Repository logo

Browsing by Author "Kelly, Eugene F., advisor"

Now showing 1 - 6 of 6
  • Thumbnail Image
    ItemOpen Access
    A study of long-term soil moisture dynamics: assessing biologically available water as a function of soil development
    (Colorado State University. Libraries, 2015) Salley, Shawn William, author; Kelly, Eugene F., advisor; Martin, Patrick H., advisor; Knapp, Alan, committee member; Kahosla, Raj, committee member
    Forecasting ecosystem responses to global change is highly uncertain in light of the alarming rates of climate change predicted by the scientific community. Rising CO₂ concentrations not only cause increased warming, but may also influence the amount and distribution of rainfall in terrestrial ecosystems. This in turn affects plant growth and the ability of ecosystems to perform important functions including nutrient cycling and decomposition. Soil moisture is considered the major control of ecosystem structure and function, and it is considered the most limiting resource to biological activity in semi-arid grassland ecosystems. Total soil moisture potentials are controlled by edaphic properties such as texture, structure, micro-porosity, bulk density, soil depth, clay mineralogy, and organic matter content. Physical and chemical properties interact with hydrologic inflows and outflows to control soil moisture causing the soil to act as a store and regulator in the water flow system of the overall ecosystem. Thus, the soil acts as both temporary storage of precipitation inputs and as a regulator controlling the partition between inputs and the major outflows: evapotranspiration, runoff, leaching, and flow between organisms. Understanding the pedologic controls of water retention is critical in considering the long-term dynamics of ecosystems and projecting the consequence of global change. The focus of my dissertation is twofold: to elucidate the change in water holding characteristics of soils through pedogenesis and to quantify how global change will impact soil moisture in the U.S. Great Plains. In order to best address my research questions, I began by studying two established soil-chronosequences in northeast Colorado and central Wyoming to assess the characteristics of soil's physical and chemical properties. I examined how they control the biologically available water holding capacities that change predictably as a function of soil age. Next, I examined other notable soil chronosequences across the western United States to test the millennial evolution of soil water holding capacities through various climates and soil parent materials. Finally, I used a soil moisture simulation to spatially model the historical, contemporary, and future projections of soil moisture on the Great Plains. I found in semi-arid ecosystems that three broad stages of soil development exist and are linked to landscape ages that are ecologically and biogeochemically significant: aggrading, equilibrium, and retrogressive stages. Soils in the aggrading stage are typically weakly developed, have genetically simple horizon differentiation, and minimal water retention. Prominent clay and carbonate features are expressed in the equilibrium stage soils which show more complex soil horizonation, structure, aggregation, and porosity. Within these intermediate soils, the capacity to store water reaches a maximum. Declining or retrogressive stage soils show losses of clays and carbonates, have undergone extensive leaching, and the soil's capacity to store water is at a minimum compared to the aggrading and equilibrium stages. Furthermore, I confirmed when modeling soil moisture in the Great Plains that course-textured landscapes store less soil water and when accompanied with disturbance are more vulnerable to climate change. Overall, my dissertation focuses on understanding the role pedogenesis has on soil water holding characteristics and how global change impacts semiarid landscapes. My results have helped improve understanding of long-term ecosystem biophysical feedbacks through quantifying soil moisture retention characteristics across soil age and climatic processes by linking soil water properties to climatic and pedogenic variables.
  • Thumbnail Image
    ItemOpen Access
    Integrating basic remote sensing, terrain analysis and geostatistical methods to generate spatially explicate continuous soil attribute maps for Fraser Experimental Forest
    (Colorado State University. Libraries, 2010) Norman, John Barstow, author; Kelly, Eugene F., advisor; Rhoades, Chuck, Affiliate, committee member; Reich, Robin M., committee member
    Hans Jenny's Factors of Soil Formation, a system of quantitative pedology (1941), concisely summarized and illustrated many of the basic principles of pedology utilized to date (Jenny, 1941). This state factor model became the backbone for soil survey research and production because it proposed that a limited number of environmental factors could largely explain the distribution of soils within and among ecosystems. Advances in soil chemistry, soil physics, soil mineralogy, and soil biology, as well as in the basic sciences have helped increase our fundamental understanding of the spatial distribution of soil. In addition, new tools and new dimensions to the study of soil formation have evolved with the increasing power and utility of Geographical Information Systems (GIS) and geostatistical analysis to further quantify the complex spatial relationships of soils and landscapes. These advances have resulted in a new field of study termed pedometrics, which focuses on the application of mathematical and statistical methods for the study of the distribution and evolution of soils. This study implements pedometric principles and methods to develop high resolution and spatially explicate soil attribute maps for Fraser Experimental Forest (FEF) based on simple terrain, remote sensing and geostatistical analyses. The soil attribute models developed for this study provided a continuous representation of soil properties (Total soil depth, A-horizon and O-horizon thickness) at a fine scale (0.001 ha). These spatial models can be used as inputs to hydrological and ecological models to further evaluate the soil's influence on water chemistry and vegetation distributions, and to provide an initial platform for future soil survey activities in FEF. In addition to developing soil attribute surfaces for FEF, I tested the statistical, spatial and cost efficiencies of the Spatially Balances Survey (SBS) design developed to sample soils and inform the geostatistical models for FEF.
  • Thumbnail Image
    ItemOpen Access
    Pedological and ecological controls on biogenic silica cycling in grass dominated ecosystems
    (Colorado State University. Libraries, 2009) Melzer-Drinnen, Susan E., author; Kelly, Eugene F., advisor
    The biogeochemical behavior of silica is closely linked to the carbon cycle as marine Si-based diatoms are a major control on the distribution of silica in oceans, and play a major role in controlling atmospheric pCO2 via the "biological pump." The importance of biological controls on silica cycling in the terrestrial environment has only recently been known and our studies point to grasslands and grass dominated ecosystems as important repositories. Although the structure and ecological functioning of these ecosystems are strongly influenced by fire and grazing, the role of these key ecological drivers in the production and storage of Si represents a significant knowledge gap. Additionally, the effect of biogenic silica dissolution on the weathering of rock with different mineral assemblages is also insufficiently understood. I evaluated the effects of fire, grazing and parent material on the range and variability of plant derived biogenic silica stored in plant biomass and soils by sampling plants and soils in the mesic grasslands of North America and savannas of South Africa. Using these and other intensive study sites, along with extant productivity and soil texture data I estimated the global Si storage based on two approaches: "measure and multiply" and "paint by numbers".
  • Thumbnail Image
    ItemOpen Access
    Soil evolution on a terrace chronosequence in the Wind River Basin, Wyoming
    (Colorado State University. Libraries, 1994) Peacock, Charles R., author; Kelly, Eugene F., advisor; Barbarick, K. A., committee member; Wohl, Ellen E., 1962-, committee member
    A series of strath terraces overlain with alluvial deposits from glacial and inter-glacial periods were used to develop a chronosequence. The sequence of soils examined in this study illustrate the effects of time on soil formation. Clay and carbonate percentages showed significant increases over time. Other indicators of soil evolution were less useful in evaluating the relationship between time and soil properties. Mineralogy characterization shows a predominance of smectite throughout the clay size fractions at each site. Chlorite, vermiculite and palygorskite are also abundant as well as intergrades of chlorite-smectite and mica-smectite. Results of this study demonstrate the dominance of aeolian additions to soil vs. chemical weathering in these environments. This work provides a greater understanding of the relationship between soil properties and time and should prove useful to pedologists, geologists and other scientists interested in landscape evolution.
  • Thumbnail Image
    ItemOpen Access
    The impacts of long-term cultivation on soil degradation in the San Luis Valley, Colorado
    (Colorado State University. Libraries, 2016) Daniels, Judith Marie, author; Kelly, Eugene F., advisor; Butters, Gregory, committee member; Melzer, Susan E., committee member; von Fischer, Joe, committee member
    Essentially all agricultural lands globally are under pressure to meet the food demands of an additional 2 billion people over the next 20 years. All of the agroecosystems possess limitations that constrain their ability to optimize production, however, these limitations are magnified in semi-arid regions where permanent, seasonal or periodic moisture deficiency results in evaporation and transpiration rates that exceed precipitation. Traditional cultivation practices that utilize modern technology have resulted in substantial amounts of soil loss through wind and water erosion, decreased soil organic matter, reduction in soil water-holding capacity, and alterations to the microbial community composition. Cultivation also affects soil chemical processes and conditions (e.g., pH, cation exchange complexes, electric conductivity, and sodium adsorption ratio) that can lead to further soil degradation. Changes in one or more of these properties often have direct or indirect effects on the fertility of soils, which influence resiliency and soil health. While research has clearly established the most common modifications to soil systems from cultivation, further investigation is needed in semi-arid regions to identify the critical links between physical, chemical, and biological properties that regulate resiliency and soil degradation. In establishing these critical links, I evaluated the importance of parent material (basalt versus granite) in assessing the impacts on the physical, chemical, and biogeochemical soil properties as a function of cultivation, specifically sprinkler and flood irrigation. I also distinguished microbial community composition by parent material and land use and identified key soil properties that regulate changes in microbial community structure by sampling native and cultivated soils in the San Luis Valley (SLV), located in the South Central part of Colorado. The SLV is a high elevation semi-arid agroecosystem with basalt and granite substrates, that receives 177 mm of precipitation annually and the potential evapotranspiration that exceeds 1016 mm. The SLV has also has a 150-year history of irrigated agriculture practices, which add an additional 153 to 1226 mm of water during the growing season. This alters the natural climate and possibly results in some degree of land degradation. Overall, the results indicate the importance of parent material (basalt vs. granite), as a soil forming factor in assessing the impact of cultivation on soil degradation processes. The initial clay percent in the native soils was 20% for basalt and 18% for granite. The additional accumulation of clay from irrigation was slightly higher for basalt soil, (22%) and 20% for granite soils. Soils derived from basalt have greater quantities of the major cations while soils derived from granite have lower quantities and a poor nutrient status. Soils derived from basalt have greater percentage of soil organic carbon in the soil surface horizons than soils derived from granite. The uncultivated soils derived from basalt classify as saline-sodic while those derived from granite were consistently non-saline, non-sodic. As a function of irrigation, the nutrient concentrations of calcium, magnesium, sodium, potassium, chloride and sulfate were reduced in basalt soils while concentrations increased in granite. In addition, the greatest accumulation of clay and soil organic carbon occurred in granite soils with flood irrigation which resulted in similar concentrations as the basalt soils. Also, basalt soils re-classified as non-saline and non-sodic while those derived from granite remain consistently non-saline non-sodic. These results demonstrate a convergence among the basalt and granite soil properties as a function of land use. Using the ester-linked fatty acid methyl ester (EL-FAMEs), which evaluates differences among soil microbial community composition based on the condition variables of parent material (granite and basalt) and treatments (control, sprinkler, and flood). The results indicated that total microbial biomass and the stress ratios differed between basalt and granite with flood irrigation and the most variation was observed in the basalt-flooded soils. The fungi-to-bacteria ratios were the same in basalt and granite soils and both irrigation types (sprinkler and flood). Arbuscular Mycorrhizal (AM) Fungi did not differ between basalt and granite, however, the concentrations of AM fungi increased in irrigated soils, suggesting alfalfa and pasture hay grasses nurture root biomass. The correlations analysis identified pH, magnesium, sodium, potassium, chloride, and organic carbon as being the primary soil properties associated with the microbial communities in both soils and treatment types. The results from the sensitivity model for microbial communities in granite soils indicated changes in these soil properties were more pronounced pH, magnesium, sodium, potassium, chloride, and soil organic carbon in both sprinkler and flood irrigation. While the microbial communities in basalt soils were sensitive to pH and soil organic carbon in both irrigation practices; the responses were negligible compared to granite soils. Physical soil properties were not significant in determining correlations or sensitivities among the microbial communities. Overall, my data revealed the importance of communally evaluating the physical, chemical, and biological properties in determining the key properties that collectively regulate resiliency and indicate soil degradation. The key indicators in this study are soil texture, bulk density, clay, soil organic matter, sodium, chloride, sulfate, and AM Fungi microbial communities, which provide a benchmark for quantifying the magnitude and directional change of soils in cultivated systems with respect to their native counterparts. The findings revealed that long-term cultivation in the SLV has not degraded the soils according to the indices used. The parameters used this study improve the understanding of long-term irrigation impacts on agroecosystems in arid and semi-arid regions by linking the substrate properties with the soil-forming factors and irrigated water quality. This study provides the key information that can be used as a matrix by which to evaluate the impacts of climate change and a growing global population in other water-limited regions.
  • Thumbnail Image
    ItemOpen Access
    Weathering and soil properties on catenary sequences in forest and alpine ecosystems of the central Rocky Mountains
    (Colorado State University. Libraries, 2017) Bergstrom, Robert Mark, author; Kelly, Eugene F., advisor; Rhoades, Charles C., committee member; Borch, Thomas, committee member; Melzer, Suellen, committee member; Martin, Patrick H., committee member
    The evolution of soil landscapes can be evaluated by studying soil properties along catenary sequences—soil sequences that are hydrologically and topographically connected along hillslopes from higher elevation to lower elevation. Using the catena model, I investigated the manifestation of soil forming factors in conditioning weathering and soil development in the Mountain Ecosystems of the Fraser Experimental Forest (FEF), Colorado. The research outlined and presented in this dissertation is preceded by a short narrative on soil forming properties, hillslope models, and assessing weathering in soils. The work presented in this dissertation is a result of a multidisciplinary framework for pedological research, derived from the integration of and consideration of pedology, geomorphology, and hydrology. The future of pedological research will involve the assimilation of multidisciplinary approaches and thinking. This dissertation elucidates on (1) the distribution of soil properties along soil catenas and their implication for hydrologic and biogeochemical linkages across landscapes, (2) the evaluation of chemical alteration thru modeling soil strain along soil catenas, (3) the quantification and distribution of soil elemental fluxes along soil catenas, and (4) the determination of the contributions of weathering and atmospheric inputs to landscapes at FEF. My field sites were located in FEF, a model site of the alpine and forested environments of the central Rocky Mountains. The FEF is an ideal setting to study the interaction of soil forming factors in complex mountain terrain. A combination of traditional and more modern methods to explore the linkages between soil properties along mountain catenas were employed in order to gain insight into soil landscape evolution in complex mountain terrain. I established eight catenas along relatively steep mountain hillslopes while constraining the lithologic differences along the soil landscapes. Vegetative changes along these catenas could not be ignored; rather, the differences provided insight into the influence of vegetative cover on soil properties. Soils were sampled along the catenas, beginning in the mountaintop landscapes (crests or summit) and ending in the mountainbase landscapes, where wetlands along riparian corridors dominate. Soil morphology and soil chemistry along the catenas provided understanding into the evolution of soil landscapes at FEF and their connectedness to the hydrologic flowpaths along these hillslopes. Results suggested that these soil landscapes are in various states of evolution, marked by the relative development of illuvial and elluvial horizons, and that the landscapes are dominated by subsurface lateral flow. The data also suggested that atmospheric deposition may be an important contributor to pedogenesis in these landscapes and that there are expected hot-spots of nutrient accumulations in the mountainbase landscapes, where upland soils have transported and deposited dissolved ions and fine soil particles into wetland soils along riparian corridors. The next question became: does the distribution of elements along soil landscapes reflect what was expected from the aforementioned analyses and is the fate of elements controlled by the landscape positions? What is the balance between the atmospheric contributions to weathering and internal cycling of cations? Subsequently, the analysis for soils along the catenas was extended to model soil strain within the soil landscapes, quantify mass fluxes and distribution of elements within the soil landscapes, and quantify the atmospheric contributions to weathering in these systems. Results indicated that dilation in upper soil horizons reflect the textural patterns in the same horizons across all landscapes—supporting the notion that the soils along theses catenas have been strongly influenced by additions via atmospheric deposition, and this influence is detectable across entire hillslopes. Also, modeled soil strain indicated that great pedogenic additions have occurred in the mountainbase landscapes—supporting the notion that dissolved ions and fine soil material have been transported and deposited downslope via subsurface lateral flow. Calculated elemental flux values indicated that soil nutrients originating the upland landscape positions are transferred to lower landscapes through the mountainflanks, and are deposited in the mountainbase landscapes, where the soils were found to be enriched in the following major elements—Ca, Na, K, Al, Fe, and Mg. In turn, the impact of atmospheric contributions to soil landscapes along a catena was revealed. The data suggested that surface soil horizons are more strongly influenced by atmospheric contributions than subsurface horizons. Likewise, subsurface horizons are increasingly more influenced by the weathering of parent material moving from higher soil landscapes to lower soil landscapes. Lastly, results suggest that the isotopic signature within mountaintop soil landscapes is coupled to vegetative cover and snowfall and snowmelt hydrology dynamics. The soil catena model endures as a framework for providing insight into the relationships of soil forming factors across gradients of variation.