Configuration and validation of an oceanic physical and biogeochemical model to investigate coastal eutrophication: case study in the Southern California Bight

Kessouri, Fayçal; McLaughlin, Karen; Sutula, Martha; Bianchi, Daniele; Ho, Minna; McWilliams, James C.; Renault, Lionel; Molemaker, M. Jeroen; Deutsch, Curtis; Leinweber, A.

doi:10.1002/essoar.10504012.1

Cited by 6 publications

(12 citation statements)

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“…Thus, ANTH largely simulates the effects of nutrient and carbon enrichment of the SCB caused by human activities. The model is validated against in situ physical and biogeochemical observations from the Bight monitoring program, CalCOFI, and other data sources, including satellite observations (26). This validation shows an excellent agreement of the ANTH simulation with observations of nutrients, O2, carbon, phytoplankton, and their dynamics.…”

Section: Significancementioning

confidence: 83%

“…5. The model is validated against a comprehensive database of physical and biogeochemical observations (65) from the SCB and provides a realistic representation of physical and biogeochemical cycles in the SCB (26). The model code is available at 10.5281/zenodo.3988618 (66), the in situ data used for model validation at 10.5281/zenodo.3988574 (67), and local land-based and atmospheric nutrient input data at 10.5281/zenodo.4448224 (64).…”

Section: Methodsmentioning

confidence: 99%

“…1 B and E). While the largest concentrations driven by natural upwelling are observed north of Ventura and along the Santa Barbara coast in the CTRL simulation (26), terrestrial nutrients inputs drive persistent, or "chronic," high phytoplankton biomass (24) along the Los Angeles and Orange County coastlines (Fig. 1 B and C).…”

Section: Observed and Simulated Coastal Eutrophicationmentioning

confidence: 97%

“…Submarine outfalls were designed to release wastewater as nutrient-enriched plumes below the pycnocline (30). Because they are fresher than ambient seawater, these plumes rise to neutrally buoyant depths of about 30 to 45 m (26,31) and then are swept along isobaths by the alongshore-flowing coastal current (Fig. 2A).…”

Section: Nutrient Sources Driving Coastal Eutrophicationmentioning

confidence: 99%

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Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system

Kessouri

McWilliams

Bianchi

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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Global change is leading to warming, acidification, and oxygen loss in the ocean. In the Southern California Bight, an eastern boundary upwelling system, these stressors are exacerbated by the localized discharge of anthropogenically enhanced nutrients from a coastal population of 23 million people. Here, we use simulations with a high-resolution, physical–biogeochemical model to quantify the link between terrestrial and atmospheric nutrients, organic matter, and carbon inputs and biogeochemical change in the coastal waters of the Southern California Bight. The model is forced by large-scale climatic drivers and a reconstruction of local inputs via rivers, wastewater outfalls, and atmospheric deposition; it captures the fine scales of ocean circulation along the shelf; and it is validated against a large collection of physical and biogeochemical observations. Local land-based and atmospheric inputs, enhanced by anthropogenic sources, drive a 79% increase in phytoplankton biomass, a 23% increase in primary production, and a nearly 44% increase in subsurface respiration rates along the coast in summer, reshaping the biogeochemistry of the Southern California Bight. Seasonal reductions in subsurface oxygen, pH, and aragonite saturation state, by up to 50 mmol m−3, 0.09, and 0.47, respectively, rival or exceed the global open-ocean oxygen loss and acidification since the preindustrial period. The biological effects of these changes on local fisheries, proliferation of harmful algal blooms, water clarity, and submerged aquatic vegetation have yet to be fully explored.

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Section: Significancementioning

confidence: 83%

Section: Methodsmentioning

confidence: 99%

Section: Observed and Simulated Coastal Eutrophicationmentioning

confidence: 97%

Section: Nutrient Sources Driving Coastal Eutrophicationmentioning

confidence: 99%

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Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system

Kessouri

McWilliams

Bianchi

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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“…The value of such observations extends beyond the testing of the hypothesis that wastewater plumes affect water column biogeochemical parameters (pH, DO, chlorophyll a) and rates of nutrient and carbon cycling. To support California's climate action strategies, a spatially explicit, 3-dimensional numerical ocean model of the SCB was developed and is being applied to examine the relative effects of climate change, natural climate cycles, and local terrestrial and atmospheric carbon and nutrient inputs (Kessouri et al, 2020;Deutsch et al, 2021). However, in order to support conversations on the utility of nutrient management as a climate change mitigation strategy, such models must be validated carefully against observations of biogeochemical state and rate data.…”

Section: Introductionmentioning

confidence: 99%

Influence of anthropogenic nutrient inputs on rates of coastal ocean nitrogen and carbon cycling in the Southern California Bight, United States

McLaughlin

Howard

Robertson

et al. 2021

Elementa: Science of the Anthropocene

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Coastal nitrogen enrichment is a global environmental problem that can influence acidification, deoxygenation, and subsequent habitat loss in ways that can be synergistic with global climate change impacts. In the Southern California Bight, an eastern boundary upwelling system, modeling of wastewater discharged through ocean outfalls has shown that it effectively doubles nitrogen loading to urban coastal waters. However, effects of wastewater outfalls on rates of primary production and respiration, key processes through which coastal acidification and deoxygenation are manifested, have not been directly linked to observed trends in ambient chlorophyll a, oxygen, or pH. Here, we follow a “reference-area” approach and compare nutrient concentrations and rates of nitrification, primary production, and respiration observed in areas within treated wastewater effluent plumes to areas spatially distant from ocean outfalls where we expected minimal plume influence. We document that wastewater nutrient inputs had an immediate, local effect on nutrient stoichiometry, elevating ammonium and nitrite concentrations by 4 µM and 0.2 µM (on average), respectively, and increasing dissolved nitrogen-to-phosphorus ratios 7-fold within the plume. Chlorophyll a increased slightly by 1 µg L–1 in the upper 60 m of the water column (on average), and δ13C and δ15 N of suspended particulate matter, an integrated measure of primary production, increased by 1.3% and 1%, respectively (on average). Nitrification rates within the plume increased by 17 nmol L–1 day–1 (on average). We did not observe a significant near-plume effect on δ18O and δ15 N of dissolved nitrate + nitrite, an indicator of nitrogen assimilation into biomass, on rates of primary production and respiration or on dissolved oxygen concentration, suggesting that any potential impact from wastewater on these key features is moderated by other factors, notably water mass mixing. These results indicate that a “reference-area” approach may be insufficient to document regional-scale impacts of nutrients.

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The Shelf‐To‐Basin Transport of Iron From the Northern U.S. West Coast to the Pacific Ocean

Pham,

Damien,

McCoy

et al. 2024

Global Biogeochemical Cycles

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Release of iron (Fe) from continental shelves is a major source of this limiting nutrient for phytoplankton in the open ocean, including productive Eastern Boundary Upwelling Systems. The mechanisms governing the transport and fate of Fe along continental margins remain poorly understood, reflecting interaction of physical and biogeochemical processes that are crudely represented by global ocean biogeochemical models. Here, we use a submesoscale‐permitting physical‐biogeochemical model to investigate processes governing the delivery of shelf‐derived Fe to the open ocean along the northern U.S. West Coast. We find that a significant fraction (∼20%) of the Fe released by sediments on the shelf is transported offshore, fertilizing the broader Northeast Pacific Ocean. This transport is governed by two main pathways that reflect interaction between the wind‐driven ocean circulation and Fe release by low‐oxygen sediments: the first in the surface boundary layer during upwelling events; the second in the bottom boundary layer, associated with pervasive interactions of the poleward California Undercurrent with bottom topography. In the water column interior, transient and standing eddies strengthen offshore transport, counteracting the onshore pull of the mean upwelling circulation. Several hot‐spots of intense Fe delivery to the open ocean are maintained by standing meanders in the mean current and enhanced by transient eddies and seasonal oxygen depletion. Our results highlight the importance of fine‐scale dynamics for the transport of Fe and shelf‐derived elements from continental margins to the open ocean, and the need to improve representation of these processes in biogeochemical models used for climate studies.

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Configuration and validation of an oceanic physical and biogeochemical model to investigate coastal eutrophication: case study in the Southern California Bight

Cited by 6 publications

References 0 publications

Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system

Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system

Influence of anthropogenic nutrient inputs on rates of coastal ocean nitrogen and carbon cycling in the Southern California Bight, United States

The Shelf‐To‐Basin Transport of Iron From the Northern U.S. West Coast to the Pacific Ocean

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