Award: OCE-1361514

The research developed a new and novel instrument (the Eddy Covariance Hydrogen ion and Oxygen Exchange System, ECHOES) that measures the exchange of metabolically important constituents between the ocean and organisms living on and within the seafloor. The instrument relies of the vertical transport of dissolved chemicals that is mediated by ocean currents and their interactions with the bottom, or the turbulent vertical transport. The vertical water velocities were measured using Doppler principles and are combined with high frequency measurements of both oxygen and pH. Oxygen is used as a tracer of benthic photosynthesis and respiration, providing the net metabolism of the benthic community. The pH is a net measure of the metabolism by benthic communities as well as the net rates of calcification and dissolution. Comparing these two flux rates (oxygen and pH, or the hydrogen ion (H+) concentration) and complementary measurements of the carbonate equilibria in seawater allows for the determination of the net ecosystem metabolism and the net ecosystem calcification. The system employs oxygen (O2) optodes and a newly developed micro-flow cell H+ ion selective field effect transistor; these sensors displayed sufficient precision and rapid enough response times to measure concentration changes associated with turbulent exchange. Discrete samples of total alkalinity and dissolved inorganic carbon were used to determine the background carbonate chemistry of the water column and relate the O2 and H+ fluxes to benthic processes. The ECHOES system was deployed in a eutrophic estuary (Waquoit Bay, Massachusetts, USA), and revealed that the benthos was a sink for acidity during the day and a source of acidity during the night. The H+ and O2 fluxes were also determined using benthic flux chambers, for comparison with the ECHOES rates. Chamber fluxes co-varied with ECHOES fluxes but were ~4 times lower in magnitude. This difference was likely due to suppressed porewater advection in the chambers and changes in the chemistry of the enclosed chamber overlying water. The individual H+ and O2 fluxes were highly correlated in each data set (ECHOES and chambers), and both methods yielded H+ fluxes that could not be explained by O2 metabolism alone. The ECHOES system provides a new tool for determining the influence of benthic biogeochemical cycling on coastal ocean acidification and carbon cycling. The system will also have direct applications in carbonate-dominated ecosystems where the H+ exchange rates can be used to determine rates of dissolution and calcification. This research has developed a new tool for the evaluation of the health and status of coastal waters, which provide significant resources, shoreline protection, fisheries, and tourism for a large portion of the human population. The development of better tools for evaluating these systems will have an impact on the general environmental sustainability and management of these important coastal ecosystems. Last Modified: 07/09/2015 Submitted by: Matthew Long