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Study Shows Global Marine Dead Zones Increased by One-Third Since 1995
15 August 2008
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| Cumulative increase in dead zones through time reported in the scientific literature. Systems are grouped by decade of first documented account. Click to enlarge. Credit: AAAS |
A global study led by Virginia Institute of Marine Sciences (VIMS), College of William and Mary, Professor Robert Diaz shows that the number of “dead zones”—hypoxic areas of the seafloor that cannot sustain marine life—has increased by a third between 1995 and 2007. The study appears in the 15 August edition of the journal Science.
The study tallies 405 dead zones in coastal waters worldwide, affecting a total area of more than 245,000 km 2 (95,000 mi2)—an area about the size of New Zealand. The largest dead zone in the US, at the mouth of the Mississippi, covers more than 22,000 km2 (8,500 mi2), roughly the size of New Jersey. A dead zone also underlies much of the main-stem of Chesapeake Bay, each summer occupying about 40% of its area and up to 5% of its volume. (Earlier post.)
Diaz and collaborator Rutger Rosenberg of the University of Gothenburg in Sweden say that dead zones are now “the key stressor on marine ecosystems” and “rank with over-fishing, habitat loss, and harmful algal blooms as global environmental problems.”
There is no other variable of such ecological importance to coastal marine ecosystems that has changed so drastically over such a short time as DO [dissolved oxygen]. We believe it would be unrealistic to return to preindustrial levels of nutrient input, but an appropriate management goal would be to reduce nutrient inputs to levels that occurred in the middle of the past century, before eutrophication began to spread dead zones globally.
—Diaz and Rosenberg
Diaz began studying dead zones in the mid-1980s after seeing their effect on bottom life in the Patapsco River near Baltimore. His first review of dead zones in 1995 counted 305 worldwide. That was up from his count of 162 in the 1980s, 87 in the 1970s, and 49 in the 1960s. He first found scientific reports of dead zones in the 1910s, when there were 4.
The worldwide distribution of coastal oxygen depletion is associated with major population centers and watersheds that deliver large quantities of nutrients. Most of these systems were not hypoxic when first studied, but it appears that from the middle of the past century, the DO concentrations of many coastal ecosystems have been adversely affected by eutrophication. The observed declines in DO have lagged about 10 years behind the increased use of industrially produced nitrogen fertilizer that began in the late 1940s, with explosive growth in the 1960s to 1970s. For marine systems with data from the first half of the 20th century, declines in oxygen concentrations were first observed in the 1950s in the northern Adriatic Sea, between the 1940s and 1960s in the northwestern continental shelf of the Black Sea, and in the 1980s in the Kattegat. Localized declines of DO levels were noted in the Baltic Sea as early as the 1930s, but it wasn’t until the 1960s that hypoxia became widespread. Localized hypoxia had also been observed since the 1930s in the Chesapeake Bay and since the 1970s in the northern Gulf of Mexico and many Scandinavian coastal systems. Paleo-indicators (foraminifera ratios and organic and inorganic compounds) show that hypoxia had not been a naturally recurring event in these ecosystems. The number of dead zones has approximately doubled each decade since the 1960s.
—Diaz and Rosenberg
Dead zones occur when excess nutrients, primarily nitrogen and phosphorus, enter coastal waters and help fertilize blooms of algae. When these microscopic plants die and sink to the bottom, they provide a rich food source for bacteria, which in the act of decomposition consume dissolved oxygen from surrounding waters. Major nutrient sources include fertilizers and the burning of fossil fuels.
Diaz says that many ecosystems experience a progression in which periodic hypoxic events become seasonal and then, if nutrient inputs continue to increase, persistent. Earth’s largest dead zone, in the Baltic Sea, experiences hypoxia year-round. Chesapeake Bay experiences seasonal, summertime hypoxia through much of its main channel.
Diaz and Rosenberg note that hypoxia tends to be overlooked until it starts to affect organisms that people eat.
Diaz and Rosenberg also point out a more fundamental effect of hypoxia: the loss of energy from the marine food chain. By precluding or stunting the growth of bottom-dwellers such as clams and worms, hypoxia robs their predators of an important source of nutrition.
Diaz and VIMS colleague Linda Schaffner estimate that Chesapeake Bay now loses about 10,000 metric tons of carbon to hypoxia each year, 5% of the Bay’s total production of food energy. The Baltic Sea has lost 30% of its food energy—a condition that has contributed to a significant decline in its fisheries yields.
Diaz’s global hypoxia study was funded in part by the National Oceanic and Atmospheric Administration.
Resources
Robert J. Diaz and Rutger Rosenberg (2008) Spreading Dead Zones and Consequences for Marine Ecosystems. Science Vol. 321. no. 5891, pp. 926 - 929 doi: 10.1126/science.1156401
August 15, 2008 in Sustainability | Permalink | Comments (12) | TrackBack (0)
Comments
Posted by: Polly | August 15, 2008 at 04:14 AM
Polly, geneticists could try developing GM crops that are nitrogen fixing and don't require as much fertilizer.
Also, if memory serves, research in Australia suggests that agrichar is as effective as fertilizer for increasing crop yields. I don't know if it could also be washed into the sea and promote algae growth or not.
Posted by: JMartin | August 15, 2008 at 06:38 AM
Planting less corn would be a massive first step.
Posted by: Tripp | August 15, 2008 at 09:20 AM
JMartin:
You have a very good question.
Would Agrichar or Terra Preta eventually drain to the ocean and do as much damage as chemical fertilizers. It remains to be fully tested.
Biomass and wastes pyrolising would produce syngas and black waste or agrichar or terra preta which in turn good be used as a fertilizer.
Since about 10 tonnes of agrichar is required per hectar, millions and even billions of tonnes would be required to replaced chemical fertilizers. A few thousand pyrolising machines would be required + loads of biomass + loads of energy to keep the process going. Could enough agrichar/fertilizer be evenually produced to satify all farmers needs?
The interesting part is that the main product (syngas) could be used to produce liquid fuel to replaced imported oil and supply some of the energy required for the pyrolising process.
Posted by: HarveyD | August 15, 2008 at 09:33 AM
We cannot survive if the ocean becomes dead.
Posted by: Lulu | August 15, 2008 at 12:16 PM
Scientists have been trying to engineer nitrogen fixation for a long time. Its not trivial.
Posted by: marcus | August 15, 2008 at 12:59 PM
Three things could significantly reduce nutrients run-off from human activities:
Tertiary treatment of sewage (already mandated in developed countries);
Proper treatment of livestock manure (anaerobic digestion mostly) with recovery and reuse of nitrogen and phosphorous nutrients (ongoing in developed countries);
Use of controlled-release granulated fertilizer in agriculture instead of mostly urea solutions – like used for lawn maintenance.
Posted by: Andrey Levin | August 15, 2008 at 03:00 PM
JMartin,
did a little research on nitrogen fixing trees. One of the consequences warned about was that too many nitrogen fixing trees would have similar effects as too much over fertilization from chemicals. I would expect the same effect from other nitrogen fixing plants.
It really doesn't matter where the nitrogen comes from. As long as it gets into the runoff, you will get the same problem. Part of the problem is land use change. Wetlands used to soak up excess fertilizer but these areas have been decimated in recent years.
If algae bio fuel ever becomes viable, water runoff from farms could be pretreated to get large blooms which could be later processed to biofuels. But thats a large if especially in terms of creating the infrastructure needed.
This is a problem of developed countries and is an externality that has been largely overlooked and ignored. Pig waste for instance has been used directly as fertilizer with the expected consequences.
The number of dead zones are going up partially due to emulation from the developing world, mimicking the processes of the first but with far less regulation than the first world practices (which are less than ideal in the first place in this regard).
Posted by: aym | August 15, 2008 at 05:05 PM
MBD. Are researching algae farming using aquaculture waste. Many references in search engine.
While they recognise the damage to hard corals and native fish populations by excessive nutrient flows and competition from nutrient loving algae's, The larger interest should be treatment at as near to source of the land based nutrient from farming and sewage.
This is an invisible energy flow where we H.saps gather, manufacture fertilizer products which then pour out into the environment. That's a bucket with a big hole.
The economics of good money into making a bad outcome.
Because no body is able to take responsibility.
This demonstrates how good outcomes for the environment shouldn't be seen as too costly. Doing nothing is the only too costly option.
Making a dollar from this fertilizer waste through Algae is still gaining ground and credibility with more detailed accounting.
My beef is that the responsibility has been avoided untill the economic argument can be demonstrated.
Posted by: arnold | August 15, 2008 at 08:06 PM
I am not expert on nitrogen fixing plants as such, but
My understanding is that the nitrogen is locked up in the plant while it lives.
Logically this leave more available to surrouding plants.
Of course the other, industrial source of nitrogen has a much larger footprint as competition for feedstock, concentrations more easily leading to pollution overwhelming the capacity of natural systems to cope,
and of course huge contributions of greeenhouse gases.
Posted by: arnold | August 15, 2008 at 08:21 PM
A major part of everglades restoration is the construction of STA's (surface water treatment areas). They are massive shallow reservoirs with emergent vegetation which acts as a filter. Instead of agricultural runoff going from ditches to canals & then directly into the everglades, these STA's clean up & dramatically reduce toxins. This could be done wherever there are dead zones.
Check it out:
http://www.evergladesplan.org/about/rest_plan_pt_01.aspx
Posted by: ejj | August 16, 2008 at 02:25 PM
Surely the answer for all (the farmer and the environment as a whole) is to avoid unnecessary (excessive) application of fertilizer. One step toward eliminating this problem could be provided by...http://www.qinetiq.com/home/newsroom/news_releases_homepage/2008/3rd_quarter/qinetiq_achieves_uk.html
Posted by: RBL | August 27, 2008 at 03:46 AM
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2 quotes and 2 questions:
1.) Diaz and Rosenberg say the key to reducing dead zones is “to keep fertilizers on the land and out of the sea.”
Diaz says that goal is shared by farmers concerned with the high cost of buying and applying nitrogen to their crops. “They certainly don’t want to see their dollars flowing off their fields into the Bay,” says Diaz. “Scientists and farmers need to continue working together to develop farming methods that minimize the transfer of nutrients from land to sea.”
No mention of how to 'keep fertilizers on the land and out of the sea' - any practical suggestions?
2. "Dead zones occur when excess nutrients, primarily nitrogen and phosphorus, enter coastal waters and help fertilize blooms of algae. When these microscopic plants die and sink to the bottom, they provide a rich food source for bacteria, which in the act of decomposition consume dissolved oxygen from surrounding waters."
No mention of harvesting the algal bloom for biofuel before the plants die & sink to the bottom.
The largest dead zone in the US, at the mouth of the Mississippi, is by coincidence adjacent to oil refineries. Any chance of getting the oil/gas firms to process algae for fuel?
Has any research been done on the cost-effectiveness of harvesting the algae for biofuel?
It sounds like dead zones are an external cost of fossil fuels. Logically a levy on oil & gas should fund research & mitigation measures.
Normally, external costs are paid for by direct taxation of the product, like the tax on tobacco to fund health care in Europe.
Somehow, a direct tax on fossil fuel fertilizer seems like the classic lead balloon with no chance of passing into legislation.