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AGU 2013: Transient Storage versus Hyporheic Exchange in Low-gradient Headwater Streams

Abstract season is upon us. I’ll be at AGU, where there looks to be loads of good sessions, including one on “Groundwater-Surface Water Interactions: Physical, biological, and chemical relevance“. Hopefully, my work (abstracted below) will be part of this session.

Transient Storage versus Hyporheic Exchange in Low-gradient Headwater Streams

A.J. Jefferson, S.M. Clinton, M. Osypian

In-channel storage and hyporheic exchange are components of transient storage that exist as a function of geomorphology and which can have contrasting effects on nutrient retention, temperature, and biological communities. In order to evaluate and predict the effects of geomorphic changes on the biogeochemical and ecological functioning of transient storage zones, in-channel storage needs to be quantified separately from hyporheic exchange. In four headwater streams, we used salt injections modeled in OTIS-P to quantify total transient storage fluxes and piezometer measurements to quantify hyporheic fluxes. In the mixed bedrock-alluvial streams, restoration increased both in-channel and hyporheic exchange fluxes, but in-channel transient storage was dominant. In the fully alluvial streams, total transient storage fluxes were ~100 times greater in the stream which had undergone restoration than in one where no restoration had occurred. Conversely, hyporheic fluxes were ~400 times smaller in the restored alluvial stream. Thus, in the restored stream, hyporheic flux was <1% of total transient storage flux, while in the unrestored stream, hyporheic flux accounted for up to 75% of total transient storage fluxes. This difference in the contribution of the hyporheic zone to total transient storage appears to be a function of both channel morphology and bed sediments, primarily the creation of pools and reduction in sediment size that occurred as a result of restoration. These dramatic variations in the magnitude and relative proportions of in-channel and hyporheic fluxes that occur across low-gradient, headwater streams may be an important control on reach-scale biogeochemical and ecosystem functioning.

Brock Freyer defends his MS on the Mighty Mississippi

Two people, standing behind a boat, with river and bluffs in the background.

Brock and Anne at the end of field work on the Mississippi River, July 2008.

Today, Brock Freyer will be defending the results of his M.S. research. The title of his research project is: Fluvial Response to River Management and Sediment Supply: Pool 6 of the Upper Mississippi River System, Southeastern Minnesota.

Brock’s committee is composed of Anne Jefferson (advisor), John Diemer and Ross Meentemeyer.

The defense is on Tuesday April 23, 2013, at 1:30 pm in McEniry 307 of UNC Charlotte. As Brock is currently located in Alaska, this will be a Skype defense. All are welcome to attend.

Abstract:

In this age of environmental restorations and rehabilitations, the scale and extent of projects have been getting larger and more expensive. In the Upper Mississippi River System (UMRS) the U.S. Army Corp of Engineers (USACE) has begun the task of restoring the negative effects that over a century of river management has incurred. Due to the scale and cost of such projects, it is essential to understand the natural and human processes that have affected the river system. In the UMRS, erosion and land loss are considered the dominant geomorphological trend, but Pool 6 of the UMRS is an exception to this norm. In Pool 6, deposition and land growth in recent decades have allowed the river morphology to begin reverting to its condition prior to intense river management. Through the application of varied chronological data sets within ArcGIS, spatial variations were measured to better understand where and why changes have occurred. A nested study area approach was applied to Pool 6 by dividing it into three scales: a general Pool wide observation; a smaller more in-depth observation on an area of island emergence and growth in the lower pool; and a subset of that section describing subaqueous conditions utilizing bathymetric data. The results from this study have indicated that site-specific geographic and hydrologic conditions have contributed to island emergence and growth in Pool 6. In Pool 6 land has been emerging at an average rate of 0.08km2/year since 1975.  Within lower Pool 6, land has been emerging on an average rate of 18m2/year since 1940. The bathymetric subset has shown that sediments on average have gained 2.41m in vertical elevation, which translates into just under 828,000 m3 of sediments being deposited in 113 years.  By identifying and describing these conditions river managers will be able to apply such knowledge to locate or reproduce similar characteristics within degraded sections of the UMRS. If the observations hold true in other locations, restoration efforts will be cheaper, more self-sustaining, promote natural fluvial dynamics, and ultimately be much more successful.

We are currently preparing a manuscript for publication.

Mackenzie Osypian defends her thesis on stream restoration and transient storage

Woman in stream with PVC pipes (piezometers)

Mackenzie tending to piezometers in one of her streams.

Mackenzie Osypian is defending her MS research in Civil Engineering at UNC Charlotte, April 22nd at 4:00 pm in McEniry Hall 441 on the UNC Charlotte campus. Mackenzie is advised by Anne Jefferson and Sandra Clinton. John Daniels and Jim Bowen are on her committee.

Mackenzie’s research is titled: “Evaluating restoration effects on transient storage and hyporheic exchange in urban and forested streams.”  Her abstract is below:

Millions of dollars are spent each year on restoration projects designed to improve stream habitat, but few studies have investigated effects of restoration on groundwater- surface water interactions. Hyporheic exchange and transient storage in four second-order streams (urban/forest; restored/unrestored) were studied by measuring geomorphology, streambed vertical head gradients and water fluxes, and by using conservative, impulse-loaded tracer studies along with the OTIS model. Total storage exchange and percent hyporheic exchange were found by utilizing the OTIS P parameters and the sum of downwelling fluxes calculated in SURFER. The upwelling and downwelling varied between -1.783 m/m to 3.760 m/m in the restored urban stream, which contains large step structures, while the unrestored urban stream had no measured upwelling or downwelling (0 m/m) along the reach, which is incised to bedrock.  The forested restored stream had a smaller range of hydraulic gradients (-0.012 m/m to 1.99 m/m) compared to the forested unrestored stream, which ranged from -0.725 m/m to 0.610 m/m. The forested unrestored reach had the highest percent of hyporheic exchange, reaching 22% during the winter season. The urban restored has the smallest percent of hyporheic exchange of 0% across all seasons due to the exposure of bedrock in the streambed. The restored reaches were found to have between 0% and 6% of total transient storage exchange occurring in the hyporheic zones, with some seasonal variability.

The results indicate that restoration increases the hyporheic storage when the stream has incised to bedrock, but that large in-channel storage is also created. When the stream has an alluvial bed (as in the forested streams), the percent of hyporheic flow compared to total storage is reduced. The forested unrestored stream had the largest average hydraulic conductivity of 0.006 cm/s compared to the forested restored, 0.001 cm/s, and the urban restored, 0.001 cm/s.  The restored forested site had a maximum area to storage area ratio of 247 m2/m2 in the spring, which was higher than the forested unrestored site. That site had a maximum of 16.4 m2/m2, which occurred during the fall season.

We are currently preparing her thesis for publication.

Condit Dam Removal video

No excited Gordon like at Marmot Dam, but this is one exciting “blow and go” dam removal video. This was Condit Dam on the White Salmon River in Washington in October 2011. Spectacular to watch, and even neater knowing that there was important (and hair-raising) science being done both upstream and downstream of the dam throughout the dam removal process.

Anne’s November Navigations

Cross-posted at Highly Allochthonous

I’m not joining the exodus of geoscientists to AGU this week; I’m still recovering from November.

I’m not sure whether I spent more time in Ohio or outside of it last month. The month started with the rain and runoff from our brush with Superstorm Sandy, but by November 2nd I had a car packed full of conference and research gear and was heading south to North Carolina. The drive south was a great chance to watch all sorts of geology go by at interstate speeds. I started out in the glaciated Appalachian Plateau, drove south of the glacial limit, crossed the Ohio River, and was soon in the heart of the Appalachians and West Virginia‘s coal mining country. On Interstate 77, the border between West Virginia and Virginia seems to mark the dramatic transition the Valley and Ridge Province, then it is up on to the Blue Ridge and finally down the Blue Ridge Escarpment and into the Piedmont and North Carolina, finally arriving in Charlotte after eight hours of driving. Climatically, I left the cold and damp, drove through the snow left behind by Sandy, and ended up in the warm, sunny, and very dry south.

The Geological Society of America meeting was a busy time. I convened two sessions, helped lead a field trip and had more meetings for committees and with colleagues than I care to remember. But it was a great time to hear about exactly the sorts of science that I find most interesting and to get out in the field with 50 friends and colleagues to talk about new ideas in geomorphology.

  • Geomorphology of the Anthropocene: The Surficial Legacy of Past and Present Human Activities. We had an amazing slate of speakers that packed the room, fantastic poster presenters that drew a crowd, and we were able to announce that we will be editing a special issue of the new journal Anthropocene with papers from the session. Then the journal’s publisher threw us a special reception.
  • Hydrology of Urban Groundwater, Streams, and Watersheds. This session featured another roster of incredible speakers and a kick-ass set of posters featuring many of my students and colleagues from UNC Charlotte.
  • Kirk Bryan Field Trip: Piedmont Potpourris: New Perspectives on An Old Landscape (and Some of its Younger Parts. The annual syn-meeting field trip of the Quaternary Geology and Geomorphology division always features good scenery and intense but friendly discussions. This year we looked at an old mill dam site in an urban stream and channel heads and terrace soils near the Catawba River, and then we climbed a monadnock to talk about Blue Ridge escarpment retreat and the long term evolution of landscapes. Plus, we had a delicious lunch of NC barbecue on our able and charismatic field trip leader’s front lawn.

Missy Eppes atop a red soil pit.

Field trip leader Missy Eppes atop a typically red soil profile, on a terrace above the Catawba River.


50 geomorphologists on the front steps

An enthusiastic and well fed group of geomorphologists and Quaternary geologists on a delightful November day.


Geomorphologists on a rock listening to Ryan McKeon

On top of Crowders Mountain, learning from Ryan McKeon.

After the meeting was over, I stuck around Charlotte for a few days, with plans to do a tracer injection in one of my local field sites. As I’ve already shown you, that didn’t work out so well. So I headed back north.

Back in Ohio, I did some exploring of Cuyahoga Valley National Park, which was timely given that I am just about to submit a proposal to do work in the headwater streams in and around the park. I also spent a wonderful day with someone from the Ohio EPA, looking at dam removal and stream restoration sites in the region.

Stream with sediment and trees

Headwater stream near Brandywine Creek, CVNP, November 2012.

My fun explorations of Ohio streams were tempered with sadness though. Just before Thanksgiving, my sweet, 14-year old canine companion, Cleo passed away. She was my longest running and most faithful field assistant, and I’ll miss her forever.

Dog meets spring

Cleo, in ~2005, at one of my PhD field sites.

But then it was off to Baltimore to visit with Claire Welty and the folks at the Center for Urban Environmental Research and Education, who do some of the coolest urban hydrology work around. They also host the Baltimore Ecosystem Study field site.

Sign on door reads "Baltimore Ecosystem Study"

That was just the warm-up for the real reason for my trip, giving a seminar in the Department of Geography and Environmental Engineering at The Johns Hopkins University. My talk was on “drainage network evolution is driven by coupled changes in landscape properties and hydrologic response,” in which I attempted to integrate the Oregon Cascades, North Carolina Piedmont, and urban landscapes. It was a thrill and an honor to give a Reds Wolman seminar at JHU, which is my undergraduate alma mater, and the experience was made even more memorable by a morning spent exploring stream restoration sites with Profs. Peter Wilcock and Ciaran Harman. We saw some sites that made some sense, and some that were a bit…non-sensical? I will come out and say it, I’m not a fan of what happened to the little granite pegmatite knickpoint where I went as an undergraduate to try to pretend I wasn’t really in the city. But a bit farther upstream, I could see the value in installing some nice structures that stabilized banks and increased accessibility to the stream in a park popular with joggers and dog-walkers.

JHU profs Wilcock and Harman discuss the restoration of Baltimore's Stony Run

JHU profs Wilcock and Harman discuss the restoration of Baltimore’s Stony Run

And that pretty much brought me to the end of November. I’m looking forward to no travel in December, at least until the end of the month. But that doesn’t mean I won’t stay busy.

Call for GSA abstracts on urban hydrology and anthropogenic geomorphology

I’m convening two fantastic sessions at the upcoming Geological Society of America meeting in Charlotte, North Carolina on November 4-7, 2012. For both sessions there are incredible invited speakers lined up, and all we need to make them an overwhelming success is a strong showing of contributed abstracts. That’s where you come in. If you are interested in the way humans interact with hydrology or landscapes, please consider submitting an abstract by August 14th.

Low head dam

An urban stream in Freedom Park, Charlotte, NC


T101. Hydrology of Urban Groundwater, Streams, and Watersheds
conveners: Anne J. Jefferson, John M. Sharp
This session explores how urbanization affects water quantity, quality, and ecohydrology in groundwater and surface water systems. Field and modeling studies of flow, recharge, water balance, groundwater-stream interactions, water quality, and contamination are welcome. Confirmed invited speakers are Laura Toran, Christina Tague, and Ken Howard.

A straight, ditched stream in northeastern Ohio

A straightened and ditched stream in northeastern Ohio is probably the legacy of agriculture

T24. Geomorphology of the Anthropocene: The Surficial Legacy of Past and Present Human Activities
conveners: Anne J. Jefferson, Karl W. Wegmann, Anne Chin
This session explores the legacy of human activities and land use on earth surface processes and landforms. Studies on the impacts of agriculture, mining, urbanization, and forestry in prehistoric, historic, and modern times are welcome. Confirmed invited speakers are Ellen Wohl, Allan James, and Gary Stinchcomb.

If the descriptions above don’t match your research, but you know someone who would be perfect, please share with them or send me their contact information and I’ll personally reach out. Even if you just think these topics might be interesting to listen to for a few minutes or hours, plan on attending the sessions in November. I’ll share details of dates, times, and locations when the final program is announced.

Cross-posted at Highly Allochthonous

New paper in press: Jefferson and McGee, Channel network extent …in the North Carolina Piedmont

Jefferson, A. and McGee, R.W. in press. Channel network extent in the context of historical land use, flow generation processes, and landscape evolution in the North Carolina Piedmont, Earth Surface Processes and Landforms

Here’s the abstract:

Intensive agricultural land use in the 18th through early 20th centuries on the southeastern Piedmont resulted in substantial soil erosion and gully development. Today, many historically farmed areas have been abandoned and afforested, and such landscapes are an opportunity to study channel network recovery from disturbance by gullying. Channel initiation mapping, watershed area-slope relationships, and field monitoring of flow generation processes are used to identify channel network extent and place it in hydrologic, historical and landscape evolution context. In six study areas in the North Carolina Piedmont, 100 channel heads were mapped in fully-forested watersheds, revealing a channel initiation relationship of 380=A*S1.27, where A is contributing area (m2) and S is local slope (m/m). Flow in these channels is generated by subsurface and overland flow. The measured relative slope exponent is lower than expected based on literature values of ~2 for forested watersheds with subsurface and overland flow, suggesting that the channel network extent may reflect a former hydrological regime. However,geomorphic evidence of recovery in channel heads within fully forested watersheds is greater than those with present day pasture. Present day channel heads lie within hollows or downslope of unchanneled valleys, which may be remnants of historical gullies, and area-slope relationships provide evidence of colluvial aggradation within the valleys. Channel network extent appears to be sensitive to land use change, with recovery beginning within decades of afforestation. Channel initiation mapping and area-slope relationships are shown to be useful tools for interpreting geomorphic effects of land use change.

The paper is now available on-line at: http://onlinelibrary.wiley.com/doi/10.1002/esp.3308/abstract.

One of the channel heads mapped in our paper. Cleo, our longest-serving lab member, is sadly uncredited in the acknowledgements.

AGU 2011 abstract: Understanding channel network extent in the North Carolina Piedmont in the context of legacy land use, flow generation processes, and landscape dissection

The following talk will be presented by Anne at the 2011 AGU fall meeting on Wednesday, December 7th from 9 to 9:15 am in the session “EP31G. Predictive Understanding of Coupled Interactions Among Water, Life, and Landforms II.” It will be in rooms 2022-2024, and the abstract acceptance said something about video on demand.

Understanding channel network extent in the North Carolina Piedmont in the context of legacy land use, flow generation processes, and landscape dissection

Anne J. Jefferson and Ralph W. McGee
Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC

Nearly all land in the eastern US Piedmont region was cleared for intensive agriculture following European settlement, but some areas have been afforested over the last century. In these areas, an extensive ephemeral stream network drains into perennial headwater streams. In order to understand the present-day functioning of the ephemeral network in afforested watersheds, we mapped 102 channel head positions at 6 sites and monitored 6 channels at 2 sites in North Carolina’s Piedmont. The ephemeral channels are activated by subsurface flow from high intensity precipitation with wet or dry soils, or long duration precipitation with wet soils. Overland flow does not occur upslope of channel heads in forested watersheds, but it is observed in present-day pastures and fields.

Channel head contributing areas range from 0.1 – 3.0 ha, with local slopes that average 0.13 (range: 0.04 – 0.36). The relationship between slope and area at the channel heads has the form c = AS1.1, with an exponent much lower than the commonly reported exponent of ~2 that is associated with subsurface or saturation overland flow. Instead, the lower exponent may reflect the legacy of 18th-19th century of intense land use and degraded cover, which may have produced turbulent overland flow upslope of channels. Though established by relict land use conditions, we suggest that this network extent is maintained by the frequent activation of the channels through subsurface flow under forest cover. Further, channel heads are located within or downslope of colluvial hollows suggesting that gullying from historical land use is not the most extensive channel network experienced by the Piedmont over the course its landscape evolution, and that the dissection of the landscape may be the result of a precipitation and land cover regime much different from the modern one.

Gully down to bedrock, Morrow Mountains State Park, North Carolina (photo by A. Jefferson)

Gully down to bedrock, Morrow Mountains State Park, North Carolina (photo by A. Jefferson)

GSA 2011 abstract: Spatial variability in groundwater-stream interactions in first-order North Carolina Piedmont streams

At the 2011 GSA Meeting in Minneapolis next week, I’ll be presenting the following talk in the session “Monitoring and Understanding Our Landscape for the Long Term through Small Catchment Studies I: A Tribute to the Career of Owen P. Bricker.” My talk is in Minneapolis Convention Center: Room M100FG, on Wednesday, 12 October 2011 at 9:30 am.

Spatial variability in groundwater-stream interactions in first-order North Carolina Piedmont streams

JEFFERSON, Anne J. and MOORE, Cameron, Dept. of Geography and Earth Sciences, University of North Carolina at Charlotte,

Groundwater upwelling and hyporheic exchange are spatially variable in three first-order Piedmont streams, resulting in variable discharge, water chemistry and temperature. Stream gradient, valley confinement, and woody debris jams appear to be the major controls on the distribution and size of upwelling zones. Temperature and specific conductance values at 25 m intervals on 18 dates revealed distinct zones of groundwater-stream interaction, confirmed by discharge and piezometer measurements. Baseflow accumulates unevenly along the streams, with upper reaches in confined valleys generally gaining discharge more rapidly than lower reaches. Elevated calcium concentrations occur in groundwater upwelling zones, such as in a 50 m reach in which baseflow triples. Near their mouths, where the streams reach a river floodplain, baseflow quantity and chemistry may be influenced by a larger groundwater system. At a smaller scale, spatial variability in stream chemistry and streambed hydraulic gradients are dominantly controlled by the size and position of woody debris jams. Fine sediment wedges extend 5-15 m upstream of the 0.25-1 m high jams, and strong down-welling hydraulic gradients occur in these areas. Upwelling of water with higher specific conductance and moderated temperatures occurs downstream of the jams. Nitrate concentrations decreased up to 50% immediately below large woody debris jams, while ammonium concentrations tended to be highest there.

Rapid urbanization in the Carolina Piedmont is drastically altering headwater catchments, but well-documented reference watersheds are lacking. The measurements described above are from three first-order streams in forested watersheds, with permanent protection by a land conservancy. Their hydrology and water chemistry demonstrates the rich spatial variability of Piedmont headwater streams, and we hope that long-term study of these sites provides useful understanding for stream restoration and watershed management.

Debris jam and sediment in a first order Deep Creek at Redlair. Photo by Cameron Moore.

Debris jam and sediment in a first order Deep Creek at Redlair. Photo by Cameron Moore.

Chapman Abstract: Top down or bottom up? Volcanic history, climate, and the hydrologic evolution of volcanic landscapes

In July 2011, Anne was a plenary speaker at the Chapman Conference on The Galápagos as a Laboratory for the Earth Sciences in Puerto Ayora, Galapágos. Anne was tasked with reviewing the state-of-knowledge of volcanic island hydrology and identifying pressing questions for future research in this 40 minute talk. The following is the abstract which she submitted when she began the task.

Top down or bottom up? Volcanic history, climate, and the hydrologic evolution of volcanic landscapes

Volcanic landscapes are well suited for observing changes in hydrologic processes over time, because they can be absolutely dated and island chains segregate surfaces of differing age. The hydrology of mafic volcanic landscapes evolves from recently emplaced lava flows with no surface drainage, toward extensive stream networks and deeply dissected topography. Groundwater, a significant component of the hydrologic system in young landscapes, may become less abundant over time. Drainage density, topography, and stream and groundwater discharge provide readily quantifiable measures of hydrologic and landscape evolution on volcanic chronosequences. In the Oregon Cascades, for example, the surface drainage network is created and becomes deeply incised over the same million-year timescale at which springs disappear from the landscape. But chronosequence studies are of limited value if they are not closely tied to the processes setting the initial conditions and driving hydrologic evolution over time.

Landscape dissection occurs primarily by erosion from overland flow, which is absent or limited in young, mafic landscapes. Thus, volcano hydrology requires conceptual models that explain landscape evolution in terms of processes which affect partitioning of water between surface and subsurface flows. Multiple conceptual models have been proposed to explain hydrologic partitioning and evolution of volcanic landscapes, invoking both bottom up (e.g., hydrothermal alteration) and top down processes (e.g., soil development). I suggest that hydrologic characteristics of volcanic islands and arcs are a function of two factors: volcanic history and climate. We have only begun to characterize the relative importance of these two drivers in setting the hydrologic characteristics of volcanic landscapes of varying age and geologic and climatic settings.

Detailed studies of individual volcanoes have identified dikes and sills as barriers to groundwater and lava flow contacts as preferential zones of groundwater movement. Erosion between eruptive episodes and deposits from multiple eruptive centers can complicate spatial patterns of groundwater flow, and hydrothermal alteration can reduce permeability, decreasing deep groundwater circulation over time. Size and abundance of tephra may be a major geologic determinant of groundwater/surface water partitioning, while flank collapse can introduce knickpoints that drive landscape dissection. The combination of these volcanic controls will set initial conditions for the hydrology and drive bottom up evolutionary processes.

Climatic forcing drives many top down processes, but understanding the relative effectiveness of these processes in propelling hydrologic evolution requires broader cross-site comparisons. The extent of weathering may be a major control on whether water infiltrates vertically or moves laterally, and we know weathering rates increase until precipitation exceeds evapotranspiration. Weathering by plant roots initially increases porosity, but accumulation of weathered materials, such as clays in soils, can reduce near-surface permeability and promote overland flow. Similarly, eolian or glacial inputs may create low permeability covers on volcanic landscapes.

View into the crater of Sierra Negra Volcano on Isabella Island, Galapagos

View of the 2005 lava inside the crater of Sierra Negra Volcano on Isabella Island, Galapagos. Photo by A. Jefferson