The National Corn Growers Association released a report arguing that there is no connection between the use of nitrogen fertilizers on corn in the Midwestern US and the seasonal “Dead Zone” in the Gulf of Mexico.
There is no point mincing words about what this “analytical white paper”. It is the corn equivalent of irrational climate change skepticism. This is one truly shoddy piece of work. I encourage others in the scientific community to respond either independently or to append the critique offered here.
First, let’s review the actual science.
The “dead zone” in question, discussed many times before on this blog, is generated most summers on the continental shelf of the northern Gulf of Mexico. Nutrients originating in the Mississippi River Basin in the spring fuel the production of algae (primary production) in the surface waters along the continental shelf. The algae die and sink to the bottom, or something else eats the algae and the fecal matter from the something else sinks to the bottom. All that organic matter needs to decompose, and the process of decomposition (respiration) consumes oxygen. So the bottom waters on the continental shelf during the summer become very depleted in oxygen, or “hypoxic”.
Scientific research over the last few decades has shown that the increase in nitrogen flow from the Mississippi and neighbouring Atchafalaya Rivers since the 1950s has driven the development of these large seasonal periods of hypoxia. The evidence comes from basic ecological theory on nutrient limitation, lab experiments, tracking of the Mississippi River plume, long-term data analysis, sediment cores, isotopic analysis and mathematical modeling. While other nutrients like phosphorus and silica are important, nitrogen is the primary culprit.
There are many possible explanations for the increased flow of nitrogen out of the Mississippi-Atchafalaya River Basin (MARB) including fertilizer use, manure use, NOx emissions from cars and sewage. A simple nutrient budget shows nitrogen fertilizer use in the MARB has increased 20-fold since the 1950s. And today, most of that nitrogen fertilizer is applied to corn fields. Measurements and mathematical modeling of nitrogen loss from corn fields show that corn production is a primary source of nitrogen to the Mississippi and Atchafalaya Rivers, and hence, a primary driver of the development of what's come to be called the “Dead Zone”.
The author of the NCGA report (from the consulting firm StrathKirn Inc.) attempt to counter the mass of scientific evidence with the following largely baseless and unscientific arguments. Basically, he throws a bunch of stuff at the wall to see if anything sticks. I’ll go one by one through the report's chain of five incorrect and comically inconsistent assertions:
Assertion #1: Oxygen levels on the continental shelf are not low in comparison to other parts of the ocean.
This is misleading and irrelevant. First, the large regions of upwelling in the open ocean have low oxygen concentration due to high primary production. There’s no sense in contrasting the naturally and persistently low oxygen levels in the eastern Pacific to the intermittent, seasonal hypoxia on the continental shelf of the Gulf of Mexico. Second, even if there were some sense in this comparison, the data resolution of these maps is far too poor to capture a hypoxia area, which, while among the largest in the world, is still at its largest on the order of 20,000 km2 [here’s a test – can you clearly delineate New Jersey on that map?]. The global map of marine nitrogen concentrations is even more ridiculous. The data is far too coarse to capture the plume of the Mississippi River.
Assertion #2: Hypoxia doesn’t affect the fishery (not there is any hypoxia).
The report shows no change in fish catch over the years. As Steve Carpenter of the University of Wisconsin mentioned in an e-mail, the problem is the report analyses data on fish landings, not fishing effort. The boats may come back with the same weight in fish – but it takes more time and money to get those fish.
Assertion #3: Nitrogen from the Mississippi and Atchafalaya doesn’t cause the hypoxia (not that the hypoxia affects the fishery, or that there is any hypoxia in the first place).
This argument is advanced through a series of graphs relating annual nitrogen export, annual river flow and the annual extent of the hypoxic zone. There are a number of problems here. The nitrogen and flow data are shown only since 1985, despite data existing back to the 1950s. If the graph went back thirty years, you’d see the 2-3fold increase in nitrogen export occurred between the 1950s and the 1980s. Instead, the author reports no evidence of a trend in nitrogen of hypoxia since 1993. That’s not the issue – the issue is the hypoxic zone began growing large in the 1980s because fertilizer use increased between the 1950s and the 1980s, and further increases in corn planting, say for ethanol production, may further increase the average annual extent of hypoxia.
The other glaring problem with this argument is that the report uses no statistics whatsoever. For example, after a chart of nitrogen export and hypoxia extent since 1985 is this unsupported passage:
Again, there appears to be an association between water flow and the amount of nitrite (NO2) plus nitrate (NO3), but these do not relate well to the size of the hypoxic zone (except that they are all low in the year 2000). Thus, many of the statements about the relationship between water flow, nitrogen, and the size of the hypoxic zone are inaccurate.
Some actual statistical analysis, or frankly, just eyeballing the graph, would suggest that there is a significant relationship between the annual nitrogen export from the MARB and the annual extent of the hypoxic zone. It is not a perfect one-to-one relationship between nitrogen and the extent of hypoxia because of how the weather effects mixing of oxygen in the Gulf, the load of other nutrients and a myriad of other mitigating factors. If the author had done any research, they’d find proper statistical analysis and explanations in dozens of published papers, including this one of from my own work, a 2007 paper in Limnology and Oceanography:
Between 1985 and 2004, there is a significant relationship (r2 > 0.61) between midsummer hypoxia area and the May + June nitrate flux (Fig. 1). The strength of this relationship is limited by a number of other variables, including the advection of sub-pycnoclinal waters on the continental shelf, summer tropical storms that increase vertical mixing, recycling of N sequestered in shelf sediments during previous years, and the input of other nutrients such as phosphorus (Rabalais et al. 2002; Scavia et al. 2003; Wawrik et al. 2004).
Assertion #4: Not very much nitrogen is applied to corn (not that nitrogen causes hypoxia, or that hypoxia affects the fishery, or that there is any hypoxia in the first place).
The report displays a graph illustrating that non-crop uses of nitrogen fertilizer, like fertilizer used on lawns, is equal to or greater than the use of nitrogen fertilizer on corn. The problem, or I should say, the most glaring problem? It is national data. Over 90% of the corn grown in the US, and over 90% of the nitrogen fertilizer applied to corn in the US, is grown in the MARB. A 1999 EPA report estimated that non-agricultural fertilizer use is only 5% of total U.S fertilizer use - and that percentage of total fertilizer use in the major producing states of the Corn Belt.
Assertion #5: No nitrogen runs off of corn fields (not that much nitrogen is applied to corn, or that nitrogen causes hypoxia, or that hypoxia affects the fishery, or that there is any hypoxia in the first place).
The report proudly claims that the same amount of nitrogen is now removed during the corn harvest (i.e. in the grain) than is applied as fertilizer, so there can’t be any extra nitrogen left over to run off into the river. Fertilizer use efficiency has indeed increased over the years thanks to genetic technology and improved management. In other word, farmers are getting higher yields with the same amount of nitrogen fertilizer. That is positive news.
But the calculation in the paper is full of flaws. To name just one: the contention that fertilizer inputs = crop outputs = no nitrogen runoff only makes sense if fertilizer were the one and only source of nitrogen to the crops. For one, there is the mineralization of nitrogen in the soil – plant matter on the ground is naturally broken down by microbes, a process that released nitrogen from the plant matter to replenish the soil. This is a fundamental part of soil chemistry. The whole reason the Midwest is good land for growing corn is the high natural mineralization rates!
Final take-home message of the report: The US has a lot of golfers.
The report concludes that all other analyses are ignoring all the fertilizer applied to lawns and present maps and data to support this conclusion. The calculations are extremely suspect. First, the author assumes that the fraction of land devoted to lawns is greater in the MARB than in the rest of the country. Analysing the lawn data, eyeballing the national map, or simply reflecting about the fact that 4/5ths of the US population live outside the MARB, shows that this is a ridiculous assumption. Second, the report assumes that all the fertilizer not applied to corn, wheat, soybeans or cotton – which amounts to about 25% of annual fertilizer sales - is applied to lawns. This ignores all other crops grown in the United States, as well as all the fertilizer applied to rangelands and forests.
The report goes on to argue:
Since most lawns are cut and mulched there is relatively little removal of N, unlike the grain in corn. Consequently, a major portion of the N applied to lawns may be available for leaching… the net N available for leaching per acre is almost infinitely higher for lawns than from corn.
Not only does this argument incorrectly imply that no plant residue whatsoever is ever left behind after harvest to replenish the soil, it ignores the fact that unlike lawns, many corn fields are artificially drained by pipes or drainage tiles, such that excess nitrogen easily leaches to the nearest stream.
All told, the NCGA report is an embarrassment.
There are some legitimate outstanding questions about the nitrogen-hypoxia problem and definitely some legitimate critiques of the media coverage. In particular, the coverage often gives the mistaken impression that corn is the only source of nitrogen, that the hypoxic zone covers a large fraction of the Gulf of Mexico, that water at all depths is hypoxia, and that hypoxia is a permanent phenomena, rather than a seasonal occurrence. The NCGA could have issued on a report on those real concerns. Instead, it issued this dishonest mess of half-truths and pseudo-science.
Sunday, July 05, 2009
Abuse of science and logic by the National Corn Growers Association
Friday, October 24, 2008
"Ocean deoxygenation"
Our friend Caspar Henderson has been searching for a good short phrase to describe the increase the ocean's "oxygen minimum zones" expected to happen as a result of climate change. His query led to a pretty fascinating exchange between a number of experts and the suggestion of ocean deoxygenation.
Just what is this "deoxygenation"?
A lot of intermediate and deep parts of the open ocean are depleted in oxygen. It is natural. First, algae growth on the surface leads to a rain of dead matter to the bottom. Decomposition of that material consumes oxygen. The deep oxygen can be refreshed by oxygen diffusing out of the air into surface waters if there is a lot of vertical mixing. But if the water is highly "stratified" -- say, a light, warm layer lying about a cold, dense layer -- there is little vertical mixing of waters.
This mechanism alo explains coastal hypoxic zones like the famous Gulf of Mexico "Dead Zone". The waters on the continental shelf of the northern Gulf are very stratified, thanks to the influx of fresh, light water from the Mississippi River. Hypoxia develops in the bottom water during the summer in part because of the lack of vertical mixing. That's why when a hurricane blows through, and the water gets all mixed, the dead zone tends to dissipate, or at least decrease in severity and extent.
The "ocean deoxygenation" concern comes from the fact that if climate change heats up the surface ocean, we get more stratification, less vertical mixing, and expansion of the existing ocean minimum zones in the ocean. Recent evidence suggests that is just what is happening.
Large areas of the intermediate and deep ocean have "naturally" low levels of oxygen.
Friday, August 15, 2008
Over 400 dead zones around the world (Science)
The latest issue of Science features a new review of the world's marine dead zones. Scientists have now reported over 400 regions of the coastal ocean like the Gulf of Mexico dead zone where nutrient pollution fuels the depletion of oxygen from the bottom waters, threatening ecosystem function and marine species. Most of these "hypoxic" - less than 2 mL of oxygen per litre of water - and anoxic zones arose in the last few decades due to nitrogen fertilizer use and associated intensive agricultural activities, and to industrial pollution.
The map below shows the dead zone along with a measure of the human footprint on land. The dead zones have also been plotted on Google Maps.
Monday, March 17, 2008
Hypoxic zones around the world
The World Resources Institute and scientist Bob Diaz of Virginia Marine Institute have compiled a new map of the world's coastal hypoxia zones like the famous Gulf of Mexico "Dead Zone" we discuss in the recent PNAS paper on nitrogen pollution and corn production for ethanol. The new map includes 169 documented hypoxic areas, 233 are areas of concern and 13 areas in recovery.
Bottom-water hypoxia can develop when high input of nutrients like nitrogen promote the excessive algae growth. When algae eventually dies and sinks to the bottom, it decomposes, and that process depletes oxygen from the water.
It is worth noting hypoxia will not arise anywhere simply because nutrients are added. To get things started, you still need to feed the algae, and nutrient pollution does the trick. But certain
coastal areas are more naturally prone to hypoxia.
If, for example, the water column is highly "stratified", by that I mean less dense water lying above more dense water there is little mixing between the surface and the bottom waters (think of making a simple oil and vinegar salad dressing). It is then difficult for oxygen from the air to diffuse to the bottom and replace the oxygen consumed by decomposition.
The outlet of big rivers like the Mississippi can be ideal for hypoxia development because the fresh and therefore lighter water introduced by the river creates a stratified water column. That explains some of the year-to-year dynamics of the hypoxic zones like the Gulf Dead Zone. First, hypoxia development can be much worse in a wet or flood year because of the addition of more nutrients and the increased stratification. Second, if a hurricane blows through the Gulf, it encourages mixing just like you do by shaking that bottle of salad dressing, and can break-up the Dead Zone.
The new map supposedly includes only human-driven cases of hypoxia. Which raise the question, what is the cause of the zone between very sparsely populated Somerset and Cornwallis Islands in Nunavut, in the Canadian Arctic? If you have an answer, let me know.
Monday, July 30, 2007
Dead Zone in Gulf is third largest since 1985
Though I'm reticent to link to any news article under the cable-TV-news-ish heading "Planet in Peril", CNN reports that this summer's Gulf of Mexico dead zone has been measured at about 20, 460 km2 in size. That makes it the third largest since measurement began in 1985.
The hypoxic zone was expected to be unusually large this year because of the high flux of nitrogen -- the nutrient that fuels the high productivity on the continental shelf that leads to the consumption of oxygen from the bottom waters -- from the Mississippi River this spring. The blame can likely be placed on the weather and possibly even the increase in corn planting (due to high prices / ethanol demand).
Now off to grab my cape. The planet is in peril.
Friday, April 20, 2007
The truth on greenhouse gases and meat consumption
Last week, Washington Post George Will wrote a sadly uniformed column attacking the public campaigns to reduce greenhouse gas emissions. It drew the usual array of responses and partisan blustering (left, right, ridiculous).
At heart was Time Magazine’s “Global Warming Survival Guide” which featured advice like 51 Tips on Saving the Environment, never mind that global warming is not merely an environmental problem, and that many of the tips have nothing to do with the environment, rather with improving human health.
Tip #22 -- Skip the Steak – claims that livestock is responsible for around 18% of the world’s greenhouse gas emissions. That’s not a mistake. The number comes from a prominent UN report released last year.
What Time, what George Will and what the vast majority of commentators on this subject get wrong is why livestock is responsible for such a large proportion of the world’s GHG emissions.
Columnists and pundits love to joke about cow farts and manure – producing methane and nitrous oxide, respectively – like they’re in bad Adam Sandler movie. That is an important source of GHG. But, in reality, the majority of the emissions attributable to livestock are not coming out the back end, but coming from all the energy used to grow the grain that is fed to livestock.
The United States alone grows almost half of the world’s corn and soybeans. And more than two-thirds of that production is used to manufacture animal feed. It requires an enormous volume of oil, to produce fertilizer and run farm machinery, and an enormous area of land. In turn, it is responsible in part for a number of ecological problems, like the “Dead Zone” in the Gulf of Mexico.
Will seems to mistakenly stumble upon this point, in the midst of some sarcasm, but :
Ben & Jerry's ice cream might be even more sinister [than a steak]: A gallon of it requires electricity-guzzling refrigeration and four gallons of milk produced by cows that simultaneously produce eight gallons of manure and flatulence with eight gallons of methane. The cows do this while consuming lots of grain and hay, which are cultivated by using tractor fuel, chemical fertilizers, herbicides and insecticides, and transported by fuel-consuming trains and trucks.
The concept is right, the comparison is flat wrong. Producing a gram of dairy protein requires only a fraction of the energy of producing a gram of meat protein, especially beef (for the simple reason you don’t kill the cow every time you milk it).Of the feed produced in the United States, only 12% is devoted to dairy cattle (see here). The rest goes to beef cattle, poultry and pork production. That’s why you often hear claims that we should all eat less meat, but not less dairy.
In essence, this problem is not about meat consumption. It is about devoting a significant proportion of our energy and our land to produce meat. One of the biggest obstacles to reducing greenhouse gas emissions in the future will be diet. We may or may not be exporting democracy to the world, but we certainly are exporting our meat-rich diets. As meat consumption rises in China and other parts of the developing world, the challenge of reducing oil consumption and reducing greenhouse gas emissions will grow. More on that later.
Friday, March 30, 2007
What the record corn crop actually means
U.S. farmers are expected to plant 37 million hectares of corn this spring, the largest area of corn since “the Allies invaded Normandy”. It is a 15% increase from last year, all thanks to the demand for ethanol. At the same time, the planted area of soybeans is expected to be 11% lower than last year.
That’s 90.5 million acres of corn, in American English (sick of getting sent data in pounds, cubic feet per second and acres, I'm a on one-person quest to convert to USDA and the USGS to metric).
The media has been all over this today. The coverage I've seen is largely missing the point.
Corn and soybeans are the two prominent crops in the central U.S. For the past 10-15 years, the “Corn Belt” has really been the “Corn and Soybean Belt”. In 2006, the planted area of corn was 31.9 million ha; of soybeans, 30.6 million hectares. The crops are often grown in rotation – corn on a field one year, soy the next – since the nitrogen-fixing soy helps reduce fertilizer needs on corn (and residual nitrogen from corn helps the soy the next year). Both crops are largely used to generate animal feed, a sizeable chunk of which is exported to Europe and Asia.
We’re not about to discover more fertile farmland in the US. The additional corn to produce ethanol is largely coming two ways:
1. Replacing other crops. Since soybeans and corn are usually grown together, the surge in corn means less soy being grown. That means fewer soy available as feed, both here and overseas.
2. Reducing other uses of corn. The major uses of corn are animal feed, exports (mostly feed), food and now fuel. The domestic animal feed isn’t changing substantially lest we change our diets; the domestic food is a small fraction; the surplus here is coming from exports.
Those headlines about the impending choice between food and fuel? That’s not happening here, at least not yet. Ethanol is being generated in the US via planting more corn (at the expense of soy) and exporting less corn. The result is not less food in the store. It is less grain being sold for feed overseas.
That has market implications and environmental implications overseas(more on the environmental side later). As has been widely reported – the “tortilla effect” in Mexico – the price of corn has been high because the supply is being diverted (from exports for feed) to ethanol. It is important to remember that plenty of other factors affect food and crop prices. People seem to be getting carried away blaming ethanol for everything, like the price of wheat, which is rarely used for feed or to generate ethanol.
As for the US, with a 15% increase in planting of heavily fertilized corn, at the expensive of largely unfertilized soybeans, there may also be a record amount of nitrogen in central US soils this summer. A wet spring means a large hypoxic zone is likely to appear in the northern Gulf of Mexico next summer.
Wednesday, October 25, 2006
A rise in the number of dead zones
The latest count of hypoxic or "dead" zones in coastal oceans around the world is up to almost 200, according to scientists at a recent UN Environment Program meeting in Beijing.
As I've mentioned before, these areas of low oxygen are usually caused by excess loading of nutrients by nitrogen (from things like fertilizer). The nutrients cause lots of algae to grow, and when the algae dies and decomposes, much of the oxygen in the water at the bottom is consumed. The lack of oxygen makes life difficult for fish and other organisms living in the deep waters near the coast.
The "dead zone" in the Gulf of Mexico near the mouth of the Mississippi River is one of the best known examples. Robert Diaz from the College of William and Mary, who has published surveys of the world's hypoxic zones in the past, reports that hypoxia is now common in Fosu Lagoon, Ghana; the Pearl River Estuary and the Changjiang River, China; the Elefsis Bay, Aegean Sea, Greece; Paracas Bay, Peru; Mondego River, Portugal; Montevideo Bay, Uruguay and the Western Indian Shelf.
