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La Notte A.,European Commission - Joint Research Center Ispra | Maes J.,European Commission - Joint Research Center Ispra | Grizzetti B.,European Research Council Executive Agency | Bouraoui F.,European Commission - Joint Research Center Ispra | Zulian G.,European Commission - Joint Research Center Ispra
International Journal of Biodiversity Science, Ecosystems Services and Management | Year: 2012

This case study tested an approach for large-scale monetary valuation of water purification services based on spatially explicit, biophysical mapping of nitrogen retention in river networks. The study area for the case study was the Mediterranean bio-geographical region. The monetary value of nitrogen retention was assessed using replacement costs (RCs), based on the construction, operation and maintenance of constructed wetlands (CWs). The value of nitrogen retention by rivers in 2005 was estimated at €2167 km-1, on average. If the capacity or the potential of rivers and lakes to retain nitrogen was considered, the monetary value was €35,000 km-1 on average, much higher than the effective retention. The coupling between a biophysical model simulating the transport and retention of nitrogen in the aquatic environment and monetary estimates of potential and realized nitrogen removal resulted in detailed spatial information of one of the benefits that are provided by rivers and streams. © 2012 Taylor & Francis. Source

Herrero-Bervera E.,University of Hawaii at Manoa | Krasa D.,European Research Council Executive Agency | Van Kranendonk M.J.,University of New South Wales
Physics of the Earth and Planetary Interiors | Year: 2016

We have conducted a whole-rock type magnetic and absolute paleointensity determination of the red dacite of the Duffer Formation from the Pilbara Craton, Australia. The age of the dated rock unit is 3467 ± 5 Ma (95% confidence). Vector analyses results of the step-wise alternating field demagnetization (NRM up to 100 mT) and thermal demagnetization (from NRM up to 650 °C) yield three components of magnetization. Curie point determinations indicate three characteristic temperatures, one at 150–200 °C, a second one at ∼450 °C and a third one at ∼580 °C. Magnetic grain-size experiments were performed on small specimens with a variable field translation balance (VFTB). The coercivity of remanence (Hcr) suggests that the NRM is carried by low-coercivity grains that are associated with a magnetite fraction as is shown by the high-temperature component with blocking temperatures above 450 °C and up to at least 580 °C. The ratios of the hysteresis parameters plotted as a modified Day diagram show that most grain sizes are scattered within the Single Domain (SD) and the Superparamagnetic and Single Domain SP-SD domain ranges. In addition to the rock magnetic experiments we have performed absolute paleointensity experiments on the samples using the modified Thellier-Coe double heating method to determine the paleointensities. Partial-TRM (p-TRM) checks were performed systematically to document magnetomineralogical changes during heating. The temperature was incremented by steps of 50 °C between room temperature and 590 °C. The paleointensity determinations were obtained from the slope of Arai diagrams. Our paleointensity results indicate that the paleofield obtained was ∼6.4 ± 0.68 (N = 11) micro-Teslas with a Virtual Dipole Moment (VDM) of 1.51 ± 0.81 × 1022 Am2, from a medium-to high-temperature component ranging from 300 to 590 °C that has been interpreted to be the oldest magnetization yet recorded in paleomagnetic studies of the Duffer Formation. The absolute paleointensity is relatively low and we interpret this low-paleofield bias a result of a thermochemical remanent magnetization (TCRM) process that indicates a possible underestimate of the paleofield by a factor of four for the red dacite of the Duffer Fm. © 2016 Elsevier B.V. Source

Krasa D.,European Research Council Executive Agency | Muxworthy A.R.,Imperial College London | Williams W.,University of Edinburgh
Geophysical Journal International | Year: 2011

Palaeomagnetic observations are being used in increasingly sophisticated geological and geophysical interpretations. It is therefore important to test the theories behind palaeomagnetic recording by rocks, and this can only be achieved using samples containing precisely controlled magnetic mineralogy, grain size and interparticle spacing, the last of which controls the degree of magnetostatic interactions within the samples. Here we report the room- and low temperature magnetic behaviour of a set of samples produced by the nano-scale patterning technique electron beam lithography. The samples consist of 2-D arrays of near-identical magnetite dots of various sizes, geometries and spatial configurations, with dot sizes from ranging from near the single domain threshold of 74-333 nm. We have made a series of magnetic measurements including hysteresis, first-order-reversal curve measurements and remanence acquisition, many as a function of temperature between 20 and 300 K, to quantify the samples' behaviour to routine palaeomagnetic measurement procedures. We have also examined the behaviour of saturation isothermal remanences (SIRM) to cooling and warming cycling of the sample below room temperature. In addition, we investigated the samples' responses to alternating-field demagnetization of room temperature induced SIRM, anhysteretic remanent magnetization (ARM) and partial ARM. ARM was used as a non-heating analogue for natural thermoremanence. Given the 2-D spatial distribution of the samples, in all the experiments we conducted both in-plane and out-of-plane measurements. Generally, the samples were found to display pseudo-single-domain hysteresis characteristics, but were found to be reliable recorders of weak-field remanences like ARM. For the closely packed samples, the samples' magnetic response was highly dependent on measurement orientation. © 2011 The Authors Geophysical Journal International © 2011 RAS. Source

Grizzetti B.,European Commission - Joint Research Center Ispra | Grizzetti B.,European Research Council Executive Agency | Bouraoui F.,European Commission - Joint Research Center Ispra | Aloe A.,European Commission - Joint Research Center Ispra
Global Change Biology | Year: 2012

During the last decades human activity has altered the natural cycle of nitrogen and phosphorus on a global scale, producing significant emissions to waters. In Europe, the amount of nutrients discharged from rivers to coastal waters as well as the effects of mitigation measures in place are known only partially, with no consistent temporal and spatial cover. In this study, we quantify the loads and concentration of nitrogen and phosphorus discharged in the European seas over the period 1985-2005, and we discuss their impact on coastal ecosystems. To support our analysis, a catchment database covering the whole of Europe was developed together with data layers of nutrients diffuse and point sources, and the statistical model green was used to estimate the annual loads of nitrogen and phosphorus discharged in all European seas. The results of this study show that during the last 20 years, Europe has discharged 4.1-4.8 Tg yr -1 of nitrogen and 0.2-0.3 Tg yr -1 of phosphorus to its coastal waters. We show that beside the North Sea and part of the Baltic Sea, annual nutrient exports have not changed significantly, in spite of the implementation of measures to reduce nutrient sources, and that the N P ratio has increased steadily, especially in the North, Mediterranean and Atlantic seas. The response of river basins to changes in inputs was not linear, but influenced by climatic variations and nutrients previously accumulated in soils and aquifers. An analysis of the effects of European environmental policies shows that measures to reduce phosphorus were more successful that those tackling nitrogen and that policies aimed at point sources were more effective or more effectively implemented than those controlling pollution from diffuse sources. The increase of the N P ratio could fuel eutrophication in N-limited coastal ecosystems, reducing biodiversity and the ecosystem's resilience to future additional anthropogenic stress, such as climate change. © 2011 Blackwell Publishing Ltd. Source

Muxworthy A.R.,Imperial College London | Krasa D.,European Research Council Executive Agency | Williams W.,University of Edinburgh | Almeida T.P.,Imperial College London
Geochemistry, Geophysics, Geosystems | Year: 2014

A suite of near-identical magnetite nanodot samples produced by electron-beam lithography have been used to test the thermomagnetic recording fidelity of particles in the 74-333 nm size range; the grain size range most commonly found in rocks. In addition to controlled grain size, the samples had identical particle spacings, meaning that intergrain magnetostatic interactions could be controlled. Their magnetic hysteresis parameters were indicative of particles thought not to be ideal magnetic recorders; however, the samples were found to be excellent thermomagnetic recorders of the magnetic field direction. They were also found to be relatively good recorders of the field intensity in a standard paleointensity experiment. The samples' intensities were all within ∼15% of the expected answer and the mean of the samples within 3% of the actual field. These nonideal magnetic systems have been shown to be reliable records of the geomagnetic field in terms of both direction and intensity even though their magnetic hysteresis characteristics indicate less than ideal magnetic grains. Key Points Nonideal magnetic systems accurately record field direction Weak-field remanences more stable than strong-field remanences © 2014. The Authors. Source

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