fog harvesting for a thirstier world

With droughts becoming more frequent and severe globally, people across the world have been finding creative ways to get a little more water. The residents of Lima, Peru, have long long struggled with a scarcity of fresh water. Bordering the inhospitably dry Atacames desert, Lima recieves a scant 1.5 cm of rainfall annually. Lima’s main fresh water source is glacial runoff from the high Andes during the spring and summer. Unfortunately, Andean glaciers are rapidly disappearing due to climate warming, and Peruvians are struggling to adapt to a future of even more severe water shortage.

The people of Lima do, however, have a plentiful supply of one form of water- fog. Fog sweeps up the South American coast from the Southern Pacific Ocean and rolls over the slopes of Lima year round. In the rural villages surrounding Lima, fog harvesting has been used by farmers for thousands of years. Cæsalpinia spinosa , commonly known as the Tara tree, is a small, shurb-like tree native to Peru that has evolved to survive in this arid environment by literally sucking water out of the air. Excess water that the Tara trees do not use runs off the trees and replenishes groundwater that has been lost due to years of drought. It also provides a convenient source of fresh drinking water for locals.

Gaia Vince reported for Science last month from a shantytown just outside Lima that has decided to scale up and modernize this age-old technique. On the tops of sand dunes, residents have constructed a series of 4 meter high mesh nets for trapping fog water. These nets are stretched  taught and faced perpendicular to the prevailing wind. As tiny fog droplets stick to the nets, they clump together and form large drops, which are collected as runoff by the bucketful. In conjunction with fog harvesting nets, locals have planted saplings that will soon be large enough to trap water themselves. This system has already been successful enough that nearby villages have set up similar projects. In the future, fog harvesting forests could provide Peruvian communities with an entirely self-sustaining means of obtaining water.

If you’re interested in learning more about fog harvesting, you can check out , a nonprofit organization devoted  implementing fog harvesting projects for rural communities.

lemmings demystified

Imagine a lemming.

If you, like me, have never seen one of these creatures or bothered to read up on them, you may be picturing a furry, yellow/orange little creature that travels in large groups. And occasionally commit mass suicide. Sound about right? Other myths and misconceptions about lemmings abound. A theory dating back to the 16th century proposes that lemmings fall out of the sky on stormy winter days, only to die suddenly when fresh grass begins to grow in the spring.

This is what a lemming actually looks like! It’s a herbivorous rodent thats population ranges from well north of the Arctic circle down into Norway and other parts of northern Scandinavia. They do not hibernate over winter, but remain remarkably active, burrowing through the snow to search for food. They are notable in the small scientific community that studies wild rodents for their chaotic population fluctuations. When population densities become very high, lemmings may migrate long distances, crossing rivers or even lakes to find new homes. Many will drown or be killed by predators in this process. These perilous journeys are what probably gave rise to the popular myth about lemmings committing mass suicide.

An entirely different theory about lemming population dynamics was proposed by researchers in Greenland and became a hit among ecologists for portraying what may be the simplest predator-prey interaction in the world. These scientists studied the collard lemming in Karup Valley, a high arctic-tundra site located at 72 degrees north latitude. In this harsh environment, lemmings are preyed upon by four species: the stoat, the arctic fox, the snowy owl and the long-tailed skua. The study points to the key role that these predators play in curbing lemming populations. With the exception of the stoat, lemming predator populations are finely attuned to lemming population density. When populations of lemmings reach a certain critical mass, predator density spikes, which in turn leads to a rapid drop in lemming populations. The fox, owl, and skua are all responsible for keeping lemming populations in check in the winter. The stoat, however, hunts lemmings year round. When the other three predators have stopped hunting lemmings towards the end of summer, the influence of stoat predation increases and is ultimately believed to cause lemming population crashes.

Take home message? Mass suicide, though far more dramatic and intriguing, may in fact be a simple coupling of rodent population booms with intense cyclical predation. Sometimes science takes the drama out of life.

Check out my new blog here.



Maybe we should reconsider raking our leaves

I recently learned a fascinating fact about leaf raking that should be painfully obvious to a forest ecologist- it’s bad for trees! Every spring, deciduous trees produce leaves that they use throughout the growing season for photosynthesis and sugar production.  Plants concentrate essential nutrients such as nitrogen, potassium, calcium and magnesium in their leaves, as these nutrients are all required in relatively high amounts to perform photosynthesis.

As winter approaches and the growing season ends, trees withdraw many of the proteins and nutrients they have stockpiled in leaves back into their woody tissue, so that these nutrients can be recycled to make new leaves the following year. However, most trees are able to do even better than this- after their leaves have fallen, the nutrients that couldn’t be recaptured in time are decomposed into the surface soil surrounding the tree, and will be available for uptake through the roots several years later. This regular flux of plant essential nutrients back to the soil through leaf litter means that plants depend on those same nutrients, year after year, to grow new leaves.

In fact, if you look at the typical architecture of a deciduous tree, it is no accident that probably appears like two umbrellas attached together at their handles. The top umbrella is the above ground parts of a tree from the base of the trunk to its canopy. The bottom umbrella is inverted and planted into the ground. It is composed of a main taproot that drives straight down into the earth, and lateral roots that branch out horizontally. Of these lateral roots are branching networks of finer and finer “root hairs” and associated fungi that are able, through their enormous surface area, to mine the soil underneath a tree for nutrients. Everything that is dropped from the top umbrella should theoretically be recoverable by this root system.

I’d imagine most of you can already see where this is going, but I find that sometimes simple truths are quite elusive. When we rake our leaves in the fall to maintain our clean, grassy lawns, we are removing loads of nutrients that our trees are expecting to get back! We are creating an artificially open, leaky system, that trees have spent millions of evolutionary years refining. A recent paper in a relatively esoteric research journal, “Nutrient Cycling in Agroecosystems” (who reads that??) attempted to quantify the impact of historic leaf raking on old agricultural towns in central Europe. The fascinating bit of historical information in this paper is that centuries ago, medieval farmers actually knew that leaves were a great nutrient source- farmers removed leaves from nearby forests specifically to use as fertilizer on their fields. This paper claims that the result of historic leaf raking is that the “majority of central European forests were severely depleted of nutrients…when modern long-term rotation forestry became the dominant form of forest land use”.

So next fall, when you’re pulling out your rakes or enlisting your kids to do so for a few dollars, think carefully about your trees. In all likelihood, the average patch of suburban lawn is already so nutrient depauperate from numerous land use changes (deforestation, asphalt paving, over-fertilization, the cultivation of a monoculture of non-native grasses, to name a few) that removing a few leaves isn’t going to make a big difference. But if I’ve learned anything from Malcom Gladwell, it’s that little changes that add up to produce big effects, and if medieval Europeans were knowingly removing nutrients from their forests, I figured modern suburbanites should at least be aware.

Acid oceans and the next 800,000 years

Have you heard the term “ocean acidification” being thrown around in the popular media recently? If you have heard a bit about this phenomenon but you’re not a climate scientist, it’s likely that you’ve been left with the impression that ocean acidification is yet another in a long list of the potentially nasty consequences of climate change. Probably something for the scientists to be concerned about, but not nearly as pressing as the melting of polar ice caps or the possibility of a twenty foot rise in sea level. However, given the invaluable ecosystem services and role in climate regulation that our oceans provide, I find it shocking that so little attention has been paid to ocean acidification, a process that we understand much more precisely than the elusive changes in global climate associated with rising CO2 levels.

Ocean water is slightly basic, just around pH 8 (the water we drink is generally neutral or slightly acidic, around pH 7). When CO2 from the atmosphere dissolves at the ocean surface, it reacts with water to form a balance of different “carbonate species”. The most abundant form that this dissolved CO2 converts into is bicarbonate, HCO−3. The prevalence of bicarbonate in oceans is due to their basicity. However, as more CO2 dissolves in water, the balance of carbonate species shifts. Bicarbonate begins losing a hydrogen ion and becoming carbonate, CO-3. This results in a release of free hydrogen ions (H+) into the water, which increase its acidity.

If you’re not a chemist, why would you be remotely interested in the balance of carbonate and hydrogen in the water? The reason ocean pH is so important is that all organisms and biological processes that occur in the ocean are finely attuned to changes in water chemistry, much as we can feel the slightest changes in atmospheric chemistry  that cause the difference between a hot sticky day and a hot dry day. However, the acidification of oceans isn’t just a comfort problem for marine organisms- a slight attenuation of ocean pH can represent a lethal environmental change.

Many marine organisms produce exoskeletons made of calcium carbonate. Calcium carbonate, molecular formula CaCO3,  forms when a calcium atom and a carbonate ion bond together and precipitate out of solution. This is called calcification. It is essential to the survival of corals, a variety of shelled invertebrates, and single celled planktonic organisms that play an essential role in ocean photosynthesis and nutrient cycling. However, an increased abundance of H+ ions in the water interferes with the formation of calcium carbonate. In fact, calcium carbonate formation is so sensitive to pH that a fraction of a pH unit can make the difference between a habitable and a lethal environment.

So, a summary of why we should be worried about CO2 in the oceans: Increased CO2 alters the balance of carbonate in ocean water and causes the release of protons, which by definition increases acidity. This in turn prevents the formation of calcium carbonate, which is essential to the survival of a variety of marine organisms.

What kind of damage are we looking at if calcium carbonate stops forming? One of the largest challenge climate scientists face is giving accurate predictions of the ramifications of climate change (the other is communicating these predictions and their significance to the public, a task which has thus far been a resounding failure). The most useful resource we have in making these predictions is the past. Climates have been highly variable over geologic history, and the earth has experienced periods of much higher CO2 levels and correspondingly warmer climates. With regard to oceans, we know ocean CO2 levels increased dramatically about 251 million years ago, at the end of an era known as the Permian. The end of the Permian also marks the largest extinction event in Earth’s history, with up to 96% of all marine species disappearing. There is still much debate as to the cause of the Permian extinction, but there is growing evidence that rapid acidification may have been a primary driver in the oceans. But how fast is ocean pH dropping today compared to past acidification events?  William Howard of the Antarctic Climate and Ecosystems Cooperative Research Center in Hobart, Tasmania stated this past July that  “the current rate of ocean acidification is about a hundred times faster than the most rapid events” in the geologic past.

Maybe this is a little dramatic. But whether or not we believe that acidification caused a huge extinction event in the past, the fact remains that the functioning of many marine ecosystems today is entirely dependent on the ability of a select group of organisms to precipitate calcium carbonate. Coral reefs provide the a habitat for thousands of other species, but without their calcareous exoskeletons, their soft tissues would not be able to survive. Calcareous phytoplankton nourish huge regions of open ocean due to their ability to produce sugars from sunlight. Many human populations rely on calcifying shellfish as a valuable food and economic resource.

Globally, ocean pH has already dropped about 0.1 unit. A drop of another 0.3 to 0.5 pH units is predicted by 2100. In most surface oceans, this level of pH change will make the precipitation of solid calcium carbonate energetically impossible. In short, we are on a trajectory for change that we may only have a small window of opportunity to alter, if our chance has not already past. If we are worried about economic costs associated with dramatically reducing our CO2 emissions today, it might be valuable in our cost-benefit analysis to consider the reduction in quality of life our children will face in a world whose oceans are biologically impoverished.

the meaning of life

when most people hear the word “virus”, the first image that comes to mind is generally something along the lines of a sick person, an epidemic, trips to the doctors office, vaccinations, or, for those with some biology background, a crystalline, nightmarish spider-alien injecting DNA into a defenseless cell. viruses are generally perceived as perpetrators of malaise, a scourge to society that modern science can and will eventually eradicate. only in the past decade, since the advent of fast and relatively cheap genetic sequencing technology, have scientists begun to recognize the staggering diversity of viruses in the world, many of which are entirely benign and have no known ecological function. the dawning realization that really are just about everywhere- they are ten times more abundant than bacteria in the ocean- indicates an incredibly effective strategy for self-propagation. this strategy in turn represents  a form of existence so simple that scientists have been debating for decades whether or not viruses can be classified as life.

despite their apparent simplicity, understanding viruses has been one of biology’s greatest challenges since the beginnings of the molecular revolution. the traits that we have discovered to be ubiquitous among viruses are relatively straightforward. generally, a virus consists of a single piece of naked DNA, encapsulated in some sort of protein-based coat. viruses cannot be considered cells because they contain none of the internal machinery necessary for growth or self-replication. instead, many viruses replicate by inserting their DNA into the cells of a host. this invading DNA is able to co-opt the host cell’s own replication proteins, and turn the host into a small factory for new viruses.

many but not all of the viruses that cause human disease use this strategy, and they often do so with alarming efficiency. another common viral replication strategy is to insert DNA into a host, and integrate that DNA into the hosts own DNA. viruses that employ this strategy are effectively choosing symbiosis inside a host, and replicate themselves in step with the host cell’s own cycle.

it may seem strange that some viruses act aggressively- invading, replicating and moving on once they have plundered all the resources available, while others choose a life of harmless symbiosis within their host. how can we come up with a general definition for all viruses if this is the case? shouldn’t we classify these critters as two unique types – neither truly alive perhaps, but fundamentally different in their non-living existence?

to answer this question, one must think carefully not about what viruses are doing but why. in both cases, a fragment of DNA is simply trying to replicate itself in the most effective way possible. for some, this means integrating itself into an organism, and reproducing in concert with the organisms own generations. for others, it means rape, kill, pillage and burn. viruses  are the ultimate narcissists- no ambitions for complex structure or function,, simply a raw, unabashed need for self-propagation.

if existence driven entirely by the need to replicate and produce more of oneself what it means to be a virus, i don’t think it’s a far stretch of the imagination to draw parallels with organisms that we officially classify as “alive”. with simple single-celled life, the similarity is easy to see. unicellular bacteria are essentially DNA vessels, but with extra compartments for the tools and machinery required to replicate. some single-celled bacteria do reproduce sexually and, in exchanging DNA, produce offspring that are not genetic clones. nevertheless, the idea is essentially still simple propagation of genes, but given one more level of complexity in that the replication process is self-sufficient.

but how much similarity can there possibly be between a complex, multi-cellular organism, and a single replicating strand of DNA? try thinking of a complex organism, like a cat, horse, or even human, as a nation of cells. each cell is an individual citizen, and each citizen has a specialized job that he must perform as an effective member of the community. if too many citizens dissent, or get lazy, and choose not to perform their allocated jobs, the community falls apart. and what do these citizens, many of whom look and act very different, and would certainly never be caught getting coffee or drinks together, all have in common? dependency on each other for replication.

a human being is orders of magnitude more complex than a virus, and I am not trying to diminish that complexity, or even to claim that it can be reduced to aggregate of cells driven by a simple process. but the common purpose of genes, in everything from their rawest form that do not even consider living, to the most complex organism evolution has produced, speaks to the ancestry we all share.

wyrd evolution

A population essentially evolves through the accumulation of random changes in its genetic makeup over time. These genetic changes modify organisms’ phenotypes, and over time change the distribution of traits in a population. Many traits which become prevalent in a population do so because they make the population more “evolutionarily fit”- better able survive and reproduce in its environment. Darwin coined the famous term “natural selection”to describe this phenomenon, though he wasn’t aware of the complex genetic mechanisms underlying it.

Evolutionary theory is anchored on the principle that the biology of the past has shaped the diversity we see today. Though countless examples in nature substantiate the important role of natural selection in evolution, it is important to understand that natural selection itself is not a conscious force. Rather, it is it is a pattern that produces predictable outcomes. Stochastic probability tells us that, over a long enough time and with large enough populations, traits that allow organisms to produce more offspring will come to dominate a population, simply because the individuals possessing these traits will pass along more of their genes into the next generation.

Because evolution by natural selection is not a conscious force, and because it must work to improve upon what already exists in nature, evolution cannot rapidly produce superanimals that are perfectly adapted to their environments. As the French biochemist Francois Jacob once eloquently described it, evolution is a tinkerer that works to improve upon what is already there, but its creative freedom is heavily constrained by existing body plans and biochemical pathways. Moreover, natural selection works to optimize organisms, not isolated systems. A trait that may seem advantageous, such as a genetic mutation producing enhanced night vision, may be helpful for a large predator on the Savannah, but useless for a cave fish that is rarely exposed to any sunlight and must use other sensory systems to perceive its environment. The cave fish would not develop improved eyesight because the selective advantage conferred by this ability would not outweigh its energetic costs.

As this last example begins to illustrate, natural selection is often working in concert with another force known as selective constraint. When a gene, biochemical pathway, or phenotypic trait is under selective constraint, it is maintained over evolutionary time. There are many reasons that selective constraint could operate. A biochemical pathway could be so fundamental to an organisms ability to survive that any small alterations to that pathway would be lethal. A limb or sensory organ could already be well suited for its environment, or the benefits of  making any changes to it may not outweigh the costs. A single mutation event in a gene encoding an essential protein could alter the protein’s structure and make it useless.

Natural selection and selective constraint are two important paradigms for understanding evolution. They are not the entire story, but they do help us to understand how evolution produces produces change but also propagates sameness. An alien visiting earth 3 billion years ago could not have imagined that the simple life he discovered would lead to the overwhelming diversity we see today. And yet in spite of all the novelty and innovation that has appeared over evolutionary time, this diversity has drawn upon itself, reaching outwards without  breaking its ties to the past.

what is ‘wyrd’?

etymology of “wryd”: an old English word that primarily means “that which comes to pass”. wyrdscience describes natural phenomena and pressing scientific questions which provide us not only with a mechanical understanding of the world, but insight into the social, cultural, and environmental changes that are coming to pass on our planet.

a more metaphysical interpretation of wyrd is that everything in the universe is constantly changing and moving towards some other state, but simultaneously being drawn into itself. all changes an object goes through can be understood through its past, and the myriad of possible trajectories of a change event tend to converge to a single, predictable outcome. wyrd as interpreted this way is useful in understanding many fundamental scientific concepts.

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