Seasonal variability of community structure and breeding activity in marine phytal harpacticoid copepods on Ulva pertusa from Pohang,east coast of Korea

Seasonal changes in community structure and reproductive status of phytal harpacticoid copepods in the shallow sublittoral bottom at two sites (Masan-ri and Guryongpo) in Pohang (Korea) are described monthly over a period of 1 year (October 1996 to September 1997). A total of 36 harpacticoid species was identified and the numerically dominant copepods were made up of the families Porcellidiidae and Tisbidae. Although the number of species did not show a seasonal trend, total harpacticoid density revealed a favorable distribution for the warmer season (spring and summer) at both sites. Multiple linear regression analyses showed that univariate indices such as density, evenness and diversity are closely associated with certain environmental parameters. For example, the dominant species fluctuated seasonally in abundance and their maximum densities were found to be temperature- (+ with Porcellidium ofunatense) and nutrient-dependent (+ with Scutellidium longicauda acheloides, + with Zaus unisetosus, and ? with P. wandoensis). In addition, the dominant species appeared to breed year round and their reproductive indices are significantly correlated with some environmental parameters such as temperature (?), pH (+), and phosphate (+). Three species (S. l. acheloides, P. wandoensis, and P. ofunatense) showed maximum density two or three months after their reproductive activity reached a maximum. Overall, the seasonal changes in a phytal harpacticoid community could be explained by combinations of environmental parameters supporting the complexity and biodiversity for this specific group of species in coastal ecosystems.     

Holocene and Eemian climatic optima in the Korean Peninsula based on textural and carbon isotopic records from the stalagmite of the Daeya Cave,South Korea

Textural and stable isotopic records from the absolute-dated stalagmite of the Daeya Cave (DY-1) provide new insights into the climatic evolution of the Korean Peninsula during the Holocene and Eemian climatic optima. The stalagmite yielded ages of 8572 ± 227 to 5907 ± 158 and 1,23,456 ± 535 to 1,19,837 ± 1089 years, which coincide with the Holocene and Eemian climatic optima, respectively. The stalagmite’s δ¹³C record closely resembles previously reported Chinese speleothem δ¹⁸O data. Thus it can be suggested that textural and geochemical results of the DY-1 reflect East Asian monsoon intensity, which is forced by summer insolation patterns in the northern hemisphere. Lighter carbon isotopic compositions, well-developed fibrous calcite crystals, and their relatively faster growth rate in the stalagmite sample are interpreted to reflect the warmest and wettest climate conditions of the Holocene and Eemian interglacials. Both climatic optima took place when insolation was decreasing from its maximum level, temperature in Greenland was highest, and sea level approached its maximum level. These climatic optima also coincide with decreasing Antarctic temperatures. Compared the DY-1 data to other proxies, it is suggested that the Holocene and Eemian climatic optima developed through a balance among boreal insolation, monsoon intensity, and sea level (also continental ice volume), which are the main climatic forcing factors in the northern hemisphere. These trends also follow the bi-polar seesaw mechanism as previously described.     

Enhancement of the channel routing module in SWAT

The objective of this study is to demonstrate that the channel flow routing techniques used in the Soil and Water Assessment Tool (SWAT) can be sometimes inappropriate for runoff simulation in small basins. Simulated hydrographs have a tendency to underestimate peak flows or may send a false signal during the recession periods when SWAT is applied to the Mihocheon Basin in South Korea. This was particularly evident for sub‐basins that had a short travel time of much less than a day. In order to enhance the channel routing module in SWAT, an alternative routing technique in which Manning relationship is combined with a simple channel reach continuity equation is proposed in the present study. The advantage of the proposed routing technique is that parameters are readily available from channel morphological data and that it is applicable to small basins. Through simulations of specific events, this routing module that is incorporated into SWAT is almost free from instability errors and produces realistic flow depths and velocities unlike the original version of SWAT with Muskingum method. Copyright © 2009 John Wiley & Sons, Ltd.     

A note on the consolidation settlement of a rigid circular foundation on a poroelastic halfspace

This paper uses Biot's poroelasticity approach to examine the consolidation behaviour of a rigid foundation with a frictionless base in contact with a poroelastic halfspace. The mathematical development of the mixed boundary value problem involves a set of dual integral equations in the Laplace transform domain which cannot be conveniently solved by employing conventional procedures. In this paper, a numerical solution is developed using a scheme where the contact normal stress is approximated by a discretized equivalent. The influence of limiting drainage boundary conditions at the entire surface of the halfspace on the degree of consolidation of the rigid circular foundation is investigated. The results obtained in this study are compared with the corresponding results given in the literature. Copyright © 2016 John Wiley & Sons, Ltd.     

Convection in a rotating annulus having sidewalls of height-dependent thermal conductance

Abstract

Thermal convection in a vertically-mounted, rotating annulus of a particular design proposed by Davies and Walin (1977) is investigated. The annulus used in the present study differs from the conventional type in some important aspects: the sidewalls are finitely conducting, and the thermal conductance of the sidewalls is height-dependent. The theoretical model due to Davies and Walin is briefly recounted. The present study aims to verify the theoretical model; we have acquired numerical solutions to the governing Navier-Stokes equations. The numerical results are supportive of the theoretical contentions. The near-linear dependence of the isothermal slope on the parameter D, which is a function of Ω and ΔT, is corroborated within reasonable limits. New data on the vertical and radial structures of the meridional and azimuthal flows are presented. The numerical results also confirm that the shape of the sidewall thickness has a substantial influence on the meridional flow patterns. In the bulk of the interior flow field, the dominant azimuthal flow field and the temperature field are linked by the thermal wind relation.     

Trends,drivers and impacts of changes in swidden cultivation in tropical forest-agriculture frontiers: A global assessment

This meta-analysis of land-cover transformations of the past 10–15 years in tropical forest-agriculture frontiers world-wide shows that swidden agriculture decreases in landscapes with access to local, national and international markets that encourage cattle production and cash cropping, including biofuels. Conservation policies and practices also accelerate changes in swidden by restricting forest clearing and encouraging commercial agriculture. However, swidden remains important in many frontier areas where farmers have unequal or insecure access to investment and market opportunities, or where multi-functionality of land uses has been preserved as a strategy to adapt to current ecological, economic and political circumstances. In some areas swidden remains important simply because intensification is not a viable choice, for example when population densities and/or food market demands are low. The transformation of swidden landscapes into more intensive land uses has generally increased household incomes, but has also led to negative effects on the social and human capital of local communities to varying degrees. From an environmental perspective, the transition from swidden to other land uses often contributes to permanent deforestation, loss of biodiversity, increased weed pressure, declines in soil fertility, and accelerated soil erosion. Our prognosis is that, despite the global trend towards land use intensification, in many areas swidden will remain part of rural landscapes as the safety component of diversified systems, particularly in response to risks and uncertainties associated with more intensive land use systems.     

Carbon dioxide,water vapor and sensible heat fluxes over a tallgrass prairie

Fluxes of CO₂, water vapor and sensible heat were measured in a grassland ecosystem near Manhattan, Kansas, employing the eddy correlation technique. The vegetation at this site is dominated by big bluestem (Andropogon gerardii), switchgrass (Panicum virgatum), and indiangrass (Sorghastrum nutans). Diurnal patterns of the energy budget components and CO₂ fluxes are evaluated on a few selected days. Influence of high atmospheric evaporative demand and low availability of soil water are examined on (a) energy partitioning, and (b) the magnitudes and patterns of atmospheric carbon dioxide exchange.Published as Paper No. 8470, Journal Series, Nebraska Agricultural Research Division.     

Sediment yield in South Africa — A preliminary geographical analysis

The study examines the spatial relationships between sediment yield and 15 independent environmental variables in 54 catchments in South Africa. Rooseboom's (1978) data on the sediment yield from the catchments were standardized for a single time period. Bivariate regression analyses reveal no simple relationships. Multivariate regression analyses conducted for the whole and various sub-areas of South Africa indicate that latitude and longitude are the primary variables affecting spatial variations in sediment yield. This may be as a result of latitude and longitude being surrogate variables reflecting variation in other environmental variables (e. g. geology, vegetation). Within the sub-areas, 43.4% to 97.8% of the variation in sediment yield is explained by the combined variation in a number of different environmental variables. This study highlights a need for the collection and analysis of more sediment yield data, which would allow the analyses to be refined, to predict sediment yields from ungauged catchments in South Africa.     

Radial growth rates and Pb ages of hydrothermal massive sulfides from the Juan de Fuca Ridge

Activities of ²³⁸U, ²²⁸Ra, ²²⁶Ra and ²¹⁰Pb were determined in submarine hydrothermal massive sulfides by nondestructive, gamma-ray spectrometry. The samples were collected by the manned submersible DSRV “Alvin” from active hydrothermal fields on the Endeavour Segment and Axial Seamount of the Juan de Fuca Ridge. ²¹⁰Pb activities are mostly below the equilibrium level with ²²⁶Ra, which is linearly correlated with the concentration of Ba, Sr and Ca in the deposits. The ratios of²²⁶Ra to the alkaline earth elements indicate that hydrothermal alteration of the underlying oceanic crust is the dominant source of Ra in the sulfide deposits.The ²¹⁰Pb/Pb ratios measured in many of the sulfides are higher than the ratio obtained for a basalt source of ²¹⁰Pb, probably because of ²¹⁰Pb ingrowth from ²²⁶Ra within the sulfide deposits. An isochron approach employing ratios of ²¹⁰Pb/Pb and ²²⁶Ra/Pb yielded an initial ²¹⁰Pb/Pb ratio in the range of 0–0.57 dpm/μg Pb, implying that the crustal residence time of the hydrothermal fluid in the Endeavour Segment is very short ( < 10 years) and that basalt alteration is the only source of the ²¹⁰Pb and Pb. For the hydrothermal fluid in Axial Seamount, a residence time of 10–20 years is estimated on the basis of the initial ²¹⁰Pb/Pb and ²²⁸Ra/²²⁶Ra ratios of a sulfide chimney. Both residence time estimates are consistent with the results of previous studies. We have estimated the upper limits of sample ages ranging from tens to a hundred years for 12 samples, with the remaining seven samples indicating ages close to or older than 150 years, the practical limit of the ²¹⁰Pb/Pb dating technique.A concentrically sectioned sulfide chimney from Axial Seamount yielded mean radial growth rates ranging from a few tenths to a few mm/year based on gradients of ²¹⁰Pb/Pb and ²²⁸Ra/²²⁶Ra activity ratios, whereas a similarly sectioned chimney from the Endeavour Segment, although collected from the top of an active “black smoker” vent, displayed no ²¹⁰Pb or ²²⁸Ra activity. Our results have implications for the duration and periodicity of hydrothermal circulation and associated mineral deposition at mid-ocean ridges.     

Getting Personal: Reflexivity,Positionality, and Feminist Research*

Feminist and poststructural challenges to objectivist social science demand greater reflection by the researcher with the aim of producing more inclusive methods sensitive to the power relations in fieldwork. Following a discussion of contrasting approaches to these power relations, I present a reflexive examination of a research project on sexual identities. My reflections highlight some of the key ethical questions that face researchers conducting fieldwork, especially with regard to the relationship between the researcher and those being researched. My discussion of these dilemmas reflect the situated and partial nature of our understanding of “others.” I argue that the researcher's positionality and biography directly affect fieldwork and that fieldwork is a dialogical process which is structured by the researcher and the participants.