Organic Carbon Burial Rates in the Coastal Everglades: An Ecosystem-Scale Assessment of Spatio-Temporal Variability

EPA Grant Number: F13B20216
Title: Organic Carbon Burial Rates in the Coastal Everglades: An Ecosystem-Scale Assessment of Spatio-Temporal Variability
Investigators: Breithaupt, Joshua
Institution: University of South Florida
EPA Project Officer: Lee, Sonja
Project Period: August 25, 2014 through August 25, 2016
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2013) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Marine Sciences

Objective:

The main objective of this research is to understand how environmental influences (including extensive anthropogenic alteration of south Florida hydrology, sea level rise and numerous tropical storms and hurricanes) contributed to changes in the rates of sediment accumulation and carbon burial in the coastal Everglades in the 20th century. The majority of coastal Everglades soils are either organic peat or carbonate mud, both of which can be ephemeral given the right environmental conditions. Distinguishing whether apparent rate changes in the record should be dominantly attributed to mechanisms of delivery or mechanisms of degradation is a key question. Quantifying the fractions of soil organic carbon that originate with seagrass, algae, phytoplankton, marsh, or mangrove material is needed to assess whether a change in the type of carbon buried throughout the estuary has changed over the period of interest.

Approach:

This research utilizes soil cores collected from a variety of mangrove and marsh environments along the Shark, Harney and Broad Rivers, which drain the southwestern coastal Everglades. Soil cores are being radiometrically dated using Pb-210 and Cs-137 to determine rates of sediment accretion, as well as the mass accumulation of various constituents, including organic and carbonate carbon and nutrients (nitrogen and phosphorous). These accretion and accumulation records will then be related to historical records of freshwater flow, sea level rise and storm occurrences. Differentiating the respective contributions of (a) production or delivery and (b) preservation or destruction will be done by comparing, in each core, fluxes of potentially ephemeral sediments with fluxes of stable and refractory sediments. Using a multi–end-member mixing model, nutrient ratios (C:N:P) and stable isotopes (δ13C and δ15N) will be used to identify different vegetation contributions (seagrass, algae, phytoplankton, marsh and mangrove) to soil organic matter throughout the estuary. Collaborative work with members of the South Florida Water Sustainability and Climate and Florida Coastal Everglades Long-term Ecological Research programs will be vital to synthesize these data into the larger scope of hydro-economic considerations.

Expected Results:

Coastal carbon burial rates are controlled by many factors, including those related to local hydrology, such as salinity, water depth and inundation time. The historical reduction in freshwater supply to the coastal Everglades—increasing salinity and reducing water depth—is likely to have had the greatest impacts in the upper estuary, leading to lower overall carbon burial rates. Conversely, sea level rise and storm influences (such as mangrove mortality and surge-scouring and deposition of sediments) are likely to have had the greatest impact in the lower estuary, leading to increased carbon burial rates. The fraction of mangrove carbon in the soil is expected to be greatest mid-estuary, with increasing contributions from seagrass in the lower estuary and marsh grasses in the upper estuary.

Potential to Further Environmental/Human Health Protection

By providing a broad spatial assessment of how the Everglades landscape has responded to environmental influences over the past century, this research will assess regions within the study area that may be most vulnerable to future change. This information will be important to both the National Park management charged with protecting an essential national resource and the ecologists and fisheries managers working in these changing habitats. Additionally, by constraining the influence of freshwater flow on historical carbon burial throughout the region, this research will equip ecosystem managers and policymakers with data to better evaluate how to sustainably allocate freshwater in view of future ecological, societal and agricultural needs.

Supplemental Keywords:

carbon storage, climate change, sea level rise

Progress and Final Reports:

  • 2015
  • Final