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.