Stories tagged Life Science

Feb
21
2010

Nike's new prototype- the retro model: The running foot is soooo 2 million years ago, but you wait long enough and everything comes back.
Nike's new prototype- the retro model: The running foot is soooo 2 million years ago, but you wait long enough and everything comes back.Courtesy perpetualplum
Have you ever run barefoot? It’s great! I’ve never really thought about why I like it, but some really cool biomechanics research coming out of Harvard suggests that there may be some evolutionary reasons for my enjoyment. Homo sapiens and our early ancestors have engaged in endurance running for more than a million years, and have done so with no shoes, or with minimal footwear (sandals, moccasins, etc.). The researchers wanted to know how these early humans (and some humans today, let’s not forget) were able to run comfortably and safely sans shoes. Daniel Lieberman, professor of human evolutionary biology at Harvard, and his crew found that barefoot runners land either on the balls of their feet or mid-foot (the balls of their foot and heel at the same time), while shod runners land on their heels, or heel-strike, to use the lingo. This makes sense when you look at the structure of our feet; our strong, high arch acts like a spring when we run, and this spring can only be loaded when we first land on our forefoot. It wasn’t until the 1970’s when running shoes came equipped with highly cushioned heels that it began to seem normal to run heel-to-toe. (Some research even suggests that not just running shoes, but all shoes are detrimental to our foot health)
With some super advanced equipment (Harvard undergrads are so lucky), Lieberman saw how much of an impact heel-striking causes. When you heel-strike, your foot comes to a dead stop, causing your foot and leg to have to absorb all of that kinetic energy (a force which is 2-3 times your body weight). When you land on your forefoot, however, some of that kinetic energy is converted into rotational energy as your foot goes from toe to heel. This is obviously much less jolting. The researchers hypothesize that heel-striking is the cause of a lot of running-related repetitive stress injuries, and by avoiding heel-striking, more runners could see less of these types of injuries.
If you want to try running barefoot (and I recommend), Lieberman cautions that you shouldn’t just jump into it (especially if it is February in Minnesota), but rather start slowly. Running barefoot uses different muscles and it takes a little while for your feet to get used to it if you’ve been a shod runner your whole life. Who knows, your feet may be your new favorite shoes.

Feb
17
2010

What is it?: It's... ah... you know, whatever.
What is it?: It's... ah... you know, whatever.Courtesy Reytan
Roll up your sleeves and prepare a glass of filtered water, Buzzketeers, because it’s time to learn about the Guinea worm. It’s time to learn about the Guinea worm… hard!

In case the title of this post didn’t spoil it for you already, or if your mother printed out the page but cut off the title, or in case your eyes just don’t read letters that big, the Guinea worm grows to be up to three feet long. Inside you. And even though everything that enters my body must first pass through flame, it still freaks me out.

The parasitic guinea worm, or dracunculiasis (which means “afflicted with little dragons”—you’ll see why in a second), was once found in 20 countries across Asia and Africa, but improved sanitary conditions have reduced its range to just 4 countries in Sub-Saharan Africa. Which is cool, because the Guinea worm is super gross and bad, but not good enough, because the Guinea worm is super gross and bad.

The worm works like this: little worm larvae swim around in puddles and ponds until they get eaten by teeny, tiny crustaceans called copepods (sort of like little shrimp). They live and grow inside the copepods until the copepods get swallowed by people drinking unfiltered water. (Just to be clear, this isn’t just any unfiltered water. If you’ve got electricity to power a computer to read this, there’s pretty much zero chance that there are any worm-carrying copepods in your water. If it came from a tap and not a puddle, you’re probably cool. And even if it came from a puddle, you’re probably still cool.) The copepods get dissolved in the drinkers’ stomach acid, but not the baby worms, which then move from the stomach to the abdominal cavity. There, the worms mate. The male worms die and get absorbed, but the female worms wriggle their way deeper into the body, and grow. And grow and grow. Until they’re about three feet long. They live inside their human host for a year, and then they form a blister somewhere on the surface of the person’s body. When the blister bursts, the female worm emerges just a little bit. The worm releases chemicals that cause the blister to have a very painful burning sensation, and when the host puts the affected area in water to cool it, the worm releases hundreds of thousands of worm larvae into the water, where the cycle can begin again.

As if that whole experience weren’t uncomfortable enough, the treatment isn’t a whole lot better. Because there’s no medicine for Guinea worm infection, the adult worm itself must be removed. The way to do that is to grab the exposed bit of the worm and wrap it around a twig or a piece of cloth, and then twisting the twig. But it has to be done slooooowly so as to not break the worm while it’s still inside your muscles—the process, which is said to be extremely painful, can take up to a month before the worm is fully removed. It’s thought that the ancient symbol for medicine, a snake wrapped around a rod may have been inspired by this procedure.

So, you know… ouch, blech, ouch.

Becoming infected once confers no protection from getting infected again, so people can get Guinea worms over and over again, and in addition to being painful, the blister the worm creates can make the sufferer vulnerable to more dangerous infections.

The good news is that preventing infection is relatively simple; infected people shouldn’t wash in water that will be used for drinking, and simple filters can keep people from ingesting the copepods that carry the worm larvae.

President Jimmy “Billy who?” Carter’s non-profit organization, The Carter Center, has been working for the last 20 years to eradicate the parasite. Despite some pretty significant barriers, it is expected that dracunculialisis will be the second disease, after smallpox, to be completely eradicated through human efforts. (Here’s a recent article on that.)

From what I’ve read (and what the Carter Center says), it looks like humans are the Guinea worm’s only host. So it seems to me that eradicating the infection would cause the extinction of the species. Think about that for a second. Usually sciencey types are pretty much completely against driving other organisms to extinction. But it seems like this one… considering how it pretty much only makes life worse for people who are already dealing with some serious challenges… should maybe… maybe… go extinct? I mean, obviously, right? But try that one on for size; I bet you haven’t often said to yourself that you’re cool with something going extinct. It’s a strange experience.

(If you just can’t deal with it, Here’s a website devoted to saving the Guinea worm. It’s satire, but subtle enough that you could probably play along. But, um, remember that sometimes the Guinea worm emerges from the eyes or genitals of its host. Just saying.)

Feb
17
2010

Ibex: Capra ibex
Ibex: Capra ibexCourtesy Nino Barbieri
A recent article in the Journal of Archaeological Science reminded me of the importance of the Scientific Method Often we hear new and exciting scientific theories that seem plausible, especially if these ideas are presented in prestigious journals. However, the beauty of the Scientific Method is its verifiability, whether or not the data can be recreated through repetitive testing (If we truly believed everything the first time, our budding young scientists would have nothing to do!)

Michael Campana from the University of Cambridge and colleagues from across the UK and Ireland recently ran a sequence of DNA tests on 18th and 19th century parchments made from animal skins in order to reveal the complexities of ancient parchment analysis. Parchment is one of the most valuable archaeological and historical artifacts that can be used to understand not only language and history, but DNA testing on it can reveal clues to animal population studies, animal husbandry, different historical animal breeds, and provenance (where the animal or skins originated from). In the case of the Dead Sea Scrolls, DNA testing on the parchment could reveal what type of animal was used and possibly where it came from, providing additional data for questions regarding who wrote the scrolls.

Campana and colleagues analyzed both mitochondrial and autosomal genetic data using stable isotope, genetic, phylogenetic and ion beam analysis. All samples were considered to be well preserved and ideal samples for accurate testing. All but one parchment produced multiple DNA sequences that matched several different species including cow, goat, sheep, and even human. In other words, a parchment assumed to be made from one individual of one species, gave conflicting results as more than one species or more than one individual. Of course it can be assumed the parchment was not made of human skin and therefore human genetic data must have came from handling and processing of the parchment, but parchments can also be contaminated in long-term storage or contact with each other. Testing results can also be skewed by glues and inks or other preparatory treatments used to improve the surface. All of these factors need to be considered when testing truly ancient parchment like the Dead Sea Scrolls.

Previous DNA test results from 2001 and 1996 on the Dead Sea Scrolls produced results pointing to a single species, either ibex (Capra ibex) or domestic goat. While these results may indeed be correct, the likelihood that the results were so exact, when testing such as Campana's and colleagues on better preserved and more recent parchment were so complex, questions the accuracy of the earlier DNA testing. Of course we must not forget, precious artifacts like the Dead Sea Scrolls can not be needlessly dissected to offer unlimited samples for DNA testing labs. But as, Campana states, “Improving our understanding of parchment's DNA content would allow us to develop a predictive model for sampling of historic manuscripts.”

So the messages for today, bravo for the Scientific Method and go see the Dead Sea Scrolls at the Science Museum! Learn the science, archaeology, history and more that surround these amazing artifacts. Ask questions like: did the scroll writers choose ibex for some scrolls over goat because they thought these documents were so special or was ibex as readily available as any other animal species? Did the handling of the scrolls by shepherds who supposedly found them contaminate the actual scroll DNA with sheep, human or goat DNA? What can DNA testing tell us about other ancient artifacts? As long as there are unanswered questions, no matter how small, there will be a need for scientific investigation; which is good news for our future scientists!

Feb
14
2010

Naked Mole Rat: a mighty survivor both hairless and nearly blind
Naked Mole Rat: a mighty survivor both hairless and nearly blindCourtesy MissTessmacher
The naked mole rat (Heterocephalus glaber) is truly one of the most remarkable animals on this earth. On average 3 inches long and weighing just over an ounce, one would not think this creature so high and mighty. However, its unusual traits have brought it under more medical scrutiny and established an ever increasing presence in research laboratories. Stories have rung for years about how the only species to survive a world Armageddon would be cockroaches and rats. My money is on the naked mole rat.

While called a rat, they are one of 37 species of mole rats globally and are more closely related to guinea pigs and porcupines than other Rodentia. Limited to parts of East Africa, they spend their lives under ground in a highly social commune of individuals, all governed by a queen. This is very similar to the eusociality seen in bees and ants. The queen is the only female to breed, with all other individuals serving as guards or workers. This unusual social life for a mammal in a colony can lead to fierce competitions among females when the old queen dies. It may take days or weeks of power struggle before life in the colony returns to normal.

In search of plant tubers for sustenance, they dig through the dirt with their teeth, developing a system of burrows that can carry on for miles. One of the naked mole rats remarkable features is its ability to survive in the high carbon dioxide environments of these tunnels. Their extremely low metabolic rate and high absorption of oxygen allow them to overcome the limitations of the cramped and congested space. Research has found that these mole rats are void of a pain transmitter called Substance P found in other mammals, and have an uncanny resistance to the oxidative stress of daily metabolism.

Researchers hope this could lead to new insights into the process of aging. Captive research colonies have had individuals live as long as 28 years. That is more than nine times as long as a research mouse! This longevity and unique durability lead even more scientists to consider the naked mole rat for captive study populations in the fight against other afflictions like stroke and cancer. If these superman-like traits haven’t given you a deeper appreciation for such a tiny hairless creature, perhaps you just need a clever ditty to sing their praises. Oh! …you so UGLY!

Feb
13
2010

The Horse in Motion - Edward Muybridge: Eadweard Muybridge used photography to study animal movements - helping to answer a much debated question about whether or not all four of a horse's hooves left the ground at the same time during a gallop.
The Horse in Motion - Edward Muybridge: Eadweard Muybridge used photography to study animal movements - helping to answer a much debated question about whether or not all four of a horse's hooves left the ground at the same time during a gallop.Courtesy Eadweard Muybridge

Scientists who study animal behavior have always had their work cut out for them. For one thing, animal behavior is complex, often involving tiny movements that are not visible to the naked eye. When studying the behavior of animals in groups, this can become even more complicated. Where do you begin to look for patterns? How do you make sense of what you see?

Another difficultly of studying animal behavior comes in designing research tools and experiments that don't interfere with the animal's natural environment. If you've ever tried to walk up to a bird or a squirrel, you know how hard it can be to get close enough to take a good look. The slightest movement or sound, even smells that humans can't smell, can put animals on edge, which might alter the way that they behave.

Over the years, recording equipment and new technologies have made it possible to study animal behavior in new ways. From the invention of photography, which allowed researchers to "freeze" animals and then to set those images in motion, studying how animals move - to newer kinds of imaging techniques that allow today's scientists to observe animal behavior in difficult situations, studying imperceptible changes in their bodies and brains as they move.

This article from The Scientist magazine details how a few researchers have overcome obstacles to studying animal behavior, including the story of a researcher who uses infrared heat-sensing cameras to study the flight trajectories of bats in Brazil. Using ordinary cameras, the necessary lights would disturb the natural behavior of the bats, but infrared cameras give researchers a glimpse of how a very large group of bats behaves at night.

This technology can also be used to study the collective group behavior of other creatures, from very large elephants, to butterflies. Check out the video below to see what bat researchers in Brazil saw when they put these cameras inside a cave.

Feb
09
2010

Playing with fire: Delicious fire.
Playing with fire: Delicious fire.Courtesy esherman
The people of the world wait, their breath held, their tongues clenched between their teeth, open cans of Fresca frozen halfway to their mouths. What do you mean, JGordon? Does soda give me cancer? Or not?

Well?!

Don’t worry, folks. It’s mostly “or not.” Or is it? Or not.

You may have heard (or read—I call it “hearing with your eyes”) that soft drinks might raise your chances of developing cancer. That was probably hard to hear (or read—I call “listening through your face-holes”), because I know you’re generally pro-soda, and generally anti-cancer, and you had been living your life in the hope that there would never be any conflict between the two. You can probably go on living like that, because it’s unlikely that pop is really going to give you cancer, but you should be aware that the world is a complicated place, and your soda and your cancer are sadly not excluded from the complications.

See, a the results of a study out of the University of Minnesota were recently published claiming that there seemed to be a link between the regular consumption of soft drinks (sugar-sweetened carbonated beverages) and a higher incidence of pancreatic cancer. Pancreatic cancer isn’t one of the fun cancers (like, ah, cancer of the… nothing). Although relatively rare, the three-year survival rate for people diagnosed with pancreatic cancer is about 30%, and the survival rate after five years is only 5%.

The study was based on a 14-year survey of 60,524 men and women in Singapore. Of that group, 142 people developed pancreatic cancer. Examining the lifestyles of those who did and did not develop cancer, the researchers found that people who drank two or more soft drinks a week (5 was the average) had an 87% increase in their chances of getting cancer. And because Singapore is a fairly wealthy country with good health care, the scientists think that the results could apply fairly well to western countries as well.

Oh, no! Right? I can’t give up RC Cola!

Well… eh. The thing to keep in mind is it’s all very complicated. Even if there was a direct link between sift drink consumption and pancreatic cancer, your chances of developing the cancer, even as a soda drinker, would still be very small. But, the thing is, there isn’t necessarily a direct link between the two; there’s an association here, but maybe not a causal link. That is, people who drink soda are more likely to get pancreatic cancer, but we don’t know it’s the soda that causes the cancer.

Soft drink consumption itself was associated with behavior like smoking and red meat consumption, so it’s difficult to say that it’s just the soft-drinking (as it were) that contributes to the increased cancer risk.

Researchers do think, however, that it’s possible that soda could be involved in a causal relationship with the cancer. The high sugar levels in soda probably contribute to increased insulin production and presence in the body, which may contribute to pancreatic cancer cell growth. The study also found, however, that there was no association between fruit juice consumption and pancreatic cancer, which sort of makes me wonder. Lots of fruit juice, after all, is very sugary (even if it’s not quite so sweet as most soda). So does it have something to do with the type of sweetener used? Most soda in this country is sweetened with corn syrup, but that’s not necessarily the case in other countries (see Coca Cola for an example), and there’s some debate as to how the body might react to different sweeteners.

Anyway, you aren’t completely taking your life in your hands if you finish that can of Fresca. (Fresca was probably a bad example, seeing as how it uses artificial sweeteners, and will probably give you a totally different kind of cancer.) You’re better off just taking the dip out of your mouth. It’s gross with Fresca anyhow.

Feb
08
2010

The Discovery of King Tut: Howard Carter, staging the discovery of King Tut, in 1922.
The Discovery of King Tut: Howard Carter, staging the discovery of King Tut, in 1922.Courtesy Wiki Media Commons
Science Buzz bloggers have been buzzing about this topic for some time, but as the time draws near, I thought I would jump in for those new to Science Buzz. The rapidly expanding field of DNA analysis is now being used to verify the genealogy of the great kings of Egypt. Zahi Hawass, chief of the Supreme Council of Antiquities in Egypt, has announced that on February 17th, 2010 he will be revealing the results of DNA testing on the famous mummy of the boy king, Tutankhamun. DNA testing has already been done on King Amenhotep III (who reigned from approximately 1388 to 1351 BCE) for comparison as he is believed to be either Tut’s father or grandfather. The mummy of Amenhotep’s son, Akhenaten (who could be Tut’s father), has yet to be found. Researchers also plan to test the DNA of two mummified fetuses found in the tomb to determine if they are related to Tut and shed light on whether King Tut’s bride, daughter of Akhenaten, was his full sister or half sister.

Despite the popularity of King Tut and the splendid artifacts found in his tomb, he is actually only a minor figure in the history of Egyptian pharaohs, reigning for a mere 10 years in a time of great unrest. The story of Akhenaten is more interesting. Akhenaten, who ruled from 1352 to 1336 BCE, is famous for changing both religion and artistic style in Egypt, what is now known as the Amarna Period. Akhenaton introduced a new monotheistic cult of worship surrounding the sun disc Aten and excluded all other Egyptian gods from being worshipped in an effort to suppress the powerful priesthood of Amun.

Pharaoh Akhenaten: Classic Amarna Period sculpture of the Pharaoh Akhenaten.
Pharaoh Akhenaten: Classic Amarna Period sculpture of the Pharaoh Akhenaten.Courtesy Hajor and Wiki Media Commons
Artwork during the Amarna Period took on a more naturalistic style and often emphasized affectionate family scenes of the Pharaoh with his wife Nefertiti and their children. Of interest to many art historians is the depiction of Akhenaten himself. He is represented with an accentuated feminine appearance, rounded protruding belly, wide hips, long slender limbs, and a long thin face. Some believe it is a purposeful political depiction stressing his belief in equality of the sexes, some suggest he was a hermaphrodite, and others suggest he had Marfan’s syndrome. People with Marfan’s syndrome are usually very tall with long thin arms and legs, have thin faces, and funnel shaped chests. Unfortunately, until his mummy is located this will remain a mystery.

When Akhenaten died, the priests of Amun regained power, striking Akhenaten’s name from Egyptian records, reversed all of his religious and governmental changes, and returned the capitol to Thebes. His son, Tutankhaten changed his name to Tutankhamun to honor Amun and became the now famous boy king ruling from 1336 to 1327 BCE.

Mr. Hawass has announced plans to test all the royal mummies using their new $5 million DNA lab in the Egyptian museum. However, there is some concern in the scientific field that he will not submit results to labs outside Egypt for independent verification as is common practice in DNA testing. For example, DNA results of Hatshepsut, Egypt’s famous, powerful and only female pharaoh have never been released. Our fascination with the pharaohs is sure to continue for many more centuries.

Feb
08
2010

Viral hemorrhagic septicemia: a fish infected with the virus
Viral hemorrhagic septicemia: a fish infected with the virusCourtesy Dr. Mohamed Faisal
No… not a rock bass (even though it has a red iris). Nor any normal walleye you might be lucky enough to snag. This fish you might not even need to actually catch. It could be floating next to the boat along with most of the other fish in your favorite river, lake, or reservoir. That is if the dreaded VHS continues to spread and strike us deep in the land of 10,000 lakes. Move over zebra mussel, Eurasian milfoil, and the Asian carp, VHS is viral hemorrhagic septicemia and the latest migrant in the spread of invasive species.

Viral hemorrhagic septicemia (VHS) is a virus. It is a small invading critter that can be quite infectious. Not all fish will show obvious signs. Those that do can exhibit hemorrhaging in the eyes, around the fins, or on the gills. Bloating, erratic behavior, bulging eyes, or even lesions could also be present. On the inside, the disease will attack the liver, kidneys, spleen or swim bladder. Those fish that do survive can still be infected and spread the disease. Blood, urine and even the reproductive fluids of infected fish can pass on the virus. Larger fish can get it from eating smaller infected fish.
Fish kill: sights like this are all the more possible with the new viral invader
Fish kill: sights like this are all the more possible with the new viral invaderCourtesy JoelDeluxe

The disease can be wide spread and is known to affect up to 28 different species of fish. Some of the fish kills have numbered in the tens of thousands. Many of our popular game fish are susceptible. Walleye, Northern Pike, Muskellunge, Smallmouth Bass, Perch, Crappies, Bluegills, Sheepshead and many others are on the list. Even some species of shiner bait fish have been found to carry the disease. While deadly for many fish, the disease is of no harm to humans. The warmth of our bodies is too hot for the virus to survive.

The virus has been known for many decades, but until recently was mainly a scourge of European fish farms. Viral hemorrhagic septicemia was first detected in American coastal waters in 1988, among the salmon populations of the Pacific Northwest. Then in 2005, tested fish showed up positive between Lake Huron and Lake Erie, and were confirmed in samples harvested two years earlier. Now, local news just recently reported on a Cornell study that found VHS diseased fish in the bay waters of the Duluth-Superior harbor on the western edges of Lake Superior. Make no mistake… the ‘bleeding fish’ disease is here at our doorstep.

Guests of the inland waterways will be reminded to be vigilant in safe boating and fishing practices by local resource managers. Be mindful not to transport fish, plants, or bait from one water body to another. Keep those live-wells empty, and dry or rinse that boat! It will fall upon all of us to remain vigilant. Let’s not allow this disease to become a crippling blow to our native fisheries. If we do, it is possible that we’ll witness many seasons of massive fish kills.

More good VHS information:
Wisconsin Dept. of Natural Resources

Univ. of Wisconsin Sea Grant

Feb
07
2010

Underwater, or “internal” waves, unlike the familiar wind-generated surface waves, occur due to density stratification often generated by coastal tides. These internal wave can lead to redistribution of nutrients and minerals. Internal waves can also cause vertical “velocity shear”, intensifying the vertical mixing process within the water column and bringing suspended particles and nutrients to the surface. Understanding and tracking these internal waves is another way to monitor the vital signs of an estuary.

Internal waves
Internal wavesCourtesy CMOP

CMOP successfully launched its new autonomous underwater vehicles (AUV) to help scientists gain a better understanding of the Columbia River estuary. One of the first studies to use these vehicles will be directed at internal waves. Craig McNeil, oceanographer from the Applied Physics Laboratory at the University of Washington and CMOP investigator, is using AUV’s to study the generation and propagation of internal waves in the Columbia River estuary and plume. He's interested in the physics of internal waves and mixing near the sea surface and the sea floor.

McNeil said,

“Scientists speculate that some bottom following internal waves have closed circulations that traps water and biology. The AUVs will help us sample these waves so we can better understand these complex mixing mechanisms.”

One upcoming experiment will study the dynamics of the freshwater plume as it spreads out over the denser saltwater of the coastal ocean. Of particular interest is to compare measured observations with theoretical predictions. McNeil will program the vehicles to travel into the advancing plume and navigate through the plume front. This will allow CMOP to study the progression of internal waves that are known to be generated at the advancing plume front and determine their propagation speed.

Watch researchers deploy the AUV: Watch Craig, Troy, and Trina deploy the AUV in the Columbia River.
Watch researchers deploy the AUV: Watch Craig, Troy, and Trina deploy the AUV in the Columbia River.Courtesy CMOP

Before those measurements could take place, McNeil needed to test the vehicles’ capabilities in the field. Along with oceanographer Trina Litchendorf and field engineer Troy Swanson, McNeil tested the vehicle in Lake Washington over the winter months. By spring the team was ready to take it through its paces in the Columbia River estuary.

They traveled to Astoria, Oregon, and met up with CMOP’s field team for the vehicle’s first mission in the river. They decided initial tests would be conducted during slack tide due to the limits of the vehicle in strong currents. The mission was based on tidal cycle information supplied by CMOP’s cyber-team. The expected velocities during slack tide would be less than 0.5 m/s or about 1 knot, which was in the acceptable range for the vehicles

The vehicle was deployed near the first transponder set by the team in the North Channel of the Columbia River. There it performed a compass calibration and proceeded to its first designated waypoint. To make sure it was on track, McNeil monitored the vehicle’s position with a device called the Ranger. The Ranger's transponder receives status updates from the vehicle.

Water temperature map: This figure shows a map of water temperature recorded by the CTD on the AUV during its first mission in the North Channel of the Columbia River estuary westward of the Astoria Bridge.
Water temperature map: This figure shows a map of water temperature recorded by the CTD on the AUV during its first mission in the North Channel of the Columbia River estuary westward of the Astoria Bridge.Courtesy CMOP

The results of the mission were a success. The vehicle traveled upon its designated coordinates and collected salinity and temperature data. Now the team has a better understanding of how to control the vehicle’s navigation in the river, which means it will be able to perform longer missions.

McNeil and his team will now use the AUVs to study various physical processes in the Columbia River estuary, including internal waves, currents, and mixing of various biogeochemical components of the water; all of these adding to our understanding of the estuary’s vital signs.

More photos of the AUV deployment: More photos of the AUV deployment
More photos of the AUV deployment: More photos of the AUV deploymentCourtesy CMOP

Feb
07
2010

Estuaries are coastal areas in which rivers and oceans meet. Thus, they include both fresh and salt water, each of which support different ecological communities of plants and animals, large and small. Salinity (“saltiness”) of the estuary is a measure of its health--a vital sign--for those communities.

In some cases, salt-water from the ocean side of the estuary can begin to “intrude” on an area previously dominated by fresh water. It is important to be able to measure and monitor this aspect estuary health.

CMOP has developed a remote sensing device that opens the way for scientists to better understand and predict salinity intrusions in estuaries.

Circuit analog for dipole source on river bed
Circuit analog for dipole source on river bedCourtesy CMOP

Oceanographer Thomas Sanford, Ph.D., and his team from the Applied Physics Laboratory at the University of Washington, have developed a bottom-mounted instrument for measuring electrical conductivity in the water column, which can be transformed into salinity readings.

The current process for measuring salinity involves sensors that provide “point” observations. Sanford’s instrument provides measurements of integrated salinities across the entire water column, allowing a more representative description of salinity intrusion.

How does it work?

Sanford’s approach is to produce a low-frequency electrical current and measure the resulting electric field at a nearby dipole receiver. The received electrical field is a function of the electrical conductivity of the water column and the sediments.

Quasi-static electrical analog circuit: The quasi-static electrical analog circuit for electric currents divided between the parallel resistors of saline water (Rw ) and the sediment (Rs ) is such that: Vr /Is = CRwRs /(Rw + Rs ) = C(Σw + Σs )-1 , ∴ Σw = CIs/Vr – Σs, where Σw is the conductance (vertical integral of σ) of the river, C is an empirical calibration value, Is is the source current, Vr is the receiver voltage and Σs is the conductance of the sediments
Quasi-static electrical analog circuit: The quasi-static electrical analog circuit for electric currents divided between the parallel resistors of saline water (Rw ) and the sediment (Rs ) is such that: Vr /Is = CRwRs /(Rw + Rs ) = C(Σw + Σs )-1 , ∴ Σw = CIs/Vr – Σs, where Σw is the conductance (vertical integral of σ) of the river, C is an empirical calibration value, Is is the source current, Vr is the receiver voltage and Σs is the conductance of the sedimentsCourtesy CMOP

Sanford’s team deployed the system in the Columbia River estuary before and during a flood tide. At the same time, they took measurements with a CTD, a standard oceanography-sampling device that reads Conductivity, Temperature and Depth. As the layer of seawater thickened, they observed the decreased resistance of the water column caused the receiver voltage to decrease.

Previous studies in the Columbia River had demonstrated a tight correlation between electrical conductivity and salinity. This correlation permits the conversion of electrical conductivity to salinity. Sanford’s team collected a time series of water-column electrical conductivity that they converted to salinity. The inferred salinity was shown to agree with the salinity readings from the CTD.

Vertically integrated salinity: Observed vertically integrated salinity from CTD casts (red dots) compared to that inferred from the electrical measurements using the electrical conductance time series fitted to the equation: Sw = 8.82*(CIs/Vr -Σs ), where C is an empirical coefficient equal to 43, Is is source current and Vr is observed electric field and Σs an offset caused by leakage into the sediments equal to 8. Blue dots are observed electrical conductance and the continuous curve is the electrical conductance, both converted by salinity by the factor 8.82 psu/S/m.
Vertically integrated salinity: Observed vertically integrated salinity from CTD casts (red dots) compared to that inferred from the electrical measurements using the electrical conductance time series fitted to the equation: Sw = 8.82*(CIs/Vr -Σs ), where C is an empirical coefficient equal to 43, Is is source current and Vr is observed electric field and Σs an offset caused by leakage into the sediments equal to 8. Blue dots are observed electrical conductance and the continuous curve is the electrical conductance, both converted by salinity by the factor 8.82 psu/S/m.Courtesy CMOP

What's next?

CMOP researchers are looking at Sanford’s new sensor as an opportunity to better explain processes as diverse as internal waves, estuarine turbidity, and summer blooms of phytoplankton (tiny mobile plants that sometimes collect in massive “blooms” in surface waters in estuaries). They expect to improve computer models that are designed to depict the variable conditions of the estuary, and anticipate changes associated with climate and human impact. Once demonstrated for the Columbia River, the new sensor has the potential to be used in estuaries around the world.