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

Abstract

Given annual occurrences of hypoxia, harmful algal blooms, and evidence of coastal acidification, the potential impacts of climate change on water quality are of increasing concern in the U.S. Pacific Northwest estuaries such as the Salish Sea. While large‐scale global climate projections are well documented, our understanding of the nearshore estuarine‐scale response is not as well developed. In this study, the future response within the Salish Sea fjord‐like environment was examined using the Salish Sea Model driven by downscaled outputs from the National Center for Atmospheric Research climate model Community Earth System Model. We simulated a single projection of 95‐year change under the representative concentration pathway 8.5 greenhouse gas emissions scenario. Results indicate that higher temperatures, lower pH, and decreased dissolved oxygen levels in the upwelled shelf waters in the future would propagate into the Salish Sea. Results point to potential changes in average Salish Sea temperature (≈+1.51 °C), dissolved oxygen (≈−0.77 mg/L), and pH (acidification −0.18 units) in the Y2095 relative to historical Y2000. The algal biomass in the Salish Sea could increase by ≈23% with a potential species shift from diatoms toward dinoflagellates. The region of annually recurring hypoxia could increase from <1% today to ≈16% in the future. The results suggest that the future response in the Salish Sea is less severe relative to the change predicted near the continental shelf boundary. This resilience of the Salish Sea may be attributed to the existence of strong vertical circulation cells that provide mitigation and serve as a physical buffer, thus keeping waters cooler, more oxygenated, and less acidic.

Temperature and salinity, not acidification, predict near-future larval growth and larval habitat suitability of Olympia oysters in the Salish Sea

“…To analyze near-future changes in the larval phase, we used data from the Pacific Northwest National Laboratory's Salish Sea Model 50,71 , a hydrodynamic and water quality model of the Salish Sea, including a baseline condition in the year 2014, and a future projected oceanographic condition for the year 2095 modeled under an RCP 8.5 high CO 2 emissions scenario. Each model includes roughly 16,000 nodes throughout the larger Salish Sea region with values at 10 sigma layers between surface and bottom at each node.…”

Representing the function and sensitivity of coastal interfaces in Earth system models

“…This is particularly true for the hydrodynamic components of these 3D baroclinic tools that use turbulence closure schemes for parameterizing eddy viscosity and mixing processes. As a result, the models accurately reproduce tidal circulation, stratification, and exchange flows in the estuaries extending from the upstream river inflow boundary to the ocean boundary typically set at the continental shelf 54 . When applied in high resolution over the nearshore intertidal regions, the models employ wetting and drying techniques to represent flooding 97 and are able to represent tidal processes over tidal distributaries, tidal flats and marsh regions.…”

“…For example, mangroves cover 0.1% of the Earth's surface 50 but are among the most productive carbon-sequestering ecosystems on Earth (1023 Mg C ha −1 ) and thus are hot spots for carbon storage and uptake from regional 51 to global scales 52 . More broadly, estuaries could be considered hot spots for productivity, carbon storage 53 , and/or decomposition 54 depending on hydrologic factors such as water residence time, estuarine exchange flow patterns, and position of the estuarine turbidity maximum zone 11 . For example,…”

An Integrated Multi-Model Decision Support Framework for Evaluating Ecosystem-Based Management Options for Coupled Human-Natural Systems

“…Listed models were developed in whole or in part by EPA, except the Pacific Northwest National Laboratory's Salish Sea Model. Model references: VELMA (Abdelnour et al 2011(Abdelnour et al , 2013McKane et al 2014b); SMURF (Snyder et al 2019); CORESET (Melbourne-Thomas et al 2011a, b); HexSim (Schumaker et al 2014); EPA H2O (Russell et al 2015); HWBI (Orlando et al 2017); Salish Sea Model (Khangaonkar et al 2018(Khangaonkar et al , 2019; CMAQ (Luecken et al 2019); BenMAP-CE (Davidson et al 2007;Berman et al 2012) decision makers in balancing ecological, economic and social criteria over timescales relevant to immediate needs and long-term planning goals. A major challenge in modeling coastal ecosystems is the establishment of a coupled human-natural modeling framework capable of addressing transfers of terrestrial nutrients and toxic chemicals to marine waters, and consequent impacts on marine life and ecosystem goods and services.…”

“…• Existing Oregon State University ENVISION Puget Sound applications (Bolte and Vache 2010; http://envision.bioe.orst.edu/StudyAreas/PugetSound/). • Ongoing EPA Puget Sound applications of VELMA (McKane et al 2018a, b, c) • Pacific Northwest National Laboratory applications of the Salish Sea Model (SSM) (Khangaonkar et al 2018(Khangaonkar et al , 2019, coupled with National Oceanic and Atmospheric Administration applications of the Atlantis model (Levin et al 2009), for simulating the circulation and fate of terrestrial pollutant inputs within the Puget Sound marine ecosystem and consequent impacts on water quality, fisheries and threatened food web species. • Existing and new ENVISION plug-ins developed by EPA and others for extending ENVISION's applicability to coastal ecosystems (Tables 1 and 2).…”