Sensitivity of the regional ocean acidification and carbonate system in Puget Sound to ocean and freshwater inputs

Abstract

While ocean acidification was first investigated as a global phenomenon, coastal acidification has received significant attention in recent years, as its impacts have been felt by different socio-economic sectors (e.g., high mortality of shellfish larvae in aquaculture farms). As a region that connects land and ocean, the Salish Sea (consisting of Puget Sound and the Straits of Juan de Fuca and Georgia) receives inputs from many different sources (rivers, wastewater treatment plants, industrial waste treatment facilities, etc.), making these coastal waters vulnerable to acidification. Moreover, the lowering of pH in the Northeast Pacific Ocean also affects the Salish Sea, as more acidic waters get transported into the bottom waters of the straits and estuaries. Here, we use a numerical ocean model of the Salish Sea to improve our understanding of the carbonate system in Puget Sound; in particular, we studied the sensitivity of carbonate variables (e.g., dissolved inorganic carbon, total alkalinity, pH, saturation state of aragonite) to ocean and freshwater inputs. The model is an updated version of our FVCOM-ICM framework, with new carbonate-system and sediment modules. Sensitivity experiments altering concentrations at the open boundaries and freshwater sources indicate that not only ocean conditions entering the Strait of Juan de Fuca, but also the dilution of carbonate variables by freshwater sources, are key drivers of the carbonate system in Puget Sound.

Salish Sea Response to Global Climate Change, Sea Level Rise, and Future Nutrient Loads

“…The pH levels in the Salish Sea also are affected by upwelling induced acidification. In addition, recent sensitivity experiments with the Salish Sea Model have shown that the dilution of carbonate system constituents by freshwater sources is another key driver of the carbonate system response in Puget Sound (Bianucci et al, ). This carbonate dilution also affects spatial and temporal distribution of pH levels.…”

“…For this effort, we included 19 state variables: two species of phytoplankton (diatoms P1 and dinoflagellates P2), labile and refractory dissolved organic carbon and particulate organic carbon, NH 4 , nitrate (NO 2 + NO 3 ), labile and refractory dissolved organic nitrogen and particulate organic nitrogen, PO 4 , DO, DIC, and total alkalinity. The biogeochemical model includes new upgrades, a sediment diagenesis module that allows directly coupled interaction between the water column and sediments through the processes of organic sediment settling and burial and remineralization and carbonate chemistry with DIC, total alkalinity, p CO2, and pH (Bianucci et al, ; Pelletier et al, ). With the aid of improvements described above, observed biogeochemical cycles (i.e., salinity, temperature, DO, nitrate, algal biomass, and pH) in the Salish Sea, including near‐bed hypoxia in locations such as the Lynch Cove region of Hood Canal, have been reproduced.…”

“…The biogeochemical component of the Salish Sea Model has been described in detail previously (Khangaonkar et al, , ). The model has been tested over multiple years and subjected to sensitivity level testing with variation in forcing/loading either due to anthropogenic causes or due to stressors associated with climate change projections (Bianucci et al, ; Roberts et al, ).…”

Analysis of Hypoxia and Sensitivity to Nutrient Pollution in Salish Sea

“…In an earlier effort, Khangaonkar et al () showed that this pathway could be significant, so it is now explicitly included in the model. The model now also includes a sediment diagenesis module (Bianucci et al, ; Pelletier et al, ), which allows direct coupled interaction between the water column and sediments through the processes of organic sediment settling, burial, and remineralization. The sediment module generates nutrient fluxes including sediment oxygen demand.…”

“…The sediment module generates nutrient fluxes including sediment oxygen demand. The model also includes carbonate chemistry with dissolved inorganic carbon, total alkalinity, pCO 2 , and pH (Bianucci et al, ; Pelletier et al, ).…”