Using End-Member Models to Estimate Seasonal Carbonate Chemistry and Acidification Sensitivity in Temperate Estuaries

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 (ohm(a)), and pH sensitivity (beta DIC). We find winter conditions are estimated within observational uncertainty. Spring-summer primary productivity elevates observed pH and ohm(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 mu mol kg(-1), since the pre-industrial period resulting in significant decreases in pH (0.2) and ohm(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 ohm(a) decrease occured in summer.

Automated summary

This study measured the carbonate system in two temperate estuaries, one isolated and the other well-connected, between 2015 and 2018. The results showed that winter conditions were estimated within the range of observational uncertainty. However, spring-summer primary productivity elevated pH and mineral saturation states above theoretical lines, beyond uncertainty. The study also found that both estuaries were sensitive in winter and likely to experience rapid pH changes with increased inorganic carbon inputs.