B21A-01 0830h
Sr isotope ratio as an index of geology of the adjacent forested watersheds in central Japan
Totsukawa-Sanko watershed in the central part of Japan includes more than fifty adjacent small watersheds. They are managed using forest rotation practice in a unit of watershed. We surveyed the geological difference among the watersheds using Sr isotope ratio in streamwater as an index of geological distribution. Ca$^{2+}$, Mg$^{2+}$ and SO$_{4}$$^{2-}$ concentrations of the streamwater on the right bank were higher than those on the left bank. However, it is often indicated that Ca$^{2+}$, Mg$^{2+}$ and SO$_{4}$$^{2-}$ concentrations were influenced by the disturbances on soils and vegetations by forestry practice such as a clear-cutting. While there was no clear change in Sr isotope ratio among the watersheds with different age from the clear-cutting, the difference was clearly shown in Sr isotope ratio of the streamwater between the topographical position of the watersheds. Namely, Sr isotope ratio of streamwater on the right bank was significantly higher than it on the left bank in spite of the site history. These results suggest that Sr isotope ratio is useful for evaluate a difference of bedrock geology in spite of the site history of different sub-catchments.
B21A-02 0830h
Characterization of Groundwater N$_{2}$O in a Temperate Forested Ecosystem
Productions of N$_{2}$O via microbiological processes from terrestrial ecosystems are esti-mated to play an important role in the global budget of N$_{2}$O, although quantification of its production rates contains relatively high uncertainty because of high spatio-temporal heterogeneity as to N$_{2}$O dynamics in soils. Thus, better understanding on the dynamics of N$_{2}$O in terrestrial ecosystems is important not only to reduce the uncertainty in the N$_{2}$O budget, but also to expand our knowledge on nitrogen cycle because production and consumption of N$_{2}$O contain multiple processes regulated by many environmental factors in highly heterogeneous media. Isotopomer ratios of N$_{2}$O is a promising tool to elucidate how N$_{2}$O is produced and/or consumed in soil because each process might leave unique isotopic signatures in N$_{2}$O, resulting in its different isotopomer ratios. Here, we measured isotopomer ratios of N$_{2}$O in a temperate coniferous forested ecosystem (Kiryu Watershed) in Japan where permanent groundwater exists in lower part of mountain slope, whose level can fluctuate according to rain events. Considerable amount of N$_{2}$O was observed in soil gas and groundwater in the lower part of the slope, although emission of N$_{2}$O from soil surface (measured by static chamber method) was hardly observed in this watershed even in the lower part of mountain slope where soil moisture condition is considered to be anoxic, favorable for denitrification in the preliminary study. Thus, we focused on dissolved N$_{2}$O in groundwater and springwater in this study where denitrification can occur intermittently according to rain events. $\delta^{15}$N$^{bulk}$ and $\delta^{18}$O of dissolved N$_{2}$O in groundwater fell into the same ranges as observed in other studies. Dissolved N$_{2}$O in springwater had lower $\delta^{15}$N$^{bulk}$ and $\delta^{18}$O values than that of groundwater, which suggests that N$_{2}$O in springwater was influenced by N$_{2}$O produced possibly by locally-occurring denitrification near the spring where water flows through surface soil layer with high organic content. Together with data of "site preference" of N$_{2}$O as well as N and O isotopic ratios of nitrate, we will discuss the usefulness of isotopomer ratios of N$_{2}$O as an indicator for denitrification or nitrification process in groundwater.
B21A-03 0830h
Nitrate Dynamics in Forest Ecosystems with Various Histories, Using Stable Isotope Measurements
Nitrate (NO$_{3}$$^{-}$) input to forest ecosystems as aerosol or acid rain has been increased in these days. Thus, an elucidation of the fate of NO$_{3}$$^{-}$ added to forest ecosystems is essential for better managements of forest ecosystems. In recent decades many tracer experiments using heavy nitrogen (N) isotope ($^{15}$N) to detect movement of supplied N has been conducted, but it is difficult to trace in-situ N movement with this method because N limits biological activity and the information derived from N-addition might be somewhat different from the one we need to picture the actual N cycle. The purpose of this study is to reveal the change of N cycle system in many forest ecosystems with different plantation histories by measuring stable isotope ratios of N and oxygen (O) in NO$_{3}^{-}$. It has been reported that atmospheric NO$_{3}^{-}$ has high $\delta^{18}$O and soil-derived NO$_{3}^{-}$ has low $\delta^{18}$O, and denitrification increases both $\delta^{18}$O and $\delta^{15}$N of residual NO$_{3}^{-}$. Streamwater samples are collected at Field Science Education and Research Center (FSERC), Kyoto University, Japan and cedar plantations near FSCRC, where we can measure differences in nitrogen dynamics between natural forests and forested ecosystems. Moreover, forested watersheds have various history of cedar plantations (Fukushima et al. in this issue), so we can measure changes of nitrogen dynamics with the succession of the forest ecosystems (0-yr to 86-yrs old). We conversed NO$_{3}^{-}$ to nitrous oxide by denitrifier method reported by Casciotti et. al. , and measured stable isotope ratios ($\delta^{18}$O and $\delta^{15}$N) with GC/IRMS. Results show that $\delta^{18}$O of NO$_{3}^{-}$ in streamwater of younger forest is high and the one from older forest is low, though $\delta^{15}$N data are almost constant in spite of the difference of the plantation history. This result suggests that streamwater of younger forest contains considerable amounts of atmospheric NO$_{3}^{-}$, while the one of older forest contains soil-derived NO$_{3}^{-}$ (produced by nitrification in soil) to larger extent. Thus, younger forest cannot utilize atmospheric NO$_{3}^{-}$ and NO$_{3}^{-}$ is directly discharged, while older forest can immobilize (or utilize) atmospheric NO$_{3}^{-}$ in the ecosystem discharging mostly NO$_{3}^{-}$ of the microbe origin. It indicates that residence time of NO$_{3}^{-}$ would differ for the every age; younger forests have shorter residence time of NO$_{3}^{-}$ within ecosystems, while older forests have longer one.
B21A-04 0830h
Isotopic analysis of gorgonian skeletons provides a 30-year record of pollution on the Florida Reef Tract
Research in shallow tropical reef environments has shown that 15N of coral and algal tissue is a sensitive (and cost-effective) means of assessing sewage stress on reefs. Similarly, recent work in deep-water gorgonians has shown that they record surface productivity. We extended these findings, and used analyses of gorgonians to produce a 30-year record of sewage loading for the Florida Keys. Specimens of Plexaura homomalla were collected at depths of about 10m, at a subset of the sites used by the Coral Reef Monitoring Project (CRMP) in the Florida Keys National Marine Sanctuary. Colonies sampled were less than 1m high: the bases were cut, a small section of stem excised, and the colony re-attached to the bottom using marine epoxy. Branch tips were also sampled. In the lab, the stems were sectioned, and the annual bands sampled for analysis. The oldest coral went back to the early 70's. 15N values of the branch tips and the outermost skeletal layer were identical, and were tightly correlated with nutrient values in the surrounding water. In the Sanctuary, sites may roughly be divided into cleaner, offshore sites, many of which are SPA's (Special Protection Areas), and those closer to shore-for convenience, we have dubbed these "clean" and "dirty." Over the past 30 years, the 15N of gorgonians from the clean sites has remained constant, within the margin of variance induced by periodic upwelling. Over the same period of time, the dirty sites show a steady, statistically highly-significant increase of about 1 per mil, with most of the increase coming in the last 10 years. There may be an obvious cause for the recent decline in corals on the Florida Reef Tract: land-based sources of pollution.
B21A-05 0830h
The Carbon Isotope Composition of DNA Extracted from Paleosol Organic Horizons
Recent work has recognized nucleotide sequences from land plant nucleic acids as the oldest authenticated fossil deoxyribonucleic acid (DNA), making the inference of plant taxonomy possible in substrates devoid of plant macrofossils and microfossils. If the C isotope relationship between bulk plant tissue and associated plant nucleic acids were known, fossil plant nucleic acids could be analyzed for $\delta$$^{13}$C value and used as land plant isotopic substrates within mixed organic material. Toward this end, $\delta$$^{13}$C values of nucleic acids isolated from 12 higher plant species spanning the full phylogenetic diversity of seed plants were determined. Extracted nucleic acids were dominated by double-stranded DNA containing fragments of {\it rbcL} gene $\sim$ 350 base pairs in length. The C isotope compositions of plant nucleic acids were found to be enriched in $^{13}$C relative to bulk plant tissue by a constant value = 1.39\permil. I will also report on recent efforts to extract, verify and isotopically analyze DNA from mixed organic substrates of known age. Mixed organic material was collected from the buried A-horizons present in the entisols (specifically: Sandy Siliceous Mesic Typic Psammaquents) of Cape Henlopen State Park near Lewes, Delaware. These fossil soils were subjected to $^{14}$C dating, DNA extraction and subsequent $\delta$$^{13}$C analysis. The method used to extract nucleic acids from mixed organic material consisted of three main steps: homogenization of cellular material, deproteinization of DNA, and precipitation of nucleic acids. Nucleic acid content in the resultant substrates was verified in two ways: by spectrophotometry and through the amplification of PCR products. I will also explore, as an ultimate goal, the determination of $\delta$$^{13}$C value in specific and varied plant taxonomic groups that once lived in a fossil soil, using isolated DNA as the experimental substrate.
B21A-06 0830h
Bacterial Desorption in Water Saturated Porous Media in the Presence of Rhamnolipid Biosurfactant
This research investigated the effects of transients in elution chemistry on bacterial desorption in water-saturated porous media. Two typical gram-positive bacterial strains of {\it Lactobacillus casei} and {\it Streptococcus mitis} were used as the model bacteria in this research. These two strains were first deposited in the porous medium, after which the medium with deposited bacteria was flushed with rhamnolipid biosurfactant solutions with step increase in concentrations and pulse-type bacterial releases were obtained. Bacterial desorption was quantified from bacterial breakthrough curves. It was found that bacterial retention in silica sand corresponded to bacterial interaction free energies with silica sand evaluated at the equilibrium distance, which were calculated based on the independently determined bacterial, sediment and solution surface thermodynamic properties. With the increase of rhamnolipid biosurfactant concentrations, interactions between bacteria and silica sand decreased, and consequently less bacteria were retained. Decrease in interactions between bacteria and silica sand with increasing rhamnolipid biosurfactant concentrations was attributed to the decrease of the solution electron acceptor parameter of Lewis acid/base component of surface tension. Increase in rhamnolipid biosurfactant concentrations favored the decrease of solution electron acceptor parameter of Lewis acid/base component of surface tension, and consequently decreased the interactions between bacteria and silica sand.
B21A-07 0830h
Changes in Organic Carbon From Land to Ocean in the Waipaoa Sedimentary System, New Zealand.
Small mountainous rivers, such as the Waipaoa, collectively deliver up to 40% of the suspended sediment load and 17$-$35% of the riverine particulate organic carbon (POC) load to the world ocean. The muddy Waipaoa River drains a steep, 2205 km$^{2}$ catchment located on the active collisional Hikurangi Margin of New Zealand. River discharge is 15 Mt of suspended load annually, some of which is stored temporarily on the floodplain, but most is transported seaward to depocentres on the continental shelf and slope. This study outlines the trends in organic carbon (OC) geochemistry of terrestrial erosion-derived sediment in 7 cores located on the Waipaoa River floodplain and adjacent continental margin. The influence of particle size on OC was accounted for by analyzing individual size fractions (>25 $\mu$m, 4$-$25 $\mu$m, <4 $\mu$m) as well as the bulk samples, and normalizing %OC to the surface area (SA) of the <4$-$$\mu$m fractions. The carbon loadings (OC:SA) of the clay fractions range from 0.33 to 0.53 mg OC m$^{-2}$, slightly lower than continental margin sediments from elsewhere. Associated $\delta$$^{13}$C values increase from $-$26.2$\permil$ for floodplain sediments to $-$21.6$\permil$ for upper slope sediments, probably in response to the addition of marine-sourced OC. From a mass balance analysis, the contribution from marine OC steadily rises seawards, from $\sim$56% for inner-shelf sediments (27-m water depth) to $\sim$91% for upper slope sediments (1428 m). These findings for the Poverty Bay margin are consistent with other continental margin studies, with the terrestrial component of the OC decreasing with distance offshore as it is replaced by marine OC. Of note is a distinct mud layer 13$-$22 cm below the inner shelf seabed. Bulk samples from this layer have higher carbon contents, higher C:N ratios and lighter $\delta$$^{13}$C values than sediments above and below. We tentatively equate the layer with the 1988 Cyclone Bola flood $-$ an event that appears to have caused the rapid dispersal of terrigenous OC across the shelf, with subsequent rapid burial preserving its terrigenous signature.