH4 (micromol L-1)--concentration of dissolved ammonium in overlying water at plot PO4 (micromol L-1)--concentration of dissolved orthophosphate in overlying water at plot SiO2 (micromol L-1)--concentration of dissolved silicate in overlying water at plot PW Salinity (psu)--salinity of porewater collected from plot NO3 + NO2 (micromol L-1)--concentration of dissolved nitrate + nitrate in porewater collected from plot NH4 (micromol L-1)--concentration of dissolved ammonium collected from porewater at plot Soil T (°C)--temperature of surface soil at plot pH--pH of the top 5 cm of soil at the plot Bulk Density (g cm-3)-bulk density of the top 5 cm of soil at the plot Water Content (%)-gravimetric water content of the top 5 cm of soil at the plot organic C (%)--organic carbon content of the top 5 cm of soil at the plot total N (%)--total nitrogen content of the top 5 cm of soil at the plot total P (micrograms pre gram dry weight)--total phosphorus content of the top 5 cm of soil at the plot NO3-N (micromol N gdw-1)--extractable nitrate concentration of the top 5 cm of soil at the plot NH4-N (micromol N gdw-1)--extractable ammonium concentration of the top 5 cm of soil at the plot PO4 (micromol P gdw-1)--extractable phosphate concentration of the top 5 cm of soil at the plot Total Target Alkanes--total concentration of target alkanes in the top 5cm of soil at the plot (analyses performed by Overton lab at LSU) Total Target Aromatics--total concentration of target aromatics in the top 5cm of soil at the plot (analyses performed by Overton lab at LSU)

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