Skip to comments.Satellite observes agricultural runoff causing algal blooms
Posted on 12/09/2004 8:45:38 AM PST by cogitator
Direct Link Discovered Between Agricultural Runoff And Algal Blooms In Sea
Scientists have found the first direct evidence linking large-scale coastal farming to massive blooms of marine algae that are potentially harmful to ocean life and fisheries.
Researchers from Stanford University's School of Earth Sciences made the discovery by analyzing satellite images of Mexico's Sea of Cortez, also known as the Gulf of California - a narrow, 700-mile-long stretch of the Pacific Ocean that separates the Mexican mainland from the Baja California Peninsula.
Immortalized in the 1941 book Sea of Cortez, by writer John Steinbeck and marine biologist Edward Ricketts, the region remains a hotspot of marine biodiversity and one of Mexico's most important commercial fishing centers.
The results of the Stanford study will be presented at the annual meeting of the American Geophysical Union (AGU) in San Francisco on Dec. 13.
Algal blooms occur naturally when cold-water upwellings bring from the seafloor to the surface nutrients that stimulate the rapid reproduction and growth of microscopic algae, also known as phytoplankton. These events often benefit marine ecosystems by generating tons of algae that are consumed by larger organisms.
But several phytoplankton species produce harmful blooms, known as red or brown tides, which release toxins in the water that can poison mollusks and fish. Excessively large blooms can also overwhelm a marine ecosystem by creating oxygen-depleted "dead zones" in the ocean.
Scientists have long suspected that many harmful blooms are fueled by fertilizer runoff from farming operations, which in many regions pour tons of excess nitrogen and other nutrients into rivers that eventually flow into coastal waters. However, some agricultural industry groups contend that there is not enough evidence to link farm runoff to red tides or dead zones.
To assess the impact of agriculture on marine algae, Stanford scientists turned their attention to one of Mexico's most productive coastal farming regions - the Yaqui River Valley, which drains into the Sea of Cortez.
"The Yaqui Valley agricultural area is 556,000 acres [225,000 hectares] of irrigated wheat," said Pamela A. Matson, the dean of Stanford's School of Earth Sciences and co-author of the AGU study. "The entire valley is irrigated and fertilized in very short windows of time during a six-month cycle. The excess water from irrigation runs off through streams and channels into the estuaries, and then out to sea."
Matson and her colleagues wondered if each fertilization and irrigation event would trigger a noticeable phytoplankton bloom near the mouth of the Yaqui River, which is located on the mainland side of the Sea of Cortez.
To find out, the researchers analyzed a series of images from an orbiting NASA satellite called SeaWiFS, which is equipped with special light-sensitive instruments that can detect phytoplankton floating near the surface of the sea.
"These instruments measure the level of greenness in the water," explained Kevin R. Arrigo, an associate professor of geophysics at Stanford and co-author of the AGU paper. "The greener the water, the more phytoplankton there are."
Stanford doctoral candidate Mike Beman carefully analyzed dozens of SeaWiFS images taken over the Sea of Cortez from 1998 through 2002. The results were dramatic.
"I looked at five years of satellite data," said Beman, lead author of the study. "There were roughly four irrigation events per year, and right after each one, you'd see a bloom appear within a matter of days."
Each bloom was enormous, he said, covering from 19 to 223 square miles (50 to 577 square kilometers) of the Sea of Cortez and lasting several days. "Sometimes eddies actually pulled the plumes across the gulf, from the mainland side all the way to the Baja Peninsula," Beman added.
"Mike found that immediately following each one-week window in which much of the valley was irrigated, there was a response in the ocean off the coast of the Yaqui Valley," Matson explained.
"We were quite surprised," Arrigo added, noting that the AGU paper marks the first time that scientists have documented a "one-to-one correspondence between an irrigation event and a massive algal bloom."
Red tides and dead zones
According to the researchers, artificially induced algal blooms could have major impacts on recreational and commercial fishing, major industries in the Sea of Cortez. Red tides, for example, can cause outbreaks of life-threatening diseases, such as paralytic shellfish poisoning, which can shut down mussel and clam harvesting for long periods of time.
Another concern is hypoxia, or oxygen depletion, which is caused by excessive algae growth. As the algal mass sinks, it is consumed by bacteria, which use up most of the oxygen in the water as they multiply. The result is an oxygen-depleted dead zone at the bottom of the sea where few creatures can survive.
A massive dead zone appears every summer in the Gulf of Mexico off the coast of Louisiana and Texas. Scientists believe that agricultural runoff from the Mississippi River plays a pivotal role in creating this annual dead zone, which measured 8,500 square miles (22,000 square kilometers) in 2002-an area bigger than the state of Massachusetts.
"In the Sea of Cortez, there's the possibility that hypoxia could occur at a local scale, which could be devastating to the shrimp and shellfish industries," Matson said.
"Shrimp fisheries are very important economically, and they're already under a lot of stress from overfishing and aquaculture. It is possible that agricultural runoff could cause additional stress if it does lead to toxic blooms or hypoxia." She and her colleagues plan to conduct follow-up studies to assess the ecological impact of Yaqui Valley runoff events.
"The availability of high-resolution satellite data has opened up a whole new opportunity to look at the importance of what's going on on land in the sea," Matson added. "This study shows that you have to pay attention to the land-sea connections."
Until they start taking out those ChemLawn trucks with RPGs, I'm afraid the situation is hopeless. Every manicured lawn is dumping nutrients right into the watershed. It's all gotta go somewhere!
This is a big problem in the Great Lakes region as well. From our digital orthophotos we can see algal blooms as well as sediment plumes coming from the tributaries. This is going to be a hotbed issue.
Excess nutrient input is probably the biggest remaining pollution problem in the United States right now -- most of the more noxious and dangerous chemicals and substances have been pretty well (with some exceptions) cleaned up. But improving stormwater runoff and wastewater treatment is difficult and expensive.
The solution to pollution is dilution, right???
I agree, I've done some work with the CSO (combined sewer overflow) problems in the Great Lakes region. Many communities still have these antiquated waste water treatment plants that discharge untreated water directly into lakes, streams, etc. after rain events. Instead of separating storm and sewer water, they often take the bandaid approach of increasing the plants water retention capacity. There are hundreds of communities that aren't in compliance with the EPA's NPDES (National Pollution Discharge Elimination System) permiting system. At least around here communities don't seem to care as the polluted water flows into surrounding communities, eventually ending up in Lake Michigan. A people wonder why the beaches are closed due to contamination.
Very punny! But actually, you are correct...although it really doesn't solve the problem, it just disperses pollutants over a larger area.
I grew up in New London, WI and went to college at UW-Oshkosh. One of the big environmental issues while I was in high school and college was the sad state of the Fox River that flows from Lake Winnebago to Green Bay. At the time, it was a mess. It's substantially better now, and the improvement shows that progress can be made. It's still got problems, mainly PCBs, but they're being addressed.
Speaking of eutrophication, you ever go to Lake Koshkenog (spelling?). My grandmother lived on that lake near Edgerton, WI until she passed away a few years ago. That has to be the most algae fill lake I have ever seen!
Excess nutrient input is probably the biggest remaining pollution problem in the United States right now
Considering all of today's triumphant technology, surely there must be a way to convert excess nutrient input to a new form of breathtaking breakfast cereal !!! ;-))
Koshkenong. I've been by it on I-90 but never actually to it. Any idea why it was so green? (There's a lot of dairy around there -- I might be able to guess.)
Not until they quit dumping sewage sludge on agricultural land, (within 25 ft. of the water).
Too much concentration of just about anything can be considered a pollutant these days! The so called pollutants come directly, or indirectly from the ground and even the ground it'self is considered a "pollutant" by militant GANG-GREEN when ANY erosion occurs... it's called TURBIDITY and according to them... MUST be eliminated!!!
In 1998, I attended a much ballyhooed conference attended by both Clinton and Bruce Babbit at Lake Tahoe about lake clarity. As usual, one could only submit questions on 3x5 cards in advance. It rained heavily that day and I submitted two and one was "I noticed on the way in here through the parking lots that a lot of ugly yellow stuff was being washed down the parking lot drains and into the lake! It appeared to be coming from our beautiful pine trees! What program does the Federal Government have in place to stop this detrimental substance from polluting the lake?"
The other question I submitted was, "Erosion is perceived as the prime cause of degradation in lake clarity. Since the time Lake Tahoe was formed, how does one explain how all the buildable level and semi-level land got into this basin and the lake remain as pristine as it has been?"
Its more of an indirect effect. Untreated wastewater is generally rich in organic matter. This organic matter feeds the bacteria and algae normally present in healthy water sources. The presence of excessive amounts of nutrients discharged as a result of untreated wastewater will cause an increase in concentration of both bacteria and algae within the surface water. Beside organic matter, wastewater also contains both organic and oxidizable inorganic compounds. These organic and inorganic compounds directly and indirectly consume the available oxygen present in the ecosystem. This process is called eutrification and will eventually kill off other living organisms (plants, animals, & insects) in the aquatic system.
I meant to ping you to this discussion. I think you will probably have many enlightening things to add to offset my rhetorical questions, platitudes, puns and hypercritical replies. So get in here, quick!!!
From what little I know/remember of that area, Lake Koshkenog was formely farmland. The native americans farmed it previously and then I believe white settlers also farmed it. Somehow we altered the Rock River (most likely dammed upstream) and the farmland flooded. I remember hearing the Lake has only a maximum depth of 7 feet, so that would support that theory-- pretty shallow for a lake that size. So I would assume the lake bed soil was already pretty nutrient rich to begin with and I'm sure the nearby dairy industry doesn't help.