Paleoenvironmental implications of taxonomic variation among δN values of chloropigments

Natural variations in the ratios of nitrogen isotopes in biomass reflect variations in nutrient sources utilized for growth. In order to use δ¹⁵N values of chloropigments of photosynthetic organisms to determine the corresponding δ¹⁵N values of biomass - and by extension, surface waters - the isotopic offset between chlorophyll and biomass must be constrained. Here we examine this offset in various geologically-relevant taxa, grown using nutrient sources that may approximate ocean conditions at different times in Earth’s history. Phytoplankton in this study include cyanobacteria (diazotrophic and non-diazotrophic), eukaryotic algae (red and green), and anoxygenic photosynthetic bacteria (Proteobacteria), as well as environmental samples from sulfidic lake water. Cultures were grown using N₂, NO₃⁻, and NH₄⁺ as nitrogen sources, and were examined under different light regimes and growth conditions. We find surprisingly high variability in the isotopic difference (δ¹⁵N_biomass − δ¹⁵N_{chloropigment}) for prokaryotes, with average values for species ranging from −12.2‰ to +11.7‰. We define this difference as ε_por, a term that encompasses diagenetic porphyrins and chlorins, as well as chlorophyll. Negative values of ε_por reflect chloropigments that are ¹⁵N-enriched relative to biomass. Notably, this enrichment appears to occur only in cyanobacteria. The average value of ε_por for freshwater cyanobacterial species is −9.8 ± 1.8‰, while for marine cyanobacteria it is −0.9 ± 1.3‰. These isotopic effects group environmentally but not phylogenetically, e.g., ε_por values for freshwater Chroococcales resemble those of freshwater Nostocales but differ from those of marine Chroococcales. Our measured values of ε_por for eukaryotic algae (range = 4.7-8.7‰) are similar to previous reports for pure cultures. For all taxa studied, values of ε_por do not depend on the type of nitrogen substrate used for growth. The observed environmental control of ε_por suggests that values of ε_por could be useful for determining the fractional burial of eukaryotic vs. cyanobacterial organic matter in the sedimentary record.     

An Ecosystem Services Approach to Sustainable Livelihoods in the Homegardens of Kandy,Sri Lanka

ABSTRACT

The Kandyan homegardens, or forest gardens, of central Sri Lanka are diverse, smallholder agroforestry ecosystems that for 2000 years have reflected evolving environmental, economic, and social livelihood needs. An ecosystem services approach interrogated homegarden changes over the last 10 years in 31 Kandyan households. Livelihood strategies favouring homegardens were found to have broader benefits across household, national, and global scales than those favouring commercial simplification or those abandoning cultivation for alternative incomes. Livelihood benefits beyond income included resilience to economic and environmental shocks; food security; and higher stocks of biological and agricultural diversity. This revealed overlooked socio-ecological feedbacks between drivers that frustrated interventions to sustain homegarden livelihoods, including increased wild animal incursions thwarting household climate adaptation and disaster recovery; global organic and fair trade incentives reducing food security and livelihood resilience; and national seed and animal regulations counteracting homegarden sustainability programs. Despite these pressures, households maintained homegarden systems for their cultural, aesthetic and eating preferences. An ecosystem services approach can complement sustainable livelihood approaches by identifying overlooked environmental and cultural benefits; reveal livelihood feedbacks from drivers of ecosystem change; avoid unintended consequences from interventions; and capitalise on synergies between stakeholder priorities.     

Non－LTE Analysis of the Sodium Abundance of Metal－Poor Stars in the Galactic Disk and Halo

We performed an extensive non-LTE analysis of the neutral sodiumlines of Na I 5683/5688, 5890/5896, 6154/6161, and 8183/8195 in disk/halo starsof types F-K covering a wide metallicity range (-4 [Fe/H] +0.4), using ourown data as well as data collected from the literature. For comparatively metal-rich disk stars (-1 [Fe/H] +0.4) where the weaker 6154/6161 lines are thebest abundance indicators, we confirmed [Na/Fe] ～ 0 with an "upturn" (i.e., ashallow/broad dip around -0.5 [Fe/H] 0) as already reported in previousstudies. For the metal-deficient halo stars, where the much stronger 5890/5896 or8183/8195 lines subject to considerable (negative) non-LTE corrections amountingto 0.5 dex have to be used, our analysis suggests mildly "subsolar" [Na/Fe] valuesdown to ～ -0.4 (with a somewhat large scatter of ～±0.2 dex) on the average at thetypical halo metallicity of [Fe/H] ～ -2, followed by a rise again to a near-solar ratioof [Na/Fe] ～ 0 at the very metal-poor regime [Fe/H] ～ -3 to -4. These resultsare discussed in comparison with the previous observational studies along with thetheoretical predictions from the available chemical evolution models.     

Surface heat balance and pan evaporation trends in Eastern Asia in the period 1971–2000

Climatic variations over Eastern Asia, including the Tibetan Plateau, were analysed using meteorological data for 32 points in the period 1971 to 2000. Changes in heat and water balances were examined using potential evaporation E_P, and a wetness index WI, as suggested by Kondo and Xu ( 1997a,b ). Climate zones, including the humid, semi‐humid, semi‐arid and arid climate types, in Eastern Asia identified by the wetness index matched the vegetation distribution. Average monthly temperatures increased over the 30 years, with the sharpest increase in February. In general, temperature increases were larger in the north than in the south. Air temperature increased by more than 0·05 K yr⁻¹ in northern China. The data showed that diurnal temperature ranges have decreased in recent years. From the Tibetan Plateau, through central China, to southern northeast China, there has been an increase in potential evaporation and pan evaporation, which may be related to both higher temperatures and a lack of surface water. Increasing long‐wave radiation flux is apparent in every month and in the interannual trends. This is in contrast to the solar radiation flux. On the other hand, trends for relative humidity and cloud cover were negative, but positive for water vapour pressure. Copyright © 2005 John Wiley & Sons, Ltd.     

Parametric excitation of alfvén wave by magnetosonic wave with oblique propagation

A parametric excitation of the Alfvén wave (k^A, ω_a) by the magnetosonic wave (K₁^fs, ω_1fs), which propagates obliquely to the static magnetic field, has been analyzed. The theoretical model for a one-fluid with uniform, unbounded, ideally conducting and compressible plasma is employed. The resonance conditions are chosen such as, $\text{k}{}_1{}^{\mathrm{fs}}\text{=}\text{k}{}_1{}^{\mathrm{fs}}\text{+}\text{k}{}^{\mathrm{A}}$ and ω_1fs ? ω_A = δ ～ ω_2fs. The p wave is assumed to be strong enough, so that the pump wave is given as a constant. In both the case of the standing and the propagating pump the growth rates of the excited waves depend on not only the pump power but also the β-ratio. In the standing pump the threshold pump intensity of the oscillating instability is zero at the perfect matching. It is found that we can obtain a larger growth rate of the parametric excitation of Alfvén wave by the fast magnetosonic pump wave for θ_1f ～ 70–80° and the occurrence regions of parametric excitations are localized at the resonance point in the magnetosphere (β ～ m_e/m_i). It is concluded that the parametric instability of Pc3 range HM-waves is the more possible theory than the linear resonance theory.     

Comparison of landslide susceptibility based on a decision-tree model and actual landslide occurrence: The Akaishi Mountains, Japan

This paper proposes a statistical decision-tree model to analyze landslide susceptibility in a wide area of the Akaishi Mountains, Japan. The objectives of this study were to validate the decision-tree model by comparing landslide susceptibility and actual landslide occurrence, and to reveal the relationships among landslide occurrence, topography, and geology. Landslide susceptibility was examined through ensemble learning with a decision tree. Decision trees are advantageous in that estimation processes and order of important explanatory variables are explicitly represented by the tree structures. Topographic characteristics (elevation, slope angle, profile curvature, plan curvature, and dissection and undissection height) and geological data were used as the explanatory variables. These topographic characteristics were calculated from digital elevation models (DEMs). The objective variables were landslide occurrence and reactivation data between 1992 and 2002 that were depicted by satellite image analysis. Landslide susceptibility was validated by comparing actual data on landslides that occurred and reactivated after the model was constructed (between 2002 and 2004).This study revealed that, from 2002 to 2004, landslides tended to occur and reactivate in catchments with high landslide susceptibility. The landslide susceptibility map thus depicts the actual landslide occurrence and reactivation in the Akaishi Mountains. This result indicates that the decision-tree model has appropriate accuracy for estimating the probabilities of future landslides. The tree structure indicates that landslides occurred and reactivated frequently in the catchments that had an average slope angle exceeding ca. 29° and a mode of slope angle exceeding 33°, which agree well with previous studies. A decision tree also quantitatively expresses important explanatory variables at the higher order of the tree structure.