Combining limnology and palaeolimnology to investigate recent regime shifts in a shallow,eutrophic lake     

Linda Randsalu-Wendrup  Daniel J. Conley  Jacob Carstensen  Lars-Anders Hansson  Christer Brönmark  Sherilyn C. Fritz  Preetam Choudhary  Joyanto Routh  Dan Hammarlund 《Journal of Paleolimnology》2014,51(3):437-448

In this study, we demonstrate that an integrated approach, combining palaeolimnological records and limnological monitoring data, can increase our understanding of changing ecological patterns and processes in shallow lakes. We focused on recent regime shifts in shallow Lake Krankesjön, southern Sweden, including the collapse of the clear-water state in 1975 and its subsequent recovery in the late 1980s. We used diatom, hydrocarbon and biogenic silica sediment records, in concert with limnological data sets on nutrient concentrations, water clarity, chlorophyll-a and water depth, to investigate the shifts. The shift from clear to turbid conditions was abrupt and occurred over 1 to 2 years, whereas recovery of the clear-water state was more gradual, taking 4–5 years. In 1978, shortly after the first regime shift in water clarity, the diatom community underwent a significant shift. It became less diverse, with decreased abundance of epiphytic and planktonic taxa. Despite rising phosphorus concentrations and lower abundance of submerged macrophytes, Lake Krankesjön has remained in the clear-water state over the past 20 years, although this state seems to be increasingly unstable and susceptible to collapse. The complex reactions of the entire lake ecosystem to major changes in lake-water clarity, as shown by the palaeolimnological variables investigated in this study, emphasize the importance of careful lake and catchment management if a stable, clear-water state is desired.  相似文献   

Sustainability of Mediterranean Deltaic and Lagoon Wetlands with Sea-Level Rise: The Importance of River Input     

John Day  Carles Ibáñez  Francesco Scarton  Didier Pont  Philippe Hensel  Jason Day  Robert Lane 《Estuaries and Coasts》2011,34(3):483-493

We report on a decadal trend of accretionary dynamics in the wetlands of several northwestern Mediterranean deltas and a lagoon system, all of them with high rates of wetland loss. Wetland vertical accretion and surface elevation change were measured at 55 riverine, marine, and impounded sites in four coastal systems: the Ebro delta, Spain; the Rhône delta, France; and the Po delta and Venice Lagoon, Italy. Vertical accretion and elevation change ranged between 0 and 25 mm year^?1 and were strongly correlated. The highest rates of elevation gain occurred at riverine sites where vertical accretion was highest. We conclude that areas with high sediment input, mainly riverine, are the only ones likely to survive accelerated sea-level rise, especially if recent higher estimates of 1 m or more in the twenty-first century prove to be accurate. This is the first study where the importance of river input on wetland survival has been demonstrated at a decadal time scale over a broad geographical area.  相似文献   

Efficient identification of exoplanetary transit candidates from SuperWASP light curves     

A. Collier Cameron  D. M. Wilson  R. G. West  L. Hebb  X.-B. Wang  S. Aigrain  F. Bouchy  D. J. Christian  W. I. Clarkson  B. Enoch  M. Esposito  E. Guenther  C. A. Haswell  G. Hébrard  C. Hellier  K. Horne  J. Irwin  S. R. Kane  B. Loeillet  T. A. Lister  P. Maxted  M. Mayor  C. Moutou  N. Parley  D. Pollacco  F. Pont  D. Queloz  R. Ryans  I. Skillen  R. A. Street  S. Udry  P. J. Wheatley 《Monthly notices of the Royal Astronomical Society》2007,380(3):1230-1244

  相似文献   

The Monitor project: searching for occultations in young open clusters     

S. Aigrain  S. Hodgkin  J. Irwin  L. Hebb  M. Irwin  F. Favata  E. Moraux  F. Pont 《Monthly notices of the Royal Astronomical Society》2007,375(1):29-52

The Monitor project is a photometric monitoring survey of nine young (1–200 Myr) clusters in the solar neighbourhood to search for eclipses by very low mass stars and brown dwarfs and for planetary transits in the light curves of cluster members. It began in the autumn of 2004 and uses several 2- to 4-m telescopes worldwide. We aim to calibrate the relation between age, mass, radius and where possible luminosity, from the K dwarf to the planet regime, in an age range where constraints on evolutionary models are currently very scarce. Any detection of an exoplanet in one of our youngest targets (≲10 Myr) would also provide important constraints on planet formation and migration time-scales and their relation to protoplanetary disc lifetimes. Finally, we will use the light curves of cluster members to study rotation and flaring in low-mass pre-main-sequence stars.
The present paper details the motivation, science goals and observing strategy of the survey. We present a method to estimate the sensitivity and number of detections expected in each cluster, using a simple semi-analytic approach which takes into account the characteristics of the cluster and photometric observations, using (tunable) best-guess assumptions for the incidence and parameter distribution of putative companions, and we incorporate the limits imposed by radial velocity follow-up from medium and large telescopes. We use these calculations to show that the survey as a whole can be expected to detect over 100 young low and very low mass eclipsing binaries, and ∼3 transiting planets with radial velocity signatures detectable with currently available facilities.  相似文献   

Isochrone ages for field dwarfs: method and application to the age–metallicity relation     

Frédéric Pont  Laurent Eyer 《Monthly notices of the Royal Astronomical Society》2004,351(2):487-504

  相似文献   

Chemical composition of urban aerosols in Toulouse, France during CAPITOUL experiment     

A. I. Calvo  V. Pont  C. Liousse  B. Dupré  A. Mariscal  C. Zouiten  E. Gardrat  P. Castera  C. G. Lacaux  A. Castro  R. Fraile 《Meteorology and Atmospheric Physics》2008,102(3-4):307-323

  相似文献   

Empirical evidence for tidal evolution in transiting planetary systems     

Frédéric Pont 《Monthly notices of the Royal Astronomical Society》2009,396(3):1789-1796

Most transiting planets orbit very close to their parent star, causing strong tidal forces between the two bodies. Tidal interaction can modify the dynamics of the system through orbital alignment, circularization, synchronization and orbital decay by exchange of angular moment. Evidence for tidal circularization in close-in giant planet is well known. Here, we review the evidence for excess rotation of the parent stars due to the pull of tidal forces towards spin-orbit synchronization. We find suggestive empirical evidence for such a process in the present sample of transiting planetary systems. The corresponding angular momentum exchange would imply that some planets have spiralled towards their star by substantial amounts since the dissipation of the protoplanetary disc. We suggest that this could quantitatively account for the observed mass–period relation of close-in gas giants. We discuss how this scenario can be further tested and point out some consequences for theoretical studies of tidal interactions and for the detection and confirmation of transiting planets from radial velocity and photometric surveys.  相似文献   

The stratigraphic record and processes of turbidity current transformation across deep‐marine lobes          下载免费PDF全文

Ian A. Kane  Anna S. M. Pontén  Brita Vangdal  Joris T. Eggenhuisen  David M. Hodgson  Yvonne T. Spychala 《Sedimentology》2017,64(5):1236-1273

Sedimentary facies in the distal parts of deep‐marine lobes can diverge significantly from those predicted by classical turbidite models, and sedimentological processes in these environments are poorly understood. This gap may be bridged using outcrop studies and theoretical models. In the Skoorsteenberg Formation (South Africa), a downstream transition from thickly bedded turbidite sandstones to argillaceous, internally layered hybrid beds, is observed. The hybrid beds have a characteristic stratigraphic and spatial distribution, being associated with bed successions which generally coarsen and thicken‐upward reflecting deposition on the fringes of lobes in a dominantly progradational system. Using a detailed characterization of bed types, including grain size, grain‐fabric and mineralogical analyses, a process‐model for flow evolution is developed. This is explored using a numerical suspension capacity model for radially spreading and decelerating turbidity currents. The new model shows how decelerating sediment suspensions can reach a critical suspension capacity threshold beyond which grains are not supported by fluid turbulence. Sand and silt particles, settling together with flocculated clay, may form low yield strength cohesive flows; development of these higher concentration lower boundary layer flows inhibits transfer of turbulent kinetic energy into the upper parts of the flow ultimately resulting in catastrophic loss of turbulence and collapse of the upper part of the flow. Advection distances of the now transitional to laminar flow are relatively long (several kilometres) suggesting relatively slow dewatering (several hours) of the low yield strength flows. The catastrophic loss of turbulence accounts for the presence of such beds in other fine‐grained systems without invoking external controls or large‐scale flow partitioning and also explains the abrupt pinch‐out of all divisions of these sandstones. Estimation of the point of flow transformation is a useful tool in the prediction of heterogeneity distribution in subsurface systems.  相似文献   

Rainwater Chemistry and Wet Deposition over the Equatorial Forested Ecosystem of Zoétélé (Cameroon)     

L. Sigha-Nkamdjou  C. Galy-Lacaux  V. Pont  S. Richard  D. Sighomnou  J. P. Lacaux 《Journal of Atmospheric Chemistry》2003,46(2):173-198

Within the framework of IDAF (IGAC DEBITS AFRICA: International GlobalAtmospheric Chemistry/DEposition of Biogeochemically Important TraceSpecies/Africa) network, data analysis is realised on precipitation chemical composition collected in Zoétélé, in Southern Cameroon. This station, located atabout 200 km from the Atlantic Ocean, is representative of a so-called `Evergreen Equatorial Forest' ecosystem. An automatic wet-only precipitation collector was operated at the station from 1996 to 2000. The rainfall regime, associated with eastward advection of moist and cool monsoon air masses, amounts to an average of 1700 mm/year. Inorganic and organic content of the precipitation were determined by IC in 234 rainfall events, representing a total 4,583 mm of rainfall from an overall of 7,100 mm.The mean annual precipitation chemistry and wet deposition fluxes characteristic of an African equatorial forest are quantified. Typical atmospheric gases and particles sources influence the precipitation chemical content and the associated deposition of chemical species. Indeed, hydrogen concentration is the highest (12.0 eq.L^–1) of the IDAF measurements, leading to acid rains with a low mean pH 4.92. The mineral species are dominated by nitrogenous compounds (NH₄ ⁺:10.5 and NO₃ ^–: 6.9 eq.L^–1), Ca²⁺ (8.9 eq.L^–1) and SO₄ ^{2 –} 5.1 eq.L^–1. Relationship between Ca^{2 +} and SO₄ ^{2 –} indicated aterrigeneous particulate source and an additional SO₄ ^{2 –} contributionprobably due to swamps and volcano emissions. Na⁺ and Cl^–concentrations, around 4.0 eq.L^–1, seem very low for this site,accounting for the marine source. Besides, strong correlations between NH₄ ⁺/K⁺/Cl^– indicate the biomass burning originof these species. Accordingly, precipitation chemistry in Zoétéléis influenced by three major sources: biogenic emissions from soil and forest ecosystems, biomass burning from savannah, and terrigenous signature from particles emissions of arid zones; and three minor sources: marine, volcano and anthropogenic. In spite of the relatively low concentration of all these elements, the wet deposition is quite significant due to the high precipitation levels, with for example a nitrogenous compounds deposition of 34 mmol.m^–2.yr^–1.  相似文献   

Comparison between the fish communities of lakes, reservoirs and rivers: can natural systems help define the ecological potential of reservoirs?     

Pascal Irz  Mélanie Odion  Christine Argillier  Didier Pont 《Aquatic Sciences - Research Across Boundaries》2006,68(1):109-116

  相似文献