Award: OCE-1459521

PI: Zhaohui Aleck Wang, Kevin Kroeger, and Meagan Gonneea Awardee: Woods Hole Oceanographic Institution, USGS Woods Hole Science Center Vegetated coastal wetlands, such as intertidal salt marshes, may export a significant but unaccounted amount of dissolved inorganic carbon (DIC) and total alkalinity (TA) via tidal exchange to the coastal ocean. They are potentially comparable to global riverine and other coastal carbon fluxes. These are important but under-studied aspects of the global carbon and alkalinity budgets. Particularly, the magnitude, source, composition and effects of these fluxes on the carbon cycle and carbonate chemistry in coastal water has, not been vigorously assessed in the past due to either lack of high-resolution measurements that can capture their true variability, or simply being unnoticed and ignored. The overarching goal of this project is to understand the role of coastal salt marshes in altering carbonate chemistry, alkalinity and carbon budgets of the coastal ocean, and its role in modifying buffering capacity of coastal ocean. The major intellectual merits and outcomes for this project include: 1) A suite of automated systems and in-situ sensors were deployed at a salt marsh site on Cape Cod, MA to obtain much-needed high-resolution data for the first time to capture near-continuous variability of DIC exports from salt marshes. The derived DIC fluxes represent a significant improvement in quantifying carbon exports from salt marshes using both direct in situ measurements and a modeling approach. Such a comparative approach helped to discern true uncertainties in measuring and modeling carbon export fluxes from salt marshes; 2) The study comprehensively examined the profound effects of marsh exports of DIC and TA on carbonate chemistry of coastal waters on the timescales ranging from tidal to annual cycles; 3) This study conducted an in-depth investigation of the composition and sources of marsh exported TA in tidal waters; 4) The project was the first to examine the contribution of organic acid charge groups in DOC to total alkalinity (i.e., organic alkalinity) and its effects on carbonate speciation and CO2 fluxes in marsh-influenced coastal waters. Based on this study, a conceptual model was proposed to describe a new biogeochemical link between the DOC and DIC pools in coastal oceans via the effects of organic alkalinity; 5) This study was also among the first to use isotopes to identify major DIC sources in tidal exchange water; 6) The results and methodology derived from this project have directly contributed to several US coastal carbon synthesis activities, such as the 2nd US State of the Carbon Cycle Report (SOCCR-2). The new results from this project have been made available to a larger audience and public through the Biological and Chemical Oceanography Data Management Office (www.bco-dmo.org) and the ScienceBase USGS data portal (www.sciencebase.gov). The project's findings have been published in two peer-reviewed articles so far, one in revision, and two more manuscripts are under preparation. The project has also helped to train one postdoctoral scholar, two PhD students, three undergraduate summer interns, and six technical assistants. Salt marsh ecosystems are recognized as an important natural carbon sink as well as a site of rapid carbon turn over and export to the coastal ocean. They also serve as nurseries for commercial fisheries with their high productivity contributing to coastal biodiversity. How climate change associated higher temperatures, CO2 levels and sea level rise might impact the net effect of salt marshes on the coastal ocean remains an open question. The findings from this study help to address this question and inform policy makers and resource managers to make protection and preparation plans for the future. They can also inform wetland managers about the carbon science in these valuable coastal systems. Particularly, this project is directly related to wetland 'blue carbon' and the potential to manage carbon in coastal ecosystems. It thus contributes to foster scientifically informed decision making on vital coastal resources, and to make corresponding plans and policies to promote sustainable usage of coastal resources. Last Modified: 08/20/2019 Submitted by: Zhaohui 'aleck' Wang