Alkalinity cycling and carbonate chemistry decoupling in seagrass mystify processes of acidification mitigation

Abstract The adverse conditions of acidification on sensitive marine organisms have led to the investigation bioremediation methods as a way abate local acidification. This phytoremediation, by macrophytes, is expected reduce severity in nearshore habitats short timescales. Characterizing efficacy phytoremediation can be challenging residence time, tidal mixing, freshwater input, and limited capacity fully constrain carbonate system lead erroneous conclusions. Here, we present situ observations chemistry relationships seagrass comparing dense (DG), patchy (PG), no grass (NG) Zostera marina pools high intertidal experiencing intermittent flooding. High-frequency measurements pH, alkalinity (TA), total-CO 2 elucidate extreme diel cyclicity all parameters. DG pool displayed frequent decoupling between pH aragonite saturation state (Ω arg ) suggesting pH-based inferences remediation misinterpreted Ω independent stressors for some bivalves. Estimates show had an integrated ΔTA 550 μmol kg −1 over 12 h period, which ~ 60% > PG NG pools. We conclude with mixed photosynthesizers (i.e., pool) result less .