Matching Items (11)
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Description
Sedimentary basins in the Afar Depression, Ethiopia archive the progression of continental breakup, record regional changes in east African climate and volcanism, and host what are arguably the most important fossiliferous strata for studying early human evolution and innovation. Significant changes in rift tectonics, climate, and faunal assemblages occur between

Sedimentary basins in the Afar Depression, Ethiopia archive the progression of continental breakup, record regional changes in east African climate and volcanism, and host what are arguably the most important fossiliferous strata for studying early human evolution and innovation. Significant changes in rift tectonics, climate, and faunal assemblages occur between 3-2.5 million years ago (Ma), but sediments spanning this time period are sparse. In this dissertation, I present the results of a geologic investigation targeting sediments between 3-2.5 Ma in the central and eastern Ledi Geraru (CLG and ELG) field areas in the lower Awash Valley, using a combination of geologic mapping, stratigraphy, and tephra chemistry and dating. At Gulfaytu in CLG, I mapped the northern-most outcrops of the hominin-bearing Hadar Formation (3.8-2.9 Ma), a 20 m-thick section of flat-lying lacustrine sediments containing 8 new tephras that directly overlie the widespread BKT-2 marker beds (2.95 Ma). Paleolake Hadar persisted after 2.95 Ma, and the presence and characteristics of the Busidima Formation (2.7-0.016 Ma) indicates Gulfaytu was affected by a reversal in depositional basin polarity. Combined with regional and geophysical data, I show the Hadar Formation underlying CLG is >300 m thick, supporting the hypothesis that it was the lower Awash Pliocene depocenter. At ELG, I mapped >300 m of sediments spanning 3.0-2.45 Ma. These sediments coarsen upward and show a progression from fluctuating lake conditions to fluvial landscapes and widespread soil development. This is consistent with the temporal change in depositional environments observed elsewhere in the lower Awash Valley, and suggests that these strata are correlative with the Hadar Formation. Furthermore, the strata and basalts at ELG are highly faulted, and overprinted by shifting extension directions attributed to the northern migration of the Afar triple junction. The presence of fossiliferous beds and stone tools makes ELG a high-priority target for anthropological and archaeological research. This study provides a new temporally-calibrated and high-resolution record of deposition, volcanism, and faulting patterns during a period of significant change in the Afar.
ContributorsDiMaggio, Erin Nicole (Author) / Arrowsmith, J Ramon (Thesis advisor) / Whipple, Kelin X (Committee member) / Heimsath, Arjun M (Committee member) / Clarke, Amanda B (Committee member) / Reed, Kaye E (Committee member) / Arizona State University (Publisher)
Created2013
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Description
The Himalaya are the archetypal example of a continental collision belt, formed by the ongoing convergence between India and Eurasia. Boasting some of the highest and most rugged topography on Earth, there is currently no consensus on how climatic and tectonic processes have combined to shape its topographic evolution. The

The Himalaya are the archetypal example of a continental collision belt, formed by the ongoing convergence between India and Eurasia. Boasting some of the highest and most rugged topography on Earth, there is currently no consensus on how climatic and tectonic processes have combined to shape its topographic evolution. The Kingdom of Bhutan in the eastern Himalaya provides a unique opportunity to study the interconnections among Himalayan climate, topography, erosion, and tectonics. The eastern Himalaya are remarkably different from the rest of the orogen, most strikingly due to the presence of the Shillong Plateau to the south of the Himalayan rangefront. The tectonic structures associated with the Shillong Plateau have accommodated convergence between India and Eurasia and created a natural experiment to test the possible response of the Himalaya to a reduction in local shortening. In addition, the position and orientation of the plateau topography has intercepted moisture once bound for the Himalaya and created a natural experiment to test the possible response of the range to a reduction in rainfall. I focused this study around the gently rolling landscapes found in the middle of the otherwise extremely rugged Bhutan Himalaya, with the understanding that these landscapes likely record a recent change in the evolution of the range. I have used geochronometric, thermochronometric, and cosmogenic nuclide techniques, combined with thermal-kinematic and landscape evolution models to draw three primary conclusions. 1) The cooling histories of bedrock samples from the hinterland of the Bhutan Himalaya show a protracted decrease in erosion rate from the Middle Miocene toward the Pliocene. I have attributed this change to a reduction in shortening rates across the Himalayan mountain belt, due to increased accommodation of shortening across the Shillong Plateau. 2) The low-relief landscapes of Bhutan were likely created by backtilting and surface uplift produced by an active, blind, hinterland duplex. These landscapes were formed during surface uplift, which initiated ca. 1.5 Ma and has totaled 800 m. 3) Millennial-scale erosion rates are coupled with modern rainfall rates. Non-linear relationships between topographic metrics and erosion rates, suggest a fundamental difference in the mode of river incision within the drier interior of Bhutan and the wetter foothills.
ContributorsAdams, Byron A (Author) / Whipple, Kelin X (Thesis advisor) / Hodges, Kip V (Thesis advisor) / Heimsath, Arjun M (Committee member) / Arrowsmith, Ramon (Committee member) / Hurtado, Jose M (Committee member) / Arizona State University (Publisher)
Created2014
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Description
Climate and its influence on hydrology and weathering is a key driver of surface processes on Earth. Despite its clear importance to hazard generation, fluvial sediment transport and erosion, the drawdown of atmospheric CO2 via the rock cycle, and feedbacks between climate and tectonics, quantifying climatic controls on long-term erosion

Climate and its influence on hydrology and weathering is a key driver of surface processes on Earth. Despite its clear importance to hazard generation, fluvial sediment transport and erosion, the drawdown of atmospheric CO2 via the rock cycle, and feedbacks between climate and tectonics, quantifying climatic controls on long-term erosion rates has proven to be one of the grand problems in geomorphology. In fact, recent attempts addressing this problem using cosmogenic radionuclide (CRN) derived erosion rates suggest very weak climatic controls on millennial-scale erosion rates contrary to expectations. In this work, two challenges are addressed that may be impeding progress on this problem.

The first challenge is choosing appropriate climate metrics that are closely tied to erosional processes. For example, in fluvial landscapes, most runoff events do little to no geomorphic work due to erosion thresholds, and event-scale variability dictates how frequently these thresholds are exceeded. By analyzing dense hydroclimatic datasets in the contiguous U.S. and Puerto Rico, we show that event-scale runoff variability is only loosely related to event-scale rainfall variability. Instead, aridity and fractional evapotranspiration (ET) losses are much better predictors of runoff variability. Importantly, simple hillslope-scale soil water balance models capture major aspects of the observed relation between runoff variability and fractional ET losses. Together, these results point to the role of vegetation water use as a potential key to relating mean hydrologic partitioning with runoff variability.

The second challenge is that long-term erosion rates are expected to balance rock uplift rates as landscapes approach topographic steady state, regardless of hydroclimatic setting. This is illustrated with new data along the Main Gulf Escarpment, Baja, Mexico. Under this conceptual framework, climate is not expected to set the erosion rate, but rather the erosional efficiency of the system, or the steady-state relief required for erosion to keep up with tectonically driven uplift rates. To assess differences in erosional efficiency across landscapes experiencing different climatic regimes, we contrast new CRN data from tectonically active landscapes in Baja, Mexico and southern California (arid) with northern Honduras (very humid) alongside other published global data from similar hydroclimatic settings. This analysis shows how climate does, in fact, set functional relationships between topographic metrics like channel steepness and long-term erosion rates. However, we also show that relatively small differences in rock erodibility and incision thresholds can easily overprint hydroclimatic controls on erosional efficiency motivating the need for more field based constraints on these important variables.
ContributorsRossi, Matthew (Author) / Whipple, Kelin X (Thesis advisor) / DeVecchio, Duane E (Committee member) / Vivoni, Enrique R (Committee member) / Arrowsmith, J Ramon (Committee member) / Heimsath, Arjun M (Committee member) / Arizona State University (Publisher)
Created2014
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Description
Quantifying the temporal and spatial evolution of active continental rifts contributes to our understanding of fault system evolution and seismic hazards. Rift systems also preserve robust paleoenvironmental records and are often characterized by strong climatic gradients that can be used to examine feedbacks between climate and tectonics. In this thesis,

Quantifying the temporal and spatial evolution of active continental rifts contributes to our understanding of fault system evolution and seismic hazards. Rift systems also preserve robust paleoenvironmental records and are often characterized by strong climatic gradients that can be used to examine feedbacks between climate and tectonics. In this thesis, I quantify the spatial and temporal history of rift flank uplift by analyzing bedrock river channel profiles along footwall escarpments in the Malawi segment of the East Africa Rift. This work addresses questions that are widely applicable to continental rift settings: (1) Is rift-flank uplift sufficiently described by theoretical elliptical along-fault displacement patterns? (2) Do orographic climate patterns induced by rift topography affect rift-flank uplift or morphology? (3) How do uplift patterns along rift flanks vary over geologic timescales? In Malawi, 100-km-long border faults of alternating polarity bound half-graben sedimentary basins containing up to 4km of basin fill and water depths up to 700m. Orographically driven precipitation produces climatic gradients along footwall escarpments resulting in mean annual rainfall that varies spatially from 800 to 2500 mm. Temporal oscillations in climate have also resulted in lake lowstands 500 m below the modern shoreline. I examine bedrock river profiles crossing the Livingstone and Usisya Border Faults in northern Malawi using the channel steepness index (Ksn) to assess importance of these conditions on rift flank evolution. River profiles reveal a consistent transient pattern that likely preserves a temporal record of slip and erosion along the entire border fault system. These profiles and other topographic observations, along with known modern and paleoenvironmental conditions, can be used to interpret a complete history of rift flank development from the onset of rifting to present. I interpret the morphology of the upland landscape to preserve the onset of extensional faulting across a relict erosion surface. The linkages of individual faults and acceleration of slip during the development of a continuous border fault is suggested by an analysis of knickpoint elevations and Ksn. Finally, these results suggest that the modern observed climate gradient only began to significantly affect denudation patterns once a high relief rift flank was established.
ContributorsRobinson, Scott M (Author) / Heimsath, Arjun M (Thesis advisor) / Whipple, Kelin X (Thesis advisor) / Arrowsmith, Ramon J (Committee member) / Arizona State University (Publisher)
Created2014
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Description
Sedimentary basins are defined by extensional tectonics. Rugged mountain ranges stand in stark relief adjacent to muted structural basins filled with sediment. In simplest terms, this topography is the result of ranges uplifted along normal faults, and this uplift drives erosion within upland drainages, shedding sediment into subsiding basins. In

Sedimentary basins are defined by extensional tectonics. Rugged mountain ranges stand in stark relief adjacent to muted structural basins filled with sediment. In simplest terms, this topography is the result of ranges uplifted along normal faults, and this uplift drives erosion within upland drainages, shedding sediment into subsiding basins. In southeastern Arizona's Basin and Range province extensional tectonics waned at approximately 3-5 Myr, and the region's structural basins began transitioning from internal to external drainage, forming the modern Gila River fluvial network. In the Atacama Desert of northern Chile, some basins of the Central Depression remain internally drained while others have integrated to the Pacific Ocean. In northern Chile, rates of landscape evolution are some of the slowest on Earth due to the region's hyperarid climate. While the magnitude of upland erosion driven by extensional tectonics is largely recorded in the stratigraphy of the structural basins, the landscape's response to post-tectonic forcings is unknown.

I employ the full suite of modern geomorphic tools provided by terrestrial cosmogenic nuclides - surface exposure dating, conventional burial dating, isochron burial dating, quantifying millennial-scale upland erosion rates using detrital TCN, quantifying paleo-erosion rates using multiple TCN such as Ne-21/Be-10 and Al-26l/Be-10, and assessing sediment recycling and complex exposure using multiple TCN - to quantify the rates of landscape evolution in southeastern Arizona and northern Chile during the Late Cenozoic. In Arizona, I also use modern remnants of the pre-incision landscape and digital terrain analyses to reconstruct the landscape, allowing the quantification of incision and erosion rates that supplement detrital TCN-derived erosion rates. A new chronology for key basin high stand remnants (Frye Mesa) and a flight of Gila River terraces in Safford basin provides a record of incision rates from the Pliocene through the Quaternary, and I assess how significantly regional incision is driving erosion rates. Paired nuclide analyses in the Atacama Desert of northern Chile reveal complex exposure histories resulting from several rounds of transport and burial by fluvial systems. These results support a growing understanding that geomorphic processes in the Atacama Desert are more active than previously thought despite the region's hyperarid climate.
ContributorsJungers, Matthew Cross (Author) / Heimsath, Arjun M (Thesis advisor) / Whipple, Kelin (Committee member) / Arrowsmith, Ramon (Committee member) / Vivoni, Enrique (Committee member) / DeVecchio, Duane (Committee member) / Arizona State University (Publisher)
Created2014
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Description
The San Andreas Fault (SAF) is the primary structure within a system of faults accommodating motion between the North American and Pacific plates. Physical models of faulting and characterizations of seismic hazard are informed by investigations of paleoseismology, slip distribution, and slip rate. The impact of earthquakes on people is

The San Andreas Fault (SAF) is the primary structure within a system of faults accommodating motion between the North American and Pacific plates. Physical models of faulting and characterizations of seismic hazard are informed by investigations of paleoseismology, slip distribution, and slip rate. The impact of earthquakes on people is due in large part to social vulnerability. This dissertation contributes an analysis about the relationships between earthquake hazard and social vulnerability in Los Angeles, CA and investigations of paleoseismology and fault scarp array complexity on the central SAF. Analysis of fault scarp array geometry and morphology using 0.5 m digital elevation models along 122 km of the central SAF reveals significant variation in the complexity of SAF structure. Scarp trace complexity is measured by scarp separation, changes in strike, fault trace gaps, and scarp length per SAF kilometer. Geometrical complexity in fault scarp arrays indicates that the central SAF can be grouped into seven segments. Segment boundaries are controlled by interactions with subsidiary faults. Investigation of an offset channel at Parkfield, CA yields a late Holocene slip rate of 26.2 +6.4/- 4.3 mm/yr. This rate is lower than geologic measurements on the Carrizo section of the SAF and rates implied by far-field geodesy. However, it is consistent with historical observations of slip at Parkfield. Paleoseismology at Parkfield indicates that large earthquakes are absent from the stratigraphic record for at least a millennia. Together these observations imply that the amount of plate boundary slip accommodated by the main SAF varies along strike. Contrary to most environmental justice analyses showing that vulnerable populations are spatially-tied to environmental hazards, geospatial analyses relating social vulnerability and earthquake hazard in southern California show that these groups are not disproportionately exposed to the areas of greatest hazard. Instead, park and green space is linked to earthquake hazard through fault zone regulation. In Los Angeles, a parks poor city, the distribution of social vulnerability is strongly tied to a lack of park space. Thus, people with access to financial and political resources strive to live in neighborhoods with parks, even in the face of forewarned risk.
ContributorsToké, Nathan A (Author) / Arrowsmith, J R (Thesis advisor) / Boone, Christopher G (Committee member) / Heimsath, Arjun M (Committee member) / Shock, Everett L (Committee member) / Whipple, Kelin X (Committee member) / Arizona State University (Publisher)
Created2011
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Description
Drylands (arid and semi-arid grassland ecosystems) cover about 40% of the Earth's surface and support over 40% of the human population, most of which is in emerging economies. Human development of drylands leads to topsoil loss, and over the last 160 years, woody plants have encroached on drylands, both of

Drylands (arid and semi-arid grassland ecosystems) cover about 40% of the Earth's surface and support over 40% of the human population, most of which is in emerging economies. Human development of drylands leads to topsoil loss, and over the last 160 years, woody plants have encroached on drylands, both of which have implications for maintaining soil viability. Understanding the spatial variability in erosion and soil organic carbon and total nitrogen under varying geomorphic and biotic forcing in drylands is therefore of paramount importance. This study focuses on how two plants, palo verde (Parkinsonia microphylla, nitrogen-fixing) and jojoba (Simmondsia chinensis, non-nitrogen fixing), affect sediment transport and soil organic carbon and total nitrogen pools in a dryland environment north of Phoenix, Arizona. Bulk samples were systematically collected from the top 10 cm of soil in twelve catenae to control for the existence and type of plants, location to canopy (sub- or intercanopy, up- or downslope), aspect, and distance from the divide. Samples were measured for soil organic carbon and total nitrogen and an unmanned aerial system-derived digital elevation map of the field site was created for spatial analysis. A subset of the samples was measured for the short-lived isotopes 137Cs and 210Pbex, which serve as proxy erosion rates. Erosional soils were found to have less organic carbon and total nitrogen than depositional soils. There were clear differences in the data between the two plant types: jojoba catenae had higher short-lived isotope activity, lower carbon and nitrogen, and smaller canopies than those of palo verde, suggesting lower erosion rates and nutrient contributions from jojoba plants. This research quantifies the importance of biota on influencing hillslope and soil dynamics in a semi-arid field site in central AZ and finishes with a discussion on the global implications for soil sustainability.
ContributorsAlter, Samuel (Author) / Heimsath, Arjun M (Thesis advisor) / Throop, Heather L (Committee member) / Walker, Ian J (Committee member) / Arizona State University (Publisher)
Created2018
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Description
Dryland ecosystems are integral to the global agricultural system and play an important role in soil carbon (C) storage. Despite their importance, drylands are currently facing many challenges including climate-change induced rainfall variability and soil degradation. These challenges are predicted to have effects on the soil microbial communities in drylands.

Dryland ecosystems are integral to the global agricultural system and play an important role in soil carbon (C) storage. Despite their importance, drylands are currently facing many challenges including climate-change induced rainfall variability and soil degradation. These challenges are predicted to have effects on the soil microbial communities in drylands. Compost, an organic soil amendment, is a land management strategy that has been proposed to increase soil C storage as well as improve soil conditions in drylands, specifically in restoration and agricultural sites where degradation has affected soil properties like microbial biomass and respiration. Compost additions and rainfall variability may interact to affect soil moisture, an important catalyst for microbial activity. Assessing microbial activity responses under compost applications and variable moisture will aid in understanding how land management strategies will be affected by climate change in the future. This study investigates how soil microbial activity from a degraded dryland restoration site is affected by different compost applications amounts and variable soil moistures. A laboratory incubation study was conducted in a controlled environmental chamber for 60 days. Soils were amended with different treatments of compost (0, 0.35, and 0.70 g cm -2) and water pulses (5, 10, and 15 mm) in a full factorial design. Each treatment received the same cumulative amount of water throughout the incubation, but pulses were administered in different frequencies (every 5, 10, and 15 days). Soil respiration and soil water content were measured daily, and microbial biomass was measured at the end of the incubation to assess treatment effects on microbial activity. Microbial respiration and soil water content increased with increasing compost additions and water pulse sizes. Microbial biomass did not have consistent increases with compost additions or water pulse size. Cumulative microbial respiration was highest with the large-infrequent pulse size and smallest with the small-frequent pulse size. These results suggest that microbial activity and carbon dynamics in soils where compost amendments are used will respond to future changes in precipitation variability. The results of this study can aid in understanding how microbial activity is influenced by compost applications, which will be critical in making informed management decisions in the context of climate change.
ContributorsAmari, Katherine Nicole (Author) / Throop, Heather L (Thesis advisor) / Ball, Becky A (Committee member) / Blankinship, Joseph C (Committee member) / Gherardi, Laureano A (Committee member) / Cueva Rodriguez, Alejandro H (Committee member) / Arizona State University (Publisher)
Created2021
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Description
In arid and semiarid areas of the southwestern United States and northwestern México, water availability is the main control on the interactions between the land surface and the atmosphere. Seasonal and interannual variations in water availability regulate the response of water and carbon dioxide fluxes in natural and urban landscapes.

In arid and semiarid areas of the southwestern United States and northwestern México, water availability is the main control on the interactions between the land surface and the atmosphere. Seasonal and interannual variations in water availability regulate the response of water and carbon dioxide fluxes in natural and urban landscapes. However, despite sharing a similar dependance to water availability, landscape characteristics, such as land cover heterogeneity, landscape position, access to groundwater, microclimatic conditions, and vegetation functional traits, among others, can play a fundamental role in modulating the interactions between landscapes and the atmosphere. In this dissertation, I study how different landscape characteristics influence the response of water and carbon dioxide fluxes in arid and semiarid urban and natural settings. The study uses the eddy covariance technique, which calculates the vertical turbulent fluxes within the boundary layer, to quantify water, energy, and carbon dioxide fluxes within local patches. Specifically, the study focused on three main scopes: (1) how vegetation, anthropogenic activity, and water availability influence carbon fluxes in four urban landscapes in Phoenix, Arizona, (2) how access to groundwater and soil-microclimate conditions modulate the flux response of three natural ecosystems in northwestern México during the North American monsoon, and (3) how the seasonal hydrologic partitioning in a watershed with complex terrain regulates the carbon dioxide fluxes of a Chihuahuan Desert shrubland. Results showed a differential response of landscapes according to their land cover composition, access to groundwater or functional traits. In Chapter 2, in urban landscapes with irrigation, vegetation activity can counteract carbon dioxide emissions during the day, but anthropogenic sources from the built environment dominate the carbon dioxide fluxes overall. In Chapter 3, across an elevation-groundwater access gradient, low elevation ecosystems showed intensive water use strategies linked to a dependance to shallow or intermittent access to soil moisture, while a high elevation ecosystem showed extensive water use strategies which depend on a reliable access to groundwater. Finally, in Chapter 4, the mixed shrubland in complex terrain showed an evenly distributed bimodal vegetation productivity which is supported by an abundant water availability during wet seasons and by carry-over moisture in deeper layers of the soil during the dry season. The results from this dissertation highlight how different forms of water availability are responsible for the activity of vegetation which modulates land surface fluxes in arid and semiarid settings. Furthermore, the outcomes of this dissertation help to understand how landscape properties regulate the flux response to water availability in urban and natural areas.
ContributorsPerez Ruiz, Eli Rafael (Author) / Vivoni, Enrique R (Thesis advisor) / Sala, Osvaldo E (Committee member) / Throop, Heather L (Committee member) / Whipple, Kelin X (Committee member) / Yepez, Enrico A (Committee member) / Arizona State University (Publisher)
Created2021
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Soil organic carbon (SOC) is a critical component of the global carbon (C) cycle, accounting for more C than the biotic and atmospheric pools combined. Microbes play an important role in soil C cycling, with abiotic conditions such as soil moisture and temperature governing microbial activity and subsequent soil C

Soil organic carbon (SOC) is a critical component of the global carbon (C) cycle, accounting for more C than the biotic and atmospheric pools combined. Microbes play an important role in soil C cycling, with abiotic conditions such as soil moisture and temperature governing microbial activity and subsequent soil C processes. Predictions for future climate include warmer temperatures and altered precipitation regimes, suggesting impacts on future soil C cycling. However, it is uncertain how soil microbial communities and subsequent soil organic carbon pools will respond to these changes, particularly in dryland ecosystems. A knowledge gap exists in soil microbial community responses to short- versus long-term precipitation alteration in dryland systems. Assessing soil C cycle processes and microbial community responses under current and altered precipitation patterns will aid in understanding how C pools and cycling might be altered by climate change. This study investigates how soil microbial communities are influenced by established climate regimes and extreme changes in short-term precipitation patterns across a 1000 m elevation gradient in northern Arizona, where precipitation increases with elevation. Precipitation was manipulated (50% addition and 50% exclusion of ambient rainfall) for two summer rainy seasons at five sites across the elevation gradient. In situ and ex situ soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were measured in precipitation treatments in all sites. Soil CO2 flux, microbial biomass C, extracellular enzyme activity, and SOC were highest at the three highest elevation sites compared to the two lowest elevation sites. Within sites, precipitation treatments did not change microbial biomass C, extracellular enzyme activity, and SOC. Soil CO2 flux was greater under precipitation addition treatments than exclusion treatments at both the highest elevation site and second lowest elevation site. Ex situ respiration differed among the precipitation treatments only at the lowest elevation site, where respiration was enhanced in the precipitation addition plots. These results suggest soil C cycling will respond to long-term changes in precipitation, but pools and fluxes of carbon will likely show site-specific sensitivities to short-term precipitation patterns that are also expected with climate change.
ContributorsMonus, Brittney (Author) / Throop, Heather L (Thesis advisor) / Ball, Becky A (Committee member) / Hultine, Kevin R (Committee member) / Munson, Seth M (Committee member) / Arizona State University (Publisher)
Created2019