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1.
The attenuation of P- and S-waves in Southeastern Sicily was estimated by applying two different methods in time and frequency domains. We analyzed waveforms from about 290 local events (0.6≤ML≤4.6) recorded at a three-component digital network.By applying the pulse broadening method to the first P-wave pulse, we found an average Qp value of ca. 140. The application of the frequency decay method provided a Qp value of ca. 120, in the low-frequency band (3-9 Hz). Conversely, in the high frequency range (16-27 Hz) the average Qp is significantly larger (ca. 640). The frequency decay method was also applied to S-waves spectra. In the low frequency range (2-5 Hz) the estimated average Qs is ca. 190. As for Qp, also Qs, in the high frequency range (16-27 Hz), is larger (ca. 700). These results evidenced a frequency dependence of both the quality factors Qp and Qs, as commonly observed in tectonically active zones characterized by high degree of heterogeneity.  相似文献   

2.
The earthquakes in Kaliningrad, West Russia on the 21st of September 2004 were unexpected in a seismically quiet area. The main shock of magnitude mb = 5 was widely felt around the Baltic Sea. A comparison with some historic earthquakes in Northern Europe shows that its perceptibility area is smaller than that of the 1904 Oslo Graben earthquake of an estimated magnitude (ML) 5.4 but larger than those of the 1759 Kattegat and 1819 Lurøy earthquakes. The latter are claimed to have had magnitudes (MS) in the range of 5.7-6.0. An analysis of the Lg phase of the Kaliningrad earthquakes as recorded at a number of European stations accords only weakly with the macroseismic intensity pattern that shows fast attenuation towards west-northwest and southeast. The strike-slip focal mechanism of the main shock is discussed in the context of remnant glacial rebound stresses in generating present-day seismicity in N. Europe.  相似文献   

3.
We investigate the seismic properties of modern crustal seismicity in the northwestern Sierras Pampeanas of the Andean retroarc region of Argentina. We modelled the complete regional seismic broadband waveforms of two crustal earthquakes that occurred in the Sierra de Velasco on 28 May 2002 and in the Sierra de Ambato on 7 September 2004. For each earthquake we obtained the seismic moment tensor inversion (SMTI) and tested for its focal depth. Our results indicate mainly thrust focal mechanism solutions of magnitudes Mw 5.8 and 6.2 and focal depths of 10 and 8 km, respectively. These results represent the larger seismicity and shallower focal depths in the last 100 years in this region. The SMTI 2002 and 2004 solutions are consistent with previous determinations for crustal seismicity in this region that also used seismic waveform modelling. Taken together, the results for crustal seismicity of magnitudes ≥5.0 in the last 30 years are consistent with an average P-axis horizontally oriented by an azimuth of 125° and T-axis orientation of azimuth 241° and plunge 58°. This modern crustal seismicity and the historical earthquakes are associated with two active reverse faulting systems of opposite vergences bounding the eastern margin of the Sierra de Velasco in the south and the southwestern margin of the Sierra de Ambato in the north. Strain recorded by focal mechanisms of the larger seismicity is very consistent over this region and is in good agreement with neotectonic activity during the last 11,000 years by Costa (2008) and Casa et al. (in press); this shows that the dominant deformation in this part of the Sierras Pampeanas is mainly controlled by contraction. Seismic deformation related to propagation of thrusts and long-lived shear zones of this area permit to disregard previous proposals, which suggested an extensional or sinistral regime for the geomorphic evolution since Pleistocene.  相似文献   

4.
We studied the morphological and biochemical changes of mitochondria-rich cells (MRCs) of a demersal teleost, Paralichthys olivaceus, during exposure to 0.98, 2.97 and 4.95 kPa pCO2. The apical opening area of MRCs increased 2.2 and 4.1 times by 24 h exposure to 2.97 and 4.95 kPa pCO2, respectively, while the cross-sectional area or density of MRCs did not change. Gill Na+/K+-ATPase activity more than doubled at 72 h and then returned to the pre-exposure level at 168 h in 0.98 kPa pCO2, while it increased 1.7 times at 24 h at 4.95 kPa. These results indicate that the apical opening area of MRCs and the gill Na+/K+-ATPase activity may be used as an indicator of acute (up to 72 h), but not chronic, impacts of high (>1 kPa) seawater CO2 conditions in P. olivacues. Limitations of those parameters as indices of CO2 impacts are discussed.  相似文献   

5.
In the Jungwon area, South Korea, two contrasting types of deep thermal groundwater (around 20–33 °C) occur together in granite. Compared to shallow groundwater and surface water, thermal groundwaters have significantly lower δ18O and δD values (> 1‰ lower in δ18O) and negligible tritium content (mostly < 2 TU), suggesting a relatively high age of these waters (at least pre-thermonuclear period) and relatively long subsurface circulation. However, the hydrochemical evolution yielded two distinct water types. CO2-rich water (PCO2 = 0.1 to 2 atm) is characterized by lower pH (5.7–6.4) and higher TDS content (up to 3300 mg/L), whereas alkaline water (PCO2 = 10− 4.1–10− 4.6 atm) has higher pH (9.1–9.5) and lower TDS (< 254 mg/L). Carbon isotope data indicate that the CO2-rich water is influenced by a local supply of deep CO2 (potentially, magmatic), which enhanced dissolution of silicate minerals in surrounding rocks and resulted in elevated concentrations of Ca2+, Na+, Mg2+, K+, HCO3− and silica under lower pH conditions. In contrast, the evolution of the alkaline water was characterized by a lesser degree of water–rock (granite) interaction under the negligible inflow of CO2. The application of chemical thermometers indicates that the alkaline water represents partially equilibrated waters coming from a geothermal reservoir with a temperature of about 40 °C, while the immature characteristics of the CO2-rich water resulted from the input of CO2 in Na–HCO3 waters and subsequent rock leaching.  相似文献   

6.
The aim of our search is the analysis of aftershock temporal series following a mainshock with magnitude M ≥ 7.0. Investigating aftershock behavior may find the key to explain better the mechanism of seismicity as a whole.In particular, the purpose of this work is to highlight some methodological aspects related to the observation of possible anomalies in the temporal decay. The data concerning the temporal series, checked according to completeness criteria, come from the NEIC-USGS data bank. Here we carefully analyze the New Guinea 29 April 1996 seismic sequence.The observed temporal series of the shocks per day can be considered as a sum of a deterministic contribution (the aftershock decay power law, n(t) = K·(t + c)−p + K1) and of a stochastic contribution (the random fluctuations around a mean value represented by the above mentioned power law). If the decay can be modeled as a non-stationary Poissonian process where the intensity function is equal to n(t) = K·(t + c)−p + K1, the number of aftershocks in a small time interval Δt is the mean value n(t)·Δt, with a standard deviation .  相似文献   

7.
The Pontides are characterized by a series of Mesozoic-Cenozoic fold belts comprising a N-vergent foreland fold and thrust belt in the Western Pontides and a concave, upward-shaped fold belt in the Eastern Pontides. The curvature of the fold belt follows the Caucasus which may imply a phase of oroclinal bending. In order to test whether the fold curvature represents a phase of oroclinal bending, a paleomagnetic study has been carried out in the Eastern Pontides on late Cretaceous and middle Eocene volcanic and sedimentary rocks from 29 sites. Rock magnetic studies reveal medium-temperature components with an unblocking temperature of 400–580 °C, indicating pseudo-single domain titanomagnetite as the most abundant carrier of magnetic remanence in the middle Eocene rocks studied here. In the upper Cretaceous rocks, a high-temperature component with an unblocking range of 580–650 °C was isolated. Stepwise thermal and alternating field demagnetization isolated two components of remanent magnetization in middle Eocene rocks comprising a low unblocking temperature/coercivity component near the present field direction and a characteristic remanent magnetization (ChRM) component of Ds = 332.3°, Is = 49.9° (k = 33.3, α95 = 9.2°, N = 15 sites). A positive fold test at a 95% confidence level and a reversal test indicate a primary magnetization. Component analysis of the upper Cretaceous rocks identifies a stable ChRM Ds = 160.3°, Is = −45.0°, (k =  85.6, α95 = 6.0°, N =  8 sites) following removal of secondary remanence. Their ChRM direction passes fold and reversal tests at a 95% confidence level. Both the upper Cretaceous and middle Eocene paleomagnetic data from the Eastern Pontides and the Lesser Caucasus clearly demonstrate evidence of oroclinal bending that occurred contemporaneouslywith the convergence between Arabia and Eurasia in the Paleocene.  相似文献   

8.
The role of static stress changes in triggering an earthquake has long been debated in the fields of geophysics and fault mechanics. Valuable data sets for the study of static triggering were provided within the 1-year period following the devastating 1999 Chi-Chi (Taiwan) earthquake (MW=7.6), during which more than 20,000 aftershocks occurred. In this study, stress waves generated by the Chi-Chi earthquake were calculated using a source rupture model in conjunction with a layered elastic model. Static (permanent) stress changes were extracted from the long-period offsets in the stressgrams. Correlations between the calculated stress changes and seismicity were analyzed at different depths and over varying time intervals to ascertain the impact effects of stress changes on triggering aftershocks. Correlations between prior seismicity rates and static stress changes imposed by the Chi-Chi event were low, while correlations between late seismicity rates and static stress changes were much higher. This indicates that static stress changes did affect the occurrence of the Chi-Chi aftershock sequence. The percentage of early aftershocks at shallow depths (0-10 km) in static stress-enhanced areas within 2 weeks of the main shock was high but decreased considerably at greater depths (>10 km) and over longer time periods. It is concluded that static stress changes at depths of 0-10 km played a major role in triggering crustal aftershocks, especially those that occurred within 2 weeks of the main shock. In the deeper crust, static stress changes may have been modified by viscous flow, and at later times, perturbed by earlier, larger aftershocks. Although the correlations between seismicity rate changes and static stress changes are imperfect, a region that was anti-triggered is detected when these two results are compared. Static stress changes are presumably not the only aftershock triggering mechanism, but they definitively play a major role in triggering shallow aftershocks.  相似文献   

9.
The southern Yellow Sea (SYS), located to the north of the East China Sea (ECS), was considered part of the ECS when Tsunogai et al. (1999) proposed the “continental shelf pump” (CSP) hypothesis. However, the original CSP carbon dioxide (CO2) uptake flux (2.9 mol C m−2 yr−1) appears to have been overestimated, primarily due to the differences between the SYS and the ECS in terms of their CO2 system. In this paper, we estimated air-sea CO2 fluxes in the SYS using the surface water partial pressure of CO2 (pCO2) measured in winter, spring, and summer, as well as that estimated in fall via the relationship of pCO2 with salinity, temperature, and chlorophyll a. The results indicate that overall, the entire investigated area was a net source of atmospheric CO2 during summer, winter, and fall, whereas it was a net sink during spring. Spatially, the nearshore area was almost a permanent CO2 source, while the central SYS shifted from being a CO2 sink in spring to a source in the other seasons of the year. Overall, the SYS is a net source of atmospheric CO2 on an annual scale, releasing ∼7.38 Tg C (1 Tg=1012 g) to the atmosphere annually. Thus, the updated CO2 uptake flux in the combined SYS and ECS is reduced to ∼0.86 mol C m−2 yr−1. If this value is extrapolated globally following Tsunogai et al. (1999), the global continental shelf would be a sink of ∼0.29 Pg C yr−1, instead of 1 Pg C yr−1 (1 Pg=1015 g).The SYS as a net annual source of atmospheric CO2 is in sharp contrast to most mid- and high-latitude continental shelves, which are CO2 sinks. We argue that unlike the ECS and the North Sea where carbon on the shelf could be exported to the open ocean, the SYS lacks the physical conditions required by the CSP to transport carbon off the shelf effectively. The global validity of the CSP theory is thus questionable.  相似文献   

10.
A spatial and temporal study on data collected along the longitudinal gradient of the Principal Channel of Bahía Blanca estuary, Argentina, was carried out during 1992–1993. At nine stations, phytoplankton abundance, chlorophyll a (Chl-a) concentration, inorganic nutrient levels, Secchi disk depth, euphotic depth:mixing depth ratio (Zeu:Zm), salinity and temperature were recorded. Phytoplankton abundance, Chl-a concentration and nutrient levels decreased towards the outer zone of the estuary. The inner zone (stations 1 and 2), which was characterized by high turbidity, high nutrient concentrations and high Zeu:Zm (>0.16, [critical mixing ratio]), registered the highest phytoplankton abundance and Chl-a concentrations. Temporal variability of data was also noteworthy in this zone. The highest biomass values thus corresponded to June, July, August and the beginning of spring (18 μg Chl-a L−1 and 9×106 cells L−1) concomitantly with a diatom bloom. In the middle zone (stations 3–6), a strong phytoplankton biomass decrease was observed and it coincided with both deep-mixed depths and low Zeu:Zm (<0.16). The outer zone (stations 7–9), which was characterized by low phytoplankton biomass values and low nutrient levels all along the year, was the area mostly influenced by waters from the adjacent continental shelf. In view of the above, it can be concluded that the most important primary production in the Bahía Blanca would be produced in the shallow inner zone during winter, being the spatial reach of the phytoplankton biomass principally limited to estuarine waters. Presumably, less than 5% of such biomass may reach the coastal area of the estuary.  相似文献   

11.
The complexity of the relationships between Alexandrium minutum (A.m.) concentration in the water ([A.m.]w), Paralytic Shellfish Poisoning contamination in the digestive gland ([PSP]dg) and valve behavior was explored in oysters Crassostrea gigas. Two experiments were conducted, during which oysters’ valve behaviour were analyzed. Oysters, first acclimated for 10-days with the non harmful microalgae Heterocapsa triquetra (H.t.), were exposed to four microalgae mixtures at constant total concentrations of 10 × 103 cells ml−1 (experiment-1) and 5 × 103 cells ml−1 (experiment-2): 100% A.m.; 50% A.m.-50% H.t.; 25% A.m.-75% H.t.; 100% H.t. At the end of experiment-2, [PSP]dg were measured.At 10 × 103 cells ml−1, the microalgal ingestion decreased (p < 0.05) with increasing [A.m.]w but not at 5 × 103 cells ml−1 (p > 0.05). The frequency of microclosures specifically increased with [A.m.]w (p < 0.05) and the opening duration with [PSP]dg (p < 0.0001). Oysters exhibiting the maximum increase in opening duration also exhibited the highest [PSP]dg. The results are discussed in terms of oyster physiology and origin of the behavioral response.  相似文献   

12.
Low tide rainfall may represent an important but little studied process affecting sediment fluxes on intertidal mudflats. In this study, we simulated rainfall events on an intertidal mudflat (median grain size=18.4 μm) of low slope (1 in 300) then quantified effects on sediment erodibility. Treatments consisted of a high (4.1 mm min−1 for 6 min) and low (0.36 mm min−1 for 60 min) rain intensity, chosen to match naturally occurring events and experiments were conducted seasonally (May and August) to encompass variations in ambient sediment stability. Changes in bed elevation due to rainfall were estimated using marked rods and sediment erodibility parameters (mass of sediment eroded at a flow velocity of 0.3 m s−1 (ME-30, g m−2) and critical erosion velocity (Ucrit, m s−1)) were determined in annular flumes (bed area=0.17 m2). Ambient/control sediment erodibility in May (ME-30=211 g m−2, Ucrit=0.18 m s−1) was higher than in August (ME-30=30 g m−2, Ucrit=0.26 m s−1) and was correlated with changes in biological activity. In May, surface sediment was influenced by high densities of the bioturbating snail Hydrobia ulvae (1736 ind. m−2) and low biomass of the sediment stabilising microphytobenthos (5.7 μg chlorophyll a cm−2). In contrast, in August H. ulvae densities were low (52 ind. m−2) and microphytobenthic biomass higher (9.2 μg chlorophyll a cm−2). The high rain treatment caused a decrease in bed elevation of between 1.5 mm (May) and 4.4 mm (August) and significantly reduced sediment organic content and microphytobenthic biomass. Rainfall increased sediment erodibility; compared to ambient sediments ME-30 increased by a factor of 1.4× in May and 8.8× in August and caused a 10–30% decline in Ucrit. The seasonal difference in treatment effect was due to the change in ambient sediment stability. The low rain treatment in August had no effect on bed elevation, microphytobenthic biomass or sediment erodibility. In May, the same treatment caused a reduction in bed elevation (0.5 mm) and microphytobenthic biomass but counter-intuitively, a decrease in sediment erodibility (ME-30 was reduced by 40%, Ucrit increased by 5%) compared to controls. We attribute this result to removal by rainfall of easily eroded surface flocs and biogenic roughness which resulted in an underlying sediment with a smoother surface and greater resistant to erosion. Results suggest that high intensity rain events may destabilise intertidal sediments making them more susceptible to erosion by returning tidal currents and that the sediment eroded during such events may represent a considerable fraction (up to 25%) of the seasonal variation in shore elevation. The impact of natural rain events are likely to vary considerably due to variations in droplet size, intensity and duration and the interaction with ambient sediment stability.  相似文献   

13.
The metabolic balance between production and respiration in plankton communities of the Gulf of Papua was investigated in May 2004. Water samples taken at 19 stations were allocated to groups on the basis of physico-chemical characteristics. Oxygen consumption and production in flasks incubated in the dark and in the light was determined by micro-Winkler titration. Dark bottle respiration in samples influenced by the estuarine plume averaged 3.09±1.92 (SD) mmol O2 m−3 d−1 and production within surface light bottles averaged 7.63±3.36 (SD)  mmol O2 m−3 d−1. Corresponding values in stations more typical of the central Gulf of Papua were 1.68±1.30 (SD) mmol O2 m−3 d−1 and 1.08±2.25 (SD) mmol O2 m−3 d−1. Despite a shallow (<10 m) euphotic zone within the plume stations, phytoplankton production in the surface layers was sufficiently high to subsidise total water column respiration. Integrating production and respiration over the water column resulted in a calculation of net community production (NCP) of 626±504 (SD) mg C m−2 d−1, and community respiration (CR) of 712±492 mg C m−2 d−1 at the plume stations, with an average P:R ratio of 1.97. In the offshore group NCP was 157±450 (SD) mg C m−2 d−1 and CR was 1620±1576 mg C m−2 d−1. The average P:R ratio was 1.27. Three of the 7 stations allocated to the offshore group were net heterotrophic. In contrast to earlier studies in the area indicating that the Gulf of Papua waters is heterotrophic [Robertson, A.I., Dixon, P., Alongi, D.M., 1998. The influence of fluvial discharge on pelagic production in the Gulf of Papua, Northern Coral Sea. Estuarine, Coastal and Shelf Science 46, 319–331], our data indicate that in May 2004 the Gulf was in positive metabolic balance, but by only ∼120 mg C m−2 d−1. We conclude that waters of the Gulf of Papua under riverine influence are net autotrophic, but that within the central Gulf there is a fine metabolic balance alternating between autotrophy and heterotrophy.  相似文献   

14.
We used data of local earthquakes collected during two recent passive seismic experiments carried out in southern Italy in order to study the seismotectonic setting of the Lucanian Apennine and the surrounding areas. Based on continuous recordings of the temporary stations we extracted over 15,600 waveforms, which were hand-picked along with those recorded by the permanent stations of the Italian national seismic network obtaining a dense, high-quality dataset of P- and S-arrival times. We examined the seismicity occurring in the period 2001–2008 by relocating 566 out of 1047 recorded events with magnitudes ML ≥ 1.5 and computing 162 fault-plane solutions. Earthquakes were relocated using a minimum one-dimensional velocity model previously obtained for the region and a Vp/Vs ratio of 1.83. Background seismicity is concentrated within the upper crust (between 5 and 20 km of depth) and it is mostly clustered along the Lucanian Apennine chain axis. A significant feature extracted from this study relates to the two E–W trending clusters located in the Potentino and in the Abriola–Pietrapertosa sector (central Lucania region). Hypocentral depths in both clusters are slightly deeper than those observed beneath the Lucanian Apennine. We suggest that these two seismic features are representative of the transition from the inner portion of the chain to the external margin characterized by dextral strike-slip kinematics. In the easternmost part of the study area, below the Bradano foredeep and the Apulia foreland, seismicity is generally deeper and more scattered. The sparse seismicity localized in the Sibari Plain, in the offshore area along the northeastern Calabrian coast and in the Taranto Gulf is also investigated thanks to the new recordings. This seismicity shows hypocenters between 12 and 20 km of depth below the Sibari Plain and is deeper (foci between 10 and 35 km of depth) in the offshore area of the Taranto Gulf. 102 well-constrained fault-plane solutions, showing predominantly normal and strike-slip character with tensional axes (T-axes) generally NE oriented, were selected for the stress tensor analysis. We investigated stress field orientation inverting focal mechanism belonging to the Lucanian Apennine and the Pollino Range, both areas characterized by a more concentrated background seismicity.  相似文献   

15.
The attenuation characteristics of Indian lithosphere and its comparison with different tectonic settings in the world are determined from the observations of the Q for Lg(QLg)-, and S(QS)-waves in the 1-30 Hz frequency range. The scattering is approximated with a Gaussian distribution of spherical scatterers. To approximate single scattering, we use Dainty's [Geophy. Res. Lett. 8 (11) (1981) 1126] model that attenuation is given by 1/Q(ω) = 1/Qi + g(ω)v/ω, where Qi is intrinsic Q due to anelastic attenuation, v is shear wave velocity, ω is angular frequency, g = ∫n(a)σ da is the total scattering coefficient for S-to-S scattering, n(a) da is the number of scattering spheres of radius a per unit volume, and σ is the scattering cross-section for the sphere. We find that if n(a) is described by a simple two parameter (a0 and c) Gaussian of amplitude c and standard deviation and mean a0, the attenuation data for different regions of the world are well approximated over the frequency band of seismic observations. Our major findings are: (1) the maximum effect of scattering on attenuation occurs at 0.84 Hz or a wavelength of 4.16 km; (2) the values of g are frequency dependent. Values of g are of the order of 10−3 km−1 at 1-30 Hz, varying from 0.0031 to 0.01 and 0.001 to 0.0083 km−1 for tectonically active and stable regions, respectively; (3) regions of active tectonics and seismicity generally have lower Qi values (1000) than that in stable regions (2000); and (4) regions of high Qi value exhibit low intensity of scattering.  相似文献   

16.
The recent earthquake sequences of 2012 (northern Italy) and 2013 (Marche offshore) provided new, fundamental constraints to the active tectonic setting of the outer northern Apennines. In contrast to the Po Plain area, where the 2012 northern Italy earthquakes confirmed active frontal thrusting, the new focal mechanisms obtained in this study for the 2013 Marche offshore earthquakes indicate that only minor thrust fault reactivation occurs in the Adriatic domain, even for a theoretically favourably oriented maximum horizontal compression. Recent seismicity in this domain appears to be mainly controlled by transcurrent crustal faults dissecting the Apennine thrust belt. The along-strike stress field variation from the Po Plain to the Adriatic area has been quantitatively investigated by applying the multiple inverse method (MIM) to the analysis of the entire seismicity recorded from January 1976 to August 2014, from the top 12 km of the crust (fault plane solutions from 127 earthquakes with MW ≥ 4), allowing us to obtain a comprehensive picture of the state of stress over the outer zone of the fold and thrust belt. The present-day stress field has been defined for 39 cells of 1.5° × 1.5° surface area and 12 km depth. The obtained stress field maps point out that, although the entire outer northern Apennines belt is characterized by a sub-horizontal maximum compressive axis (σ1), the minimum compression (σ3) is sub-vertical only in the Po Plain area, becoming sub-horizontal in the Adriatic sector, thus confirming that the latter region is dominated by an active tectonic regime of strike-slip type.  相似文献   

17.
Long-term historical records of rainfall (P), runoff (Q) and other climatic factors were used to investigate hydrological variability and trends in the Volta River Basin over the period 1901-2002. Potential (Ep) and actual evaporation (E), rainfall variability index (δ), Budyko’s aridity index (IA), evaporation ratio (CE) and runoff ratio (CQ) were estimated from the available hydroclimatological records. Mann-Kendall trend analysis and non-parametric Sen’s slope estimates were performed on the respective time series variables to detect monotonic trend direction and magnitude of change over time.Rainfall variability index showed that 1968 was the wettest year (δ = +1.75) while 1983 was the driest (δ = −3.03), with the last three decades being drier than any other comparable period in the hydrological history of the Volta. An increase of 0.2 mm/yr2 (P < 0.05) was observed in Ep for the 1901-1969 sub-series while an increased of 1.8 mm/yr2 (P < 0.01) was recorded since 1970. Rainfall increased at the rate of 0.7 mm/yr2 or 49 mm/yr between 1901 and 1969, whereas a decrease of 0.2 mm/yr2 (6 mm/yr) was estimated for 1970-2002 sub-series. Runoff increased significantly at the rate of 0.8 mm/yr (23 mm/yr) since 1970. Runoff before dam construction was higher (87.5 mm/yr) and more varied (CV = 41.5%) than the post-dam period with value of 73.5 mm/yr (CV = 23.9%). A 10% relative decrease in P resulted in a 16% decrease in Q between 1936 and 1998. Since 1970, all the months showed increasing runoff trends with significant slopes (P < 0.05) in 9 out of the 12 months. Possible causes, such as climate change and land cover change, on the detected changes in hydroclimatology are briefly discussed.  相似文献   

18.
Diffusion in stratified porous media is common in the natural environment. The objective of this study is to develop analytical solutions for describing the diffusion in layered porous media with a position-dependent diffusion coefficient within each layer. The orthogonal expansion technique was used to solve a one-dimensional multi-layer diffusion equation in which the diffusion coefficient is expressed as a segmented linear function of positions in the porous media. The behavior of the solutions is illustrated using several examples of a three-layer system, with constant diffusion coefficient α1 in layer 1 (0 < x < l1), α3 in layer 3(l2 < x < l3), and a linearly position-dependent diffusion coefficient α1(1 + Δ(x − l1)/(l2 − l1)) in the center layer (Δ = α3/α1 − 1). Because of the asymmetry of the layered system, the diffusion and related concentration distributions are also asymmetrical. For a given Δ value, the smaller the value of (l2 − l1)/l3, the more significant the accumulation of concentration in the middle transition zone (l1 < x < l2), the sharper the change in the concentration profile of spatial distribution. Therefore, transition between two layers has significant effects on diffusion.  相似文献   

19.
Hudson River sediment microcosms from Piles Creek (PC), Piermont Marsh (PM), and Iona Island (II) were amended with ∼100 mM nitrate or sulfate to stimulate anaerobic bioremediation. Nitrate and sulfate decreased over two years of field incubation and the fraction of these losses due to diffusion to the water column was predicted using Fick’s law. Apparent diffusion (Dapp) values of 1-4 × 10−10 m2 s−1 predicted the majority of loss/gain from/to the sediments by 700 d, but not at all times. Effective diffusion (Deff) values predicted by the porosity function (Deff = Dmol ε4/3) were larger than those observed in the field, and field data indicates a cube power relationship: Deff = Dmol ε3. Dapp greatly increased in surficial layers at PM and PC in year two, suggesting that bioadvection caused by bioturbating organisms had occurred. The effects of bioturbation on transport to/from the sediments are modeled, and results can be applied to various sediment treatment scenarios such as capping.  相似文献   

20.
A three-dimensional two-phase flow model is coupled to a non-linear reactive transport model to study the efficacy of potassium permanganate treatment on dense, non-aqueous phase liquid (DNAPL) source removal in porous media. A linear relationship between the soil permeability (k) and concentration of manganese dioxide precipitate ([MnO2(s)]), k = ko + Srind [MnO2(s)], is utilized to simulate nodal permeability reductions due to precipitate formation. Using published experimental column studies, an Srind = −5.5 × 10−16 m2 L/mg was determined for trichloroethylene (TCE) DNAPL. This Srind was then applied to treatment simulations on three-dimensional TCE DNAPL source zones comprising either DNAPL at residual saturations, or DNAPL at pooled saturations.  相似文献   

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