Contributing Areas to Domestic Wells in Dipping Sedimentary Rocks under Extreme Recharge Events

We use particle tracking to determine contributing areas (CAs) to wells for transient flow models that simulate cyclic domestic pumping and extreme recharge events in a small synthetic watershed underlain by dipping sedimentary rocks. The CAs consist of strike-oriented bands at locations where the water table intersects high-hydraulic conductivity beds, and from which groundwater flows to the pumping well. Factors that affect the size and location of the CAs include topographic flow directions, rock dip direction, cross-bed fracture density, and position of the well relative to streams. For an effective fracture porosity (n_e) of 10⁻⁴, the fastest advective travel times from CAs to wells are only a few hours. These results indicate that wells in this type of geologic setting can be highly vulnerable to contaminants or pathogens flushed into the subsurface during extreme recharge events. Increasing n_e to 10⁻³ results in modestly smaller CAs and delayed well vulnerability due to slower travel times. CAs determined for steady-state models of the same setting, but with long-term average recharge and pumping rates, are smaller than CAs in the models with extreme recharge. Also, the earliest-arriving particles arrive at the wells later in the steady-state models than in the extreme-recharge models. The results highlight the importance of characterizing geologic structure, simulating plausible effective porosities, and simulating pumping and recharge transience when determining CAs in fractured rock aquifers to assess well vulnerability under extreme precipitation events.     

Marine algae are ‘taught’ the basics of angular momentum

Advanced modelling studies and high-resolution observations have shown that flows related to instability of the mesoscale (~ 1–10 km scale) may provide both the fertilisation mechanism for nutrient-depleted (oligotrophic) surface waters and a subduction mechanism for the rapid export of phytoplankton biomass to the deep ocean. Here, a detailed multidisciplinary analysis of the data from an example high-resolution observational campaign is presented. The data provide direct observations of the transport of phytoplankton through baroclinic instability. Furthermore, the data confirm that this transport is constrained by the requirement to conserve angular momentum, expressed in a stratified water column as the conservation of potential vorticity. This constraint is clearly seen to produce long thin filaments of phytoplankton populations strained out along isopycnal vorticity annuli associated with mesoscale frontal instabilities.     

Sedimentology,palaeoecology and geochronology of Last Interglacial deposits from Deeping St James,Lincolnshire, England

Pollen, plant macrofossil, molluscan and coleopteran data from organic muds below the low terrace of the River Welland at Deeping St James, Lincolnshire indicate deposition in the mixed oak forest phase of a Late Pleistocene interglacial. Coleopteran and molluscan data suggest summer temperatures up to 4°C warmer than at present in eastern England, and plant macrofossil material suggests a climate more continental than that of Britain in the Holocene. No direct analogue of this biota, however, exists currently in Europe. Biostratigraphical indications from the pollen coleoptera and Mollusca suggest an age in the Ipswichian Interglacial. Thermoluminescence dates between 120 ka and 75 ka and amino-acid ratios with a mean of 0.11 show that deposition of the sediments took place during Oxygen Isotope Stage 5. This accurate dating of a partial Ipswichian succession allows discussion of the ages of a number of other interglacial sites in eastern England of assumed Ipswichian age. Copyright © 1999 John Wiley & Sons, Ltd.     

The Pushtashan juvenile suprasubduction zone assemblage of Kurdistan (northeastern Iraq): A Cretaceous (Cenomanian) Neo-Tethys missing link

The Pushtashan suprasubduction zone assemblage of volcanic rocks, gabbros, norites and peridotites occurs in the Zagros suture zone, Kurdistan region, northeastern Iraq. Volcanic rocks are dominant in the assemblage and consist mainly of basalt and basaltic andesite flows with interlayered red shale and limestone horizons. Earlier lavas tend to be MORB-like, whereas later lavas display island arc tholeiite to boninitic geochemical characteristics. Tholeiitic gabbros intrude the norites and display fractionation trends typical of crystallisation under low-pressure conditions, whereas the norites display calc-alkaline traits, suggesting their source included mantle metasomatised by fluids released from subducted oceanic crust. Enrichment of Rb, Ba, Sr, Th and the presence of negative Nb anomalies indicate generation in a suprasubduction zone setting. Trondhjemite and granodiorite intrusions are present in the volcanic rocks, gabbros and norites. SHRIMP U-Pb dating of magmatic zircons from a granodiorite yields a mean~(206)Pb/~(238)U age of 96.0 ±2.0 Ma(Cenomanian). The initial ε_(Hf) value for the zircons show a narrow range from +12.8 to+15.6, with a weighted mean of + 13.90±0.96. This initial value is within error of model depleted mantle at 96 Ma or slightly below that, in the field of arc rocks with minimal contamination by older continental crust. The compositional bimodality of the Pushtashan suprasubduction sequence suggests seafloor spreading during the initiation of subduction, with a lava stratigraphy from earlyerupted MORB transitioning into calc-alkaline lavas and finally by 96 Ma intrusion of granodioritic and trondhjemitic bodies with juvenile crustal isotopic signatures. The results confirm another Cretaceous arc remnant preserved as an allochthon within the Iraqi segment of the Cenozoic Zagros suture zone. Implications for the closure of Neo-Tethys are discussed.     

Pfiesteria shumwayae (Pfiesteriaceae) in New Zealand

Pfiesteria shumwayae Steidinger et Burkholder is now known to be present in New Zealand and occurs in estuaries around the country. The presence of Pfiesteria was initially determined by a polymerase chain reaction (PCR)‐based detection assay, using oligonucleotide primers targeted at ribosomal DNA extracted from estuarine water and sediments. Presence was confirmed by isolation from fresh sediments in the presence offish (Oreochromis mossambicus), followed by identification by scanning electron microscopy. The New Zealand isolates of P. shumwayae were ichthyotoxic in bioassays, but there is no historic evidence offish kills in New Zealand associated with the dinoflagellate.     

Influence of strong monsoon winds on the water quality around a marine cage-culture zone in a shallow and semi-enclosed bay in Taiwan

Influences of marine cage culture and monsoonal disturbances, northeasterly (NE) and southwesterly (SW) monsoons on the proximal marine environment were investigated across a gradient of sites in a semi-enclosed bay, Magong Bay (Penghu Islands, Taiwan). Elevated levels of ammonia produced by the cages were the main pollutant and distinguished the cage-culture and intermediary zones (1000 m away from the cages) from the reference zone in the NE monsoon, indicating currents produced by the strong monsoon may have extended the spread of nutrient-enriched waters without necessarily flushing such effluents outside Magong Bay. Moreover, the levels of chlorophyll-a, dissolved oxygen, and turbidity were distinguishable between two seasons, suggesting that resuspension caused by the NE monsoon winds may also influence the water quality across this bay. It indicated that the impacts of marine cage culture vary as a function of distance, and also in response to seasonal movements of water driven by local climatic occurrences.     

Core–mantle boundary topography as a possible constraint on lower mantle chemistry and dynamics

The origin of large low shear-wave velocity provinces (LLSVPs) in the lowermost mantle beneath the central Pacific and Africa is not well constrained. We explore numerical convection calculations for two proposed hypotheses for these anomalies, namely, thermal upwellings (e.g., plume clusters) and large intrinsically dense piles of mantle material (e.g., thermochemical piles), each of which uniquely affects the topography on Earth's core–mantle boundary (CMB). The thermochemical pile models predict a relatively flat but elevated CMB beneath piles (presumed LLSVPs), with strong upwarping along LLSVP margins. The plume cluster models predict CMB upwarping beneath upwellings that are less geographically organized. Both models display CMB depressions beneath subduction related downwelling. While each of the two models produces a unique, characteristic style of CMB topography, we find that seismic models will require shorter length scales than are currently being employed in order to distinguish between the end-member dynamic models presented here.     

Black–White and Hispanic–White Segregation in U.S. Counties

Residential segregation in metropolitan areas has been the subject of much research, but this article analyzes patterns of white–black and white–Hispanic segregation in counties across the United States. Our purpose was to understand county variations in this one dimension of inequality. Conceiving of segregation as relative inequality of access to neighborhood resources, we measured segregation in 2000 by the index of dissimilarity (D) calculated by blocks, mapped the index values, and correlated them with census variables. Three filters enabled us to eliminate counties with characteristics that could have corrupted the analyses, leaving us with more than 1,000 counties in each analysis. Both minority groups were less segregated from whites in the West and South and in metropolitan counties. Lower segregation was strongly associated with higher minority socioeconomic status and higher percentages of minorities living in housing built in the 1990s, and Hispanic–white segregation was lower where more Hispanics were U.S.-born or English proficient. The racial threat hypothesis was supported only weakly and inconsistently. Mapping made it possible to identify regional and local patterns of high and low segregation as well as the lower segregation of suburban counties in some large metropolitan areas.     

Using GIS and large-scale digital data to implement hedonic pricing studies

This paper describes how a standard GIS package can be used to convert large-scale vector digital data (point, line and annotation features) into polygons using standardised and replicable methods. Building area, garden and land use polygons are all derived from such data (Ordnance Survey LandLine.Plus). These entities are then combined with further sources of digital data to derive more refined information such as property types. Finally, complex DEMs are developed for use in visibility studies. The variables calculated are subsequently employed in a property valuation study where many are found to be significant determinants of property price. The main exception is variables relating to viewsheds, although it is argued that this does not invalidate the techniques used in their deviation but highlights the difficulties involved in modelling a large number of variables in a property price analysis.