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Looking back at the Upper Mississippi River, moving forward

A student and I are working on finishing a project that has lingered for too many years: a careful analysis of the cumulative effects of river management on islands in the lower part of Pool 6 of the Mississippi River, near my hometown of Winona, Minnesota. There will be a MS thesis soon and hopefully a journal manuscript shortly to follow that, but for now, I’m enjoying discovering new and old research and resources on “the father of waters.”

First, check out this 17-minute silent film on the 1927 Mississippi River flood:

For more information on the film made by the Signal Corps in the 1930s, head here:

Then, check out this 2012 publication from the USGS on “A Brief History and Summary of the Effects of River Engineering and Dams on the Mississippi River System and Delta.”

Finally, there’s a paper just out in Geophysical Research Letters by Frans et al. titled “Are climatic or land cover changes the dominant cause of runoff trends in the Upper Mississippi River Basin?.”

And that’s my afternoon reading sorted.

New report: Challenges and Opportunities in the Hydrologic Sciences

The “blue book” has been updated and you can read and download a pre-publication PDF on the National Academies’ website for free. I’ve just been listening to a CUAHSI webinar summarizing the report, and I was please to see that a lot of the questions I’m interested in were highlighted by the committee that updated the report. For instance, there was specific mention of urban hydrology (and how changes to flowpaths and quantity alter water quality), the co-evolution of hydrology, landscapes, and life, and the need to understand the controls on the low flow extent of streams. I’ll be reading sections of this report in coming months, and if you want to get a sense of the state of hydrologic science, you would probably do well to start here too.

Cynthia Barnett, award winning water journalist and author, to speak at UNC Charlotte

Cynthia Barnett

Cynthia Barnett (photo supplied by Ms. Barnett)

I’m excited to announce that Cynthia Barnett will be speaking on campus next week. She’s an outstanding thinker and writer about water conservation, particularly as it pertains to the eastern United States, where our sense of water-richness has lulled us into complacency.

From the press release:

Award-winning journalist and author Cynthia Barnett will visit UNC Charlotte to discuss water ethic for America at 7 p.m., Wednesday, Sept. 21, in the College of Health and Human Services, Room 128.

Barnett’s talk is the first stop for a tour about the book “Blue Revolution: Unmaking America’s Water Crisis,” scheduled for national release Sept. 20. “Blue Revolution” is said to be the first book to call for a national water ethic. Barnett uses the Catawba River as an example to illustrate the important role that water plays in America’s energy supply. The book combines investigative reporting with solutions from across the country and the globe to show how communities and nations have come together in a shared ethic to reduce consumption and live within their water means.

Barnett also is the author of “Mirage: Florida and the Vanishing Water of the Eastern U.S.” A veteran journalist, she won the national Sigma Delta Chi prize for investigative magazine reporting and a gold medal for best nonfiction in Florida book awards.  A book signing follows this free, public presentation, which is cosponsored by the UNC Charlotte Ethics Center, IDEAS Center and the Department of Geography and Earth Sciences.

BlueRevolutionCoverCynthia will also be available to meet with students and faculty in CHHS 128 from 4 to 5 pm. Please stop by, say hi, and ask your water questions.

I’m currently devouring a copy of Cynthia’s new book, so look for a review of the book here or elsewhere in the coming weeks.

New paper: Seasonal versus transient snow and the elevation dependence of climate sensitivity in maritime mountainous regions

Snowline near Skykomish, Washington (photo on Flickr by RoguePoet, used under Creative Commons)

Snowline near Skykomish, Washington (photo on Flickr by RoguePoet, used under Creative Commons)

Jefferson, A. 2011. Seasonal versus transient snow and the elevation dependence of climate sensitivity in maritime mountainous regions, Geophysical Research Letters, 38, L16402, doi:10.1029/2011GL048346.


In maritime mountainous regions, the phase of winter precipitation is elevation dependent, and in watersheds receiving both rain and snow, hydrologic impacts of climate change are less straightforward than in snowmelt-dominated systems. Here, 29 Pacific Northwest watersheds illustrate how distribution of seasonal snow, transient snow, and winter rain mediates sensitivity to 20th century warming. Watersheds with >50% of their area in the seasonal snow zone had significant (? ? 0.1) trends towards greater winter and lower summer discharge, while lower elevations had no consistent trends. In seasonal snow-dominated watersheds, runoff occurs 22–27 days earlier and minimum flows are 5–9% lower than in 1962, based on Sen’s slope over the period. Trends in peak streamflow depend on whether watershed area susceptible to rain-on-snow events is increasing or decreasing. Delineation of elevation-dependent snow zones identifies climate sensitivity of maritime mountainous watersheds and enables planning for water and ecosystem impacts of climate change.

Bacteria in the sky, making it rain, snow, and hail

ResearchBlogging.orgCross-posted at Highly Allochthonous

Even though we all think of the freezing point of water as 0 °C, very pure water remains a liquid until about -40 °C. Water crystallizes to ice in the presence of tiny nucleation particles in the atmosphere. These particles can be sea spray, soot, dust … and bacteria.

Bacteria are particularly good at ice nucleation (IN), causing it to occur at temperatures as high as -2 °C. As Ed Yong described 3 years ago:

Ice-forming bacteria like Pseudomonas syringae rely on a unique protein that studs their surfaces. Appropriately known as ice-nucleating protein, its structure mimics the surface of an ice crystal. This structure acts as a template that forces neighbouring water molecules into a pattern which matches that of an ice lattice. By shepherding the molecules into place, the protein greatly lowers the amount of energy needed for ice crystals to start growing.

USDA photo of ice on flowers

Ice on fruit tree flowers. There because of bacteria? (USDA photo)

The fact that bacteria like P. syringae nucleate ice crystals has been known for decades. They can be used for gee-whiz science demonstrations, and, at a much larger scale, as one method for creating artificial snow. On the flip side, the presence of P. syringae is also also makes plants more likely to be frost damaged at temperatures just below freezing. Only in the last several years, though, has the role of bacteria in producing precipitation from the atmosphere begun to be appreciated.

First, Brent Christner and colleagues discovered that every freshly fallen snow sample they collected, even in Antarctica, contained these ice nucleating bacteria. In the resulting 2008 Science paper, they noted:

The samples analyzed were collected during seasons and in locations (e.g., Antarctica) devoid of deciduous plants, making it likely that the biological IN we observed were transported from long distances and maintained their ice-nucleating activity in the atmosphere…our results indicate that these particles are widely dispersed in the atmosphere, and, if present in clouds, they may have an important role in the initiation of ice formation, especially when minimum cloud temperatures are relatively warm.

Then researchers in the Amazon rainforest discovered that primary biological aerosol (PBA) particles, including plant fragments, fungal spores…and yes, bacteria, were a dominant contributor to ice nucleation in clouds above the rainforest. (Even the though the Earth surface is hot in the Amazon, high enough in the troposphere, it’s still below freezing.) As Pöschl and colleagues reported in Science in 2010:

Measurements and modeling of IN concentrations during AMAZE-08 suggest that ice formation in Amazon clouds at temperatures warmer than –25°C is dominated by PBA particles… Moreover, the supermicrometer particles can also act as “giant” [cloud condensation nuclei] CCN, generating large droplets and inducing warm rain without ice formation.

The latest contribution to the growing understanding of bacteria’s role in precipitation was recently presented at the American Society of Microbiology meeting. Alexander Michaud studied hailstones that fell on his Montana State University campus, and as reported by the BBC:

He analysed the hailstones’ multi-layer structure, finding that while their outer layers had relatively few bacteria, the cores contained high concentrations. “You have a high concentration of ‘culturable’ bacteria in the centres, on the order of thousands per millilitre of meltwater,” he told the meeting.

What all of this adds up to is that we now know that bacteria and other biological particles are prevalent in the atmosphere around the world and are stimulating multiple forms of precipitation. As a hydrologist, I think I can wrap my head around this. But what’s really wild is the feedback between biological productivity and precipitation and the possibility that the ice nucleating bacteria moving in the atmosphere may be an evolutionary trait.

Precipitation stimulated by ice nucleation above an ecosystem where the bacteria or other biological particles were emitted sustains the ecosystem that created those particles. As Pöschl et al write:

Accordingly, the Amazon Basin can be pictured as a biogeochemical reactor using the feedstock of plant and microbial emissions in combination with high water vapor, solar radiation, and photo-oxidant levels to produce [secondary organic aerosols] SOA and PBA particles (31, 32). The biogenic aerosol particles serve as nuclei for clouds and precipitation, sustaining the hydrological cycle and biological reproduction in the ecosystem.

Or, in discussion of the recent hailstone findings [from the BBC]:

Dr Christner, also present at the meeting, said the result was another in favour of the bio-precipitation idea – that the bacteria’s rise into clouds, stimulation of precipitation, and return to ground level may have evolved as a dispersal mechanism. … “We know that biology influences climate in some way, but directly in such a way as this is not only fascinating but also very important.”

Tara Smith lolbacteria

and ur rainz and ur hailz (image created by Tara Smith on the Aetiology blog)

Christner, B., Morris, C., Foreman, C., Cai, R., & Sands, D. (2008). Ubiquity of Biological Ice Nucleators in Snowfall Science, 319 (5867), 1214-1214 DOI: 10.1126/science.1149757

Pöschl U, Martin ST, Sinha B, Chen Q, Gunthe SS, Huffman JA, Borrmann S, Farmer DK, Garland RM, Helas G, Jimenez JL, King SM, Manzi A, Mikhailov E, Pauliquevis T, Petters MD, Prenni AJ, Roldin P, Rose D, Schneider J, Su H, Zorn SR, Artaxo P, & Andreae MO (2010). Rainforest aerosols as biogenic nuclei of clouds and precipitation in the Amazon. Science (New York, N.Y.), 329 (5998), 1513-6 PMID: 20847268

Geology is destiny: globally mapping permeability by rock type

Cross-posted at Highly Allochthonous

Permeability (the ease with which a fluid moves through a material) is the ultimate goal of many hydrogeologic investigations, because without that information it is impossible to quantify subsurface water and heat flow rates or understand contaminant transport. Yet permeability is notoriously difficult to quantify, both at the local-scale and the landscape-scale. Permeability varies over 13 orders of magnitude across rock and sediment types, because of differences in pore sizes, geometry, and connectedness. Loose gravel could have permeability as high as 10-7 m2, but unfractured igenous and metamorphic rocks could be as low as 10-20 m2. The diagram below is an example of the sort of relationship between rock type and permeability shown near the beginning of every major hydrogeology textbook.

Typical ranges of permeability for different rock types, usually based on hydraulic measurements made at wells.

Typical ranges of permeability for different rock types, usually based on hydraulic measurements made at wells.

Most of the time, hydrogeologists are happy to just to get permeability to within an order of magnitude or two. Knowing permeability is not just useful for those interested in in water supply problems and transport of contaminants. For scientists who model watersheds or land-atmosphere interactions in climate models, being able to easily estimate landscape-scale permeability would be incredibly helpful.

In a new paper in Geophysical Research Letters, scientists from Canada, Germany, the Netherlands, and the US have just done a big favor for those scientists. Gleeson et al. (2010) compiled the first regional-scale maps of permeability for the North American continent and the terrestrial globe. They are interested in permeability in the uppermost 100 m of the subsurface, but below the water table, where all pore spaces are saturated with water. They defined regional-scale as greater than 5 km, because they wanted to avoid influences by things like individual fractures. Using previously published hydrogeologic models, in which permeability was calibrated against groundwater flow, tracers, or heat fluxes, Gleeson and colleagues identified permeability values for 230 hydrogeologic units, grouping them into seven “hydrolithologic” categories, by rock type.

The scientists compared the permeability values from the models to the expected permeabilities for each rock type based on smaller-scale measurements (like those used to make the graph above), and they found reasonably good correspondence. They also examined whether permeability values within each hydrolithologic category were correlated with the scale of the model used to generate them. They found that permeability was scale-independent above 5 km, except in carbonates, where large karst features may result in changing permeability with increasing area.

Using pre-existing geologic maps for North America and the world, Gleeson and colleagues divided the Earth into their hydrolithologic categories. For each category, they calculated the geometric mean of the modeled permeability values, and applied that mean permeability to all of the map units in that category. The resultant maps show the distribution of permeability across the land surface.

Portion of Figure 3c from Gleeson et al. (2010, Geophysical Research Letters).

Portion of Figure 3c from Gleeson et al. (2010, Geophysical Research Letters) showing the permeability distribution across North America. North of the dashed line is continuous permafrost and in that region, the map likely significantly over-estimates permeability.

The global map uses a single geology dataset, so there are no weird boundaries in the data, but it is of coarse resolution. The North American map (shown above) is at much finer resolution (75 km2 mean polygon area, with 262,111 polygons), but it has a few odd edges that correspond to state and national borders. The authors point to these boundary problems in their discussion of caveats, along with the problems associated with permafrost, deep unsaturated zones in arid areas, and deep weathering in the tropics. In addition, the use of a single permeability value for each category will necessarily lump together some terrains with similar rock types but differing geologic histories and resultant permeabilities (e.g., the High and Western Cascades in Oregon).

The work of Gleeson and colleagues represents an important first step in translating regional-scale geologic data into permeability fields. These maps will be useful for continental-scale and larger earth system models and for data sparse regions. Their methodology also raises some interesting possibilities for subdividing the hydrolithologic categories in areas where there are more hydrogeologic model data available, but where there hasn’t been comprehensive hydrogeologic modeling. Finally, their finding that regional-scale model values are in accord with the ranges reported in every hydrogeology textbook is a significant confirmation of the fall-back position of many students of hydrogeology: “If you have no data from wells in your field area, use a textbook to estimate permeability from the rock type.”

Gleeson, T., Smith, L., Moosdorf, N., Hartmann, J., Dürr, H., Manning, A., van Beek, L., & Jellinek, A. (2011). Mapping permeability over the surface of the Earth Geophysical Research Letters, 38 (2) DOI: 10.1029/2010GL045565

Snow, water, digital imaging, metamorphism…and a guillotine!

Cross-posted at Highly Allochthonous

When water infiltrates past the ground surface and begins to percolate through the soil’s unsaturated zone, it doesn’t move downward like an even sheet. Instead, fast fingers of water move downward along pores, roots and other places where flow is easier than through the soil matrix, and water lenses accumulate horizontally where there are changes to less permeable soil horizons. The same principles apply to snow, with the added bonus that the water flowing and the matrix is flowing through are made up of the same substance, separated only by a temperature threshold. So you can get some really complicated dissolution/melting and precipitation/freezing reactions going on throughout the snow profile.

A good way to see these patterns is to apply dyed water to the land or snow surface and then dig a soil or snow pit to examine where the dye ends up. Now Williams et al. (2010) have devised a really cool device for taking sequential, thin, uniform slices of snow off the wall of a snow pit, so that they can see and measure the 3-D structure of preferential flow within the snow profile. They call their device a snow guillotine, because it is basically a sharp blade mounted on a frame that sits on top of the snow surface. A camera is also attached to the frame, at fixed distance from the blade. The blade and camera are mounted on a slider, so after taking a slice and an image of the snow and dye, the scientists can slide it a specified distance and take another slice exposing a new snow surface. (Of course, being good field scientists, all of this can be packed into a remote site, as shown below.)

Figure 4 from Williams et al (2010)
Image from Williams et al (2010) showing the snow guillotine in operation in a dyed snowpack in Colorado. Ski boot for scale.

After the scientists have taken all the slices and photos they want, they can go back to their warm, cozy offices and apply digital image processing techniques to the photos to quantify the 3-D patterns of preferential flow. The vertical images are rectified and can be stacked together into data cubes, allowing the researchers to examine the horizontal centimeter-meter scale patterns as well. You can see this in animated movie of one of their snowpacks in the supplemental materials (no paywall!).

This paper details the results of two dye experiments conducted in Colorado in May and June 2003. Both experiments occurred in isothermal (0 C) snowpacks, but in the second experiment the snow had been isothermal for a longer period of time and had ablated (melted + sublimated) more extensively than in the first dye application. The first experiment showed significant vertical and horizontal heterogeneity, particularly in the upper 20-55 cm of the snowpack, where there were up to 300 distinct vertical preferential flowpaths per square meter. At interfaces between snow layers (i.e., snow that fell at different times) there was significant lateral flow, probably as a result of permeability changes at those boundaries. In lower parts of the snowpack, downward flow was somewhat more evenly distributed and the preferential flowpaths tended to be larger. In the second experiment, more snow metamorphism had occurred, resulting in larger grain sizes and open spaces. In this snowpack, there was still some preferential flow, but, in general, flow was much more evenly distributed throughout the matrix. This finding brings into focus how the snow’s thermal history controls meltwater pathways.

All together then, the dye experiments, cut and photographed by the guillotine setup, and digitally processed in the lab emphasize the importance the small scale (cm to m) heterogeneity on flow through porous media. This isn’t super surprising to people who have spent time studying water flow through soils, but when you are dealing with snow, you add thermodynamics and a matrix that can dramatically metamorphose over time scales of hours to days to weeks to the mix. That adds a level of complexity that makes my mind boggle a little bit, yet Williams et al. have found a simple method to collect to field measurements and process the images in a way that lets them quantitatively describe these flowpaths and will hopefully contribute to a better understanding of the processes and interactions between snowpacks and snowmelt.

Williams, M., Erickson, T., & Petrzelka, J. (2010). Visualizing meltwater flow through snow at the centimetre-to-metre scale using a snow guillotine Hydrological Processes, 24` (15), 2098-2110 DOI: 10.1002/hyp.7630

Diversity in the geosciences and the impact of social media

Cross-posted at Highly Allochthonous

ResearchBlogging.orgOne year ago, Kim Hannula, Pat Campbell, Suzanne Franks, and I launched a survey about women geoscientists reading and writing in the blogosphere. We presented the results at the Geological Society of America meeting, and Kim wrote a great post summarizing and discussing our data. Then I took Kim’s post, polished it up with great wording and thinking suggestions from all of the co-authors and submitted it for publication. It went out to reviewers and a few months later, we were accepted for publication.

In the September issue of GSA Today, you can find our article on The Internet as a resource and support network for diverse geoscientists. We wrote the article with with the idea of reaching beyond the audience that already reads blogs (or attends education/diversity sessions at GSA), with the view that we might be able to open some eyes as to why time spent on-line reading and writing blogs and participating in Twitter might be a valuable thing for geoscientists to be doing. And, of course, we had some data to support our assertions.

GSA Today is an open-access journal, so everyone can and should go ahead and read the whole 2-page paper. But if you want a few highlights, here are some selections from the paper:

The online opportunities for mentoring, networking, and knowledge sharing may be particularly valuable for women and minority geoscientists. Virtual networks offer opportunities to provide support and reduce the professional isolation that can be felt in physical work environments where there are few colleagues of a similar gender, race, or ethnicity. …

Women reported professional and social benefits from reading blogs. We used a five-point scale (1: strongly agree; 3: neutral; 5: strongly disagree) to assess perceived benefits. Of the professional benefits, respondents were most positive about learning things outside their specialty (avg. 1.9), followed by learning within their specialty (avg. 2.3), learning about pedagogy (avg. 2.4), and learning about technology (avg. 2.5). Based on these responses, we conclude that these women blog readers perceive positive professional benefits from their online reading. This suggests that social and other online media could be strategically used to supplement the resources available to all geoscientists, regardless of their gender, ethnicity, geographic location, or employment status. …

Geoscience students perceived the strongest benefits from blog reading, while faculty most strongly agreed that blogs helped them find role models and normalize their experience by finding that many other faculty share their experiences and perspectives. Women in industry perceived less social benefit from blog reading than those in academia, but women in government were the most negative about their blog-reading experiences. In particular, their responses indicated that blog reading had not been helpful to them in finding role models. …

Blogs and other social media may provide a source of community and role models for women geoscientists and help in the recruitment and retention of women from undergraduate education to faculty or industry careers. Our survey results show that blogs are already providing valuable benefits to white, academic women geoscientists, but that existing social media networks could be doing a better job of supporting minority geoscientists and those outside academia. We believe that professional societies, employers, funding agencies, and individual geoscientists should recognize the potential value of social media for supporting a diverse geoscience community. To be effective, such recognition should be accompanied by policies that encourage geoscientists to actively participate in geoscience-related social media opportunities. …

As a white woman geoscientist in academia, I have definitely personally and professionally benefited from my blog reading and writing time. (I even have a publication to show for it!) But I would to love to hear more from minority and outside-of-academia geoscientists about what blogs, Twitter, and other internet-based forms of support could be doing to better support you. As you can see from the paragraph above, what we ended up advocating was that institutional support for blogging and blog-reading would help increase participation. We thought that, with increased participation, more minority and outside-of-academia geosciences voices would emerge, helping others find support, community, role models, and mentoring in voices similar to their own. Meanwhile those of us closer to the white/academic end of the spectrum could learn from all that a diverse geoscientist community has to offer.

One final note, I’m a newbie member of the Diversity in the Geosciences committee for the Geological Society of America. If you have ideas for how GSA could be doing a better job of promoting and supporting diversity off-line and/or on-line, please let me know.

Jefferson, A.J., Hannula, K.A., Campbell, P.B., & Franks, S.E. (2010). The Internet as a resource and support network for diverse geoscientists GSA Today, 20 (9), 59-61 : 10.1130/GSATG91GW.1