<p>Land use histories affect the rate and pattern of soil nutrients at regional and global scale. However, former studies have rarely focused on soil trace elements (B, Mn, Zn, Cu and Fe). In this study, we aimed at the long-term biogeochemical cycling pattern and spatial heterogeneity of soil trace elements in response to land use changes. We conducted experiment at Calhoun experiment forest in SC and surrounded relic hardwood forest, cultivated land and secondary pine forests with contrasting land use histories in a statistically rigorous and spatially explicit design. Our first study indicated that spatial heterogeneity is greatly reduced in many soil properties by agricultural practices, but that successional forest growth on previously cultivated soils re-structures heterogeneity of soil properties within a few decades. We document cases in which land use alters both the soil property's central tendencies and their heterogeneity (C, N, CN, Ca, K), and cases in which changes are apparent in central tendency but much less so in their heterogeneity (Db). In our second study, samples of the upper 0.6-m mineral soil archived in 1962 and 1997 revealed three cycling patterns: 1) Extractable B and Mn were significantly depleted because tree uptake of B and Mn from mineral-soil greatly outpaced resupplies from atmospheric deposition, mineral weathering, and deep-root uptake. 2) Extractable Zn and Cu changed little during forest growth, indicating that nutrient resupplies kept pace with accumulations by the aggrading forest. 3) Oxalate-extractable Fe increased substantially during forest growth, by about 10-fold more than accumulations in tree biomass. This study indicated that forest Fe cycling is qualitatively different from that of other macro- and micro-nutrients. Thirdly, our results revealed that long-term cultivation substantially diminished the activity of soil iron oxides relative to forest growth. Forest Fe cycling is derived from mineral soil weathering, which suggests a need to explore the underlying mechanisms by which bioturbation (e.g.earthworms) mediates transformations of iron bioavailability and oxidation of organic matter in soils. Overall, the wide range of responses to land use changes among the ecosystem's trace elements and other biogeochemical features illustrates the great dynamics of the soil system over time scales of decades to centuries.</p> / Dissertation

<p>The Piedmont region of the southeastern United States has undergone considerable land-use change since settlement by Europeans and Africans. Forests were cleared for agriculture, followed centuries later by land abandonment. Following abandonment, natural recruitment, plantings for erosion control, and plantation forestry have resulted in a large area of the region covered by loblolly pine, Pinus taeda. Today, the Piedmont is a mosaic of farm fields, pastures, pine forests, and relic woodlots. The Calhoun Experimental Forest, located in Union County, SC, has provided a unique history of land use change's alteration of soil properties and processes, the ability of reforestation to restore or deplete soil fertility, and provided insights into the effects this change has on biological diversity.</p><p>In this work, the diversity of fungi living in soil is examined in the context of land-use change and soil biogeochemical change in and around the Calhoun Forest. This study uses molecular tools to identify fungal species from soil and to identify mycorrhizal associates of loblolly pine in a bioassay of propagule diversity, and proposes a novel use of quantitative PCR to quantify the relative abundance of major fungal families affected by land-use change.</p><p>Fungal diversity in soils is high in all land uses, but fungal communities shift from agricultural field communities largely comprised of unicellular ascomycetes and basal lineages to forest communities dominated by saprophytic and symbiotic basidiomycetes. In addition to this shift across a land use gradient, fungal communities are also responding to changes in carbon quantity and quality, biologically available nitrogen and phosphorus, pH, acidity and texture.</p><p>ECM propagule communities also differ across a land use gradient of cultivated fields, grasslands, pine forests, and mixed hardwood stands. There are few ECM propagules able to associate with loblolly pine in cultivated and grassland soils. There is a trend towards higher ECM diversity in the hardwood and pine soils, and both of those soil communities are distinct from each other as well as from soils from field treatments.</p><p>Quantitative PCR, coupled with a nested set of taxon-specific, fungal primers, is a potential way to estimate the abundance of the given taxon relative to all fungi in an environmental DNA. Primers specific to several taxonomic level of fungi were tested to confirm amplification in PCR, then were tested for taxonomic specificity by generating clone libraries with environmental DNA. Several of the successful primers were tested with soil DNA extracts in QPCR and the calculated ratios of fungal abundance varied widely by method of analysis. The results suggest that many repeated measurements and many replicates are required for a robust estimate of the relative abundance of a specific taxon.</p> / Dissertation

This study is aimed at understanding the physical and chemical effects that changes in water content have on uranium leaching in sediment containing gravel. It was hypothesized that leaching will be more efficient under unsaturated conditions because flow will be restricted to the smallest pores and will have the most contact with the uranium contaminated sediment. Under saturated conditions, a large portion of the flow will bypass the < 2 mm material, and in turn not come into contact with uranium contaminated material. Batch adsorption and desorption experiments were performed on < 2 mm ERDF sediment to determine the linearity and reversibility of sorption processes and to aid in the interpretation of the leaching experiments. Results of the desorption experiments on aged, contaminated sediments show that the mass percent of sorbed U(VI) released to solution decreased as the sorbed concentration of U(VI) decreased. The opposite trend was observed on freshly contaminated sediments. This indicated that aging increased U(VI) affinity for the solid phase and was attributed to either the crystallization of calcite, which incorporated a portion of the sorbed U(VI) as it crystallized, or the presence of voids in basaltic lithic fragments accessed by diffusion. Column leaching experiments were performed at two water contents on artificially contaminated sediment collected from the Department of Energy’s (DOE) Hanford Site, Washington state. The sediment contained 81.3% gravel (> 2 mm) by mass. Non-reactive tracers were well fit with the convection-dispersion equation (CDE) at both high and low water contents indicating physical equilibrium. The column experimental data were fitted to an analytical solution to the CDE; the results of the modeling show an increase in the distribution coefficient (Kdeffective) with decreasing water content. Several potential explanations for this trend were proposed; one is based on a physical effect in which solute exposure to reactive surfaces changes as a function of water content and the others are based on results of the batch desorption experiments. This work has important implications for the Hanford Site where there is ongoing research regarding the persistence of U(VI) in the vadose zone and underlying aquifer.

The objective of this study was to investigate the need for domestic wastewater to receive secondary treatment when being applied to the soil by subsurface drip irrigation (SDI). SDI uniformly distributes wastewater into the soil, which optimizes the soil’s chemical, physical, and biological capacity to remove waste constituents. Because of these advantages, many regulatory jurisdictions are allowing SDI at sites that previously were prohibited from using conventional trench-based soil application systems because of shallow soil restrictions. However, most of these regulatory agencies also require that the wastewater receives secondary treatment (dissolved organic carbon reduction) before the SDI system. At issue is whether the enhanced soil-based renovation provided by SDI should eliminate the necessity for secondary treatment before SDI.Two SDI systems were installed and monitored at two sites in Tennessee. These locations were residential developments served by a septic tank effluent pump (STEP) collection system, a recirculating media filter (fine gravel media), and SDI dispersal. At both locations, SDI plots were established to receive primary treated (septic tank effluent) and secondary treated (recirculating media filter effluent) wastewater. In close proximity to randomly selected SDI emitters, soil samples were extracted. Soil cores were analyzed to determine saturated hydraulic conductivity (Ksat), and pore water samples were analyzed for nitrate, total nitrogen, total carbon, and total phosphorus. Results indicate that the primary-treated sites had lower Ksat values, higher nitrate and higher total nitrogen levels than the secondary-treated side and the background soil. Interestingly, the primary treated side had less total carbon and the background phosphorus concentration was twice that of the primary and secondary treated sides. Primary effluent showed a decrease in concentration for all constituents with increased depth. Secondary treatment does result in a higher quality effluent but is not needed when applying effluent with a SDIS.

Soil organic matter (SOM) provides many ecosystem services that are necessary for continued ecosystem function. The accumulation of SOM in an ecosystem is a function of its persistence time which can range from days to thousands of years. Ecosystem properties including dominant vegetation type, soil texture, and soil moisture in various habitats can regulate the persistence time of SOM. Wetlands, because of their associated ecosystem properties, promote SOM accumulation, but little has been done to determine the ecosystem properties that regulate its persistence over time. In west-central Florida, urbanization and increased water demands have suppressed water tables in isolated wetland ecosystems via hydrological connectivity between ground and surficial waters. In this study, variability in wetland ecosystem properties, in particular dominant vegetation type and hydrological parameters, were tested as mechanisms driving SOM accumulation and stability. Cypress wetlands had significantly more organic matter, carbon (C), and nitrogen (N) than herbaceous marshes. In addition, increased wetland inundation promoted stable SOM accumulation in forested wetlands. By increasing the percent time a forested wetland spent aerobic, decreases occurred in both labile and stable C and N pools. As large storage units of SOM, the decreases in both labile and stable C and N pools in wetland soils have large implications for global C and N cycling. Increased manipulation of wetland water levels, especially in short time scales, can mineralize both short-term and long-term storage units of C and N. Globally, the increase mineralization of large SOC and SON stocks would exacerbate the release of air and water quality pollutants. The sensitivity of both labile and stable SOM pools draws concern when anticipating continued water demands and land use changes of the Tampa Bay region.

The extent of revegetation in the Colorado River delta in Mexico is described, with emphasis on the return of native cottonwood (Populus fremontii ) and willow (Salix gooddingii) trees. Low-level aerial and satellite remote sensing methods were combined with ground surveys to census the vegetation in a 100 km reach of riparian corridor in Mexico. Although the invasive plant, saltcedar (Tamarix ramosissima), still dominates the riparian zone, native trees now account for 23% of the vegetation in the delta. Multi-band digital camera images obtained by aircraft were used to calculate the Normalized Difference Vegetation Index (NDVI) and scored for percent vegetation cover (NDVI:%C has r = 0.91***). A Thematic Mapper (TM) image taken concurrently with the aerial survey was similarly classified, and by comparing scenes on the TM and aerials, it was possible to calibrate NDVI with percent vegetation on the TM image. This information was used to conduct a change analysis relating flows in the Colorado River with summer vegetation patterns on TM images for the years 1992-1999. The results support the importance of pulse floods in restoring the ecological integrity of arid-zone rivers. This dissertation also compared transpiration rates of three Sonoran Desert riparian trees using sap flow and leaf temperature methods using constructed canopies (two of each species: Populus fremontii (cottonwood), Salix gooddingii (willow) and Tamarix ramosissima (saltcedar)) in an outdoor experiment in Tucson, Arizona. Canopies were measured over 11 days for both sap flow and canopy and air temperature differential (Tc-Ta) under non stressed and stressed conditions. Objective 1: to determine the strength of the relationship between transpiration (Et) and Tc-Ta to determine if Tc-Ta can be a useful remote sensing method to measure Et for these species. Objective 2: to compare Et rates among species, to determine if the invasive species, saltcedar, has higher Et rates or ecophysiological advantages over the native trees species. We conclude that the Tc-Ta method could be useful in estimating Et by remote sensing over riparian corridors, and that native trees are not at an ecophysiological disadvantage to saltcedar so long as sufficient non-saline soil moisture is available to support Et.

In desert grasslands of the southwestern United States, Prosopis velutina (mesquite), an N-fixing legume, has proliferated from historic drainage locations into more xeric grassland plains. This expansion is forming a more heterogenous soil nutrient topography in grasslands, N-pools are becoming localized under mesquite canopies, yet the rate and extent of this sequestration remains relatively unknown. Repeated prescribed burning has been used to control Prosopis distribution, but effects of fires on grassland soil nutrient distribution and aboveground plant biomass are also largely unknown. I examined recent research concerning P. velutina natural history, emphasizing characteristics that contribute to range expansion. I also evaluated Prosopis management practices---which include herbicide treatment, prescribed burning, grazing reduction, and mechanical removal---and management goals---which involve complete removal, no removal, and limited removal. Of these, limited removal is the most beneficial, using an herbicide application followed by periodic prescribed burning. In 1997 I established a study area at Fort Huachuca Military Reservation in southeastern Arizona, selecting two adjacent sites with similar soil composition and topography but different fire histories. I examined spatial and seasonal changes in composition and distribution of available soil N and litterfall. My results indicated these were more spatially and temporally heterogenous on sites with low fire frequency and high P. velutina stand development. In 1998 I selected nine sites at Fort Huachuca on two upland surfaces located < 1 km apart, with similar soil physical characteristics and fire frequencies ranging from 0 to 5 fires/decade. I evaluated relationships between fire frequency, soil nutrient status (pH, available P, organic C, total N, and available N), and aboveground plant biomass, including that of the non-native Eragrostis lehmanniana (Lehmann lovegrass). Soil pH and ammonium significantly decreased with increased fire frequency on one surface, and available P significantly decreased with increased fire frequency on the other surface. Available P and pH were significantly different between the 2 surfaces, but aboveground biomass was similar. Soil nutrient status and biomass were not related, suggesting plant-available soil nutrients may not control plant distribution or recovery following fire. E. lehmanniana biomass was negatively correlated with native grass and forb biomass, and tended to increase with increasing fire frequency. Surface litter and E. lehmanniana biomass were correlated, and may increase fire frequency, an important consideration when implementing grassland fire management practices.

The effects of land-use history in the Animas Mountains, New Mexico (AM) and the Sierra los Ajos, Sonora (SLA) were studied in relation to morphological and soil chemical characteristics, radial and basal area growth, and forest structure. Litter depth, organic matter, total nitrogen, CEC, and exchangeable cations were greater in the AM than in the SLA, apparently as a result of differences in fire frequency and other land uses. Seasonal precipitation (October-January) was reconstructed for the AM. Annual precipitation (July-July) was reconstructed for the SLA. July PDSI was reconstructed for both mountain ranges. Fires in the AM were preceded by relatively wet conditions two years before the fire year. No significant climate-fire relationship was found in the SLA. Tree radial and basal area increase differed between mountain ranges, suggesting that annual growth was influenced by differences in land-use history. Fire suppression activities and other land uses in the AM apparently have produced an increase in tree density and dominance of shade-tolerant but less-fire resistant species (i.e. Douglas-fir, southwestern white pine, pinyon pine). More frequent fires and logging activities in the SLA apparently have produced lower tree densities and dominance by shade-intolerant ponderosa pine.

The critical zone is the interface between abiotic and biotic constituents that spans from the vegetation canopy through the groundwater and represents an open system shaped by the climate, topography, and vegetation communities of a given environment. Four studies were completed to examine soil development, specifically mineral weathering and soil carbon storage, across semiarid sites spanning the Santa Catalina Mountain Critical Zone Observatory (SCM-CZO). The Santa Catalina Mountain Critical Zone Observatory is located along an environmental gradient in southern Arizona where co-varying climate and vegetation community properties have generated distinct changes in soil development across a relatively short distance (<20 miles). Soil, saprock, and parent rock were sampled on north-facing slopes from five climate-vegetation zones spanning desert scrub to mixed conifer forest. Within each climate-vegetation zone, samples were collected from two divergent summit and two convergent footslope landscape positions to account for topographic controls on mineral transformation. In the first study, the soil morphologic, physical, and chemical properties collected for all samples were combined with profile development indices to quantify soil variation with landscape position across the SCM-CZO. The results of this research demonstrated that climate and landscape position exert significant control on soil development in semiarid ecosystems, and that the profile development index is an effective tool for detecting these regional to hillslope scale variations in soil properties. The second study consisted of a cross-scale analysis of feldspar mineral transformation across the selected research sites to connect measures of pedon-scale soil development, depletions of feldspar and sodium in bulk soil, and elemental losses across feldspar grains at the microscale. Results indicated that greater soil development in the mixed conifer pedons corresponded to increased total feldspar and sodium losses. Desert scrub soils presented less evidence for feldspar transformation including lower profile development indices, gains in total feldspar percentages attributed to dust deposition, and less Na chemical depletion at the microscale. Greater soil development in convergent positions relative to adjacent divergent sites was consistent across all sites, with the highest degree of total feldspar depletion occurring in the conifer convergent locations. The third study focused on the physical distribution and mean residence time of soil organic carbon (SOC) in the SCM-CZO soils described for the first two studies. Surface (0-10 cm) and subsurface (30-40 cm) samples were collected from the aforementioned granitic regolith profiles. The soils were characterized using total C and N, δ¹³C, Δ¹⁴C, and radiocarbon derived mean residence time (MRT) estimates of bulk soil and physically separated C fractions to quantify SOC change with climate, vegetation, and landscape position. The results document a shift in SOC stabilization mechanisms across bioclimatically distinct ecosystems from mineral-associated SOC in the desert scrub soils to a mixture of mineral and occluded SOC in the conifer soils. Soils in the convergent landscapes concentrated the most SOC and typically exhibited the longest residence times across all locations. The fourth study examined the geochemical and mineralogical properties of the SCM-CZO soils across regional and hillslope scales of study to quantify soil development in semiarid environments. X-ray fluorescence and x-ray diffraction were used to characterize the elemental and mineralogical properties of the soils and parent material. Desert scrub dust samples were analyzed using x-ray fluorescence. The results indicate that mineral and base cation depletion were greatest in the convergent landscape positions at both sites and increased from the hot, moisture-limited desert scrub sites to the wetter, more productive conifer ecosystems. Enrichments in mica and select elements (i.e., Fe, Mg) suggested that dust deposition was a significant contributor to soil development across all sites. Geochemical estimates of dust fraction inputs confirmed this finding with dust composing up to 35% of the regolith material in the mixed conifer convergent soils. Clay mineral assemblage was dominated by halloysite and smectite minerals in the desert scrub site, reflecting complex climatic and mineral microtextural interactions in the dry, silica-rich desert environment. Clay minerals at the mixed conifer site exhibited the greatest degree of mineral transformation in the SCM, consisting of vermiculite, illite, kaolinite, and minor amounts of smectite and gibbsite. These findings confirm the interactive role of climate, vegetation, and landscape position in shaping the critical zone, where greater moisture availability and biological production are likely driving increased soil organic carbon storage and mineral weathering across various scales of study.

After emergencies involving chemical spills it is of great importance that correct measures are taken with short notice, both for the security of people and in order to minimize future environmental consequences. The RIB-unit at the Swedish Rescue Services Agency initiated this study, the aim of which is to propose changes to the existing chemical transport calculation tool: Chemical Spill 3.4, included in RIB - Integrated Decision Support for Civil Protection, so that it can be used for decision support as well as in preventive work. A rough estimation of chemical transport in the subsurface is considered being of great importance when making decisions during emergency response operations. The proposition presented in this report is a non site specific chemical transport model which is designed to give a rough estimation of NAPL flow in homogenous isotropic soil shortly after an instantaneous release. The model can be used at two levels; both in situations without access to information on subsurface properties, and with more accuracy in situations with knowledge of the included parameters. For that reason the user can choose among predefined alternatives or assign the parameters a numeric value to increase the quality of the model output. The predefined alternatives are represented by default values for different parameters in the model. Suggested model output are vertical and horizontal transport of NAPL phase, horizontal transport of dissolved chemical in the aqueous phase, as well as the amounts of spill that are evaporated and entrapped in the soil, all at the time specified by the user. Moreover the maximum transport of the chemical phase and time to groundwater pollution are given. To make the uncertainty of the model clear for the user the results are given as the most likely value together with the smallest and largest values that can be expected. Equations presented in this report describe a selection of subsurface processes which occur after a release of chemicals. The selection is made with the aim to reach satisfying result when the model is used within its domain without making the model complicated for the user. Therefore simplifying assumptions have been made in the descriptions of some processes while some other processes are neglected. Simplifications have been based on recognized references or on theoretical arguments, but the overall performance of the model as well as some of the default input parameters need to be further tested and validated before the new version of the model can be included in RIB. However, compared with the existing version Chemical Spill 3.4 several changes have been suggested; including additional processes, development of default values and making model uncertainty clear to the user. These changes are thought to significantly improve the existing model. / Vid olyckor med kemikalieutsläpp är det av stor vikt att rätt åtgärder snabbt vidtas, både för människors säkerhet och för att minimera framtida miljökonsekvenser. Räddningsverkets RIB-enhet initierade den här studien vars mål är att ge förslag på modellteknisk förbättring av det befintliga beräkningsprogrammet Kemspill Mark 3.4, som ingår i programpaketet RIB - Integrerat beslutsstöd för skydd mot olyckor, så att det i framtiden kan användas som beslutsstöd vid räddningsinsats efter kemikalieutsläpp samt vid förebyggande planeringsarbete. En grov vägledning om kemikaliens spridning anses vara av stor betydelse för att räddningstjänsten ska kunna fatta rätt beslut vid en insats. Förslaget som presenteras i denna rapport är en icke platsspecifik spridningsmodell anpassad för vätskor med begränsad löslighet i vatten och ger en grov uppskattning av spridning i homogen och isotrop mark inom några timmar efter ett momentant utsläpp. Modellen ska kunna användas på två nivåer; för att ge en mycket grov uppskattning av spridningen även utan tillgång på uppgifter om markegenskaper, samt med större noggrannhet då informationen finns. Med anledning av detta kommer användaren ges möjlighet att välja bland fördefinierade alternativ eller att ange indata numeriskt för att öka noggrannheten. De fördefinierade valen representeras av typvärden för olika parametrar i modellen. Den nya modellen i förslaget ger vid angiven tid vertikal och horisontell spridning av fri kemikaliefas, horisontell spridning av löst förorening i vattenfas samt hur stor andel av utsläppet som hålls kvar i marken respektive har avdunstat från spillytan. Dessutom anges kemikaliefasens maximala spridning och hur lång tid det tar för utsläppet att nå grundvattnet. För att tydliggöra modellens osäkerhet för användaren ges utdata som det mest sannolika värdet tillsammans med det största och minsta värdet som är sannolikt. Ekvationerna som presenteras i rapporten beskriver ett urval av de processer som sker i marken vid ett kemikalieutsläpp. Urvalet har gjorts med utgångspunkt att uppnå tillfredställande resultat inom modellens domän utan att komplicera för användaren och därmed har förenklande antaganden gjorts för att beskriva vissa förlopp medan andra försummats helt. Förenklingarna har grundats på vedertagna referenser eller på teoretiskt resonemang. Validering av modellresultat samt vissa typvärdens intervall krävs före inkludering i RIB. Jämfört med det befintliga Kemspill Mark 3.4 har dock stora förändringar föreslagits; fler processer inkluderas, typvärden utvecklas och modellens osäkerhet görs tydlig för användaren. Förändringar tros medföra en signifikant förbättring av modellen.