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1.
In the present work, we built a mathematical model of polychlorinated biphenyl (PCB) bioaccumulation in Perna viridis, namely, a one-compartment model with a time dependent incorporation rate R (μg g−1 lipid per ppb water per day), with positive substrate cooperativity as the underlying physical mechanism. The temporal change of the PCB concentration Q (μg g−1 lipid) in the soft tissues of the mussel depends on the competition of the input rate RW and the output rate kQ, where W is the concentration of PCB in water (ppb water) and k is the elimination rate (per day). From our experimental data, k=0.181±0.017 d−1. The critical concentration in water Wc for positive substrate cooperativity was found to be 2.4 ppb. Below Wc, R is a constant. For a water concentration of 0.5 ppb Aroclor 1254, R=24.0±2.4 μg g−1 lipid ppb−1 d−1. Above Wc, positive substrate cooperativity comes into effect and R becomes a function of time and dependent on the concentration Q in a form R=γQ/(Q+δ). This is the case for a water concentration of 5 ppb Aroclor 1254, where γ=15.1 μg g−1 lipid ppb−1 d1 and δ≈200 μg g−1 lipid. From this model, the uptake is exponentially increasing when the PCB concentration in the mussel is small compared to 200 μg g−1 lipid, and hyperbolically increasing when the concentration is large compared to 200 μg g−1 lipid, which are consistent with the experimental data. The model is useful for understanding the true processes taking place during the bioaccumulation and for risk assessment with higher confidence. Future experimental data which challenge the present model are anticipated and in fact desirable for improvement and perfection of the model. 相似文献
2.
Variation in riverine phosphorus between 1994 and 2003 as affected by land-use and loading reductions in six medium-sized to large German rivers 总被引：1，自引：0，他引：1
Land use and in-stream transformation exert great influence on concentrations and loads of phosphorus (P) in rivers. We aimed to display differences in the courses of total P (TP) and soluble reactive P (SRP) concentrations and loads in six medium-sized to large rivers in the central region of Germany, and to identify the reasons for different long-term trends. Therefore, we applied multivariate statistics to 10-year-time series (1994–2003) of TP, SRP, discharge (Q), water temperature (T), pH, dissolved organic carbon (DOC), total organic carbon (TOC), dissolved oxygen (DO), total iron (Fe), and total manganese (Mn). Statistical results were related to land use in the catchments of the rivers. TP concentrations ranged between 0.02 and 0.78 mg l−1, and SRP concentrations ranged between 0.01 and 0.44 mg l−1. Q correlated negatively with TP and SRP concentrations over the entire year. Furthermore, Fe correlated significantly and positively to TP and SRP and therefore, ferric hydroxides likely were the major P sorption sites. DOC showed significant positive correlation to SRP particularly in spring, indicating manure exposure in early spring as a major source of both, DOC and SRP. Significant negative correlations between DO and SRP in summer hint at internal P loading in rivers or in flushed lakes. Different forms of land use were the reasons of enhanced or retarded recovering from previous increases in P concentrations. High portions of arable land within some of the catchments impeded the process of decreases since 1996 because of remaining high-diffuse emissions from fertilized soils. Agricultural practices, exposing fertilizer to soils within the river catchments and high Q in early spring caused high TP and SRP loads to downstream systems, and evoked risks for downstream river reaches. 相似文献
3.
Stephen Childress 《Physics of the Earth and Planetary Interiors》1979,20(2-4):172-180
The alpha-effect is studied at large magnetic Reynolds numbers (R) for certain simple steady flows. The flux sheets created by a two-dimensional cellular flow sustain an of order R−1/2 at large values of R. For an analogous helical axisymmetric motion the mean electromotive force gives a finite nonzero limit of as R → ∞, this being a consequence of the existence of an intense axial flux rope. The latter estimate may be typical of steady three-dimensional motion. 相似文献
4.
We investigated the upper mantle anelastic structure beneath the northern Philippine Sea region, including the Izu-Bonin subduction zone and the Shikoku Basin. We used regional waveform data from 69 events in the Pacific and the Philippine Sea slabs, recorded on F-net and J-array network broadband stations in western Japan. Using the S–P phase pair method, we obtained differential attenuation factors, δt*, which represent the relative whole path Q. We conducted a tomographic inversion using 978 δt* values to invert for a fine-scale (50–100 km) three-dimensional anelastic structure.
The results shows two high-Q regions (QP>1000) which are consistent with the locations of the Pacific and the Philippine Sea slabs. Also there is a low-Q (QP110) area extending to the deeper parts (350–400 km) of the model just beneath the old spreading center and the Kinan Seamount Chain in the Shikoku Basin. A small depth dependence of the laterally averaged QP was found, with values of 266 (0–250 km), 301 (250–400 km), and 413 (400–500 km). 相似文献
5.
Combining measurements of transpiration and stable isotopes of water to determine groundwater discharge from forests 总被引：3，自引：0，他引：3
Discharge of saline groundwater from Eucalyptus forests on a semi-arid floodplain was directly determined by first measuring transpiration rates from the forests, and then partitioning the transpiration flux into groundwater discharge and soil water depletion. This partitioning was achieved by identifying the source of the transpired water with naturally occurring stable isotopes of water. Transpiration rates were low, being about 0.3 mm day−1 from three E. largiflorens sites and up to 2 mm day−1 from an E. camaldulensis site. There was no significant variation in transpiration across seasons, indicating that transpiration was limited by environmental factors other than evaporative demand. Despite its salinity (electrical conductivities of 11–33 dS m−1), the groundwater was used by the forests at all sites and all times, and made up 100% of transpiration in more than half of the measurements, and 40–80% in the remainder. There was some consistency in water uptake patterns. E. camaldulensis tended to take up shallow soil water and groundwater simultaneously, as did trees at one of the E. largiflorens sites. At the driest sampling time, however, groundwater was the only source of water for trees at both of these sites. Trees at the remaining two E. largiflorens sites generally relied solely on the groundwater. The tree water source results indicate that groundwater discharge fluxes were between 40 and 100% of the transpiration fluxes at these sites. These groundwater discharge fluxes were small in terms of regional groundwater balances, but would be important in the salinisation of the soils. Additionally, uptake of water from the soil profile by the trees substantially increased groundwater discharge compared with discharge from the soils had they been bare of vegetation. 相似文献
6.
K. Righter M. J. Drake G. Yaxley 《Physics of the Earth and Planetary Interiors》1997,100(1-4):115-134
We report new metal-silicate partition coefficients for Ni, Co and P at 7.0 GPa (1650–1750°C), and Ni, Co, Mo, W and P at 0.8, 1.0 and 1.5 GPa (1300–1400°C). Guided by thermodynamics, all available metal-silicate partition coefficients, D(i), where i is Ni, Co, P, Mo and W, are regressed against 1/T, P/T, lnf(O2), ln(1 − Xs) (XS is mole fraction of S in metallic liquid) and nbo/t (non-bridging oxygen/tetrahedral cation ratio, a silicate melt compositional-structural parameter) to derive equations of the following form: ln D(i) = aln f(O2) + (b/T) + (cP/T) + d(nbo/t) + eln(1 − XS) + f. Expressions for solid metal-liquid silicate and liquid metal-liquid silicate partition coefficients are derived for S-free and S-bearing systems.
We investigate whether Earth's upper-mantle siderophile element abundances can be reconciled with simple metal-silicate equilibrium. Sulfur-free metallic compositions do not allow a good fit. However, Ni, Co, Mo, W and P abundances in the upper mantle are consistent with simple metal-silicate equilibrium at mantle pressures and temperatures (27 GPa, 2200 K, ΔIW(iron-wüstite) = −0.15, nbo/t = 2.7; XS = 0.15). Although these conditions are near the anhydrous peridotite solidus, they are well above the hydrous solidus and probably closer to the liquidus. A hydrous magma ocean and early mantle are consistent with predicted planetary accretion models. These results suggest that siderophile element abundances in Earth's upper mantle were established by liquid metal-liquid silicate equilibrium near the upper-mantle-lower-mantle boundary. 相似文献
7.
为理解震源机制和所作用的应力张量之间的关系,模拟了东西向挤压、垂直向拉张的挤压应力体系,南北向挤压、东西向拉张的走滑应力体系和垂直向挤压、东西向拉张的拉张应力体系所产生震源机制及其剪应力和正应力的表现.结果表明:挤压应力体系可以产生逆断型、走滑型和逆走滑型的震源机制,并随着应力形因子R的增大,逆断型震源机制数目逐渐减小,而走滑型和逆走滑型震源机制数目逐渐增加;走滑应力体系兼有各种类型的震源机制,随着R值的增大,正断型和正走滑型震源机制数目逐渐减小,而逆断型和逆走滑型震源机制数目逐渐增加;拉张应力体系兼有正断型、走滑型和正走滑型震源机制,随着R值的增加,正断型震源机制数目逐渐增加,而走滑型和正走滑型震源机制数目逐渐减小.挤压应力体系在震源机制节面上的最大剪应力分布在R=0时沿倾角45°分布,随着R值增大至1,逐渐演变为沿着以(0°,90°)和(180°,90°)为中心的圆弧分布;拉张应力体系的最大剪应力分布则随着R值自0增大至1,最大剪应力自以(0°,90°)和(180°,90°)为中心的圆弧分布逐渐演变为沿倾角45°分布;走滑应力体系则随着R值自0增大至1,最大剪应力自以(0°,90°)和(180°,90°)为中心的圆弧分布逐渐演变为以(90°,90°)为中心的圆弧分布.三种应力体系所表现的震源机制P,T轴分布呈现复杂多样性:R越小,震源机制的T轴分布在拉张主应力周围的区域范围越小,而P轴分布在挤压轴周围的区域范围越大,R=0.5时两者分布区域范围均衡,R超过0.5时越接近1,震源机制的P轴分布在挤压主应力周围的区域范围越小,而T轴分布在拉张轴附近的区域范围越大. 相似文献
8.
One of the best indicators of the potential erosion risks is the rainfall–runoff erosivity factor (R) of the revised universal soil loss equation (RUSLE). Frequently, however, there is not enough data available to compute the R value, and other parameters, such as the modified Fournier index (Fmod), are used instead. But RUSLE is less effective if only the alternative procedures exist. One of the major discrepancies between R and the alternative parameters is time resolution: individual storms are used to calculate R while monthly averages over the year are used to calculate Fmod.
In this study, a multiple linear regression (r2=0.89) involving monthly EI30, monthly rainfall for days with ≥10.0 mm and monthly number of days with rainfall ≥10.0 mm, for the Algarve region, is presented. Twenty-seven years of monthly rainfall erosivity values were computed for the 32 standard daily-read raingauge stations of the Algarve region. 相似文献
9.
In the first part of this paper, the impact of forestry, agriculture and urban activities on the quality of surface water is analysed. Daily data from 15 forest and agricultural experimental catchments of the Institute of Hydrology, Slovak Academy of Sciences are used. It is shown, that the nitrate concentrations in surface water have decreased in Slovakia since 1989 as a result of decreased use of inorganic nitrogen fertilisers (lower intensity of agricultural production in Slovakia owing to recent economic changes). The annual nitrate specific load varies from 5.90 to 110 kg ha−1 year−1, the annual sulphate load varied from 29.16 to 509.60 kg ha−1 year−1 and the annual phosphate load varied from 0.0098 to 0.0224 kg ha−1 year−1 during 1990–1992.
In the second part, a two-step method of three-component hydrograph separation of rain-, soil- and groundwater is proposed. The method is used in the Manelo-Gribov microbasin (O.95 km2) in Eastern Slovakia. The annual contribution of surface runoff in total runoff volume was 57.5%, the contribution of interflow runoff was 21.1%, and the contribution of groundwater was 21.4%, during the period from 1 August to 31 July 1992. A deterministic regression model for predicting daily nitrate concentrations from values of stream daily discharge and flow component data was developed. A set of 1421 modelled NO3−1 data was compared with the set of measured data. 相似文献
10.
To examine nitrate persistence, detailed geochemical profiling, using core-squeezed water and piezometer samples, was carried out at five sites in southern Ontario where groundwater is moving downward in silt-rich aquitard sediments at rates of 16 to more than 20 cm year−1. Elevated levels of NO3−-N (5–50 mg 1−1) that occur in the shallow groundwater as a result of agricultural activity, were found to be consistently attenuated, generally to very low levels (< 0.05 mg 1−1-N), at the ‘redoxcline’, the horizon marking the boundary between the surficial weathered (brown) sediments and the underlying unweathered (grey) sediments. Tritium dating suggests that groundwater at the redoxcline depths (3–5 m) was recharged between 1970 and 1980, thus the N03 depletion appears to result from biodegradation reactions since no major landuse changes have occurred during this period. The close association of the nitrate depletion zones with the redoxcline, where, in particular, sediment sulphur contents increase abruptly, and where also porewater SO42− levels increase, suggests that the dominant attenuation reaction is autotrophic denitrification using reduced sulphur compounds present in the unweathered sediment as the electron donor. Mass balance calculations suggest that the increase in the downward rate of migration of the redoxcline, owing to added sulphur consumption from NO3− contamination, is only about 1 mm year−1 at these sites. Review of the literature indicates that most silt- and clay-rich sediments have S contents in the same range, or higher, than those investigated here, thus, in most cases where aquifers are overlain by several metres or more of unweathered confining sediments, it is likely that a high degree of protection is afforded from surficial NO3− contamination. 相似文献
11.
J.N. Walsh P.A. Taylor A. Buckley T.W. Darling J. Schreuer M.A. Carpenter 《Physics of the Earth and Planetary Interiors》2008,167(1-2):110-117
Values of bulk modulus (K), shear modulus (G) and mechanical quality factor (Q) have been determined for polycrystalline samples across the CaTiO3 (CST0)–SrTiO3 (CST100) solid solution by resonant ultrasound spectroscopy. Because of similarities with low frequency elastic and anelastic anomalies due to twin wall motion reported in previous studies, a working hypothesis is developed in which dissipation processes are interpreted in terms of twin wall displacements. At high temperatures in CST50 the stability field of the I4/mcm structure is marked by the disappearance of all resonance peaks (superattenuation). This is attributed to anelastic domain wall sliding. At room temperature the I4/mcm phase of CST70 and CST80 has values of G which are lower than those of cubic or orthorhombic phases, and a concomitant drop in Q is interpreted as implying that the domain wall pinning process reported elsewhere to occur below 400–450 K is only partial. A similar drop in G and Q was found in CST95 below the transition at 238 K. The I4/mcm ↔ Pbcm transition in CST70 at 230 K is marked by an abrupt increase in Q, suggesting that mobile twins in crystals with the I4/mcm structure become effectively immobile in antiferroelectric crystals with the Pbcm structure. The I4/mcm ↔ Pnma transition in CST50 is marked by a similarly abrupt increase in Q, consistent with twin walls becoming effectively immobile also in crystals with the Pnma structure. A fall in Q below 800 K in CST0, however, could imply that a degree of twin wall mobility might develop in Pnma crystals if the tetragonal spontaneous strain departs significantly from zero. The remarkable attenuation behaviour of crystals with the I4/mcm structure at the relatively low stress conditions which apply during resonances of a parallelepiped with edge dimensions of 2–4 mm, is consistent with the view that a characteristic signature for tetragonal CaSiO3 in the Earth's lower mantle should be a marked attenuation of seismic waves. 相似文献
12.
Jennifer Kung Sally M. Rigden Ian Jackson 《Physics of the Earth and Planetary Interiors》2000,120(4):195-314
The elastic moduli of ScAlO3 perovskite, a very close structural analogue for MgSiO3 perovskite, have been measured between 300 and 600 K using high precision ultrasonic interferometry in an internally heated gas-charged pressure vessel. This new capability for high temperature measurement of elastic wave speeds has been demonstrated on polycrystalline alumina. The temperature derivatives of elastic moduli of Al2O3 measured in this study agree within 15% with expectations based on published single-crystal data. For ScAlO3 perovskite, the value of (∂KS/∂T)P is −0.033 GPa K−1 and (∂G/∂T)P is −0.015 GPa K−1. The relative magnitudes of these derivatives agree with the observation in Duffy and Anderson [Duffy, T.S., Anderson, D.L., 1989. Seismic velocities in mantle minerals and the mineralogy of the upper mantle. J. Geophys. Res. 94, 1895–1912.] that |(∂KS/∂T)P| is typically about twice |(∂G/∂T)P|. The value of (∂KS/∂T)P for ScAlO3 is intermediate between those inferred less directly from V(P,T) studies of Fe-free and Fe- and Al-bearing MgSiO3 perovskites [Wang, Y., Weidner, D.J., Liebermann, R.C., Zhao, Y., 1994. P–V–T equation of state of (Mg,Fe)SiO3 perovskite: constraints on composition of the lower mantle. Phys. Earth Planet. Inter. 83, 13–40; Mao, H.K., Hemley, R.J., Shu, J., Chen, L., Jephcoat, A.P., Wu, Y., Bassett, W.A., 1991. Effect of pressure, temperature and composition on the lattice parameters and density of (Mg,Fe) SiO3 perovskite to 30 GPa. J. Geophys. Res. 91, 8069–8079; Zhang, Weidner, D., 1999. Thermal equation of state of aluminum-enriched silicate perovskite. Science 284, 782–784]. The value of |(∂G/∂T)|P for ScAlO3 is similar to those of most other mantle silicate phases but lower than the recent determination for MgSiO3 perovskite [Sinelnikov, Y., Chen, G., Neuville, D.R., Vaughan, M.T., Liebermann, R.C., 1998. Ultrasonic shear wave velocities of MgSiO3 perovskite at 8 GPa and 800K and lower mantle composition. Science 281, 677–679].
Combining the results from the previous studies and current measurements on ScAlO3 perovskite, we extracted the parameters (q and γ0) needed to fully specify its Mie–Grüneisen–Debye equation-of-state. In this study, we have demonstrated that acoustic measurements of KS(T), unlike V(P,T) data, tightly constrain the value of q. It is concluded that ScAlO3 has ‘normal’ γ0 (1.3) and high q (3.6). The high value of q indicates that ScAlO3 has very strong intrinsic temperature dependence of the bulk modulus; similar behaviour has been observed in measurements on Fe- and Al-bearing silicate perovskites (Mao et al., 1991; Zhang and Weidner, 1999). 相似文献
13.
The composition and temporal distribution of planktonic diatoms were studied in three small shallow karstic lakes – Modro Oko, Desne, and Kuti – throughout the seasons in 1994, 1995, 1997, and 1998. Physico-chemical parameters did not differ among the three lakes, except for NO3 concentrations. Altogether, 137 diatom taxa within 41 genera were found in all three lakes combined. The highest number of taxa belonged to the genera Surirella (13), Navicula (12), andCymbella (9). Most taxa were tychoplanktonic, with true panktonic taxa contributing only 14% of the total. Despite their physical-chemical similarity, the lakes showed differences in the structure and dynamics of their diatom communities. Blooms occurred at different times in each of the lakes, and community similarity (Jaccard index) among all three was low (17.6–29.1%). The highest mean values of surface diatom abundance in Modro Oko (2199 cells L−1), Desne (7900 cells L−1), and Kuti (20690 cells L−1) were not significantly different. Margalef's species richness index did not differ either among the lakes or seasonally. Only five diatom taxa in quantitative samples, and 22 taxa in net-samples, were common to all lakes. The most frequent diatoms were Cyclotella striata (56–93%), Fragilaria ulna (50–67%), and Asterionella formosa (27–83%). The most abundant taxa in Modro Oko, Desne, and Kuti were, respectively, Cymbella sp. 1 (402 cells L−1), Cyclotella striata (3000 cells L−1) and Asterionella formosa (20690 cells L−1). Eighteen taxa were recorded for the first time in Croatia: Amphora commutata, Caloneis amphisbaena var. subsalina, C. silicula var. peisonis, Campylodiscus echeneis, Coscinodiscus lacustris, Denticula elegans, Gyrosigma acuminatum var. lacustre, G. distortum var. parkeri, G. fasciola, Navicula menisculus var. menisculus, N. pusilla, N. helensis, Stauroneis parvula var. prominula, Staurosira construens f. subsalina, Stephanodiscus sp. 1, Surirella gracilis, S. ovalis, and S. striatula. The genus Stephanodiscus was recorded for the first time in Croatia. 相似文献
14.
D. Jongmans D. Demanet C. Horrent M. Campillo F.J. Sanchez-Sesma 《Soil Dynamics and Earthquake Engineering》1996,15(8):549-559
Seismic experiments were conducted in Mexico City in order to determine the dynamic characteristics of the soft clay layer present at the surface in the lake bed zone. In-situ measurements of Vp, Vs, Qp and Qs were performed in the Texcoco lake area. Qs values ranging from 8 to 60 have been found from the surface down to 30 m depth, while Vs values are between 30 and 115 m/s for the same depths. These relatively low Q values support the idea that surface waves generated at the edges of the Mexico basin cannot propagate very far in the structure. During this study, the elastic characteristics of the surficial basalt layers outcropping in the hill zone have also been investigated. Very low P-wave velocity values (500–800 m/s) have been found in the basalt. In the hill zone where basalts are interbedded with soil, numerical modeling has shown that such low values can only be partially explained by the relation between wavelength and basalt thickness and that other mechanisms, like fracturation, must be involved. 相似文献
15.
Mark B. Green Scott W. Bailey John L. Campbell Kevin J. McGuire Amey S. Bailey Timothy J. Fahey Nina Lany David Zietlow 《水文研究》2021,35(8):e14300
Small catchments have served as sentinels of forest ecosystem responses to changes in air quality and climate. The Hubbard Brook Experimental Forest in New Hampshire has been tracking catchment water budgets and their controls – meteorology and vegetation – since 1956. Water budgets in four reference catchments indicated an approximately 30% increase in the evapotranspiration (ET) as estimated by the difference between precipitation (P) and runoff (RO) starting in 2010 and continuing through 2019. We analyzed the annual water budgets, cumulative deviations of the daily P, RO and water budget residual (WBR = P − RO), potential ET (PET) and indicators of subsurface storage to gain greater insight into this shift in the water budgets. The PET and the subsurface storage indicators suggest that this change in WBR was primarily due to increasing ET. While multiple long-term hydrological and micrometeorological data sets were used to detect and investigate this change in ET, additional measurements of groundwater storage and soil moisture would enable better estimation of ET within the catchment water balance. Increasing the breadth of long-term measurements across small gauged catchments allows them to serve as more effective sentinels of substantial hydrologic changes like the ET increase that we observed. 相似文献
16.
Maria Staudinger Michael Stoelzle Stefan Seeger Jan Seibert Markus Weiler Kerstin Stahl 《水文研究》2017,31(11):2000-2015
One of the most important functions of catchments is the storage of water. Catchment storage buffers meteorological extremes and interannual streamflow variability, controls the partitioning between evaporation and runoff, and influences transit times of water. Hydrogeological data to estimate storage are usually scarce and seldom available for a larger set of catchments. This study focused on storage in prealpine and alpine catchments, using a set of 21 Swiss catchments comprising different elevation ranges. Catchment storage comparisons depend on storage definitions. This study defines different types of storage including definitions of dynamic and mobile catchment storage. We then estimated dynamic storage using four methods, water balance analysis, streamflow recession analysis, calibration of a bucket‐type hydrological model Hydrologiska Byråns Vattenbalansavdelning model (HBV), and calibration of a transfer function hydrograph separation model using stable isotope observations. The HBV model allowed quantifying the contributions of snow, soil and groundwater storages compared to the dynamic catchment storage. With the transfer function hydrograph separation model both dynamic and mobile storage was estimated. Dynamic storage of one catchment estimated by the four methods differed up to one order of magnitude. Nevertheless, the storage estimates ranked similarly among the 21 catchments. The largest dynamic and mobile storage estimates were found in high‐elevation catchments. Besides snow, groundwater contributed considerably to this larger storage. Generally, we found that with increasing elevation the relative contribution to the dynamic catchment storage increased for snow, decreased for soil, but remained similar for groundwater storage. 相似文献
17.
Streamwater chemistry is described for three streams draining undisturbed, evergreen broad-leaved forested catchments on phyllites in NE Spain: two streams with no or negligible flow in summer are located in the Prades massif, and one perennial stream is in the wetter Montseny mountains. Weekly data for a study period of 2–4 years are provided to (1) describe the seasonal variations in streamwater chemistry, (2) analyse the relationship between stream discharge and solute concentrations using a two-component mixing model and (3) search for patterns of temporal variation in stream solute concentrations after discounting the effects of discharge. At Prades, concentrations of all analysed ions, except NO−3, showed marked seasonal variations in stream water, whereas at Montseny only ions related to mineral weathering (HCO−3, Na+, Ca2+ and Mg2+) showed strong seasonality. Ion concentrations were more closely dependent on instantaneous discharge at Montseny than at Prades. The residuals of the relationship between solute concentrations and discharge retained a strong seasonality at Prades, but not at Montseny. These differences are related to the major hydrochemical processes that determine the streamwater chemistry at each site. The same processes are probably operative in the three catchments, but are of varying relative importance. At Montseny, the mixing of waters of different chemical composition seems to be the major process controlling streamwater chemistry, although the soilwater end-member composition predicted by the mixing model applied did not match the measured soilwater chemistry. In the drier Prades catchments, the two major hydrochemical processes determining the seasonal variation of streamwater chemistry are (1) the restart of flow after the summer drought, which flushes out the solutes accumulated during the dry period, and (2) the seasonal changes in groundwater chemistry that result from the interplay of water residence time, temperature and CO2 partial pressure. In Mediterranean catchments with relatively high precipitation, such as Montseny, the seasonal variation in the streamwater chemistry is largely determined by the same processes as at humid-temperate sites, whereas in drier Mediterranean catchments, such as Prades, the major hydrochemical processes are clearly distinct. 相似文献
18.
G. Gold-Bouchot R. Sim -Alvarez O. Zapata-P rez J. Gü emez-Ricalde 《Marine pollution bulletin》1995,31(4-12):439-445
Oyster tissues may be affected by the concentration of ions in the water (i.e. salinity) and by contaminants such as petroleum hydrocarbons and heavy metals. Oyster populations from three coastal lagoons (Mecoacan, Camen and Machona) in the Mexican state of Tabasco, in the southern Gulf of Mexico, were sampled for pollution studies during June, September and November 1992 and May 1993. No statistically significant relationships were found between the concentration of contaminants in the body tissues of organisms and their shell length, soft tissue weight and particulate matter; however, a significant correlation was found between condition index and salinity (r = −0.72). Generally, the lowest weights, shell lengths and indices of condition were found in Mecoacan. The concentrations of cadmium and zinc were inversely related to salinity (r = −0.52 and r = −0.32, respectively), so a riverine input is suspected. On average, 63% of the individual oysters showed histopathological lesions, which can be related to salinity and to the concentrations of cadmium and the unresolved fraction of hydrocarbons (UCM). The response of each of the tissues analysed was different. The percentage of individuals with damage in the digestive diverticulum increased linearly with UCM (r = 0.71), but in a saturation-response fashion (Y = B0 − B0/(1 + XB1) r = 0.66) with cadmium. The percentage of individuals with damage in the gills increased linearly with weight (r = 0.68), cadmium (r = 0.60) and UCM (r = 0.60). The lesions in the connective tissue decreased linearly (r = −0.82) with salinity, but increased in a saturation-response way (r = 0.83) with cadmium. Finally, the percentage of individuals with lesions in the digestive tube decreased linearly with salinity (r = −0.59). Only the damage to the gills and digestive diverticula were dependent on gonadal maturity, while damage to the connective tissue was dependent on the sex of the individual. 相似文献
19.
In this paper, we examined the role of bedrock groundwater discharge and recharge on the water balance and runoff characteristics in forested headwater catchments. Using rigorous observations of catchment precipitation, discharge and streamwater chemistry, we quantified net bedrock flow rates and contributions to streamwater runoff and the water balance in three forested catchments (second‐order to third‐order catchments) underlain by uniform bedrock in Japan. We found that annual rainfall in 2010 was 3130 mm. In the same period, annual discharge in the three catchments varied from 1800 to 3900 mm/year. Annual net bedrock flow rates estimated by the chloride mass balance method at each catchment ranged from ?1600 to 700 mm/year. The net bedrock flow rates were substantially different in the second‐order and third‐order catchments. During baseflow, discharge from the three catchments was significantly different; conversely, peak flows during large storm events and direct runoff ratios were not significantly different. These results suggest that differences in baseflow discharge rates, which are affected by bedrock flow and intercatchment groundwater transfer, result in the differences in water balance among the catchments. This study also suggests that in these second‐order to third‐order catchments, the drainage area during baseflow varies because of differences between the bedrock drainage area and surface drainage area, but that the effective drainage area during storm flow approaches the surface drainage area. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
20.
P. Hejda V. Krop
ek E. Petrovský T. Zelinka J.
atecký 《Physics of the Earth and Planetary Interiors》1992,70(3-4):261-272
The behaviour of some magnetic properties of natural and synthetic haematite of different grain size is examined. The natural haematite was obtained from the hydrothermal deposit Kada
(Czech and Slovak Federal Rep.). Six grain-size fractions ranging from 120 to 40 μm were prepared by means of sieving and two further fractions down to 5 μm by wet ultrasonic sieving. Since the behaviour of the fractions is similar, that of only four representative samples is reported. In addition, the behaviour of one submicron synthetic haematite fraction (0.5 μm) prepared by oxidation of ferrous sulphate (uniform in size and shape) was investigated.
The initial remanence value (Jr) seems to increase with decreasing grain size. During alternating field (AF) demagnetization, all fractions behaved similarly, except for the submicron fraction which is considerably softer than the others. Normalized (isothermal remanent magnetization) IRM acquisition curves were similar for all fractions.
Parameters of the anisotropy of magnetic susceptibility (AMS) display significant changes, mainly during IRM acquisition. During AF demagnetization, the anisotropy degree P exhibits a slight increase (some %), while the behaviour of the shape factor T is complicated. The anisotropy ellipsoid exhibits a tendency to rotate. Significant changes in the AMS parameters occur during IRM acquisition. Curves of P and T vs. IRM acquisition field, for various grain-size fractions, show no coherent pattern. For all the samples studied, the T vs. H curve exhibits a threshold value at which change in the type of arrangement of easy axis of magnetization occurs. For the IRM acquisition fields higher than some 320 kA m−1, the minimum susceptibility axis parallels the direction of the IRM acquisition field.
Hysteresis curves of the fractions are similar to each other. The Preisach distribution function was determined and it indicates that the reversible part of the magnetization process plays an important role comparatively. Based on the coercivity data presented no unambiguous conclusion could be drawn from the single-domain (SD)-multidomain (MD) transition, associated with a coercivity maximum. 相似文献