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 31 毫秒
1.
In Mediterranean coastal catchments, water management for preservation of pine forests and other natural areas faces particular challenges. Limited rainfall, water consumption by vegetation as well as subsidence, drainage and salt water intrusion all play an important role. Traditionally forest and water management are carried out independent of one another and do not consider water budget calculations. We show with this study that is very important to have quantitative information of all the components of the water budget as well as the size of the fresh water lenses in the aquifer to be able to integrate the water- and forest management. We use an integrated hydrologic-ecologic methodology based on easily attainable data to assess the monthly water budget of a coastal catchment, Marina Romea (Ravenna, Italy). We present detailed monthly water table records, rainfall data, drainage data, tree density and tree perimeter and use published sap flow measurements of single pine trees (Pinus Pinea) to quantify the actual transpiration of single pine trees in different periods of the year. Transpiration amounts to 10–30 l per day per tree. These values are confirmed by independent estimates of tree transpiration based on our water budget calculations: 9–34 l/tree/day. Because typically there are so many trees in planted pine forests, the total transpiration rates over the whole watershed take up a large percentage (up to 200 %) of the precipitation. In Marina Romea, four monitoring periods out of twelve, the tree transpiration is larger than precipitation. In nine monitoring periods, drainage in the watershed is larger than precipitation or tree water transpiration. The measurements and calculations show that not much freshwater is left to recharge the fresh water lens underneath Marina Romea. Monthly monitoring of groundwater table elevation and salinity in the pine forest of Marina Romea from March 2007 to February 2008 shows that the groundwater table strongly fluctuates and groundwater salinity is constantly very high (up to 17.7 g/l). Analytical calculations based on the Ghyben Herzberg Dupuit principle suggest that even a small continuous annual recharge of 15 mm could form a 2-m deep freshwater lens in the unconfined aquifer. This freshwater lens is not present in the study area and this is due to the fact that tree water transpiration and drainage take out most of the fresh water coming into the watershed. In catchments like Marina Romea, water consumption by the (natural) vegetation and seasonal differences as well as the fact that fresh water lenses are limited in salty surroundings should be taken into account in water and forest management.  相似文献   

2.
Understanding sources and rates of recharge to the Badain Jaran Desert in northern China is important for assessing sustainability of the area’s oasis lake ecosystem and its water resources in general. For this purpose, direct recharge was investigated with the chloride mass balance method for 18 unsaturated zone profiles (6–16 m depth). Spatial variability is low across the area (range in mean Cl in profiles: 62–164 mg/L Cl), largely attributable to the uniformity of sandy unsaturated zone conditions. No strong correlations between environmental factors of profile locations and recharge rates were found, though a weak relationship between recharge and vegetation density was suggested. The study area’s complex dune morphology appears to have no measurable impact on recharge variability. Mean estimated diffuse recharge is 1.4 mm/year (1.0–3.6 mm/year for 95% confidence level), approximately 1.7% of mean annual precipitation. Temporal fluctuations in recharge due to climate variability are apparent and there is good correspondence in temporal trends over a time span of 200–300 years. Water balance considerations indicate that direct recharge is insufficient to support the numerous perennial lakes in the study area, suggesting that diffuse recharge presently plays a minor role in the overall water balance of the desert’s shallow Quaternary aquifer.  相似文献   

3.
Saltwater has invaded the coastal aquifer along the southern Adriatic coast of the Po Plain in Italy. The topography, morphology and land use of the region is complex: rivers, canals, wetlands, lagoons, urban, industrial and agricultural areas and tourist establishments all coexist in a small area. Water table and iso-salinity maps show that in four study areas (Ancona-Bellocchio, Marina Romea, San Vitale Forest, Cervia) out of five, the water tables are below sea level and saltwater has replaced freshwater in the aquifer. The fifth area (Classe Forest) has a relatively pristine freshwater aquifer thanks to an average water-table height of 2 m above sea level, a lower hydraulic conductivity (< 7.7 m/day) and a continuous dune system along the coast. Only in this area is the topography high enough to maintain freshwater heads that can counteract saltwater intrusion according to the Ghyben-Herzberg principle. Furthermore, the climate, with an average yearly precipitation of 606 mm and an average temperature of 14.4°C, allows for little recharge of the aquifer. Ongoing subsidence, encroachment of sea water along rivers and canals, as well as drainage from agricultural land also enhance the salinization process.  相似文献   

4.
The Nyamandhlovu aquifer is the main water resource in the semi-arid Umguza district in Matebeleland North Province in Zimbabwe. The rapid increase in water demand in the city of Bulawayo has prompted the need to quantify the available groundwater resources for sustainable utilization. Groundwater recharge estimation methods and results were compared: chloride mass balance method (19–62 mm/year); water-table fluctuation method (2–50 mm/year); Darcian flownet computations (16–28 mm/year); 14C age dating (22–25 mm/year); and groundwater modeling (11–26 mm/year). The flownet computational and modeling methods provided better estimates for aerial recharge than the other methods. Based on groundwater modeling, a final estimate for recharge (from precipitation) on the order of 15–20 mm/year is believed to be realistic, assuming that part of the recharge water transpires from the water table by deep-rooted vegetation. This recharge estimate (2.7–3.6% of the annual precipitation of 555 mm/year) compares well with the results of other researchers. The advantages/disadvantages of each recharge method in terms of ease of application, accuracy, and costs are discussed. The groundwater model was also used to quantify the total recharge of the Nyamandhlovu aquifer system (20?×?106–25?×?106 m3/year). Groundwater abstractions exceeding 17?×?106 m3/year could cause ecological damage, affecting, for instance, the deep-rooted vegetation in the area.  相似文献   

5.
The processes and rates of groundwater recharge in arid and semiarid environments are highly related to local climate parameters, particularly precipitation. The chloride profile of an unsaturated zone in an arid and semiarid region can be used to infer the recharge history and past changes in climate, by extension. In this study, a 17-m chloride profile was collected from the sandy loess in the northwestern Chinese Loess Plateau, which also lies in the transition zone between desert and loess. A 71-year groundwater recharge history was reconstructed using the chloride mass balance method with an annual Cl? input of 0.84 g/m2/year. The reconstructed history revealed a long-term decline in recharge with multiple shorter-term oscillations. Five recharge stages between 1938–1946, 1947–1955, 1956–1975, 1976–2000, and 2001–2008 AD were identified, where the lowest average recharge value was 25.1 mm/a in 1976–2000 AD and the highest was 71.7 mm/a in 1947–1955 AD. Climate conditions during these five periods were also inferred based on the reconstructed recharge rates with the knowledge that high recharge corresponds to more humid climates. The climate over the past 71 years generally became drier in the study area, despite some fluctuations. The reconstructed recharge rates, calculated from 1/Cl? in the profile, exhibited the same variability as annual precipitation measured in the region, both in long- and short-term oscillations over the period from 1955 to 2008. The chloride concentration variations in the profile, indicating changes in recharge flux, also well correlated with annual precipitation anomalies in the region to the east of 100°E in China for the whole study period. These comparisons verified that it is feasible to study not only groundwater recharge, but also past climate change using a chloride profile from the sandy loess area. The results suggested that unsaturated zones of sandy loess may be valuable archives for reconstructing recharge history and regional paleoclimate changes in the region.  相似文献   

6.
For semi-arid regions, methods of assessing aquifer recharge usually consider the potential evapotranspiration. Actual evapotranspiration rates can be below potential rates for long periods of time, even in irrigated systems. Accurate estimations of aquifer recharge in semi-arid areas under irrigated agriculture are essential for sustainable water-resources management. A method to estimate aquifer recharge from irrigated farmland has been tested. The water-balance-modelling approach was based on VisualBALAN v. 2.0, a computer code that simulates water balance in the soil, vadose zone and aquifer. The study was carried out in the Campo de Cartagena (SE Spain) in the period 1999–2008 for three different groups of crops: annual row crops (lettuce and melon), perennial vegetables (artichoke) and fruit trees (citrus). Computed mean-annual-recharge values (from irrigation+precipitation) during the study period were 397 mm for annual row crops, 201 mm for perennial vegetables and 194 mm for fruit trees: 31.4, 20.7 and 20.5% of the total applied water, respectively. The effects of rainfall events on the final recharge were clearly observed, due to the continuously high water content in soil which facilitated the infiltration process. A sensitivity analysis to assess the reliability and uncertainty of recharge estimations was carried out.  相似文献   

7.
Improvement in modern water resource management has become increasingly reliant on better characterizing of the spatial variability of groundwater recharge mechanisms. Due to the flexibility and reliability of GIS-based index models, they have become an alternative for mapping and interpreting recharge systems. For this reason, an index model by integrating water balance parameters (surface runoff, actual evapotranspiration, and percolation) calculated by Thornthwaite and Mather’s method, with maps of soil texture, land cover, and terrain slope, was developed for a sustainable use of the groundwater resources. The Serra de Santa Helena Environmental Protection Area, next to the urbanized area of Sete Lagoas (MG), Brazil, was selected as the study area. Rapid economic growth has led to the subsequent expansion of the nearby urban area. Large variability in soil type, land use, and slope in this region resulted in spatially complex relationships between recharge areas. Due to these conditions, the study area was divided into four zones, according to the amount of recharge: high (>?100 mm/year), moderate (50–100 mm/year), low (25–50 mm/year), and incipient (>?25 mm/year). The technique proved to be a viable method to estimate the spatial variability of recharge, especially in areas with little to no in situ data. The success of the tool indicates it can be used for a variety of groundwater resource management applications.  相似文献   

8.
This study aims to characterise the hydrogeology and hydrochemistry of the Parmelia aquifer and to understand controls on recent water-level changes as these are needed to underpin a quantitative analysis of recharge. The Parmelia aquifer, a layered sequence of sand, silt and discontinuous lenses of clay, receives diffuse rainfall recharge on its outcrop and groundwater recharge occurs across the Dandaragan Plateau at different rates. Water levels have risen steadily over the last three decades between 10 and 55 cm/y in response to the replacement of native vegetation with pasture and annual crops. The mean aquifer properties from sediment analyses indicate a very wide range of porosity (8.9 – 49.5 %) with an arithmetic mean of 26% and consequently a very broad range of specific yield (0.0004 – 0.4) with an arithmetic mean of 0.14. Groundwater in the Parmelia aquifer has an underlying meteoric origin with compositional changes due to reactions with silicate minerals and leaching of chloride that has concentrated in the soil by evapotranspiration. The hydrochemistry sampled at different depths and locations in the aquifer indicates that the groundwater is not well mixed, and variations arise due to relatively recent recharge that has undergone evaporation in some areas.  相似文献   

9.
Freshwater-lens thickness and long-term changes in freshwater volume in coastal aquifers are commonly assessed through repeated measurement of salinity profiles from monitor wells that penetrate into underlying salt water. In Hawaii, the thickest measured freshwater lens is currently 262 m in dike-free, volcanic-rock aquifers that are overlain by thick coastal sediments. The midpoint depth (depth where salinity is 50% salt water) between freshwater and salt water can serve as an indicator for freshwater thickness. Most measured midpoints have risen over the past 40 years, indicating a shrinking lens. The mean rate of rise of the midpoint from 1999–2009 varied locally, with faster rates in highly developed areas (1.0 m/year) and slower rates in less developed areas (0.5  m/year). The thinning of the freshwater lenses is the result of long-term groundwater withdrawal and reduced recharge. Freshwater/salt-water interface locations predicted from measured water levels and the Ghyben-Herzberg principle may be deeper than measured midpoints during some periods and shallower during other periods, although depths may differ up to 100 m in some cases. Moreover, changes in the midpoint are slower than changes in water level. Thus, water levels may not be a reliable indicator of the amount of freshwater in a coastal aquifer.  相似文献   

10.
Groundwater recharge sets a constraint on aquifer water balance in the context of water management. Historical data on groundwater and other relevant hydrological processes can be used to understand the effects of climatic variability on recharge, but such data sets are rare. The climate of the Canadian prairies is characterized by large inter-annual and inter-decadal variability in precipitation, which provides opportunities to examine the response of groundwater recharge to changes in meteorological conditions. A decadal study was conducted in a small (250 km2) prairie watershed in Alberta, Canada. Relative magnitude of annual recharge, indicated by water-level rise, was significantly correlated with a combination of growing-season precipitation and snowmelt runoff, which drives depression-focussed infiltration of meltwater. Annual precipitation was greater than vapour flux at an experimental site in some years and smaller in other years. On average precipitation minus vapour flux was 10 mm y?1, which was comparable to the magnitude of watershed-scale groundwater recharge estimated from creek baseflow. Average baseflow showed a distinct shift from a low value (4 mm y?1) in 1982–1995 to a high value (15 mm y?1) in 2003–2013, indicating the sensitivity of groundwater recharge to a decadal-scale variability of meteorological conditions.  相似文献   

11.
In Togo, the hydrogeology of the sedimentary coastal aquifers along the Gulf of Guinea has been studied for the last three decades to define the recharge processes and the origin and evolution of the salinity. Isotope hydrology and fluid geochemistry suggest that the current recharge of all aquifers, both confined and unconfined, occurs through the crystalline basement and the Plio-Quaternary deposits. Two main groundwater mineralization processes are observed: the first one, in recharge areas, is due to farming, village and city life and concerns unconfined aquifers (crystalline basement, Continental Terminal and Quaternary sediments); the second one is a mixing process between recent freshwater and fossil saline water still present in the deep confined aquifers inland, several kilometers away from the coast. Brackish water was trapped in low-permeability lenses of confined aquifers (Eo-Palaeocene and Maastrichtian) during the Quaternary, in periods of low recharge, notably during the last glacial maximum (LGM), and has not yet been flushed out. Hydrodynamic simulations indicate that, at that time, the aquifers experienced a maximum seawater intrusion as far as 20–22 km inland, depending on the palaeo-recharge value at the outcrops.  相似文献   

12.
The Indian Ocean Tsunami of December 26, 2004 devastated coastal ecosystems across South Asia. Along the coastal regions of South India, increased groundwater levels (GWL), largely caused by saltwater intrusion, infiltration from inundated land, and disturbance of freshwater lenses, were reported. Many agencies allocated funding for restoration and rehabilitation projects. However, to streamline funding allocation efforts, district-level groundwater inundation/recession data would have been a useful tool for planners. Thus, to ensure better preparedness for future disaster relief operations, it is crucial to quantify pre- and post-tsunami groundwater levels across coastal districts in India. Since regional scale GWL field observations are not often available, this study instead used space gravimetry data from NASA’s Gravity Recovery and Climate Experiment (GRACE), along with soil moisture data from the Global Land Data Assimilation Systems (GLDAS), to quantify GWL fluctuations caused by the tsunami. A time-series analysis of equivalent groundwater thickness was developed for February 2004–December 2005 and the results indicated a net increase of 274 % in GWLs along coastal regions in Tamil Nadu following the tsunami. The net recharge volume of groundwater due to the tsunami was 16.8 km3, just 15 % lower than the total annual groundwater recharge (19.8 km3) for the state of Tamil Nadu. Additionally, GWLs returned to average within 3 months following the tsunami. The analysis demonstrated the utility of remotely sensed data in predicting and assessing the impacts of natural disasters.  相似文献   

13.
Water and nutrient availability for crop production are critical issues in (semi)arid regions. Unsaturated-zone Cl tracer data and nutrient (NO3 and PO4) concentrations were used to quantify recharge rates using the Cl mass balance approach and nutrient availability in the Thar Desert, Rajasthan, India. Soil cores were collected in dune/interdune settings in the arid Thar Desert (near Jaisalmer) and in rain-fed (nonirrigated) and irrigated cropland in the semiarid desert margin (near Jaipur). Recharge rates were also simulated using unsaturated zone modeling. Recharge rates in sparsely vegetated dune/interdune settings in the Jaisalmer study area are 2.7–5.6 mm/year (2–3% of precipitation, 165 mm/year). In contrast, recharge rates in rain-fed agriculture in the Jaipur study area are 61–94 mm/year (10–16% of precipitation, 600 mm/year). Minimum recharge rates under current freshwater irrigated sites are 50–120 mm/year (8–20% of precipitation). Nitrate concentrations are low at most sites. Similarity in recharge rates based on SO4 with those based on Cl is attributed to a meteoric origin of SO4 and generally conservative chemical behavior in these sandy soils. Modeling results increased confidence in tracer-based recharge estimates. Recharge rates under rain-fed agriculture indicate that irrigation of 20–40% of cultivated land with 300 mm/year should be sustainable.  相似文献   

14.
Although shallow groundwater (<50 mbgl) sustains the vast majority of improved drinking-water supplies in rural Africa, there is little information on how resilient this resource may be to future changes in climate. This study presents results of a groundwater survey using stable isotopes, CFCs, SF6, and 3H across different climatic zones (annual rainfall 400–2,000 mm/year) in West Africa. The purpose was to quantify the residence times of shallow groundwaters in sedimentary and basement aquifers, and investigate the relationship between groundwater resources and climate. Stable-isotope results indicate that most shallow groundwaters are recharged rapidly following rainfall, showing little evidence of evaporation prior to recharge. Chloride mass-balance results indicate that within the arid areas (<400 mm annual rainfall) there is recharge of up to 20 mm/year. Age tracers show that most groundwaters have mean residence times (MRTs) of 32–65 years, with comparable MRTs in the different climate zones. Similar MRTs measured in both the sedimentary and basement aquifers suggest similar hydraulic diffusivity and significant groundwater storage within the shallow basement. This suggests there is considerable resilience to short-term inter-annual variation in rainfall and recharge, and rural groundwater resources are likely to sustain diffuse, low volume abstraction.  相似文献   

15.
Sustainable groundwater management requires knowledge of recharge. Recharge is also an important parameter in groundwater flow and transport models. Spatial variation in recharge due to distributed land-us.e, soil texture, topography, groundwater level, and hydrometeorological conditions should be accounted for in recharge estimation. However, conventional point-estimates of recharge are not easily extrapolated or regionalized. In this study, a spatially distributed water balance model WetSpass was used to simulate long-term average recharge using land-use, soil texture, topography, and hydrometeorological parameters in Dire Dawa, a semiarid region of Ethiopia. WetSpass is a physically based methodology for estimation of the long-term average spatial distribution of surface runoff, actual evapotranspiration, and groundwater recharge. The long-term temporal and spatial average annual rainfall of 626 mm was distributed as: surface runoff of 126 mm (20%), evapotranspiration of 468 mm (75%), and recharge of 28 mm (5%). This recharge corresponds to 817 l/s for the 920.12 km2 study area, which is less than the often-assumed 1,000 l/s recharge for the Dire Dawa groundwater catchment.  相似文献   

16.
Spatially distributed recharge is compared at two different scales using three different modeling approaches within the semi-arid Okanagan Basin, British Columbia, Canada. Regional recharge was modeled by mapping results for one-dimensional soil columns from the water-balance code HELP (Hydrologic Evaluation of Landfill Performance, V3.80D). The regional model was then compared to two, independently derived, local-scale models to ensure local trends were captured in the regional model, and to compare modeling methods. Average annual recharge, predicted by the regional model, varied from no recharge to 186 mm/yr. For the north Okanagan (Vernon area), regional estimates were compared to Richards’ equation-based MIKE-SHE (V2007) estimates, which showed a significant difference in average annual recharge: 7 mm/yr (MIKE-SHE) and 109 mm/yr (HELP). In the south Okanagan (Oliver area), regional estimates were compared to high-resolution, local HELP estimates. Similar values of average annual recharge were obtained: 34 mm/yr (local) and 42 mm/yr (regional). A comparison with measured actual evapotranspiration data in the north Okanagan, showed HELP over-predicted recharge compared to MIKE-SHE by under-predicting evapotranspiration during summer months. Thus, the use of HELP in semi-arid areas may be limited if accurate estimates of recharge are needed. However, results may give satisfactory groundwater model calibrations results because of high uncertainty in hydraulic properties.  相似文献   

17.
The effects of climate change on the groundwater systems in the Grote-Nete catchment, Belgium, covering an area of 525 km2, is modeled using wet (greenhouse), cold or NATCC (North Atlantic Thermohaline Circulation Change) and dry climate scenarios. Low, central and high estimates of temperature changes are adopted for wet scenarios. Seasonal and annual water balance components including groundwater recharge are simulated using the WetSpass model, while mean annual groundwater elevations and discharge are simulated with a steady-state MODFLOW groundwater model. WetSpass results for the wet scenarios show that wet winters and drier summers are expected relative to the present situation. MODFLOW results for wet high scenario show groundwater levels increase by as much as 79 cm, which could affect the distribution and species richness of meadows. Results obtained for cold scenarios depict drier winters and wetter summers relative to the present. The dry scenarios predict dry conditions for the whole year. There is no recharge during the summer, which is mainly attributed to high evapotranspiration rates by forests and low precipitation. Average annual groundwater levels drop by 0.5 m, with maximum of 3.1 m on the eastern part of the Campine Plateau. This could endanger aquatic ecosystem, shrubs, and crop production.  相似文献   

18.
A time-series approach to the estimation of recharge rate in unconfined aquifers of highly variable water level is proposed. The approach, which is based on the water-table fluctuation method (WTF), utilizes discrete water-level measurements. Other similar techniques require continuous measurements, which makes them impossible to apply in cases where no data from automatic loggers are available. The procedure is deployed at the Ressacada Farm site, southern Brazil, on a coastal shallow aquifer located in a humid subtropical climate where diurnal water-level variations of up to 1 m can follow a precipitation event. The effect of tidal fluctuations on the groundwater levels is analyzed using a harmonic component builder, while a time-variable drainage term is evaluated through an independent analysis and included in the assessment. The estimated recharge values are compared with those obtained from the continuous measurements showing a good agreement with the approaches for discrete dataset intervals of up to 15 days. Subsequently, the estimated recharge rates are incorporated into a transient groundwater-flow model and the water levels are compared showing a good match. Henceforth, the approach extends the applicability of WTF to noncontinuous water-level datasets in groundwater recharge studies.  相似文献   

19.
The sea levels along the semi-arid South Texas coast are noted to have risen by 3–5 mm/year over the last five decades. Data from General Circulation Models (GCMs) indicate that this trend will continue in the 21st century with projected sea level rise in the order of 1.8–5.9 mm/year due to the melting of glaciers and thermal ocean expansion. Furthermore, the temperature in South Texas is projected to increase by as much as 4 °C by the end of the 21st century creating a greater stress on scarce water resources of the region. Increased groundwater use hinterland due to urbanization as well as rising sea levels due to climate change impact the freshwater-saltwater interface in coastal aquifers and threaten the sustainability of coastal communities that primarily rely on groundwater resources. The primary goal of this study was to develop an integrated decision support framework to assist land and water planners in coastal communities to assess the impacts of climate change and urbanization. More specifically, the developed system was used to address whether coastal side (primarily controlled by climate change) or landward side processes (controlled by both climate change and urbanization) had a greater control on the saltwater intrusion phenomenon. The decision support system integrates a sharp-interface model with information from GCMs and observed data and couples them to statistical and information-theoretic uncertainty analysis techniques. The developed decision support system is applied to study saltwater intrusion characteristics at a small coastal community near Corpus Christi, TX. The intrusion characteristics under various plausible climate and urbanization scenarios were evaluated with consideration given to uncertainty and variability of hydrogeologic parameters. The results of the study indicate that low levels of climate change have a greater impact on the freshwater-saltwater interface when the level of urbanization is low. However, the rate of inward intrusion of the saltwater wedge is controlled more so by urbanization effects than climate change. On a local (near coast) scale, the freshwater-saltwater interface was affected by groundwater production locations more so than the volume produced by the community. On a regional-scale, the sea level rise at the coast was noted to have limited impact on saltwater intrusion which was primarily controlled by freshwater influx from the hinterlands towards the coast. These results indicate that coastal communities must work proactively with planners from the up-dip areas to ensure adequate freshwater flows to the coast. Field monitoring of this parameter is clearly warranted. The concordance analysis indicated that input parameter sensitivity did not change across modeled scenarios indicating that future data collection and groundwater monitoring efforts should not be hampered by noted divergences in projected climate and urbanization patterns.  相似文献   

20.
This article analyses the hydrogeochemical processes, linked to the freshwater–seawater mixing zone, which can be caused by continuous pumping from a detrital coastal aquifer. It was necessary to construct an experimental plot, drilling three boreholes along a line perpendicular to the coast. A complete physico-chemical analysis was done of all water samples taken. The percentage of seawater, calculated from Chloride and 18Oxygen concentrations, varied between 55 and 90 %. The ionic deltas (Δ) calculated, and the saturation indices (SI) of mineral phases susceptible to precipitation or dissolution, allowed a series of hydrogeochemical processes to be identified that occur as a consequence of the advance of marine intrusion into the coastal band, and of aquifer flushing. Based on the major elements, the fraction of exchange (βI) was calculated for samples ranging from seawater to freshwater, and this revealed that differences in βI could explain the hydrochemistry of the mixing zone. The main processes recognised include precipitation of dolomite, dissolution of gypsum, fixation of sulphur salts and cation exchange. Most of the ion exchange took place between Na and Calcium + Magnesium ions. The process of fixation or liberation of these ions is probably determined by the advance or recession of the saline wedge, and/or by recharge during rainy periods. The behaviour of Magnesium is more sensitive to small variations in salinity, whilst Calcium behaves more homogeneously. The high percentage of seawater in the samples studied favours the speed and magnitude of processes such as ion exchange, and the intervention of magnesium is also a key.  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