Quantifying Exchangeable Dissolved Organic Carbon (EDOC) in Hurricane Harvey (2017) and Hurricane Florence (2018) Rainwater

Abstract

Exchangeable dissolved organic carbon (EDOC) refers to the pool of dissolved organic compounds that are available for diffusion across the air-water interface. This study addresses the rainwater organic carbon deposited on land by two hurricanes, Hurricanes Harvey (2017) and Florence (2018). Samples were analyzed for total dissolved carbon (TDC), non-purgeable organic carbon (NPOC), and dissolved inorganic carbon (DIC). From the TDC, NPOC, and DIC measurements, EDOC was calculated as follows: EDOC = TDC - NPOC - DIC. In Pearland, Texas, during Hurricane Harvey TDC ranged from approximately 0.31-3.6 mg L-1 (VWA 1.8 mg L-1) and NPOC ranged from 0.26-3.6 mg L-1 (VWA 0.99 mg L-1). Calculations for EDOC yielded results of 0-0.9 mg L-1 (VWA 0.88 mg L-1). In League City, Texas, TDC ranged from approximately 0.65-1.9 mg L-1 (VWA 1.1 mg L-1) and NPOC ranged from 0.37-1.6 mg L-1 (VWA 0.82 mg L-1). Calculations for EDOC yielded results of 0.2-0.3 mg L-1 (VWA 0.28 mg L-1). For both Pearland and League City, EDOC comprised approximately 30% of the total dissolved carbon in rainwater. Samples collected during Hurricane Florence in Winterville, North Carolina, had TDC concentrations of approximately 0.2-1.1 mg L-1 (VWA 0.8 mg L-1), NPOC concentrations of 0.5-0.6 mg L-1 (VWA 0.53 mg L-1), and EDOC concentrations of 0.3-0.6 mg L-1 (VWA 0.37 mg L-1). EDOC comprised approximately 53% of the total dissolved carbon in rainwater in Winterville during Hurricane Florence. In general, though rainwater NPOC varied as a function of rainfall, EDOC concentrations remained steady throughout each storm. Lack of EDOC measurements in rainwater DOC may lead to large errors in the air/water exchange of carbon and to an incomplete understanding of the global carbon cycle. Moving forward it is imperative that this carbon pool be quantified and characterized for its composition and reactivity.