Massive 8,000-mile 'dead zone' could be one of the gulf's largest
"JUST OFF THE coast of Louisiana and Texas where the Mississippi River empties, the ocean is dying. The cyclical event known as the dead zone occurs every year, but scientists predict that this year's could be one of the largest in recorded history. Annual spring rains wash the nutrients used in fertilizers and sewage into the Mississippi. That fresh water, less dense than ocean water, sits on top of the ocean, preventing oxygen from mixing through the water column. Eventually those freshwater nutrients can spur a burst of algal growth, which consumes oxygen as the plants decompose. [...]"
Source: National Geographic
NOAA forecasts very large ‘dead zone’ for Gulf of Mexico
"NOAA scientists are forecasting this summer’s Gulf of Mexico hypoxic zone or ‘dead zone’ – an area of low to no oxygen that can kill fish and other marine life – to be approximately 7,829 square miles, or roughly the size of Massachusetts. The annual prediction is based on U.S. Geological Survey river flow and nutrient data. [...]"
Flooding Makes Big 'Dead Zone' Off Louisiana Coast Likely
"The year's widespread flooding has made it likely that a big, oxygen-starved "dead zone" off Louisiana's coast will form this summer, the head of the National Centers for Coastal Ocean Science said Thursday. Preliminary computer model runs "indicate a large to very large year," for the area where there's too little oxygen to support marine life, Steven Thur told the Mississippi River/Gulf of Mexico Hypoxia Task Force during a meeting livestreamed from Baton Rouge. [...]"
Source: The New York Times
Extent of the annual Gulf of Mexico hypoxic zone influences microbial community structure
"Rich geochemical datasets generated over the past 30 years have provided fine-scale resolution on the northern Gulf of Mexico (nGOM) coastal hypoxic (≤ 2 mg of O2 L-1) zone. In contrast, little is known about microbial community structure and activity in the hypoxic zone despite the implication that microbial respiration is responsible for forming low dissolved oxygen (DO) conditions. [...]"
Source: PLoS ONE
Authors: Lauren Gillies Campbell et al.
Yield stability analysis reveals sources of large-scale nitrogen loss from the US Midwest
"Loss of reactive nitrogen (N) from agricultural fields in the U.S. Midwest is a principal cause of the persistent hypoxic zone in the Gulf of Mexico. We used eight years of high resolution satellite imagery, field boundaries, crop data layers, and yield stability classes to estimate the proportion of N fertilizer removed in harvest (NUE) versus left as surplus N in 8 million corn (Zea mays) fields at subfield resolutions of 30 × 30 m (0.09 ha) across 30 million ha of 10 Midwest states. [...]"
Source: Scientific Reports
Authors: Bruno Basso et al.
'Dead zone' volume more important than area to fish, fisheries
Dubravko Justic, the Texaco Distinguished Professor in the LSU Department of Oceanography & Coastal Sciences, and Research Associate Lixia Wang recently co-authored a study suggesting that measuring the volume rather than the area of the Gulf of Mexico's dead zone, is more appropriate for monitoring its effects on marine organisms.
"The dead zone, a hypoxic zone, is a region of low oxygen that results from runoff of high nutrients, such as nitrogen and phosphorus, often found in fertilizer, flowing from the Mississippi River into the coastal ocean. It is the largest recurring hypoxic zone in the U.S., occurring most summers, and is located off the coast of Louisiana. This nutrient pollution, coupled with other factors, is believed to have a negative impact on fisheries because it depletes the oxygen required to support most marine life in bottom and near-bottom waters. [...]"
Source: Science Daily
Hypoxic volume is more responsive than hypoxic area to nutrient load reductions in the northern Gulf of Mexico – and it matters to fish and fisheries
"While impacts of low oxygen on marine organisms have been reviewed from physiological and ecological perspectives, relating broad population- and ecosystem-level effects to the areal extent of hypoxia (dissolved oxygen concentration below 64 µM, or 2 mg/l) has proven difficult. We suggest that hypoxic volume is a more appropriate metric compared to hypoxic area because volume better integrates the effects of hypoxia on ecological processes relevant to many marine taxa. [...]"
Source: IOP Science
Authors: Donald Scavia et al.
A Novel Approach for Measuring the Gulf of Mexico Dead Zone: Toward Better Temporal and Spatial Estimates for Management Applications
"Nearly every summer, a large hypoxic zone forms in the northern Gulf of Mexico. Research on the causes and consequences of hypoxia requires reliable estimates of hypoxic extent, which can vary at submonthly time scales due to hydro-meteorological variability. Here, we use an innovative space-time geostatistical model and data collected by multiple research organizations to estimate bottom-water dissolved oxygen (BWDO) concentrations and hypoxic area across summers from 1985 to 2016. [...]"
Source: Environmental Science and Technology
Authors: V. Rohith Reddy Matli et al.
What could cause the Mississippi Bight to become hypoxic?
"Coastal regions with low dissolved oxygen (known as hypoxia) can lead to poor water quality and harm regional fisheries. These areas of low dissolved oxygen are expanding and expected to continue growing in coming years due to human impacts on the environment.
A recent article published in Continental Shelf Research explores aspects of the environmental conditions that can potentially lead to hypoxia in the Mississippi Bight region of the northern Gulf of Mexico. This area extends from Apalachicola in Florida to the Mississippi River Delta. [...]"
Tracking sea surface salinity and dissolved oxygen on a river-influenced, seasonally stratified shelf, Mississippi Bight, northern Gulf of Mexico
"River discharge, and its resulting region of freshwater influence (ROFI) in the coastal ocean, has a critical influence on physical and biogeochemical processes in seasonally stratified shelf ecosystems. Multi-year (2010–2016) observations of satellite-derived sea surface salinity (SSS) and in situ water column hydrographic data during summer 2016 were used to investigate physical aspects of the ROFI east of the Mississippi River Delta to better assess regional susceptibility to hypoxia in the summer months. [...]"
Source: Continental Shelf Research
Authors: Brian Dzwonkowski et al.