首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 33 毫秒
1.
Attention has been paid for the levels, sources and health risks of atmospheric aliphatic and polycyclic aromatic hydrocarbons (n-alkanes and PAHs) in remote areas, however, few studies have focused on those in the Tibetan Plateau. In this study, 18 pairs of atmospheric samples were obtained during the period from August 2006 to July 2007 in Lhasa, the capital city of Tibet. Both gas-phase and particulate-phase n-alkanes and PAHs were measured. Concentrations of n-alkanes (gas + particulate phase, 99.1–480.9 ng/m3) and PAHs (gas + particulate phase, 11.4–72.5 ng/m3) in Lhasa are lower than those in many cities. The sources of n-alkanes related to biological and petroleum sources were 67 and 33%, respectively. According to the results of diagnostic ratios and principal component analysis, emission of traffic vehicles was one of the important PAH sources, and sources of benzo(a)pyrene was likely attributed to incense burning. Good simulations were obtained by traffic soot-based model for fluoranthene, pyrene and benzo(a)anthracene, while, wood soot-based model fitted the experimental results of benzo(a)pyrene better. This meant atmospheric fate of PAHs was mainly influenced by the adsorptive partitioning that occurred during traffic and incense burning procedures. In addition, the benzo[a]pyrene-equivalent carcinogenic power (BaPE) in the present study (0.1–1.6 ng/m3) is lower than those in other cities and also the air quality standard of China, suggesting that atmospheric PAHs caused low health risks.  相似文献   

2.
Solute dynamics of meltwater of Gangotri glacier,Garhwal Himalaya,India   总被引：2，自引：0，他引：2  
The present study investigates solute dynamics of meltwater of Gangotri glacier system in terms of association of different chemical compounds with the geology of the area. In the meltwater, the presence of cations varied as c(Mg2+) > c(Ca2+) > c(Na+) > c(K+), while order of concentration of anions has been c(HCO3 −) > c(SO4 2−) > c(Cl−) > c(NO3 −) in years 2003 and 2004. The magnesium and calcium are found as the dominant cations along with bicarbonate and sulphate as dominant anions. The high ratios of c(Ca2+ + Mg2+)/total cations and c(Ca2+ + Mg2+)/c(Na+ + K+) indicate that the meltwater chemistry of the Gangotri glacier system catchment is mostly controlled by carbonate weathering. Attempts are made to develop rating curves for discharge and different cations. Sporadic rise in discharge without corresponding rise in concentration of most of cations is responsible for their loose correlation in a compound valley glacier like Gangotri glacier.  相似文献   

3.
This study investigated the potential for the uranium mineral carnotite (K2(UO2)2(VO4)2·3H2O) to precipitate from evaporating groundwater in the Texas Panhandle region of the United States. The evolution of groundwater chemistry during evaporation was modeled with the USGS geochemical code PHREEQC using water-quality data from 100 groundwater wells downloaded from the USGS National Water Information System (NWIS) database. While most modeled groundwater compositions precipitated calcite upon evaporation, not all groundwater became saturated with respect to carnotite with the system open to CO2. Thus, the formation of calcite is not a necessary condition for carnotite to form. Rather, the determining factor in achieving carnotite saturation was the evolution of groundwater chemistry during evaporation following calcite precipitation. Modeling in this study showed that if the initial major-ion groundwater composition was dominated by calcium-magnesium-sulfate (>70 precent Ca + Mg and >50 percent SO4 + Cl) or calcium-magnesium-bicarbonate (>70 percent Ca + Mg and <70 percent HCO3 + CO3) and following the precipitation of calcite, the concentration of calcium was greater than the carbonate alkalinity (2mCa+2 > mHCO3− + 2mCO3−2) carnotite saturation was achieved. If, however, the initial major-ion groundwater composition is sodium-bicarbonate (varying amounts of Na, 40–100 percent Na), calcium-sodium-sulfate, or calcium-magnesium-bicarbonate composition (>70 percent HCO3 + CO3) and following the precipitation of calcite, the concentration of calcium was less than the carbonate alkalinity (2mCa+2 < mHCO3- + 2mCO3−2) carnotite saturation was not achieved. In systems open to CO2, carnotite saturation occurred in most samples in evaporation amounts ranging from 95 percent to 99 percent with the partial pressure of CO2 ranging from 10−3.5 to 10−2.5 atm. Carnotite saturation occurred in a few samples in evaporation amounts ranging from 98 percent to 99 percent with the partial pressure of CO2 equal to 10−2.0 atm. Carnotite saturation did not occur in any groundwater with the system closed to CO2.  相似文献   

4.
The present study highlights the first evidence of hydrothermal mineral Thenardite (Na2SO4) from Puga geothermal area, North-western Himalayan belt in Ladakh Geothermal Province, India, which is unequivocal evidence for the presence of high-temperature hydrothermal fluid activity from one of the thickest crust areas of the Earth. The Puga geothermal belt illustrates a fault-bounded hydrothermal system with a clearly defined conductive zone, coinciding with Kiagar Tso fault typically exemplifying a shallow-level medium enthalpic geothermal reservoir. The hydrogeochemistry suggests that thermal and non-thermal waters are of Na-Cl-HCO3 and Ca-Mg-HCO3 type, respectively, with neutral to near alkaline pH. The silica and cation geothermometry reveal sub-surface temperatures around 150 °C and 250 °C, respectively, at shallow depth; however, >250 °C is anticipated at the deepest levels (~3 km). Stable isotope (δD and δ18O) studies explicate depletion of isotopic content for thermal waters over Puga river water and radiogenic isotope (3H) suggests matured thermal waters with ongoing water-rock interactions. The recharge altitude estimation and physiographic studies put forth that geothermal reservoir is recharged with the ice masses located at an altitude of 6458 m above mean sea level (msl) in the west of Puga valley, probably from the highest peak of Polokong La mountain. The two key processes participating in regulation of proportions of the dissolved salts in the thermal waters are silicate weathering and ion-exchange kinetics. The powder X-ray diffraction study reveals a major occurrence of hydrothermal mineral thenardite in the hot spring deposits for the first time along with huge encrustations of trona, borax, calcite and elemental sulfur. The high-temperature fluids encounter thenardite, pyrite, and jarosite-bearing minerals in basement rock causing enrichment of SO42− and Cl− in geothermal waters. The temperature-dependent speciation modelling (50 °C–200 °C) for major ion Na+ reveals the composition of the reservoir fluid (~150 °C): Na+ > NaCO3− > NaSO4− > NaHCO3 > NaF > NaOH. A conceptual evolution model of thermal waters involving the recharge-deep circulation-mixing-discharge of thermal springs is hence put forth in the study using various hydrogeochemical insights.  相似文献   

5.
During June 2003, a period of mid level discharge (17,400 m−3 s−1), a parcel of water in the lower Mississippi River was sampled every 2 h during its 4-d transit from river km 362 near Baton Rouge to km 0 at Head of Passes, Louisiana, United States. Properties measured at the surface during each of the 48 stations were temperature, salinity, dissolved organic carbon (DOC), total dissolved nitrogen, dissolved macronutrients (NO3+NO2, PO4, Si(OH)4), chlorophylla (chla; three size fractions: < 5 μm, 5–20 μm, and > 20 μm) pigment composition by HPLC, total suspended matter (TSM), particulate organic carbon (POC), and particulate nitrogen (PN). Air-water CO2 flux was calculated from surface water dissolved inorganic carbon and pH. During the 4 d transit, large particles appeared to be settling out of the surface water. Concentrations of chla containing particles > 20 μm declined 37%, TSM declined 43%, POC declined 42% and PN declined 57%. Concentrations of the smaller chla containing particles did not change suggesting only large particulate materials were settling. There was no measurable loss of dissolved NO3, PO4, or Si(OH)4, consistent with the observation that chla did not increase during the 4-d transit. DOC declined slightly (3%). These data indicate there was little autotrophic or heterotrophic activity in the lower Mississippi River at this time, but the system was slightly net heterotrophic.  相似文献   

6.
We evaluate rock fall hazard along the railway corridor to Jerusalem, Israel, in the Soreq and Refaim valleys. For the purpose, we use a combination of historical information on past rock fall events, field surveys aided by the interpretation of aerial photographs, and numerical rock fall modeling. Historical information indicates that on July 11, 1927 an m L 6.2 Dead-Sea transform earthquake caused rock falls in the studied area. The seismically induced rock falls damaged the railway tracks. Field observations revealed that the source area for the 1927 failures was located in the Aminadav formation, at the contact with the Moza formation. At the stratigraphic contact, rock blocks 100–101 m3 in size are formed as a result of tensile stresses and associated fracturing in the dolomite of the Aminadav formation, combined with continuous creep of the blocks on the marl of the underlying Moza formation. We use topographical, geological, and geomorphological information to calibrate a three-dimensional numerical simulation of rock falls in the studied area. We use the results of the numerical modeling, and additional independent information, to assess rock fall hazard and the associated risk in the Soreq and Refaim valleys. Results indicate that in the studied area, rock fall risk to the railway line to Jerusalem is due primarily to Dead-Sea transform earthquakes, with m L  > 6. We identify nine sections of the railway line where rock fall risk exists, for a total length of 2.5 km. We further note that seismically induced rock falls can produce damage to the road network in the studied area, make it difficult or impossible for earthquake casualties to reach hospitals in Jerusalem. We conclude offering recommendations on how to mitigate the risk posed by earthquake-induced rock falls in the studied area.  相似文献   

7.
Mantle derived xenoliths in India are known to occur in the Proterozoic ultrapotassic rocks like kimberlites from Dharwar and Bastar craton and Mesozoic alkali igneous rocks like lamrophyres, nephelinites and basanites. The xenoliths in kimberlites are represented by garnet harzburgites, lherzolites, wehrlite, olivine clinopyroxenites and kyaniteeclogite varieties. The PT conditions estimated for xenoliths from the Dharwar craton suggest that the lithosphere was at least 185 km thick during the Mid-Proterozoic period. The ultrabasic and eclogite xenoliths have been derived from depths of 100–180 km and 75–150 km respectively. The Kalyandurg and Brahmanpalle clusters have sampled the typical Archaean subcontinental lithospheric mantle (SCLM) with a low geotherm (35 mW/m2) and harzburgitic to lherzolitic rocks with median Xmg olivine > 0.93. The base of the depleted lithosphere at 185–195 km depth is marked by a 10–15 km layer of strongly metasomatised peridotites (Xmg olivine > ∼0.88). The Anampalle and Wajrakarur clusters 60 km to the NW show a distinctly different SCLM; it has a higher geotherm (37.5 to 40 mW/m2) and contains few subcalcic harzburgites, and has a median Xmg olivine = 0.925. In contrast, the kimberlites of the Uravakonda and WK-7 clusters sampled quite fertile (median Xmg olivine ∼0.915) SCLM with an elevated geotherm (> 40 mW/m2). The lamrophyres, basanites and melanephelinites associated with the Deccan Volcanic Province entrain both ultramafic and mafic xenoliths. The ultramafic group is represented by (i) spinel lherzolites, harzburgites, and (ii) pyroxenites. Single pyroxene granulite and two pyroxene granulites constitutes the mafic group. Temperature estimates for the West Coast xenoliths indicate equilibration temperatures of 500–900°C while the pressure estimates vary between 6–11 kbar corresponding to depths of 20–35 km. This elevated geotherm implies that the region is characterized by abnormally high heat flow, which is also supported by the presence of linear array of hot springs along the West Coast. Spinel peridotite xenoliths entrained in the basanites and melanephelinites from the Kutch show low equilibrium temperatures (884–972°C). The estimated pressures obtained on the basis of the absence of both plagioclase and garnet in the xenoliths and by referring the temperatures to the West Coast geotherm is ∼ 15 kbar (40–45 km depth). The minimum heat flow of 60 to 70 mW/m2 has been computed for the Kutch xenolith (Bhujia hill), which is closely comparable to the oceanic geotherm. Xenolith studies from the West Coast and Kutch indicate that the SCLM beneath is strongly metasomatised although the style of metasomatism is different from that below the Dharwar Craton.  相似文献   

8.
Groundwater in Palnad sub-basin is alkaline in nature and Na+-Cl−-HCO3− type around Macherla-Karempudi area in Guntur district, Andhra Pradesh. Total dissolved solids (TDS) show strong positive correlation with Cl−, Na+, Ca2+ and Mg2+, and positive correlation with SO42−, K+ and HCO3−. Calcareous Narji Formation is the dominant aquifer lithology, and water-rock interaction controls the groundwater chemistry of the area. Chloro-alkaline indices (CAI) are positive at Miriyala, Adigopula, Mutukuru, Macherla and Durgi suggesting replacement of Na+ and K+ ions from water by Mg++ and Ca++ ions from country rock through base exchange reactions. Negative CAI values are recorded at Terala, Rayavaram and Nehrunagar, which indicate exchange of Na+ and K+ from the rock as cation-anion exchange reaction (chloro-alkaline disequilibrium). TDS range from 91 to 7100 ppm (Avg. 835 ppm) and exceed the prescribed limit of drinking water around Mutukuru, Durgi, Rayavaram, Khambampadu and Ammanizamalmadaka areas. Scanty rainfall and insufficient groundwater recharge are the prime factors responsible for high salinity in the area. Fluoride content ranges from <1 to 3.8 ppm and contaminated areas were identified around Macherla (1 sq km; 3.8ppm), Mandadi (1 sq km, 2.1ppm) and Adigopula (2 sq km, <1 to 3.7 ppm). The % Na+ content varies from 17 to 85 with the mean value of 57, and eighty (80) samples showed higher %Na+ in comparison to the prescribed limit of 60 for irrigation water. Sodium Adsorption Ratio (SAR) and % Na+ in relation to total salt concentration indicate that groundwater (51%) mostly falls under doubtful to poor quality for irrigation purpose. Groundwater of Adigopula village is fluoride contaminated and remedial measures are suggested to improve the water quality.  相似文献   

9.
The source of fluoride toxicity in Muteh area,Isfahan, Iran   总被引：1，自引：0，他引：1  
Endemic dental fluorosis has been observed in most inhabitants of three villages of Muteh area, located in northwest of Isfahan province, with mottled enamel related to high levels of fluoride in drinking water (1.8–2.2 ppm). Forty-seven groundwater samples from six villages were collected and fluoride concentrations along with physico-chemical parameters were analyzed. Fluoride concentration in this area varies from 0.2 to 9.2 mg/l with highest fluoride level at Muteh gold mine (Chahkhatun mine). Fluoride concentration positively correlates with pH and HCO3 − indicating that alkaline pH provides a suitable condition for leaching of fluoride from surrounding rocks. The district is mainly covered by three lithological units, namely, metamorphic and granite rocks, alluvial sediments, and carbonate rocks. Factor analysis shows that parameters can be classified into four components: electrical conductivity (EC), total dissolved solids (TDS), Cl−, Na+ and K+, pH and F−, SO4 2−and Mg2+, HCO3 − and Ca2 +. The groundwaters from the three geological units were compared using Mann–Whitney U test. The order of median fluoride concentration is: metamorphic and granite rocks > alluvial sediments > carbonate rocks. Hence, the fluoride content is most probably related to fluoride-bearing minerals such as amphibole and mica group minerals in metamorphic and granitic rocks. The concentration of fluoride in drinking water wells located near the metamorphic complex in Muteh area is above 2 ppm.  相似文献   

10.
About 24 samples from hand-dug wells and boreholes were used to characterize concentrations of the main inorganic ions in a laterite environment under semi-arid climatic conditions in Tikaré, northern Burkina Faso. It was found that the most represented groundwater anion in groundwater was HCO3 − with average levels of 49.1 mg/L in the dry season and 33.5 mg/L in the rainy season. The most represented cation was Ca2+ with mean concentrations of 13.7 and 9.5 mg/L, respectively. The main processes, which influence the concentrations of these ions, are evaporation (dry season), local enrichment of recharge water in some elements, ion exchange and fixation by clay minerals (in case of K+). The best correlations were found between Ca2+ and Mg2+ (r = 0.95), Cl− and Na+ (r = 0.95), HCO3 − and Mg2+ (r = 0.89), HCO3 − and Ca2+ (r = 0.89), and between HCO3 − and Na+ (r = 0.80). In general, the quality of the groundwater from the different wells sampled for this study was good enough to serve as drinking water. However, there were situations where the quality of water was polluted because of anthropogenic contaminants (mainly NO3 −, K+, Cl−) from septic tanks and manure pits located in the vicinity of some sampled wells. In addition, application of fertilizers also represents a potential anthropogenic contamination source with regard to SO4 2−, Ca2+, K+, Na+, and Mg2+. Considering the high concentrations of SO4 2−, Mg2+, Na+ and Ca2+ found in one borehole, the deeper, fractured aquifers were also likely to be enriched in these elements. In contrast, the shallow aquifers are likely to be contaminated with Cl−, NO3 − and K+. Cl− and K+ seem to be locally present in recharge water as shown by their relative higher mean concentrations in the rainy season samples.  相似文献   

11.
The Oylat spa is located 80 km southeast of Bursa and 30 km south of Ineg?l in the Marmara region. With temperature of 40°C and discharge of 45 l/s, the Oylat main spring is the most important hot water spring of the area. Southeast of the spa the Forest Management spring has a temperature of 39.4°C and discharge of 2 l/s. The G?z spring 2 km north of the spa, which is used for therapy of eye disease, and cold waters of the Saadet village springs with an acidic character are the further important water sources of the area. EC values of Main spring and Forest Management hot spring (750–780 μS/cm) are lower than those of Saadet and G?z spring waters (2,070–1,280 μS/cm) and ionic abundances are Ca > Na + K > Mg and SO4 > HCO3 > Cl. The Oylat and Sızı springs have low Na and K contents but high Ca and HCO3 concentrations. According to AIH classification, these are Ca–SO4–HCO3 waters. Based on the results of δ18O, 2H and 3H isotope analyses, the thermal waters have a meteoric origin. The meteoric water infiltrates along fractures and faults, gets heated, and then returns to surface through hydrothermal conduits. Oylat waters do not have high reservoir temperatures. They are deep, circulating recharge waters from higher enhanced elevations. δ13CDIC values of the Main spring and Forest Management hot spring are −6.31 and −4.45‰, respectively, indicating that δ13C is derived from dissolution of limestones. The neutral pH thermal waters are about +18.7‰ in δ34S while the sulfate in the cold waters is about +17‰ (practically identical to the value for the neutral pH thermal waters). However, the G?z and Saadet springs (acid sulfate waters) have much lower δ34S values (~+4‰).  相似文献   

12.
Water soluble components of PM10 Chongqing, China   总被引：1，自引：0，他引：1  
The concentrations of water soluble ions (Na+, NH4 +, K+, Mg2+, Ca2+, NO3 -, Cl-, and SO 4 2- ) in PM10 samples collected on cellulose filters by a medium-volume cascade impactor were determined, which were obtained from three kinds of areas in Chongqing: industrial area (Jiulongpo district), commercial and residential area (Jiangbei district) and background area (Jinyun Mountain in the Beibei district). The results showed that except for the background site, the annual average values of PM10 are 23% – 61% higher than the national air quality standard (GradeII) (0.1 mg/m3), even that the value of the control site is still 20% higher than American standard (0.05 mg/m3). This implied that serious pollution of fine particles occurred in Chongqing. Nine kinds of soluble ions in water of PM10 were analyzed by ion chromatography (IC) and the annual average concentrations follow the order of [SO 4 2- ] > [NO3 -] > [Cl-] > [F-], and [Ca2+] > [NH4 +] > [K+] > [Na+] > [Mg2+]. Their values were different in these areas: the industrial area > the commercial and living area > the control area. As for NH4 +, K+, Ca2+, NO3 - and SO 4 2- , their seasonal average concentrations show a similar variation trend: the values in spring and fall were higher than those in summer and winter. The seasonal average concentrations of [Cl-], [F-], [Na+] and [Mg2+] are much lower than those of other ions. However, the concentrations of [Na+] changed more greatly in different seasons than those of the other three ions. Correlation coefficients showed that the three areas have been polluted by coal smoke and dust to different extents, while some local resources of pollution should be taken into consideration as well.  相似文献   

13.
The Mazhuangshan area is located in the east of the Aqikekuduke Island Arc, where there are distributed intermediate-acid magmatic rocks emplaced during the Middle-Late Carboniferous. There are more than 20 orebodies in the area with an average gold grade 6.4 × 10−6 at present. The dominant metallic minerals are natural gold, auriferous silver, natural silver, pyrite and galena. Pyrite is the key gold carrier, high in Fe and low in S. Wall-rock alterations mainly include pyritization, silicification, and sericitization. Carbonation alteration was extensive at the late stage, often resulting in a high-grade orebody. Three mineralization stages may be distinguished. The peak homogenization temperatures of primary fluid inclusions range from 240 to 260°C. Mineralization pressures and depths are 47.2–68.8 MPa and 1.6–2.3 km respectively, showing the ore-forming features of hypergene gold deposit. The average salinity is 15 wt% NaCl equivalent. Fluid inclusion geochemistry data show that Ca2+ is far higher than Mg2+, and mK +/mNa +, mNa2 +/mCa 2+ (0.001∼0.338), mΣCl/mΣS and mΣC/mΣS ratios change with the reduction parameter [R = (CO + CH4)/CO2] and temperature. And the gold contents of ores and gangues are positively correlated withR.  相似文献   

14.
 An integrated geological, geoelectrical and hydrochemical investigation of shallow groundwater occurrence in the Ibadan area, southwestern Nigeria, is presented. The primary objective was to characterise the groundwater in a typical low-latitude environment underlain by Precambrian crystalline basement complex rocks. The dominant rocks comprise suites of gneisses and quartzites. Chemical analyses of the groundwater show that the mean concentration of the cations is in the order Na>Ca>Mg>K while that for the anions is Cl>HCO3>NO3>SO4. Statistical analyses, using the product-moment coefficient of correlation, indicate positive correlations between the following pairs of parameters: TDS and conductivity (r=0.96); Na++Mg2+ and Cl– (r=0.95); Na++K+ and Ca2+ (r=0.43); Na++K+ and HCO3 – (r=0.17); Ca2+ and Mg2+ (r=0.74); Ca2+ and HCO3 – (r=0.33); Ca2++Mg2+ and HCO3 – (r=0.31) and pH and HCO3 – (r=0.54). A very weak negative correlation was recorded between pH and Cl–, with r=–0.003. Five groundwater groups have been identified, namely, (1) the Na-Cl, Na-Ca-Cl, Na-Ca-(Mg)-Cl; (2) the Ca-(Mg)-Na-HCO3-Cl, Na-Ca-HCO3-Cl, and Ca-HCO3-Cl; (3) the Ca-(Mg)-Na-HCO3, Ca-Na-HCO3; (4) Ca-Na-Cl-(SO4)-HCO3 and (5) the Ca-(Mg)-Na-SO4-HCO3. The different groups reflect the diversity of bedrock types and consequently also of the products of weathering. Most of the water sampled is unfit for drinking on account of the high NO3 – content. It can, however, be used for irrigation purposes as the sodium hazard is low while the salinity hazard ranges from low to medium. Resistivity soundings indicate the presence of a thick weathering profile, which could be up to 60 m. Such sites should be the target for any long-term and sustainable groundwater development in the area. Received: 15 April 1998 · Accepted: 4 July 1998  相似文献   

15.
Geochemical processes that take place in the aquifer have played a major role in spatial and temporal variations of groundwater quality. This study was carried out with an objective of identifying the hydrogeochemical processes that controls the groundwater quality in a weathered hard rock aquifer in a part of Nalgonda district, Andhra Pradesh, India. Groundwater samples were collected from 45 wells once every 2 months from March 2008 to September 2009. Chemical parameters of groundwater such as groundwater level, EC and pH were measured insitu. The major ion concentrations such as Ca2+, Mg2+, Na+, K+, Cl−, and SO4 2− were analyzed using ion chromatograph. CO3 − and HCO3 − concentration was determined by acid–base titration. The abundance of major cation concentration in groundwater is as Na+ > Ca2+ > Mg2+ > K+ while that of anions is HCO3 − > SO4 2− > Cl− > CO3 −. Ca–HCO3, Na–Cl, Ca–Na–HCO3 and Ca–Mg–Cl are the dominant groundwater types in this area. Relation between temporal variation in groundwater level and saturation index of minerals reveals the evaporation process. The ion-exchange process controls the concentration of ions such as calcium, magnesium and sodium. The ionic ratio of Ca/Mg explains the contribution of calcite and dolomite to groundwater. In general, the geochemical processes and temporal variation of groundwater in this area are influenced by evaporation processes, ion exchange and dissolution of minerals.  相似文献   

16.
The basal area and productivity of managrove wetlands are described in relation to selected soil properties to understand the general pattern of optimum forest stature at the mouth of estuaries in the Everglades, such as the Shark River Slough, Florida (U.S.). The basal area of mangroves decreases from 40.4 m2 ha−1 and 39.7 m2 ha−1 at two stations 1.8 km and 4.1 km from the estuary mouth to 20.7 m2 ha−1 and 19.6 m2 ha−1 at two sites 9.9 km and 18.2 km from the mouth, respectively. The gradient in basal area at these four sites is mostly the result of approximately 34 yr of growth since Hurricane Donna. Wood productivity is higher in the lower estuary (10.7 Mg ha−1 yr−1 and 12.0 Mg ha−1 yr−1) than in the upper estuary (3.2 Mg ha−1 yr−1 and 4.2 Mg ha−1 yr−1). Porewater salinity among these four mangrove sites during seasonal sampling in 1994 and 1995 ranged from 1.6 g kg−1 to 33.5 g kg−1, while sulfide was generally<0.15 mM at all sites. These soil values indicate that abiotic stress cannot explain the decrease in forest structure along this estuarine gradient. Concentrations of nitrogen (N) and phosphorus (P) are more closely related to patterns of forest development, with higher soil fertility at the mouth of the estuary as indicated by higher concentrations of extractable ammonium, total soil P, and available P, along with higher ammonium production rates. The more fertile sites of the lower estuary are dominated by Laguncularia racemosa, whereas the less fertile sites in the intermediate and upper estuary are dominated by Rhizophora mangle. Relative N mineralization per unit of total N is higher in the lower estuary and is related positively to concentrations of available P, indicating the importance of turnover rates and nutrient interactions to soil fertility. Concentrations of Ca-bound P per volume soil in the lower estuary is 40-fold higher than in the upper estuary, and along with an increase in residual P in the upper estuary, indicate a shift from mineral to organic P along the estuarine gradient. Mineral inputs to the mouth of Shark River estuary from the Gulf of Mexico (rather than upland inputs) apparently control the patterns of mangrove structure and productivity.  相似文献   

17.
A contaminated site from a downstream municipal solid waste disposal site in Brazil was investigated by using a 3D resistivity and induced polarization (IP) imaging technique. This investigation purpose was to detect and delineate contamination plume produced by wastes. The area was selected based on previous geophysical investigations, and chemical analyses carried out in the site, indicating the presence of a contamination plume in the area. Resistivity model has successfully imaged waste presence (ρ < 20 Ωm), water table depth, and groundwater flow direction. A conductive anomaly (ρ < 20 Ωm) outside wastes placement was interpreted as a contamination plume. Chargeability model was also able to imaging waste presence (m > 31 mV/V), water table depth, and groundwater flow direction. A higher chargeability zone (m > 31 mV/V) outside wastes placement and following conductive anomaly was interpreted as a contamination plume. Normalized chargeability (MN = m/ρ) confirmed polarizable zone, which could be an effect of a salinity increase (contamination plume), and the clay presence in the environment.  相似文献   

18.
Deep‐water sediments in the Molasse Basin, Austria, were deposited in a narrow foreland basin dominated by a large channel belt located between the steep Alpine fold and thrust belt to the south and the gentler northern slope off the Bohemian Massif. Several gas fields occur outside the channel belt, along the outer bend of a large meander. Accumulation of these overbank sediments reflects a complicated interplay between slope accommodation and debris‐flow and turbidity‐flow interaction within the channel. The tectonically oversteepened northern slope of the basin (ca 2 to 3°) developed a regionally important erosional surface, the Northern Slope Unconformity, which can be traced seismically for >100 km in an east–west direction and >20 km from the channel to the north. The slope preserves numerous gullies sourced from the north that eroded into the channel belt. These gullies were ca 20 km long, <1 km wide and ca 200 m deep. As the channel aggraded, largely inactive and empty gullies served as entry points into the overbank area for turbidity currents within the axial channel. Subsequently, debris‐flow mounds, 7 km wide and >15 km long, plugged and forced the main channel to step abruptly ca 7 km to the south. This resulted in development of an abrupt turn in the channel pathway that propagated to the east and probably played a role in forming a sinuous channel later. As debris‐flow topography was healed, flows spread out onto narrow area between the main channel and northern slope forming a broad fine‐grained apron that serves as the main gas reservoir in this area. This model of the overbank splay formation and the resulting stratigraphic architecture within the confined basin could be applied in modern and ancient systems or for subsurface hydrocarbon reservoirs where three‐dimensional seismic‐reflection data is limited. This study elucidates the geomorphology of the oversteepened slope of the under‐riding plate and its effects on the sedimentation.  相似文献   

19.
Many Gulf of Mexico estuaries have low ratios of water volume to bottom surface area, and benthic processes in these systems likely have a major influence on system structure and function. The purpose of this study was to determine the spatiotemporal distribution of biomass and community composition of subtidal benthic microalgal (BMA) communities in Galveston Bay, TX, USA, compare BMA community composition and biomass to phytoplankton in overlying waters, and estimate the potential contribution of BMA to the trophodynamics in this shallow, turbid, subtropical estuary. The estimates of BMA biomass (mean = 4.21 mg Chl a m−2) for Galveston Bay were within the range of the reported values for similar Gulf of Mexico estuaries. BMA biomass in the central part of the bay was essentially homogeneous, whereas biomass at the seaward and upper bay ends of the transect were significantly lower. Peridinin, fucoxanthin, and alloxanthin were the three carotenoids with the highest concentrations, with fucoxanthin having the highest mean concentration (1.82 mg m−2). The seaward and landward ends of the transect differed from the central region of the bay with respect to the relative abundances of chlorophytes, cyanobacteria, and photosynthetic bacteria. Benthic microalgal community composition also showed a gradual shift over time due to changes in the relative abundances of photosynthetic bacteria, cryptophytes, dinoflagellates, and cyanobacteria. Major changes in community composition occurred in the spring months (March to April). On an areal basis, BMA biomass in Galveston Bay occurred at minor concentrations (16.5%) relative to phytoplankton. Furthermore, the concentrations of carotenoid pigments for phytoplankton and BMA (fucoxanthin, alloxanthin, and zeaxanthin) were correlated (r = 0.48 to 0.61), suggesting a close linkage between microalgae in the water column and sediments. The contribution of BMA to the primary productivity of the deeper waters (>2 m) of Galveston Bay is probably very small in comparison to shallower waters along the bay margins. The significant similarities in the community composition of phytoplankton and BMA illustrate the potential importance of deposition and resuspension processes in this turbid, shallow estuary.  相似文献   

20.
In this study, the hydrochemical characteristics of shallow groundwater in a coastal region (Khulna) of southwest Bangladesh have been evaluated based on different indices for drinking and irrigation uses. Water samples were collected from 26 boreholes and analyzed for major cations and anions. Other physico-chemical parameters like pH, electrical conductivity (EC), and total dissolved solids were also measured. Most groundwater is slightly alkaline and largely varies in chemical composition, e.g. EC ranges from 962 to 9,370 μs/cm. The abundance of the major ions is as follows: Na+ > Ca2+ > Mg2+ > K+ = Cl− > HCO3 − > SO4 2− > NO3 −. Interpretation of analytical data shows two major hydrochemical facies (Na+–K+–Cl−–SO4 2− and Na+–K+–HCO3 −) in the study area. Salinity, total hardness, and sodium percentage (Na%) indicate that most of the groundwater samples are not suitable for irrigation as well as for domestic purposes and far from drinking water standard. Results suggest that the brackish nature in most of the groundwaters is due to the seawater influence and hydrogeochemical processes.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号