2018 ESA Annual Meeting (August 5 -- 10)

PS 7-83 - Impacts of prop-scar damage on carbon and nitrogen pools in Thalassia testudinum seagrass meadows

Monday, August 6, 2018
ESA Exhibit Hall, New Orleans Ernest N. Morial Convention Center
Rachel N. Arney, Forestry, Mississippi State University, Mississippi State, MS, Heather D. Alexander, Department of Forestry, Mississippi State University, Mississippi State, MS, Alison Shepherd, Division of Fish and Wildlife, NJ Department of Environmental Protection, NJ and Abdullah F. Rahman, School of Earth, Environmental, and Marine Sciences, The University of Texas at Rio Grande Valley, Brownsville, TX
Background/Question/Methods

Seagrass meadows are carbon (C) sinks and nitrogen (N)-limited systems that experience nitrogen loading and rapid degradation due to anthropogenic and climate stressors. Understanding how C and N storage in seagrass changes over time post-disturbance can contribute to restoration success in Blue Carbon ecosystems (seagrass meadows, salt marshes, and mangrove forests). Our study seeks to quantify C and N pools stored in seagrass soils of the hypersaline Lower Laguna Madre (LLM), TX and to determine how recreational boat scarring impacts these pools. To determine C and N pool changes due to boat scarring, we quantified pools at the soil surface (top 20 cm) and to a 1-m depth across a chronosequence of different aged boat scars (1-4 yr., 4-6 yr., 6-9 yr., 10+ yr.) in Thalassia testudinum-dominated beds and compared those pools to adjacent unscarred beds.

Results/Conclusions

Unscarred seagrass meadows of the LLM stored on average ~ 93 Mg C/ha and 6 Mg N/ha in the top 1 m of soils, with ~25% of these pools stored in the top 20 cm. Propeller scarring initially redistributed the organic-rich pools within the top 20 cm of the soil horizon, exposing higher bulk density mineral soils with lower %C and %N contents. Thus, C and N pools in the top 1 m of soils beneath propeller scars < 10-year-old were similar to those in unscarred areas, but the mechanisms contributing to these pools was different. Most importantly, scars > 10-year-old had %C, %N, and bulk density characteristics that approached pre-disturbed (or unscarred) levels, producing C and N pools similar to unscarred areas. Thus, scarring leads to a change in soil properties that contribute to C and N pools, which take at least 10 years to return to undisturbed conditions. Ultimately, this data can elucidate the mechanisms driving C and N pools in vulnerable seagrass ecosystems and help us understand the rate at which seagrass meadows recover post-disturbance.