Recent Developments Concerning High-Velocity Clouds

I summarize the new developments in HVC research that have occurred in the pastfew years. These include a) the determination of approximate distances to someIVCs and HVC complex A; b) the measurement of the metallicity of the MagellanicStream and the conclusion that tidal forces are dominant in creating the Stream;c) the derivation that the metallicity of complex C is 0.1 solar, with someevidence for metallicity variations; d) the result that N/O in complex C is 0.2times the solar ratio, a value otherwise only seen in dwarf galaxies and DampedLyα systems; e) the discovery of high-velocity OVI absorption, bothassociated with previously known HI HVCs and in directions without a HI HVC;f) the proposal that HVCs form a population of objects permeating the LocalGroup.     

The impact of wildfire on baseflow recession rates in California

The effect of wildfire on peak streamflow and annual water yield has been investigated empirically in numerous studies. The effect of wildfire on baseflow recession rates, in contrast, is not well documented. The objective of this paper was to quantify the effect of wildfire on baseflow recession rates in California for both individual watersheds and for all the study watersheds collectively. Two additional variables, antecedent groundwater storage and potential evapotranspiration, were also investigated for their effect on baseflow recession rates and postfire baseflow recession rate response. Differences between prefire and postfire baseflow recession rates were modeled statistically in 8 watersheds using a mixed statistical model that accounted for fixed and random effects. For the all‐watershed model, antecedent groundwater storage, potential evapotranspiration, and wildfire were each found to be significant controls on baseflow recession rates. Wildfire decreased baseflow recession rates 52.5% (37.6% to 66.0%), implying that postfire reductions in above‐ground vegetation (e.g., decreased interception, decreased evapotranspiration) were a stronger control on baseflow recession rate change than hydrophobicity. At an individual watershed scale, baseflow recession rate response to wildfire was found to be sensitive to intraannual differences in antecedent groundwater storage in 2 watersheds, with the effect of wildfire on baseflow recession rates being greater with lower levels of antecedent groundwater storage. Examination of burn severity for a subset of the study watersheds pointed to riparian zone burn severity as a potential primary control on postfire recession rate change. This study demonstrates that wildfire may have a substantial impact on fluxes to and from groundwater storages, altering the rate at which baseflow recedes.     

Storylines: an alternative approach to representing uncertainty in physical aspects of climate change

Investigating the relationships between climate extremes and crop yield can help us understand how unfavourable climatic conditions affect crop production. In this study, two statistical models, multiple linear regression and random forest, were used to identify rainfall extremes indices affecting wheat yield in three different regions of the New South Wales wheat belt. The results show that the random forest model explained 41–67% of the year-to-year yield variation, whereas the multiple linear regression model explained 34–58%. In the two models, 3-month timescale standardized precipitation index of Jun.–Aug. (SPI_JJA), Sep.–Nov. (SPI_SON), and consecutive dry days (CDDs) were identified as the three most important indices which can explain yield variability for most of the wheat belt. Our results indicated that the inter-annual variability of rainfall in winter and spring was largely responsible for wheat yield variation, and pre-growing season rainfall played a secondary role. Frequent shortages of rainfall posed a greater threat to crop growth than excessive rainfall in eastern Australia. We concluded that the comparison between multiple linear regression and machine learning algorithm proposed in the present study would be useful to provide robust prediction of yields and new insights of the effects of various rainfall extremes, when suitable climate and yield datasets are available.     

Contrasting sorption behaviours affecting groundwater arsenic concentration in Kandal Province,Cambodia

Natural arsenic(As)contamination of groundwater which provides drinking water and/or irrigation supplies remains a major public health issue,particularly in South and Southeast Asia.A number of studies have evaluated various aspects of the biogeochemical controls on As mobilization in aquifers typical to this region,however many are predicated on the assumption that key biogeochemical processes may be deduced by sampled water chemistry.The validity of this assumption has not been clearly established even though the role of sorption/desorption of As and other heavy metals onto Fe/Mn(hydr)oxides is an important control in As mobilization.Here,selective chemical extractions of sand-rich and clay-rich sediments from an As-affected aquifer in Kandal Province,Cambodia,were undertaken to explore the potential role of partial re-equilibrium through sorption/desorption reactions of As and related solutes(Fe,Mn and P)between groundwater and the associated solid aquifer matrix.In general,groundwater As is strongly affected by both pH and Eh throughout the study area.However,contrasting sorption behaviour is observed in two distinct sand-dominated(T-Sand)and clay dominated(T-Clay)transects,and plausibly attributed to differing dominant lithologies,biogeochemical and/or hydrogeological conditions.Sorption/desorption processes appear to be re-setting groundwater As concentrations in both transects,but to varying extents and in different ways.In T-Sand,which is typically highly reducing,correlations suggest that dissolved As may be sequestered by sorption/re-adsorption to Fe-bearing mineral phases and/or sedimentary organic matter;in T-Clay Eh is a major control on As mobilization although binding/occlusion of Fe-bearing minerals to sedimentary organic matter may also occur.Multiple linear regression analysis was conducted with groups categorised by transect and by Eh,and the output correlations support the contrasting sorption behaviours encountered in this study area.Irrespective of transect,however,the key biogeochemical processes which initially control As mobilization in such aquifers,may be "masked" by the re-setting of As concentrations through in-aquifer sorption/desorption processes.     

Airborne measurements of the impact of ground-based glaciogenic cloud seeding on orographic precipitation

Data from in situ probes and a vertically-pointing mm-wave Doppler radar aboard a research aircraft are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. A previous study (Geerts et al., 2010) has shown that radar reflectivity tends to be higher during seeding periods in a shallow layer above the ground downwind of ground-based silver iodide (AgI) nuclei generators. This finding is based on seven flights, conducted over a mountain in Wyoming (the Unites States), each with a no-seeding period followed by a seeding period. In order to assess this impact, geographically fixed flight tracks were flown over a target mountain, both upwind and downwind of the AgI generators. This paper examines data from the same flights for further evidence of the cloud seeding impact. Composite radar data show that the low-level reflectivity increase is best defined upwind of the mountain crest and downwind of the point where the cloud base intersects the terrain. The main argument that this increase can be attributed to AgI seeding is that it is confined to a shallow layer near the ground where the flow is turbulent. Yet during two flights when clouds were cumuliform and coherent updrafts to flight level were recorded by the radar, the seeding impact was evident in the flight-level updrafts (about 610 m above the mountain peak) as a significant increase in the ice crystal concentration in all size bins. The seeding effect appears short-lived as it is not apparent just downwind of the crest.     

Experimental insights into consolidation rates during one-dimensional loading with special reference to excess pore water pressure

Acta Geotechnica - Consolidation rate has significant influence on the settlement of structures founded on soft fine-grained soil. This paper presents the results of a series of small-scale and...     

Critical tissue copper residues for marine bivalve (Mytilus galloprovincialis) and echinoderm (Strongylocentrotus purpuratus) embryonic development: conceptual, regulatory and environmental implications

Critical tissue copper (Cu) residues associated with adverse effects on embryo-larval development were determined for the Mediterranean mussel (Mytilus galloprovincialis) and purple sea urchin (Strongylocentrotus purpuratus) following laboratory exposure to Cu-spiked seawater collected from San Diego Bay, California, USA. Whole body no-observed-effect-residues (NOER) were similar, with means of 21 and 23mugg(-1)dw, for M. galloprovincialis and S. purpuratus, respectively. Mean whole body median effect residues (ER50) were 49 and 142mugg(-1)dw for M. galloprovincialis and S. purpuratus, respectively. The difference in ER50s between species was reduced to a factor of <2 when expressed as soft tissue residues. Coefficients of variation among whole body-ER50s were 3-fold lower than median waterborne effect concentrations (EC50) for both species exposed to samples varying in water quality characteristics. This suggests that tissue concentrations were a better predictor of toxicity than water concentrations. The CBRs described herein do not differentiate between the internal Cu concentrations that are metabolically available and those that are accumulated and then detoxified. They do appear, however, to be well enough related to the level of accumulation at the site of action of toxicity that they serve as useful surrogates for the copper concentration that affects embryonic development of the species tested. Results presented have potentially important implications for a variety of monitoring and assessment strategies. These include regulatory approaches for deriving saltwater ambient water quality criteria for Cu, contributions towards the development of a saltwater biotic ligand model, the conceptual approach of using CBRs, and ecological risk assessment.     

Design and use of web lectures to enhance GIS teaching and learning strategies: the students’ opinions

The goal of this research is to design, use and evaluate a set of web lectures, specifically tailored to the needs of students in higher education who follow geographic information system -related courses. Since education in geographic information system includes theoretical concepts and practical experience, both of these teaching strategies will be implemented in the web lectures. The user-centered design approach is used in the design process to increase the acceptance of the web lectures and the motivation to use them: perceived usefulness and ease of use. The results show that the students appreciate the initial set of web lectures, but that they need to be motivated more to use them (especially when theoretical topics are covered). Students still value the “traditional” face-to-face lectures and see the web lectures as an ideal complement.     

Experimental measurements and modeling of sorption competition on montmorillonite

The source terms arising from radioactive/toxic metal waste repositories will contain a multitude of dissolved metal species, as do natural systems. The influence of sorption competition on the uptake of safety-relevant metals, and the effects this may have on transport rates to the biosphere, is an important repository performance assessment issue which has not, as yet, been resolved. The main aim of this work was to quantify the influence of competition between metals in different valence states on their individual sorption characteristics under conditions dominated by pH-dependent sorption. The sorption experiments were carried out on Na- and Ca-montmorillonites using various combinations and concentrations of Co(II), Ni(II), Zn(II), Eu(III), Nd(III), Am(III), Th(IV), and U(VI). For metals sorbing at trace concentrations in a background electrolyte containing a competing metal up to mmolar concentrations, and pH values generally greater than 6, all of the experimental results were consistent with the observation that metals with similar chemistries (valence state, hydrolysis behavior) compete with one another, but metals with dissimilar chemistries do not compete, i.e., competition is selective. For example Eu, Nd, and Am exhibit unambiguous sorption competition effects, as do Ni, Co, and Zn. On the basis of the above preliminary criteria, competition between divalent transition metals and trivalent lanthanides, Th(IV), and U(VI) and between Th (IV) and U(VI) would not be expected, and this is found experimentally. In general, neither single-fixed-site capacity models nor two-site (strong/weak) models with fixed capacities, whether with or without electrostatic terms, are capable of modeling the spectrum of experimental results presented here. To explain the competitive effects observed it is proposed that multiple sets of strong sites exist as subsets of the 40 mmol kg⁻¹ of weak sites present in the montmorillonite conceptual model. It is shown that if the 2SPNE SC/CE sorption model is extended to include multiple strong sites, and the average site capacity and protolysis constant values defined in previous publications are assigned to each of the sets of strong sites, then the model can be used to reproduce all of the experimental data, provided it can be specified which groups of metals are competitive and which are not.     

Human‐affected disturbances in vegetation cover and peatland development in the late Holocene recorded in shallow mountain peatlands (Central Sudetes,SW Poland)

The aim of this study is to assess the impact of biotic and abiotic factors on peatland formation in the Central Sudetes (central Europe) during the late Holocene. The research methodology adopted allowed us to determine whether vegetation development and shallow peatland formation were affected by human activity. Knowledge of past changes might be useful in evaluating recent and future changes, and to avoid pitfalls in the present management of peatland ecosystems. A palaeoecological research study of four peatlands was conducted in the Sto?owe Mountains (Central Sudetes, SW Poland). The results showed that these shallow peatlands originated in the middle to late Holocene (from 3301 BC to AD 1137). Palaeoecological records reflect continuous human impact on vegetation development and peat accumulation from the Middle Ages to the present (late Holocene). The strongest agrarian settler activity is observed in the High Middle Ages (AD 1200–1500). The human‐induced or wildfires observed in the late Holocene were an integral component of peatland ecosystems in the Central Sudetes. Moreover, palaeoecological analysis (sphagnum spores decline) and radiocarbon dating (AD 1870) confirmed drainage of the study area in the 19th century, which greatly affected the vegetation communities.