carbon Isotopes

Ciguatera Toxins in the food chain revealed by Stable Isotopes

Winter A., Tosteson T.R. Ciguatera Toxins in the food chain revealed by Stable Isotopes. Bulletin de la Sociatie de Pathologie Exotique, Vol 85, Is 5 Pt 2, 1992 pp. 510-513.

CARBON AND OXYGEN STABLE ISOTOPES IN THE TOA BAJA WELL, PUERTO RICO: IMPLICATIONS FOR BURIAL DIAGENESIS AND HYDROCARBON GENERATION

GONZALEZ, LA. 1991. Carbon and oxygen stable isotopes in the toa-baja well, puerto-rico - implications for burial diagenesis and hydrocarbon generation rid D-5476-2011. Geophysical Research Letters 18 (3) (MAR): 533-6.

Abstract: 
The Toa Baja Well was drilled on the coastal plains of northern Puerto Rico with a total depth of 2705m [Larue, 1990]. Interstratified limestone, quartz-bearing calcareous sandstones, and shales dominate the uppermost 580 m and are separated from underlying rocks by an unconformity. Below this unconformity continuing tototal depth, lithologies encountered consist of volcaniclastic sandstones/siltstones, pelagic carbonates, volcanic flows and either plutonic rocks or coarse-grained immature sandstones derived from plutonic bodies....

Stable Isotopic Studies of Earthworm Feeding Ecology in Tropical Ecosystems of Puerto Rico

Hendrix, PF, SL Lachnicht, MA Callaham, and XM Zou. 1999. Stable isotopic studies of earthworm feeding ecology in tropical ecosystems of puerto rico. Rapid Communications in Mass Spectrometry 13 (13): 1295-9.

Abstract: 
Feeding strategies of earthworms and their influence on soil processes are often inferred from morphological, behavioral and physiological traits. We used 13C and 15N natural abundance in earthworms, soils and plants to explore patterns of resource utilization by different species of earthworms in three tropical ecosystems in Puerto Rico. In a high altitude dwarf forest, native earthworms Trigaster longissimus and Estherella sp. showed less 15N enrichment (delta 15N = 3–6%) than exotic Pontoscolex corethrurus (15N = 7–9%) indicating different food sources or stronger isotopic discrimination by the latter. Conversely, in a lower altitude tabonuco forest, Estherella sp. and P. corethrurus overlapped completely in 15N enrichment (delta15N = 6–9%), suggesting the potential for interspecific competition for N resources. A tabonuco forest converted to pasture contained only P. corethrurus which were less enriched in 15N than those in the forest sites, but more highly enriched in 13C suggesting assimilation of C from the predominant C4 grass. These results support the utility of stable isotopes to delineate resource partitioning and potential competitive interactions among earthworm species. Copyright # 1999 John Wiley & Sons, Ltd.

Estimating the assimilation of mangrove detritus by fiddler crabs in Laguna Joyuda, Puerto Rico, using dual stable isotopes

France, R. 1998. Estimating the assimilation of mangrove detritus by fiddler crabs in laguna joyuda, puerto rico, using dual stable isotopes. Journal of Tropical Ecology 14 (JUL): 413-25.

Abstract: 
Dual stable isotope analyses (delta 13C and delta 15N) of fiddler crabs from a forest-fringed, land-locked lagoon in Puerto Rico indicated the differential assim- ilation of material from ingested sediments. Fiddler crabs preferentially selected foi niitrogen-fixing benthic microalgae (cyanobacteria) over vascular plant detritus. These results question the assumption that mangrove detritus is always the prin- cipal source of energy to estuariiie consumers. Previous research fiom this lagoon as well as from Amazonia suggests that the magnitude of lan-d-wvater ecotonal coupling may be low for these particular tropical systems where benthic algal productivity is presumably high.

Evaluation of the fidelity of isotope records as an environmental proxy in the coral Montastraea

Watanabe, T., A. Winter, T. Oba, R. Anzai, and H. Ishioroshi. 2002. Evaluation of the fidelity of isotope records as an environmental proxy in the coral montastraea. Coral Reefs 21 (2) (JUL): 169-78.

Abstract: 
Many studies of climate variability in the Tropical Ocean have used high-resolution chemical tracer records contained in coral skeletons. The complex architecture of coral skeletons may lead to the possibility of biases in coral records and it is therefore important to access the fidelity of coral geochemical records as environmental proxies. Coral skeletal records from the same coral colony, and even the same corallite, may show large variation due to differing extension rates, formational timing of the skeletal elements, colony topography, and sampling resolution. To assess the robustness of the skeletal record, we present d13C and d18O data based on different sampling resolutions, skeletal elements, and coral colonies of Montastraea faveolata species complex, the primary coral used for climate reconstruction in the Atlantic. We show that various skeletal elements produce different isotopic records. The best sampling rate to resolve the full annual range of sea surface temperature (SST) is 40 samples per year. This sampling frequency also consistently recovered SST variability measured at weekly intervals. A sampling rate of 12 times per year recovered 84% of the annual range recording average monthly SST changes through the year. Six samples per year significantly decreased the ability to resolve the annual SST range. The d18O recorded from two adjacent colonies were very similar, suggesting that this isotope can be trusted to record environmental changes. The d13C, on the other hand, remained highly variable, perhaps as a result of the activity of symbiotic algae (zooxanthellae).

Carbon Isotope Characterization of Vegetation and Soil Organic Matter in Subtropical Forests in Luquillo, Puerto Rico

Von Fischer J.C., Tieszen L.L., Carbon Isotope Characterization of Vegetation and Soil Organic Matter in Subtropical Forests in Luquillo, Puerto Rico. Biotropica Vol 27(2), 1995 pp 138-148.

Abstract: 
We examined natural abundances of "3C in vegetation and soil organic matter (SOM) of subtropical wet and rain forests to characterize the isotopic enrichment through decomposition that has been reported for temperate forests. Soil cores and vegetative samples from the decomposition continuum (leaves, new litter, old litter, wood, and roots) were taken from each of four forest types in the Luquillo Experimental Forest, Puerto Rico. SOM 613C was enriched 1.6%o relative to aboveground litter. We found no further enrichment within the soil profile. The carbon isotope ratios of vegetation varied among forests, ranging from -28.2%o in the Colorado forest to -26.9%o in the Palm forest. Isotope ratios of SOM differed between forests primarily in the top 20 cm where the Colorado forest was again most negative at -28.0%o, and the Palm forest was most positive at -26.5%o. The isotopic differences between forests are likely attributable to differences in light regimes due to canopy density variation, soil moisture regimes, and/or recycling of CO2. Our data suggest that recalcitrant SOM is not derived directly from plant lignin since plant lignin is even more "3C depleted than the bulk vegetation. We hypothesize that the anthropogenic isotopic depletion of atmospheric CO2 (ca 1.5%o in the last 150 years) accounts for some of the enrichment observed in the SOM relative to the more modern vegetation in this study and others. This study also supports other observations that under wet or anaerobic soil environments there is no isotopic enrichment during decomposition or with depth in the active profile.

Carbon Sequestration and Plan Community Dynamics Following Reforestation of Tropical Pasture

Silver W.L., Kuppers L.M., Lugo A.E. et al. Carbon Sequestration and Plan Community Dynamics Following Reforestation of Tropical Pasture. Ecological Applications, Vol 14(4), 2004 pp 1115-1127.

Abstract: 
Conversion of abandoned cattle pastures to secondary forests and plantations in the tropics has been proposed as a means to increase rates of carbon (C) sequestration from the atmosphere and enhance local biodiversity. We used a long-term tropical reforestation project (55–61 yr) to estimate rates of above- and belowground C sequestration and to investigate the impact of planted species on overall plant community structure. Thirteen tree species (nine native and four nonnative species) were planted as part of the reforestation effort in the mid to late 1930s. In 1992, there were 75 tree species (.9.1 cm dbh) in the forest. Overall, planted species accounted for 40% of the importance value of the forest; planted nonnative species contributed only 5% of the importance value. In the reforested ecosystem, the total soil C pool (0–60 cm depth) was larger than the aboveground C pool, and there was more soil C in the forest (102 6 10 Mg/ha [mean 6 1 SE]) than in an adjacent pasture of similar age (69 6 16 Mg/ha). Forest soil C (C3-C) increased at a rate of ;0.9 Mg·ha21·yr21, but residual pasture C (C4-C) was lost at a rate of 0.4 Mg·ha21·yr21, yielding a net gain of 33 Mg/ha as a result of 61 years of forest regrowth. Aboveground C accumulated at a rate of 1.4 6 0.05 Mg·ha21·yr21, to a total of 80 6 3 Mg/ha. A survey of 426 merchantable trees in 1959 and 1992 showed that they grew faster in the second 33 years of forest development than in the first 22 years, indicating that later stages of forest development can play an important role in C sequestration. Few indices of C cycling were correlated with plant community composition or structure. Our results indicate that significant soil C can accumulate with reforestation and that there are strong legacies of pasture use and reforestation in plant community structure and rates of plant C sequestration.

CARBON ISOTOPES (δ13C & Δ14C) AND TRACE ELEMENTS (Ba, Mn, Y) IN SMALL MOUNTAINOUS RIVERS AND COASTAL CORAL SKELETONS IN PUERTO RICO

Moyer RP (2008) Carbon Isotopes (δ13C & Δ14C) and Trace Elements (Ba, Mn, Y) in Small Mountainous Rivers and Coastal Coral Skeletons in Puerto Rico. Ph.D. Dissertation, The Ohio State University, School of Earth Sciences, Columbus, OH. 260pp.

Abstract: 
Tropical small mountainous rivers (SMRs) may transport up to 33% of the total carbon (C) delivered to the oceans. However, these fluxes are poorly quantified and historical records of land-ocean carbon delivery are rare. Corals have the potential to provide such records in the tropics because they are long-lived, draw on dissolved inorganic carbon (DIC) for calcification, and isotopic variations within their skeletons are useful proxies of palaeoceanographic variability. The ability to quantify riverine C inputs to the coastal ocean and understand how they have changed through time is critical to understanding global carbon budgets in the context of modern climate change. A seasonal dual isotope (13C & 14C) characterization of the three major C pools in two SMRs and their adjacent coastal waters within Puerto Rico was conducted in order to understand the isotope signature of DIC being delivered to the coastal oceans. Additionally a 56-year record of paired coral skeletal C isotopes (δ13C & Δ14C) and trace elements (Ba/Ca, Mn/Ca, Y/Ca) is presented from a coral growing ~1 km from the mouth of an SMR. Four major findings were observed: 1) Riverine DIC was more depleted in δ13C and Δ14C than seawater DIC, 2) the correlation of δ13C and Δ14C was the same in both coral skeleton and the DIC of the river and coastal waters, 3) Coral δ13C and Ba/Ca were annually coherent with river discharge, and 4) increases in coral Ba/Ca were synchronous with the iii timing of depletions of both δ13C and Δ14C in the coral skeleton and increases in river discharge. This study represents a first-order comprehensive C isotope analysis of major C pools being transported to the coastal ocean via tropical SMRs. The strong coherence between river discharge and coral δ13C and Ba/Ca, and the concurrent timing of increases in Ba/Ca with decreases in δ13C and Δ14C suggest that river discharge is simultaneously recorded by multiple geochemical records. Based on these findings, the development of coral-based proxies for the history of land-ocean carbon flux would be invaluable to understanding the role of tropical land-ocean carbon fluxes in the context of global climate change.

Suppression of methanogenesis by dissimilatory Fe(III)- reducing bacteria in tropical rain forest soils: implications for ecosystem methane flux

Teh, Y.A., Dubinsky, E.A., Silver, W.L., and Carlson, C.M.
(2008) Suppression of methanogenesis by dissimilatory Fe
(III)-reducing bacteria in tropical rain forest soils: implications
for ecosystem methane flux. Glob Change Biol 14:
413–422.

Abstract: 
Tropical forests are an important source of atmospheric methane (CH4), and recent work suggests that CH4 fluxes from humid tropical environments are driven by variations in CH4 production, rather than by bacterial CH4 oxidation. Competition for acetate between methanogenic archaea and Fe(III)-reducing bacteria is one of the principal controls on CH4 flux in many Fe-rich anoxic environments. Upland humid tropical forests are also abundant in Fe and are characterized by high organic matter inputs, steep soil oxygen (02) gradients, and fluctuating redox conditions, yielding concomitant methanogenesis and bacterial Fe(III) reduction. However, whether Fe(III)-reducing bacteria coexist with methanogens or competitively suppress methanogenic acetate use in wet tropical soils is uncertain. To address this question, we conducted a process-based laboratory experiment to determine if competition for acetate between methanogens and Fe(III)-reducing bacteria influenced CH4 production and C isotope composition in humid tropical forest soils. We collected soils from a poor to moderately drained upland rain forest and incubated them with combinations of C-13-bicarbonate, C-13-methyl labeled acetate ((CH3COO-)-C-13), poorly crystalline Fe(III), or fluoroacetate. CH4 production showed a greater proportional increase than Fe2+ production after competition for acetate was alleviated, suggesting that Fe(III)-reducing bacteria were suppressing methanogenesis. Methanogenesis increased by approximately 67 times while Fe2+ production only doubled after the addition of (CH3COO-)-C-13. Large increases in both CH4 and Fe2+ production also indicate that the two process were acetate limited, suggesting that acetate may be a key substrate for anoxic carbon (C) metabolism in humid tropical forest soils. C isotope analysis suggests that competition for acetate was not the only factor driving CH4 production, as C-13 partitioning did not vary significantly between (CH3COO-)-C-13 and (CH3COO-)-C-13 + Fe(III) treatments. This suggests that dissimilatory Fe(III)-reduction suppressed both hydrogenotrophic and aceticlastic methanogenesis. These findings have implications for understanding the CH4 biogeochemistry of highly weathered wet tropical soils, where CH4 efflux is driven largely by CH4 production.
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