Now showing items 1-20 of 22

• #### A Multiple Stable Isotope Study Of Steller Sea Lions And Bowhead Whales: Signals Of A Changing Northern Environment

The North Pacific and Arctic marine realm is currently experiencing dramatic environmental changes as a result of global climate change. Stable isotope analysis of western arctic bowhead whales (WABW, Balaena mysticetus ) and Steller sea lions (SSL, Eumetopias jubatus) were conducted to examine the influence of these changes on life history characteristics (migration and foraging) of these marine mammals. WABW baleen plates were analyzed for their stable oxygen and hydrogen isotope composition (delta 18O and deltaD) and were compared to the delta18O and deltaD in water and zooplankton prey along their seasonal migratory route. The delta18O and deltaD varied along the baleen (8 to 18�; -180 to -80�, respectively) and corresponded to stable isotopic differences in zooplankton from the winter (Bering Sea) and summer (eastern Beaufort Sea) habitats of WABW. Baleen delta18O and deltaD confirmed the seasonal annual migration of WABW and were subsequently compared to historical sea ice concentrations (SIC). This illustrated that WABW migration patterns appeared to have altered concomitant with changes in SIC. Years with a higher SIC (colder climate regimes) correlated with the largest difference in deltaD between winter and summer in WABW baleen during the period from 1972 to 1988. For a similar time period (1955 to 2000), the feeding ecology of SSL was also examined by analyzing the stable carbon and nitrogen isotope compositions (delta13C and delta 15N, respectively) of archived SSL bone and tooth collagen. Both delta 15N and delta13C varied greatly with location and sample year (14.6 to 20.5�; - 16.7 to -11.8�, respectively), with a significant change in delta13C observed around the 1976 regime shift. Bottom-up processes may have limited growth of SSL populations throughout this region over time, with animals focusing their foraging on offshore regions to mitigate this environmental change. Stable isotope analyses of historical samples of WABW (baleen) and SSL (bone and tooth collagen) both illustrated that recent environmental changes influenced the ecology (migration and feeding) of these marine mammals in the recent past.
• #### Adaptations Of The Bacterial Flywheel For Optimal Mineral Cycling In Oligotrophic Surface Waters

Nutrient cycling in a subarctic oligotrophic lake was explored using current kinetic theory for organisms adapted to low nutrient environments with emphasis on bacterial contributions to system function. Techniques were refined which minimize sample disturbance and contamination for the purpose of accurately measuring bacterioplankton activity. Seasonal variations in DNA content, cell mass, species composition, specific affinity for amino acids and cell yield were observed. Quasi-steady state formulae describe bacteria as a flywheel in nutrient cycling; energy is conserved within a relatively constant biomass by varying bacterial activity with nutrient availability. The bacterial flywheel paradigm provides a bacteriocentric view of mineral cycling, linking kinetics to specific cytoarchitectural properties while maintaining links to substrate and grazing pressures. As an extention of the microbial loop paradigm, the flywheel becomes essential at high latitudes. In winter, low solar input interrupts the microbial loop so that the dissolved organic carbon (DOC) pool is cycled through bacteria only. This activity allows bacterioplankton to persist through winter and respond rapidly to springtime warming and nutrients. Microbial adaptations to seasonal variations in nutrient availability and temperatures were examined within the bacterial flywheel framework. Organisms are well-adapted to a narrow (17&deg;C) in situ temperature range. Activation energies for small warming were low at the temperature extremes (20.6 kJ mol -1 at 0.5°C; -32 kJ mol-1 at 17°C) and high in spring (110 kJ mol-1 at 1.2°C). Nutrition varies by season, supplied in large part by amino acids in spring and summer. Winter growth rates are at least 0.013 day-1 whereas partial growth rate on amino acids for that season is only 2.8 x 10-5 day -1. It is proposed that winter organisms rely on diffusion transport and/or shift toward concurrent use of a large suite of substrate types for growth and maintenance.
• #### Assessment And Prediction Of Potentially Mineralizable Organic Nitrogen For Subarctic Alaska Soils

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.
• #### Carbon Cycling In Three Mature Black Spruce ( Picea Mariana [Mill.] B.S.P.) Forests In Interior Alaska

Climate warming in high latitudes is expected to alter the carbon cycle of the boreal forest. Warming will likely increase the rate of organic matter decomposition and microbial respiration. Faster organic matter decomposition should increase plant available nutrients and stimulate plant growth. I examined these predicted relationships between C cycle components in three similar black spruce forests (Picea mariana [Mill] B.S.P) near Fairbanks, Alaska, that differed in soil environment and in-situ decomposition. As predicted, greater in-situ decomposition rates corresponded to greater microbial respiration and black spruce aboveground growth. However root and soil respiration were both greater at the site where decomposition was slowest, indicating greater C allocation to root processes with slower decomposition. It is unclear what environmental factor controls spruce allocation. Low temperature or moisture could cause spruce to increase belowground allocation because slower decomposition leads to low N availability, but foliar N concentration was similar across sites and root N concentration greater at the slow decomposition site. The foliar isotopic composition of 13C indicated soil moisture was lower at the site with greater root and soil respiration. From a literature review of mature black spruce forests, it appears drier (e.g. Alaska) regions of the boreal forest have greater soil respiration because of greater black spruce C allocation belowground. Organic matter characteristics identified with pyrolysis gas chromatography-mass spectrometry correlated with microbial processes, but organic matter chemistry less influenced C and N mineralization than did temperature. Also, differences among sites in C and net N mineralization rates were few and difficult to explain from soil characteristics. Warming had a greater influence on C and N mineralization than the mediatory effect of soil organic matter chemistry. In this study, spruce root C allocation varied more among the three stands than other ecosystem components of C cycling. Spruce root growth most affected the annual C balance by controlling forest floor C accumulation, which was remarkably sensitive to root severing. Predicting the response of black spruce to climate change will require an understanding of how spruce C allocation responds to available moisture and soil temperature.
• #### Decomposition and adsorption of peptides in Alaskan coastal marine sediments

In organic-rich coastal sediments, hydrolyzable amino acids make up a substantial fraction of the sedimentary content of organic nitrogen. How this organic nitrogen resists decomposition and is preserved in sediments is poorly understood. In order to investigate the factors controlling mineralization and preservation of hydrolyzable amino acids, decomposition and adsorption of peptides were studied in suboxic and anoxic pore water and sediments from Resurrection Bay (RB) and Skan Bay (SB), Alaska. Five tritium-labeled peptides, basic di-lysine, acidic di-glutamic acid, and neutral di-alanine, tri-alanine and hexa-alanine, were used as tracers. In filtered pore water, the hydrolysis rates were usually low. The exception was that the initial enzymatic hydrolysis of di-alanine and di-glutamic acid was rapid in SB pore water. The hydrolysis rates of both peptides increased with concentration. In sediments, hydrolysis was found to be the rate-limiting step of peptide decomposition. Alanyl and glutamyl peptides were hydrolyzed faster than lysyl peptide, and the hydrolysis rates among alanyl peptides decreased with increasing molecular weight. Peptide hydrolysis was affected more by molecular structure than by oxic or anoxic conditions. Adsorption of lysyl peptide to sediments was greater than that of other peptides. Basicity enhanced peptide adsorption more than increased molecular weight. Sedimentary organic matter was mainly responsible for peptide adsorption. The different patterns of peptide adsorption in RB and SB sediments were related to the greater total organic carbon concentration in SB sediment. Some of the peptide adsorption was irreversible. Adsorbed peptides were more resistant to biological decomposition than dissolved peptides. Adsorption may be an important step in the process of peptide preservation in sediments, and thus the preservation of sediment organic matter during early diagenesis.
• #### Ecology of birch litter decomposition and forest floor processes in the Alaskan taiga

Our view of an ecological process is influenced by the scale of our hypotheses and experiments. The forest floor can be examined as a system, where processes that affect ecosystem carbon and nutrient cycling are controlled by macroscale variables (seasonal climatic changes), which in turn affect microscale controls over microbial activity. In the forest floor of Alaskan taiga, annual layers of Equisetum (horsetail) litter demarcate cohorts of birch litter. We collected samples of the forest floor monthly during September 1992, and in June-September 1993. Forest floor material was separated into each of the three most recent litter cohorts, plus the Oe layer, and the Oa layer. Overall, respiration potential decreased with depth of litter (litter age), but showed no change over time. Nitrogen mineralization potential increased with depth, and fluctuated over time. Microbial biomass did not vary with depth, but did increase greatly in September in conjunction with increased litter moisture. Litter C:N ratio decreased with time and varied with depth according to the year-to-year variation in litter quality. Our hypothesis that microbial activity on a particular litter cohort is a function of the litter quality, the vertical position of the litter in the forest floor, and the timing of the observation within seasonal macroclimatic cycles was supported. The distribution of some taxa of soil fauna correlated with depth. In these cases, the fauna were likely constrained mostly by differences in the microclimate of the forest floor strata. Other soil fauna varied over time, likely in response to differences in the microbial community. Yet other faunal distributions showed an interaction between depth and time, apparently responding to a combination of changes in microclimate and changes in food availability. The creatures that live in water pores may also have responded to an increase in habitat space as the top-most litter strata became wetter. "Cascading" microcosms containing material from these forest floor strata showed a temporary suppression of respiration by leachates from the newer litter on underlying forest floor material. Traditional litterbag techniques were also used to show changes in nitrogen that indicate winter microbial activity.
• #### Export Of Carbon, Nitrogen And Major Solutes From A Boreal Forest Watershed: The Influence Of Fire And Permafrost

Detailed observations of stream, soil, and groundwater chemistry were used to determine the role of fire, permafrost and snowmelt processes on the fluxes of carbon, nitrogen and major solutes from interior Alaskan catchments. We examined an experimentally burned watershed and two reference watersheds that differ in permafrost coverage (high, 53%; medium-burn, 18%; and low, 4%) during the FROSTFIRE prescribed burn in July 1999. The fire elevated stream nitrate concentrations for a short period during the first post-fire storm, but nitrate declined thereafter, suggesting that less severe fires that leave an intact riparian zone may have only a short-term effect on stream chemistry. Nevertheless, we found fundamental differences in hydrochemical differences between watersheds due to the presence of permafrost. Flowpaths in the low-permafrost, likely from the riparian zone, depleted stream nitrate levels while flowpaths in the high permafrost watershed, generated from more distant hillslopes, were a source of nitrate. All watersheds were sources of organic solutes during snowmelt and summer storms. On an annual basis, watersheds were net sources of every individual ion or element (Cl-, PO42- , SO42-, DOC, DON, NO3 -, Na+, K+ Mg2+, Ca2+) except NH4+, which was a small fraction of the total N concentration in streams. The concentration of NO 3- was high for an ecosystem with low atmospheric N deposition and compared to non-Alaskan boreal and temperate watersheds, resulting in net N loss. These findings suggest that boreal watersheds in the discontinuous region of interior Alaska may be fundamentally different in their capacity to retain N compared to ecosystems with net N retention.
• #### Hydrologic Controls On Carbon Cycling In Alaskan Coastal Temperate Rainforest Soils

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

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.
• #### Methane Emissions From Lakes In Northeast Siberia And Alaska

Large uncertainties in the budget of atmospheric methane (CH4), an important greenhouse gas whose relative greenhouse effect is 23 times stronger than that of carbon dioxide (CO2), limit the accuracy of climate-change projections. Concentrations of atmospheric CH 4 have been rising during recent decades, particularly at high northern latitudes. The causes of this increase are not well understood. Here I describe and quantify an important source of methane---bubbling from northern lakes---that has not been incorporated in previous regional or global methane budgets. I introduce a new method to accurately measure ebullition (bubbling), which accounted for 95% of CH4 emissions from North Siberian thaw lakes. Documenting the patchiness of ebullition increased previous estimates of CH4 flux from lakes 5-fold in Siberia and 2.5- to 14-fold in Alaska. Extrapolating estimates of measured fluxes, I show that North Siberian yedoma (Pleistocene-aged organic-rich loess) thaw lakes emit 3.8 Tg CH 4 yr-1. An independent mass-balance approach based on carbon lost from permafrost that thawed beneath lakes revealed that lakes emit 4-5 Tg CH4 yr-1. Adding these emissions significantly increases present estimates of northern wetland contributions (<6-40 Tg yr-1) to the atmospheric CH4 budget. Thermokarst (thaw) erosion was the primary driver of CH4 emissions in lakes. A 14.7% expansion of thaw lakes from 1974 to 2000 increased lake CH 4 emissions by 58% in Siberia, demonstrating a positive feedback to climate warming. The Pleistocene age of CH4 (14C age 35,570-42,800 years in Siberia and 14,760-26,020 years in Alaska) emitted from hotspots along active thermokarst margins of lakes demonstrated that recruitment of a previously sequestered carbon source contributes to this feedback. Finally, reconstruction of yedoma's distribution at the Last Glacial Maximum together with compilation of thaw lake basal ages that developed at the onset of Holocene warming, suggested that thaw lake development contributed up to 70% of the rapid increase in atmospheric CH4 during deglaciation. About 425 Gt C remain preserved in the yedoma ice complex in North Siberia. If this Siberian permafrost warms more rapidly in the future as projected, the positive feedback of ebullition from expanding thaw lakes could increase the rate of high-latitude warming.
• #### Modeling The Influences Of Climate Change, Permafrost Dynamics, And Fire Disturbance On Carbon Dynamics Of High -Latitude Ecosystems

A Soil Thermal Model (STM) with the capability to operate with a 0.5-day internal time step and to be driven with monthly input data was developed for applications with large-scale ecosystem models. The use of monthly climate inputs to drive the STM resulted in an error of less than 1�C in the upper organic soil layer and in an accurate simulation of seasonal active layer dynamics. Uncertainty analyses identified that soil temperature estimates of the upper organic layer were most sensitive to variability in parameters that described snow thermal conductivity, moss thickness, and moss thermal conductivity. The STM was coupled to the Terrestrial Ecosystem Model (TEM), and the performance of the STM-TEM was verified for the simulation of soil temperatures in applications to black spruce, white spruce, aspen, and tundra sites. A 1�C error in the temperature of the upper organic soil layer had little influence on the carbon dynamics simulated for a black spruce site. Application of the model across the range of black spruce ecosystems in North America demonstrated that the STM-TEM has the capability to operate over temporal and spatial domains that consider substantial variations in surface climate. To consider how fire disturbance interacts with climate change and permafrost dynamics, the STM was updated to more fully evaluate how these factors influence ecosystem dynamics during stand development. The ability of the model to simulate seasonal patterns of soil temperature, gross primary production, and ecosystem respiration, and the age-dependent pattern of above-ground vegetation carbon storage was verified. The model was applied to a post-fire chronosequence in interior Alaska and was validated with estimates of soil temperature, soil respiration, and soil carbon storage that were based on measurements of these variables in 1997. Sensitivity analyses indicate that the growth of moss, changes in the depth of the organic layer, and nitrogen fixation should be represented in models that simulate the effects of fire disturbance in boreal forests. Furthermore, the sensitivity analyses revealed that soil drainage and fire severity should be considered in spatial application of these models to simulate carbon dynamics at landscape to regional scales.
• #### Natural abundance of nitrogen(15) in a subarctic lake and biogeochemical implications to nitrogen cycling

Stable isotope ratios of nitrogen ($\delta\sp{15}$N) were employed to track the origin and fate of nitrogen in a subarctic lake, Alaska. The annual planktonic nitrogen cycle was dominated by N$\sb2$ fixation in spring and NH$\sb4\sp+$ assimilation in summer. In winter, microbial nitrification was the major sink for NH$\sb4\sp+$ and denitrification was accounted for most of the loss of NO$\sb3\sp-.$ The small isotope fractionation in nitrification is proposed as a result of substrate (NH$\sb4\sp+)$ limitation. The temporal and spatial homogeneity of the $\delta\sp{15}$N of dissolved organic nitrogen may be related to its large pool size and refractory nature. A stable isotope mass balance suggests that the winter phytoplankton was only composed of 10 to 20% of the suspended organic matter in water column due to low primary productivity during the ice cover period. A close correlation between $\delta\sp{15}$N of phytoplankton and $\delta\sp{15}$N of dissolved pools indicates that NH$\sb4\sp+$ was the predominant nitrogen source for non-N$\sb2$-fixing algae. The similarity of $\delta\sp{15}$N between a spring blue-green bloom and N$\sb2$ suggests an atmospheric origin for nitrogen. A mixing model estimated that the blue-green algal bloom derived approximately 70% of its nitrogen from molecular nitrogen. This fixed nitrogen was further transferred to higher trophic levels via the food chain and to other primary producers following mineralization. The $\delta\sp{15}$N of aquatic macrophytes indicates that non-rooted species obtained their nitrogen from the water column while rooted species obtained their nitrogen largely from the sediment. Evidence from dual isotope tracers ($\delta\sp{15}$N and $\delta\sp{13}$C) suggests that the zooplankton were supported by phytoplankton throughout the growing season despite an apparent abundance of detritus in the water column. Benthic fauna relied on either phytoplankton detritus or other organic matter in the sediment. The $\delta\sp{15}$N data exhibit only two to three trophic levels in both planktonic and the benthic communities in Smith Lake.
• #### Nitrogen oxide photochemistry in high northern latitudes during spring

The transport of NOy reservoir species from midlatitudes into the Arctic and the thermal and photochemical breakup of these species has been proposed to be the most important NOx source during spring, and may have an important influence on the ozone budget. This has not yet been shown to be correct. The objective of this research is to understand the sources of NOx and ozone in high latitudes during spring. To measure NOx, a high sensitivity chemiluminescence NO detector and a photolytic converter for NO$\sb2$ were constructed. The detection limits for NO and NO$\sb2$ were 1.70 and 5.67 part per trillion (pptv) in a one-hour average, respectively. Springtime NOx measurements were carried out concurrently with measurements of ozone, PAN, J(NO$\sb2$), and other species during 1994 at the Zeppelin station on Svalbard, and during 1993 and 1995 at Poker Flat, Alaska. The median mixing ratios of NOx, PAN and ozone at Svalbard were 23.7, 237.0 pptv, and 39.0 parts per billion (ppbv), respectively. During a few ozone depletion events in the Arctic marine boundary layer ozone and NOx mixing ratios were as low as 4 ppbv and 0.9 pptv, respectively. Halogen chemistry is probably responsible for both effects. The median NOx, PAN and ozone mixing ratios at Poker Flat were 79.5 pptv, 85.9 pptv, and 40.6 ppbv, respectively. During April and May diurnal cycles of PAN, ozone and temperature were observed and anticorrelated with the water mixing ratio. We interpret this to be the result of mixing with higher layers of the troposphere during the day. At both locations thermal PAN decomposition was an important NOx source. At Svalbard PAN decomposition was small, and the in-situ ozone production rates are an insignificant contribution to the ozone budget. Because of the higher temperatures, PAN decomposition rates, NOx mixing ratios, and in-situ ozone production rates are higher at Poker Flat. A contribution from this production to the overall ozone budget was visible during some periods. These results indicate that stable ozone precursors which are transported into the Arctic from anthropogenic sources can influence the ozone budget in high latitudes.

• #### Soil consumption of atmospheric methane: Importance of microbial physiology and diversity

Recently, atmospheric CH$\sb4$ concentration has risen dramatically, apparently due to human activities. Since is CH$\sb4$ is involved in several atmospheric processes that regulate Earth's climate, it is important that we understand the factors that control its atmospheric concentration. One such factor is biological CH$\sb4$ consumption in well-drained soils. Although this sink may comprise nearly one-tenth of the annual destruction of atmospheric CH$\sb4$, We know relatively little about it. I conducted a research project to investigate the influences of CH$\sb4$ supply, soil moisture, dissolved salts, and NH$\sb4\sp+$-fertilizer on the activity of soil CH$\sb4$ oxidizers. When starved of CH$\sb4$, two upland taiga soils gradually lost their capacities to oxidize CH$\sb4$, indicating that the process was not merely fortuitous, and that the organisms involved were truly methanotrophic. The relationship between soil moisture and CH$\sb4$ consumption was parabolic, with maximum oxidation occurring at a moisture level that achieved the maximum possible CH$\sb4$ diffusion rate, while minimizing water stress on the methanotrophs. Optimal soil moisture occurred in a relatively narrow range among an array of physically dissimilar soils, providing that moisture content was expressed as a percentage of the water holding capacity fo a particular soil, rather than as absolute water content. In recent years, one of the most intensely investigated controls on soil CH$\sb4$ consumption has been its inhibition by NH$\sb4\sp+$-fertilizer. In addition to NH$\sb4\sp+,$ however, I found that other ions inhibited CH$\sb4$ oxidation. In some soils non-NH$\sb4\sp+$ ions were so toxic that they completely masked the NH$\sb4\sp+$ effect. It is crucial, therefore, to control for salt effects when investigating NH$\sb4\sp+$-inhibition. In both field and laboratory experiments, CH$\sb4$ consumption in a birch soil was sensitive to NH$\sb4\sp+$, whereas a spruce soil was unaffected. In the birch soil, NH$\sb4\sp+$ apparently inhibited methanotroph growth, rather than enzymatic CH$\sb4$ oxidation, whereas methanotrophs in the spruce soil were apparently insensitive to NH$\sb4\sp+$. These results suggest that the primary landscape-level control over the response of soil CH$\sb4$ consumption to NH$\sb4\sp+$-fertilization is the cross-site distribution of physiologically distinct CH$\sb4$ oxidizers.
• #### Soil Nitrogen Transformations And Retention During A Deciduous To Coniferous Successional Transition

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.
• #### Taphonomic Analysis Of Fish Remains From The Mink Island Site (Xmk-030): Implications For Zooarchaeological And Stable Isotopic Research

This dissertation is focused on shedding the taphonomic overprint at the Mink Island site (XMK-030) to assess temporal variability of the fish bone assemblage and to establish sample selection criteria for stable isotope (delta15N, delta13C) analysis. These retrospective data may be used to identify the causes and consequences of long-term variability in local fish assemblages when combined with modern fisheries and paleo-oceanographic data. To use these data, it is essential to account for the effects of biostratinomic and diagenic agents. Intertaxa and inter-elemental differences in bone density, shape, size, protein, and lipid content result in differing preservation and contamination potential. Without mitigating for the effects of these biostratinomic and diagenic agents, temporal changes in abundance may be skewed in favor of skeletal elements that best survive destruction. Moreover, stable isotope values may reflect differences in preservation and contamination rather than variability in ecosystem structure and function. The results of several experiments conducted to assess preservation and contamination levels of Mink Island fish bones revealed that: 1) Preservation and contamination potential are linked with completeness percentages and burial duration, but not with bone volume density; 2) Pacific cod dentaries that are intact, unburned, and free of visible contaminants are best suited for stable isotope analysis; 3) The modified Bell pretreatment method is validated for archaeological fish bones; and 4) Because color-affecting contaminants cannot be removed without heat, color-based methods are unsuitable for assessing the cooking/burning stage of archaeological fish bones. Interactions among humans and fishes at Mink Island were assessed using a four-stage resource depression and intensification model. The Mink Island occupants shifted their focus from small flatfishes during Stage I (7500-4500 cal. BP), to Pacific cod and sculpins during Stages II (4500-2800 cal. BP) and III (2800-900 cal. BP), to a mixture of taxa (sculpins, cods, herring, and salmon) during Stage IV (900-400 cal. BP). A decrease in Pacific cod fork lengths indicates that resource depression occurred during Stage II. Taxonomic proportion, evenness, salmon index, and skeletal element representation data demonstrate that salmon intensification did not occur during any stage at Mink Island.
• #### The Development And Application Of Stable Oxygen And Hydrogen Isotope Analyses Of Chironomidae (Diptera) As Indicators Of Past Environmental Change

Environmental change continues to be of increasing interest to scientists in all disciplines, and there is a paramount need to gain a comprehensive understanding of the impacts of environmental change in the past to better predict the future. A challenge associated with interpreting past change is a lack of reliable proxies to infer past environmental conditions preserved in the fossil record. My research has been dedicated to developing techniques associated with analyzing the stable oxygen and hydrogen isotopic composition (delta18O and deltaD) of subfossil chironomid (Chironomidea: Diptera) headcapsules (primarily composed of chitin) preserved in lake sediments as a new proxy of past hydrological environmental changes. My developments have included: (1) assessing and modeling the potential of contamination sources during sample preparation; and (2) culturing chironomid larvae under controlled, replicated laboratory conditions, to examine the degree to which water and diet influence the delta18O and deltaD of chironomids. My growth experiment demonstrated that 69.0+/-0.4% of oxygen and 30.8+/-2.6% of hydrogen in chironomid larvae are derived from habitat water using a two-end member mixing model. The delta18O of chironomids remains can better constrain past habitat water isotopic changes compared to deltaD, due to 69% of the chironomid oxygen being influenced by habitat water. Having examined these methodological issues I then applied stable oxygen isotope analyses of fossil chironomid remains preserved in a sediment core from Idavain Lake, in southwest Alaska. The core represents the last ~16,000 years to the present and isotope analyses of chironomids from the core showed that the delta18O of past lake water had changed since deglaciation. Large variation in delta18O of chironomids (up to 20&permil;) are interpreted as alternating shifts in atmospheric flow regimes that are predominant in southwest Alaska, which are consistent with other evidence of past environmental changes at Idavain Lake (i.e. pollen, delta13C, delta15N, C/N). A zonal flow regime appears to have been dominant from 16,000 to 13,800 cal yr BP, 11,000 to 10,500 cal yr BP, 10,000 to 8,000 cal yr BP, and during a majority of the periods from 8,200 to 3,500 cal yr BP and from 2,000 cal yr BP to present. A mixed modern flow regime seems to have been dominant during the periods from 13,000 to 11,000 cal yr BP, 10,500 to 10,000 cal yr BP, 6,000 to 5,500 cal yr BP and 2,500 to 1,800 cal yr BP. These shifts in moisture regime appear to coincide with a series of glacier advances and recessions along the Gulf of Alaska. Thus, stable isotopic analysis of chironomid headcapsules is a promising tool for indicating paleoenvironmental change.
• #### The Geochemistry Of Manganese, Iron And Phosphorus In An Arctic Lake

Sediment redox processes were investigated in an oligotrophic, arctic lake containing metal oxide crusts in oxidizing surficial sediments (up to 22% Mn and 26% Fe). Toolik Lake, Alaska, a 12,000 year old kettle lake, has the lowest Pb-210 derived sedimentation rates reported for any lake (27 g m('-2) yr('-1)). Three independent methods for estimation of Mn, Fe and P retention within the lake (stream budgets, sediment traps and sediment burial rates) provide similar rates. Of the amounts entering the lake, 28% of P, 50% of Mn and 55% of Fe are retained. Common water column removal mechanisms for these elements and organic C are suggested by sediment trap data. A steady state diagenetic model with terms for diffusion, reduction and oxidation shows that Mn and Fe crusts migrate within surficial sediments. Metal oxide burial rates are equivalent to oxide dissolution rates (reduction), rates of upward diffusion of soluble divalent metals and metal precipitation rates (oxidation). High inputs of labile Mn and Fe from streams, plus low sedimentation and organic matter oxidation rates are important for crust formation. Approximately 12% of Mn and 2% of acid reducible Fe retained by the lake since its formation exist as diagenetic oxides; the rest is buried within reducing sediment. Sediment inorganic P migrates with Fe to form P enriched sediment zones with pore water PO(,4) concentrations beneath these zones regulated by vivianite (Fe(,3)(PO(,4))(,2) 8H(,2)O) formation. The migration of Mn and Fe within sediments results in the enrichment of Ba, Co, Ca, Ni, Ra-226 and carbonate in metal oxide enriched sediments. Barium is enriched in Mn crusts because of diagenetic migration.
• #### The Role Of Fire In The Carbon Dynamics Of The Boreal Forest

The boreal forest contains large reserves of carbon and across this region, wildfire is a common occurrence. To improve the understanding of how wildfire influences the carbon dynamics of this region, methods were developed to incorporate the spatial and temporal effects of fire into the Terrestrial Ecosystem Model (TEM). The historical role of fire on carbon dynamics of the boreal region was evaluated within the context of ecosystem responses to changing atmospheric CO2 and climate. These results show that the role of historical fire on boreal carbon dynamics resulted in a net sink of carbon, however, fire plays a major role in the interannual and decadal scale variation of source/sink relationships. To estimate the effects of future fire on boreal carbon dynamics, spatially and temporally explicit empirical relationships between climate and fire were quantified. Fuel moisture, monthly severity rating, and air temperature explained a significant proportion of observed variability in annual area burned. These relationships were used to estimate annual area burned for future scenarios of climate change and were coupled to TEM to evaluate the role of future fire on the carbon dynamics of the North American boreal region for the 21st century. Simulations with TEM indicate that boreal North America is a carbon sink in response to CO2 fertilization, climate variability, and fire, but an increase in fire leads to a decrease in the sink strength. While this study highlights the importance of fire on carbon dynamics in the boreal region, there are uncertainties in the effects of fire in simulations with TEM. These uncertainties are associated with sparse fire data for northern Eurasia, uncertainty in estimating carbon consumption, and difficulty in verifying assumptions about the representation of fires that occurred prior to the start of the historical fire record. Future studies should incorporate the role of dynamic vegetation to more accurately represent post-fire successional processes, incorporate fire severity parameters that change in time and space, and integrate the role of other disturbances and their interactions with future fire regime.