B21D-0905 0800h
A new method of quantifying contributions from nitrification and denitrification. Tree species effects on soil sources of N$_{2}$O.
Soil microorganisms produce N$_{2}$O through denitrification and nitrification. Here we propose the new method to accurately distinguish contributions of nitrification or denitrification to the N$_{2}$O production. This method is based on the application of the NH$_{4}$NO$_{3}$ (substrate for both processes) with low level of oxygen isotopes enrichment (ca. 1.6 atom excess, %). During nitrification, the first atom of oxygen in nitrous oxide derives from atmospheric O$_{2}$ and the second from H$_{2}$O, while in denitrification, all oxygen atoms of the formed N$_{2}$O originate from oxygen of NO$_{3}$$^{-}$. Thus applying enriched $^{18}$O-NO$_{3}$$^{-}$ and measuring $^{18}$O-N$_{2}$O thereafter it is possible to distinguish the two processes. We used the Siberian afforestation experiment with six dominant in Siberia tree species grown artificially for about 30 y on initially homogeneous soil. The soil samples from all species were incubated at the two moisture levels to test whether the isotopic signatures of oxygen in N$_{2}$O will be more enriched at high moisture level due to increase of denitrifier-derived N$_{2}$O. Overall, both tree species and soil moisture strongly affected not only the N$_{2}$O production but also $^{18}$O-N$_{2}$O with significant interaction between the two factors. This indicates that the role of denitrification and nitrification is different under different tree species and grassland as well as that with increase of soil moisture the part of denitrification is increasing not uniformly but species-dependent. We have shown that at low soil moisture (30% of WHC), the N$_{2}$O efflux is very low but nitrification contributes to 62-92% of the all N$_{2}$O formed. At high moisture (90% of WHC), the efflux is increasing by 10-100 times and the contribution of nitrification is declining to 10-25% and denitrification is responsible for most of the flux.
B21D-0906 0800h
Hydrogen Isotope Fractation Between Water and Algal Lipids of Three Strains of {\it Botryococcus braunii} Under Controlled Conidtions
Understanding of precipitation anomaly variations is essential to the reconstruction of paleo-El Nino at the low latitudes. In enclosed lakes, where lake level is affected by the balance between precipitation and evaporation only, water $\delta$D reflects precipitation patterns. Freshwater algae, which utilize lake water for photosynthesis, should incorporate such signal in the hydrogen isotopes of their tissues. However, a fundamental question still exits: do algal lipid biomarkers truly record lake water hydrogen isotopic ratios? We have measured hydrogen isotope fractionation by freshwater algae Botryococcus braunii (3 strains) grown under controlled conditions in the lab. In order to establish a good relationship between lipid $\delta$D and water $\delta$D, for each strain we set up cultures in five waters with different $\delta$D. $\delta$D of alkadienes and botryococcenes of Botryococcus brauni measured on GCIRMS showed strong positive linear relation with water $\delta$D (R$^{2}$=0.99). Hydrogen isotopic ratios in the algal hydrocarbons are about 165 $\permil$ more negative compared to the water at the start while they are 270 $\permil$ more negative compared to water $\delta$D at harvest. Such linear relationships establish a foundation for reconstructing lake water level and thus precipitation anomaly by analyzing $\delta$D of algal lipids preserved in lake sediments.
B21D-0907 0800h
Carbon Sources to Authigenic Carbonate Rock at Chemosynthetic Communities: Lower Slope of the Gulf of Mexico
Flux of biogenic methane, crude oil and associated hydrocarbon gases occurs from the deep subsurface to the seafloor, water column, and atmosphere of the Gulf of Mexico slope. Chemosynthetic communities occur at sites of relatively high gas flux, frequently with gas hydrate, but always with authigenic carbonate rock \(ACR\). ACR contains carbonate carbon derived from microbial hydrocarbon oxidation that geologically sequesters much fossil carbon, perturbing the carbon cycle. ACR was collected using the ALVIN from sites with chemosynthetic communities in Alaminos Canyon, Atwater Valley, and the Florida Escarpment areas at water depths as much as 3.3 km. Bulk $\delta$13C was measured and carbonate petrology used to identify carbonate cements, normal marine carbonate, and non-carbonate components such as metal oxides and sulfides. ACR is depleted in 13C. However, the $\delta$13C of major hydrocarbon types is typically more depleted in 13C than the associated ACR. For example, the mean $\delta$13C of biogenic methane seeps in the Gulf slope is -74.0\permil PDB but the lightest bulk ACR measured in the study area is -46.6\permil PDB. Carbonate cements from hydrocarbon oxidation are shown to enclose skeletal remains of chemosynthetic fauna such as mussels, clams, as well as other fauna characterized by normal marine carbonate \(\sim 0\permil PDB\). The best explanation of why the $\delta$13C of ACR does not closely correspond to that of the hydrocarbon starting products is that normal marine carbon dilutes the $\delta$13C from hydrocarbon oxidation and thus affects the bulk isotopic properties of ACR.
B21D-0908 0800h
Carbon Biogeochemistry of Marine Sediments at the ODP Leg 204, Hydrate Ridge
ODP Leg 204 was drilled on the Oregon continental margin to determine the distribution and concentration of gas hydrates in an accretionary ridge. The microbiological communities and biogeochemical properties of the hydrates are of special interest. Our goal was to study carbon biogeochemistry in the marine sediments collected from boreholes 1245B, 1245C, 1250D, 1244E and 1244F. The total organic carbon of all boreholes had a narrow range of \delta$^{13}$C values (-21.3 to -22.3\permil), indicating the predominance of a homogeneous source. Lipids were extracted from bulk sediment and separated into neutral-, glycol- and polar-fractions using silicic acid columns. The polar lipids were treated further for analyses of phospholipids fatty acids (PLFA) and compound-specific carbon isotope ratios. Total PLFA was low (less than 80 pmol/g) in boreholes 1245B and 1245C and generally decreased with depth. Total PLFA in borehole 1250D, however, increased with depth, ranging from 33 pmol/g at 30.24 mbsf (meters below seafloor) to 426 pmol/g at 134.7 mbsf. On the other hand, total PLFA in boreholes 1244E and 1244F were high (338.1 to 444.2 pmol/g) but without any obvious trends with depth. Overall, saturated fatty acids were predominant (less than 45% to 82%) in these borehole sediments and terminally branched fatty acids, indicative of sulfate-reducing bacteria, were up to 15% of total PLFA. In borehole 1250D, saturated fatty acids decreased from greater than 80% at the top of the core to less than 45% at depth. Meanwhile, the monounsaturated fatty acids increased from several percent to more than 20% with depth. The \delta$^{13}$C values of PLFA ranged from -45\permil to -50\permil, which were significantly lower than bulk organic carbon. It is unclear, however, whether these low values are attributed to the anaerobic oxidation of methane, which is known to occur in other gas hydrates of the Hydrate Ridge and Gulf of Mexico.
B21D-0909 0800h
Carbon Isotope Signatures of Microbial Mats in the Jackson Mountain Hot Spring, Nevada
The long-term goal of this study is to determine the diversity, ecological function, and CO2 fixation pathways of novel microorganisms in Nevada hot springs. A survey of 16 hot springs in Nevada in May 2004 showed large variations in pH (5.5-9.4) and temperature (36-96°C), which may have significant impact on microbial diversity and primary production by autotrophs. In this study, we select the Jackson Mountain hot spring for a detailed carbon-isotope study along a temperature-and-pH gradient during the formation of travertine (carbonate) deposits. Field measurements indicated that temperature decreased from 68.8-72.3 °C at the vents to 44 °C at the end of slope; the corresponding pH increased from 7.3-7.4 at the vents to 8.3 at the base of slope. Isotopic compositions of dissolved inorganic carbon increased slightly from -3.77 per mil at the vent to -3.2 per mil down gradient. Mat materials were collected along the temperature-and-pH gradient for analyses of bacterial phospholipid fatty acids (PLFA). We expect that temperature will be a major control on the distribution of PLFA in the changing microbial communities because microbial lipid compositions are sensitive to temperature variation. Isotopic fractionations between lipid biomarkers and total biomass are expected to provide insight about the dominant CO2 fixation pathways in different microbial communities growing in different temperature environments.
B21D-0910 0800h
Mycorrhizal Fungi Provide Most of the Nitrogen for Symbiotic Arctic Plants: $^{15}$N Evidence
When soil nitrogen is in short supply, most terrestrial plants form symbioses with fungi (mycorrhizae) in which fine hyphal threads take up soil nitrogen, transport it into plant roots, and in return receive plant sugars. Because the transfer rates are very difficult to measure in nature, ecologists need new tools by which to assess the role of mycorrhizal fungi in carbon and nitrogen cycling. Recent studies indicate that the natural abundance of $^{15}$N taken up from the soil by hyphae is changed during transfer of nitrogen to roots; the result is large differences among the natural abundance of $^{15}$N in soil, symbiotic plants, and symbiotic fungi that depend on the mass balance of nitrogen in the mycorrhizal symbiosis. Measurements were carried out in acidic tussock tundra at the Toolik Lake LTER site in Arctic Alaska (68\deg N 149\deg W). The \delta$^{15}$N of soil N was 1.5%, of soil ammonium was 1.5%, of ericoid and ectomycorrhizal plants was -5.0%, and of ectomycorrhizal fungi was 7.0 parts per mille%. The mass balance of the $^{15}$N shows that the plants received 61-86% of their nitrogen from the fungal hyphae. These values, when combined with known plant growth rates, reveal that the plants provided 7-16% of their photosynthetic carbon to the fungi for growth and respiration, or about 25% of all carbon allocated to belowground processes. This analytical technique could be readily applied to other nitrogen-limited ecosystems such as many temperate and boreal forests to quantify the importance for terrestrial carbon and nitrogen cycling of mycorrhizally mediated transfers at the plant-soil interface.
B21D-0911 0800h
The carbon isotope behaviour during sea water evaporation in salinas as related to the biogeochemical cycle of carbon.
Field measurements and sampling of hypersaline solutions have been realized in the salinas of Santa Pola (Spain) during June 2000 and May 2001. We have followed the geochemical and isotopic evolutions of the solutions along the sea water evaporitic pathway and during a nycthemeral cycle in four evaporitic basins (two carbonate basins, one gypsum basin and one halite basin). There are important differences from one year to another : during May 2001, the \delta$^{13}$C values of DIC were enriched by 1\permil to 5\permil compared to June 2000, indicating organic productivity levels higher in May 2001 than in June 2000. The alkalinity, dissolved oxygen, dissolved organic carbon (DOC) and \delta$^{13}$C values of DIC show large changes from night to day with variable amplitude in the different basins, being more important in the first evaporitic basins where carbonate organic-rich sediments are deposited. The large interannual and nycthemeral variabilies of the \delta$^{13}$C values of DIC in marine evaporitic settings show that these environments are very sensitive to the external and internal constraints which drive the evaporation rate, the mineral precipitation, as well as the organic productivity-regeneration levels. Because inorganic and biological processes in evaporating marine solutions control the carbon cycle and the carbon isotope fractionations, they are both recorded in the geochemistry of the solutions and in the \delta$^{13}$C values of DIC. During sea water evaporation up to halite saturation, the \delta$^{13}$C values of DIC vary in a wide range between -5\permil and +10\permil, following four major steps . 1) carbonate precipitation causes the initial drop of the \delta$^{13}$C values ; 2) algal production (photosynthesis) is responsible for $^{13}$C enrichments in the solutions while organic matter remineralization in the sediment release $^{13}$C -poor CO$_{2}$ in the overlying solutions causing major decreases of \delta$^{13}$C values of DIC in the solutions ; 3) In the basins where gypsum and halite are deposited, the formation of hard evaporitic crusts at the basin floor inhibits gas and ion diffusion from the sediment toward the overlying solutions ; 4) large $^{13}$C enrichments in the heaviest brines results mostly from CO$_{2}$ evasion during evaporation and probably also from the $^{13}$C -poor CO$_{2}$ uptake by the bacterial biomass.
B21D-0912 0800h
A Revised Isotope Fractionation Model for Dissimilatory Sulfate Reduction in Sulfate Reducing Bacteria
Sulfur isotope fractionation during dissimilatory sulfate reduction is related to the stepwise reduction of sulfate to sulfide within the cells of the bacteria. The magnitude of fractionation is dependent on the interplay between different reduction steps in a chain of reactions. One of the most intriguing questions in sulfur isotope geochemistry stems from the observation that in natural environments, sulfides are commonly depleted in $^{34}$S by -45\permil to -70\permil relative to sulfate whereas maximum sulfur isotope difference between produced sulfides and sulfate of around -46\permil have been obtained in laboratory cultures. A maximum fractionation of 47\permil was also predicted by the model of sulfate reduction introduced by Rees (1973). The Rees model is commonly accepted but since its introduction, new information about sulfate reduction and isotope fractionation processes has become available in the literature that demands an update of some of its assumptions. We present a improved model for bacterial sulfate reduction which includes revised fractionation factors for the sulfite-sulfide step, a multi-step reduction of sulfite to sulfide including reverse flows and an exchange flux of sulfide between the cell and ambient water. With this model we show that, contrary to the model of Rees (1973), isotope fractionations well in excess of -47\permil are possible. Therefore, some of the large sulfur isotope fractionations observed in nature may be explained without the need of alternate pathways involving the oxidative sulfur cycle as proposed by Canfield and Thamdrup (1994). In particular, we speculate that large fractionations should occur under hypersulfidic conditions and substrate limitation. We obviously do not disregard the involvement of processes related to the oxidative cycle of sulfur in near-surface environments, but our model suggests that this is not a prerequisite condition to obtain large isotope fractionations. References: Canfield D. E. and Thamdrup B. (1994) Science, 266, 1973-1975. Rees (1973) Geochimica et Cosmochimica Acta, 37, 1141-1162
B21D-0913 0800h
Use of carbon isotopes to identify and characterize microbial signatures in hydrothermal settings
To further explore the diversity of the microorganisms, their adaptations to extreme environmental conditions and their relationship with geothermal sinter formation, we examined the lipids preserved in six sinters of the Taupo Volcanic Zone (TVZ), New Zealand. These sinters contain microbial remains, but the process of mineralisation has rendered them largely unidentifiable. In contrast, lipids, including free fatty acids, 1,2-diacylglycerophospholipids, 1,2-di-O-alkylglycerols, glycerol dialkyl glycerol tetraethers and 1-O-alkylglycerols, are abundant and can be used as chemotaxonomic indicators. However, interpretation of lipid data and microbial signatures can be complicated by 1) allochthonous (pollen, leaves, fungal spores) inputs; 2) the presence of novel lipids or unknown origin; and 3) the production of the same compounds by a range of microorganisms. This is particularly true in hydrothermal settings, where microorganisms will biosynthesize compounds not commonly attributed to Bacteria or Archaea. Compound-specific carbon isotope analyses can help decipher the lipid signature by distinguishing different organic matter sources. For example, in all TVZ sinters, fatty acids with carbon numbers ranging from C$_{22}$ to C$_{32}$ are present; typically these are attributed to higher plants but they could also represent microbial adaptations to high temperatures. Consistent with the former interpretation, in three of four sinters, high-molecular-weight fatty acid carbon isotopic compositions range from -29 to -32 per mil. However, in a fourth sinter, in which fatty acids are most abundant, their carbon isotopic compositions range from -27 to -41 per mil in a pattern indicative of mixing of two different sources, one of which is almost certainly microbial. Carbon isotopic analyses also shed new light on the sources of novel compounds. Present at one hydrothermal site is a novel series of macrocyclic diethers, analogous to macrocyclic archaeol found in M. jannaschii but with a hydrocarbon skeleton consistent with a bacterial origin. These compounds are enriched in $^{13}$C compared to co-occurring compounds, including normal diethers, suggesting that they derive from a different organism and that they utilise a carbon assimilation pathway that does not discriminate strongly against $^{13}$C (e.g. the reverse tricarboxylic acid pathway or the 3-hydroxypropionate pathway). These results, combined with environmental data, provide useful insight into the metabolism of the source organisms and, thus, their phylogeny, guiding future microbial studies of this setting.
B21D-0914 0800h
Identification of Biologically-Produced Organic Matter in an Aquifer System using Stable Isotope Labeling
The carbon cycle in aquifer systems is poorly understood. In particular, the role of prokaryotic and eukaryotic microbes in the cycling of organic matter (OM) has not been well documented. The goal of this work was to utilize stable isotopes in combination with geochemical and microbial methods to study microbially-mediated OM transformations in aquifers and aquifer sediments. A laboratory flow-through column experiment was conducted with sediment collected from a pristine, shallow, coastal plain aquifer. The groundwater medium was amended with low levels of an isotopically labeled nutrient, 13C-acetate. At pre-determined time points, organic matter (OM) was isolated from the sediment and groundwater. OM components were analyzed by isotope-ratio GC-MS and electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The incorporation of 13C was examined for both the aqueous phase and sediment bound OM. Analyzing both dissolved and adsorbed fractions enabled us to determine the relative importance of each on microbe-mediated OM transformations. The incorporation of 13C allowed us to estimate residence times of different organic matter fractions and to answer fundamental questions about organic matter lability in the subsurface environment.
B21D-0915 0800h
Microbial Community Evolution as Evidenced by Isotopic Incorporation into Phospholipid Fatty Acids in a Model Aquifer System
Stable isotope probing (SIP) of biomarkers such as phospholipid fatty acids (PLFAs) has been used successfully to identify active microbial communities in a variety of environments. We are interested in extending this approach to examine the evolution of microbial communities over time. We tested this capability within the context of a larger experiment examining the role of microbes in mediating transformations of organic matter within an aquifer system. A laboratory flow-through column experiment was conducted with sediment collected from a pristine, shallow, coastal plain aquifer. The groundwater medium was amended with low levels of an isotopically labeled substrate, 13C-acetate, for approximately one month and then with non-labeled acetate for one month. PLFAs were extracted from sediments prior to and after labeled-acetate addition. In addition, PLFAs were isolated from effluent samples during selected time points within the two-month experiment. Incorporation of the 13C label into the PLFAs was monitored using isotope-ratio GC/MS. Because some PLFAs can be used to infer the presence of specific microbial groups, we used the relative concentration of different PLFAs and the timing and degree of isotopic incorporation (or loss) to examine the progression of different microbial communities within our model system. This powerful method can be used to untangle the complex interactions within microbial systems and can be extended to a variety of ecosystems.
B21D-0916 0800h
Radiocarbon-based assessments of the role of fungal species in decomposition
We used natural radiocarbon signatures to determine if species of decomposer fungi specialize on different pools of organic matter in the soil. Specifically, we examined natural radiocarbon signatures of mushrooms to estimate the average integrated age of C compounds metabolized by individual species. This method takes advantage of rapid changes in atmospheric radiocarbon signatures of carbon dioxide since the early 1960s, when several years of above-ground weapons testing produced a spike in atmospheric $\Delta$$^{14}$C. This signature has been rapidly declining since then. Therefore, we can measure radiocarbon signatures of tissues and determine the time at which their component C was originally photosynthesized. We conducted our study in a fire chronosequence in boreal forests near Delta Junction, Alaska. The chronosequence includes sites burned in severe fires during the summers of 1999, 1987, and 1956. A "control" site was established in a neighboring 80 yr old black spruce forest. In 2002, we collected mushrooms each week from six 50 m long transects in each site. Mushrooms were weighed and assigned to species based on morphological and molecular analyses (i.e. typing by restriction fragment length polymorphism). Saprotrophic species could be distinguished from ectomycorrhizal species based on $^{15}$N and $^{13}$C signatures. Specifically, saprotrophic mushrooms had $\delta$$^{15}$N values less than 4.66\permil and $\delta$$^{13}$C values greater than -23.1\permil. We then measured the $\Delta$$^{14}$C values of mushrooms from 20 of the most abundant saprotrophic species. Radiocarbon signatures varied widely among species, implying that species take up C from compounds that range in turnover time. For example, fungi of the Polyporaceae often grow on woody debris in our sites, and their $\Delta$$^{14}$C signatures (-65.1 to 15.0\permil) indicate the use of several decades-old, recalcitrant C. These fungi are known to possess the necessary enzymes for lignin degradation, so lignocellulose is a likely C source. In contrast, an unidentified saprotrophic gilled mushroom displayed a $\Delta$$^{14}$C signature close to that of the atmosphere (77.5\permil), which would occur if that species were taking up recently-photosynthesized, labile C. Species that incorporate older C (7 to 14 yr old C and $<$50 yr old C) were most abundant in the two youngest sites, potentially because woody debris from dead black spruce trees is common in both. Most fire-related woody debris had decomposed after 46 years, which may underlie the decline at that stage in populations of fungal species that use older C. Fungal species that use young C (0 to 7 yr old C) tend to proliferate in the intermediate-aged sites, where quaking aspens produce large quantities of litter. Our results suggest that fungal species perform different functions in decomposition in boreal forests, and that radiocarbon analyses can be used to examine the influence of fungal community composition on soil carbon dynamics.
B21D-0917 0800h
Hydrogen-Isotopic Systematics of Lipid Biosynthesis in Hydrogen-Consuming Anaerobes and Aerobes
In anoxic sediments, molecular hydrogen (H$_{2}$) is a key intermediate in the transfer of electrons between H$_{2}$-producing (e.g., fermentative) bacteria and H$_{2}$-consuming microbes, including sulfate-reducing bacteria (SRB). H$_{2}$ is a potential source of lipid-bound hydrogen for SRB, as are water and organic matter. Relative to these other potential sources, H$_{2}$ typically is markedly depleted in deuterium. If hydrogen from strongly D-depleted H$_{2}$ is incorporated into SRB lipids, the isotopic signal could be preserved over geologic time in biomarker compounds in the sediments. The accumulation of characteristically D-depleted SRB biomarkers may thus provide a quantitative measure of sulfate reduction (and hence of carbon remineralization by SRB) in the ancient environment. Ongoing experiments are designed to quantify the relative contributions of H$_{2}$, water, and organic matter to lipid-bound hydrogen in SRB, as well as to determine the associated hydrogen-isotopic fractionations. {\it Desulfobacterium autotrophicum}, a facultative autotroph, is grown in pure culture under various isotopically defined conditions. Water in the media and key metabolites are monitored for D/H. The produced biomass is harvested, and D/H ratios of individual lipid compounds are measured. Isotopic mass-balance calculations based on these data will allow us to determine 1) hydrogen-isotopic compositions of SRB lipids, 2) effects of growth conditions on D/H ratios, and 3) the biochemical sources for lipid-bound hydrogen. Similar experiments are underway to identify and quantify the controls on stable hydrogen-isotopic fractionation during lipid biosynthesis in syntrophic cocultures and in pure cultures of H$_{2}$-consuming, aerobic (i.e., knallgas) bacteria. Taken together, these experiments will provide a first test of our hypothesis that D/H ratios in lipids can be used to quantify carbon remineralization by SRB in modern, and potentially ancient, sediments.
B21D-0918 0800h
Examining Influence of Fog and Stratus Clouds on Bishop Pine Water Budgets, Channel Islands, CA
We present the first results from a project whose goal is to advance our basic understanding of the role that fog and persistent stratus clouds play in ecological processes in the California Channel Islands. Our work is focused on a population of Bishop Pines ({\it Pinus muricata}) on Santa Cruz Island (SCI), the largest, most topographically complex and most biologically diverse island along the California coast. This is the southernmost population (except for an outlier stand near San Vicente, Baja California), and tree growth appears to be water-limited in such a marginal habitat. We hypothesize that persistent fog and low stratus clouds enhance the water balance of these trees via direct water inputs (fog drip and foliar absorption) and reduced solar heating. To assess these possible effects, we have established weather stations and fog and rain collectors throughout the largest Bishop pine stand on SCI. Initial analysis of weather data shows dramatic differences in solar loading over short distances. We present data on the isotopic content (oxygen-18 and hydrogen-2) of water samples collected from winter 2003 to summer 2004. The samples we collected include fogwater, rainfall, water vapor, soil water, leaf and xylem water, and stream water. We also collected and analyzed leaf biomass and soil organic matter samples at periodic intervals for carbon-13 content. These latter data are evaluated in light of extensive leaf-level ecophysiological data collected in the field and as part of a parallel greenhouse study.
B21D-0919 0800h
Salmon-Eating Grizzly Bears Exposed to Elevated Levels of Marine Derived Persistent Organic Pollutants
The coastal grizzly bears of British Columbia (BC, Canada) rely heavily on salmon returning from the Pacific Ocean, whereas interior bears do not have access to or readily utilize this marine-derived food source. Since salmon have been shown to accumulate persistent organic pollutants (POPs) from the North Pacific Ocean, we hypothesized that salmon consumption by grizzly bears would be reflected by an increase in the POP burden. To test this hypothesis we collected hair and fat tissue from grizzlies at various locations around BC to compare salmon-eating (coastal) grizzlies to non-salmon-eating (interior) grizzlies. We characterized the feeding habits for each bear sampled by measuring the stable carbon and nitrogen isotope signature of their hair. The positive relationship between 13C/12C and 15N/14N isotopic ratios suggests that the majority of the meat portion of the diet of coastal grizzlies is coming from salmon, rather than from terrestrial or freshwater sources. By contrast, stable isotope ratios revealed that interior bears have an almost exclusive vegetarian diet with no marine influence. As hypothesized, the coastal grizzly bears have significantly greater OC pesticide and lower-brominated PBDE congener body burden than the interior grizzlies. We also found a positive relationship between C and N isotope ratios and these same POP contaminants in bear tissue. Overall, these results demonstrate that Pacific salmon represents a significant vector delivering both OC pesticides and PBDEs to BC coastal grizzly bears.
http://www.biogeochemistry.uvic.ca
B21D-0920 0800h
Sources of Variability in the Stable Carbon Isotopic Signatures of Fungal Methyl Chloride
The atmospheric budgets of the stratospheric ozone-depleting methyl halides are currently poorly constrained by known sources and sinks. Use of an isotopic mass balance technique may clarify these budgets by constraining the magnitudes of unknown or previously estimated fluxes, or by suggesting potential additional sources or sinks. The utility of this approach will depend not only on being able to measure the relevant source signatures and loss kinetic isotope effects contributing to their atmospheric budgets, but also on our ability to assess the variability in these terms. We investigated sources of variability in the isotopic signatures associated with one component of the methyl chloride budget: production by wood-rot fungi. Using controlled laboratory cultures, measurements of the stable carbon isotopic signatures of growth medium, biomass, respired CO2, CH3Cl, and the carbon mass balance were made over the growth cycle of Inonotus andersonii. Fractionations between medium and biomass (1 permil), as well as biomass and gases (5 permil), were nearly constant during exponential and stationary phase growth. However, the signatures varied across fungal species and type of substrate. A survey of several Phellinus and Inonotus strains grown on C3 plant-derived medium resulted in CH3Cl with delta13C values ranging from -48.2 to -26.4 permil. Other species, including freshly isolated P. robustus and I. andersonii monocultures produced CH3Cl, but in insufficient quantities to determine the isotopic signature. Similarly, field samples of live and blue oak woods rotting through action of these two species did produce CH3Cl when augmented with 10 mM KCl/water solution, but in insufficient quantities to determine isotopic signature. Growth of I. andersonii on C4 plant-derived medium resulted in a larger depletion in the delta13C value of CH3Cl as compared to substrate (18 permil) than for C3 plant-derived medium (7 permil). The amount of available oxygen also plays a role in the capability of the fungi to produce CH3Cl. The range of isotopic signatures measured in this study, while large, is not unique enough from other known CH3Cl sources to change the average global signature of sources to the atmosphere.