<p> Nitric Oxide is an important molecule in human cells. It is responsible for multiple functions in various systems including the cardiovascular, immune, nervous, digestive, and reproductive systems. Nitric oxide is synthesized by the enzyme nitric oxide synthase, and its activity is controlled by the levels of asymmetric dimethyl arginine (ADMA) which in turn are controlled by Dimethylaminohydrolase (DDAH). DDAH is an important enzyme for study due to its ability to indirectly control nitric oxide synthase. 2-chloroacetimidine is an inhibitor of DDAH. Synthesizing molecules that contain a 2-chloroacetimidine moiety and a retrievable chemical tail could prove to be instrumental in further studying DDAH and other enzymes with similar reactivity in their active sites. </p>

<p> For over 3.5Ga microbial activities have profoundly altered planetary geochemistry. In particular, sulfur-cycling hydrothermal vent communities have been important players in shaping biogeochemistry and the habitability of Earth. However, the remote nature of deep-sea vents makes investigations challenging. Using the White Point (WP) shallow-sea hydrothermal vent field as a proxy, I employed molecular sequencing, fluorescent in situ hybridization (FISH) and ³⁵S-radiotracer assays to investigate the diversity and function of chemoautotrophic microbial mats. This study revealed a highly active and diverse sulfur-cycling microbial community. Potential epibiotic associations between sulfur-oxidizing (SOxB) and sulfate/sulfur-reducing bacteria (SRB) were identified using FISH. Comparative analyses of 16S rRNA sequences revealed the WP sulfur vent microbial mat community to be similar to deep-sea microbial communities from hydrothermal vents in a range of biotopes and lithologic settings and supported the relevancy of the WP hydrothermal sulfur-vent microbial mats as an excellent model for studying "thiobiotic" vent communities.</p>

<p>ABSTRACT Carbon isotope measurements (&#948;13C) across tree rings retain long-term annual and seasonal climate trends that can be used to extend historical records in regions where instrumental observations are limited or unavailable. The &#948;13C value measured from successive tree-rings reflects changes in stomatal conductance, which varies as a stress response to changes in environmental moisture. In relatively dry environments, a decrease in moisture leads to a reduction in stomatal conductance and causes an observable increase in the measured tree-ring &#948;13C composition. Thus, changes in fractionation can be an indicator of varying water-stress associated with changing temperatures. Here, I investigate the use of annually resolved &#948;13C data to identify twentieth century Arctic temperature trends. I present a new annually resolved &#948;13C dataset spanning 50 years (1912-1961) from three Larix cajanderi tree cores collected in far northeastern Siberia. The dataset yields a strong correlation (r = 0.55) with an increase in temperatures associated with the Early Twentieth Century Warming (ETCW) event (1925 to 1946). In order to investigate whether this Arctic-wide temperature anomaly can be identified from other Arctic tree-ring sites, I compiled &#948;13C data from thirteen previously published high-latitude (>62 &#730;N) tree-ring chronologies. The combined dataset, which spanned nearly the entire twentieth century (1900-1998), identified a strong negative relationship (r = -0.53, p < 0.01) between net carbon isotope fractionation and temperature. This Arctic-wide tree-ring dataset showed strong correlation across the ETCW in particular (r = -0.86), as well as across the interval of rapid late twentieth century anthropogenic warming (r = -0.50). Identification of both the natural ETCW and the current anthropogenic Late Twentieth Century Warming (LTCW) event (1966 to 1998) demonstrates the potential for tree-ring &#948;13C records to extend our knowledge of Arctic temperature change beyond the limited historical record.

<p> Belowground competition presents a threat to the production and sustainability of tree-grass ecosystems. Management scenarios designed to optimize the spatial and temporal distribution of soil resources will improve resource-use efficiency and promote greater co-production. We conducted three experiments to assess competition dynamics between loblolly pine and switchgrass. </p><p> In a three-year field trial, loblolly pine and switchgrass were intercropped across varying competitive intensities. Interspecific competition decreased loblolly pine annual growth; however, establishing vegetation exclusion zones surrounding pines largely mitigated these effects. Switchgrass yields were less affected by interspecific competition compared to pines and land equivalency ratios indicated that with proper management co-production yields may exceed those of switchgrass monoculture. Switchgrass was a constant and significant competitor across all years while loblolly pine resource use was minimal in year 1 but increased in subsequent years. </p><p> In a short-term greenhouse experiment, native soil was amended with biochar and inorganic N fertilizer and the effects of these amendments upon soil properties and switchgrass productivity were assessed. Biochar increased soil pH, total soil carbon, and soil moisture. However, N fertilization had negligible effects upon soil properties. Plant response to biochar was neutral to negative while N fertilization increased switchgrass foliar biomass but no interactive effects of the amendments were observed. Although the effects of biochar upon switchgrass production were trivial, its positive influence upon soil properties suggests a potential for mitigating competitive interactions. </p><p> Finally, a field-scale study examined co-production of loblolly pine and switchgrass over two years in response to competition control, biochar, and N fertilizer. As expected, interspecific competition reduced soil resources and decreased plant productivity. Biochar increased total soil C and soil moisture levels but had relatively minor impacts upon other aspects of soil fertility or plant production. Nitrogen fertilization acidified soil pH and decreased total soil C and N but positively affected loblolly pine foliar N concentrations and switchgrass yields. A positive association between soil inorganic N and switchgrass yield suggests the species competitive influence may be increased with greater N supply.</p>

Organisms that grow by skeletal accretion contain a geochemical record of environmental conditions--they are, in effect, biological chart recorders. Thus, shell-bearing organisms are an important source of data on modern and ancient environments. Geochemical analysis of shell material sampled along an ontogenetic profile can provide time-series of the environmental variation experienced when the organism was growing. However, variations in growth rates and complete cessations of growth can bias biogeochemical archives. Thus, careful calibration of environmental conditions with shell growth is critical if reliable records are desired. Here, I present several studies designed to understand the relationship between bivalve shell growth and environmental variation. This is accomplished through careful calibration of temperature, geochemical variability, and growth increment variation (sclerochronology). I then apply the findings of these calibration studies to address paleobiological and paleoclimatic questions. I conducted a cross-calibration study relating annual temperature variation with stable oxygen isotope (δ¹⁸O) variation. I used daily increments to assign dates to each δ¹⁸O sample. I then compared the geochemically based temperature estimates with the actual temperatures from the same dates. Results indicate that combined geochemical and sclerochronological analyses can provide reliable estimates of environmental variation, as well as shed light on aspects of the clam's biology, such as the rate and timing of shell growth. The results of this study were then incorporated into a more generalized investigation of the relationship between annual temperature variation and growth rate. This study indicates that the resolution and fidelity of geochemically based environmental reconstructions depends strongly on growth rate and duration. Together, the results of these studies were applied to address paleobiological and paleoclimatic issues. First, I used sclerochronologically calibrated annual isotope profiles to detect time-averaging and spatial mixing. This study indicates that short duration time-averaging (<50 years), previously undetectable using traditional dating techniques, can be identified using oxygen isotope variation. Results also suggest that within-habitat spatial mixing can be detected. Results of the calibration studies were also applied to paleoclimate questions. Seasonality is an important aspect of paleoclimate reconstruction and is often inferred from annual oxygen isotopic variation in fossil shells. However, because many organisms do not grow throughout the year, their shells do not record the full range of seasonal temperatures. This limitation can be overcome by using stable oxygen isotope variation from two species, each of which continues to grow while the other has shut down. The method was demonstrated using two common venerid bivalves from the eastern Pacific. The reconstructed estimate of seasonality matches published sea-surface temperature data from the same site. I also used differences in δ¹⁸O values and daily increment numbers from modern and Pleistocene (last interglacial, ∼125,000 ybp) bivalves to estimate temperature change in the shallow marine environment off the coast of southern California. Data indicate that temperatures were∼3°C cooler than present, however, more data are needed to confirm these initial results.

Organic matter amendments have long been known to improve native organic matter content, aggregation and structure of soils. In the laboratory, however, organic matter amendments to autoclaved soils have no such effect. This may explain the failure of many reclamation attempts on mine tailing wastes, which often proceed without regard for the microbiological processes necessary for soil formation and cycling of plant nutrients. In this study, incubation of tailing waste with soil microbes and a simple carbon source proved sufficient to increase the formation of water stable aggregates from tailing particles. Autoclaved control samples showed no change in aggregation. The incorporation of microbial cell mass into the mineral matrix of the tailing was observed using scanning electron microscopy. These results suggest that microbial activity is necessary in order to incorporate organic matter into the abiotic matrix of tailing, promoting aggregation and ultimately soil formation from this material.

The purpose of this study is to examine the effects of land use and hydrology on surface water quality in a semi-arid watershed. Six synoptic sampling events were performed along the upper San Pedro River, AZ, USA before, during, and after the 2002 monsoon season. Water samples were analyzed for conservative solutes, nutrients, and organic matter. During non-monsoon baseflow periods, conservative solutes indicated limited hydrologic connection between regions. Protected reaches had significantly higher DOC concentrations and agricultural reaches had significantly higher DON and NO₃-N levels. In contrast, solute concentrations during the monsoon season indicated all regions were hydrologically linked. DOM and NO₃-N concentrations increased as terrestrially derived solutes were flushed into the stream. Nutrient loads were variable suggesting that changes in nutrient concentrations were related to individual reaches. This research demonstrates that hydrologic flowpaths and land cover are important controls on surface water quality at the reach and river scales.

No description available.

<p> Hydrogen isotope ratios (&delta;D) in various types of leaf waxes, including n-alkanoic acids, extracted from lacustrine sediments are becoming increasingly popular for understanding past climate changes. Leaf-wax &delta;D values track precipitation &delta;D, and provided that controls on precipitation &delta;D are known, changes in leaf wax &delta;D can be used to reconstruct these changes in the past. Seventy-six sediment samples from Andrew Lake, Adak Island, Alaska, extending to 4800 years ago (4.8 ka) were analyzed for &delta;D of <i> n</i>-alkanoic acids. &delta;D values of isolated C₂₈ <i> n</i>-alkanoic acids show a strong inverse correlation with October-May storminess (days with >19 mm of precipitation) over the meteorological record (r² = 0.58, p &lt; 0.02), and a similarly strong correlation with total precipitation amount. This implies that isotopes in precipitation on Adak Island are strongly influenced by the amount effect. Shifts in precipitation amount and storminess are associated with shifts in the North Pacific hydroclimate, which is driven by the Aleutian Low during fall and winter. Low &delta;D values indicate high precipitation amount/storminess on Adak Island, which correlates well to a weak or westward Aleutian Low as inferred from other sites, while high &delta;D values indicate lower precipitation amount and generally correlate with a stronger or more eastward Aleutian Low. Results from Adak Island were combined with evidence from previously published paleoclimate studies from southern Alaska and the Yukon to reveal a more complete spatial picture of hydroclimatological changes for the last 5000 years. Variability in &delta;D since 3.5 ka is related to changes in North Pacific atmospheric circulation patterns including the Aleutian Low. High precipitation amount/storminess during the Medieval Climate Anomaly (&sim;850 to 1050 AD) on Adak Island is consistent with evidence from other studies that suggest a weakened Aleutian Low. Evidence of decrease precipitation during the early Little Ice Age (&sim;1200 to 1500 AD) gave way to wetter conditions during the latter half (&sim;1500 to 1900 AD). A wet late LIA is consistent with the results from coastal studies in southern Alaska, suggesting another period of a weakened Aleutian Low. This study is part of a multi-proxy investigation involving two lakes on Adak Island including analyses of pollen, biogenic silica, chironomids, isotopes in diatoms, and other proxies to help increase our knowledge about past hydroclimate in the North Pacific.</p>

The relative rates of calcite (CaCO3) precipitation and dissolution largely determine the preservation and subsequent accumulation of carbonate in the geologic record and are fundamental parameters for predicting the fate of fossil fuel carbon dioxide as well as the sequestration of several co-precipitated trace elements. Here we use the surface techniques, atomic force microscopy (AFM) and vertical scanning interferometry (VSI) to elucidate the nanoscale mechanisms of calcite growth and dissolution from nonstoichiometric and microbial solutions. Our results clearly demonstrate that the Ca 2+/CO32- ratio of carbonate solutions, at constant saturation, determines both the kinetics and anisotropy of step advancement. Anisotropic step velocities, in turn, alter step generation rates at screw dislocations, thereby significantly affecting the overall growth and dissolution rates of calcite surfaces. These results reflect different mechanistic roles for the cation and anion during both growth and dissolution and suggest limitations on the application of concentration-based rate laws in solutions of varying ionic ratios. Further, this study offers clear demonstration that the crystal surface exerts a primary control on growth and dissolution rates through step-specific and defect-directed interactions, producing differences in rate that could not be predicted from considerations of bulk chemistry alone. Further insight into calcite dissolution in natural systems was achieved by investigating the effect of Shewanella oneidensis MR-1 surface colonization on the dissolution rates of calcite (CaCO3) and dolomite (CaMg(CO 3)2). By quantifying and comparing the significant processes occurring at the microbe---mineral interface, a mechanistic understanding of the way in which microbes alter the dissolution rates of carbonate minerals was achieved. MR-1 attachment under aerobic conditions was found to influence carbonate dissolution through two distinct mechanistic pathways: (1) inhibition through interference with etch pit development and (2) catalytic removal of carbonate material at the cell---mineral interface during irreversible attachment to the mineral surface. The relative importance of these two competing effects was found to vary with the solubility of the carbonate mineral studied. This study demonstrates the dynamic and competitive relationship between microbial surface colonization and mineral dissolution that may be expected to occur in natural environments.