Darren Reilly, co-advised in the Watershed Hydrology Lab, won first place in the student poster competition for his work on groundwater contamination in northeastern Pennsylvania at the Mudrocks Symposium and Student Expo, co-hosted by the Appalachian Geological Society and Eastern Section AAPG, in Morgantown, W.Va.
Currently browsing category
Brandon S. Blue will defend his M.S. in Earth Sciences at UNC Charlotte on Monday, July 23rd, 2012 at 10:30 am in McEniry 329. His presentation is open to the public. Brandon’s project is Seasonal Urban Stream Temperature Response to Storm Events Within the Piedmont of North Carolina. He is co-advised by Anne Jefferson and Sara McMillan, and Craig Allan is on his committee.
WordPress just emailed me this handy review of blog stats for last year. According to them, these are the posts and pages that got the most views in 2010. Given that the point of this blog is to (1) keep prospective students and other people interested in my research and teaching up-to-date on opportunities and activities and (2) collect my on-line writings in one place, I’m pretty pleased with the mix of posts that show up in this list. I think in 2011 I’ll be experimenting with ways to do more of the first item here and more research oriented blogging both here and at Highly Allochthonous.
Megafloods from Glacial Lake Missoula June 2009
The latest Where on Google Earth image featured a gorgeous alluvial fan in the Zagros mountains of Iran. The Google Earth imagery does not show this fan in flood, but an ASTER image from a few years ago does.
Image credit to: NASA/GSFC/METI/ERSDAC/JAROS and U.S./Japan ASTER Science Team
Link to NASA ASTER image gallery: http://asterweb.jpl.nasa.gov/gallery-detail.asp?name=iranfan
I’d say see for yourself in Flash Earth, but unfortunately the imagery appears to be pretty poor quality for this area: http://www.flashearth.com/?lat=28.994958&lon=55.049338&z=8.5&r=0&src=nasa.
Inspired by Brian’s theme for the month, this basin and range landscape in central Idaho caught my eye. I love the way the center-pivot irrigation boundaries outline the edges of the alluvial fans. Closer examination reveals even more juxtaposition, as a river cuts through the middle of the valley, further limiting the extent of agricultural and human influence. I’d imagine that the arable areas have been somewhat dynamic of historical time as the river changes course and as the fans continue to build. In the second image, you can see some incomplete irrigated circles, where presumably the alluvial fan is too active to allow agricultural productivity.
The flash earth imagery is also rather nice. http://www.flashearth.com/?lat=44.553052&lon=-113.819471&z=11.9&r=319&src=msa
It’s been kind of quiet around here lately. Maybe because it is mid-summer in the Northern Hemisphere and all of my fellow geopathologists are at the beach?
Speaking of beaches, I was scoping out the Dorset coast of England looking for a famous fossil forest locality when I spotted this beautiful example of coastal geomorphology processes. Some sort of break in the resistant coastline has allowed waves to excavate this lovely inlet called Lulworth Cove, which now sports a textbook example of wave refraction and the dispersal of wave energy that allows a beach to develop. Oh and that fossil forest? It’s the Jurassic Purbeck Fossil Forest and it’s in the center of the frame.
Where are we? N 50.62 W 2.24
It starts when when a water molecule in precipitation lands on the ground, and it ends when that same water molecule leaves the watershed as streamflow. In between, that molecule may move over the land surface, through the soil in big holes (macropores) or in tiny spaces between grains in the soil, through the bedrock as groundwater, or any combination of those pathways. How long it takes for the water molecule to make its journey, what hydrologists call the transit time, depends on the flow paths that it takes. And that transit time, in turn, affects biogeochemical processing and contaminant persistence. Inversely, if hydrologists can measure the distribution of transit times for a particular watershed, they can infer things about the storage, flowpaths, and sources of water in the watershed. Thus, transit time distributions help us peek into the hidden inner workings of the watershed….if we understand what we are really measuring and what those measurements are really telling us. And that topic is one of lots of active research in the community of watershed hydrologists, and its the subject of a number of recently published papers.
In what seems to be an annual tradition, Hydrological Processes has devoted their June issue to topics relating to catchment hydrology and flowpath tracers. This year, the focus is Preferential Flowpaths and Residence Time Distributions and it’s edited by Keith Beven. It’s the sort of issue that makes me want to go over to the library stacks and spend the day in a comfy chair reading and enjoying the journal from cover to cover. While all of the articles in this special issue make my pulse race a little, here are a couple that really strike my fancy:
McDonnell, J., McGuire, K., Aggarwal, P., Beven, K., Biondi, D., Destouni, G., Dunn, S., James, A., Kirchner, J., Kraft, P., Lyon, S., Maloszewski, P., Newman, B., Pfister, L., Rinaldo, A., Rodhe, A., Sayama, T., Seibert, J., Solomon, K., Soulsby, C., Stewart, M., Tetzlaff, D., Tobin, C., Troch, P., Weiler, M., Western, A., Wörman, A., & Wrede, S. (2010). How old is streamwater? Open questions in catchment transit time conceptualization, modelling and analysis Hydrological Processes, 24 (12), 1745-1754 DOI: 10.1002/hyp.7796
In this invited commentary, McDonnell and 28 colleagues lay out the definition of transit time and the current limits of our understanding on its controls in watersheds and its relationship to hydrograph characteristics, groundwater, and biogeochemical processing. They then provide their research vision for pushing past these limits, through a combination of field research and advances in modeling.
Kirchner, J., Tetzlaff, D., & Soulsby, C. (2010). Comparing chloride and water isotopes as hydrological tracers in two Scottish catchments Hydrological Processes, 24 (12), 1631-1645 DOI: 10.1002/hyp.7676
Oxygen isotopes of water and chloride concentrations have been widely used to estimate watershed travel times. They are generally regarded as conservative tracers, but they are not perfect. Here Kirchner et al. compare the time series of the two tracers for a pair of Scottish catchments and show that while both tracers exhibit strongly damped signals relative to precipitation, the travel times calculated using oxygen isotopes were 2-3 times longer than for chloride. So it seems that both tracers are telling us similar things about the ways that catchments move and store water, but that quantitative estimates of travel time are going to be tricky to compare across tracers.
Stewart, M., Morgenstern, U., & McDonnell, J. (2010). Truncation of stream residence time: how the use of stable isotopes has skewed our concept of streamwater age and origin Hydrological Processes, 24 (12), 1646-1659 DOI: 10.1002/hyp.7576
The stable isotopes of water have a shelf life of about 5 years or less. It’s not that they break down (they are stable isotopes, after all); it’s that seasonal input signals get damped over time, so that ages greater than 5 years can’t be resolved. In contrast, tritium (the unstable isotope of hydrogen) has a half life of ~12.4 years. A few decades ago, water ages were estimated using tritium, which conveniently had a bomb peak that made a handy marker of recharge in the early 1960s. These days, water ages are usually estimated by the stable isotopes alone. In this paper, Stewart et al suggest that we are missing part of the story when we use just stable isotopes, because we effectively discount any contributions from water >5 years since it feel from the sky. Incidentally, those contributions that we have been neglecting? That’s the bedrock groundwater and it might be quite important to explaining the behavior of streams. Stewart et al. suggest that we return to embracing tritium as part of a “dual isotope framework” so that we can more accurately quantify groundwater contributions to streamflow. The issue of the shape of travel time distributions (are they exponential or fractal?) is explored in more detail in a paper by Godsey et al. in the same issue and Soulsby et al. explore how relationships between transit times and hydrograph and watershed characteristics might be used to estimate streamflows in data-sparse mountain watersheds.