Method for determining stable isotope ratios of dissolved organic carbon in interstitial and other natural marine waters

A procedure is described for the analysis of the stable carbon isotopic composition of dissolved organic carbon (DOC) in natural waters from marine and higher-salinity environments. Rapid (less than 5 min) and complete oxidation of DOC is achieved using a modification of previous photochemical oxidation techniques. The CO₂ evolved from DOC oxidation can be collected in less than 10 min for isotopic analysis. The procedure is at present suitable for oxidation and collection of 1–5 μmol of carbon and has an associated blank of 0.1–0.2 μmol of carbon.Complete photochemical oxidation of DOC standards was demonstrated by quantitative recovery of CO₂ as measured manometrically. Isotopic analyses of standards by photochemical and high-temperature sealed-tube combustion methods agreed to within 0.3.. Photochemical oxidation of DOC in a representative sediment pore-water sample was also quantitative, as shown by the excellent agreement between the photochemical and sealed-tube methods. The δ¹³C values obtained for pore-water DOC using the two methods of oxidation were identical, suggesting that the modified photochemical method is adequate for the isotopically non-fractionated oxidation of pore-water DOC.The procedure was evaluated through an analysis of DOC in pond and pore waters from a hypersaline microbial mat environment. Concentrations of DOC in the water column over the mat displayed a diel pattern, but the isotopic composition of this DOC remained relatively constant (average δ¹³C = −12.4.). Pore-water DOC exhibited a distinct concentration maximum in the mat surface layer, and δ¹³C of pore-water DOC was nearly 8. lighter at 1.5–2.0-cm depth than in the mat surface layer (0–0.5-cm depth). These results demonstrate the effectiveness of the method in elucidating differences in DOC concentration and δ¹³C over biogeochemically relevant spatial and temporal scales. Carbon isotopic analysis of DOC in natural waters, especially pore waters, should be a useful probe of biogeochemical processes in recent environments.     

Urban structures as marine habitats: an experimental comparison of the composition and abundance of subtidal epibiota among pilings, pontoons and rocky reefs

There remains little understanding of the relationship between the ecologies of urban habitats (pilings and pontoons) and natural habitats (rocky reef) for sessile plants and animals (epibiota) living on urbanised coasts. This study describes the structure of subtidal assemblages of epibiota among pilings, pontoons and adjacent rocky reef in Sydney Harbour, Australia. I tested the prediction that the experimental provision of substrata of the same age and composition in all three habitats would produce assemblages that: (1) differed among all three habitats; and (2) differed most on floating pontoons relative to the two fixed habitats (pilings and reef). As predicted, the results suggested that both pilings and pontoons, particularly the latter, create novel habitats for epibiotic assemblages independent of age and composition of substratum. It is not fully understood why these urban structures act as such different habitats from natural rocky reefs. The important point is that they are different and we are yet to understand the implications of this for the ecology of coastal areas subject to urbanisation.     

Distribution,abundance and carbon isotopic composition of gaseous hydrocarbons in Big Soda Lake,Nevada: An alkaline,meromictic lake

Distribution and isotopic composition (δ¹³C) of low molecular weight hydrocarbon gases were studied in Big Soda Lake (depth = 64 m), an alkaline, meromictic lake with permanently anoxic bottom waters. Methane increased with depth in the anoxic mixolimnion (depth = 20–35 m), reached uniform concentrations (55 μM/l) in the monimolimnion (35–64 m) and again increased with depth in monimolimnion bottom sediments (>400 μM/kg below 1 m sub-bottom depth). The μ¹³C[CH₄] values in bottom sediment below 1 m sub-bottom depth (<?70 per mil) increased with vertical distance up the core (δ¹³C[CH₄] = ?55 per mil at sediment surface). Monimolimnion δ¹³C[CH₄] values (?55 to ?61 per mil) were greater than most δ¹³C[CH₄] values found in the anoxic mixolimnion (92% of samples had δ¹³C[CH₄] values between ?20 and ?48 per mil). No significant concentrations of ethylene or propylene were found in the lake. However ethane, propane, isobutane and n-butane concentrations all increased with water column depth, with respective maximum concentrations of 260, 80, 23 and 22 nM/l encountered between 50–60 m depth. Concentrations of ethane, propane and butanes decreased with depth in the bottom sediments. Ratios of $\text{CH}{}_4\text{[C}{}_2\text{H}{}_6\text{+ C}{}_3\text{H}{}_8\text{]}$ were high (250–620) in the anoxic mixolimnion, decreased to ~161 in the monimolimnion and increased with depth in the sediment to values as high as 1736. We concluded that methane has a biogenic origin in both the sediments and the anoxic water column and that C₂-C₄ alkanes have biogenic origins in the monimolimnion water and shallow sediments. The changes observed in δ¹³C[CH₄] and $\text{CH}{}_4\text{(C}{}_2\text{H}{}_6\text{+ C}{}_3\text{H}{}_8\text{)}$ with depth in the water column and sediments are probably caused by bacteria] processes. These might include anaerobic methane oxidation and different rates of methanogenesis and C₂ to C₄ alkane production by microorganisms.     

A kind of development? Spatial and structural changes in the beef cattle industry of Papua New Guinea

The PNG cattle industry grew slowly until after 1963 when both expatriate-owned ranches and locally-owned smallholder schemes expanded with the assistance of foreign aid. This expansion continued throughout the country until the mid-1970's when the number of cattle in both sectors began to decline and production stabilised. Ranches faced a future of political uncertainty whilst the prestige associated with being the owner of a smallholder scheme was not reflected in increased incomes for those involved; demands on labour were high, management skills lacking and incomes from cash crops were usually higher. The economic and social differentiation that followed cattle smallholding emphazised existing disparities. Increased local demands for beef imports have encouraged a revised national policy directed at producing beef on locally owned but principally expatriate managed ranches on a limited number of available grassland sites. This policy which is now being implemented may also minimise both local economic defferentiation and regional inequalities.Fieldwork was completed in 1979 during secondment to the institute of Applied Social and Economic Research in Port Moresby, Papua New Guinea. I am grateful to them for logistical and financial support.     

An experimental investigation of the Hashin-Shtrikman bounds on two-phase aggregate elastic properties

Existing data supporting or disputing the validity of the Hashin-Shtrikman bounds on the elastic properties of multiphase aggregates often do not consider porosity, elastic anisotropy, or experimental errors. In this experiment, two-phase aggregates of KCl + (NH₄Br, TlBr, CsCl, NaCl, Cu, and LiF) at every 20% volume fraction were vacuum hot-pressed and the compressional and shear velocities were measured with a computer-controlled ultrasonic interferometer to ±0.2%. The ratio of the shear moduli, μ, (phase 2/KCl) varied from about 1 to 5, producing a range of separations between the theoretical two-phase Hashin-Shtrikman bounds for the composites. Samples were generally 99% or better of the theoretical density, with less than 1% velocity anisotropy. Porosity corrections were applied assuming spherical pores, based on the observed velocity-pressure behaviour. Velocities agreed with the HS bounds calculated from the end-member single-crystal stiffnesses when anisotropy was taken into account.The velocity data were also used to estimate the bulk modulus, K, and shear modulus of the second phase by means of the matrix method — taking the K and μ of KCl as known and calculating the moduli of the other phase assuming that the measured velocities were the two-phase Hashin-Shtrikman bounds or the Voigt-Reuss-Hill average. A narrow range of moduli estimates results only if the μ's of both phases are fairly closely matched. For μ's mismatched by a factor of 5, the theoretical uncertainty in the estimates can be 10 times larger than the experimental uncertainty. Estimates using the VRH average can lie outside the HS-based results.     

Stable isotopic compositions of carbonates from the Mesoproterozoic Bangemall Group, northwestern Australia

Marine carbonate rocks from the Mesoproterozoic Bangemall Group of northwestern Australia show little deviation (+/-1.3%) in whole-rock delta 13C(carb)-values about a mean of -0.5%. This narrow range persists despite close sampling (every 10-20 m) through long sections (up to 2500 m) that are geographically widespread (up to 250 km apart), over many depositional environments (supralittoral to outer shelf), sediment sources (stromatolitic bioherms to detrital calcilutites) and rock types (pure limestones to dolomitic shales). The only major excursions from the norm seem related to unusual environmental or post-depositional processes, as they are correlated with large enrichments (to -3%) or depletions (to -16%) in 18O. Relatively heavy delta 13C-values, up to +2.5%, occur in a single bed of brecciated ferruginous dolostone at a single locality; these abnormal values may result from local evaporitic conditions. Limey and shaley nodular dolostones have delta 13C-values as low as -4.3%, probably caused by remineralization of organic matter during late and patchy dolomitization. Most notably, sharp negative excursions in delta 13C, up to -8.4%, occur in bleached kerogen-free rocks with mineral assemblages of dolomite + quartz + calcite +/- tremolite + talc, reflecting isotopic re-equilibration in thick metamorphic aureoles around dolerite intrusions. General environmental variations are minor, with delta 13C-values of peritidal facies tending to be slightly positive whereas those of subtidal facies are slightly negative. There are no strong secular trends, but subtle fluctuations within the range -2 to +l% can be correlated along the northwestern margin of the basin. This resembles the pattern seen in other Mesoproterozoic successions, but is markedly unlike the heavy background (> +5%) and extreme variations (up to l0%) in delta 13C evident in Neoproterozoic successions of similar thickness and environmental setting. Hence, in contrast to the Neoproterozoic, the global rate of organic carbon burial was probably fairly constant during deposition of the Bangemall Group, and perhaps generally during the Mesoproterozoic, as was the redox state of the atmosphere and hydrosphere.     

Heterogeneity in hedonic modelling of house prices: looking at buyers’ household profiles

This paper introduces household-level data into hedonic models in order to measure the heterogeneity of implicit prices regarding household type, age, educational attainment, income, and the previous tenure status of the buyers. Two methods are used for this purpose: a first series of models uses expansion terms, whereas a second series applies Geographically Weighted Regressions. Both methods yield conclusive results, showing that the marginal value given to certain property specifics and location attributes do vary regarding the characteristics of the buyer’s household. Particularly, major findings concern the significant effect of income on the location rent as well as the premium paid by highly-educated households in order to fulfil social homogeneity.     

Application of Species Distribution Models to Identify Estuarine Hot Spots for Juvenile Nekton

Modeling the distribution and habitat capacities of key estuarine species can be used to identify hot spots, areas where species density is significantly higher than surrounding areas. This approach would be useful for establishing a baseline for evaluating future environmental scenarios across a landscape. We developed species distribution models for early juvenile life stages of brown shrimp (Farfantepenaeus aztecus), white shrimp (Litopenaeus setiferus), blue crab (Callinectes sapidus), and spotted seatrout (Cynoscion nebulosus) in order to delineate the current coastal hot spots that provide the highest quality habitat conditions for these estuarine-dependent species in Louisiana. Response curves were developed from existing long-term fisheries-independent monitoring data to identify habitat suitability for fragmented marsh landscapes. Response curves were then integrated with spatially explicit input data to generate species distribution models for the coastal region of Louisiana. Using spatial autocorrelation metrics, we detected clusters of suitable habitat across the Louisiana coast, but only 1% of the areas were identified as true hot spots with the highest habitat quality for nekton. The regions identified as hot spots were productive fringing marsh habitats that are considered the most vulnerable to natural and anthropogenic impacts. The species distribution models identify the coastal habitats which currently provide the greatest capacity for key estuarine species and will be used in the Louisiana coastal planning process to evaluate how species distributions may change under various environmental and restoration scenarios.     

Devensian organic interstadial deposits and ice sheet extent in Buchan,Scotland

Pre-Late Devensian organic deposits in the Buchan area of northeast Scotland were investigated for their geomorphological and palaeoecological (pollen, plant macrofossils, coleoptera) properties. Close ecological agreement exists between fossil indicators and allows the inference that the environment in the vicinity of the deposits was a dwarf shrub tundra of the type met today in high latitude areas of Scandinavia and arctic Russia. The latest in a series of radiocarbon dates from the site produced determinations beyond the limits of the method, although the geomorphological and fossil evidence appears to point to an interstadial date within Oxygen Isotope Stages 5a or 5c. The site has special significance for arguments concerning the much-debated concept of ‘Moraineless Buchan’; indeed, evidence is presented which supports the concept of extensive ice sheet glaciation during the Late Devensian for this crucial geographical area. If Buchan is to be seen as a further casualty amongst other disputed ice-free enclaves, then a return to earlier models of extensive ice sheet glaciation in the Late Devensian of Scotland would seem to be necessary. © 1998 John Wiley & Sons, Ltd.     

Physical disturbance and subtidal habitat structure on open rocky coasts: Effects of wave exposure, extent and intensity

Canopy-forming algae occur across of range of energy environments (i.e., wave sheltered to exposed coasts) where disturbances are frequent (i.e., gap formation) and benthic patterns largely reflect variation in post-disturbance processes. Disturbances vary in extent (area affected) and intensity (degree of damage), and this may affect recolonisation at local scales. On an open oceanic coast, we tested whether habitat structure (patches of canopy algae) differed between heavy and relatively lighter wave exposure (sheltered vs. exposed sides of islands), and whether wave exposure affected the response of prominent habitat-formers to varying disturbance regimes (different sizes of partial and complete canopy removal). Observations of naturally occurring patterns showed sheltered coasts to be characterised by small patches of fucoids, whereas exposed coasts were characterised by large patches of kelp. Canopy-gaps were larger at exposed than sheltered coasts, and mixed canopies constituted > 24% of the subtidal rocky habitat independently of wave exposure. Experimental disturbances showed the local density of kelps to affect recovery through greater recruitment to partial clearings (80% canopy removal). Fucalean algae, on the other hand, mainly recruited into complete clearings (100% removal), but when their recruits were abundant, they also recruited into partial clearings. The covers of filamentous, turf-forming algae increased in all clearings, and more so at exposed than sheltered sites. Extent of disturbance had no detectable effect on recolonisation by canopy-forming algae across the scales examined (i.e., 1.5 m, 3 m diameter loss of canopy). Recolonisation varied among islands kilometres apart, and correlations (r > 0.85) between cover of canopies and cover of their recruits in clearings at the scale of sites, suggested that differences in propagule supply could account for variation in patterns of recolonisation at scales of kilometres. There was no evidence to suggest that the effect of disturbance depended on wave exposure within the range of exposures tested in this study (i.e. open coasts). We recognise that wave exposure can be fundamental to habitat structure of subtidal rocky coasts, but we suggest that its influence may be mediated by the biological setting (e.g., canopy composition).