Field determination of the water balance of the Areuse River delta,Switzerland

Abstract

The water balance during a period of one year (15 October 1990–15 October 1991) was determined at an experimental site in the Areuse River delta (Switzerland). The groundwater recharge rates were found to be 36 and 33% of total precipitation according to evapotranspiration estimates based on the Primault (1962) and the Penman-Monteith methods, respectively. Variations in the water storage were obtained by weekly measurements with a neutron probe. Observed hydraulic gradients indicated a zero-flux plane between depths of 0.55 and 1.02 m that separated the infiltration zone from the zone of evapotranspiration in all seasons.     

Synoptic climatology of Northern Hemisphere available potential energy collapses

Three recurring regional patterns of extratropical baroclinic development associated with synoptic‐scale collapses of Northern Hemisphere available potential energy (APE) are identified using a 1979–95 time series derived from the National Centers for Environmental Prediction (NCEP) reanalysis. A time series of the intraseasonal signal (from 1.6 to 180 days) of APE is used to discern an average cycle of approximately 3 days in the APE generation rate d A /d t (referred to as APE depletion rate if negative). An APE depletion event is defined as a fall and subsequent rise in the time series of d A /d t associated with this cycle. We define synoptic‐scale APE collapses as APE depletion events with maximum depletion rates (d A /d t _min) and maximum APE falls (Δ A _min) of less than −0.145× 10⁶ J m⁻² day⁻¹ and −0.280×10⁶ J m⁻², respectively. All are cold season (15 October–15 April) events. APE collapses were classified based on the evolution of regional synoptic patterns during the 2 days centered at the time of d A /d t _min . All are accompanied by deep tropospheric warming. The west Pacific warm surge (Type A) is driven by cyclogenesis over Japan and anticyclogenesis over the west‐central North Pacific. The Bering warm surge (Type B) is associated with an intense southerly flow across the Bering Strait brought on by cyclogenesis near the Kamchatka Peninsula and an intense anticyclone over Alaska. The Atlantic Canada warm surge (Type C) is characterized by an onshore flow of warm air ahead of a continental storm track over eastern North America.     

Corundum-bearing residues produced through the evaporation of natural and synthetic hibonite

Abstract— We have produced corundum-bearing residues through the evaporation of natural and synthetic hibonite samples. The sequence of major element losses as well as volatility related trace element fractionations in these residues are similar to those previously observed in residues from the evaporation of chondritic starting material, which suggests that the processes by which these fractionations occur may be largely independent of the starting material used. However, the mineralogy of the residues does depend on the composition of the starting material and, to some extent, on the conditions under which evaporation took place. Similarly, the degree of isotopic mass fractionation observed in the residues is composition-dependent. This observation means that it may be possible to use isotopic data for several elements to constrain the compositions of precursor materials of Ca-Al-rich inclusions, which have an evaporation origin. Although corundum-bearing inclusions are known, their origins are complex and variable, and the scarcity of such inclusions indicates that melting of hibonite, with or without concomitant evaporation, must have been a rare process in the solar nebula. By evaporating mixtures of synthetic oxides of the rare earth elements, we have reproduced the patterns of Group III inclusions and some of the characteristics of ultrarefractory patterns. However, the extreme conditions required to do so indicate that refractory inclusions with these patterns probably have a condensation rather than evaporation origin.     

THE SENSITIVITY OF TWO DISTRIBUTED NON-POINT SOURCE POLLUTION MODELS TO THE SPATIAL ARRANGEMENT OF THE LANDSCAPE

Distributed hydrological models are becoming increasingly complex with respect to spatial phenomena, and with the widespread availability of spatial data from GIS, this trend is likely to increase. In all such models the spatial arrangement of phenomena, such as soil properties and land-use categories is fundamental, and so the arrangement should have an influence on the model output. Testing for this influence we term spatial sensitivity analysis. Here, we report on the spatial sensitivity of two widely used models, AgNPS (agricultural non-point source pollution model) and ANSWERS (areal nonpoint source watershed environment response simulation). The input spatial data were subjected to spatially random mixing to varying degrees, such that the organized landscape became disorganized. The chemical discharge from AgNPS, and the sediment and water discharge from ANSWERS, are examined. In both cases most outputs exhibited little or no sensitivity to the spatial distribution of most input data. Only infiltration-related inputs produced large variations, but these changes were not in the sense that might have been predicted. Although the analytical methods used require further refinement, there must now be some doubt as to the validity of the models, and whether they repay their computational complexity. Furthermore, it is felt that spatial sensitivity analysis should become a fundamental part of the verification of all such models. © 1997 by John Wiley & Sons, Ltd.     

Logging in deep water wells in central Jutland, Denmark

During a search for unpolluted resources, new wells have been drilled to a deep confined aquifer in central Jutland. Since little is known about the extent and vulnerability of the deep reservoir, geophysical logging was used to supplement hydraulic well-testing. Gamma-ray, SP and resistivity logs were recorded in the boreholes. Gamma-logs were also recorded in two cased wells. Analysis of the logs, combined with information from samples, shows an unconfined aquifer of quartz and mica sand to a depth of about 55 m at Grindsted. Below this level there is a 40 m thick aquitard with an apparent southerly dip. The aquitard is composed of interbedded sand, silt and clay. The deep confined aquifer extends from 95 to 110 m below the surface at Grindsted. Both the aquitard and the deep aquifer are provisionally dated as Early/Middle Miocene. The electrical logs discriminate well between sand, silt and clay beds. If a suitable mud is used in the well it is possible to calculate the formation water resistivities in good agreement with water samples obtained after completion. From the resistivity logs formation factors were calculated in the range 3–5 using no-invasion departure curves. The high content of heavy mineralsin the Tertiary deposits makes it impossible to obtain precise lithological information from the gamma-ray log. On the other hand this log provides clear markers for identifying the hydrogeological units in the well-bores.     

THE EFFECT OF SYNOPTIC SCALE WEATHER SYSTEMS ON SUB‐SURFACE SOIL TEMPERATURES IN A DIURNAL FROST ENVIRONMENT: PRELIMINARY OBSERVATIONS FROM SUB‐ANTARCTIC MARION ISLAND

Marion Island in the South Indian Ocean has a maritime climate dominated by diurnal frost processes in the landscape. We test the hypothesis that synoptic time‐scale measurements are essential in understanding the drivers of diurnal frost processes. Preliminary results from automated microclimate measurements in a polar desert habitat show that diurnal soil surface temperatures on Marion Island are influenced by a complex interaction of radiation balance, air mass circulation, cloud cover and snow. The passage of synoptic scale weather systems influences soil thermal characteristics through changes in dominance of the radiation budget. Soil frost on Marion appears to be dependent on clear skies, while synoptic weather systems affect the duration and intensity of soil frost processes and non‐radiative heat fluxes. Air circulation patterns at Marion Island influence diurnal scale temperature fluctuations and its direct and indirect interactions with ecosystem processes. The data suggest that in a maritime sub‐Antarctic environment the climatic drivers of soil frost occur at a finertemporal resolution than for seasonal and permafrost environments and needs to be measured at a diurnal time‐scale to be meaningful.     

The Cocos and Carnegie Aseismic Ridges: a Trace Element Record of Long-term Plume-Spreading Center Interaction

The aseismic Cocos and Carnegie Ridges, two prominent bathymetricfeatures in the eastern Pacific, record 20 Myr of interactionbetween the Galápagos hotspot and the adjacent GalápagosSpreading Center. Trace element data determined by inductivelycoupled plasma-mass spectrometry in >90 dredged seamountlavas are used to estimate melt generation conditions and mantlesource compositions along the ridges. Lavas from seamount provinceson the Cocos Ridge are alkalic and more enriched in incompatibletrace elements than any in the Galápagos archipelagotoday. The seamount lavas are effectively modeled as small degreemelts of a Galápagos plume source. Their eruption immediatelyfollows the failure of a rift zone at each seamount province'slocation. Thus the anomalously young alkalic lavas of the CocosRidge, including Cocos Island, are probably caused by post-abandonmentvolcanism following either a ridge jump or rift failure, andnot the direct activity of the Galápagos plume. The seamountshave plume-like signatures because they tap underlying mantlepreviously infused with Galápagos plume material. Whereasplume heterogeneities appear to be long-lived, tectonic rearrangementsof the ridge plate boundary may be the dominant factor in controllingregional eruptive behavior and compositional variations. KEY WORDS: mantle plume; mid-ocean ridge; Galápagos; abandoned rift; partial melting of the mantle     

Effect of Clay Minerals on Transport of Surfactants Dispersed Multi-walled Carbon Nanotubes in Porous Media

Clay minerals can hinder the transport of various contaminants in soil and aquifer, but how clay minerals affect the transport of nanoparticles in aquifers has not been investigated in depth. In this paper, the transport of surfactants dispersed multi-walled carbon nanotubes (MWCNTs) in well-defined quartz sand and mixtures of quartz sand and clay minerals (kaolinite and montmorillonite) with varying ionic strengths was studied. Sodium dodecyl benzenesulfonate (SDBS) and octyl-phenol-ethoxylate (TX100) MWCNT suspensions can migrate through quartz sand easily, but the presence of less than 2% w/w clay minerals in quartz sand can significantly hinder the transport of MWCNT suspensions, especially at high ion strength (0.6 mM CaCl2). The inhibition mechanism of clay minerals for surfactant-dispersed MWCNTs in porous media is the interception of MWCNTs. Kaolinite has stronger inhibition effect for MWCNTs transport than montmorillonite because more kaolinite can be retained in the quartz sand. Adsorption of surfactants by clay minerals does not affect the transport of MWCNTs significantly. This finding is important for the environmental assessment of MWCNT transport risks in soils and aquifers.     

Low-Temperature, Low-Pressure Metamorphism of Mn-rich Rocks in the Lienne Syncline, Venn--Stavelot Massif (Belgian Ardennes), and the Role of Carpholite

Low-grade Mn-rich metamorphic rocks of the Lienne syncline (westernpart of the Venn–Stavelot Massif, Belgian Ardennes) havebeen re-examined to evaluate the petrological significance ofcarpholite proper, Mn^2$ Al₂[Si₂O₆](OH)₄. Metamorphic P–Tconditions of these rocks are estimated to be {small tilde}300C1–2 kbar, which is in accordance with the exclusive occurrenceof carpholite in low-P rocks such as hydrothermal environmentselsewhere. Carpholite of the Lienne syncline exclusively occursin quartz-rich segregations. Its composition is close to end-member.Thermodynamic calculations confirm that carpholite is a stablephase at low-pressure–low-temperature conditions, in contrastto ferro- and magnesiocarpholite, which are high-pressure minerals.No information is available on the high-P behaviour of carpholite.The occurrence of carpholite is partly closely associated withspessartine-bearing country rocks, or carpholite is alteredto assemblages with spessartine, sudoite, chlorite, muscoviteand paragonite. Spessartine in these rocks contains minor amountsof hydrogarnet component {(H/4)/[Si$(H/4)] = 0.03–0.06}.The presence of carpholite-spessartine assemblages in theselow-P rocks is in contrast to high-pressure metamorphic rocksfrom other areas, where parageneses such as fem/magnesiocarpholite–chloritoidor magnesiocarpholite–chlorite–kyanite occur. Theappearance of carpholite–garnet assemblages in low-P Mn-richrocks can be explained by contrasting phase relations becauseof a high Mn–Mg partition coefficient between the mineralsunder consideration. In rhodo-chrosite-bearing veins in theLienne syncline, nearly complete replacement of carpholite byspessartine and chlorite is due to the continuous reaction carpholite$ rhodochrosite $ quartz = spessartine $ chlorite $ H₂O $ CO₂,which defines a very low X_co, in the temperature range underconsideration. It is suggested that spessartine (possibly containingsome hydrogarnet component), during prograde metamorphism atlow pressure, becomes stable at a temperature of {small tilde}300C KEY WORDS: carpholite; spessartine; sudoite; Venn–Stavelot Massif; Ardemes ^*Corresponding author. Fax: x49/531/3918131. e-mail: t.theye{at}tu.bs.de