• Assessment And Prediction Of Potentially Mineralizable Organic Nitrogen For Subarctic Alaska Soils

      Zhao, Aiqin; Zhang, Mingchu (2011)
      The objective of this study was to identify a rapid laboratory technique to predict potentially mineralizable organic N for subarctic Alaska soils. Soil samples were taken from major agricultural area of subarctic Alaska. Laboratory incubation followed by kinetic model fit was first used to select a best model to estimate potential soil N mineralization. By correlating the model estimated organic N pool sizes and different chemical extracted organic N, I then found the best chemical method to estimate soil potentially mineralizable N. Spectroscopic properties of water extractable organic matter were also determined and correlated with model estimated organic N pool sizes in order to improve the estimation of soil mineralizable N pool. Finally, the best chemical method and spectroscopic property were used in the selected best kinetic model for the prediction of soil N mineralization in field incubation. Model comparisons showed that models with fixed rate constants were better than that the ones with rate constants estimated from simulation. Among models with fixed rate constants, fixed double exponential model was best. This model differentiated active mineralizable organic N pool with a fixed rate constant of 0.693 week-1 and slow mineralizable organic N pool with a fixed rate constant of 0.051 week-1. By correlating model estimated organic N pool size and chemical extracted organic N amount, I found that the potentially mineralizable organic N size was closely correlated with hot (80 �C) water extractable organic N or 1 M NaOH hydrolysable organic N. By correlating model estimated organic N size and spectroscopic characteristics of water extractable organic matter, I found that the active mineralizable organic N pool was correlated with humification index in cold (22 �C) water extraction (R 2=0.89, p<0.05), which indicates that characterizing extracted organic matter was a useful tool to improve the estimation of soil organic N pools. In summary, potential mineralizable organic N in soils from subarctic Alaska can be estimated by hot water extractable organic matter or 1 M NaOH hydrolysable organic N, which accounted for 70% and 63% of the variation in potentially mineralizable organic N, respectively. This approach will provide fundamental insight for farmers to manage N fertilizer application in agricultural land and also provide some basic information for ecologists on predicting N release from Alaska soil that can be used for assessing the N impact on ecosystem.
    • Effects of climatic variability on the active layer and permafrost

      Romanovsky, Vladimir Eugeni; Osterkamp, T. E.; Hopkins, D. M.; Weeks, W. F.; Wendler, G. D.; Zarling, J. P. (1996)
      This thesis represents a collection of papers on the response of the active layer and permafrost to climatic variations on different time scales. Quantitative estimates of the amplitudes of the Milankovich rhythms in several regions of the Russian permafrost zone were used in numerical simulations of permafiost dynamics. The results of modeling explained many aspects of the permafrost distribution and its vertical structure within Russia. Spatial and temporal variability of the air, ground surface and permafrost temperatures were also analyzed using daily temperature data (upper 0.9 m) from 1986-1993 and results of annual temperature measurements in boreholes (nominally 60 m) from 1983-1995 at three sites in the Prudhoe Bay region of Alaska. Three numerical models which are based on different numerical methods and are used for calculations of the ground thermal regime were compared with each other, with analytical solutions, and with temperature data. Several approximate analytical solutions for the temperature regime and thickness of the active layer were introduced. The calculations were used to estimate the interannual variability of the thermal properties of soils which appear to be a result of interannual variations of the average water content during the summer in the upper part of the active layer. Precise temperature data together with computer modeling provided essential new information on dynamics of unfrozen water content in the ground in natural undisturbed conditions during freezing and the subsequent cooling of the active layer. A layer with unusually large unfrozen water content was found to exist at the depth of freeze-up. The same set of data was used to reconstruct daily permafrost temperatures from 1986-1993 for all depths down to 55 m. Mean annual temperature profiles for each year of 1987-1992 show significant interannual variations within the upper 40 m in a good agreement with published data. A numerical model of the temperature field in permafrost near its southern limits was developed to study the influence of short-term climatic variations (with periods of 300 and 90 years) on permafrost dynamics.
    • Effects Of Migratory Geese On Nitrogen Availability And Primary Productivity In Subarctic Barley Fields

      Pugin, Jennifer Adrienne; Sparrow, Stephen (1996)
      Agricultural areas are important for migratory geese, providing easy access to high energy foods. Geese affect agricultural production by removing biomass and by depositing fecal nutrients. This study used $\sp{15}$N as a tracer to examine the quantitative effects of fecal nitrogen contributions on agricultural production.<p> During winter 1994-95, 12-week lab incubations were conducted to determine net nitrogen and carbon mineralization potentials in soils amended with barley straw, grain, and goose feces. The greatest rates of nitrogen mineralization occurred in the soil amended with goose feces. Carbon mineralization occurred at the greatest rate in the soil amended with grain.<p> In comparison to barley grain and straw, goose feces provided the greatest amount of available nitrogen to the soil and to subsequent crops, and consequently higher barley yields (59 and 62% increase, respectively). However, supplementary fertilizer is still necessary for farmers to obtain maximum barley yields. <p>
    • Hydrologic Controls On Carbon Cycling In Alaskan Coastal Temperate Rainforest Soils

      D'Amore, David V.; David, Valentine, (2011)
      The northern perhumid North American Pacific coastal temperate rainforest (NCTR) extends along the coastal margin of British Columbia and southeast Alaska and has some of the densest carbon stocks in the world. Northern temperate ecosystems such as the NCTR play an important role in the global balance of carbon flows between atmospheric and terrestrial pools. However, there is little information on key components of the forest carbon budget in this region. Specifically, the large pool of soluble carbon that is transferred from soils via streamwater as dissolved organic carbon (DOC) certainly plays a role in the total carbon balance in wet forests such as the NCTR. In order to address this information gap, I applied the concept of hydropedology to define functional landscape units based on soil type to quantify soil carbon fluxes and apply these estimates to a conceptual model for determining the carbon balance in three NCTR watersheds. The strong hydrologic gradient among ecosystems served as a template for constructing a conceptual design and approach for constraining carbon budget estimates in the watersheds. Replicated hydropedologic units were identified in three classes: sloping bogs, forested wetlands, and uplands. Estimates of annual soil respiration and DOC fluxes from the hydropedologic types were obtained through seasonal measurements combined with temperature-dependent models. Soil respiration fluxes varied significantly across the hydrologic gradient where soil respiration was 78, 178, and 235 g CO2 m -2 y-1 in sloping bogs, forested wetlands and uplands respectively. Average DOC flux was 7.7, 30.3, to 33.0 g C m-2 y-1 in sloping bog, forested wetland, and upland sites respectively. Estimates of carbon efflux from the terrestrial ecosystem was combined with values of net primary productivity from remote sensing to determine net ecosystem production (NEP). The average NEP estimated in three NCTR watersheds was 2.0 +/- 0.8 Mg C ha-1. Carbon loss as DOC was 10--30% of the total carbon flux from the watersheds confirming the importance of this vector of carbon loss in the NCTR. The watershed estimates indicate that forests of the NCTR serve as a carbon sinks consistent with the average worldwide rate of carbon sequestration in terrestrial ecosystems.
    • Mechanisms Of Soil Carbon Stabilization In Black Spruce Forests Of Interior Alaska: Soil Temperature, Soil Water, And Wildfire

      Kane, Evan S.; Valentine, David (2006)
      The likely direction of change in soil organic carbon (SOC) in the boreal forest biome, which harbors roughly 22% of the global soil carbon pool, is of marked concern because climate warming is projected to be greatest in high latitudes and temperature is the cardinal determinant of soil C mineralization. Moreover, the majority of boreal forest SOC is harbored in surficial organic horizons which are the most susceptible to consumption in wildfire. This research focuses on mechanisms of soil C accumulation in recently burned (2004) and unburned (~1850-1950) black spruce (Picea mariana [Mill.] BSP) forests along gradients in stand productivity and soil temperature. The primary research questions in these three chapters address: (1) how the interaction between stand production and temperature effect the stabilization of C throughout the soil profile, (2) the quantity and composition of water soluble organic carbon (WSOC) as it is leached from the soil across gradients in productivity and climate, and (3) physiographic controls on organic matter consumption in wildfire and the legacy of wildfire in stable C formation (pyrogenic C, or black carbon). Soil WSOC concentrations increased while SOC stocks decreased with increasing soil temperature and stand production along the gradients studied. Stocks of BC were minuscule in comparison to organic horizon SOC stocks, and therefore the C stabilizing effect of wildfire was small in comparison to SOC accumulation through arrested decomposition. We conclude that C stocks are likely to be more vulnerable to burning as soil C stocks decline relative to C sequestered in aboveground woody tissues in a warmer climate. These findings contribute to refining estimates of potential changes in boreal soil C stocks in the context of a changing climate.
    • Phenanthrene Adsorption And Desorption By Melanoidins And Marine Sediment Humic Acids

      Terschak, John Andrew; Henrichs, Susan M. (2002)
      Sediments are major reservoirs of persistent petroleum contamination in marine environments. Petroleum hydrocarbons associate with the sediment organic matter, of which humic acids are an important constituent. This study examined the role that humic acid and its structure plays in the kinetics and mechanisms of polycyclic aromatic hydrocarbon (PAH) interactions with sediments. Natural humic acids, with a wide range of properties, were isolated from Alaska coastal marine sediments. Melanoidins were synthesized and used as humic acid analogs. The humic acids were characterized by elemental and isotopic analyses, Fourier transform infrared spectroscopy, and cross-polarized magic angle spinning 13C nuclear magnetic resonance spectroscopy. The humic acids were coated onto a standard montmorillonite clay, and the adsorption and desorption of phenanthrene was measured using a radiotracer. Adsorption required about one week to reach steady state, indicative of slow diffusion of PAH within the humic acid. The composition of the humic acids had a greater effect on phenanthrene adsorption than their concentrations on the clay. Organic carbon normalized adsorption partition coefficients were closely correlated with the sum of amide and carboxylic carbons, a measure of the polarity of the humic acids, but were independent of initial phenanthrene concentration, indicating that the binding sites were unlimited and uniform in strength. This explains the fact that initial adsorbed concentration of phenanthrene had no effect on subsequent phenanthrene adsorption. Desorption of phenanthrene was not related to any of the humic acid structural characteristics measured. The initial desorption rate was linearly related to the initial adsorbed concentration, as expected for a diffusive process, and was negatively correlated with the carbon content of the humic acid coated clay. Under most conditions, desorption was complete after one to seven days; there was little evidence for irreversible adsorption. Because of the substantial variability of adsorption and desorption behavior with organic matter characteristics, interactions of aromatic hydrocarbons with marine sediments cannot be predicted based on total organic matter concentration alone. Information on aspects of organic matter composition is needed in order to make accurate predictions.
    • Phytoremediation strategies for recalcitrant chlorinated organics

      Schnabel, William Edwin; White, Daniel (2000)
      The purpose of the research was to investigate novel strategies for the phytoremediation of recalcitrant chlorinated organic soil contaminants. The recalcitrance of many chlorinated organics is related to chemical stability and bioavailability. Mycorrhizal fungi have the potential to enhance the degradation of such compounds through the action of lignolytic enzyme systems, and to increase the bioavailability of such compounds through increased root surface area and reach. Furthermore, the addition of surfactants has the potential to increase compound bioavailability via increased solubility. The organochlorine pesticide aldrin, and the polychlorinated biphenyl 3,3'4,4 '-tetrachlorobiphenyl (TCB) were chosen as representative recalcitrant contaminants. Feltleaf willow (Salix alaxensis) and balsain poplar (Populus balsamifera) were chosen as vegetative species likely to be useful for phytoremediation in sub-arctic ecosystems. Mixed-culture mycorrhizal fungi were first shown to be capable of taking up the hydrophobic contaminants in vitro. In the same experiments, surfactant addition increased the level of contaminant uptake. In subsequent vegetative uptake studies, mycorrhizal infection was highly correlated with the uptake of aldrin and TCB in the willow systems. In the poplar systems, this correlation was not as strong. Once taken up into the vegetative matrix of either species, most of the carbon originating from the chlorinated compounds existed as bound transformation products. Additionally, water-soluble transformation products of aldrin were formed in all of the soils tested, and such transformations were enhanced in the presence of vegetation. TCB transformation products were not detected in any of the soils tested. Surfactant addition did not impact the fate of either contaminant in the vegetative uptake studies. The surfactants, in the concentrations added, did not sufficiently solubilize the contaminants into the soil solution. The results of these studies indicated that the phytoremediation of recalcitrant chlorinated organics such as aldrin and TCB could be enhanced through the action of mycorrhizal fungi, and that surfactant addition has the potential to increase mycorrhizal uptake. Field studies were recommended, involving the use of specific degradative fungal species and effective surfactants.
    • Soil Fertility And Corn And Soybean Yield And Quality In A Six-Year Nitrogen And Phosphorus Fertilization Experiment

      Anthony, Peter M.; Sparrow, Stephen; Malzer, Gary; David, Valentine,; Zhang, Mingcho (2012)
      Optimum management of nitrogen (N) and phosphorus (P) fertilizers for corn [Zea mays L.] and soybean [Glycine max (L.) Merr.] production requires quantitative understanding of multiple soil processes and crop responses, including supply and immobilization of N and P by soil, the response of yield and quality to nutrient availability, and the relationships and interactions between N and P cycling, crop response, and other soil physical and chemical variables. We conducted a six-year experiment on two 16-ha fields on glacial-till soils in south-central Minnesota. In each year of a corn--soybean rotation, we measured soil physical and chemical parameters and grain yield and quality at a 0.014-ha resolution within each field. These observations coincided with placement of a randomized complete block, split plot design of N and P fertilizer treatments. Spatial patterns of mineralizable N were consistent over time. Mineralizable N was highly correlated to soil nitrate at a well-drained site, but not at a poorly-drained site. Increases in available soil P per kg of net P addition were significantly related to soil pH. Within fields, spatial patterns of soybean yields were highly correlated across years, and we observed consistent relationships between yield and soil variables. Overall, soybean yield related positively to soil P and Zn and negatively to pH at all site-years. Quadratic-plateau regression models of soybean yield in relation to soil P and Zn indicate that in high pH soils at these sites, yield is optimized when soil P and Zn levels are higher than current recommendations. Corn yields responded significantly to N rate and N rate by P rate interaction in all site-years. Whole-field economic optimum N rate differed significantly by site-year and by P treatment at some site-years. Site-specific P fertilization should account for spatial variation in soil P buffering capacity. Nitrogen mineralization and NxP nutrient interactions should be accounted for in agronomic management decisions for corn production. The consistent influence of soil pH on nutrient cycling and crop response indicates the potential benefit to amelioration of high pH in calcareous glacial-till soils. Results highlight the significance of spatial variability in nutrient cycling to crop management.
    • Soil Nitrogen Transformations And Retention During A Deciduous To Coniferous Successional Transition

      Brenner, Richard E.; Boone, Richard D. (2005)
      The mineralization, retention and movement of soil nitrogen (N) was investigated in forest types which encompass one of the most dramatic plant successional transitions in the boreal forest---the shift from deciduous, mid-succession, stands of balsam poplar (Poputus balsamifera) to coniferous, late-succession, stands of white spruce (Picea glauca). Nitrogen is an essential nutrient that often limits plant productivity in the boreal forest. Nitrogen uptake by plants is constrained by the activity of soil microbes and their associated exoenzymes which depolymerize (break down) organic molecules and release forms of N that are useable by plants (e.g., amino acids, ammonium and nitrate). The availability of labile carbon (C) is generally thought to limit soil microbes; however, it has been hypothesized that soil microbes in floodplain stands of balsam poplar are actually N limited. Balsam poplar trees also have large N requirements; thus, the overall demand for N is considerable in these stands and biological N retention should be high. In contrast, lower primary productivity and more recalcitrant soil organic matter in white spruce stands should result in comparatively less immobilization and less retention of N in this stand type. Experimental N additions resulted in the acceleration of net N mineralization and nitrate leaching in both stand types, probably because biological N demand was rapidly satiated. In balsam poplar soil, net nitrification was greatly stimulated by N additions; while in white spruce soil only net ammonification was stimulated; indicating that different mechanisms control ammonium oxidation or nitrate immobilization in these stands. Nitrogen additions did not affect soil microbial biomass in either stand. Results from a laboratory soil incubation study indicate that, compared to mid-succession soil, soil organic matter in late succession stands was more labile and the mineralization of C and N were significantly more temperature sensitive. Thus, climatic warming may result in the release of a larger proportion of soil C and N from late succession stands. A separate study examining soil solution N concentrations and movement showed that the Tanana River is a source of active layer nitrate during the growing season in both mid and late succession stands.
    • The Influence Of Soil Cryostructure On The Creep And Long Term Strength Properties Of Frozen Soils

      Bray, Matthew Thomas (2008)
      The time dependent mechanical properties of ice-rich frozen soils were studied in relation to their cryostructure. The CRREL permafrost tunnel was the primary source of the studied ice-rich soils. Mapping of the permafrost geology of the main adit of the CRREL permafrost tunnel was performed and reinterpreted in the context of a cryofacial approach. The cryofacial approach in based on the concept that cryostructure is dependent on how a soil was deposited and subsequently frozen. Three main soil cryostructures were determined to represent the main aspects of the permafrost geology. Soils with micro-lenticular cryostructure represent the original ice-rich syngenetic permafrost formed during the Pleistocene. Reworked sediment due to fluvial-thermal erosion resulted in soils with massive cryostructure and soils with reticulate-chaotic cryostructure. Ice bodies within the tunnel include syngenetic wedge ice and secondary thermokarst cave ice deposits. A testing program for determining the time dependent mechanical properties, including the creep and long term strength characteristics of permafrost in relation to soil cryostructure, was performed. Undisturbed frozen soils include silty soil containing micro-lenticular, reticulate-chaotic, and massive cryostructure. Remolded silt from the tunnel was used to create artificial samples with massive cryostructure for comparison to the undisturbed frozen soils. In addition to frozen silt, undisturbed ice facies were tested. These included syngenetic wedge ice, Matanuska basal glacial ice, and Matanuska glacial ice. Testing methods include uniaxial constant stress creep (CSC) tests and uniaxial relaxation tests. It was shown that soil cryostructure and ice facies influences the creep and long term strength properties of frozen soils. It was shown that remolded soils provide non-conservative creep and long term strength estimates when extrapolated to undisturbed frozen soils. Minimum strain rate flow laws show that at low stresses, undisturbed soils creep at a faster rate than remolded soils. At high stresses, frozen soils creep at a faster rate than ice. It was also shown that the unfrozen water content influences the mechanical properties of frozen soils and that the unfrozen water content is influenced by soil cryostructure. Through cryostructure, the permafrost geology is related to the time dependent mechanical properties of frozen soils.