Semester of Graduation

Fall 2021

Degree

Master of Science (MS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Blue carbon sequestration and storage in mangroves largely result from belowground biomass allocation in response to flooded anaerobic soil conditions and nutrient availability. Biomass allocation to belowground roots is a major driver of mangrove soil formation and organic matter accumulation leading to blue carbon storage potential. Belowground biomass sampling in mangroves is labor intensive, limiting data availability on biomass stocks, particularly for large roots (>20 mm diameter) and necromass (dead roots). The mangrove nutrient model (NUMAN) uses mostly literature values to parameterize a soil cohort approach to simulate depth distribution of root mass and organic carbon concentration. We evaluated performance of NUMAN at mangrove sites in Rookery Bay, Shark River and Taylor Slough in the Florida Coastal Everglades using a trench method to include large roots and necromass across diverse mangrove geomorphologies. Mean (± SE) total root biomass (to 0.4 m depth) was largest at Taylor Slough (64.6 ± 12.6 Mg ha-1), followed by Shark River (27.4 ± 11.4 Mg ha-1), and Rookery Bay (17.9 ± 1.4 Mg ha-1). Root biomass at each site was greater using the trench method compared to sampling with cores, and this pattern was especially apparent at Shark River where large roots account for ~52% of root biomass. Total root mass, root biomass, and root necromass did not differ with depth to 0.4 m. Lignin content, total carbon, and lignin:N ratios were significantly greater in necromass compared to biomass across all sites. Carbon-rich dead roots are critical to our estimates of belowground carbon storage using the trench method, resulting in significant underestimates in organic carbon stored belowground if ignored in sampling designs. Necromass contributes to refractory organic matter pools in the soil that are retained and contribute significantly to belowground carbon storage. This contribution from dead roots was a critical component to predicting realistic accretion rates at each site. Mangrove biomass allocation in belowground root and soil compartments varies depending on coastal environmental settings and forest ecology. It is important to consider these conditions when determining appropriate sampling protocols for belowground biomass. Including necromass in the NUMAN model allows us to better evaluate accretion rates and carbon sequestration rates across diverse mangrove typologies in South Florida.

Committee Chair

Robert R. Twilley

DOI

10.31390/gradschool_theses.5433

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