The relationship between carbonate chemistry, estuarine metabolism, and spring-neap tidal cycles in a northern temperate estuary

Abstract Many estuaries are highly productive areas for shellfish aquaculture while also subject to low alkalinity and low aragonite saturation state (𝛀Ar) from both offshore and freshwater. Due to the influence and interaction of these source water conditions and the biological processes that occur within the estuary, 𝛀Ar can be highly variable. To better understand how 𝛀Ar changes from daily to seasonal time scales within estuaries, we described high frequency changes in aragonite saturation state in the largest oyster growing region in northern New England, the Damariscotta River estuary, Maine, in 2018 using hourly buoy data and discrete samples. 𝛀Ar ranged from 1 to 2.5 between late May and early October with daily ranges frequently exceeding 0.5. 𝛀Ar was predominantly controlled by temperature and salinity at the seasonal scale but driven by ecosystem metabolism on daily - bi-weekly time scales. The prominent feature of this system was the importance of spring-neap tidal cycles, with spring tides increasing turbidity, nitrate, and respiration, and decreasing primary production, dissolved oxygen, and 𝛀Ar. Here, we disentangle the strong interconnection between estuary morphology, tides, ecosystem metabolism, and 𝛀Ar in an important oyster growing area with implications for the timing of seeding, site selection, water quality management, and analyzing future acidification scenarios in estuaries that share similar oceanographic conditions.