Strong Dynamics in Tidal Marsh DOC Export in Response to Natural Cycles and Episodic Events From Continuous Monitoring

Abstract

AbstractThe role of tidal wetlands as hotspots for carbon and nutrient exchange with adjacent waters has been well documented, but large uncertainties remain regarding the physical and biogeochemical controls on these fluxes, which have significant implications for coastal carbon cycling and budgets. This study elucidates the variability in lateral wetland dissolved organic (DOC) fluxes tidally, seasonally, and during extreme weather events for a brackish wetland within a sub‐estuary of the northwestern Chesapeake Bay, USA. Continuous fluxes from the wetland‐draining tidal creek were calculated based on DOC concentrations ([DOC]) estimated using optical and physicochemical properties measured in situ with concurrent water flow data. Mean export was found to be 8.59 (±1.20) kg C (n = 1,128) tidal cycle−1 and annual flux from the wetland to sub‐estuary was 200.66 (±28.09) g C m−2 yr−1. Peaks in DOC flux were associated with Hurricane Joaquin in 2015, where just two tidal cycles accounted for ∼5% of annual export. Analysis of tidal creek water quality measurements reveal seasonal and tidal dependencies. Highest [DOC] and largest low versus high tide differences were observed in summer, corresponding to more fresh plant biomass and its mobilization, consistent with results from Fourier transform ion cyclotron resonance mass spectrometry. Despite summer highs in tidal creek [DOC], monthly DOC fluxes were greatest in early fall due to higher water flows. The annual flux presented here is higher than fluxes previously reported for this system, highlighting the importance of continuous measurements for monitoring carbon export under a wide range of environmental conditions.