News

Slightly smaller-than-average 2020 ‘dead zone’ predicted for Chesapeake Bay

"Researchers from the University of Michigan, the Chesapeake Bay Program and the University of Maryland Center for Environmental Science are forecasting a slightly smaller-than-average Chesapeake Bay “dead zone” this year, due to reduced rainfall and less nutrient-rich runoff flowing into the bay from the watershed this spring. [...]"

Source: University of Michigan

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Quantifying the contributions of riverine vs. oceanic nitrogen to hypoxia in the East China Sea

Abstract.

"In the East China Sea, hypoxia (oxygen ≤ 62.5 mmol m−3) is frequently observed off the Changjiang (or Yangtze River) estuary covering up to about 15 000 km2. The Changjiang is a major contributor to hypoxia formation because it discharges large amounts of freshwater and nutrients into the region. However, modeling and observational studies have suggested that intrusions of nutrient-rich oceanic water from the Kuroshio Current also contribute to hypoxia formation.  [...]"

Source: Biogeosciences
Authors: Fabian Große et al.
DOI: 10.5194/bg-17-2701-2020

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Short-term effects of hypoxia are more important than effects of ocean acidification on grazing interactions with juvenile giant kelp

Abstract.

"Species interactions are crucial for the persistence of ecosystems. Within vegetated habitats, early life stages of plants and algae must survive factors such as grazing to recover from disturbances. However, grazing impacts on early stages, especially under the context of a rapidly changing climate, are largely unknown. [...]"

Source: Scientific Reports
Authors: Crystal A. Ng & Fiorenza Micheli 
DOI: 10.1038/s41598-020-62294-3

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Effects of spatial variability on the exposure of fish to hypoxia: a modeling analysis for the Gulf of Mexico

Abstract.

"The hypoxic zone in the northern Gulf of Mexico varies spatially (area, location) and temporally (onset, duration) on multiple scales. Exposure to hypoxic dissolved oxygen (DO) concentrations (< 2 mg L−1) is often lethal and exposure to 2 to 4 mg L−1 often causes the sublethal effects of decreased growth and fecundity on individuals of many fish species. We simulated the movement of individual fish within a high-resolution 3-D coupled hydrodynamic-water quality model (FVCOM-WASP) configured for the northern Gulf of Mexico to examine how spatial variability in DO concentrations would affect fish exposure to hypoxic and sublethal DO concentrations. [...]"

Source: Biogeosciences
Authors: Elizabeth D. LaBone et al.
DOI: 10.5194/bg-2020-51

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Short- and long-term impacts of variable hypoxia exposures on kelp forest sea urchins

Abstract.

"Climate change is altering the intensity and variability of environmental stress that organisms and ecosystems experience, but effects of changing stress regimes are not well understood. We examined impacts of constant and variable sublethal hypoxia exposures on multiple biological processes in the sea urchin Strongylocentrotus purpuratus, a key grazer in California Current kelp forests, which experience high variability in physical conditions. [...]"

Source: Scientific Reports
Authors: Natalie H. N. Low & Fiorenza Micheli 
DOI: 10.1038/s41598-020-59483-5

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Fish Diet Shifts Associated with the Northern Gulf of Mexico Hypoxic Zone

Abstract.

"The occurrence of low dissolved oxygen (hypoxia) in coastal waters may alter trophic interactions within the water column. This study identified a threshold at which hypoxia in the northern Gulf of Mexico (NGOMEX) alters composition of fish catch and diet composition (stomach contents) of fishes using fish trawl data from summers 2006–2008. Hypoxia in the NGOMEX impacted fish catch per unit effort (CPUE) and diet below dissolved oxygen thresholds of 1.15 mg L−1 (for fish CPUE) and 1.71 mg L−1 (for diet). CPUE of many fish species was lower at hypoxic sites (≤ 1.15 mg L −1) as compared to normoxic regions (> 1.15 mg L −1), including the key recreational or commercial fish species Atlantic croaker Micropogonias undulatus and red snapper Lutjanus campechanus. [...]"

Source: Estuaries and Coasts
Authors: Cassandra N. Glaspie et al.
DOI: 10.1007/s12237-019-00626-x

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Upwelling Bays: How Coastal Upwelling Controls Circulation, Habitat, and Productivity in Bays

Abstract.

"Bays in coastal upwelling regions are physically driven and biochemically fueled by their interaction with open coastal waters. Wind-driven flow over the shelf imposes a circulation in the bay, which is also influenced by local wind stress and thermal bay–ocean density differences. Three types of bays are recognized based on the degree of exposure to coastal currents and winds (wide-open bays, square bays, and elongated bays), and the characteristic circulation and stratification patterns of each type are described. Retention of upwelled waters in bays allows for dense phytoplankton blooms that support productive bay ecosystems.  [...]"

Source:  Annual Review of Marine Science
Authors: John L. Largier
DOI: 10.1146/annurev-marine-010419-011020

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Dead-zone report card reflects improving water quality in Chesapeake Bay

"An annual model-based report on "dead-zone" conditions in the Chesapeake Bay during 2019 indicates the total volume of low-oxygen, "hypoxic" water was on the high end of the normal range for 1985 to 2018, a finding that scientists consider relatively good news.

 

Dr. Marjy Friedrichs, a Virginia Institute of Marine Science professor and report card co-author, says "Even with environmental conditions that favor severe hypoxia, including record-high river input and light winds, our analysis shows that the total amount of hypoxia this year was within the normal range seen over the past 35 years."

Source: Phys.org

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Wind-driven stratification patterns and dissolved oxygen depletion in the area off the Changjiang (Yangtze) Estuary

Abstract.

"The area off the Changjiang Estuary is under strong impact of fresh water and anthropogenic nutrient load from the Changjiang River. The seasonal hypoxia in the area has variable location and range, but the decadal trend reveals expansion and intensification of the dissolved oxygen (DO) depletion. [...]"

Source: Biogeosciences
Authors: Taavi Liblik et al.
DOI: 10.5194/bg-2019-421

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Coral Mortality Event in the Flower Garden Banks of the Gulf of Mexico in July 2016: Local Hypoxia due to Cross-Shelf Transport of Coastal Flood Water

Abstract.

"Remotely sensed and in situ data, in tandem with numerical modeling, are used to explore the causes of an episode of localized but severe mortality of corals, sponges, and other invertebrates at the Flower Garden Banks (FGB) National Marine Sanctuary in July 2016. [...]"

Source: Continental Shelf Research
Authors: Matthieu Le Hénaff et al.
DOI: 10.1016/j.csr.2019.103988

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