Ecological Forecasting And The Science Of Hypoxia In Chesapeake Bay Pdf
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- Dead zone (ecology)
- Marine Dead Zones: Understanding the Problem
- Ecological Forecasting and the Science of Hypoxia in Chesapeake Bay
Dead zone (ecology)
Dead zones are hypoxic low- oxygen areas in the world's oceans and large lakes , which causes these bodies of water to fail to support the marine life living there. However, in the s, oceanographers began noting increased instances and expanses of dead zones.
These occur near inhabited coastlines , where aquatic life is most concentrated. In March , when the recently established UN Environment Programme published its first Global Environment Outlook Year Book GEO Year Book , it reported dead zones in the world's oceans where marine life could not be supported due to depleted oxygen levels.
Some of these were as small as a square kilometre 0. A study counted dead zones worldwide. Aquatic and marine dead zones can be caused by an increase in nutrients particularly nitrogen and phosphorus in the water, known as eutrophication. These chemicals are the fundamental building blocks of single-celled, plant-like organisms that live in the water column, and whose growth is limited in part by the availability of these materials.
Eutrophication can lead to rapid increases in the density of certain types of these phytoplankton , a phenomenon known as an algal bloom. Limnologist Dr. David Schindler , whose research at the Experimental Lakes Area led to the banning of harmful phosphates in detergents, warned about algal blooms and dead zones,. This isn't just a prairie problem. Global expansion of dead zones caused by algal blooms is rising rapidly.
The major groups of algae are Cyanobacteria , green algae , Dinoflagellates , Coccolithophores and Diatom algae. An increase in the input of nitrogen and phosphorus generally causes Cyanobacteria to bloom.
Other algae are consumed and thus do not accumulate to the same extent as Cyanobacteria. The bacterial degradation of their biomass consumes the oxygen in the water, thereby creating the state of hypoxia. Dead zones can be caused by natural and by anthropogenic factors.
Natural causes include coastal upwelling and changes in wind and water circulation patterns. Use of chemical fertilizers is considered the major human-related cause of dead zones around the world.
Runoff from sewage, urban land use, and fertilizers can also contribute to eutrophication. Notable dead zones in the United States include the northern Gulf of Mexico region,  surrounding the outfall of the Mississippi River, the coastal regions of the Pacific Northwest, and the Elizabeth River in Virginia Beach, all of which have been shown to be recurring events over the last several years.
Additionally, natural oceanographic phenomena can cause deoxygenation of parts of the water column. For example, enclosed bodies of water, such as fjords or the Black Sea , have shallow sills at their entrances, causing water to be stagnant there for a long time. In many cases, OMZs are permanent or semipermanent areas. Remains of organisms found within sediment layers near the mouth of the Mississippi River indicate four hypoxic events before the advent of synthetic fertilizer.
In these sediment layers, anoxia -tolerant species are the most prevalent remains found. The periods indicated by the sediment record correspond to historic records of high river flow recorded by instruments at Vicksburg, Mississippi.
Changes in ocean circulation triggered by ongoing climate change could also add or magnify other causes of oxygen reductions in the ocean. In August , a report suggested that the US meat industry and agroeconomic system are predominantly responsible for the largest-ever dead zone in the Gulf of Mexico. A large portion of the crops grown in this region are used as major feed components in the production of meat animals for agribusiness companies, like Tyson and Smithfield Foods.
Dead zones can be classified by type, and are identified by the length of their occurrence: . Due to the hypoxic conditions present in dead zones, marine life within these areas tends to be scarce. Most fish and motile organisms tend to emigrate out to the zone as oxygen concentrations fall, and benthic populations may experience severe losses in when oxygen concentrations are below 0. Sulfur reduction is a particular concern as Hydrogen sulfide is toxic and stresses most organisms within the zone further, exacerbating mortality risks.
Low oxygen levels can have severe effects on survivability of organisms inside the area while above lethal anoxic conditions. Studies conducted along the Gulf Coast of North America have shown hypoxic conditions lead to reduction of reproductive rates and growth rates in a variety of organisms including fish and benthic invertebrates.
Surviving organisms tolerant of hypoxic conditions often exhibit physiological adaptations appropriate for persisting within hypoxic environments.
Examples of such adaptations include increased efficiency of oxygen intake and use, lowering required amount of oxygen intake through reduced growth rates or dormancy, and increasing the usage of anaerobic metabolic pathways. Community composition in benthic communities is dramatically disrupted by periodic oxygen depletion events, such as those of Seasonal Dead Zones and occurring as a result of Diel Cycles.
The longterm effects of such hypoxic conditions result in a shift in communities, most commonly manifest as a decrease in species diversity through mass mortality events. Reestablishment of benthic communities depend upon composition of adjacent communities for larval recruitment.
The influence of dead zones on fisheries and other marine commercial activities varies by the length of occurrence and location.
Dead zones are often accompanied by a decrease in biodiversity and collapse in benthic populations, lowering the diversity of yield in commercial fishing operations, but in cases of eutrophication-related dead zone formations, the increase in nutrient availability can lead to temporary rises in select yields among pelagic populations, such as Anchovies. For instance, an estimated 17, MT of carbon in the form of prey for fisheries has been lost as a result of Dead Zones in the Gulf of Mexico.
Indirect factors such as increased success by invasive species and increased pandemic intensity in stressed species such as oysters both lead to losses in revenue and ecological stability in affected regions. Despite most other life forms being killed by the lack of oxygen, jellyfish can thrive and are sometimes present in dead zones in vast numbers. Jellyfish blooms produce large quantities of mucus, leading to major changes in food webs in the ocean since few organisms feed on them.
The organic carbon in mucus is metabolized by bacteria which return it to the atmosphere in the form of carbon dioxide in what has been termed a " jelly carbon shunt ". The primary concern is the potential for dead zones to serve as breeding grounds for jelly populations as a result of the hypoxic conditions driving away competition for resources and common predators of jellyfish.
In the s, marine dead zones were first noted in settled areas where intensive economic use stimulated scientific scrutiny: in the U. Researchers from Baltic Nest Institute published in one of PNAS issues reports that the dead zones in the Baltic Sea have grown from approximately 5, km2 to more than 60, km2 in recent years.
Some of the causes behind the elevated increase of dead zones can be attributed to the use of fertilizers, large animal farms, the burning of fossil fuels, and effluents from municipal wastewater treatment plants. The Chesapeake's high levels of nitrogen are caused by two factors: urbanization and agriculture.
The western part of the bay is full of factories and urban centers that emit nitrogen into the air. Atmospheric nitrogen accounts for about a third of the nitrogen that enters the bay.
The eastern part of the bay is a center of poultry farming, which produces large amounts of manure. The National Geographic further stated "Since , the Chesapeake Bay Foundation has led a number of programs that aim to improve the bay's water quality and curb pollution runoff.
The Chesapeake still has a dead zone, whose size varies with the season and weather. It has been polluted by nitrogen and phosphorus, but also toxic deposits from the shipbuilding industry, the military, the world's largest coal export facility, refineries, loading docks, container-repair facilities and others, so fish had been "offlimits since the s".
In , a group formed to clean it up, adopting the mummichog as a mascot, and has removed thousands of tons of contaminated sediment. In , a acre biological dead zone called Money Point was dredged out, and this let fish return, and the wetland recover.
Overall the lake's oxygen level is poor with only a small area to the east of Long Point that has better levels. The biggest impact of the poor oxygen levels is to lacustrine life and fisheries industry. A dead zone exists in the Lower St. The Oregon coast has also seen hypoxic water transporting itself from the continental shelf to the coastal embayments. This has seemed to cause intensity in several areas of Oregon's climate such as upwelled water containing oxygen concentration and upwelled winds.
The area of temporary hypoxic bottom water that occurs most summers off the coast of Louisiana in the Gulf of Mexico  is the largest recurring hypoxic zone in the United States. According to a fact sheet created by NOAA , "seventy percent of nutrient loads that cause hypoxia are a result of this vast drainage basin".
The discharge of treated sewage from urban areas pop. It is designed to direct efforts to reduce nutrients in surface water from both point and nonpoint sources in a scientific, reasonable and cost effective manner. The area of hypoxic bottom water that occurs for several weeks each summer in the Gulf of Mexico has been mapped most years from through The size varies annually from a record high in when it encompassed more than 22, sq kilometers 8, square miles to a record low in of 39 sq kilometers 15 square miles.
The models using the nitrogen flux from the Mississippi River to predict the "dead zone" areas have been criticized for being systematically high from to , having predicted record areas in , , , , and that were never realized. In late summer the dead zone disappeared as the great drought caused the flow of Mississippi to fall to its lowest level since Some assert that the dead zone threatens lucrative commercial and recreational fisheries in the Gulf of Mexico.
Grimes makes a case that nutrient loading enhances the fisheries in the Gulf of Mexico. Shrimp trawlers first reported a 'dead zone' in the Gulf of Mexico in , but it was not until when the size of the hypoxic zone had increased that scientists began to investigate.
After , the conversion of forests and wetlands for agricultural and urban developments accelerated. In July , a dead zone was discovered off the coast of Texas where the Brazos River empties into the Gulf.
According to Fred Below , a professor of crop physiology at the University of Illinois at Urbana-Champaign , corn requires more nitrogen-based fertilizer because it produces a higher grain per unit area than other crops and, unlike other crops, corn is completely dependent on available nitrogen in soil.
The recovery of benthic communities is primarily dependent upon the length and severity of hypoxic conditions inside the hypoxic zone. Less severe conditions and temporary depletion of oxygen allow rapid recovery of benthic communities in the area due to reestablishment by benthic larvae from adjacent areas, with longer conditions of hypoxia and more severe oxygen depletion leading to longer reestablishment periods.
Small scale hypoxic systems with rich surrounding communities are the most likely to recover after nutrient influxes leading to eutrophication stop. However, depending on the extent of damage and characteristics of the zone, large scale hypoxic condition could also potentially recover after a period of a decade.
For example, the Black Sea dead zone, previously the largest in the world, largely disappeared between and after fertilizers became too costly to use following the collapse of the Soviet Union and the demise of centrally planned economies in Eastern and Central Europe. Fishing has again become a major economic activity in the region.
While the Black Sea "cleanup" was largely unintentional and involved a drop in hard-to-control fertilizer usage, the U. Other methods of reversal can be found here. From Wikipedia, the free encyclopedia. This article is about the oceanic phenomenon. For other uses, see Dead zone disambiguation. For the natural anoxic basins, see Anoxic waters. Low-oxygen areas in oceans and large lakes caused by nutrient and fertilizer pollution. Main article: Baltic Sea hypoxia. This section needs expansion.
You can help by adding to it. August Algal bloom Anoxic event Anoxic waters Cultural eutrophication Eutrophication Fish kill Hypoxia Marine pollution Ocean deoxygenation Oxygen minimum zone Shutdown of thermohaline circulation.
Marine Dead Zones: Understanding the Problem
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Use of this Web site signifies your agreement to the terms and conditions. Special Issues. Contact Us. Change code. Journal of Water Resources and Ocean Science. Beginning in the mid 20th Century the Chesapeake Bay began to show the first signs of eutrophication, with seasonal depletion of free oxygen in bottom waters hypoxia. Eutrophication is driven largely by external loading of phosphorus P and nitrogen N.
Ecological Forecasting and the Science of Hypoxia in Chesapeake Bay
Jeremy M. Testa, J. Blake Clark, William C. Dennison, E.
Increased nutrient loadings have resulted in low dissolved oxygen DO concentrations in bottom waters of the Patuxent River, a tributary of Chesapeake Bay. We synthesize existing and newly collected data to examine spatial and temporal variation in bottom DO, the prevalence of hypoxia-induced mortality of fishes, the tolerance of Patuxent River biota to low DO, and the influence of bottom DO on the vertical distributions and spatial overlap of larval fish and fish eggs with their gelatinous predators and zooplankton prey. We use this information, as well as output from watershed-quality and water-quality models, to configure a spatially-explicit individual-based model to predict how changing land use within the Patuxent watershed may affect survival of early life stages of summer breeding fishes through its effect on DO. The system is characterized by high spatial and temporal variation in DO concentrations, and the current severity and extent of hypoxia are sufficient to alter distributions of organisms and trophic interactions in the river.
September 20, — August 13, An adequate level of dissolved oxygen is necessary to support most forms of aquatic life. While very low levels of dissolved oxygen hypoxia can be natural, especially in deep ocean basins and fjords, hypoxia in coastal waters is mostly the result of human activities that have modified landscapes or increased nutrients entering these waters. Hypoxic areas are more widespread during the summer, when algal blooms stimulated by spring runoff decompose to diminish oxygen.
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