The Flax Pond Ecosystem Study: Exchanges of CO"2 Between a Salt Marsh and the Atmosphere

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Profiles of CO 2 concentration, windspeed, and temperature were used in the aerodynamic flux technique to calculate the CO 2 exchange between a Long Island salt marsh and the atmosphere. Uptake of CO 2 by the marsh during hours of sunlight and release during the night occurred during all times of the year. The rates of CO 2 exchange were highest during midsummer, 2.3 g CO 2 °m — 2 °h — 2 averaged over the daylight hours of July, and 1.3 g CO 2 °m — 2 °h — 2 averaged over the dark hours. Winter hourly rates averaged °0.2 g CO 2 °m — 2 °h — 1 for both uptake and release. The net 24—h exchange rates followed Spartina growth and senescence during the summer and fall and photosynthesis of benthic algae during the late winter and spring. There was a net uptake of CO 2 over 24 h by the marsh during all seasons except autumn. The net annual flow of carbon was from the atmosphere to Flax Pond (°300 g C°m — 2 °yr — 2 averaged over the entire marsh ecosystem). This flux was larger than the net exchange of carbon between the marsh and either uplands, sediments, or coastal waters. The net uptake of CO 2 during summer was less than the net productivity of the vascular plants, indicating that some of the CO 2 assimilated by the plants came from heterotrophic respiration within the marsh. Nevertheless, respiration by the plants was by far the largest source of CO 2 from the marsh surface. Nighttime respiration of the ecosystem released a total of °510 g C°m — 2 °yr — 1 to the atmosphere.