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21.
Nitrogen loading to Pleasant Bay, Cape Cod: application of models and stable isotopes to detect incipient nutrient enrichment of estuaries 总被引:1,自引:0,他引:1
To test and refine methods to detect nutrient enrichment and resulting eutrophication, we applied the Waquoit Bay nitrogen loading model (NLM) and Estuarine loading model (ELM) to estuaries of Pleasant Bay that receive increasing but low N loads (25-199 kg N ha(-1) yr(-1)) from land. Contributions of wastewater to these estuaries increased from 7% to 63% as N loads increased, and modeled estimates of dissolved inorganic nitrogen in the water were within approximately 27% of measured values. N isotopic signatures in suspended and benthic organic matter and in tissue of quahogs increased as wastewater contributions to N loads increased, with clams approximately 4 per thousand heavier than organic matter, indicating that even at these low N loads, N from land-derived sources moved detectably up the food web. These results extend the application of NLM and ELM to detect incipient levels of N enrichment and demonstrate that these models can be used in conjunction with isotope measurements as the basis for food web analyses in a system exposed to relatively lower N loads than previously studied. 相似文献
22.
John R. Dymond Anne-Gaelle Ausseil James D. Shepherd Lars Buettner 《Geomorphology》2006,74(1-4):70-79
Since European settlement 160 years ago, much of the indigenous forest in New Zealand hill country has been cleared for pastoral agriculture, resulting in increased erosion and sedimentation. To prioritise soil conservation work in the Manawatu–Wanganui region, we developed a model of landslide susceptibility. It assigns high susceptibility to steep land not protected by woody vegetation and low susceptibility everywhere else, following the commonly used approach for identifying inappropriate land use. A major storm on 15–16 February 2004 that produced many landslides was used to validate the model. The model predicted hills at risk to landsliding with moderate accuracy: 58% of erosion scars in the February storm occurred on hillsides considered to be susceptible. The model concept of slope thresholds, above which the probability of landsliding is high and below which the probability is low, is not adequate because below 30° the probability of landsliding is approximately linearly related to slope. Thus, reforestation of steep slopes will need to be combined with improved vegetation management for soil conservation on moderate slopes to significantly reduce future landsliding. 相似文献
23.
Geomorphological processes are an integral part of ecosystem functioning and ecosystem functioning affects geomorphological processes. Increasingly widespread acknowledgement of this simple idea is manifest in a vigorous research community engaged with questions that address the two‐way interaction between biota and geomorphology, at a range of scales and in a variety of terrestrial and aquatic environments. Geomorphological disturbances are a core element of biogeomorphological interest, and although the disciplines of geomorphology and ecology have each developed languages and theories that help to explore, model and understand disturbance events, little attempt has been made to draw together these approaches. Following a brief review of these issues, we introduce thirteen papers that investigate the interactions and feedbacks between geomorphological disturbance regimes and ecosystem functions. These papers reveal the singularity of wildfire impacts, the importance of landsliding for carbon budgeting and of vegetation accumulation for landsliding, the zoogeomorphic role of iconic and ‘Cinderella’ animals in fluvial geomorphology, biophysical interactions in aeolian, fluvial and torrential environments and the utility of living ecosystems as archives of geomorphic events. Most of these papers were first presented in a conference session at the European Geoscience Union General Assembly in 2010 and several others are from recent volumes of Earth Surface Processes and Landforms. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
24.
Annett Wolf Eleanor Blyth Richard Harding Daniela Jacob Elke Keup-Thiel Holger Goettel Terry Callaghan 《Climatic change》2008,87(1-2):75-89
We tested the sensitivity of a dynamic ecosystem model (LPJ-GUESS) to the representation of soil moisture and soil temperature
and to uncertainties in the prediction of precipitation and air temperature. We linked the ecosystem model with an advanced
hydrological model (JULES) and used its soil moisture and soil temperature as input into the ecosystem model. We analysed
these sensitivities along a latitudinal gradient in northern Russia. Differences in soil temperature and soil moisture had
only little influence on the vegetation carbon fluxes, whereas the soil carbon fluxes were very sensitive to the JULES soil
estimations. The sensitivity changed with latitude, showing stronger influence in the more northern grid cell. The sensitivity
of modelled responses of both soil carbon fluxes and vegetation carbon fluxes to uncertainties in soil temperature were high,
as both soil and vegetation carbon fluxes were strongly impacted. In contrast, uncertainties in the estimation of the amount
of precipitation had little influence on the soil or vegetation carbon fluxes. The high sensitivity of soil respiration to
soil temperature and moisture suggests that we should strive for a better understanding and representation of soil processes
in ecosystem models to improve the reliability of predictions of future ecosystem changes. 相似文献
25.
Kathleen R. Stoof-Leichsenring Annett Junginger Lydia A. Olaka Ralph Tiedemann Martin H. Trauth 《Journal of Paleolimnology》2011,45(3):353-367
Lake Naivasha, Kenya, is one of a number of freshwater lakes in the East African Rift System. Since the beginning of the twentieth
century, it has experienced greater anthropogenic influence as a result of increasingly intensive farming of coffee, tea,
flowers, and other horticultural crops within its catchment. The water-level history of Lake Naivasha over the past 200 years
was derived from a combination of instrumental records and sediment data. In this study, we analysed diatoms in a lake sediment
core to infer past lacustrine conductivity and total phosphorus concentrations. We also measured total nitrogen and carbon
concentrations in the sediments. Core chronology was established by 210Pb dating and covered a ~186-year history of natural (climatic) and human-induced environmental changes. Three stratigraphic
zones in the core were identified using diatom assemblages. There was a change from littoral/epiphytic diatoms such as Gomphonema gracile and Cymbella muelleri, which occurred during a prolonged dry period from ca. 1820 to 1896 AD, through a transition period, to the present planktonic Aulacoseira sp. that favors nutrient-rich waters. This marked change in the diatom assemblage was caused by climate change, and later
a strong anthropogenic overprint on the lake system. Increases in sediment accumulation rates since 1928, from 0.01 to 0.08 g cm−2 year−1 correlate with an increase in diatom-inferred total phosphorus concentrations since the beginning of the twentieth century.
The increase in phosphorus accumulation suggests increasing eutrophication of freshwater Lake Naivasha. This study identified
two major periods in the lake’s history: (1) the period from 1820 to 1950 AD, during which the lake was affected mainly by
natural climate variations, and (2) the period since 1950, during which the effects of anthropogenic activity overprinted
those of natural climate variation. 相似文献
26.
Konrad J. K. Buettner 《Theoretical and Applied Climatology》1954,5(3-4):377-387
Summary It is proposed for practical purposes to measure the severity of the bioclimate in extreme conditions, as encountered in aircraft, by the tolerance time. The author also suggests a more simple classification of the extreme bioclimates, as shown in Table 1. The probable kind of final fate of a human being in this bioclimate is used for its definition.The air friction causes the temperature of a modern fast airplane to rise in a degree that an equilibrium of temperature is no longer secured. The heat capacity of the cabin, of the clothes, and of the men therefore becomes important for avoiding too high temperatures.A new calculation of observed fast changes of temperature in man yields that the peripheral heat barrier of the body depends upon core temperature and not upon skin temperature. In hot environment the production of heat increases much more than has been supposed.As a consequence of recent experiments of the author about the thermal water loss from the skin the diffusion flow of the insensible perspiration can move in both directions, to and from the skin, according to the vapour pressure of the air; it represents simply the lowest value of osmotic diffusion. The diffusion ressstance of the skin is lowest when it is covered with water. Considerable amounts of water are flowing through the skin from water and solutions; amount and direction of these flows depend upon the concentration of the solutions. When the skin is sweating and exposed to the air the diffusion flow increases with sweating and can reach similar amounts. With a very damp air previously excreted sweat water can return back into the body by diffusion.
With 3 Figures.
Lecture given to the Symposium on Frontiers of man controlled flight. Los Angeles, Cal., April 1953. With the permission of the Institute of Transportation and Traffic Engineering, University of California, Los Angeles. 相似文献
Zusammenfassung Für Zwecke der Praxis wird vorgeschlagen, die Härte des Bioklimas unter extremen Bedingungen, wie sie in der Fliegerei auftreten, nach der Toleranzzeit zu bemessen (Fig. 1). Ferner wird angeregt, statt der verwirrenden Fülle extremer Bioklimate eine Einteilung wie in Tabelle 1 zu benützen. Dabei wird die wahrscheinliche Art des Endschicksals eines Menschen in diesem Bioklima für dessen Definition benutzt.Das moderne Schnellflugzeug wird durch Reibung so stark aufgeheizt, daß Temperaturgleichgewicht nicht mehr erreicht wird. Wärmekapazität von Flugzeugzelle, Kleidung und Mensch werden dadurch zu wichtigen Hilfsmitteln zur Vermeidung zu hoher Temperaturen.Eine Neuberechnung beobachteter schneller Temperaturgänge im Menschen ergibt, daß der periphere Wärmewiderstand des Körpers von der Innentemperatur und nicht von der Hauttemperatur abhängt. In heißer Umgebung steigt die Wärmebildung viel mehr an als bisher angenommen.Nach neuen Versuchen des Verf. über den thermischen Hautwasserverlust kann der Diffusionsstrom der insensiblen Perspiration, je nach dem äußeren Dampfdruck, von der Haut weg oder zu ihr hin gerichtet sein; er stellt nur den untersten Wert der osmotischen Diffusion dar. Der geringste Diffusionswiderstand der Haut findet sich bei Wasserbedeckung. Aus Wasser oder Lösungen fließen erhebliche Wassermassen durch die Haut; Größe und Richtung dieser Ströme richten sich nach der Konzentration der Lösungen. Bei schwitzender, der Luft ausgesetzter Haut nimmt der Diffusionsstrom mit dem Schwitzen zu und kann eine ähnliche Größe erreichen. Bei sehr feuchter Luft kann bereits ausgetretenes Schweißwasser wieder zurückdiffundieren.
Résumé L'auteur propose, à des fins pratiques, d'évaluer la rigueur d'un bioclimat sous des conditions extrêmes comme on les rencontre dans l'aviation, par le temps de tolérance (fig.1). Il suggère en un tableau une subdivision plus simple des bioclimats extrêmes; pour cela il définit ce climat par le sort final probable de l'organisme humain qui s'y trouve exposé.La chaleur de frottement des avions modernes est telle que l'équilibre de température n'est plus atteint. La capacité calorifique de la cabine d'avion, des vêtements et de l'homme deviennent par conséquent des moyens importants d'éviter des températures trop hautes.Un nouveau calcul de fortes variations de température observées dans l'organisme humain montre que la résistence calorifique du corps dépend de sa température interne et non de celle de la peau. La formation de chaleur augmente par forte chaleur extérieure beaucoup plus qu'on ne l'admettait jusqu'ici.D'après de nouvelles recherches de l'auteur sur la perte calorifique en eau de la peau, le courant de diffusion de la perspiration insensible peut être dirigé vers l'extérieur ou vers l'intérieur, selon la pression de vapeur de l'air; il ne représente que la valeur la plus basse de la diffusion osmotique. La plus petite résistance de la peau à la diffusion s'observe lorsque celle-ci est couverte d'eau. Dans l'eau ou dans une solution, des quantités notables d'eau traversent la peau; la direction et l'importance de ces courants dépendent de la concentration des solutions. Lorsque la peau exposée à l'air transpire, le courant de diffusion augmente avec la transpiration et peut atteindre une grandeur semblable. Dans de l'air très humide, l'eau de transpiration expulsée peut rediffuser vers l'intérieur.
With 3 Figures.
Lecture given to the Symposium on Frontiers of man controlled flight. Los Angeles, Cal., April 1953. With the permission of the Institute of Transportation and Traffic Engineering, University of California, Los Angeles. 相似文献
27.
The eruptive history of Monte Vulture has been the subject of several geochronological investigations during the past decades,
which reliably dated only a small number of eruptions. Understanding the causes of sub-optimum data yield in the past requires
an interdisciplinary approach. We re-analyzed samples from previous works and present new data on samples from the main volcano-stratigraphic
units of Monte Vulture, so as to provide an improved, consistent chronostratigraphic database. Imaging of minerals by cathodoluminescence
and backscattered electrons reveals that heterochemical, high-temperature deuteric reaction textures are ubiquitous. Such
observations are common in metamorphic rocks but had not frequently been reported from volcanic rocks. In view of the mineralogical
complexity, we base our chronological interpretation on isochemical steps, defined as steps for which the Cl/K and/or the
Ca/K ratios are constant. Isochemical steps carry the isotopic signature of chemically homogeneous mineral phases and therefore
allow a well-constrained age interpretation. Comparison of old and new 39Ar-40Ar data proves the reproducibility of age spectra and their shapes. This quantifies the analytical reliability of the irradiation
and mass-spectrometric analyses. Anomalous age spectra are a reproducible property of some specific samples and correlate
with mineralogical anomalies. The present data allow us to fine-tune the age of the volcanostratigraphic units of Monte Vulture
during the known interval of main volcanic activity from ca. 740 to 610 ka. After a very long stasis, the volcanic activity
in the Monte Vulture area resumed with diatremic eruptions, one of which (Lago Piccolo di Monticchio, the site of a palynological-paleoclimatological
drilling) was dated at ca. 140 ka. 相似文献