Human Modification of the Geomorphically Unstable Salt River in Metropolitan Phoenix

In‐stream gravel mining, massive bridge piers, and channelization have all contributed to the geomorphic instability of the Lower Salt River channel in Arizona. Dam closure, changing dam operating rules, and the frequent modification of the channel bed have decreased our ability to predict the Salt River hydrology. Engineering practice has adapted to this situation and to a public that is increasingly intolerant of service disruptions by constructing larger bridges and extending levees. Building these larger structures may be counterproductive; future construction should not constrict the channel and should re‐establish a braided river to decrease the energy available to the system.     

Floodplain–river ecosystems: lateral connections and the implications of human interference

Floodplains are ecotones that form a transition between aquatic and terrestrial environments. These important ecosystems can be described as dynamic spatial mosaics in which water plays an important role in connecting various patches on the floodplain surface. Hydrological connections facilitate the exchange of carbon and nutrients between the river channel and the floodplain and therefore influence the productivity of the entire river system. This paper examines the influence of hydrological connections on the potential exchange of dissolved organic carbon between a large Australian floodplain to a river channel, and the effects of land and water developments on these exchanges. The paper proposes that an understanding of floodplain ecosystems requires an interdisciplinary approach—a recognition of the importance of the three disciplines hydrology, geomorphology and ecology. Large-scale water-resources and floodplain development has significantly altered the spatial and temporal patterns of hydrological characteristics in the Lower Balonne floodplain, Australia. The magnitude, frequency and duration of flooding events have all been reduced. The construction of levees and water storages has also reduced the reactive floodplain surface area. The presented data show the impacts of these changes on the potential supply of dissolved organic carbon from the floodplain surface during periods of inundation. Annual reductions of up to 1293 tonnes of dissolved organic carbon supply were noted and reductions were especially significant for floods with an average recurrence interval of 2 years or less. Some small flood events no longer facilitate the potential supply of dissolved organic carbon from the floodplain to the river channel because of water-resources and floodplain developments.     

The BEAM-project: prediction and assessment of mixture toxicities in the aquatic environment

Freshwater and marine ecosystems are exposed to various multi-component mixtures of pollutants. Nevertheless, most ecotoxicological research and chemicals regulation focus on hazard and exposure assessment of individual substances only, the problem of chemical mixtures in the environment is ignored to a large extent. In contrast, the assessment of combination effects has a long tradition in pharmacology, where mixtures of chemicals are specifically designed to develop new products, e.g. human and veterinary drugs or agricultural and non-agricultural pesticides. In this area, two concepts are frequently used and are thought to describe fundamental relationships between single substance and mixture effects: Independent Action (Response Addition) and Concentration Addition. The question, to what extent these concepts may also be applied in an ecotoxicological and regulatory context may be considered a research topic of major importance, as the concepts would allow to make use of already existing single substance toxicity data for the predictive assessment of mixture toxicities. Two critical knowledge gaps are identified: (a) There is a lack of environmental realism, as a huge part of our current knowledge about the applicability of the concepts is restricted to artificial situations with respect to mixture composition or biological effect assessment. (b) The knowledge on what exactly is needed for using the concepts as tools for the predictive mixture toxicity assessment is insufficient. Both gaps seriously hamper the necessary, scientifically sound consideration of mixture toxicities in a regulatory context.In this paper, the two concepts will be briefly introduced, the necessity of considering the toxicities of chemical mixtures in the environment will be demonstrated and the applicability of Independent Action and Concentration Addition as tools for the prediction and assessment of mixture toxicities will be discussed. An overview of the specific aims and approaches of the BEAM project to fill in the identified knowledge gaps is given and first results are outlined.     

Mid‐Holocene sub‐blanket‐peat alluvia and sediment sources in the upper Liffey valley,Co. Wicklow,Ireland

A recently exposed section across a ?rst‐order valley buried beneath the regional blanket peat on hillside slopes in the upper Liffey valley, Co. Wicklow, is described. The section shows two alluvia within a shallow valley form underlain by an extensive boulder and stone line over regional till and weathered granite. ¹⁴C dates from wood in the alluvia indicate the older alluvium to have formed between 4324 ± 53 BP and 4126 ± 45 BP and the younger between 3217 ± 53 BP and 2975 ± 53 BP . The basal layer of the overlying peat yielded a date of 2208 ± 61 BP . The younger alluvium shows the effects of soil paludi?cation prior to the peat expansion. Dated pollen analyses elsewhere in the upper catchment con?rm the spread of blanket peat over most areas above 350 m after 4000–3600 BP . The buried valley was contributing sediments to the mid‐Holocene ?oodplains in the upper Liffey valley prior to the extension of blanket peat over the catchment after which sediment yields from it and the other catchment slopes declined. Copyright © 2003 John Wiley & Sons, Ltd.     

Characterisation of the Dabla Granitoids, North Khetri Copper Belt, Rajasthan, India: Evidence of Bimodal Anorogenic Felsic Magmatism

The Palaeoproterozoic Dabla granitoid pluton of the North Khetri Copper Belt is located to the east of a NNE-SSW trending lineament with numerous albite-rich intrusives, the intraplate ‘albitite line’. The Dabla pluton is essentially made up of calcic amphibole-bearing granitoids, displaying a concentric bimodal distribution of alkali-feldspar granites, comprising a microcline-albite granite and an albite-granite. The dominant rock type is pink-coloured granite, which is characterised by quartz, microcline, albite and hastingsitic hornblende, and occurs in the marginal parts of the pluton. The volumetrically subordinate albite-granite in the central part of the pluton is invariably white in colour, non-foliated and is mainly composed of quartz, albite and amphibole of actinolite to ferro-actinolite composition. The albite-granite is characterised by low K₂O (0.06-0.09%), Rb (<5 ppm) and Ba (<20 ppm), high Na₂O (7.19-7.36%) and high Na/K ratios (122.4-185.2) as compared to the granite. These rocks are not subjected to any metamorphic overprint, especially the albite-granite, which shows pristine abundances of major and trace elements. The rocks are highly evolved as reflected in their high SiO₂ (72 to 78%) contents and high DI (89.5-97) values. The Dabla granitoids are characterised by similar REE and spider patterns, displaying LREE enriched slopes, flat HREE profiles and strong negative Sr, P, Ti and Eu anomalies suggesting their comagmatic nature. Nevertheless, the granite is relatively more fractionated [(La/Yb)_N = 3.89-8.19] and show higher REE abundances (466-673 ppm) as compared to the albite-granite [(La/Yb)_N = 1.97-2.96; REE = 220-277 ppm]. Distinctive features of these rocks are their low Ca (0.21-1.53%), Mg (<0.02-0.19%), Al (11.84-12.96%) and Sr (12-46 ppm) abundances, high Zr (155-631 ppm), Y (67-156 ppm), Nb (14-91 ppm), and Ga (20-31 ppm) concentrations and high Fe*-number, high Ga/Al ratio and high agpaitic index (AI) values. These features, coupled with their ferroan, alkaline and metaluminous nature, are typical of within-plate aluminous A-type granites. The geochemical data further indicate that the Dabla magma was generated at fairly high temperature, apparently in an upper mantle region, under relatively low H₂O activities and reduced conditions and emplaced at a shallow depth in an extensional tectonic environment.     

Compression mechanisms of coesite

 The structure of coesite has been determined at ten pressures up to a maximum of 8.68 GPa by single-crystal X-ray diffraction. The dominant mechanism of compression is the reduction of four of the five independent Si–O–Si angles within the structure. There is no evidence of the fifth linkage, Si1–O1–Si1, deviating from 180°. Some Si–O bond distances also decrease by up to 1.6% over the pressure range studied. The pattern of Si–O–Si angle reduction amounts to a rotation of the Si2 tetrahedron around the [001] direction. This rotation induces significant internal deformation of the Si1 tetrahedron. Comparison of the experimental data with rigid-unit distance least-squares simulations of coesite suggests that this pattern of compression, the anomalous positive values of both s₂₃ and K′′ in the equation of state of coesite, its high elastic anisotropy and the unusual straight Si1–O1–Si1 linkage within the structure are all consequences of the connectivity of the tetrahedral framework. Received: 11 July 2002 / Accepted: 14 January 2003 Acknowledgements The help of Christian Baerlocher of ETH Zurich in providing both the DLS-76 software and advice in its use is gratefully acknowledged, as are discussions with Paul Ribbe of Virginia Tech and the comments of two anonymous reviewers. The data analysis was supported by the National Science Foundation under grant EAR-0105864 to N.L. Ross and R.J. Angel.     

Kinematics of throughgoing fractures in jointed rocks

Throughgoing fractures play a major role in subsurface fluid flow yet the kinematics of their formation, which directly impact rock flow properties, are often difficult to establish. We investigate throughgoing fractures in the Monterey Formation of California that developed by the coalescence of pre-existing joints. At Lompoc Landing, throughgoing fractures fall into three main groups: linked, linked with aperture, and breccia zones. The segmented nature of their walls provides numerous piercing points to firmly establish the sense of displacement. Analysis of displacement vectors derived from piercing points demonstrates that the NW–SE trending throughgoing fractures, often interpreted as strike–slip faults, are in fact extensional structures in origin. We suggest that this method may be applied to throughgoing fractures that form by the same mechanism in other geologic settings. Establishing kinematics of throughgoing fractures will lead to a better understanding of their contribution to subsurface fluid flow.     

Phytolith analysis from the archaeological site of Kush, Ras al-Khaimah, United Arab Emirates

Despite the wealth of archaeological sites and excellent conditions for preservation, few phytolith investigations have been undertaken from the Arabian Gulf region. The results from the Sasanian and Islamic archaeological tell of Kush, Ras al-Khaimah, United Arab Emirates, are presented. Kush is situated just inside the Gulf on an important trade route. The occupation sequence dates from the 4^th century A.D. until the 13^th century A.D., recording the development of the site in the Sasanian period, followed by the arrival of Islam in the 7^th century A.D. and the final abandonment of the site in the late 13^th century when the nearby site of al-Mataf (Julfar) began to develop closer to the present day coastline. All the samples analyzed contained abundant phytoliths (short cells, elongated cells, and groups of elongated cells) of various types. They included date palm (Phoenix dactylifera), papillae (possibly from barley (Hordeum)), and hair cells possibly from species of canary grass (Phalaris spp.). Some researchers have suggested that groups of elongated cells may indicate the presence of irrigation in semiarid environments. The present results for this class of phytoliths appeared to imply that intensive irrigation was unlikely to have taken place around Kush.     

Evidence for a large surface ablation zone in central East Antarctica during the last Ice Age

Internal isochronous ice sheet layers, recorded by airborne ice-penetrating radar, were measured along an ice flowline across a large (>1 km high) subglacial hill in the foreground of the Transantarctic Mountains. The layers, dated through an existing stratigraphic link with the Vostok ice core, converge with the ice surface as ice flows over the hill without noticeable change to their separation with each other or the ice base. A two-dimensional ice flow model that calculates isochrons and particle flowpaths and accounts for ice flow over the hill under steady-state conditions requires net ablation (via sublimation) over the stoss face for the predicted isochrons to match the measured internal layers. Satellite remote sensing data show no sign of exposed ancient ice at this site, however. Given the lack of exposed glacial ice, surface balance conditions must have changed recently from the net ablation that is predicted at this site for the last 85,000 years to accumulation.