Browsing by Subject "Land and atmospheric science"
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Item Biophysical effects on U.S. soybean agroecosystems from increasing carbon dioxide concentration.(2011-01) Bryant, Jarod J.An increase in the atmospheric concentration of carbon dioxide ([CO2]) is having an impact on many different aspects of the climate system including the surface energy budget. Several years of climatic and biological data have been collected for soybean, at the Soybean Free Air Concentration Enrichment (SoyFACE) site in Champaign, Illinois. Using these data I calibrated the Agro-IBIS (Integrated Biosphere Simulator, agricultural version) model to simulate the crop response to a CO2 enriched environment of 550 ppm and the ambient concentration of 375 ppm. Previously the model over predicted the CO2 fertilization effect at 550 ppm by overestimating the leaf area index (LAI). Realistic simulated LAI values are necessary for accurate simulation of transpiration, one component of the latent heat flux. I found that improving the phenology routine and adjusting the specific leaf area parameter results in a simulated LAI value that compares with the observations within the enriched and ambient environments. I also decreased the canopy conductance an additional 30% to simulate realistic latent heat flux values at 550 ppm. After validation at the SoyFACE site, I ran Agro-IBIS over the U.S. east of the Rocky Mountains with current and elevated CO2 concentrations. Here I show the impact that the response of soybean to elevated CO2 is expected to have on the latent and sensible heat fluxes across this domain with some areas expected to see a significant change to both of these terms of 10 – 20%. These predicted changes to the energy budget are important and need to be considered in future projections of ecosystem response to climate change.Item Examining the drivers of current and future changes in Central U.S. warm-season rainfall(2014-09) Harding, Keith John IliffWarm-season precipitation in the Central U.S. is highly variable, as severe droughts and flooding often occur in consecutive years or simultaneously. Some of the most highly productive agricultural lands are present within the region despite susceptibility to warm-season rainfall extremes. Climate change is expected to increase precipitation extremes globally, but how warm-season Central U.S. precipitation will be affected is unclear. In this study, I examine the drivers of current and future warm-season precipitation in the region as well as how the basic characteristics of summer rainfall may be affected by climate change through the use of gridded observations, reanalysis datasets, and dynamical downscaling of global climate models (GCMs). It is demonstrated that the negative phase of the Pacific-North American (PNA) teleconnection pattern enhances heavy precipitation events over the Upper Midwest by modulating the strength of the Great Plains Low Level Jet (GPLLJ), possibly enabling greater medium range prediction of Midwest heavy rain events. Similarly, I aim to reduce uncertainty in long-term projections of how precipitation may be affected by climate change by examining shortfalls in GCM-simulated warm-season precipitation and demonstrating improvement with dynamical downscaling. Using the Weather Research and Forecasting (WRF) model, two GCMs are dynamically downscaled in one historical and three future timeslices with varying anthropogenic forcing. Future warm-season precipitation in these simulations is more intense, less frequent, and occurs with more days between rain events, similar to trends in observations that show large increases in extreme rainfall events and rainfall intensity. The intensification of extreme rainfall events in future simulations is the strongest during the April-July, associated with a strengthening of the GPLLJ during those months. Heavier rainfall rates during extreme precipitation events are related to a stronger cold pool and mesohigh, which force stronger moisture convergence above the cold pool in the presence of additional low-level moisture and a drier mid-troposphere. Overall, the identification of plausible physical mechanisms that might contribute to the enhancement of heavy rainfall events in the region enables greater confidence in future projections of extreme rainfall events.Item Impact of management practices on Minnesota's specialty crop production: from biochar to tillage practices(2014-09) Nooker, EricClimate fluctuations have always been a risk to our ability to provide adequate food for the increasing global population. To reduce crop production uncertainties in this variable climate, two management practices were examined: biochar application and conservation ridge tillage. Different biochars, application rates, and soil types were evaluated for their effect on seedling emergence and plant growth of specialty crops. Increases and decreases were observed in seed emergence and plant growth rates from biochar amended soil in a greenhouse study. A slow pyrolysis corn cob biochar (5% w/w) improved seed emergence performance the greatest across five specialty crops in the 4 soil types, with increases in emergence ranging from 2 to 67%. Biochar weathering from previous trials also influenced plant growth responses, and eliminated initial negative growth effects. Yield from field plot studies were not significantly different between biochar and control treatments. No universal relationship between biochar and its impact on specialty crop growth were observed across different soil types. However, there was good correlation between the suppression in plant growth with lower availability of nitrate and higher amounts of sorbed organic compounds on the biochar. Biochar additions had the greatest positive plant impacts on sandy textured soils with low initial soil fertility, which increased growth and soil moisture retention.Secondly, the impacts of ridge and conventional tillage on the yield and quality of three sweet corn varieties, Overland, Protégé, and Ambrosia were investigated. Protégé had greater marketable yields when grown under ridge tillage compared to conventional tillage. During 2012, there were no significant differences noted between ridge and conventional tillage treatments. However, in 2013, ridge till increased cut corn yield and ear marketability compared to the conventional tilled plots, suggesting additional benefits that were not adequately captured in this 2 year study. This study suggests that increasing the soil moisture holding capacity (with biochar or other amendments) as well as utilizing ridge tillage offers a potential tool for agricultural production to buffer future climate uncertainties.Item Modeling the phenological response to climate change and its impact on carbon cycle in Northeastern U.S. forests(2015-03) Xu, HongBy controlling the timing of leaf activities, vegetation phenology plays an important role in regulating photosynthesis and other ecosystem processes. As driven by environmental variables, vegetation phenology has been shifting in response to climate change. The shift in vegetation phenology, in turn, exerts various feedbacks to affect the climate system. The magnitude of phenological change and the feedbacks has yet been well understood. The goal of this dissertation is to use phenological model with remote sensing and climate data to quantify historical and future trends in leaf onset and offset in northeastern U.S. forests, and use a dynamic ecosystem model, Agro-IBIS, to quantify the impact of phenological change on terrestrial carbon balance. This dissertation has three major parts. First, six phenological metrics based on remotely sensed vegetation index were evaluated with ground phenological observation in Agro-IBIS. Second, a modified phenological metric was used to parameterize a set of phenological models at regional scale; one model for each of leaf onset and offset were selected to examine historical trends; Agro-IBIS simulations were run to quantify the impact of phenological trends on ecosystem productivities. Finally, downscaled climate projections from global climate models under two emission scenarios were used to drive phenological models to predict the trends in leaf onset and offset in the 21st century; and the impact of photoperiod on leaf onset were particularly examined. The results of this study suggest that remotely sensed phenological metrics can be used to improve phenological models with evaluation and adjustment; advancement of leaf onset and delay of leaf offset in the past have increased productivities and could potentially mitigate the warming temperature in the future; lack of physiological understanding of the driving factors of phenology such as photoperiod could result in large uncertainties in phenological projections.Item A multi-city analysis of the natural and human drivers of the urban heat island(2014-08) Hertel, William FrederickThe world's population is increasingly moving to cities, with a present day urban population of over 3.6 billion that is expected to nearly double by 2050. One of the key features of the urban environment is an increase in temperature relative to the surrounding rural areas, called the urban heat island, which can have negative impacts on the health and wellbeing of urban dwellers. This study uses a novel approach of analyzing a large number of cities from around the world to investigate the similarities and differences in urban environments among cities to explore the behavior and drivers of the urban heat island. This methodology reveals two new conditions that increase the magnitude of the heat island - low dewpoint temperature and high air temperature. Many of the cities show increases in the magnitude of the heat island during hot or dry periods of 1.0 °C or more during the daytime and 2.0 °C at night relative to cool or humid periods. The heat wave results are of particular note due to the added stress on urban residents during periods when the population is already at risk. For cities in temperate climate regimes, differences among cities in vegetative cover or impervious surface area leads to increases in urban temperatures of up to 1.0 °C during the summer, while cities with high pollution can see reductions in the heat island by 1.5 °C. Cities in tropical or Mediterranean climates have the strongest heat islands during the dry season indicating that urban infrastructure is the key driver in these cities. These results indicate that mitigation of the urban heat island is possible by altering the urban landscape through changes in the urban vegetation and the structure of the built environment.Item Problems of physical movement in soil genesis: application of meteoric Beryllium-10 as a component of multi-tracer analysis(2014-12) Jelinski, Nicolas AdamThe physical movement of soil materials plays a globally important role in soil genesis, but knowledge of the rates and patterns of these processes and their relationship to soil morphology has lagged behind an understanding of soil chemical processes. In this study, I analyze two separate problems related to physical movement in soil genesis - that of eroded phase soils and cryoturbated soils. In each of these cases, I circumscribe these genetic problems and subsequently apply meteoric Beryllium-10 (10Be) as a critical component of multi-tracer suites at specific study sites. Eroded phase soils: I first re-evaluate the general conceptual framework of soil production and connect it to problems of eroded soil genesis in agricultural landscapes underlain by unconsolidated parent materials (Chapter 1). Then, I explore factors related to the identification and description of eroded phase soils by analyzing the distribution of eroded phase soils in the SSURGO database for the Conterminous U.S (Chapter 2). Lastly, at a field site near the town of Cyrus in west-central Minnesota, I utilize meteoric 10Be to derive rates and depths of total post-settlement erosion by developing numerical conversion models (Chapter 3). Cryoturbated soils: I describe the distribution of cryoturbated soils and gelic materials across a landscape in the central Brooks Range Alaska, a study that prompted the application of 10Be in a multi-tracer suite to understand physical movement processes in Arctic patterened ground (Chapter 4). Through the application of this tracer suite, I constrain rates of material movement in a non-sorted circle (NSC) near Abisko, Sweden. In addition to estimating movement rates throughout the NSC with other tracers, meteoric 10Be allows - for the first time - an estimate of the surficial residence time of cryoturbated parcels now in the subsurface (Chapter 5). The results of this work show that the application of meteoric 10Be and other isotopic, elemental and morphological tracers in studies of soil genesis holds significant promise for elucidating long-standing problems related to the physical movement of soil materials.Item Tracing the source and transport of atmospheric water vapor using stable isotope techniques.(2011-12) Schultz, Natalie M.The stable isotopes of hydrogen and oxygen in water can be used as environmental tracers of the hydrological and climate systems. The isotope ratios (18O/16O, 2H/1H) of water are uniquely altered by biological and physical environmental processes, making them useful tracers of the origin and transport of water throughout the atmosphere and biosphere. Technological advancements have been made that allow continuous measurements of δ18O and δ2H in the vapor phase, and have simplified the isotope analysis of liquid water. The objectives of this thesis were two-fold: (1) to address a methodological problem that has prevented the use of isotope ratio infrared spectroscopy (IRIS) analyzers in the isotope analysis of water extracted from plant and soil samples, and (2) utilize tall tower measurements of δ18O and δ2H to develop a landscape-scale understanding of the mechanisms that control isotope variations in water vapor over a range of temporal scales. The correction procedure developed for the isotope analysis of plant and soil waters using an IRIS analyzer was found to greatly reduce the erroneous isotope values, resulting in a viable alternative to the traditional method of isotope ratio mass spectrometry (IRMS) for the isotope analysis of plant and soil waters. The observed temporal variations in δ18O, δ2H, and d in water vapor resulted from a combination of local and distant biophysical processes, including boundary layer dynamics, seasonal changes in evapotranspiration (ET), and Rayleigh rainout processes. The use of these new measurements of δ18O and δ2H in the vapor phase, along with models and satellite observations will provide new information on the transport and recycling of water vapor in the atmosphere, and ultimately help diagnose changes in the atmospheric water cycle in response to climate change and land use change.