"And the wind blows, the dust clouds darken the desert blue, pale sand and red dust drift across the asphalt trails and tumbleweeds fill the arroyos. Good-bye, come again."

The global dust cycle is the most important thing that most people have never heard of. Drylands emit sediment that can be transported long distances. In many cases this is an entirely natural phenomenon, e.g. ancient lake basins tend to be poorly vegetated due to salinity and tend to be full of transportable sediment. When they were lakes they trapped dust, now they expel it. These are often the dust hotspots of the world (e.g., Koren et al. 2006). Land use including tillage and grazing are also major contributors in other cases; desertification and dust emissions are tightly linked (Breshears et al. 2003). These disturbances can turn large areas into dust emitters. Drought, which we expect to be strongly affected by climate change, can also greatly enhance dust emissions across the board (Belnap et al. 2009). Thus, dust can be considered a secondary global change factor.

The obvious impact of dust emissions in rangelands is that fertility is leaving the site (Neff et al. 2005). The less obvious impacts occur sometimes halfway around the world. Some cities regularly experience crippling dust storms which impact human respiratory health and create blinding conditions on roadways. Beijing is an excellent example, where desertification-linked dust storms have gone from a decadal phenomenon to an annual one, even closing airports for days. In the southwest USA, an endemic fungus responsible for valley fever (a disease causing pheumonia-like symptoms) is transported in dust. Some of the more amazing impacts of dusts may be positive on a global scale, in terms of our prospects for sinking carbon. The two great photosynthetic engines of the Earth, the Amazon rainforest and the oceanic phytoplankton, are both subsidized by dust-borne nutrients from drylands (Fung et al. 2000, Koren et al. 2006, Mahowold 2010).

• Beijing dust storm (Photo: Prof. Zev Levin, Dept. of Geophysics and Planetary Sciences, The Porter School of Environmental Studies, Tel Aviv, Israel)

Recently two excellent papers have appeared in Proceedings of the National Academy of Sciences about dust emissions and their impacts, and to a lesser degree the role of biocrusts as soil stabilizers.

Painter, T.S., Deems, J.S., Belnap, J., Hamlet, A.F., Landry, C.C., Udall, B. 2010. Response of Colorado River runoff to dust radiative forcing in snow. Proceedings of the National Academy of Sciences 108: 3854 - 3959. 
Back in 2006, I was shocked to hear Jayne Belnap on National Public Radio. NPR was doing a two-part series on dust research focused around the work on Tom Painter. The radio journalist even dropped the word "crusties" a time or two.










Four years later, they published this paper which documents the impacts of dust originating form the Colorado Plateau and southwest US drylands and accumulating on Rocky Mountain snowpack. Because the dust is much darker than the soil, it increases albedo and hastens melting. The authors estimate that this has resulted in initiation of melting 3 weeks earlier than ambient conditions. More importantly, the radiative forcing enhances sublimation -- the transition of solid snow to vapor -- which the authors estimate has decreased water supply to the Colorado River Basin by 5 %. This is of tremendous importance as most of the fastest growing urban areas in the USA are in the southwest and at least partially dependent on Colorado River water. As an example, Las Vegas, the city I was born in increased from about 200,000 residents to about 2,000,000 in 3 decades. All of this growth has been founded on the fantasy that there will be enough water, despite that the Colorado River has been 100% allocated for many years. Increasing dust emissions seem to argue otherwise.

Munson, S.M., Belnap, J., Okin, G.S. 2011. Responses of wind erosion to climate-induced vegetation changes on the Colorado Plateau. Proceedings of the National Academy of Sciences  doi: 10.1073/pnas.1014947108. 

The authors use a trifecta of long-term monitoring data, a wind erosion model, and an experimental validation of results using a portable wind tunnel. Primarily in perrennial grasslands the previous year temperatures dictate grass biomass in the following years. Plugging these data into Okin's wind erosion (WEMO) model suggests greater risk for enhanced dust fluxes due to probable climate warming. The fluxes are small, however, unless the biocrust is disturbed. When heavy crust disturbance is coupled with drought-stricken grasses, the fluxes have the potential to be off the hook.

 This paper is getting considerable press, e.g. the Salt Lake Tribune. For those in other countries just check out the comments on that paper to see how effective the smear campaign on climate science has been in the USA. We have an uphill battle.

Post title: Edward Abbey, The Monkeywrench Gang 

References:
Belnap, J., R. L. Reynolds, M. C. Reheis, S. L. Phillips, F. E. Urban, and H. L. Goldstein. 2009. Sediment losses and gains across a gradient of livestock grazing and plant invasion in a cool, semi-arid grassland, Colorado Plateau, USA. Aeolian Research 1:27–43.

Breshears, D. D., J. J. Whicker, C. B. Zou, J. P. Field, and C. D. Allen.  2009. A conceptual framework for dryland aeolian sediment transport along the grassland-forest continuum: Effects of woody plant canopy cover and disturbance. Geomorphology 105: 28-38.

Fung, I.Y., Meyn, S.K., Tegen, I., Doney, S.C., John, J.G., Bishop, J.K.B., 2000. Iron supply and demand in the upper ocean. Global Biogeochemical Cycles 14, 281–295.

Koren, I., Kaufman, Y.J., Washington, R., Todd, M.C., Rudich, Y., Martins, J.V., Rosenfeld, D., 2006. The Bodélé depression: a single spot in the Sahara that provides most of the mineral dust to the Amazon forest. Environmental Research Letters 1, 0140055.

Mahowald, N.M., Kloster, S., Engelstaedter, S., Moore, J.K., Mukhopadhyay, S., McConnell, J.R., Albani, S., Doney, S.C., Bhattacharya, A., Curran, M.A.J., Flanner, M.G., Hoffman, F.M., Lawrence, D.M., Lindsay, K., Mayewski, K.A., Neff, J., Rothenberg, D., Thomas, E., Thornton, P.E., Zender, C.S., 2010. Observed 20th century desert dust variability: impact on climate and biogeochemistry. Atmospheric Chemistry and Physics 10, 10875–10893.

Neff, J. C., R. L. Reynolds, J. Belnap, and P. Lamothe. 2005. Multi-decadal impacts of grazing on soil physical and biogeochemical properties in southeast Utah. Ecological Applications 15:87–95.

Did crusts kill the dinosaurs? (just kidding, but check out this Cretaceous biocrust)

Crusts are old. Maybe sometime soon I’ll write about the idea that the first terrestrial communities were cyanobacterial biocrusts, rather than true land plants…or I’ll ask someone else to do it who knows a lot more. Recently in a geology journal that few biologists are likely to wander to, Simpson et al. (2010) report on a fossilized crust from the Cretaceous. Now, the Cretaceous isn’t that old, it’s noted as the last stand of the dinosaurs and the coming out party of the angiosperms…but the amazing thing is that their fossil looks very much like a living modern day crust.

It was found in my old stomping grounds of Grand Staircase-Escalante National Monument near the contact between the Wahweap formation and the Kaiparowits formation. The fossil was located near Cottonwood Canyon where I would often camp in the shade after long hot days of hiking to remote sampling sites, and attempt to remove the multi-day sunscreen & soil crust that had accumulated on me in the nearby creek. The sandstone portions of the Wahweap formation can support some very nice biocrust today if you work harder than a cow and walk far away from water sources. So needless to say this stirs some nostalgia in me. Little did I know there were fossil crusts in the rocks, it really makes you wonder what other formations have them.

As you can see from the photos, they have a pinnacled structure like most of the Colorado Plateau crusts of today. This puzzles me a bit, we have long thought that frost heaving plays a large part in generating uplift in these pinnacled crusts. Naturally, erosion sculpts things that stick up, but eventually some equilibrium is found where the sculpted pinnacled form is well-preserved by a late successional biocrust. But the Cretaceous was a much warmer time than today, the areas where the rocks were formed would not likely have experienced frost, correct me if I’m wrong. I was similarly puzzled a few years ago when I saw a fantastic crust on the Oregon Dunes while cycle touring. It had the exact same pinnacled structure as Colorado Plateau crusts, despite the maritime climate and lack of frost. Maybe we need to rethink the origin of this structure.



Read more about the fossil crust here. All photos are from Simpson et al. 2010.

Simpson, W.S., Simpson, E.L., Wizevich, M.C., Malenda, H.F., Hillbert-Wolf, A.L., Tindall, S.E. 2010. A preserved Late Cretaceous biological soil crust in the capping sandstone member,Wahweap Formation, Grand Staircase-Escalante National Monument, Utah: Paleoclimatic implications. Sedimentary Geology 230: 139-145.

Biocrusts on the Great Wall of China

In my random web wanderings I came across a great blog "Walking the Wall" by a Emma Nicholas and Brendan Fletcher who walked the entire length of the Great Wall of China while sponsored by the Powerhouse Museum of Sydney, Australia. I recommend perusing the whole thing as there is quite a bit of material on culture, history and natural history of China. Particularly amazing to me was this: considerable portions of the wall were constructed using rammed earth. These portions of the wall are covered with biocrusts which apparently protect the wall from erosion (Photo: Nicholas & Fletcher)

Check out their post "The Living Wall", containing more photos and some info about the crusts provided by Dave Eldridge.

An affliction and an invitation

This is my attempt at creating an open conduit for networking among the growing, but still small number of researchers that can’t seem to stop studying biological soil crusts. We have a fondness for the things that other scientists can’t seem to notice. I started working on crusts because I love deserts and kept noticing these things on the soil while doing, e.g. tortoise surveys, or looking at (yawn!!) plants. My co-workers often sort of knew what they were called (crypto-somethings), but most people were at a loss to explain them. I was enthralled, they were black, white, yellow and pink, a coral reef in the Mojave desert. Fifteen or so years later, the fascination has been an endless well. I don’t think I’m alone. I heard Burk Budel give a talk and he mentioned a real-life generic name that speaks directly to this plight…Geodermatophilus. The love of the skin of the Earth might be called Geodermatophilia.

This site will be a source of information, especially for students just getting started. Hopefully finding information on biocrusts will be made much easier than it was for me, much much easier than it was for Jayne Belnap or Dave Eldridge, and much much much easier than it was for Rod Rogers, Otto Lange or Kimball Harper. My idea is to develop a blog as a fluid centerpiece. I would very much like this to evolve into our blog , in the sense of an international network of bloggers. I will periodically be recruiting new posters, especially younger ones. I will also be constructing a directory of links to biocrust researchers of the world, and may attempt to create a biocrust bibliography. This site will be a relaxed and informal source for information about meetings and conferences, new literature, and sharing of observations, photos, information, ideas, etc.

This post is an invitation to read, comment, and contribute.