Through The Sandglass

Earth Science Week: "Geology helps the land tell you stories"

It's this year's Earth Science Week - see the American Geosciences Institute and Geological Society of London sites). I have periodically attempted to join the celebrations with posts on the "Nine big ideas" and the associated videos, Earth Science Literacy, and the outstanding "known unknowns" of earth science - please have a re-visit.

These were largely ruminations on what geology is about, the "philosophy" of the science, and a little advocacy for greater awareness. The question of why geology, what makes it fascinating, were subtexts, so my attention this year has been caught by a piece from September 2015 by Julia Turner, editor in chief of Slate. Titled "Your World, Rocked: A good introduction to geology course is actually a course in time," it is an eloquent (and personal) testimony to the value (sometimes not so obvious) of even a modest exposure to how our home planet works. It is, of course from the perspective of US education, but that matters not at all - its message is universal. The "rocks for jocks" amusement in the introduction is purely American - and so true. I taught Geology 101, otherwise known as "rocks for jocks" for several years, with many rewards and frustrations. Chief amongst the latter were the many kids who told me how much they enjoyed it, having had no idea at all about geology, and regretted that they were too far down their academic path (having left the science requirement until last) to pursue it further. I doubt that problem has gone away - to the loss of the science. There were many kids who were a joy to teach and interact with (although here I do not include the young woman who entered my office, closed the door, and declared that "Professor Welland, I'd do anything for an A"). But I digress....

In celebration of Earth Science Week, and in the hope that it might persuade just one young person to take a geology class, I am taking the liberty of reproducing in its entirety Julia Turner's piece from Slate:

A good introduction to geology course is actually a course in time.

By Julia Turner

Let me start by defending geology’s honor. Is there any other discipline that a rhyme so easily reduces to ridicule? Nearly every campus has some version of “rocks for jocks,” the intro geology course touted as the easiest way for granite-brained humanities majors to fulfill their science requirements without significant intrusion on their time or erosion of their GPAs.

But you shouldn’t take geology because it’s easy. (It isn’t necessarily easy—the geology class I took, from a bright-eyed elfin woman with the pleasing, rocklike name of Jan Tullis, certainly wasn’t.) You should take geology because it will fundamentally transform the way you see the world.

I mean this literally. Understanding geology gives you a new way to interpret the visual data of the planet. Sometimes this can feel like X-ray vision or a sixth sense. The color of the soil can tell you what it’s made of. The lightning bolts of white across that cliff the highway blasted through? Quartz veins, a sign of metamorphic activity, way back, when fissures opened up in bending, cracking stone, and mineral-laden water coursed through. Looking out of a plane window at the contours of a mountain range, you can tell from shape alone whether the peaks are old or new—or rather, which are very very old and which are just old. (It’s the opposite of human aging: cragginess is a sign of relative youth, and smoothness comes only with time.) And the words! Schist. Nickeliferous. Gneiss. Each one with its own dense poetry.

Geology helps the land tell you stories. I remember flying once and noticing funny little slab-like mountains, each one distinct from the next, lying in parallel rows. Where once I would have seen only mystery, now I could imagine how those mountains came to be—a sedimentary bed, layer upon flat layer of different types of rock, broken and thrust upward by the movement of the plates, revealing a cross section in which the softer rocks had eventually eroded away, leaving only these orderly little slabs.

Geology is a gorgeous way to contemplate the abyss.

But geology does more than give you something to think about when you examine pebbles on a beach or go swimming in a quarry. You should also take geology because there is no better way to gain perspective on the fleetingness of life. Any good intro geology course is actually a course in time. You’ve heard the statistic: If the whole planet has been around for a single 24-hour day, the dinosaurs showed up at 10:56 p.m. and we just before 11:59. But imagine spending hours holding that thought in your mind, learning what happened during all the time that preceded us. Understanding, in a real way, how long the planet has been around; how slow, patient, and indifferent the movement of the rocks beneath us has been; how insignificant in the scheme of things our fervid civilizations and wars and inventions really are—this is a head trip better than any you’ll experience during the concert at Spring Fling..

Taking geology actually had a funny side effect for me. I came into the class an avid environmentalist. I was a child of the ’90s. I cared about whales. I recycled. I spent a semester on a farm. I wanted to keep humans from changing and destroying the planet. But geology complicated my understanding of this desire. The planet has been changing for millennia. It’s been destroyed and remade again and again. The temperature used to be different. The continents were in different places. Different creatures roamed the land. The environmentalist instinct to preserve the planet exactly as it is began to seem not altruistic, but selfish. The planet is a tough cookie. This pile of rocks doesn’t need saving. What we were trying to save, it seemed, was the version of the planet that works best for ourselves. And, sure, future generations and all the other species that currently live here. Still a worthy goal, of course. Perhaps an even worthier one, when you consider how unusual and unlikely Earth’s menagerie is. But geology made me think about it in a new way.

College students often enter university with an outsized view of their own significance. It’s good to study things that make you realize how unimportant you are. As a history major, I took a lot of classes that helped me understand how small my life is in the span of human existence. But there are a few courses—geology, astronomy, perhaps particle physics—that force students to confront true vastness, that make you consider the insignificance not just of your life, but of your entire species. Geology is a gorgeous way to contemplate the abyss.

This is valuable, in the end, because it both helps you care less and makes you care more. What’s a bad day in the scheme of things? But then again, why not make each one count? Something to consider, next time you contemplate the contours of the land.

Indeed.

 

re the stunning image at the head of this post: 

Credit: NASA Goddard Space Flight Center Image by Reto Stöckli (land surface, shallow water, clouds). Enhancements by Robert Simmon (ocean color, compositing, 3D globes, animation). Data and technical support: MODIS Land Group; MODIS Science Data Support Team; MODIS Atmosphere Group; MODIS Ocean Group Additional data: USGS EROS Data Center (topography); USGS Terrestrial Remote Sensing Flagstaff Field Center (Antarctica); Defense Meteorological Satellite Program (city lights)

This spectacular “blue marble” image is the most detailed true-color image of the entire Earth to date. Using a collection of satellite-based observations, scientists and visualizers stitched together months of observations of the land surface, oceans, sea ice, and clouds into a seamless, true-color mosaic of every square kilometer (.386 square mile) of our planet. These images are freely available to educators, scientists, museums, and the public.

Much of the information contained in this image came from a single remote-sensing device-NASA’sModerate Resolution Imaging Spectroradiometer, or MODIS. Flying over 700 km above the Earth onboard the Terra satellite, MODIS provides an integrated tool for observing a variety of terrestrial, oceanic, and atmospheric features of the Earth. The land and coastal ocean portions of these images are based on surface observations collected from June through September 2001 and combined, or composited, every eight days to compensate for clouds that might block the sensor’s view of the surface on any single day. Two different types of ocean data were used in these images: shallow water true color data, and global ocean color (or chlorophyll) data. Topographic shading is based on the GTOPO 30 elevation dataset compiled by the U.S. Geological Survey’s EROS Data Center. MODIS observations of polar sea ice were combined with observations of Antarctica made by the National Oceanic and Atmospheric Administration’s AVHRR sensor—the Advanced Very High Resolution Radiometer. The cloud image is a composite of two days of imagery collected in visible light wavelengths and a third day of thermal infra-red imagery over the poles.

 

"No one actually studies sand" - misconceptions and science literacy

 

For one reason or another (likely to be discussed in a future post), I have been working on an essay that attempts to address cross-cultural aspects of viewing and valuing the land and reviews the potential implications for learning geoscience through integrating "geomythology" (a less than perfect term) into the process.

Coincidentally, in the course of seemingly endless research and reading, I came a across a fascinating geoscience education story on sand. In 2014, the American National Association of Geoscience Teachers published two fascinating issues on the theme of "Teaching Geoscience in the Context of Culture and Place," full of provocative discussion and ideas. In the second issue, one particular paper caught my attention: "Where Are You From? Writing Toward Science Literacy by Connecting Culture, Person, and Place," written by Kanesa Duncan Seraphin from the Curriculum Research & Development Group and the Center for Marine Science Education, University of Hawai'i. As she writes in her abstract:

The ways in which people view the world, and by extension the ways in which they learn, are shaped by cultural context. As educators striving to build scientific literacy among our students, it is critical to bridge the gaps among disparate cultures, traditional ways of knowing, and Western science. Understanding the value of traditional knowledge and welcoming the discourse and novel viewpoints associated with cultural and place-based practices is the first step in opening the door of scientific literacy not only for indigenous students but also for students struggling to find personal relevance in science.

She discusses the disconnects in today's world between science and culture that can "distract students from effectively learning" and goes on to discuss "Activities that connect sense of place and person provide opportunities for students to learn about and integrate the human element of science with scientific research and discovery." Her focus is on personal writing that 

helps students take ownership of their learning and facilitates students’ learning awareness. Writing provides a space for students to connect with their culture and their thoughts—to think about what they know and believe, thereby promoting metacognition and purposeful knowledge generation. Writing also promotes scientific literacy by improving synthesis skills through the construction of a written record.

Among the examples she discusses is a wonderful example of the results of place-based learning by high school teachers taken first to the beach and then to the lab to pursue experimental enquiry through personal connections. The original exercises are described here, in what is, in itself, an excellent and valuable report well-worth reading). However, it's what Seraphin includes as feedback from the students that I found particularly intriguing. In their writings, the students were encouraged to record what they "used to believe" about sand and subsequently recognised as misconceptions following the learning process. Here they are:

See why I found this so fascinating? As Seraphin comments:

This type of feedback is an important information-gathering step for teachers and an important learning step for students. It also reflects the ability of writing to engage students in the learning process by providing the space and freedom for learners to express what they think (or used to think) without fear of failure.

and in her conclusions

The working hypothesis is that enhancing place and personal connections in science teaching will improve students’ self-efficacy and attachment to science learning, thereby leading to increased retention in science courses, higher test scores, better grades, and higher-quality student work. Writing often and with cultural, and place-based, relevance is therefore recommended as a thinking tool to personally and contextually connect the past, present, and future aspects of teaching and learning.

"Hear, hear" is all I can say.

 

A Reverence for Rivers (3): Piling up a heritage of conflict and litigation over water rights

 

We only have ONE hydrologic system, dammit!

School kids know that (it's in all their textbooks), geologists, geophysicists, geomorphologists, environmental scientists and ecologists, climatologists and meteorologists, resource scientists, most engineers, and a hell of a lot of people on the street know that. It is, however, a fact that seems to have escaped multitudes of politicians, policy-makers, regulators, at least one US presidential candidate, and, of course, commercial enterprises - whether out of profound and inexcusable ignorance or under the influence of vested interests and lobbies is open to question.

But it remains a fact. The entire hydrologic system - rain drops, clouds, springs, creeks, rivers, lakes, snow, ice, run-off, evapotranspiration and groundwater - is interconnected. Mess about with one bit and other parts will be affected - it's complex, but it is one single system.

The title of this post is a quotation from John Wesley Powell, a voice of knowledge and rationality that we could benefit from today - more of that, quite possibly, in a future post. Over 120 years ago, addressing an audience of (booing) vested interests in irrigation at any cost, he said:

When all the rivers are used, when all the creeks in the ravines, when all the brooks, when all the springs are used, when all the reservoirs along the streams are used, when all the canyon waters are taken up, when all the artesian waters are taken up, when all the wells are sunk or dug that can be dug, there is still not sufficient water to irrigate all this arid region.  I tell you, gentlemen, you are piling up a heritage of conflict and litigation over water rights, for there is not sufficient water to supply these arid lands.

This occasional series, A Reverence for Rivers, is dedicated to Luna Leopold and perhaps I should add John Wesley Powell. In a the previous episode I quoted from a piece, written over sixty years ago by Leopold and his colleague Harold Thomas:

There are enough examples of streamflow depletion by ground-water development, and of ground-water pollution from wastes released into surface waters, to attest to the close though variable relation between surface water and ground water.

Man has coped with the complexity of water by trying to compartmentalize it. The partition committed by hydrologists—into ground water, soil water, surface water, for instance—is as nothing compared with that which has been promulgated by the legal profession, which has on occasion borrowed from the criminal code to term some waters "fugitive" and others, a "common enemy." The legal classification of water includes "percolating waters," "defined underground streams," "underflow of surface streams," "water-courses." and "diffuse surface waters"; all these waters are actually interrelated and interdependent, yet in many jurisdictions unrelated water rights rest upon this classification.

This jurisdictional and regulatory problem of compartmentalization of water resources contrary to the facts of the way the system works has given rise to many of the profound problems we face today. So I thought it might be helpful to set out some of the facts of the relationships between ground and surface waters and the consequences of ignoring them - bear with me, this may be a summary but it's not going to be short!  

First, the interested reader can do no better than to go (as is so often the case) to the USGS. Published nearly 20 years go, Circular 1139 is titled Ground Water And Surface Water: A Single Resource. The synopsis is as follows:

As the Nation's concerns over water resources and the environment increase, the importance of considering ground water and surface water as a single resource has become increasingly evident. Issues related to water supply, water quality, and degradation of aquatic environments are reported on frequently. The interaction of ground water and surface water has been shown to be a significant concern in many of these issues. For example, contaminated aquifers that discharge to streams can result in long-term contamination of surface water; conversely, streams can be a major source of contamination to aquifers. Surface water commonly is hydraulically connected to ground water, but the interactions are difficult to observe and measure and commonly have been ignored in water-management considerations and policies. Many natural processes and human activities affect the interactions of ground water and surface water. The purpose of this report is to present our current understanding of these processes and activities as well as limitations in our knowledge and ability to characterize them.

USGS Circular1376, published in 2012, incorporated material from 1139 and proceed to document in considerable detail Streamflow Depletion by Wells—Understanding and Managing the Effects of Groundwater Pumping on Streamflow. Again, a straightforward summary:

Groundwater is an important source of water for many human needs, including public supply, agriculture, and industry. With the development of any natural resource, however, adverse consequences may be associated with its use. One of the primary concerns related to the development of groundwater resources is the effect of groundwater pumping on streamflow. Groundwater and surface-water systems are connected, and groundwater discharge is often a substantial component of the total flow of a stream. Groundwater pumping reduces the amount of groundwater that flows to streams and, in some cases, can draw streamflow into the underlying groundwater system. Streamflow reductions (or depletions) caused by pumping have become an important water-resource management issue because of the negative impacts that reduced flows can have on aquatic ecosystems, the availability of surface water, and the quality and aesthetic value of streams and rivers.

Both of these publications should be required reading for anyone, anywhere who is even remotely involved in water management and policy-making.

So let's start with a simple and fairly self-explanatory image from the USGS:

Ground-water flow paths vary greatly in length, depth, and travel time from points of recharge
to points of discharge in the groundwater system.

Groundwater, streams and wells all interact and influence water flow, but the rates of that flow vary over several orders of magnitude, from days to millennia. The architecture and physical characteristics (permeability and so on) of the aquifer system are always complex in reality and the distribution of lower permeability (confining) layers will dramatically influence the direction, amount, and rate of flow. 

In places where the water table "outcrops" - i.e., intersects with the surface - there will be a spring (as at Havasu Falls, the image at the head of this post, ultimately feeding the Colorado River), a lake or groundwater feeding the flow of a river through its bed and banks. The relationship between the water table and a body of surface water is critical - a stream can be "gaining" flow from groundwater discharge or "losing" it by flow into the water table (depletion):

Groundwater discharge into streams and rivers is commonly the major contribution to their flow which is only augmented by rainfall and surface runoff.

Different segments of a river or stream may be typically gaining or losing and this will vary with the season - if the water table falls, the river may become "disconnected" from the water table, or, in times of flood, the river level may rise higher than the water table and effectively charge storage in its banks until the level falls back to normal.

All these variations occur quite naturally depending on time and place, and the system may be stable for long periods of time. But start pumping groundwater in the vicinity of a river and the system is de-stabilized. As the caption to this next USGS illustration describes, "In a schematic hydrologic setting where ground water discharges to a stream under natural conditions (A), placement of a well pumping at a rate (Q1) near the stream will intercept part of the ground water that would have discharged to the stream (B). If the well is pumped at an even greater rate (Q2), it can intercept additional water that would have discharged to the stream in the vicinity of the well and can draw water from the stream to the well (C)."

 To quote again from the USGS:

The first clear articulation of the effects of groundwater pumping on surface water was by the well-known USGS hydrologist C.V. Theis. In a paper published in 1940 entitled "The Source of Water Derived from Wells," Theis pointed out that pumped groundwater initially comes from reductions in aquifer storage. As pumping continues, the effects of groundwater withdrawals can spread to distant connected streams, lakes, and wetlands through decreased rates of discharge from the aquifer to these surface-water systems. In some settings, increased rates of aquifer recharge also occur in response to pumping, including recharge from the connected surface-water features. Associated with this decrease in groundwater discharge to surface waters is an increased rate of aquifer recharge. Pumping-induced increased inflow to and decreased outflow from an aquifer is now called "streamflow depletion" or "capture."

So there is a critical interaction between groundwater and surface water by complex flows that take place over days, centuries and millennia, and wells can cause major changes to that interaction - streamflow can be severely depleted, water tables lowered and aquifer water volume maintenance totally disrupted. 

For here is the first of what USGS Circular 1376 intriguingly documents as "common misconceptions." That is: 

Misconception 1. Total development of groundwater resources from an aquifer system is “safe” or “sustainable” at rates up to the average rate of recharge.

This is fundamental, because we hear all the time that aquifers are being "mined" as a result of volumes pumped exceeding the recharge rate from rainfall up in the hills - it's really not as simple as this. Because streams and rivers are frequently depleted by losing water to an aquifer, particularly when wells are pumping from that groundwater supply, it is this source that is the dominant way in which an aquifer is recharged, not by water from the hills. 

The sources of water to a well are reductions in aquifer storage, increases in the rates of recharge (inflow) to an aquifer, and decreases in the rates of discharge (outflow) from an aquifer. The latter two components are referred to as capture. In many groundwater systems, the primary components of capture are groundwater that would otherwise have discharged to a connected stream or river in the absence of pumping (referred to as captured groundwater discharge) and streamflow drawn into an aquifer because of the pumping (induced infiltration of streamflow)...

Reductions in aquifer storage are the primary source of water to a well during the early stages of pumping. The contribution of water from storage decreases and the contribution from streamflow depletion increases with time as the hydraulic stress caused by pumping expands outward away from the well and reaches one or more areas of the aquifer from which water can be captured. At some point in time, streamflow depletion will be the dominant source of water to the well (that is, more than 50 percent of the discharge from the well) and after an extended period of time may become the only source of water to the well. The time at which streamflow depletion is the only source of water to a well is referred to as the time to full capture.

So, if you choose to define and manage, through regulation and policy, groundwater and surface water as two entirely separate systems, you choose a recipe for disaster - you are more often than not severely double-counting and thereby overestimating your resources and you are not managing the system at all. And yet this is exactly what California, Arizona and, indeed, all the arid States of the Western US (not to mention other States and other countries) have been doing for more than a century. This has been superbly documented in ProPublica's piece, "Less Than Zero: Despite decades of accepted science, California and Arizona are still miscounting their water supplies." That analysis, part of their extensive "Killing the Colorado" series of reports, has also been summarised in the New York Times:

John Bredehoeft, a leading hydrogeologist and former director of the federal government’s Western states water program, bluntly emphasized the importance of basic honesty in counting water.

“If you don’t connect the two, then you don’t understand the system,” he said. “And if you don’t understand the system, I don’t know how in the hell you’re going to make any kind of judgement about how much water you've got to work with.”

Until state officials do, it seems unlikely that there will be any real solution to managing the Southwest’s strained water resources for the future.

But there's another, fundamental, problem - if you can't measure, monitor, document, you can't manage - and the data are essentially not there to measure, monitor and document. For example, California, again from the New York Times:

Although the state has not updated the surveys in the last three decades, the Department of Water Resources recently reported that across most of the state groundwater levels have dropped 50 feet below historical lows, with levels in many areas in the San Joaquin Valley more than 100 feet below previous historic lows.

In California, the state’s water agency has said that the failure to account for how groundwater withdrawals affect the state’s rivers is a major impediment to a true accounting of its resources. In April [2015], authorities reported that less than half of the state’s local water agencies had complied with a 2002 law that made them eligible for state funds only if they set up groundwater management plans and determined if a connection between surface water and groundwater existed. That connection does not exist uniformly and varies depending on local geology. Only 17 percent of the state’s groundwater basins had been examined.

Indeed, California still doesn't require that water pumped from underground be measured at all, much less factored into an overall assessment of total water resources; it’s merely an option under a new law signed last September.

California’s new groundwater legislation does require local water authorities to come up with sustainable groundwater plans, but they don’t have to do that until 2020, and they don’t have to balance their water withdrawals until 2040.

To all intents and purposes, the only way we have to analyse these issues is through computer modelling - very clever and sophisticated, but, at the end of the day it is modelling, not analysis of real-world data. But assembling meaningful real-world data is not easy on a local scale and the time-frame of aquifer behaviour is a long one. Make your way through USGS Circular 1376, and you will find several regional-scale analyses of groundwater/streamflow interaction based on the statistical analysis of data, and the authors document in detail the challenges of field studies, stating that

Statistical studies such as these can be used in general to evaluate the large-scale effects of basinwide pumping on streamflow reductions. They cannot, however, account for the specific effects of pumping at individual wells, nor can they help with understanding how specific management actions might affect future depletion. Such analyses require the use of analytical or numerical models.

So we are largely stuck with modelling. It is, nevertheless, a powerful tool, and several examples are presented in the USGS document. Since we are particularly interested in water and arid lands, here is a very relevant - not to mention fascinating, sobering, and perhaps surprising - example. The situation, that of a hypothetical desert-basin aquifer with a through-flowing river along the east side of the basin, is summarised here (remember that 1 acre-foot of water equals 1233 cubic meters):

There is natural recharge from the west and, under natural conditions, inflow from the river to the aquifer in the north and outflow from the aquifer to the river further downstream. Two wells are drilled into the aquifer, one five miles from the river, the other ten. Each well then pumps at a rate of around 750,000 cubic meters per year, and continues to do so for 50 years when pumping then ceases. The analysis treats each well separately - they are not both pumping at the same time. So let's consider the effects of streamflow of the well closer to the river (but still five miles away). What we are looking at are plots of the resulting increase in flow from the river into the aquifer, decrease in flow into the river from the aquifer and the total changes to river flow (depletion):

Over the period of pumping, the river's flow is decreased by almost 25%, depriving downstream users of water. After pumping stops, the river's flow begins to recover - but note the timescale: the river has still not returned to its natural flow rate after 150 years. And nearly half of the total volume of depletion will occur after pumping stops. The effects of the more distant well are only slightly more modest - but they last much longer and the maximum depletion occurs several years after the well stops pumping.

Now this "hypothetical desert-basin aquifer" may remind you of somewhere - the Ranegras Valley of Arizona, perhaps? Where the Saudi conglomerate, Almarai, are growing alfalfa for export back home? Except that this hypothetical example only covers the effects of one well pumping: Almarai operate 18 wells, each one capable of pumping 4 or 5 times the lonely well in our hypothetical desert valley, and they have received permission to drill 8 more.

Now of course there is no flowing river in the Ranegras Valley, but there is Brouse Wash, ephemeral, yes (although prone to flash flooding), but clearly with water not far below the surface, given the vegetation and the occasional stock pond visible on Google Earth:

So the Brouse River probably flows just below the surface of the wash, and, if it flows at all, will not be doing so much longer as its water supplies the alfalfa.

The Brouse does, I believe, eventually supply modest volumes of water to the Colorado, and, interestingly, while I was researching and preparing this post, Matthew Miller and his colleagues at the USGS published a paper titled "The importance of base flow in sustaining surface water flow in the Upper Colorado River Basin", summarised by Science Daily. The research covered the upper Colorado basin (i.e. upstream from Lee's Ferry and the Grand Canyon) where 90% of the river's flow originates and the work documents that 60% of that flow is provided by groundwater. Subsequently, more than 80% of that groundwater is lost, by evapotranspiration and diversion for irrigation, before it reaches the lower river (where, amongst other problems, Lake Meade has recently been reported to be at its lowest level ever). The abstract for the paper puts it very succinctly:

The Colorado River has been identified as the most overallocated river in the world. Considering predicted future imbalances between water supply and demand and the growing recognition that base flow (a proxy for groundwater discharge to streams) is critical for sustaining flow in streams and rivers, there is a need to develop methods to better quantify present-day base flow across large regions....

Our results indicate that surface waters in the Colorado River Basin are dependent on base flow, and that management approaches that consider groundwater and surface water as a joint resource will be needed to effectively manage current and future water resources in the Basin.

Or, as Matthew Miller himself is quoted as saying, "In light of recent droughts, predicted climate changes and human consumption, there is an urgent need for us all to continue to think of groundwater and surface water as a single resource."

It couldn't have been put better - if you have made it through this post, thank you! And many thanks, as always, to the USGS.

Sunbathing in the microscopic desert jungle

The desert has its own palette, distinctive and at the same time subtle yet dramatic. There are many factors at work creating the patterns and hues of arid lands - obviously the kind of sand, the kind of rock, the vegetation, minerals and salts, desert varnish - but there are also artists at work that we can't see and barely understand: microbial communities.

We can see the mosses and the lichens, but the vast ecosystem of bacteria and fungi operates essentially invisibly; we are only beginning to scratch the surface of the desert to reveal the ubiquity and importance of microbial life in environments we often describe as "lifeless." These are communities labelled "cryptic" by biologists, a useful term disguising the fact that they are something we really don't understand very well. I found this definition helpful, from a piece in Nature a few years ago titled "Body doubles" by Alberto G. Sáez and Encarnación Lozano:

Have you ever approached someone whom you thought you knew, talked to him with familiarity, only to find out later that he was a complete stranger, albeit remarkably similar in appearance to the person you had in mind, such as a twin brother? Well, taxonomists are similarly puzzled when they come across two or more groups of organisms that are morphologically indistinguishable from each other, yet found to belong to different evolutionary lineages. That is, when they discover a set of cryptic species.

The microscopic cryptic communities of arid lands form the well-known "desert" or "cryptobiotic" crusts that we now realise play key roles in the ecosystem, cycling carbon dioxide and nitrogen, providing resources for plant life, controlling drainage and the hydrologic behaviour of the soil, and reducing erosion - and hence, atmospheric dust. 

Among the leading researchers shedding light on these cryptic communities is Ferran Garcia-Pichel at Arizona State University's School of Life Sciences. For example, in 2013, togather with international colleagues, he published a paper titled "Temperature Drives the Continental-Scale Distribution of Key Microbes in Topsoil Communities." Science summarises the work as follows:

Soil microorganisms make up a substantial fraction of global biomass, turning over carbon and other key nutrients on a massive scale. Although the soil protects them somewhat from daily temperature fluxes, the distribution of these communities will likely respond to gradual climate change. ... [We] surveyed bacterial diversity across a range of North American desert soils, or biocrusts—ecosystems in which photosynthetic bacteria determine soil fertility and control physical soil properties such as erodability and water retention. Most of the sites were dominated by one of two cyanobacterial species, but their relative proportions were controlled largely by factors related to temperature. Laboratory enrichment cultures of the two species at different temperatures also showed temperature as a primary determining factor of bacterial diversity. It is unknown if temperature will affect the distribution of other soil microorganisms, but the marked shifts of these two keystone bacterial species suggest further change is in store for these delicate ecosystems.

The work, only available behind the Science paywall, was helpfully reported by Live Science. The two dominant "keystone" bacterial species are  Microcoleus vaginatus and M. steenstrupii, the former preferring cooler conditions whereas the latter likes things hot. As temperatures vary, things become competitive and warming conditions result in the mysterious steenstrupii taking over. Now, because these communities are microscopic and cryptic, we can only measure such effects - and detect which organisms are in the soil - through sophisticated DNA analysis. It is further results of this kind of painstaking and careful work that Garcia-Pichel and his colleagues have just published in Nature. With Estelle Couradeau, also at Arizona State, as the lead author, the paper describes - startlingly - how "Bacteria increase arid-land soil surface temperature through the production of sunscreens." Microcoleus vaginatus and M. steenstrupii are far from alone, and, amongst their companions are tribes of cyanobacteria such as the hundreds of species belonging to the genera Scytonema and Tolypothrix. These little critters dislike the sun and apply a biosynthetic sunscreen, scytonemin, an alkaloid pigment that strongly absorbs solar radiation and dissipates this energy as heat. This sunscreen can be seen as patches of darker colour covering areas of desert crust, as in this photo by Garcia-Pichel from the recent report on Science Daily.

This pigmentation may protect some members of the bacterial community, but it can locally warm up the surface by as much as 10 degrees C (18 degrees F). This has a dramatic effect on the health of the cool-loving Microcoleus vaginatus, but is welcomed by M. steenstrupii, who come to dominate as the sunscreen develops, at the expense of vaginatus. As Garcia-Pichel comments:

... we can show that the darkening of the crust brings about important modifications in the soil microbiome, the community of microorganisms in the soil, allowing warm-loving types to do better. This warming effect is likely to speed up soil chemical and biological reactions, and can make a big difference between being frozen or not when it gets cold... On the other hand, it may put local organisms at increased risk when it is already quite hot.

And this has to be happening on a global scale. As Estelle Coradeau suggests, "Because globally they cover some 20 percent of Earth's continents, biocrusts, their microbes and sunscreens must be important players in global heat budgets. We estimate that there must be some 15 million metric tons of this one microbial sunscreen compound...warming desert soils worldwide."

But because we have only a poor understanding of what exactly these desert crusts are and how they work, their roles in local ecology and global systems are impossible to define. It is only through the meticulous work of Ferran Garcia-Pichel and his team, together with others such as Jayne Belnap of the USGS in Moab, Utah, that we can begin to unravel the extraordinary nature and contributions of these long-ignored microbial desert communities. As Belnap has commented:

These are the only game in town to prevent dust storms and erosion, so they're really, really critical parts of this ecosystem. Yet we've never asked the question, 'who's really in there, and what's going to happen there as things shift?'

and, as reported in a piece on Belnap in High Country News, the palette and patterns of our arid lands owe much to an invisible living world: 

She also remains convinced that the dark shadows on the desert are the true — and fragile — foundation of the Colorado Plateau. "Whenever we pull on the thread of what makes the system tick," she says, "we end up with soil crusts on the other end."

[See also Belnap's USGS site at www.soilcrust.org. Crust photos credit: Linda and Dr. Dick Buscher, Live  Science "The Mysterious World of Cryptobiotic Soil."]

 

 

Back to the Bagnold dunes - stunning images

Curiosity, that hard-working field geologist, just keeps on delivering - this is surely the selfie to end all selfies (please). The rover continues to bustle around the Bagnold dunes, sending back extraordinary images, taking samples and sieving (Ralph Bagnold would appreciate that activity). Take a look at this screenshot from an incredible 360° interactive video:

The laws of physics - and The Physics of Blown Sand and Desert Dunes - are the same everywhere. This beautiful image of the avalanching slip-face of the "Namib dune" (the glorious full resolution can be enjoyed here) could be from a desert anywhere:

The detail and the dynamics are stunning, avalanches and sand sculpture more than 70 million kilometres away:

The sieving that Curiosity has been doing delivers the smaller than 150 micron fraction to the on-board instruments for analysis and simply dumps the larger grains.

Curiosity then gets out its hand lens and takes a close look:

From the NASA description of this image:

The larger-grain portion dumped onto the ground became accessible to investigation by other instruments on Curiosity, including imaging by MAHLI and composition analysis by the Chemistry and Camera (ChemCam) and Alpha Particle X-ray Spectrometer instruments. Laser-zapping of the dump pile by ChemCam caused an elongated dimple visible near the center of this view.

The MAHLI images combined into this focus-merged view were taken on Jan. 22, 2016, after dark on the 1,230th Martian day, or sol, of Curiosity's work on Mars. The illumination source is two white-light LEDs (light-emitting diodes) on MAHLI. They shone down on the right side of the image, so shadows are toward the left. The focus-merge product was generated by the instrument autonomously combining in-focus portions of eight separate images taken at different focus settings.

The dark appearance is purposeful: The camera team chose an exposure setting that would prevent most of the white grains in this otherwise very dark sand from being over-exposed.

Perhaps it's just a sign of being of a certain age, but all this fills me with indescribable wonder.
 

A Reverence for Rivers (2)

Turn on the tap in your kitchen so that it's running at a typical (if not particularly conservative) rate of around three US gallons per minute. Ensure that your drain is working well and leave it flowing for 17 years. By then you will have used the amount of water that the State of California consumes in one minute. 

Return after one year and you will have used roughly the volume of groundwater extracted from the Central Valley in one minute.

Last month, I started what I intended to be a series of posts stimulated by "A Reverence for Rivers," the title of the address given by the great hydrogeologist, Luna Leopold, to California Governor Jerry Brown's Drought Conference held nearly thirty years ago. Leopold threw down some challenges in the "philosophy of water management" to an audience that represented all the stakeholders in management of the state's water supplies at a time of what was then a record drought. Today, those records continue to be broken as California enters its fifth consecutive year of drought, and, for much of the state, the third year of "extreme," never mind "exceptional" drought. Yes, some relief is being provided by El Nino precipitation, but that does nothing to change the drought crisis - as shown by the US Drought Monitor image above. At the end of 2014, a NASA analysis indicated that "It will take about 11 trillion gallons of water (42 cubic kilometers) -- around 1.5 times the maximum volume [potential capacity] of the largest U.S. reservoir -- to recover from California's continuing drought." That was a year ago and it's only got worse. At the time of that report, some rains had arrived, but

“It’s not time to start watering your grass,” said Jay Famiglietti, senior water scientist at NASA’s Jet Propulsion Laboratory in Pasadena and the lead researcher of the new analysis. “Looking at the numbers, it’s probably going to take about three years to fill the hole.”

The NASA team found that the Sacramento and San Joaquin river basins, key water sources for cities and farms, lost 4 trillion gallons of water each year since 2011, most of it from farmers tapping the underground supply because rivers and reservoirs were low.

How can California still find itself in this amount of trouble when, nearly thirty years ago, in his first incarnation as drought Governor, Brown declared that “this is an era of limits and there are some very hard choices to be made”? One of the reasons that I have only now embarked on this episode of the series of posts is that there are no easy answers, and research and fact-checking leads only into a black hole of conflicting data, never mind the labyrinthine political abyss of western water politics, policy and history. It is clear that, post 1997, Brown and some of the more enlightened interests in California attempted to embark on reform and future drought preparation - but many of the choices proved to be too hard. Yes, there were initiatives to reduce domestic and municipal consumption and these lasted, although Brown, in his second drought incarnation, still had to declare a State of Emergency in January 2014, and a year later, the first ever state-wide mandatory water reductions. Individual Californians and communities have dramatically reduced their consumption (with the notable exception of Beverly Hills celebrities and billionaires), but by far the largest proportion of the 38 billion gallons per day consumed by California goes to agriculture - and therein lies the rub. 

Exactly how much water does Californian agriculture use? Well, incredibly nobody really knows and nobody has the day-to-day measurements to know. You can easily, depending on the sources and assumptions, find estimates from 40% to 80% of total water use. In order to find a single group of statistics that have some credibility, it's worth consulting a report put out by the Congressional Research Service in June 2015. Attempting to rationalize the data differences, it is titled California Agricultural Production and Irrigated Water Use and begins:

California ranks as the leading agricultural state in the United States in terms of farm-level sales. In 2012, California’s farm-level sales totaled nearly $45 billion and accounted for 11% of total U.S. agricultural sales. Five counties—Tulare, Kern, Fresno, Monterey, and Merced—rank among the leading agricultural counties in the nation.

Given current drought conditions in California, however, there has been much attention on the use of water to grow agricultural crops in the state. Depending on the data source, irrigated agriculture accounts for roughly 40% to 80% of total water supplies. Such discrepancies are largely based on different survey methods and assumptions, including the baseline amount of water estimated for use (e.g., what constitutes “available” supplies). Two primary data sources are the U.S. Geological Survey (USGS) and the California Department of Water Resources (DWR). USGS estimates water use for agricultural irrigation in California at 25.8 million acre-feet (MAF), accounting for 61% of USGS’s estimates of total withdrawals. DWR estimates water use withdrawals for agricultural irrigation at 33 MAF, or about 41% of total use. Both of these estimates are based on available data for 2010. These estimates differ from other widely cited estimates indicating that agricultural use accounts for 80% of California’s available water supplies, as reported in media and news reports.

The differences result from arcane variations in the definitions of the words "use," consumption," "withdrawals," and "application." Welcome to the rabbit-hole of terminology, both technical and political. Oh, and also welcome to the "acre-foot."  An acre-foot is a volume of water equal to 325,851 gallons (around 1200 cubic metres) and represents the amount of water needed to flood an acre of land one foot deep. In the US, it is the long-standing measure of water volume.

Since Brown's initiatives following the 1970s drought, water use has dropped, partly as a result of domestic frugality, partly following increased efficiency irrigation systems - and the brutal realities of maintaining agriculture in a semi-arid land. However, the USGS reports that California in 2010 remained the chart-topper of all US states for water consumption - more than half again as much as the runner-up, Texas. And the USGS estimates that agriculture accounts for 60% of the state's thirst.

Any, even brief, review of media reports will reveal that to say that this is a controversial topic is a gross understatement. Vested interests, lobbies, open and hidden agendas, battle for dominance in issues scarcely tainted by facts or science. And these arguments also take place in a virtually policy-free environment - water regulations and laws in the arid Western US are labyrinthine, opaque, complex beyond normal comprehension and certainly unfit for purpose, particularly in California. In 1991, during yet another drought, Peter Passell, an economics writer for the New York Times, wrote that California's water system - infrastructure and laws - "might have been invented by a Soviet bureaucrat on an LSD trip... While this infrastructure was built with state and Federal money, the benefits are by tradition (and, hazily, by law) reserved for the private interests who lobbied for its construction." 

California's surface water supply system resembles nothing more than a Heath Robinson contraption or a Rube Goldberg machine, deliberately over-engineered to perform a simple task in a complicated fashion. But at least the State Government has some ability to regulate it. In a normal year that's an ability to attempt to manage and allocate perhaps 70% of the state's water consumption. In a typical drought year that drops to less than 40%. In extreme drought conditions, the state can - and does - dramatically reduce surface water allocations but then where does the other 60-70% come from? Groundwater. Over which the government has virtually no control whatsoever. It doesn't even have the knowledge or the data to manage its groundwater, never mind the legal ability to do so.

And here is the vital fact that is mostly ignored or unknown in political and commercial circles, largely because it's highly inconvenient: surface water and groundwater are part of the same system, the hydrological cycle - mess with one and you mess with the other. 

Over 60 years ago, Luna Leopold and his colleague, Harold Thomas, wrote an article titled "Ground Water in North America: The fast-growing demands on this natural resource expose a need to resolve many hydrologic unknowns." Here's an extract:

There are enough examples of streamflow depletion by ground-water development, and of ground-water pollution from wastes released into surface waters, to attest to the close though variable relation between surface water and ground water.

Man has coped with the complexity of water by trying to compartmentalize it. The partition committed by hydrologists—into ground water, soil water, surface water, for instance—is as nothing compared with that which has been promulgated by the legal profession, which has on occasion borrowed from the criminal code to term some waters "fugitive" and others, a "common enemy." The legal classification of water includes "percolating waters," "defined underground streams," "underflow of surface streams," "water-courses." and "diffuse surface waters"; all these waters are actually interrelated and interdependent, yet in many jurisdictions unrelated water rights rest upon this classification

Water habitually does not subscribe to our efforts at compartmentalization according to special interests in irrigation, industrial use, recreational use, municipal use; or to allocations of fields for the chemist, for the geologist, for the sanitary engineer, for the physicist, for this or that government agency, any more than it does to separation into areas bounded by property lines, county lines, state lines, or even some river-basin boundaries. As the areas of heavy demand expand toward each other and the necessity for water management increases, these artificial boundaries and classifications will have to yield more and more to the realities of the hydrologic cycle.

Ah yes, the lessons we have learned in 60 years. In an article in July of last year for the New York Times, Abrahm Lustgarten, an environmental reporter for ProPublica, summarized a report he had written for the site (the whole piece is well-worth reading). From the summary, titled "How the West Overcounts Its Water Supplies": 

In California, the state’s water agency has said that the failure to account for how groundwater withdrawals affect the state’s rivers is a major impediment to a true accounting of its resources. In April, authorities reported that less than half of the state’s local water agencies had complied with a 2002 law that made them eligible for state funds only if they set up groundwater management plans and determined if a connection between surface water and groundwater existed. That connection does not exist uniformly and varies depending on local geology. Only 17 percent of the state’s groundwater basins had been examined.

Indeed, California still doesn’t require that water pumped from underground be measured at all, much less factored into an overall assessment of total water resources; it’s merely an option under a new law signed last September.

California’s new groundwater legislation does require local water authorities to come up with sustainable groundwater plans, but they don’t have to do that until 2020, and they don’t have to balance their water withdrawals until 2040.

So fierce was the pushback by the agriculture industry against any regulation of underground water that the new law, somewhat perversely, explicitly barred any attempt by the state to count the groundwater withdrawals as coming from one overall water supply until local agencies had at least 10 more years to come up with — and implement — their plans.

“Those who have unlimited water supply don’t particularly like the idea of changing that,” said Fran Pavley, a Democrat and the California state senator who drafted two of the three bills that became the groundwater law. “You can’t manage what you don’t measure.”

Thomas Buschatzke, the director of Arizona’s Department of Water Resources, acknowledged that pumping from wells could dry up streams, but said the current law kept the two resources separate, and “it would be a huge upset to the economy to do away with that.”

But John Bredehoeft, a leading hydrogeologist and former director of the federal government’s Western states water program, bluntly emphasized the importance of basic honesty in counting water.

“If you don’t connect the two, then you don’t understand the system,” he said. “And if you don’t understand the system, I don’t know how in the hell you’re going to make any kind of judgment about how much water you’ve got to work with.”

Until state officials do, it seems unlikely that there will be any real solution to managing the Southwest’s strained water resources for the future.

And, in the words of Jay Famiglietti:

Managing our water in this context will require an overhaul of existing water policy that matches our modern understanding of the water cycle. Surface and groundwater are tightly interconnected and should be managed accordingly. The rule of capture for groundwater worked exceedingly well when we shot bears with muskets. Let's not kid ourselves that we're great stewards when most of our available water -- groundwater -- is still offered up in a land rush.

We must treat and price water as the precious commodity that it truly is. That means conserve, reuse, recycle, and then do it all over again. Enhanced conservation and efficiency is cheap, easy, and incredibly effective.

So, turn on your tap for a year and contemplate the disappearance of groundwater in California's Central Valley every minute. You could at least rush home and turn off the tap - the government of the State of California can't. We'll talk about all this some more in the next episode...  

 

 

2016: the year of the Bagnold dunes

Last month, NASA issued a press release to announce that the Curiosity Rover had reached the “Bagnold dunes” and was preparing to investigate. The image above is from that announcement – the landscape covered is only a few meters across, but it is extraordinary and just seems, instinctively, to be unearthly. As Nathan Bridges of the Johns Hopkins University's Applied Physics Laboratory, Laurel, Maryland, and leader of the Curiosity team's planning for the dune campaign remarked in an earlier discussion of the project:

These dunes have a different texture from dunes on Earth. The ripples on them are much larger than ripples on top of dunes on Earth, and we don't know why. We have models based on the lower air pressure. It takes a higher wind speed to get a particle moving. But now we'll have the first opportunity to make detailed observations.

Indeed. The first detailed examination of extra-terrestrial sand dunes, to take place over the next few months, will be incredibly exciting, and it is only appropriate that those dunes are, if only informally, named after Ralph Bagnold. Readers of this blog and my books will have sensed that Bagnold is something of hero of mine, and I like to refer to him as “the man who figured out how deserts work.” One only wishes that he was still around and that we could hear his reactions to Curiosity, the images, the science and engineering. I am of the generation that still has difficulty not finding this whole project incredible, and I know that Bagnold would have been totally engrossed in the science, the technology – and the people.

In his frustratingly short (but fascinating) 1990 autobiography, Sand, Wind, and War, Bagnold cryptically titled Chapter 17, “Later: 1974-1986”. In it, he writes:

One memorable event in 1977 occurred when I was asked by the National Aeronautics and Space Administration (NASA) to give the keynote address at a meeting of geologists and other space scientists.The meeting was to compare the desert landscapes of Earth and Mars. It was held for a week at Palm Desert, a new, up-and-coming offshoot of Palm Springs in Southern California. The site of the meeting had been specially chosen for the desert character of its surroundings. However, during that week it rained every day. The main thoroughfare through town, labeled Bob Hope Street, was still only dirt. It was all but washed away. 

NASA had recently sent spacecraft to orbit Mars and had succeeded in landing an unmanned craft to take close-up pictures. Those photos of the landscape revealed apparent sand dune forms much like those on Earth, in spite of the vastly different atmosphere. This had already started theories, but it was, and still is, mere guesswork as to what the stuff of the so-called dunes really is. We have no tangible evidence, and won’t have until some of it is brought back to Earth. Is it granular, like sand, or fluffy like snowflakes? And we still have but little idea of the scale of the dune heights…

I spent one evening at a McDonald’s with a small group of young scientists from NASA’s Jet Propulsion Laboratory in Pasadena. It was fascinating for an old man of eighty-one to listen to their casual talk of navigating a spacecraft two hundred million miles away as easily as an aeroplane. Man had not begun to fly at all when I was born.

The Bagnold Dunes lie in Gale crater, and are a stopping point for Curiosity on its journey up the slopes of Mount Sharp. The part of the dune field that the rover has arrived at is shown in this image – the dark band of rippled sand in front of Mount Sharp which looms intriguingly in the background.

Bethany Ehlmann of the California Institute of Technology and NASA's Jet Propulsion Laboratory is another member of the project team, and she introduces it in a great little video. As she comments, the dunes are dark because the sand grains are derived from basaltic rocks, and they cover the older, lighter-coloured, sandstones, some of which are themselves ancient dunes. Curiosity will be conducting fieldwork on what was originally called Dune 2, now the high dune, which is but a part of the much larger dune field. This beautiful image shows the dune, part of the larger dune field, and the journey of Curiosity to its current position:

In the image at the head of this post, we are only looking at a small area of the whole dune, but from imagery over the years by NASA’s orbiting HiRISE camera, it is clear that the dune is active and on the move. As Bethany Ehlman describes, echoing Ralph Bagnold, in the reduced gravity, thin atmosphere, and unknown wind conditions on Mars, exactly how sand grains are transported and dunes migrate is still a mystery. But, thanks to Curiosity, perhaps not for long.

Ralph Bagnold became frustrated by the lack of desert wind data critical for developing his pioneering work on the physics of blown sand (he moved on to the physics of water-borne sediment). But Curiosity is already on the job, gathering the wind data that will help us understand how Martian sand moves. And the Rover has an extraordinary array of other instrumentation at the end of its long robotic arm, including a sand sampler and sieves that will tell the stories of grain size distributions that Bagnold determined were so informative.

At the end of Curiosity's robotic arm is a suite of devices that enable Collection and Handling for In-situ Martian Rock Analysis, otherwise known as CHIMRA. This combination of geological tools, operated remotely hundreds of millions of miles away, is incredible:

Ralph Bagnold was not only a scientist but also an engineer who designed, developed and built his own equipment, unique and exquisitely sophisticated. As we remember him working on field measurements in Egypt’s Western Desert in 1938, it doesn’t take much imagination to visualise him not only impressed with CHIMRA, but enthusiastically contributing to the project.

[for the full image of Curiosity’s view of the High Dune, see  http://mars.nasa.gov/imgs/2015/12/mars-curiosity-rover-high-dune-up-close-fullres-pia20168-figA.jpg]   

 

Unearthly dunes

Once in a while I enjoy losing myself in the wonders of Martian landscapes. Words just don't seem necessary for this selection from the latest HiRISE images.

[All images courtesy NASA/JPL/University of Arizona and thanks to Lee Allison at Arizona Geology for the heads up on the 122 new NASA images] 

The Missing Sink: Carbon storage in the world’s deserts

Deep-rooted and completely erroneous preconceptions of our planet’s arid lands as sterile bit-players in the great game of the earth’s dynamic systems have long inhibited our scientific enthusiasm for, and understanding of, the desert. We are now beginning to catch up – take, for example, this recent headline from the American Geophysical Union:

The world's deserts may be storing some of the climate-changing carbon dioxide emitted by human activities, a new study suggests. Massive aquifers underneath deserts could hold more carbon than all the plants on land, according to the new research.

As described in a summary of this research on Science Daily:

Humans add carbon dioxide to the atmosphere through fossil fuel combustion and deforestation. About 40 percent of this carbon stays in the atmosphere and roughly 30 percent enters the ocean, according to the University Corporation for Atmospheric Research. Scientists thought the remaining carbon was taken up by plants on land, but measurements show plants don't absorb all of the leftover carbon. Scientists have been searching for a place on land where the additional carbon is being stored--the so-called "missing carbon sink."

The lead author of the report in the AGU publication, Geophysical Research Letters, is Yan Li, a desert biogeochemist with the Chinese Academy of Sciences in Urumqi, Xinjiang; he and his team examined the character of groundwaters in the gigantic closed system of the arid Tarim Basin, and came up with some fascinating – and provocative – results. Runoff waters from the surrounding mountains pick up, as a normal part of the carbon cycle, some CO₂ dissolved from the rocks and soils through which the rivers flow. However, by the time that water ends up in aquifers, the underground reservoirs beneath the desert, it contains substantial amounts of DIC, dissolved inorganic carbon.

Being able to date the carbon, Li and his colleagues could distinguish between old carbon originating from the rivers and very young carbon added to the water as it seeped through the soils of the irrigated oases along the desert margins. These are poor soils, not in themselves sources of much CO₂ - it originates from the respiration of the roots of crops and microbes in the soil. And because these crops are irrigated almost constantly, not only to keep them growing but to wash out the salts that, as in all desert agriculture, accumulate in the soil, most of the CO₂ is transported downward into the groundwater moving out below the desert to be trapped in the deep aquifers. Importantly, because of the salts, these waters are saline and alkaline and the solubility of CO₂ in saline/alkaline water is much higher than in pure or acidic water – the desert groundwater is a very significant CO₂ sink. 

Because of their ability to date the carbon dissolved in the waters, the researchers were able to establish that the levels jumped substantially in historical times as the development of the Silk Road enabled the beginnings of oasis agriculture. Man’s activities – irrigation and over-irrigation – have augmented the efficiency of this carbon sink by, it is estimated, a factor of twelve:

Based on the various rates that carbon entered the desert throughout history, the study's authors estimate 20 billion metric tons (22 billion U.S. tons) of carbon is stored underneath the Tarim Basin desert, dissolved in an aquifer that contains roughly 10 times the amount of water held in the North American Great Lakes.

The study's authors approximate the world's desert aquifers contain roughly 1 trillion metric tons (1 trillion U.S. tons) of carbon--about a quarter more than the amount stored in living plants on land.

And because this is a saline and alkaline aquifer, the water is completely unsuitable for agriculture – it will likely remain below the desert as essentially permanent carbon storage - undoubtedly not the only missing sink, but a hitherto unidentified one. As Li remarks: “The fact that such a huge carbon pool and active sink has been unstudied for so long may simply be because it is remote and hidden under deserts: out of sight, out of mind.”

 

[Image at the head of this post is of agriculture and dunes along the northern edge of the Tarim Basin, Google Earth; diagram of the process of carbon storage from Yan Li, Yu-Gang Wang, R. A. Houghton, Li-Song Tang. Hidden carbon sink beneath desert. Geophysical Research Letters, 2015; DOI:10.1002/2015GL064222]

Our arid planet

Yet again, thank you NASA. As announced last month, their latest extraordinary earth-monitoring system is in orbit, commissioned and providing data: SMAP, the Soil Moisture Active Passive mission provides a high-resolution view of continuing changes in soil moisture across our world and allows understanding, analysis and planning in an unprecedented and fascinating way.

The map above is one of several already available:

These maps of global soil moisture were created using data from the radiometer instrument on NASA's Soil Moisture Active Passive (SMAP) observatory. Each image is a composite of three days of SMAP radiometer data, centered on April 15, 18 and 22, 2015. The images show the volumetric water content in the top 2 inches (5 centimeters) of soil. Wetter areas are blue and drier areas are yellow. White areas indicate snow, ice or frozen ground.

The soil moisture scale is in cm³/cm³ and demonstrates dramatically the often-forgotten fact that drylands, home to a third of our planet’s population, comprise over 40% of the land area.

As usual, the technology is extraordinary:

For an introductory description of how the radar and radiometer instruments conspire, see http://smap.jpl.nasa.gov/observatory/overview/. The NASA press release summarises the mission and the ways in which the data will be used:

Launched Jan. 31 on a minimum three-year mission, SMAP will help scientists understand links among Earth's water, energy and carbon cycles; reduce uncertainties in predicting climate; and enhance our ability to monitor and predict natural hazards like floods and droughts. SMAP data have additional practical applications, including improved weather forecasting and crop yield predictions.

A first global view of SMAP's flagship product, a combined active-passive soil moisture map with a spatial resolution of 5.6 miles (9 kilometers), is available at:

http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA19337

During SMAP's first three months in orbit, referred to as SMAP's "commissioning" phase, the observatory was first exposed to the space environment, its solar array and reflector boom assembly containing SMAP's 20-foot (6-meter) reflector antenna were deployed, and the antenna and instruments were spun up to their full speed, enabling global measurements every two to three days.

The commissioning phase also was used to ensure that SMAP science data reliably flow from its instruments to science data processing facilities at NASA's Jet Propulsion Laboratory in Pasadena, California, and the agency's Goddard Space Flight Center in Greenbelt, Maryland.

"Fourteen years after the concept for a NASA mission to map global soil moisture was first proposed, SMAP now has formally transitioned to routine science operations," said Kent Kellogg, SMAP project manager at JPL. "SMAP's science team can now begin the important task of calibrating the observatory's science data products to ensure SMAP is meeting its requirements for measurement accuracy."

Together, SMAP's two instruments, which share a common antenna, produce the highest-resolution, most accurate soil moisture maps ever obtained from space. The spacecraft's radar transmits microwave pulses to the ground and measures the strength of the signals that bounce back from Earth, whereas its radiometer measures microwaves that are naturally emitted from Earth's surface.

"SMAP data will eventually reveal how soil moisture conditions are changing over time in response to climate and how this impacts regional water availability," said Dara Entekhabi, SMAP science team leader at the Massachusetts Institute of Technology in Cambridge. "SMAP data will be combined with data from other missions like NASA's Global Precipitation Measurement, Aquarius and Gravity Recovery and Climate Experiment to reveal deeper insights into how the water cycle is evolving at global and regional scales."

It is, to me, wondrous that even a simple examination of the three successive images from which the one at the head of this post was taken reveals clear changes over the course of a few days – I can only begin to imagine what analysis of the real data will reveal.

The UN’s map and classification of global drylands drives home their importance to the way our planet works. The new SMAP data bring this to life in a dramatic way.

  

[SMAP image credit: NASA/JPL-Caltech/GSFC]