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1.
Current efforts to assess changes to the wetland hydrology caused by growing anthropogenic pressures in the Athabasca Oil Sands Region (AOSR) require well-founded spatial and temporal estimates of actual evapotranspiration (ET), which is the dominant component of the water budget in this region. This study assessed growing season (May–September) and peak growing season (July) ET variability at a treed moderate-rich fen and treed poor fen (in 2013–2018), open poor fen (in 2011–2014), and saline fen (in 2015–2018) using eddy covariance technique and a set of complementary environmental data. Seasonal fluctuations in ET were positively related to net radiation, air temperature and vapour pressure deficit and followed trends typical for the Boreal Plains (BP) and AOSR with highest rates in June–July. However, no strong effect of water table position on ET was found. Strong surface control on ET is evident from lower ET values than potential evapotranspiration (PET); the lowest ET/PET was observed at saline fen, followed by open fen, moderately treed fen, and heavily treed fen, suggesting a strong influence of vegetation on water loss. In most years PET exceeded precipitation (P), and positive relations between P/PET and ET were observed with the highest July ET rates occurring under P/PET ~1. However, during months with P/PET > 1, increased P/PET was associated with decreased July ET. With respect to 30-year mean values of air temperature and P in the area, both dry and wet, cool and warm growing seasons (GS) were observed. No clear trends between ET values and GS wetness/coldness were found, but all wet GS were characterized by peak growing seasons with high daily ET variability.  相似文献   

2.
Stream bank erosion rates measured over a two-year period on a moorland and a forested stream in the Institute of Hydrology's Balquhidder Paired Catchments in central Scotland were compared. Bank erosion rates are generally higher on the mainstream of the moorland catchment and highest in wintger on both streams. Bank erosion is correlated with the incidence of frost: minimum temperatures measured on stream banks of the forested stream were an average of 3·7°C higher than on stream banks both outside the forest and on the moorland stream. This makes the incidence of frost on forested stream banks half as frequent. Volumes of material eroded from the mainstreams were combined with bulk density measurements and it is estimated that erosion of the mainstream banks is contributing 1·5 and 7·3 per cent of the sediment yield of the forested and moorland catchments, respectively. Analysis of the vertical distribution of erosion on the banks of both streams suggests an undercutting mechanism which is more pronounced in the moorland stream. The influence of trees on bank erosion and possible implications for the management of forest streams are discussed. © 1997 by John Wiley & Sons, Ltd.  相似文献   

3.
Freezing characteristics were investigated for a sedge covered floating fen and spruce covered swamp located beside a shallow lake in the Western Boreal Forest of Canada. Thermal properties were measured in situ for one freeze‐thaw cycle, and for two freeze‐thaw cycles in laboratory columns. Thermal conductivity and liquid water content were related to a range of subsurface temperatures above and below the freezing thresholds, and clearly illustrate hysteresis between the freezing and thawing process. Thermal hysteresis occurs because of the large change in thermal conductivity between water and ice, high water content of the peat, and wide variation in pore sizes that govern ice formation. Field and laboratory results were combined to develop linear freezing functions, which were tested in a heat transfer model. For surface temperature boundary conditions, subsurface temperatures were simulated for the over‐winter period and compared with field measurements. Replication of the transient subsurface thermal regime required that freezing functions transition gradually from thawed to frozen state (spanning the ?0·25 to ?2 °C range) as opposed to a more abrupt step function. Subsurface temperatures indicate that the floating fen underwent complete phase change (from water to ice) and froze to approximately the same depth as lake ice thickness. Therefore, the floating fen peatland froze as a ‘shelf’ adjacent to the lake, whereas the spruce covered swamp had a higher capacity for thermal buffering, and subsurface freezing was both more gradual and limited in depth. These thermal properties, and the timing and duration of frozen state, are expected to control the interaction of water and nutrients between surface water and groundwater, which will be affected by changes in air temperature associated with global climate change. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

4.
Paleomagnetic data from lithic clasts collected from Mt. St. Helens, USA, Volcán Láscar, Chile, Volcán de Colima, Mexico and Vesuvius, Italy have been used to determine the emplacement temperature of pyroclastic deposits at these localities and to highlight the usefulness of the paleomagnetic method for determining emplacement temperatures. At Mt. St. Helens, the temperature of the deposits (T dep ) at three sites from the June 12, 1980 eruption was found to be ≥532°C, ≥509°C, and 510–570°C, respectively. One site emplaced on July 22, 1980 was emplaced at ≥577°C. These new paleomagnetic temperatures are in good agreement with previously published direct temperature measurements and paleomagnetic estimates. Lithic clasts from pyroclastic deposits from the 1993 eruption of Láscar were fully remagnetized above the respective Curie temperatures, which yielded a minimum T dep of 397°C. Samples were also collected from deposits thought to be pyroclastics from the 1913, 2004 and 2005 eruptions of Colima. At Colima, the sampled clasts were emplaced cold. This is consistent with the sampled clasts being from lahar deposits, which are common in the area, and illustrates the usefulness of the paleomagnetic method for distinguishing different types of deposit. T dep of the lower section of the lithic rich pyroclastic flow (LRPF) from the 472 A.D. deposits of Vesuvius was ~280–340°C. This is in agreement with other, recently published paleomagnetic measurements. In contrast, the upper section of the LRPF was emplaced at higher temperatures, with T dep ~520°C. This temperature difference is inferred to be the result of different sources of lithic clasts between the upper and lower sections, with the upper section containing a greater proportion of vent-derived material that was initially hot. Our studies of four historical pyroclastic deposits demonstrates the usefulness of paleomagnetism for emplacement temperature estimation.  相似文献   

5.
The fluvial flux of carbon (C) from terrestrial to marine environments represents an important component of the global C‐cycle, which can transfer C from the atmosphere to sedimentary storage. Fluvial fluxes of C are also an essential resource for freshwater ecosystems, critical for habitat heterogeneity and function. As such it is crucial that we are able to quantify this flux accurately. However, at present there are a number of different techniques used to quantify concentrations of fluvial C, and these techniques vary in their accuracy. In this article, we compare particulate organic carbon (POC) measurements derived from two commonly‐used techniques; a simple combustion and loss‐on‐ignition (LOI) technique, and an oxidative–combustion and carbon dioxide (CO2) detection technique. The techniques were applied to water samples collected from 10 contrasting reference‐condition, temperate river ecosystems. The POC measurements derived from the LOI technique were up to 16 times higher (average four times higher), than those derived from the oxidative–combustion and CO2 detection technique. This difference was highly variable both across the different river ecosystems and within each river ecosystem over time, suggesting that there is no simple way of converting the mass measured by LOI to estimates of fluvial POC. It is suggested that the difference in POC measured by these two techniques is a consequence of: (1) the loss of inorganic carbon at LOI combustion temperatures of > 425 °C, (2) the potential during the LOI combustion stage to lose hygroscopic and intercrystalline water, not completely driven off by the drying stage at temperatures of < 150 °C, and (3) the variable C content of fluvial organic matter, meaning that the simple application of a fixed correction factor to values obtained from the LOI technique may not be appropriate. These findings suggest that oxidative–combustion and CO2 detection techniques are preferential for quantifying fluvial POC. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
This pilot study uses a chemical technique (KEtX) to establish vertical profiles of average monthly water temperature within river beds: the hyporheic zone at the interface between surface water and groundwater. Data are presented for two gravel-bed sites and one sand-bed site on the River Wissey, Norfolk, UK. From February to October 1992, average monthly temperatures were determined at 10cm intervals down 1 m profiles. A strong seasonal pattern was defined at all sites with hyporheic temperatures being relatively warm in winter and cool in summer. Isothermal periods occurred in March-April and September-October. Temperature ranges within the hyporheic were decreased (4.6–7.7°C) compared with those of surface waters (10 and 10.9°C). Temperature profiles were similar at all sites during winter, but the sand-bed site had relatively low temperatures at a standard depth within the hyporheic during summer and the temperature gradient became isothermal later in the autumn at this site. It is suggested that the influence of flows and substratum characteristics on temperature patterns, especially in regulated rivers, may have significant ecological implications, for example for determining the timing of salmonid fry and invertebrate emergence.  相似文献   

7.
Water losses from snow intercepted by forest canopy can significantly influence the hydrological cycle in seasonally snow‐covered regions, yet how snow interception losses (SIL) are influenced by a changing climate are poorly understood. In this study, we used a unique 30 year record (1986–2015) of snow accumulation and snow water equivalent measurements in a mature mixed coniferous (Picea abies and Pinus sylvestris ) forest stand and an adjacent open area to assess how changes in weather conditions influence SIL. Given little change in canopy cover during this study, the 20% increase in SIL was likely the result of changes in winter weather conditions. However, there was no significant change in average wintertime precipitation and temperature during the study period. Instead, mean monthly temperature values increased during the early winter months (i.e., November and December), whereas there was a significant decrease in precipitation in March. We also assessed how daily variation in meteorological variables influenced SIL and found that about 50% of the variation in SIL was correlated to the amount of precipitation that occurred when temperatures were lower than ?3 °C and to the proportion of days with mean daily temperatures higher than +0.4 °C. Taken together, this study highlights the importance of understanding the appropriate time scale and thresholds in which weather conditions influence SIL in order to better predict how projected climate change will influence snow accumulation and hydrology in boreal forests in the future.  相似文献   

8.
Evaporation of intercepted rain by a canopy is an important component of evapotranspiration, particularly in the humid boreal forest, which is subject to frequent precipitation and where conifers have a large surface water storage capacity. Unfortunately, our knowledge of interception processes for this type of environment is limited by the many challenges associated with experimental monitoring of the canopy water balance. The objective of this study is to observe and estimate canopy storage capacity and wet canopy evaporation at the sub-daily and seasonal time scales in a humid boreal forest. This study relies on field-based estimates of rainfall interception and evapotranspiration partitioning at the Montmorency Forest, Québec, Canada (mean annual precipitation: 1600 mm, mean annual evapotranspiration: 550 mm), in two balsam fir-white birch forest stands. Evapotranspiration was monitored using eddy covariance sensors and sap flow systems, whereas rainfall interception was measured using 12 sets of throughfall and six stemflow collectors randomly placed inside six 400-m2 plots. Changes in the amount of water stored on the canopy were also directly monitored using the stem compression method. The amount of water intercepted by the forest canopy was 11 ± 5% of the total rainfall during the snow-free (5 July–18 October) measurement periods of 2017 and 2018. The maximum canopy storage estimated from rainfall interception measurements was on average 1.6 ± 0.7 mm, though a higher value was found using the stem compression method (2.2 ± 1.6 mm). Taking the average of the two forest stands studied, evaporation of intercepted water represented 21 ± 8% of evapotranspiration, while the contribution of transpiration and understory evapotranspiration was 36 ± 9% and 18 ± 8%. The observations of each of the evapotranspiration terms underestimated the total evapotranspiration observed, so that 26 ± 12% of it was not attributed. These results highlight the importance to account for the evaporation of rain intercepted by humid boreal forests in hydrological models.  相似文献   

9.
The Shizishan copper-gold deposit at Tongling, Anhui Province consists of two magmato-hydrothermal mineralization types: the crypto-explosive breccia type and the skarn type. At least four episodes of boiling occurred to the ore-forming fluids in this deposit. The first episode took place in accompany with the formation of the crypto-explosive breccias. The melt-fluid inclusions giving temperatures above 600℃ and salinities higher than 42% NaCl equiv represent a residual magma related to this episode. The second episode occurred during skarnization, giving fluid temperatures of 422℃-472℃, averaging 458℃, and salinities of 10.2%-45.1% NaCl equiv. The third episode corresponds to the main mineralization stage, i.e., the quartz-sulphide stage. Fluid temperatures of this episode vary in a range of 337℃-439℃ with an average of 390℃, and salinities in a range of 3%-30% NaCl equiv. The forth episode happened at the waning stage of mineralization, giving fluid temperatures below 350℃ with an average of 265℃ and salinities of 2.1%-40.4% NaCl equiv.  相似文献   

10.
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11.
This study examined the thermal regime of a headwater stream within a clear‐cut. The stream had a complex morphology dominated by step–pool features, many formed by sediment accumulation upstream of woody debris. Maximum daily temperatures increased up to 5 °C after logging, and were positively associated with maximum daily air temperature and negatively with discharge. Maximum daily temperatures generally increased with downstream distance through the cut block, but decreased with distance in two segments over distances of tens of metres, where the topography indicated relatively concentrated lateral inflow. Localized cool areas within a step–pool unit were associated with zones of concentrated upwelling. Bed temperatures tended to be higher and have greater ranges in areas of downwelling flow into the bed. Heat budget estimates were made using meteorological measurements over the water surface and a model of net radiation using canopy characteristics derived from fisheye photography. Heat exchange driven by hyporheic flow through the channel step was a cooling effect during daytime, with a magnitude up to approximately 25% that of net radiation during the period of maximum daytime warming. Heat budget calculations in these headwater streams are complicated by the heterogeneity of incident solar radiation and channel geometry, as well as uncertainty in estimating heat and water exchanges between the stream and the subsurface via hyporheic exchange and heat conduction. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

12.
The skarns and skarn deposits are widely distributed at home and abroad. The skarn deposits include many kinds of ores and higher ore grade. Some of them are broad in scale. Scientists of ore deposits from different countries have paid and are paying grea…  相似文献   

13.
Basalts dredged from the Galapagos Rift Zone between 85°W and 100°W were analyzed by electron microprobe to determine the chemistry of the glass exteriors and included phenocrysts, microphenocrysts and quench minerals. The basalts come from both “normal” mid-ocean ridge segments and from ridge segments that cross the Galapagos Platform. The basalts fall into two chemical and geographical groups. Group A basalts come from outside the central region of the Galapagos Platform (i.e., outside 89–92.5°W) and are chemically similar to basalts from “normal” ocean ridge segments. Group B basalts come from the center of the Galapagos Platform (89–92.5°W) and are enriched in incompatible elements like “plume-influenced” basalts from the Mid-Atlantic Ridge. The spinel, olivine, plagioclase and clinopyroxene phenocrysts in both groups of basalts are low-pressure, equilibrium phases, but the chemical difference among basalts from within each group indicates high-pressure fractional crystallization is also responsible for the chemical evolution of some of these basalts. Presently, no crystallization or partial melting model can relate the chemistry of the two groups of basalts and the compositional influence of a large-ion-lithophile elements and water-rich mantle beneath the Galapagos Platform is a viable alternate hypothesis. The eruption temperature of magmas from the “normal” ridge segments, as determined by olivine-liquid thermometry is 1217±10°C, suggesting steady-state conditions but on the Galapagos Platform the eruption temperatures are lower and more variable than on the “normal” ridge (1186°C±30°C) suggesting a more complex plumbing system and the absence of a steady-state magma chamber beneath the platform.  相似文献   

14.
Microcracks can have a strong influence on the elastic and fracture mechanical properties of rocks if they are numerous, or if they are orientated in unfavourable directions in anisotropic rocks in particular. This paper presents results from a great number of mechanical tests on Stripa granite containing various amounts of microcracks. Variations in the microcrack density were obtained by shock-heating the rock at different temperatures in the range 100–600°C for 3 h.The results presented are obtained from sound velocity measurements, uniaxial compression tests, Brazilian tests and three-point bending tests. The density of microcracks in the heated rock is studied by means of optical microscopy, SEM and differential strain analysis (DSA).Some of the calculated parameters show a maximum value for specimens heat-treated at about 100°C. The tensile strength is, for instance, substantially higher for specimens shock-heated at 100°C than for non-heated ones. Another striking feature is the initial decrease of the diameter observed in specimens heat-treated at 600°C when loaded in uniaxial compression. Both optical microscopy and DSA experiments reveal a large increase in microcracking when the heat-treatment temperature exceeds 300°C.  相似文献   

15.
A thermal event reduces the number of previously registered fission tracks in a mineral dependent upon the track retention properties of the individual mineral. Apatite, sphene and zircon have retention properties over a wide range of temperatures (from 100° to 550°C); apatite data reveal information at lowest temperatures while sphene and zircon data are useful for higher temperatures.Thermal events within this temperature range of 100°C to about 550°C are suitable for study with this technique. The age of the event is determined from samples in which the fission tracks are completely erased, while minerals containing partially removed (erased) tracks provide information on the temperatures occurring during the thermal event.As a test case, the analysis of the temperatures developed by the meteorite impact which produced the Ries crater at 14.7 m.y. ago is presented.  相似文献   

16.
This paper presents the effect of the North Atlantic Oscillation (NAO) on the thermal characteristics of lakes in Poland. In the analysis, the use was made of monthly air temperatures recorded at fifteen meteorological stations, water temperatures of twelve lakes, and Hurrell’s winter NAO indices. Over the study period (1971–2010), there was a marked increase in the temperatures of both, air and lake waters. Depending on the NAO phase, water temperatures were observed to depart from mean values, being markedly higher than average (even by 1°C) in the positive winter NAO phase. The differences in water temperatures were statistically significant in the winter-spring season. In turn, in the negative NAODJFM phase lake water temperatures in winter and spring were markedly lower than average (in March even by 1.0°C). The unique response of some lakes depends on their morphometric parameters, including their mean depth.  相似文献   

17.
During the contemporaneous interval of 1796–1882 a number of significant decreases in temperature are found in the records of Central England and Northern Ireland. These decreases appear to be related to the occurrences of El Niño and/or cataclysmic volcanic eruptions. For example, a composite of residual Central England temperatures, centering temperatures on the yearly onsets of 20 El Niño events of moderate to stronger strengths, shows that, on average, the change in temperature varied by about ±0.3°C from normal, being warmer during the boreal fall–winter leading up to the El Niño year and cooler during the spring–summer of the El Niño year. Also, the influence of El Niño on Central England temperatures appears to have lasted about 1–2 years. Similarly, a composite of residual Central England temperatures, centering temperatures on the month of eruption for 26 cataclysmic volcanic eruptions, shows that, on average, the temperature decreased by about 0.1–0.2°C, typically, 1–2 years after the eruption; although for specific events, like Tambora, the decrease was considerably greater. Additionally, tropical eruptions appear to have produced greater cooling than extratropical eruptions, and eruptions occurring in boreal spring–summer appear to have produced greater cooling than those occurring in fall–winter.  相似文献   

18.
Eggs of Coregonus albula were incubated at temperatures of 1.1, 2.0, 4.9, 6.6, 8.4 and 9.9 °C. The successful hatching is optimum with 61 % at 4.9 °C; incubation time and period of hatching decrease significantly with rising temperature. The length of eleutheroembryos decreases with rising temperature, the yolk sac volume increases. Between the incubation time till hatching and the body length a significantly positive regression exists in the range of 4.9… 8.4 °C, for the yolk sac volume the regression is negative, it is significant in the range of 2.9… 6.6 °C; at the same time a negative regression exists between the yolk sac volume and the body length. Thus, low temperatures cause a delay of hatching, higher temperatures accelerate hatching and at the same time result in a reduced utilization of the yolk reserves. Besides these influences of temperature on the rate of ontogenetic processes, some autoecological consequences of the influence of temperature result, which have to be taken into account in further investigations.  相似文献   

19.
Changes in precipitation and temperature have direct effects on crop water use, water stress, crop yield, evapotranspiration, water nutrient dynamics and other indicators. This study, built on a modelling framework with the Soil and Watershed Assessment Tool (SWAT) model for the Raccoon River Watershed in central Iowa, a typical US Midwestern agricultural watershed, examines the watershed response to changes in meteorological inputs from an ensemble of ten global climate models under the A1B scenario. Changes in climate were directly applied to observations (the delta change method) assuming that the estimates of climate change are reliable even if the simulated current climate may be biased. The ensemble average for the mid‐century (1946–1965) predicted 0.7% increase in daily precipitation (monthly variation from ?11.3% to +19.5%) and 2.78 °C increase in average temperature over the entire watershed. These predictions were translated through a well‐calibrated SWAT modelling setup into 22% decrease in snowfall, 16% decrease in surface runoff, 18% decrease in baseflow, 8% increase in evapotranspiration and 17% decrease in total water yield. The spatial impact at the subwatershed level revealed a wide variation (but no defined trend) with decrease in water yield that ranged from 10% to 23%. Flow near the watershed outlet (Van Meter, Iowa) is expected to decline by 17% on an average annual basis with the highest impact occurring during summer months with a maximum 39% reduction in August. Changes in climate were found to have a clear and significant impact signal of decreasing streamflow at the watershed outlet with far‐reaching implication for drinking water supplies for the central Iowa communities. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

20.
Continuous temperature measurements at 11 stream sites in small lowland streams of North Zealand, Denmark over a year showed much higher summer temperatures and lower winter temperatures along the course of the stream with artificial lakes than in the stream without lakes. The influence of lakes was even more prominent in the comparisons of colder lake inlets and warmer outlets and led to the decline of cold‐water and oxygen‐demanding brown trout. Seasonal and daily temperature variations were, as anticipated, dampened by forest cover, groundwater input, input from sewage plants and high downstream discharges. Seasonal variations in daily water temperature could be predicted with high accuracy at all sites by a linear air‐water regression model (r2: 0·903–0·947). The predictions improved in all instances (r2: 0·927–0·964) by a non‐linear logistic regression according to which water temperatures do not fall below freezing and they increase less steeply than air temperatures at high temperatures because of enhanced heat loss from the stream by evaporation and back radiation. The predictions improved slightly (r2: 0·933–0·969) by a multiple regression model which, in addition to air temperature as the main predictor, included solar radiation at un‐shaded sites, relative humidity, precipitation and discharge. Application of the non‐linear logistic model for a warming scenario of 4–5 °C higher air temperatures in Denmark in 2070‐2100 yielded predictions of temperatures rising 1·6–3·0 °C during winter and summer and 4·4–6·0 °C during spring in un‐shaded streams with low groundwater input. Groundwater‐fed springs are expected to follow the increase of mean air temperatures for the region. Great caution should be exercised in these temperature projections because global and regional climate scenarios remain open to discussion. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

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