The non-conservative behavior of organic alkalinity in simulated Gulf of Maine Estuary mixing

Estuaries are essential coastal ecosystems facing the threat of coastal acidification due to the anthropogenic burning of fossil fuels and eutrophication. Total alkalinity is a measure of the buffering capacity in an ecosystem and is commonly comprised of both inorganic and organic species. While the contribution of inorganic species to the total alkalinity of an ecosystem is well understood, the contribution of organic alkalinity has been understudied. This investigation looked to outline the behavior of organic alkalinity during estuary mixing and identify organic pKas through Gran + Whole titrations. Freshwater endmember samples were collected from 8 estuaries of the Gulf of Maine, spanning from Maine, U.S.A to New Brunswick, Canada, in October of 2019. The endmember samples were serially diluted with certified reference material to simulate estuary mixing. The results of this investigation highlighted the non-conservative mixing behavior of organic alkalinity with increasing salinity. An extreme variability of organic alkalinity was documented in the low salinity region of estuary mixing and may be due to colloid particle and organic acid interactions. Varying organic alkalinity equivalence point calculations yielded evidence of the presence of organic species with low pKas that must be accounted for in organic and total alkalinity calculations. To better include these low pH pKa species in different estuary environments, the 4.5 equivalence point definition commonly used during titrations for determining alkalinity needs to be re-evaluated. These findings improve the understanding of organic alkalinity behavior during estuary mixing and its contribution to the total alkalinity of the system. Without this inclusion of organic alkalinity in total alkalinity determinations, the use of carbonate system models will experience bias in predicting the resilience of estuaries to future coastal acidification.

Hinckley J. A., 2021. The non-conservative behavior of organic alkalinity in simulated Gulf of Maine Estuary mixing. MSc thesis, University of New Hampshire, 45 p. Thesis.

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