Increasing a freshwater lens below a creek ridge using a controlled artificial recharge and drainage system: a case study in the Netherlands     

Pieter S. Pauw  Esther S. van Baaren  Martijn Visser  Perry G. B. de Louw  Gualbert H. P. Oude Essink 《Hydrogeology Journal》2015,23(7):1415-1430

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Understanding long-term groundwater flow at Pahute Mesa and vicinity,Nevada National Security Site,USA, from naturally occurring geochemical and isotopic tracers     

Kwicklis  Edward  Farnham  Irene  Hershey  Ronald L.  Visser  Ate  Hoaglund  John 《Hydrogeology Journal》2021,29(8):2725-2749

Recently collected naturally occurring geochemical and isotopic groundwater tracers were combined with historic data from the Pahute Mesa area of the Nevada National Security Site (NNSS), Nevada, USA, to provide insights into long-term regional groundwater flow patterns, mixing and recharge. Pahute Mesa was the site of 85 nuclear detonations between 1965 and 1992, many of them deeply buried devices that introduced radionuclides directly into groundwater. The dataset examined included major ions and field measurements, stable isotopes of hydrogen (δ²H), oxygen (δ¹⁸O), carbon (δ¹³C) and sulfur (δ³⁴S), and radioisotopes of carbon (¹⁴C) and chloride (³⁶Cl). Analysis of the patterns of groundwater ¹⁴C data and the δ²H and δ¹⁸O signatures indicates that groundwater recharge is predominantly of Pleistocene age, except for a few localized areas near major ephemeral drainages. Steep gradients in sulfate (SO₄) and chloride (Cl) define a region near the western edge of the NNSS where high-concentration groundwater flowing south from north of the NNSS merges with dilute groundwater flowing west from eastern Pahute Mesa in a mixing zone that coincides with a groundwater trough associated with major faults. The ³⁶Cl/Cl and δ³⁴S data suggest that the source of the high Cl and SO₄ in the groundwater was a now-dry, pluvial-age playa lake north of the NNSS. Patterns of groundwater flow indicated by the combined data sets show that groundwater is flowing around the northwest margin of the now extinct Timber Mountain Caldera Complex toward regional discharge areas in Oasis Valley.

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Le climat change-t-il?     

Prof. Dr. S. W. Visser 《Pure and Applied Geophysics》1948,12(1-2):1-3

Résumé Les conditions thermiques exceptionelles de l'hiver 1946–47 et de l'été 1947 sont discutées en déduisant que cela ne signifie pas un changement de climat pour l'Europe occidentale: en effet, il s'agit seulement d'une coincidence avec une période d'intense activité solaire, y ayant en général une correspondance entre les époques de grande (ou petite) variabilité du climat et les périodes de forte (ou faible) activité solaire.

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Summary The exceptional thermic conditions of the winter 1946–47 and the summer 1947 are discussed. These conditions do not mean a change of the climate of Western Europe. They concide with a period of intensive solar activity. Generally narrow connexion are present between periods of large (small) variability of the climate and large (small) solar activity.

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Natural and anthropogenic forcing of Holocene lake ecosystem development at Lake Uddelermeer (The Netherlands)     

Stefan Engels  Rogier van Oostrom  Chiara Cherli  Jennifer A. J. Dungait  Boris Jansen  J. M. van Aken  Bas van Geel  Petra M. Visser 《Journal of Paleolimnology》2018,59(3):329-347

Lake Uddelermeer (The Netherlands) is characterized by turbid conditions and annual blooms of toxic cyanobacteria, which are supposed to be the result of increased agricultural activity in the twentieth century AD. We applied a combination of classic palaeoecological proxies and novel geochemical proxies to the Holocene sediment record of Lake Uddelermeer (The Netherlands) in order to reconstruct the natural variability of the lake ecosystem and to identify the drivers of the change to the turbid conditions that currently characterize this lake. We show that the lake ecosystem was characterized by a mix of aquatic macrophytes and abundant phytoplankton between 11,500 and 6000 cal year BP. A transition to a lake ecosystem with clear-water conditions and relatively high abundances of ‘isoetids’ coincides with the first signs of human impact on the landscape around Lake Uddelermeer during the Early Neolithic (ca. 6000 cal year BP). An abrupt and dramatic ecosystem shift can be seen at ca. 1030 cal year BP when increases in the abundance of algal microfossils and concentrations of sedimentary pigments indicate a transition to a turbid phytoplankton-dominated state. Finally, a strong increase in concentrations of plant and faecal biomarkers is observed around 1950 AD. Canonical Correspondence Analysis suggests that reconstructed lake ecosystem changes are best explained by environmental drivers that show long-term gradual changes (sediment age, water depth). These combined results document the long-term anthropogenic impact on the ecosystem of Lake Uddelermeer and provide evidence for pre-Industrial Era signs of eutrophication.  相似文献   

Importance of river water recharge to the San Joaquin Valley groundwater system          下载免费PDF全文

Ate Visser  Jean E. Moran  Michael J. Singleton  Bradley K. Esser 《水文研究》2018,32(9):1202-1213

Groundwater is not a sustainable resource, unless abstraction is balanced by recharge. Identifying the sources of recharge in a groundwater basin is critical for sustainable groundwater management. We studied the importance of river water recharge to groundwater in the south‐eastern San Joaquin Valley (24,000 km², population 4 million). We combined dissolved noble gas concentrations, stable isotopes, tritium, and carbon‐14 analyses to analyse the sources, mechanisms, and timescales of groundwater recharge. Area‐representative groundwater sampling and numerical model input data enabled a stable isotope mass balance and quantitative estimates of river and local recharge. River recharge, identified by a lighter stable isotope signature, represents 47 ± 4% of modern groundwater in the San Joaquin Valley (recharged after 1950) but only 26 ± 4% of premodern groundwater (recharged before 1950). This implies that the importance of river water recharge in the San Joaquin valley has nearly doubled and is likely the result of a 40% increase in total recharge, caused by river water irrigation return flows and increased stream depletion and river recharge due to groundwater pumping. Compared with the large and long‐duration capacity for water storage in the subsurface, storage of water in rivers is limited in time and volume, as evidenced by cold river recharge temperatures resulting from fast infiltration and recharge. Groundwater banking of seasonal surface water flows and expansion of managed aquifer recharge practices therefore appear to be a natural and promising method for increasing the resilience of the San Joaquin Valley water supply system.  相似文献   

The likelihood of holding outdoor skating marathons in the Netherlands as a policy-relevant indicator of climate change     

H. Visser  A. C. Petersen 《Climatic change》2009,93(1-2):39-54

“When I was born – in 1956 – the chance of realizing a Frisian Eleven City Ice Skating Marathon in Netherlands was 1 in 4. When my daughter was born – in 1999 – this chance had diminished to 1 in 10. An enormous change in one generation!” This quote was taken from a speech by J. P. Balkenende, prime minister of the Netherlands. It illustrates how a seemingly odd indicator of climate change, the chance of organizing large-scale outdoor ice-skating marathons, can play a role in the public and political debate on climate change. Outdoor skating has a very strong public appeal in the Netherlands, and the diminishing chances of holding such events provide an additional Dutch motive for introducing climate-policy measures. Here, “ice skating marathons” are approached from three angles: (1) the societal/political angle as described above, (2) the more technical angle, of how to derive annual chances for holding large-scale marathons such as the Eleven City Marathon (‘Elfstedentocht’), and (3) the role of (communicating) uncertainties. Since the statistical approach was developed in response to communicational needs, both statistical and communicative aspects are reported on in this article.  相似文献   

Stakeholder views on restoring depleted cereal fallows in arid Tunisia: Societal barriers and possible crevices     

M. Visser  N. Maughan  A. Ouled Belgacem  M. Neffati 《Journal of Arid Environments》2011,75(11):1191-1200

All dryland countries struggle with manmade dryland degradation and climate change will reinforce this trend. In arid Tunisia (100-200 mm annual rainfall), depleted cereal fallows are a prominent feature of the desertified landscape. Based on long-term agro-ecological work with promising native steppe grasses, this work explores the societal barriers to restoring cereal fallows with these species. Interviews were conducted with 23 stakeholders (researchers, local decision makers of development agencies and land users) and 40 statements were drawn from these interviews as well as from written sources. These were sorted by 27 stakeholders (some of whom were interviewed before) following a distinct Q-sorting technique inspired by Q-methodology. Principal Components Analysis of these Q-sorts revealed three major types of barriers. (1) A widespread knowledge barrier was obvious since opinion on several agro-ecological statements was often opposite to the scientific evidence. (2) Strong convictions about the sacred nature of barley cropping and olive growing pointed to a cultural barrier to sowing steppe grasses on cereal fallows; (3) Finally, especially non-scientific agropastoralists expressed a lack of trust in any state-backed project aimed at combating desertification. Without the living proof of economic benefits of reseeding, no spontaneous uptake of reseeding can be expected.  相似文献   

The Rose Spit Eddy in Dixon Entrance: Evidence for its existence and underlying dynamics     

Malcolm J. Bowman  Andre W. Visser  William R. Crawford 《大气与海洋》2013,51(1):70-93

Abstract

The existence and dynamics of the so‐called “Rose Spit Eddy” in Dixon Entrance, British Columbia, are investigated by (i) analysing published observations of low‐frequency Eulerian and Lagrangian currents in the region; (ii) interpreting tidal residuals produced by the Hecate Model (a non‐rotating hydraulic model of Hecate Strait and Dixon Entrance); and (iii) running a barotropic, non‐linear numerical tidal model over simplified topography to investigate residuals produced over the Rose Spit sill.

Observations have consistently revealed persistent basin‐wide, surface‐intensified cyclonic shears within central and eastern Dixon Entrance. The Hecate hydraulic tidal model also produced a tidal residual cyclonic gyre in central Dixon Entrance, but with velocities considerably larger than those observed. Barotropic numerical simulations of tidal streams flowing over a representation of the Rose Spit sill produced residual flows along the sill in reasonable agreement with observations and theory. A southward‐directed jet flow was produced off Cape Chacon. Elsewhere, tidal rectification was weak. Run without the Coriolis force, organized flow along the sill broke down, although the headland jet off Cape Chacon persisted.

We submit that the observed Rose Spit eddy results from interactions between buoyancy‐driven coastal currents and tidally rectified flows generated over the Rose Spit sill, and near Cape Chacon, and perhaps indirectly, over the western flank of Learmonth Bank (which although west of the Rose Spit eddy, contributes to the cross‐channel flow across the Entrance). These regions of localized tidal stress will each favour recirculation of a portion of the coastal current within the Entrance, helping to form the eddy.

We believe that the Hecate hydraulic model eddy was generated to a significant degree by phase errors introduced at the northern open boundary, where a rocking barrier was used to force currents. A second rocking barrier also produced a large cyclonic gyre, not supported by observations, near the model's southern boundary.  相似文献   

Efficient gravity field recovery from GOCE gravity gradient observations   总被引：4，自引：2，他引：2  

R. Klees  R. Koop  P. Visser  J. van den IJssel 《Journal of Geodesy》2000,74(7-8):561-571

 An efficient algorithm is proposed for gravity field recovery from Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite gravity gradient observations. The mathematical model is formulated in the time domain, which allows the inclusion of realistic observational noise models. The algorithm combines the iterative solution of the normal equations, using a Richardson-type iteration scheme, with the fast computation of the right-hand side of the normal equations in each iteration step by a suitable approximation of the design matrix. The convergence of the iteration is investigated, error estimates are provided, and the unbiasedness of the method is proved. It is also shown that the method does not converge to the solution of the normal equations. The performance of the approach for white noise and coloured noise is demonstrated along a simulated GOCE orbit up to spherical harmonic degree and order 180. The results also indicate that the approximation error may be neglected. Received: 30 November 1999 / Accepted: 31 May 2000  相似文献   

A SCUBA survey of compact dark Lynds clouds     

A. E. Visser  J. S. Richer  C. J. Chandler† 《Monthly notices of the Royal Astronomical Society》2001,323(2):257-269

We present the first results of a submillimetre continuum survey of Lynds dark clouds. Submillimetre surveys of star-forming regions are an important tool with which to obtain representative samples of the very first phases of star formation. Maps of 24 small clouds were obtained with SCUBA, the bolometer array receiver at the James Clerk Maxwell Telescope, and 19 clouds were detected. The total dark cloud area surveyed was ∼130 arcmin², and a total gas mass of 90 M_⊙ was detected. The dust emission is in general in good agreement with the extinction of optical starlight. The observed clouds contain a newly discovered protostar in L944, and a previously known protostar IRAS 23228+4320 in L1246. Another eight starless cores, either gravitationally unbound or pre-stellar in nature, were also detected. All starless cores and protostars were detected in only seven clouds, and the remaining 17 clouds seem quiescent and do not show any signs of recent star formation activity. The 850-μm images of all detected clouds are presented, as well as 450-μm images of L328, L944, L1014 and L1262. The outflows of the protostars in L944 and L1246 were also discovered and were mapped in ¹²CO J =2→1. The detection of the young protostar in L944, which is not present in the IRAS Point Source Catalog, shows the capacity of submillimetre surveys to detect unknown protostars.  相似文献