Responses of carbonate system and CO2 flux to extended drought and intense flooding in a semiarid subtropical estuary
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2017 The Authors Limnology and Oceanography published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and Oceanography Globally, estuaries are considered important CO2 sources to the atmosphere. However, estuarine water carbonate chemistry and CO2 flux studies have focused on temperate and high latitude regions, leaving a significant data gap in subtropical estuaries. In this study, we examined water column carbonate system and airwater CO2 flux in the Mission-Aransas Estuary, a subtropical semiarid estuary in the northwestern Gulf of Mexico, by collecting samples at five System Wide Monitoring Program stations from 05/2014 to 04/2015. The carbonate system parameters (total alkalinity [TA], dissolved inorganic carbon [DIC], pH, CO2 partial pressure [pCO2], and carbonate saturation state with respect to aragonite [Ar]) and airwater CO2 flux all displayed substantial seasonal and spatial variations. Based on freshwater inflow conditions, a drought period occurred between 05/2014 and 02/2015, while a flooding period occurred from 03/2015 to 04/2015. Average DIC was 2194.7 156.8 mol kg1 and 2132.5 256.8 mol kg1, TA was 2497.6 172.1 molkg1 and 2333.4 283.1 mol kg1, pCO2 was 477 94 atm and 529 251 atm, and CO2 flux was 28.3 18.0 mmol Cm2d1 and 51.6 83.9 mmolCm2d1 in the drought and flooding period, respectively. Integrated annual airwater CO2 flux during our studied period was estimated to be 12.4 3.3 molCm2yr1, indicating that this estuary was a net CO2 source. High wind speed, warm climate, riverine input, and estuarine biogeochemical processes all contributed to the high CO2 efflux despite the modest pCO2 levels year round.
