Air‐water gas exchange and CO₂ flux in a mangrove‐dominated estuary

Abstract

[1] Mangrove forests are highly productive ecosystems, but the fate of mangrove-derived carbon remains uncertain. Part of that uncertainty stems from the fact that gas transfer velocities in mangrove-surrounded waters are not well determined, leading to uncertainty in air-water CO 2 fluxes. Two SF 6 tracer release experiments were conducted to determine gas transfer velocities (k(600) = 8.3 ± 0.4 and 8.1 ± 0.6 cm h À1 ), along with simultaneous measurements of pCO 2 to determine the air-water CO 2 fluxes from Shark River, Florida (232.11 ± 23.69 and 171.13 ± 20.28 mmol C m À2 d À1), an estuary within the largest contiguous mangrove forest in North America. The gas transfer velocity results are consistent with turbulent kinetic energy dissipation measurements, indicating a higher rate of turbulence and gas exchange than predicted by commonly used wind speed/gas exchange parameterizations. The results have important implications for carbon fluxes in mangrove ecosystems.

Dissolved carbon biogeochemistry and export in mangrove-dominated rivers of the Florida Everglades

“…As shown by Ho et al (2014), pCO 2 observed during SharkTREx 1 and 2 fall in the upper range of those reported in other estuarine (Borges, 2005) and mangrove-dominated systems (Bouillon et al, 2003(Bouillon et al, , 2007aKoné and Borges, 2008;Call et al, 2015). The mean air-water CO 2 fluxes in Shark River for SharkTREx 1 and 2 were 105 ± 9 and 99 ± 6 mmol m −2 d −1 (Ho et al, 2016).…”

“…1). The mean depths of Tarpon Bay, Shark River, and Harney River at mid-tide are 1.4 ± 0.3, 2.8 ± 0.4, and 2.6 ± 0.4 m (Ho et al, 2014), respectively, and the surface areas are 1.48 × 10 6 , 2.54 × 10 6 , and 2.75 × 10 6 m 2 , respectively. The inter-tidal zones bordering the Shark and Harney rivers are dominated by Rhizophora mangle (red mangrove), Avicennia germinans (black mangrove), Laguncularia racemose (white mangrove), and Conocarpus erectus (buttonwood).…”

“…Two field studies were conducted as part of the Shark River Tracer Release Experiment (SharkTREx 1: 20 to 25 November 2010; SharkTREx 2: 10 to 15 November 2011; Ho et al, 2014). The mean residual discharges for Shark River were 6.9 (hourly range: −2 to 19.9) and 4.9 (hourly range: −18.9 to 34.8) m 3 s −1 , during SharkTREx 1 and 2, respectively, and those for Harney River were 6.0 (hourly range: −1.6 to 22.8) and 1.9 (hourly range: −17.3 to 30.6) m 3 s −1 , during SharkTREx 1 and 2, respectively (U.S. Geological Survey, 2016).…”

“…Measurements of underway SF 6 were made with an automated SF 6 analysis system (Ho et al, 2002), which is comprised of gas extraction (membrane contactor), separation (molecular sieve 5A), and detection units (gas chromatograph equipped with an electron capture detector). Both the underway pCO 2 and SF 6 measurements are described in greater detail in Ho et al (2014) 2.5 Inventories of DIC, DOC, and DO The inventories of DIC, DOC, and DO were calculated in the same way that SF 6 inventories were determined in Ho et al (2014). The river was divided into 100 m longitudinal sections, and the measured concentrations, corrected for tidal movement to slack before ebb for each day, were assigned to each section i and then summed over the entire length of the river.…”

“…111 km 2 , and the water area is ca. 17.5 km 2 (Ho et al, 2014). Scaling the forest area by the water area of Shark River (2.5 km 2 ) yields an associated forest area of 15.9 km 2 .…”