2016

Continuous Modeling Of Hyporheic Exchange Explains Chemostasis In Glacial Meltwater Streams, Antarctica

Anonymous — Mon, 13 Aug 2018 16:54:58 +0000

Continuous Modeling Of Hyporheic Exchange Explains Chemostasis In Glacial Meltwater Streams, Antarctica Anonymous (not verified) Mon, 08/13/2018 - 10:54 Adam N Wlostowski

Wlostowski, Adam N ¹ ; Gooseff, Michael N ² ; McKnight, Diane M ³ ; Lyons, Berry W. ⁴

¹ INSTAAR
² INSTAAR
³ INSTAAR
⁴ Ohio State University

Chemostasis (comparatively minor change of solute concentrations over a wide range of discharge) of weathering-derived solutes (e.g., silica) is commonly observed in temperate streams, indicating that general rates of solute mobilization and production in the catchment are nearly equal to rates of water flux through a catchment. However, the physical controls on solute mobilization and production, which drive chemostasis, are not well understood. In the streams of the McMurdo Dry Valleys (MDVs) of Antarctica, glacial meltwater is the dominant (>98%) source of streamflow. Over 9 years of hydrologic record, we observe Si chemostasis, based on historical Si-Q regressions. We propose that hyporheic exchange maintains chemostasis of weathering-derived solutes, given that there is no lateral hillslope flow and no deep groundwater contribution to MDV streams. We test this hypothesis by developing novel hyporheic end-member mixing models (HEMMs) to estimate hyporheic exchange flux during the 6-12 week flow seasons on four streams, over 9 seasons of flow record. The model simulations reveal that 5-53% of total annual streamflow is turned over through the hyporheic zone. A greater portion of annual streamflow is turned over through hyporheic zones on longer streams, compared to shorter streams. Si-Q regressions were re-computed using HEMM simulated hyporheic flow rates (Si-QHZ) and confirm that hyporheic fluxes exert a control on Si concentrations in all streams. Results from this study confirm the hydrologic and chemical significance of hyporheic zones in the MDVs, specifically the ability of hyporheic zones to be dynamic Si sources.

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Early Snowmelt Decreases Ablation Period Carbon Uptake In A High Elevation, Subalpine Forest, Niwot Ridge, Colorado, USA

Anonymous — Mon, 13 Aug 2018 16:53:24 +0000

Early Snowmelt Decreases Ablation Period Carbon Uptake In A High Elevation, Subalpine Forest, Niwot Ridge, Colorado, USA Anonymous (not verified) Mon, 08/13/2018 - 10:53 Taylor S Winchell

Winchell, Taylor S ¹ ; Molotch, Noah P ² ; Barnard, David M ³

¹ ��ƷSM��ӰƬ

The snow ablation period is a time of great potential for carbon uptake in high-elevation, subalpine forests. During this period, water availability associated with snowmelt promotes photosynthetic carbon uptake, while snow cover diminishes carbon losses from soil respiration. Although the ablation period can be as short as two weeks, as much as 30% of the total seasonal carbon uptake can occur during this period. Varying ablation period dynamics, however, can result in varying rates of carbon uptake during this integral uptake period. We use fifteen years of observational climate flux and snow water equivalent (SWE) data for a subalpine forest in the Colorado Rocky Mountains to analyze carbon uptake trends during the annual ablation period. Specifically, we focus on how the timing of peak SWE affects carbon uptake during the ablation period. We find that when the snowmelt period occurs one month earlier than average, the forest experiences an ablation period mean air temperature of 2.7° C, approximately 5° C colder than an ablation period that occurs one month later than average. This early, colder atmospheric condition leads to daytime carbon uptake rates that are 2.5 gC/m2/day less than the later, warmer period, which results in 47 gC/m2 less ablation period carbon uptake. As most climate models project peak SWE to occur earlier under various warming scenarios, we can expect to see a trend of less carbon uptake during future ablation periods. We expect to see a decrease in total growing season carbon uptake if the post-snowmelt period is unable to compensate for the decrease in ablation period carbon uptake.

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Data Analysis Methods For Measuring Impact Of A Conservation-Focused Residential Irrigation Inspection Program

Anonymous — Mon, 13 Aug 2018 16:52:07 +0000

Data Analysis Methods For Measuring Impact Of A Conservation-Focused Residential Irrigation Inspection Program Anonymous (not verified) Mon, 08/13/2018 - 10:52 Chris Williams

Williams, Chris ¹ ; Shimabuku, Morgan ²

¹ Center for ReSource Conservation
² Center for ReSource Conservation

Utilities in the state of Colorado that annually supply more than 2,000 acre-feet of water to their customer base are required by the State of Colorado Water Conservation Board to create and implement water conservation strategies. Residential sprinkler audit programs are commonly used as a tool for Colorado municipalities to achieve their water conservation goals, but little evaluative work has been done to measure the water savings from these efforts (Mayer et al, 2015). This study presents the results from the comparison of four different methods for measuring the amount of water saved at the individual level by participants in Colorado’s largest sprinkler auditing program, Slow the Flow, a program by the Center for ReSource Conservation, offered to residents in 20+ water utility districts across the state. Analysis of water consumption billing records from two years pre- and one year post irrigation audit from over 500 residential households that participated in the program in 2014 were used to answer key questions about irrigation audit impact on water usage as well as to compare the difference between four varying methodologies for calculating water savings and other indicators of watering efficiency on the individual household level. Results show that each method provides a different value of savings for participants with a range between 0 and 19 kgal of mean savings (Fig 1). The median values also ranged from 1-16 kgal of savings. While one method may provide the most statistically and mathematically valid water savings estimations, qualitative evaluation of the different methods reveals that different methods provide unique insight into customer water usage and should therefore be chosen based off of the goals intended of the outcome of the analysis.

Mayer, P., Lander, P., and Glenn, D. 2015. Outdoor Water Use: Abundant Savings, Scarce Research: Journal AWWA, v. 107:2, p. 61-66.

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Linking Sap Flow And Stable Isotope Techniques To Understand Transpiration Dynamics In A Semiarid Shrubland

Anonymous — Mon, 13 Aug 2018 16:50:33 +0000

Linking Sap Flow And Stable Isotope Techniques To Understand Transpiration Dynamics In A Semiarid Shrubland Anonymous (not verified) Mon, 08/13/2018 - 10:50 Daphne J Szutu

Szutu, Daphne J ¹ ; Papuga, Shirley A ²

¹ ��ƷSM��ӰƬ, INSTAAR
² University of Arizona

Dryland ecosystems account for nearly 40% of terrestrial biomes, and understanding transpiration dynamics in these environments is critical to understanding how climate change will impact global water and carbon budgets. Semiarid shrublands and other dryland ecosystems are highly responsive to precipitation pulses that, depending on their size, differentially influence the distribution of moisture in the soil profile. Recent field studies have shown that transpiration dynamics and plant productivity are largely a function of deep soil moisture available after large precipitation events, regardless of where the majority of plant roots occur. We suggest that adopting a hydrologically defined two-layer conceptual framework of the soil profile is more appropriate for understanding plant water use in dryland ecosystems than a framework that is based on rooting depth. We make the assumption that shallow and deep soil layers have different isotopic signatures and use this framework to show how transpiration dynamics vary with the availability of deep soil moisture in dryland ecosystems. We present continuous eddy covariance, sap flow transpiration and soil moisture data with discrete isotopic samples of precipitation, soil, and stems taken over 18 months at a creosotebush-dominated shrubland ecosystem in southern Arizona. We found that transpiration is associated with the availability of deep soil moisture, and when transpiration rates were highest, both deep moisture and stem water were more isotopically similar to winter precipitation than summer precipitation, suggesting that winter precipitation can play an important role in supporting these ecosystems. Our study suggests that integrating sap flow and stable isotope techniques with soil moisture measurements offers a better understanding of how plant water use strategies shift with changes in source water and its availability than either technique could offer on its own. We contend that semiarid shrubs depend on deep moisture for growth and functioning and are therefore vulnerable to shifts in precipitation. Ultimately these findings should help to improve the representation of drylands within regional and global models of land surface atmosphere exchange and their linkages to the hydrologic cycle.

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A Physically Based Modeling Framework For Analyzing The Effects Of Climate Change And Land-Cover Disturbance On Suspended Sediment Transport In The Colorado Front Range

Anonymous — Mon, 13 Aug 2018 16:49:12 +0000

A Physically Based Modeling Framework For Analyzing The Effects Of Climate Change And Land-Cover Disturbance On Suspended Sediment Transport In The Colorado Front Range Anonymous (not verified) Mon, 08/13/2018 - 10:49 Jenna Stewart

Stewart, Jenna ¹ ; Livneh, Ben ²

¹ University of Colorado, Boulder and CIRES
² University of Colorado, Boulder and CIRES

Temperatures in Colorado are projected to rise by between +2.5?F and +5?F by 2050, increasing the severity of droughts, heat waves, and wildfire vulnerability. These changes present new uncertainties into the rates of soil erosion and sedimentation throughout the state. Soil erosion adds constituents to streams, altering water chemistry and streambed morphology, which can adversely affect aquatic life, water treatment, and infrastructure. Managing the effects of climate change and land-cover disturbance on water resources poses a critical challenge. The primary goal of this research is to develop a catchment response model, capable of relating weather and climate inputs to streamflow and sediment transport in the Colorado Front Range. As sedimentation rates are impacted by numerous physical processes including soil type, slope and climate, eight empirical, conceptual and physical models will be explored in an attempt to quantify uncertainty and improve predictability. A broader inquiry made here is into the efficacy of empirical, stochastic, or physically based sediment-modeling approaches under different conditions. The empirical methods to be explored include: a monovariate rating curve, a multivariate rating curve, and the USLE. Conceptual models will also be explored including: SWAT and HEC-RAS, while physically-based models identified include: WEPP, KINEROS2 and DHSVM. Here we couple the different soil loss and sediment transport equations using the Variable Infiltration Capacity (VIC) land surface model as a framework.

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Big Blocks And River Incision: A Numerical Modeling Perspective

Anonymous — Mon, 13 Aug 2018 16:48:19 +0000

Big Blocks And River Incision: A Numerical Modeling Perspective Anonymous (not verified) Mon, 08/13/2018 - 10:48 Charles M Shobe

Shobe, Charles M ¹ ; Tucker, Gregory E ² ; Anderson, Robert S ³

¹ CIRES and Department of Geological Sciences, University of Colorado
² CIRES and Department of Geological Sciences, University of Colorado
³ INSTAAR and Department of Geological Sciences, University of Colorado

Bed sediment in bedrock rivers is often enriched in large (>1 m diameter) grains in knickpoints, or reaches where the channel is unusually steep (Fig. 1). We hypothesize that clustering of large blocks in the Boulder Creek knickpoint and other steep reaches of mountain streams is a manifestation of an autogenic (internal) feedback generated by rapid river incision in well-jointed bedrock. Rivers, through erosion and steepening of their adjacent hillslopes, can force an increase in the delivery of large blocks to the channel that in turn shield the bed and retard river incision. Slowing of incision due to hillslope block delivery may inhibit knickpoint propagation and landscape adjustment. Here we use a numerical model to explore whether incision rate-dependent delivery of large blocks can explain the distribution of large grains in Boulder Creek, and whether this grain size distribution requires enough hillslope block delivery to alter channel form and adjustment rates. We argue that the channel-hillslope feedback implied by this grain size distribution may cause real landscapes to differ significantly from those predicted by present landscape evolution theory.

Model results show that when the adjacent hillslopes do not respond to rapid river incision (i.e., blocks are never supplied), the channel response to base level perturbations follows predicted shear stress behavior. When we account for block delivery from the hillslopes, our model successfully replicates the clusters of blocks in knickpoints noted in the field, suggesting that the feedback we describe may be responsible for the block size distribution in Boulder Creek and other natural settings (Fig. 2) [Attal et al., 2015; DiBiase et al., 2015]. As block delivery increases, the reach profile form becomes more convex-upward and knickzones cease retreating up the reach at predicted speeds. Our results illustrate a major complication in using signals of landscape transience such as knickpoints to extract information about landscape history.

Attal, M., S.M. Mudd, M.D. Hurst, B. Weinman, K. Yoo, and M. Naylor, 2015, Impact of change in erosion rate and landscape steepness on hillslope and fluvial sediments grain size in the Feather River basin (Sierra Nevada, California): Earth Surface Dyanmics, v. 3, p. 201-222.
DiBiase, R.A., K.X. Whipple, M.P. Lamb, and A.M. Heimsath, 2015, The role of waterfalls and knickzones in controlling the style and pace of landscape adjustment in the western San Gabriel Mountains, California: Geological Society of America Bulletin, v. 127, p. 539-559.

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Evaluation Of SMAP Soil Moisture Drying Rates

Anonymous — Mon, 13 Aug 2018 16:47:05 +0000

Evaluation Of SMAP Soil Moisture Drying Rates Anonymous (not verified) Mon, 08/13/2018 - 10:47 Peter J Shellito

Shellito, Peter J ¹ ; Small, Eric E ²

¹ Department of Geological Sciences, ��ƷSM��ӰƬ, Boulder, Colorado
² Department of Geological Sciences, ��ƷSM��ӰƬ, Boulder, Colorado

Surface soil moisture is measured both by NASA’s SMAP satellite mission and by validation networks of in situ probes. In the days after a rain event, we model the timescale of drying by fitting an exponential curve. The time constant is 20% shorter as observed by SMAP than by in situ probes. However, fitting the model to in situ observations concurrent with SMAP also reduces the time constant by 20%. We conclude that (1) SMAP observations are not frequent enough to characterize the drydown timescale in the same way in situ observations do, and (2) at the given 1-3 day observation frequency of SMAP, the satellite and in situ observations reflect the same timescale of drying.

Next, we calculate linear drying rates between pairs of consecutive SMAP overpasses. In the first 5 days after a rain event, during which the majority of drying occurs, soil moisture as measured by SMAP dries at twice the rate measured by corresponding in situ observations. We attribute this difference to a shortening of microwave penetration depth over wet soil: when only the top couple of centimeters are wetted, SMAP’s nominal 0-5 cm sensing depth is biased high.

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Geomorphic Response Of Fall River To The 2013 Flood

Anonymous — Mon, 13 Aug 2018 16:45:57 +0000

Geomorphic Response Of Fall River To The 2013 Flood Anonymous (not verified) Mon, 08/13/2018 - 10:45 Mark Schutte

Schutte, Mark ¹

¹ Olsson Associates

In Rocky Mountain National Park, the 2013 flood destabilized segments of Roaring River and deposited an unusually large amount of sand- and gravel-sized sediment near the confluence with Fall River. We initiated field studies of these two rivers in May 2014 to investigate the geomorphic response of Fall River to an increase in sediment supply. Measurements of water discharge and bed load were taken from May through August at three different locations to capture variations in sediment transport rates.

Peak transport rates coincided with the peak discharge at the upstream sampling site (FR 1), but lagged behind the peak in discharge at the lower site (FR 2) by about three weeks, which is consistent with diffusive movement of sediment as observed in earlier studies. On average, 2014 transport rates were 0.015 kg/m/s and 0.035 kg/m/s at FR-1 and FR-2, respectively. Bankfull Shields stress calculations showed a nearly constant value across the study area, about 1.56 A combination of changing slope, depth, and grain size throughout the study area resulted in the same estimated value of reference Shields stress at each site, 0.028.

Annual sediment loads estimated at each site, as well as erosion and deposition tracked by comparing cross sections measurements, both indicate a majority of the sediment deposited by the flood was eroded and transported out of the Fall River channel in 2014. Annual sediment loads were estimated from discharge- and shear stress-based empirical relations and a time series of discharge scaled to the continuous discharge of the Big Thompson River from a nearby USGS gage in Moraine Park. Annual loads estimated at FR 1 and FR 2 were about 3,000 Mg and 4,600 Mg, respectively. Relative to the estimates following the 1982 Lawn Lake flood, annual loads were lower than the three years immediately following the flood, but comparable to the loads estimated four to five years after the flood.

Analysis of the results of the field data collected indicate that Fall River experienced some erosion in 2014, transporting sediment which had been stored in its channel from the flood. Fall River was primarily able to accommodate the increase in sediment supply by adjusting its bed texture, and secondarily due well-vegetated banks which prevented channel widening. Annual sediment loads estimated from all approaches indicate that Fall River was able to transport a majority of the sediment supplied to it in 2014.

Costa, J.E., and J.E. O’Connor (1995), Geomorphically effective floods, American Geophysical Union Monograph, 89, 45-56.
Eaton, B.C., and M. Church (2004), A graded stream response relation for bed-load dominated streams, Journal of Geophysical Research, 109, 18 pp.
Parker, G., (1990), Surface-based bedload transport relation for gravel rivers, Journal of Hydraulic Research, 28 (4), 417-436.
Pitlick, J. and R. Cress, (2002), Downstream changes in the channel geometry of a large gravel bed river, Water Resources Research, 38 (10), 11 pp.
Schumm, S.A., (1969), River metamorphosis, Journal of Hydraulic Division, 95, 255-273.

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Acid Mine Drainage In Colorado: A Wicked Problem With No End In Sight

Anonymous — Mon, 13 Aug 2018 16:44:39 +0000

Acid Mine Drainage In Colorado: A Wicked Problem With No End In Sight Anonymous (not verified) Mon, 08/13/2018 - 10:44 Robert L Runkel

Runkel, Robert L ¹

¹ U.S. Geological Survey

Acid Mine Drainage (AMD) from abandoned mine lands contaminates streams and rivers throughout the Colorado Mineral Belt. Much of this contamination has persisted for decades and is likely to continue given the impediments to cleanup that are present at most sites. These impediments include a dearth of funding for cleanup, inflexibility within the Superfund program (Gustavson et al., 2007), the perpetual nature of AMD, antiquated mining laws, mixed and/or uncertain land ownership, and a lack of premining data for the development of cleanup goals. As such, AMD represents a wicked problem that is not amenable to clean, easy solutions (Lund, 2012).

The complexity of the problem is exemplified by three sites in Colorado that have been subject to remedial actions. Red Mountain Creek near Ouray, Colorado, for example, is acidic and metal rich (pH < 3.5) due to natural sources and historical mining activity. Remedial activities conducted to date include removal of mine waste and tailings, regrading and revegetation of mine wastes left in place, and installation of hydrologic controls that direct meteoric water away from contaminated areas. Despite these actions, low-flow water quality is virtually unchanged (Runkel et al., 2005).

Peru Creek, near Keystone, Colorado, is contaminated by the Pennsylvania Mine and other sources within the watershed (Runkel et al., 2013). Drainage from the Pennsylvania Mine has been greatly reduced following the emplacement of two concrete bulkheads in the primary mine tunnel, leading to improvements in water quality downstream. Establishment of a healthy fishery downstream may remain elusive, however, due to natural sources of metals and acidity that emanate from the mineralized bedrock.

The third and final site is the Animas River, near Silverton, Colorado. Extensive mining activities in the Silverton area have contaminated the Animas River for decades (Kimball et al., 2007), and this contamination was brought to national attention by the recent Gold King Mine release. As with Red Mountain Creek, cleanup activities to date have focused primarily on the removal of tailings and erosion controls on mine dumps, actions that are thought to improve water quality during rainfall/runoff events. Despite this progress, draining mine tunnels continue to result in elevated metal concentrations that persist for miles downstream. As such, additional, more expensive efforts may be needed for long-term, year-around improvement in water quality.

Gustavson, K.E., et al., 2007, Superfund and mining megasites: Environ. Sci. Tech., v. 41, p. 2667-2672.
Kimball, B.A., et al., 2007, Quantification of metal loading by tracer injection and synoptic sampling, 1996-2000: USGS Professional Paper 1651, p. 417–495.
Lund, J.R., 2012, Provoking more productive discussion of wicked problems: J. Water Resource Planning Management, v. 138, p. 193-195.
Runkel, R.L., et al., 2005, Geochemistry of Red Mountain Creek, Colorado, under low-flow conditions, August 2002: USGS SIR 2005-5101, 78 p.
Runkel, R.L., et al., 2013, Estimating instream constituent loads using replicate synoptic sampling, Peru Creek, Colorado: J. Hydrology, v. 489, p. 26-41.

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Chemostatic Cradle To Grave: Dissolved Organic Matter And The Biogeochemical Impacts Of The 2013 Boulder Flood

Anonymous — Mon, 13 Aug 2018 16:43:42 +0000

Chemostatic Cradle To Grave: Dissolved Organic Matter And The Biogeochemical Impacts Of The 2013 Boulder Flood Anonymous (not verified) Mon, 08/13/2018 - 10:43 Garrett P Rue

Rue, Garrett P ¹ ; McKnight, Diane M ² ; Gabor, Rachel ³ ; Anderson, Suzanne P ⁴

¹ INSTAAR, ENVS; University of Colorado-Boulder
² INSTAAR, CEAE, ENVS; University of Colorado-Boulder
³ Department of Geology and Geophysics, University of Utah
⁴ INSTAAR, GEOG; University of Colorado-Boulder

In September of 2013, upwards of 20 inches of rain fell across Boulder County within one week. It caused mass hillside erosion and landslides throughout the Front Range, as well as streamflow conditions congruent with a 100-year flood. This stochastic event further provided a unique opportunity to study its effect on biogeochemical watershed processes. As part of the continued monitoring of the Gordon Gulch headwater catchment by the Boulder Creek Critical Zone Observatory, the collection of water and soil samples here have allowed for long-term investigations regarding the formation of organic material within the regolith in addition to its fluvial transport. Observations of greater variability in dissolved organic matter (DOM) concentration and quality in Gordon Gulch compared to the higher order receiving stream Boulder Creek, suggests that at times the headwater stream is connected to the drainage from the upper saprolite [Burns 2014]. This coupled relationship can be further demonstrated by the pulse of high dissolved organic carbon (DOC) observed during early Spring snowmelt, which flushes out this near-surface soil organic matter (SOM) sourced from leaf litter breakdown as well as microbially-mediated alteration [Gabor et al 2014]. Given the implicit role of precipitation in connectivity of SOM into streams, with snowmelt providing the first flush of resident, interstitial organic matter, the purpose of this study is to elucidate the additional influence of an extreme hydrologic event on the mobilization DOM to its dynamic equilibrium state [Creed et al. 2015]. From samples collected in Boulder Creek across synoptic and temporal scales, processed through advanced chromatographic techniques and spectroscopic characterization, we seek to identify whether such large inputs of water additionally mobilize accumulated, recalcitrant DOM moieties through enhanced conductivity and deeper flushing of the soil/saprolite boundary. Furthermore, these findings could support the concept that similarly to stream morphology, such events also serve as an effective reset mechanism for terrestrial-aquatic biogeochemical linkages.

Creed, I.R, McKnight, D.M., Pellerin, B.A., Green, M.B., Bergamaschi, B.A.,Aiken, G.R., et al, 2015, The River as a chemosat; fresh perspectives on DOM flowing down the river continuum. Canadian Journal of Fisheries and Aquatic Sciences, v. 72, p. 1272-1285
Gabor,R., Eilers, K., McKnight,D.M., Fierer, N., Anderson, S.,2014, From the litter layer to the saprolite; Chemical changes in water-soluble soil organic matter and their correlation to microbial community composition: Soil Biology and Biochemistry v. 68, p. 166-176
Burns, M., 2014, Hillslope dissolved organic matter transport and transformation in a semi-arid headwater catchment: Masters Thesis, ��ƷSM��ӰƬ

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