Predicted Effects of Climate Change on Northern Gulf of Mexico Hypoxia

Lehrter, John C.; Ko, Dong S.; Lowe, Lisa L.; Penta, Bradley

doi:10.1007/978-3-319-54571-4_8

Cited by 22 publications

(33 citation statements)

References 44 publications

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“…These conservative assumptions limit the influence of biological processes. Assuming a 10% increase in future nutrient load, did not find a significant biological response (in terms of chlorophyll concentration and phytoplankton growth rates) in the study of Lehrter et al (), which also indicates a limited biological contribution to future oxygen changes in their simulation. An additional increase in nutrient load would enhance eutrophication and further deplete bottom oxygen, perhaps making the biological contribution to oxygen loss more important.…”

Section: Discussionmentioning

confidence: 77%

“…The simulations differ only in their initial and open boundary conditions, river discharge, and atmospheric temperature and pCO 2 but use identical wind forcing and river nutrient load (Table ). The present simulation was run for the period 2005–2010 using physical initial and boundary conditions (i.e., water temperature, salinity, and currents) from the Intra‐Americas Sea Nowcast‐Forecast System (IASNFS; Ko et al, ; Ko & Wang, ; Lehrter et al, ). In the future simulation, physical boundary conditions are from a projection of the IASNFS model, which was run with 10% larger freshwater discharge and 3°C warmer air temperature (Lehrter et al, ).…”

Section: Methodsmentioning

confidence: 99%

“…The present simulation was run for the period 2005–2010 using physical initial and boundary conditions (i.e., water temperature, salinity, and currents) from the Intra‐Americas Sea Nowcast‐Forecast System (IASNFS; Ko et al, ; Ko & Wang, ; Lehrter et al, ). In the future simulation, physical boundary conditions are from a projection of the IASNFS model, which was run with 10% larger freshwater discharge and 3°C warmer air temperature (Lehrter et al, ). In our future simulation, river input and atmospheric forcing are based on the 2005–2010 daily record used in the present simulation.…”

Section: Methodsmentioning

confidence: 99%

“…Physical forcing promotes enhanced stratification amplifying the effect of climate change on eutrophication-induced oxygen loss and acidification. The wind distribution may vary with climate change (e.g., Bakun et al, 2010Bakun et al, , 2015, but there is high uncertainty (Herrera-Estrada & Sheffield, 2017;Wuebbles et al, 2014) and no clear picture for the northern Gulf as of yet (Kulkarni & Huang, 2014;Lehrter et al, 2017). Mixing events may also vary, with fewer but stronger hurricanes projected for the Gulf of Mexico (Bruyè re et al, 2017).…”

Section: Climate and Interannual Variabilitymentioning

confidence: 99%

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Climate Change Projected to Exacerbate Impacts of Coastal Eutrophication in the Northern Gulf of Mexico

et al. 2018

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The continental shelf in the northern Gulf of Mexico experiences expansive seasonal hypoxic conditions and eutrophication‐driven acidification in bottom waters. Rising surface ocean temperatures, freshwater and nutrient inputs, and atmospheric CO2 will further exacerbate these conditions. Using a high‐resolution, regional circulation‐biogeochemical model, we simulated the spatiotemporal dynamics of oxygen and inorganic carbon in the northern Gulf of Mexico under present and a projected future (2100) climate state. Results indicate a modest expansion of the hypoxic zone, but more severe hypoxia and greater exposure to prolonged hypoxic conditions. The main drivers underlying these changes are a reduction in oxygen solubility (accounting for 60–74% of the change) and increased stratification (accounting for less than 40%). pH is projected to decrease across the shelf with lowest values in hypoxic waters where aragonite saturation will approach the saturation limit. In the model simulations, acidification is primarily driven by atmospheric and offshore CO2 levels, while the enhancement in stratification only accounts for 7% or less of the total change in pH. Decreased buffering capacity and increased stratification in the future will enhance respiration‐induced acidification (i.e., a decrease in bottom water pH by respired CO2), which will amplify the climate‐induced acidification. According to the model, the magnitude of future changes varies significantly from year to year. The largest effects are simulated in years with large freshwater discharge and upwelling‐favorable winds.

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Section: Discussionmentioning

confidence: 77%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Climate and Interannual Variabilitymentioning

confidence: 99%

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Climate Change Projected to Exacerbate Impacts of Coastal Eutrophication in the Northern Gulf of Mexico

et al. 2018

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“…These models have also been used to project future changes in O 2 conditions, for example, under climate change or due to reductions in the riverine nutrient loads. An increase in spatial extent and severity of hypoxia is predicted to occur in the future due to reduced O 2 solubility and increased stratification in a warmer climate (Laurent et al, ; Lehrter et al, ). Modeling studies on the effect of riverine N load reductions on hypoxia suggest that a reduction on the order of 60% would be sufficient to achieve the 5,000 km 2 management target (Fennel & Laurent, ) in agreement with results from statistical models (Scavia et al, ).…”

Section: Introductionmentioning

confidence: 99%

Quantifying the Relative Importance of Riverine and Open‐Ocean Nitrogen Sources for Hypoxia Formation in the Northern Gulf of Mexico

2019

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The Mississippi and Atchafalaya River System discharges large amounts of freshwater and nutrients into the northern Gulf of Mexico (NGoM). These lead to increased stratification and elevate primary production in the outflow region. Consequently, hypoxia (oxygen <62.5 mmol/m3), extending over an area of roughly 15,000 km2, forms every summer in bottom waters. High‐resolution models have significantly improved our understanding of the processes controlling hypoxia formation in the NGoM and have strongly implicated riverine nutrients as the dominant nutrient source. However, the relative importance of different nutrient sources (i.e., the Mississippi and Atchafalaya Rivers and offshore) has not been assessed before now. Here, we combine a high‐resolution model with an element tracing method to directly quantify the relative contributions of nitrogen from the two rivers and the open ocean to primary production and sediment oxygen consumption, which is the main oxygen sink contributing to hypoxia in the NGoM. Our results indicate that, averaged over 2001–2011, Mississippi and Atchafalaya nitrogen support 51 ± 9% and 33 ± 9% of summer sediment oxygen consumption, respectively, while open‐ocean nitrogen supports 16 ± 2%. The higher relative impact of Mississippi inputs results from longer transit times compared to those of Atchafalaya inputs. We also analyze the effect of riverine nitrogen load reductions and a larger diversion of discharge to the Atchafalaya River. These scenario simulations show that nutrient load reductions are most effective in mitigating hypoxia.

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Controls on Oxygen Variability and Depletion in the Patuxent River Estuary

Dreiss,

Azarnivand,

Hildebrand

et al. 2024

Estuaries and Coasts

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Oxygen depletion in coastal waters is increasing globally due primarily to eutrophication and warming. Hypoxia responses to nutrient loading and climate change have been extensively studied in large systems like the Chesapeake Bay and the Baltic Sea, while fewer studies have investigated smaller, shallower hypoxic zones. Thus, an improved understanding of the interactions of eutrophication and warming on hypoxia expansion (or reduction) in the wide variety of different estuarine environments is needed. We examined interannual controls on oxygen depletion in the Patuxent River estuary, a eutrophic sub-estuary of Chesapeake Bay where seasonal hypoxia develops annually. We conducted a spatial and temporal analysis of dissolved oxygen (DO) trends, timing, and several metrics of depletion over a long-term record (1985–2021). We found an internally generated hypoxic zone that initiates in the middle estuary, spreading upstream and downstream as the summer progresses, and that hypoxic volume days (HVD) have been increasing (0.11 per year, p = 0.03) over the record despite reduced watershed nitrogen loads and stable phosphorus loads. River flow and temperature have been increasing and are major drivers of increased HVD, with river flow explaining 40% of the interannual variation in HVD (temperature has increased 0.03 and 0.06 °C per year in summer and fall, respectively). Apparent oxygen utilization (AOU) is increasing in bottom waters in the fall, consistent with increasing trends of both water temperature and stratification strength. HVD was negatively related (r2 = 0.34, slope = −0.59*HVD) to the biomass of benthic invertebrates in the middle region of the estuary, suggesting that benthic forage for higher trophic levels will be limited by sustained hypoxia. These results indicate that current and future climate variability plays an important role in regulating oxygen depletion in the Patuxent River estuary, which reinforces the need to factor climate change into strategies for the restoration and management of estuaries.

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Predicted Effects of Climate Change on Northern Gulf of Mexico Hypoxia

Cited by 22 publications

References 44 publications

Climate Change Projected to Exacerbate Impacts of Coastal Eutrophication in the Northern Gulf of Mexico

Climate Change Projected to Exacerbate Impacts of Coastal Eutrophication in the Northern Gulf of Mexico

Quantifying the Relative Importance of Riverine and Open‐Ocean Nitrogen Sources for Hypoxia Formation in the Northern Gulf of Mexico

Controls on Oxygen Variability and Depletion in the Patuxent River Estuary

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