Boulder Creek CZO presentations, Fall AGU meeting 2011
Monday, December 5
Prototype cross-domain cyberinfrastructure for the Critical Zone
Observatories
Tom Whitenack1, Ilya Zaslavsky1, Mark W Williams2, Kerstin A Lehnert3, David G
Tarboton4, Kim Schreuders4, Anthony Keith Aufdenkampe5, Emilio Mayorga6
1. San Diego Supercomputer, UCSD, La Jolla, CA, United States.
2. University of Colorado, Boulder, CO, United States.
3. Columbia University, New York, NY, United States.
4. USU, Logan, UT, United States.
5. Stroud Water Research Center, Avondael, PA, United States.
6. University of Washington, Seattle, WA, United States.
ABSTRACT FINAL ID: IN11C-1305; SESSION TYPE: Poster SESSION TITLE: IN11C.
Cyberinfrastructure That Advances Understanding of Ecosystem Processes Posters
ABSTRACT BODY: The Critical Zone Observatory (CZO) program is a multiinstitutional, collaborative effort to advance scientific understanding of
environmental interactions in the critical zone, which extends from bedrock to the
atmospheric boundary layer and spans multiple scales and disciplines. An
integrated CZO information system that facilitates seamless analysis of hydrology,
geochemistry and geomorphology data within and across six CZO sites is being
developed. This is comprised of easy to use tools for site data managers to publish
their quality controlled data and tools for scientists to identify and access data of
interest so that they can use data from multiple sites to address cross discipline and
cross CZO hypotheses. It is based on the following principles: (1) building on the
experience of environmental observatory projects and leveraging CI development
efforts from neighboring disciplines; (2) relying on community standards for data
exchange and on state-of-the-art data cataloguing, discovery, integration and
visualization tools; (3) preserving the autonomy and minimizing requirements on
individual research sites, while creating centralized CI components that achieve
cross-CZO integration and are scalable and extensible; (4) ensuring that CZO data
are available both in a human-readable form at individual CZO sites and via web
services from the centralized components of the system.
The current prototype is designed as an evolving, operational system capable of
supporting data integration at different interoperability levels: from common
dataset-level metadata, which enables data discovery and retrieval regardless of the
type or domain system that manages it, to compatible semantics, which ensures that
metadata can be unambiguously interpreted in a cross-disciplinary setting, to
compatibility at the levels of service interfaces and information model encodings,
such as those standardized by the Open Geospatial Consortium, which enables
flexible programmatic access to the data from analysis and modeling applications.
The prototype builds on infrastructure components developed mostly within the
CUAHSI Hydrologic Information System project, and is designed to extend to
geochemical and other data being collected by CZOs. Site data managers publish
data and metadata in an agreed upon ASCII display file format on their web sites for
public access. These files are automatically ingested into the CZO central data
repository, validated against shared vocabularies, and archived in a set of centrallymanaged databases, from which they become available via standard web services
and can be visualized and analyzed using several client applications. At this early
stage, the CZO Central discovery system currently indexes about 90 resources,
including services and display files, while brokering web service access to over 15
million hydrologic observations collected at CZOs.
Hydrologic flowpaths and biogeochemical cycles in the subalpine Como Creek
catchment, Colorado Front Range, USA
Rory M Cowie1, Mark W Williams1, Morgan M Zeliff1, Jordan Parman1
1. INSTAAR, University of Colorado, Boulder, CO, United States.
ABSTRACT FINAL ID: H13C-1220; SESSION TYPE: Poster SESSION TITLE: H13C.
Seasonal Effects of Climate Variability and Change on Hydrological and
Biogeochemical Processes I Posters
ABSTRACT BODY: An outstanding question for snowmelt-dominated watersheds of
the western US are the responses of biogeochemical processes to two major drivers
of environmental change: directional changes in climate and increasing dissolved
inorganic nitrogen (DIN) deposition in wetfall. In the Colorado Front Range,
atmospheric deposition of DIN has increased several-fold in the last 25 years. In
response, nitrate concentrations at the alpine Green Lakes 4 (GL4) catchment have
increased from 1985 to 2009 by 0.27 μeq L-1 yr-1. In contrast, we see no directional
change in either nitrate concentrations or fluxes in the subalpine Como Creek
catchment. We hypothesize that differences in surface/groundwater interactions
result in the differing behavior of stream nitrate between the alpine and subalpine
catchments that are receiving similar amounts of DIN from atmospheric deposition.
For both basins we sampled precipitation, snowpack, snowmelt, surface water, and
subsurface waters. All water samples are analyzed for geochemical, nutrient and
isotopic (δ18O, δD) composition. Stream chemistry data from the last ten years at
Como Creek show increases in nitrate concentration during baseflow conditions and
then a sharp decline during snowmelt. In contrast, in the alpine basin there is sharp
increase in surface water nitrate during snowmelt. Hydrograph separation at the
alpine GL4 using end member mixing analysis (EMMA) shows that stream flow is a
mixture of three components, groundwater, talus, and new snowmelt that each
contribute to roughly a third of discharge, with talus flow supplying the majority of
nitrate. In contrast, and somewhat surprisingly, EMMA shows that for the subalpine
Como Creek basin, annual streamflow is a mixture of only two components,
groundwater and new snowmelt. During snowmelt the groundwater and snow
contributions are nearly equal and subsurface flows dominate the remainder of the
year. Newly installed piezometers at Como Creek provide evidence that the basin is
largely a losing reach during snowmelt, with water levels in the piezometers
increasing 5-7 m. After peak snowmelt however, Como Creek becomes a gaining
stream, with piezometer levels dropping. Thus, both EMMA and piezometers show
that surface-groundwater interactions are tightly coupled during snowmelt, with
snowmelt at Como first replenishing the subsurface water deficit and increasing
groundwater levels before contributing to discharge. Thus, in contrast to the alpine
GL4 basin, DIN released in snowmelt is assimilated belowground as snowmelt
infiltrates the subsurface in the subalpine basin.
Interestingly, at the subalpine Como Creek basin, isotopic and geochemical solute
concentrations undergo shifts during periods of winter baseflow prior to snowmelt.
In winter much of the stream is frozen and we hypothesize that cryo-concentration
of solutes and fractionation of isotopes may influence the concentrations of winter
stream samples.
Inverse Geochemical Reaction Path Modelling and the Impact of Climate
Change on Hydrologic Structure in Snowmelt-Dominated Catchments in the
Southwestern USA
Jessica M Driscoll1, Thomas Meixner1, Noah P Molotch2, James O Sickman3, Mark W
Williams2, Jennifer C McIntosh1, Paul D Brooks1
1. Hydrology and Water Resources, University of Arizona, Tucson, AZ, United States.
2. INSTAAR, Colorado University, Boulder, CO, United States.
3. Environmental Sciences, Univeristy of California at Riverside, Riverside, CA,
United States.
ABSTRACT FINAL ID: H13C-1221; SESSION TYPE: Poster SESSION TITLE: H13C.
Seasonal Effects of Climate Variability and Change on Hydrological and
Biogeochemical Processes I Posters
ABSTRACT BODY: Snowmelt from alpine catchments provides 70-80% of the
American Southwest’s water resources. Climate change threatens to alter the timing
and duration of snowmelt in high elevation catchments, which may also impact the
quantity and the quality of these water resources. Modelling of these systems
provides a robust theoretical framework to process the information extracted from
the sparse physical measurement available in these sites due to their remote
locations. Mass-balance inverse geochemical models (via PHREEQC, developed by
the USGS) were applied to two snowmelt-dominated catchments; Green Lake 4
(GL4) in the Rockies and Emerald Lake (EMD) in the Sierra Nevada. Both
catchments primarily consist of granite and granodiorite with a similar bulk
geochemistry. The inputs for the models were the initial (snowpack) and final
(catchment output) hydrochemistry and a catchment-specific suite of mineral
weathering reactions. Models were run for wet and dry snow years, for early and
late time periods (defined hydrologically as ½ of the total volume for the year).
Multiple model solutions were reduced to a representative suite of reactions by
choosing the model solution with the fewest phases and least overall phase change.
The dominant weathering reactions (those which contributed the most solutes)
were plagioclase for GL4 and albite for EMD. Results for GL4 show overall more
plagioclase weathering during the dry year (214.2g) than wet year (89.9g). Both wet
and dry years show more weathering in the early time periods (63% and 56%,
respectively). These results show that the snowpack and outlet are chemically more
similar during wet years than dry years. A possible hypothesis to explain this
difference is a change in contribution from subsurface storage; during the wet year
the saturated catchment reduces contact with surface materials that would result in
mineral weathering reactions by some combination of reduced infiltration and
decreased subsurface transit time. By contrast, during the dry year infiltration and
subsequent displacement of stored water that has had longer contact time with
minerals and therefore has become more geochemically evolved to produce a
greater difference between snowmelt and catchment outlet hydrochemistry. The
results for EMD show little distinction between albite weathering for wet and dry
years (55.9g and 66.0g, relatively). A hypothesis for this lack of difference in mineral
phase changes may be due to less subsurface storage capacity in EMD relative to
GL4. The spatial distribution of snowmelt has also been shown to influence the
integrated watershed response, and future work includes using the Alpine
Hydrochemical Model (AHM) to further investigate catchment response to these
spatial data. The AHM will also provide further insight of surface-groundwater
interactions through a more integrated model which includes hydrochemical,
biological and physical processes to elucidate catchment response to changes in
snowmelt dynamics.
Tuesday, December 6
Slope deposits of different genesis and ages in the Colorado Front Range
(Rocky Mts.) and their significance for the relief and the interflow within the
critical zone.
Joerg Voelkel1, Matthias Leopold1, Juliane Huber1
1. Center of Life Sciences Weihenstephan, Technische Universitaet Muenchen,
Freising, Germany.
ABSTRACT FINAL ID: EP21C-0718; SESSION TYPE: Poster SESSION TITLE: EP21C.
The Morphodynamics of Mountain Streams: Fluvial, Debris Flow, and Hillslope
Processes I Posters
ABSTRACT BODY: The Colorado Front Range is divided in five altitudinal belts
reaching from the alpine tundra (> 3.450 m a.s.l.) down to the plains (> 1.710 m
a.s.l.). Our investigations are dealing with different kinds of slope deposits, their
genesis and age. The critical zone is the heterogeneous carapace of soil and
weathered rock, and the ecosystems they support. Understanding the evolution of
the critical zone, and its sensitivity to perturbations, requires an understanding of
its architecture and the processes that produce this architecture. The Boulder Creek
Critical Zone Observatory (BC CZO) is designed to understand how weathering
(both physical and chemical) and transport processes control the structure of the
critical zone, and to explore the impact of critical zone structure on hydrological,
geochemical and biological functions of the landscape. Slope deposits are crucial
elements of the critical zone.
The 1.160 km2 Boulder Creek watershed in Colorado’s Front Range encompasses
strong contrasts in erosional regimes, and therefore contains critical zone
architectures that range from dominantly bare rock to deeply weathered profiles.
Through the late Cenozoic, a slowly eroding rocky upland comprising Precambrian
crystalline rocks has been etched in its headwaters by glaciers, and bitten into by
headward migrating stream knickzones. This has produced a landscape in which the
critical zone is captured in three states. Each of these is represented in a focus
subcatchment in the BcCZO where the critical zone will be characterized in detail.
The slope deposits show characteristic variations within the subcatchments.
Fundamental characteristics of the critical zone, together control the passage of
water, the chemical processes operating, the material strength, and the function of
subsurface ecosystems. Slope deposits of different genesis and ages play a decisive
role.
Water uptake of trees in a montane forest catchment and the
geomorphological potential of root growth in Boulder Creek Critical Zone
Observatory, Rocky Mountains, Colorado
Breanna Skeets1, 3, Holly R Barnard2, Anya Byers2
1. Department of Geology, Lawrence University, Appleton, WI, United States.
2. Department of Geography/INSTAAR, University of Colorado, Boulder, CO, United
States.
3. RESESS Internship, UNAVCO, Boulder, CO, United States
ABSTRACT FINAL ID: B21H-0366; SESSION TYPE: Poster SESSION TITLE: B21H.
Stable Isotope Fluxes in the Carbon and Water Cycles of Terrestrial Ecosystems II
Posters
ABSTRACT BODY: The influence of vegetation on the hydrological cycle and the
possible effect of roots in geomorphological processes are poorly understood.
Gordon Gulch watershed in the Front Range of the Rocky Mountains, Colorado, is a
montane climate ecosystem of the Boulder Creek Critical Zone Observatory whose
study adds to the database of ecohydrological work in different climates. This work
sought to identify the sources of water used by different tree species and to
determine how trees growing in rock outcrops may contribute to the fracturing and
weathering of rock.
Stable isotopes (18O and 2H) were analyzed from water extracted from soil and
xylem samples. Pinus ponderosa on the south-facing slope consumes water from
deeper depths during dry periods and uses newly rain-saturated soils, after rainfall
events. Pinus contorta on the north -facing slope shows a similar, expected response
in water consumption, before and after rain. Two trees (Pinus ponderosa) growing
within rock outcrops demonstrate water use from cracks replenished by new rains.
An underexplored question in geomorphology is whether tree roots growing in rock
outcrops contribute to long-term geomorphological processes by physically
deteriorating the bedrock. The dominant roots of measured trees contributed
approximately 30 - 80% of total water use, seen especially after rainfall events.
Preliminary analysis of root growth rings indicates that root growth is capable of
expanding rock outcrop fractures at an approximate rate of 0.6 – 1.0 mm per year.
These results demonstrate the significant role roots play in tree physiological
processes and in bedrock deterioration.
Turning rock into saprolite: Linking observations and models of vadose zone
dynamics and chemical weathering
Abigail L Langston1, 2, Gregory E Tucker2, 1, Robert S Anderson3, 1, Suzanne P
Anderson3, 4
1. Geological Sciences, University of Colorado, Boulder, CO, United States.
2. CIRES, Boulder, CO, United States.
3. INSTAAR, Boulder, CO, United States.
4. Geography, University of Colorado, Boulder, CO, United States.
ABSTRACT FINAL ID: EP23C-0768; SESSION TYPE: Poster SESSION TITLE: EP23C.
Quantifying Geomorphic Processes and Landscape Evolution: Linking Observations
and Models I Posters
ABSTRACT BODY: Chemical weathering of rock into saprolite requires contact
between water and unweathered rock, which occurs frequently but discontinuously
in the unsaturated zone. Saprolite is a direct precursor to mobile regolith, and the
distribution and rate of saprolite development play a role in sediment production on
hillslopes. We strive to understand both the timing and spatial distribution of
saprolite development in the subsurface, which is controlled by the delivery of fresh
water to unweathered rock. We hypothesize that climate has a strong control on
delivery of water to saprolite in the vadose zone, and hence on the rate of saprolite
formation. In addition, the rate of water delivery is strongly modulated by the local
fracture field, lending a strong heterogeneity to water delivery and weathering
rates. To test this hypothesis, we link observations of moisture content in soil and
saprolite with a numerical model of vadose zone dynamics. The moisture
measurements are taken in the Boulder Creek watershed in central Colorado. This
1160 km2 catchment, which is underlain by fractured crystalline rocks (mainly
granodiorite), ranges in elevation from high alpine peaks at 4120 m to the Colorado
piedmont at 1480 m.
The complex hydrologic architecture of the unsaturated zone necessitates a model
that can incorporate multiple permeabilities to represent the variable flow paths in
the soil, saprolite, and fractures. Therefore, we employed VS2DI, a Richards
equation-based model, on two-dimensional hillslopes to visualize flow paths in the
unsaturated zone and calculate volumetric moisture content at observation points.
We ran multiple simulations investigating the relative roles of fracture spacing and
variable timing and intensity of precipitation.
Model experiments suggest that fractures are the primary pathway for delivering
water deep below the subsurface. Where fracture density is higher, more water is
delivered to the deep subsurface, allowing more chemical weathering at depth. Our
results also indicate that both the intensity and total magnitude of precipitation
events affect the flow paths of water in the subsurface. The effects of water flux in
the subsurface on chemical weathering are modeled using a linear first-order
reactive-transport model for albite dissolution. This reactive-transport model
reveals the importance of timing and magnitude of precipitation on chemical
weathering rates, as well as the importance of fractures on the spatial distribution of
weathering in the unsaturated zone. The results indicate that the development of
saprolite is strongly controlled by the temporal distribution of precipitation
throughout the year. Water reaches deeper into unweathered rock when
precipitation is concentrated during one season rather than being evenly
distributed throughout the year. This finding suggests an intriguing link between
the saprolite development and changing climate in mountain environments.
Constraining Regolith Production on a Hillslope Over Long Timescales:
Interpreting In Situ 10Be Concentrations on an Evolving Landscape
Melissa A Foster1, 2, Robert S Anderson1, 2, Miriam Duehnforth1, Patrick J Kelly1, 3
1. INSTAAR, University of Colorado, Boulder, CO, United States.
2. Geology, University of Colorado, Boulder, CO, United States.
3. Geography, University of Colorado, Boulder, CO, United States.
ABSTRACT FINAL ID: EP23C-0776; SESSION TYPE: Poster SESSION TITLE: EP23C.
Quantifying Geomorphic Processes and Landscape Evolution: Linking Observations
and Models I Posters
ABSTRACT BODY: In situ produced 10Be cosmogenic radionuclide (CRN)
concentrations provide geomorphologists with a quantitative tool to calculate
regolith production rates in a variety of landscapes. However, the power of CRN
dating is limited by the care with which these hard-earned numbers are interpreted.
As rock is exhumed through the weathered zone, it accumulates in situ produced
CRNs. Most studies assume a steady-state condition to calculate regolith production
rates from 10Be concentrations obtained from rock at the base of mobile regolith;
ignoring decay, the regolith production rate becomes simply Poe-H/z*/[10Be].
Although the balance of regolith production and the spatial pattern of divergence
required to maintain steady regolith thickness is valid in some landscapes, steadystate is unlikely on hillslopes where time scales for generating soils are longer than
climatic cycles.
We report in situ 10Be concentrations to calculate production rates for mobile
regolith in 8 soil pits along north- and south-facing slopes in Gordon Gulch, an
intensively studied catchment in the Boulder Creek CZO. Gordon Gulch hillslopes
exhibit variable regolith and saprolite thicknesses over gneissic and granitic parent
rock; mean regolith thickness is 0.65 m. Local denudation rates in nearby
catchments are 25 ± 8 m/Ma (Dethier and Lazarus, 2006). The mean residence time
of mobile regolith in Gordon Gulch catchment is therefore 20-45 ka; less than half of
this time is spent in Holocene climatic conditions. Although Gordon Gulch presently
has mean annual temperature (MAT) ~4°C, it was likely at least 6°C cooler during
the Last Glacial Maximum, meaning that periglacial conditions likely dominated. We
therefore anticipate that parent rock could be more rapidly damaged by increased
frost-cracking, and regolith transport be enhanced by increased frost-heave; thus
steady-state conditions cannot be assumed over this timescale.
To develop strategies for interpretation of 10Be, we employ a 1D numerical hillslope
model in which regolith thickness and 10Be concentration are tracked at all hillslope
positions. 10Be concentration in rock immediately subjacent to the regolith is
updated both by decay and by production at a rate governed by the instantaneous
regolith thickness (e.g. Riggins et al., 2011). Vertically averaged 10Be concentration
in the regolith is updated by vertically averaged production rate, decay, addition
from rock released at the base of the regolith, and advection of regolith. The
resulting field of 10Be in bedrock at the regolith interface, from which one deduces
long term average regolith production rates, varies both in time and in space. Our
model indicates that regolith thickness fluctuates by tens of percent from the
average condition over the timescale of glacial-interglacial cycles. The resulting
shifts in 10Be concentrations at the base of regolith are of similar magnitude, with
greater shifts of 10Be concentrations in regolith. We will employ this model tuned to
the Gordon Gulch sites to interpret measured 10Be concentrations.
Snowmelt and the geological and ecological filters modulating climate
variability and streamflow response
Noah P Molotch1, 2, Steven M Jepsen3, Mark W Williams1, Ernesto Trujillo1, James O
Sickman4, Karl E Rittger5
1. Geography / INSTAAR, Univ of CO-Geological Sciences, Boulder, CO, United States.
2. Jet Propulsion Laboratory, CAL TECH, Pasadenca, CA, United States.
3. USGS, Lakewood, CO, United States.
4. Environmental Sciences, University of California, Riverside, CA, United States.
5. University of California, Santa Barbara, CA, United States.
ABSTRACT FINAL ID: H24D-04; SESSION TYPE: Oral SESSION TITLE: H24D.
Landscape System Response Under Change II
ABSTRACT BODY: We pose a conceptual model for mountainous regions in which
linkages between climatic drivers of hydrologic change and basin outlet streamflow
are ‘filtered’ by the biological, geomorphic, and geological structure of the critical
zone. In this regard, the timing and distribution of snowmelt plays a critical role in
these linkages as snowfall represents the dominant precipitation input to high
elevation mid-latitude systems globally. Given the sensitivity of snowmelt to
changes in air temperature, snowmelt-climate related tipping points may exist
whereby established eco-geo-hydro feedbacks may be altered or reversed. In an
effort to identify these tipping points, we showcase new capabilities in remote
sensing and modeling of the distribution of snow water equivalent and snowmelt
within the context of the aforementioned linkages. Via comparisons of snowmelt
timing and observed discharge centroids in maritime and continental climates we
reveal the nature of the geologic ‘filter’ whereby we show that highly fractured
systems can decouple the timing of snowmelt and streamflow. Examples from the
Rocky Mountains indicate that snowmelt centroid timing over a 12 year period were
as great as 42 days whereas streamflow centroid timing varied by only 9 days.
Similar analyses in surface-water dominated granitic systems in the Southern Sierra
Nevada indicate near perfect snowmelt and streamflow alignment with centroids
ranging from 65 and 56 days, respectively. Similarly, the ecological dimension of this
landscape ‘filter’ depends on the timing and distribution of snowmelt. In this regard,
we identify an elevational tipping point in water versus energy limitation whereby
snowmelt, forest greenness, and gross ecosystem exchange are highly correlated at
lower elevations (R2 = 0.47) but are decoupled at higher elevations due to energy
limitation. These results highlight the importance of snowmelt with respect to the
high to mid frequency response of the critical zone to climate change. In this regard,
future observing and modeling studies across NSF’s critical zone observatory
network will be discussed.
http://instaar.colorado.edu/mtnhydro/Mountain_Hydrology/Home.html
Wednesday, December 7
Ecohydrology of Lodgepole Pine Forests: Connecting Transpiration to
Subsurface Flow Paths and Storage within a Subalpine Catchment
Anya Byers1, Adrian Adam Harpold2, Holly R Barnard1
1. Geography, University of Colorado, Boulder, CO, United States.
2. Hydrology and Water Resources, University of Arizona, Tucson, AZ, United States.
ABSTRACT FINAL ID: H33E-1366; SESSION TYPE: Poster SESSION TITLE: H33E.
Partitioning Evaporation, Transpiration, and Deep Percolation in Vegetated
Catchments I Posters
ABSTRACT BODY: The hydrologic cycle plays a central role in regulating ecosystem
structure and function. Linked studies of both subsurface and aboveground
processes are needed to improve understanding of ecosystem changes that could
result from climate change and disturbance in Colorado’s subalpine forests. Here,
we present data from plots dominated by lodgepole pine (Pinus contorta) at the
Niwot Ridge LTER site on the Colorado Front Range that improves the process-level
understanding of the source and fate of water between subsurface storage and plant
uptake. This study utilized event-based sampling during the 2011 growing season to
investigate a paradox between water sources and rooting depth in lodgepole pine.
Findings from Niwot Ridge have shown that lodgepole, typically believed to be a
shallow-rooted species, appear to be strongly dependent on water from snowmelt
for the entire growing season. These results suggested that conifer species were
accessing water from deeper in the soil than summer monsoon rain typically
penetrated. In our study, the relationship between precipitation event size and
depth of infiltration on a seasonal and event basis, the effective rooting depth of
lodgepole pine, and hysteretic responses of transpiration to soil moisture over a
growing season were examined using measurements of tree physiological processes
(sap flux and water stress) and hydrological parameters (precipitation, soil
moisture) as well as stable water isotope composition of xylem water, mobile and
immobile soil water, snow, precipitation, and stream water. Analysis of data shows
that soil moisture in deep layers (60 and 70 cm) responds to large summer rain
events of 0.7 mm and greater, and that lodgepole sap flux increases by 15-30%
within 24 hours of monsoon events and decreases over 72 hours or until
subsequent rain. Water isotope analysis will further elucidate the source and event
response of these trees. This research helps us understand whether processes
known to occur in Mediterranean climate regimes, such as the “two water worlds”
theory that tightly bound water in soil is available to trees but is separate from
mobile water that drains to streams, also applies to continental mountainous
climates. Furthermore, understanding the mediation of hydrologic processes by
trees like lodgepole pine will improve modeling of hydrological and ecological
processes and knowledge of forest susceptibility to climate change and other
disturbance impacts.
Thursday, December 8
Subsurface Evolution: Weathering and Mechanical Strength Reduction in
Bedrock of Lower Gordon Gulch, Colorado Front Range
Patrick J Kelly1, 2, Suzanne P Anderson1, 2, Robert S Anderson2, 3, Alex Blum4, Melissa
A Foster2, 3, Abigail L Langston3, 5
1. Department of Geography, University of Colorado at Boulder, Boulder, CO, United
States.
2. INSTAAR, University of Colorado at Boulder, Boulder, CO, United States.
3. Department of Geological Sciences, University of Colorado at Boulder, Boulder,
CO, United States.
4. USGS, Boulder, CO, United States.
5. CIRES, University of Colorado at Boulder, Boulder, CO, United States.
ABSTRACT FINAL ID: EP43C-0713; SESSION TYPE: Poster SESSION TITLE: EP43C.
Earth and Planetary Surface Processes: Hillslope, Tectonic, and Weathering III
Posters
ABSTRACT BODY: Weathering processes drive mobile regolith production at the
surface of the earth. Chemical and physical weathering weakens rock by creating
porosity, opening fractures, and transforming minerals. Increased porosity provides
habitat for living organisms, which aid in further breakdown of the rock, leaving it
more susceptible to displacement and transport. In this study, we test mechanical
and chemical characteristics of weathered profiles to better understand weathering
processes. We collect shallow bedrock cores from tors and isovolumetrically
weathered bedrock in lower Gordon Gulch to characterize the mechanical strength,
mineralogy, and bulk chemistry of samples to track changes in the subsurface as
bedrock weathers to mobile regolith. Gordon Gulch is a small (2.7 km2), E-W
trending catchment within the Boulder Creek Critical Zone Observatory underlain
by Pre-Cambrian gneiss and granitic bedrock. The basin is typical of the “Rocky
Mountain Surface” of the Front Range, characterized by low relief, a lack of glacial or
fluvial incision, and deep weathering. Although the low-curvature, low-relief Rocky
Mountain Surface would appear to indicate a landscape roughly in steady-state,
shallow seismic surveys (Befus et al., 2011, Vadose Zone Journal) indicate depth to
bedrock is highly variable. Block style release of saprolite into mobile regolith could
explain this high variability and should be observable in geotechnical testing.
Gordon Gulch also displays a systematic slope-aspect dependent control on
weathering, with N-facing hillslopes exhibiting deeper weathering profiles than the
S-facing hillslope. We believe comparisons of paired geotechnical-testing, XRD, and
XRF analyses may explain this hillslope anisotropy. Rock quality designation (RQD)
values, a commonly used indicator of rock mass quality (ASTM D6032), from both
N- and S- facing aspects in Gordon Gulch indicate that granitic bedrock in both
outcrop and saprolitic rock masses is poor to very poor. Brazilian tensile testing of
outcrop core samples show relatively low tensile failure forces, and exhibit a
roughly logarithmic increase in failure force, and hence tensile strength, with depth.
For many of the granitic strength profiles, the point of greatest curvature is around
0.5 m depth. Tests reveal small-scale variation in the tensile strength, suggesting
that the tight fracture-spacing bounding blocks of saprolite plays an important role
in regolith production. The origin of the micro- and macro-fractures is unclear.
Preliminary results do not correlate clear depth-trends in mineralogy or bulk
chemistry with mechanical strength. The lack of a strong signature from chemical or
mineralogical weathering suggests that mechanical processes, such as frost cracking
or biotite hydration, may dominate.
Of Rock Damage and the Regolith Conveyor Belt: A Geomorphologist’s View of
the Critical Zone
Robert S Anderson1, 2, Suzanne P Anderson1, 3, Gregory E Tucker2, 4
1. INSTAAR, University of Colorado, Boulder, CO, United States.
2. Department of Geological Sciences, University of Colorado, Boulder, CO, United
States.
3. Department of Geography, University of Colorado, Boulder, CO, United States.
4. CIRES, University of Colorado, Boulder, CO, United States.
ABSTRACT FINAL ID: EP44B-02; SESSION TYPE: Oral SESSION TITLE: EP44B.
Quantifying Geomorphic Processes and Landscape Evolution: Linking Observations
and Models IV
ABSTRACT BODY: Models of hillslope evolution require rules for the rate of
detachment of rock into the mobile regolith layer, for the rate of mobile regolith
transport, and for channel incision or aggradation rates that serve as boundary
conditions. The evolution of material as it passes through the weathered zone is
typically ignored, making it difficult to cast proper rules for production of mobile
regolith. The current rules are therefore insufficient to address critical zone
evolution, in which the chemical, mechanical, and hydrologic properties of the rock
and the regolith matter. These properties evolve as rock is weathered during
exhumation, and they continue to evolve as particles ride the conveyor belt of
mobile regolith downslope. Models that honor specific processes involved in the
evolution of rock as it passes through the CZ will both advance models of landscape
evolution, and provide context for ecological and hydrological investigations.
Physical processes responsible for progressive damage of rock during exhumation
in the current CZOs include frost cracking and tree root cracking. If we define
damage as the density of flaws within the rock, we require rules governing the rate
of generation of new flaws, which will vary with climate, depth, and the present
state of damage. We envision a “damage-limited system” in which the likelihood of
release of rock fragments into mobile regolith depends on the accumulated damage
in the subjacent rock.
In most temperate and alpine settings relevant to the present CZOs, the ratio of a
rock’s residence time in the damage zone to the duration of a climate oscillation is
such that a rock parcel will experience the full spectrum of Quaternary climates.
This requires that we address both climate history and the damage and transport
rates associated with all Quaternary climates.
We present numerical models for rock damage, mobile regolith production, and
hillslope profile evolution. These models are motivated by the Boulder Creek CZO
Gordon Gulch catchment, in which strong contrasts in CZ development occur on
north-facing and south-facing slopes that likely reflect differences in both the
thermal state and the tree cover of the landscape. We illustrate a rule set in which
periglacial processes dominate by employing a modified rule for frost cracking to
capture the damage of rock as it is exhumed, and a formula for frost heave to
address transport of mobile regolith. Rates of both damage and transport are
functions of mean annual temperature (MAT) that we constrain with numerical
calculations that include both phase change and variations in material properties.
Climate is dependent on slope angle, and oscillates between glacial and interglacial
MATs. The resulting hilltop is asymmetrical in profile, and in thicknesses of both
mobile regolith and damage zone, matching qualitatively the characteristics of
Gordon Gulch. Climate swings result in oscillations of mobile regolith thickness that
are greatest at the base of hillslopes. Interpretation of 10Be, and of downslope
profiles of regolith properties, must honor such climatically modulated behavior.
Friday, December 9
Imaging the architecture of the Critical Zone at Boulder Creek Critical Zone
Observatory, Rocky Mountains Front Range of Colorado, USA
Matthias Leopold1, Joerg Voelkel1, David P Dethier2
1. Ecology and ecosystem manageme, Technische Universität München, FreisingWeihensteph, Germany.
2. Geosciences, Williams College, Williamtown, MA, United States.
ABSTRACT FINAL ID: H52A-05; SESSION TYPE: Oral SESSION TITLE: H52A.
Geophysics for the Critical Zone II
ABSTRACT BODY: Boulder Creek Critical Zone Observatory functions as a nucleus
for different scientific disciplines to study the development of the Critical Zone (CZ)
along an altitudinal gradient. Three catchments represent different landscape types
along this gradient. Green Lakes Valley is a typical alpine tundra area at around to
3600 m a.s.l., whereas Gordon Gulch (2700 m a.s.l.) represents a subalpine area. The
lower montane area is represented by the watershed of Betasso (1900 m a.s.l.).
We present results from all three catchments using various shallow geophysical
methods such as ground penetrating radar (GPR), electric resistivity tomography
(ERT) and party shallow seismic refraction (SSR) together with soilgeomorphological studies and results. The three study sites enormously differ in
their geomorphological, hydrological, biological and pedological parameters within
the Critical Zone of which we present the major differences along the altitudinal
gradient which include variations in thickness, composition and layering of the
sediments and soils along the slopes within the CZ. We further give first dating
results by optical stimulated luminescence (OSL) of the slope sediments in order to
elaborate a chrono-stratigraphy of the hill slope sediments.
We find layered slope sediments in various compositions in the three different
catchments dating back to glacial times where geli-solifluction must have been a
major process for sediment production and therefore for the development of the
critical zone.
Unexpected Delivery of Meteoric 10Be to Critical Zone Soils, Front Range,
Colorado
William B Ouimet1, David P Dethier2, Paul R Bierman3, Cianna Wyshnytsky4, Dylan
H. Rood5
1. Geography, University of Connecticut, Storrs, CT, United States.
2. Geosciences, Williams College, Williamstown, MA, United States.
3. Geology, University of Vermont, Burlington, VT, United States.
4. Geology, Utah State University, Logan, UT, United States.
5. Center for Accelerator Mass Spectrometry, Lawrence Livermore National
Laboratory, Livermore, CA, United States.
ABSTRACT FINAL ID: EP52D-06; SESSION TYPE: Oral SESSION TITLE: EP52D.
Innovative Isotope Methods for Characterization of Earth Surface Processes III
ABSTRACT BODY: Using meteoric 10Be in geomorphic studies requires knowing its
long-term delivery rate to the earth surface. Delivery rates vary by latitude due to
the influence of geomagnetic field intensity and solar activity and locally due to
differences in precipitation and rates of dustfall accumulation, which are
responsible for depositing primary and recycled meteoric 10Be to geomorphic
surfaces, respectively. Because influences on delivery rate vary in space and time,
recent studies emphasize the use of inventory sites where the total concentration of
meteoric 10Be is measured on stable landforms of known age to determine sitespecific, long-term delivery rates. To date, measured long-term delivery rates
typically have fallen within the range of expected rates for the site’s latitude and
modern annual rate of precipitation, including minor contributions of dust to the
total inventory of meteoric 10Be. Here, we present the results of a meteoric 10Be
inventory measured on a Pinedale (~15 ka) moraine within the Boulder Creek
Critical Zone Observatory, Front Range, Colorado. We report a long-term delivery
rate of meteoric 10Be for this site of 4.2 to 4.6 × 106 atoms/cm2/yr, significantly
higher than the expected delivery rate (1 to 1.3 × 106 atoms/cm2/yr) for it’s latitude
(40 degrees) and annual precipitation rate (85-95 cm/yr). A detailed analysis of
soils in the Front Range (of various age) indicate that long-term dust accumulation
rates are less than ~0.1 grams/cm2/kyr and therefore do not significantly influence
the total amount of meteoric 10Be delivered to geomorphic surfaces. When applied
to measured concentrations of meteoric 10Be in soils within the Gordon Gulch CZO
catchment, our high, inventory-based delivery rate suggests that hillslopes are 10 to
40 ka younger (all post-LGM) than suggested by published precipitation based
delivery rates. Furthermore, this result, combined with a long-term delivery rate
calibrated nearby on the High Plains (1200 m lower in elevation and half the
modern precipitation), indicates a different scaling between meteoric 10Be and
precipitation than recent studies would suggest.
A Simple Model for the Post-Orogenic Evolution of Mountain Ranges and
Foreland Basins
Peter Van Der Beek1, Gregory E Tucker2
1. Institut des Sciences de la Terre, Université Joseph Fourier, Grenoble, France.
2. Cooperative Institute for Research in Environmental Sciences (CIRES) and
Department of Geological Sciences, University of Colorado, Boulder, CO, United
States.
ABSTRACT FINAL ID: EP41D-0637 (Note: changed from poster to talk on Friday
afternoon in session EP53C at 3:10pm) SESSION TYPE: Oral SESSION TITLE: EP53C.
The Long Road To Flat: Toward Understanding the Drivers and Quantifying Change
in Orogens II
ABSTRACT BODY: Many mountain ranges show a surprisingly dynamic pattern of
landscape evolution during their post-orogenic phase. Although one might expect a
simple, monotonic decline in relief, erosion rate and sediment flux over time,
evidence from several inactive mountain ranges shows alternating sequences of
deposition and erosion in the adjacent foreland basins, accompanied by variations
in relief and exhumation rate in the ranges themselves, as recorded by
thermochronology data. Examples include the Rocky Mountains of Colorado, the
Pyrenees, the Western Alps, and the Atlas Mountains. Here, we explore the possible
origins of post-orogenic landscape dynamics using a simple mathematical model of
a range and basin pair, which are coupled through the mass fluxes in and out of the
basin (controlled by the range and basin relief as well as their erosional response
times) and the flexural isostatic response of the lithosphere to range thickening and
erosion. The analysis highlights the importance of mass balance. In particular, a
switch from basin erosion to renewed sedimentation requires either an increase in
sediment influx from the range, a decrease in sediment outflux beyond the basin
margin, or both. Although it is widely understood that post-orogenic changes in
erosion and sediment flux can have multiple causes (including climate change,
regional tectonic uplift or tilting, or changing lithology as rocks are exhumed), an
important implication of our analysis is that the impact of such changes must differ
in sign or magnitude between the range and the basin in order to be recorded. In
particular, renewed sedimentation in the basin, without an obvious tectonic control,
requires the ratio of range to basin response times to decrease sufficiently to offset
the increase in basin relief due to the isostatic response to range erosion. This
requirement places an important constraint on viable explanations for alternating
sequences of deposition and erosion in a decaying mountain-basin pair.
Climate Change and Nutrient Loading: Controls on Phytoplankton Growth and
Dissolved Organic Matter Quality in Lakes in Colorado (Invited)
Diane M McKnight1, Alia L Khan1, Amanda Hohner2, Fernando Rosario2
1. Inst Arctic & Alpine Res, Univ Colorado, Boulder, CO, United States.
2. Department of Civil, Environmental and Architectural Engineering, University of
Colorado, Boulder, CO, United States.
ABSTRACT FINAL ID: H54A-08; SESSION TYPE: Oral SESSION TITLE: H54A.
Coupled Hydrological and Dissolved Organic Matter Biogeochemical Processes at
Multiple Scales II
ABSTRACT BODY: Understanding connection between DOM quality and reactivity
is important for evaluating processes driving recent increases in DOC. One potential
driver may be greater phytoplankton growth associated with earlier ice-out and
concomitant increases in nitrogen loading in mountain lakes. This study examined
DOM patterns in 30 lakes and reservoirs which were sampled during the summer
algal bloom peak in Colorado. Algal species identified using a FlowCAM imaging
microscope and DOM quality was characterized by fluorescence spectroscopy. The
results showed that the DOM quality was indicative of microbial sources in lakes
with greater algal abundance and higher DOC concentrations. In low DOC lakes the
fluorescence signature suggested that photo-bleaching was also an influence. These
results indicate that further development and application of a recent model for algal
DOM production could be used in concert with climate and nutrient loading
scenarios to predict DOM concentrations and quality in CO lakes and reservoirs.
Natural and Anthropogenic Controls on the Ecosystem Services Provided by
Dissolved Organic Matter: A Case Study of the Boulder Creek Watershed
Rachel S Gabor2, 1, Diane M McKnight1, 3
1. Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder,
CO, United States.
2. Environmental Studies, University of Colorado Boulder, Boulder, CO, United
States.
3. Civil, Environmental, and Architectural Engineering, University of Colorado
Boulder, Boulder, CO, United States.
ABSTRACT FINAL ID: H54B-08; SESSION TYPE: Oral SESSION TITLE: H54B.
Ecosystem Services: Hydrology and Biogeochemistry in a World of Environmental
Change II
ABSTRACT BODY: Dissolved organic matter (DOM) performs a number of vital
functions in aquatic ecosystems, playing a substantial role in carbon and nitrogen
cycles and the bioavailability of metals as well as generally affecting water
chemistry. Additionally, it is considered the main cause of the the formation of
harmful disinfection byproducts during water treatment processes. Because DOM is
vital for ecosystem functioning, but potentially problematic for some direct human
uses of water, it proves a complex case study for the application of the ecosystem
services framework. To add to the complexity, human behavior can affect the
amount and composition of DOM in water. Increasing concentrations of DOM have
been observed in many areas of Northern Europe and North America. Hypotheses
which have been suggested to explain these increased concentrations include
changing land use, thawing peatlands, increased nitrogen deposition, and a
lessening of acid rain, a particularly interesting idea because it would be an
unintended consequence of a policy designed to protect other ecosystem functions.
This multi-year study investigates DOM in the Boulder Creek Watershed in Colorado
to better understand seasonal cycling of DOM and the link between DOM in the river
and organic matter in the catchment, which is a substantial DOM source.
Fluorescence spectroscopy was used to analyze the chemical character of the DOM
in an attempt to elucidate the watershed processes driving changes in DOM
concentration. Because flow in Boulder Creek is partially controlled by Barker dam
and reservoir, this study site provides an opportunity to investigate both natural
DOM cycling and the impact of an anthropogenic influence. By better understanding
DOM cycling and the ecosystem services it provides, we can better predict how DOM
dynamics may shift in the future and be prepared to adjust our behavior and water
treatment processes accordingly.