Trace metals and radionuclides reveal sediment sources and accumulation rates in Jordan Cove, Connecticut

Many small estuaries are influenced by flow restrictions resulting from transportation rights-of-way and other causes. The biogeochemical functioning and history of such systems can be evaluated through study of their sediments. Ten long and six short cores were collected from the length of Jordan Cove, Connecticut, a Long Island Sound subestuary, and analyzed for stratigraphy, radionuclides (¹⁴C, ²¹⁰Pb, ²²⁶Ra, ¹³⁷Cs, and ⁶⁰Co), and metals (Ag, Cd, Cu, Pb, Zn, Fe, and Al). For at least 3,800 yr, rising sea level has gradually inundated Jordan Cove, filling it with mud similar to that currently being deposited there. Long-term sediment accumulation in the cove averaged close to 0.1 cm yr⁻¹ over the last three millennia. Recent sediment accumulation rates decrease inland from 0.84 cm yr⁻¹ to 0.40 cm yr⁻¹, and are slightly faster than relative sea-level rise at this site (0.3 cm yr⁻¹). Similarity of depth distributions of trace metals was used to confirm relative sediment accumulation rates. ⁶⁰Co and Ag are derived from sources outside the cove and its watershed, presumably the Millstone nuclear power plant and regional contaminated sediments, respectively. The combined data suggest that Long Island Sound is an important source of sediment to the cove; a minor part of total sediment is supplied from the local watershed. Trace metal levels are strongly correlated with Fe but not with either organic matter or Al. Sediment quality has declined in the cove over the past 60 yr, but only slightly. Cu, Pb, and Zn data correlate strongly with Fe but not with either organic matter or aluminum. Ratios of Ag to Fe and to trace metals suggest that Ag in the cove is derived almost entirely from Long Island Sound. This result supports the notion that Fenormalized Ag can serve as a better tracer of some kinds of contamination than more common and abundant metals, like Cu, Pb, and Zn. *** DIRECT SUPPORT *** A01BY085 00008     

Development of a continuous soil moisture accounting procedure for curve number methodology and its behaviour with different evapotranspiration methods

The curve number (CN) method is widely used for rainfall–runoff modelling in continuous hydrologic simulation models. A sound continuous soil moisture accounting procedure is necessary for models using the CN method. For shallow soils and soils with low storage, the existing methods have limitations in their ability to reproduce the observed runoff. Therefore, a simple one‐parameter model based on the Soil Conservation Society CN procedure is developed for use in continuous hydrologic simulation. The sensitivity of the model parameter to runoff predictions was also analysed. In addition, the behaviour of the procedure developed and the existing continuous soil moisture accounting procedure used in hydrologic models, in combination with Penman–Monteith and Hargreaves evapotranspiration (ET) methods was also analysed. The new CN methodology, its behaviour and the sensitivity of the depletion coefficient (model parameter) were tested in four United States Geological Survey defined eight‐digit watersheds in different water resources regions of the USA using the SWAT model. In addition to easy parameterization for calibration, the one‐parameter model developed performed adequately in predicting runoff. When tested for shallow soils, the parameter is found to be very sensitive to surface runoff and subsurface flow and less sensitive to ET. Copyright © 2007 John Wiley & Sons, Ltd.     

Petroleum geoscience in Norden - exploration, production and organization

Offshore exploration in Norway and Denmark-in the North Sea, the Norwegian Sea and the Barents Sea-has involved drilling about 850 wildcat wells, resulting in about 300 oil and gas finds, of which 84 are fields with production. The recoverable resources of all these finds total about 65 billion barrels of oil equivalent. Almost all these hydrocarbons come from a Jurassic source and the main reservoirs and traps are Jurassic sandstones in fault blocks and Paleocene sandstones or Cretaceous chalks in gentle domes. The article describes four major fields-Ekofisk, Gullfaks, Ormen Lange and SnФhvitto illustrate some of the many challenges in developing and producing the hydrocarbons.
Elsewhere in Norden, there has been much less exploration. Drilling results have mostly been negative in mainland Sweden, onshore Denmark, onshore Svalbard and on- and offshore West Greenland. Minor oil finds have been made in Palaeozoic rocks in the Baltic Sea. The first wells have recently been drilled off the Faroe Islands, resulting in one discovery. No drilling has taken place on- or offshore East Greenland.
As a result of the hydrocarbon activities in Norway and Denmark, petroleum geoscience there has flourished, with 2000 geoscientists currently employed in the industry, many technical innovations made, a wealth of publically available information and a great increase in the understanding of the geology.     

Modalités de recharge d’un aquifère en zone semi-aride : cas de la nappe du Trarza (Sud-Ouest Mauritanie)

Résumé

L’aquifère du Trarza s’étend sur environ 40 000 km² dans le Sud-Ouest mauritanien, entre le fleuve Sénégal au Sud, l’Océan Atlantique à l’Ouest et la chaîne métamorphique des Mauritanides au Nord et à l’Est. La nappe libre est contenue dans les sédiments du Continental Terminal et du Quaternaire. Les campagnes de terrain menées entre 2010 et 2012 ont significativement complété les quelques mesures anciennes. Le croisement d’approches hydrodynamiques et géochimiques a montré que, dans cette zone semi-aride, la dynamique de la nappe est influencée par les multiples changements, actuels et anciens, de l’environnement (depuis les transgressions quaternaires jusqu’aux différents barrages régulant le cours du fleuve Sénégal). La nappe est principalement alimentée par l’infiltration latérale des eaux de surface du fleuve Sénégal et, dans une moindre proportion, par les précipitations. La minéralisation des eaux souterraines résulte d’interactions eau-roches et minéraux silicatés et alumino-silicatés et est localement influencée par des traces des transgressions quaternaires. L’évaporation marque fortement les eaux de surface avant et durant leur infiltration. Des calculs encore très préliminaires suggèrent une recharge annuelle inférieure ou égale à 5% des précipitations, soit de 5 à 10 mm.

Editeur Z.W. Kundzewicz

Citation Mohamed, A.-S., Marlin, C., Leduc, C., et Jiddou, M., 2014. Modalités de recharge d’un aquifère en zone semi-aride: cas de la nappe du Trarza (Sud-Ouest Mauritanie). Hydrological Sciences Journal, 59 (5), 1046–1062.     

Volatile-induced transport of HFSE, REE, Th and U in arc magmas: evidence from zirconolite-bearing vesicles in potassic lavas of Lewotolo volcano (Indonesia)

Potassium-rich calc-alkaline lavas of Lewotolo volcano, situated in the East Sunda Arc, Indonesia, contain the rare mineral zirconolite (CaZrTi₂O₇). Samples in which tiny grains of this mineral (3–25 μm in size) were found span the entire range of lava compositions (47–62 wt% SiO₂). To the best of our knowledge, this is the first record of primary zirconolite in juvenile arc volcanics. The mineral forms part of a vesicle-filling assemblage consisting of a network of quenched feldspar crystals and an SiO₂ phase, probably cristobalite. High contents of Th, U and REE (up to 9.3, 4.3 and 15.6 wt% oxide respectively) and very high Fe contents (up to 13.5 wt% Fe₂O₃) distinguish these zirconolites from those of other rock types. The extraction of volatile-rich phases with changing compositions in successive stages is considered to be responsible for the zirconolite formation. We hypothesise that a fluid capable of transporting HFSE, REE, Th and U was extracted from the magma and (partly) crystallised within voids which had formed earlier upon saturation of an aqueous fluid. Assuming that zirconolite compositions largely reflect trace metal contents of the coexisting fluid phase, significant amounts of `immobile' elements must have been transported on a macroscopic scale. Our findings thus point to a late-stage transfer of HFSE, REE, Th and U between different domains in a cooling magma body. Such a volatile-induced redistribution of trace elements at shallow levels of high-K volcanic systems may be significant for conventional geochemical modelling of magma evolution and for Th–U disequilibrium studies. Received: 3 November 1999 / Accepted: 29 February 2000     

Practical Postcalibration Uncertainty Analysis: Yucca Mountain, Nevada

The values of parameters in a groundwater flow model govern the precision of predictions of future system behavior. Predictive precision, thus, typically depends on an ability to infer values of system properties from historical measurements through calibration. When such data are scarce, or when their information content with respect to parameters that are most relevant to predictions of interest is weak, predictive uncertainty may be high, even if the model is "calibrated." Recent advances help recognize this condition, quantitatively evaluate predictive uncertainty, and suggest a path toward improved predictive accuracy by identifying sources of predictive uncertainty and by determining what observations will most effectively reduce this uncertainty. We demonstrate linear and nonlinear predictive error/uncertainty analyses as applied to a groundwater flow model of Yucca Mountain, Nevada, the United States' proposed site for disposal of high-level radioactive waste. Linear and nonlinear uncertainty analyses are readily implemented as an adjunct to model calibration with medium to high parameterization density. Linear analysis yields contributions made by each parameter to a prediction's uncertainty and the worth of different observations, both existing and yet-to-be-gathered, toward reducing this uncertainty. Nonlinear analysis provides more accurate characterization of the uncertainty of model predictions while yielding their (approximate) probability distribution functions. This article applies the above methods to a prediction of specific discharge and confirms the uncertainty bounds on specific discharge supplied in the Yucca Mountain Project License Application.     

Diatom-inferred depth models in 8 Canadian boreal lakes: inferred changes in the benthic:planktonic depth boundary and implications for assessment of past droughts

Assessment of past drought in boreal regions, a region predicted to be strongly affected by climate warming, can provide insights into future availability of water. However, limited instrumental data and paleoclimatic data are available for this assessment. To address this lack of data in the boreal region of northwest Ontario, a regional study of lakes in the Winnipeg River Drainage Basin was initiated. Diatom-inferred (D-I) depth models were developed based on surface samples collected along a depth gradient within 8 small boreal lakes. Weighted-averaging and modern analog approaches provided robust within-lake depth models for each of the study lakes, with bootstrapped r² values ranging from 0.90 to 0.98, and root-mean-squared-errors of prediction (RMSEP) between 1.1 and 2.5 m. Large differences in the estimated depth optima for three representative, but common diatom species across our 8 study lakes suggested that within-lake calibration datasets are more appropriate for inferring past drought based in depth models than a regional multi-lake calibration dataset, and that light and related variables are controlling factors governing the maximum depth of benthic taxa. A down-core application of the D-I depth models on a near-shore core from Meekin Lake, retrieved near the present-day ecotone between the benthic and planktonic diatom assemblages indicated highly similar trends in inferred depth (r = 0.96). The models have significant correlations with other metrics of changes in depth including diatom species richness (r = 0.74–0.78) and evenness (r = 0.76–0.8), thereby allowing a check on the strength and direction of the depth inferences down-core. Near-shore cores located near the benthic:planktonic transition is a sensitive region that can provide estimates of past droughts in lakes where such inferences have been difficult to estimate.     

Revisiting the death of geography in the era of Big Data: the friction of distance in cyberspace and real space

Many scholars have argued that the importance of geographic proximity in human interactions has been diminished by the use of the Internet, while others disagree with this argument. Studies have noted the distance decay effect in both cyberspace and real space, showing that interactions occur with an inverse relationship between the number of interactions and the distance between the locations of the interactors. However, these studies rarely provide strong evidence to show the influence of distance on interactions in cyberspace, nor do they quantify the differences in the amount of friction of distance between cyberspace and real space. To fill this gap, this study used massive amounts of social media data (Twitter) to compare the influence of distance decay on human interactions between cyberspace and real space in a quantitative manner. To estimate the distance decay effect in both cyberspace and real space, the distance decay function of interactions in each space was modeled. Estimating the distance decay in cyberspace in this study can help predict the degree of information flow across space through social media. Measuring how far ideas can be diffused through social media is useful for users of location-based services, policy advocates, public health officials, and political campaigners.