Using End‐Member Models to Estimate Seasonal Carbonate Chemistry and Acidification Sensitivity in Temperate Estuaries
Eleanor Simpson, Debby Ianson, Karen E. Kohfeld
Abstract
Abstract We measured the carbonate system (between 2015 and 2018) in an isolated and a well‐connected temperate estuary, both known for shellfish growth. We evaluated end‐member model estimates of inorganic carbon, alkalinity, pH, mineral saturation states (Ω a ), and pH sensitivity (βDIC). We find winter conditions are estimated within observational uncertainty. Spring‐summer primary productivity elevates observed pH and Ω a above theoretical lines, beyond uncertainty. Both estuaries are sensitive in winter and likely to experience rapid pH changes with increased inorganic carbon inputs. Summer pH sensitivity is reduced by productivity and is least sensitive in the midsalinity region. We estimate carbon increased by up to 49 μmol kg −1 , since the pre‐industrial period resulting in significant decreases in pH (0.2) and Ω a (0.5). The largest pH decrease occurred outside the minimum buffer zone, at higher salinities where carbon increase was greatest. The largest pH decrease occurred in winter, but the largest Ω a decrease occured in summer.