岩溶区矿山污染地下水的水生植物修复初步研究

选取黑藻(Hydrilla verticillata Royle)和水绵(Spirogyra communis,Hassall)作为研究对象,分析其对某铅锌矿尾矿库重金属废水的富集能力,综述重金属在黑藻和水绵体内的富集机制,探讨了利用黑藻和水绵进行岩溶矿山重金属污染水修复的应用前景。结果表明:黑藻和水绵体内的重金属绝对含量较高,并且植株长势良好,生物量大,说明这两种水生植物对重金属有避性或耐性。分析测试发现,在黑藻和水绵体内,重金属的富集系数较高,其中Pb最大,其后依次是As>Co>Mn>Cu>Cd>Zn>Ni>Cr,富集系数最少的是Hg,水绵体内的富集系数要大于黑藻。对比研究发现,这两类藻类体内的重金属含量和富集系数均高于非岩溶区。黑藻对重金属的富集机制主要有3种,即重金属作用下抗氧化酶活性增强、被动吸收和离子交换作用,而水绵特殊的分子生物结构可能是其吸附重金属的重要机制。黑藻和水绵在南方岩溶区广泛分布,利用黑藻和水绵修复重金属污染的岩溶水具有较好前景。      

Carbon-14 study of groundwater in the sedimentary rocks at the Tono study site,central Japan

Isotopic investigations using ¹⁴C of groundwater were carried out to understand the hydraulic conditions in the sedimentary rocks at the Tono study site, central Japan. ¹⁴C activities of groundwater observed range from 2 to 32 % Modern Carbon (pMC). Measured ¹⁴C activities of groundwater are corrected by the isotopic mass balance model based on ¹⁴C activities, δ¹³C values, concentrations of the dissolved inorganic carbon (DIC) and δ¹³C values of non-active carbon dissolved into the groundwater from carbonate minerals and organics. Assuming that the groundwater reservoir is comparable to the piston flow situation, the relative ¹⁴C ages of groundwaters were calculated from the corrected ¹⁴C activity. The relative ¹⁴C age suggests that the groundwater infiltration from the upper part of the sedimentary rocks to the lower part takes several thousands of years, or that the groundwater in the lower part of sedimentary rocks is derived from long distance flow from the surface through the unconformity between the sedimentary rocks and basement granite. The flow rate calculated by relative ¹⁴C ages shows similar values to those estimated by computer simulation using hydraulic pressure and conductivity data. Hydraulic conditions at the Tono study site inferred from ¹⁴C activity agree with those suggested from hydrogeological analyses. Isotopic approaches using ¹⁴C activity can be applied as geochemical evaluation for interpretations from the hydraulic study.     

Aqueous and solid phase arsenic speciation in the sediments of a contaminated wetland and riverbed

Mobility of As in the environment is controlled by its association with solid phases through adsorption and co-precipitation. To elucidate the mobilization potential of As deposited in wetland and riverbed sediments of the Wells G & H wetland in Woburn, MA as the result of decades of industrial activity, As retention mechanisms were inferred from aqueous and solid phase geochemical measurements of sediment cores. Testing included a sequential extraction method designed for and standard-tested with As phases and pE/pH equilibrium modeling. The uppermost sediments in the Wells G & H wetland contain elevated concentrations of both dissolved and solid phase As (up to 2,000 μg/L and 15,000 μg/g, respectively) and a maximum concentration between 30 and 40 cm depth. Measurements obtained in this study suggested that As in the wetland sediments was predominantly adsorbed, likely onto amorphous Fe (hydr)oxide phases and mixed valence Fe phases. In the riverbed sediments, however, a relatively greater proportion of the solid As was associated with more reduced and crystalline phases, and adsorbed As was more likely associated with Al oxide or secondary reduced Fe phases. pH–pe modeling of the Fe–As–S system was consistent with observations. The association of As with more oxidized phases in the wetland compared with the riverbed sediments may result from a combination of plant activities, including evapotranspiration-driven water table depression and/or root oxygenation.     

西北典型内陆流域地下水与湿地生态系统协同演化机制

以生态输水为代表的湿地修复工程在西北内陆流域得到了广泛应用,生态输水情形下地下水与湿地植被的交互作用决定着湿地生态系统的演化过程。以西北典型内陆流域—石羊河流域青土湖湿地为研究区,基于地下水-湿地生态系统多要素一体化动态监测网络,结合稳定同位素和卫星遥感技术手段,分析生态输水情形下的地下水动态变化与湿地植被恢复情况,从水文地质角度揭示地下水与湿地生态系统的协同演化机制。结果显示:夏季末和秋季生态输水时,湖水补给地下水且土壤含水率增大,最大土壤含水率可达0.45 m³/m³;冬季湿地湖面和表层土壤冻结,湖水对地下水补给量减少,春季冻土和湖面消融导致地下水略有回升,同时增大土壤含水率;夏季在下次生态输水前湖面面积最小(湖面面积最小约为1 km²,地下水水位最大埋深为3.6 m),部分区域地下水补给湖水,此时表层土壤含水率也最低(最小土壤含水率为0.01 m³/m³);夏季末和秋季生态输水通过将生态水储存在地下水和土壤中进而作用于次年的植被恢复与生长,增大生态输水所形成的湖面面积有助...     

Determination of groundwater flow regimes in underground storage caverns using tritium and helium isotopes

Understanding groundwater flow and chemical transport is crucial for operating underground storage caverns. Groundwater flow in the study area is mainly affected by cavern operating conditions, and groundwater chemistry in the study area is modified by disinfection activities for removing possible biological clogging and by mixing with cement pore water. It is significant to discern these two effects because wells affected by the disinfection activities, in particular, may have hydrological connections with water curtains in which disinfectant water was injected to remove the biological clogging. Concentration of tritium (³H) and helium isotopes (⁴He), and groundwater chemical compositions were used to confirm that there are hydrological connectivities between the water curtain and the well. Groundwater along the fault areas contains low total dissolved solid (TDS) and high ³H, suggesting that the faults may act as fast flow conduits, which is not inconsistent with previous studies. Certain diagnostic conditions (high concentrations of Na⁺, Cl⁻ and TDS and high pH) are presumed by the effect of disinfection activity, indicating that there are hydrological connections between the water curtain and the wells. This hypothesis is valid in YK2U and YK2L, but is not in YK12L, implying a closed system or an immobile water to explain the isotopic results.     

Geochemistry of lead contaminated wetland soils amended with phosphorus

To remediate Pb contaminated soils it is proposed that phosphorus can be amended to the soils to transform the Pb into poorly soluble Pb-phosphate mineral phases. However, remediation strategies must account for variable Pb speciation and site-specific factors. In this study soil mineralogy and Pb speciation in soils from P-amended field trials at sites within the Coeur d’Alene River Basin in Idaho, USA were investigated. The soils are contaminated from mining activities and are enriched with Fe and Mn. Selective extraction of the soils indicated that the Fe oxides are poorly crystalline. XRD of the soil clay size fractions identified quartz, muscovite, kaolinite, siderite, lepidocrocite, and chlorite minerals. Amendment with P fertilizer dissolved the siderite. No Pb–phosphate minerals were detected by XRD. Electron microprobe analysis showed direct correlations between Pb, Fe, and Mn in the unamended soils, and negative correlations between Pb and Si. Lead and Mn were strongly correlated. In the amended soils Fe and P were strongly correlated. Results indicate that the Pb is associated with poorly crystalline Fe and Mn oxides, and that added P is primarily associated with Fe oxide phases. Comparisons of pore water Pb concentrations with chloropyromorphite and plumbogummite solubility suggest that in the phosphate-amended soils the pore waters are undersaturated in these phases, whereas several of the control soil pore waters were oversaturated, indicating the added phosphate suppressed the Pb solubility. Results from this research provide insight into the geochemistry occurring in the P-remediated soils that will help in making management and remediation decisions.     

Carbon-14 age and chemical evolution of Ca(HCO3)2-type groundwater of age less than 8,000 years in a confined sandy and muddy Pleistocene aquifer, Japan

The Pleistocene Kimitsu aquifer was selected for examination of the relationship between groundwater age and chemical evolution of Ca(HCO₃)₂-type groundwater. For the most part, the aquifer is confined and composed mainly of quartz and feldspar with a small amount of calcite. The groundwater ages calculated by ¹⁴C were adjusted by using a carbon mass-balance method and corrected for effects of ¹⁴C diffusion. Groundwater ages in the Kimitsu aquifer vary from modern (upgradient) to approximately 2,400 years at 4.4 km from the edge of the recharge area. The ¹⁴C age was verified by groundwater velocity calculated from the hydraulic gradient and hydraulic conductivity. The confined groundwater evolved to Ca(HCO₃)₂-type around 50 years after recharge and this has been maintained for more than 8,300 years due to low chemical reactivity, derived from equilibrium with calcite, kaolinite and Ca-montmorillonite. In addition, high pH prevents the dissolution of Fe and Mn. Consequently, the rate of increase in electrical conductivity ranges from 10 to 30 μS/cm per 1,000 years. On the other hand, leakage from the deep region, which is recognized from high Cl^– levels, causes remarkable increases in CH₄ and HCO₃ ^– concentrations, resulting in an apparent sulfidic zone at 500-m depth in most downgradient regions.     

某地块污染调查及二氯甲烷在土壤和地下水中的分布特征

以某生物医药企业地块为研究对象,结合企业生产历史,识别该地块疑似污染区域以及关注的污染物,通过布设土壤及地下水现场采样点进行现场和实验室测试,研究土壤及地下水中监测因子的含量及分布特征,特别是对二氯甲烷的污染源及其在土壤和地下水中的分布特征进行分析,指出由于地层特征和多种有机污染物的影响,土壤中二氯甲烷的含量未超过国家标准,但在地下水中含量异常高;分析地层对二氯甲烷在土壤和地下水中垂向和侧向迁移的影响,为下一步污染防控提供依据。     

潮汐作用下的滨海湿地浅层地下水动态变化

黄河三角洲滨海湿地浅层地下水位受潮汐波动影响明显,海洋潮汐和受其影响的海岸带湿地浅层地下水具有复杂的周期性变化和趋势性变化。本文通过现场水文监测,设定时间自动采集地下水监测数据,连续监测地下水动态变化,分析地下水位与海洋潮汐波动关系,为湿地水文变化和预测分析提供科学依据。     

Recovery of chlorinated solvent trichloroethylene contaminated groundwater using a hybrid treatment system

In this laboratory pilot-scale study, a hybrid treatment system has been developed to remove chlorinated solvent trichloroethylene and fine particles from chlorinated solvent trichloroethylene-contaminated groundwater before it is applied for further recovery. The two-stage system contained fiber-ball filtration followed by nanofiltration membrane processes. The measured chlorinated solvent trichloroethylene and suspended solids of the tested groundwater were 850 μg/L and 1,052 mg/L, respectively. Up to 97.3 % of chlorinated solvent trichloroethylene and 99.9 % of SS could be removed by the hybrid system with an operational pressure of 4.1 kg/cm². The chlorinated solvent trichloroethylene removal mechanism in the fiber-ball filtration process could be due to adsorption. Approximately 98.2 and 78.6 % of chlorinated solvent trichloroethylene rejection was observed when nanofiltration membrane was used for chlorinated solvent trichloroethylene removal with the recover rate of 80 % and initial chlorinated solvent trichloroethylene concentration of 1 and 10 mg/L. Higher chlorinated solvent trichloroethylene rejection can be obtained when lower chlorinated solvent trichloroethylene concentration (1 mg/L) was applied. High chlorinated solvent trichloroethylene concentration (10 mg/L) would increase the pore size of nanofiltration, which causes the decrease in chlorinated solvent trichloroethylene rejection rate. Approximately 46.6 % of flux drop was observed when nanofiltration membrane was used along compared to the system using FF as the first treatment stage. This indicates that the application of fiber-ball filtration could maintain a higher flux of groundwater treatment. The developed fiber-ball filtration and nanofiltration hybrid membrane system is able to reduce the chlorinated solvent trichloroethylene and solid concentrations to meet the water reuse and groundwater remediation standards.     

Exploitation of groundwater resources and protection of wetland in the Yuqia Basin

In Yuqia Basin, the climate is arid and the ecologic environment is fragile, and shortage of water resources has seriously restricted the sustainable development of local economy. In order to meet the needs of industrial and domestic water in the Yuqia Basin, numerical simulation was used to evaluate the groundwater resources and potential for exploitation. The results showed that the mathematical model and calculation parameters used were mainly in accordance with practical situation. The calculated value of the underground water level is consistent with measured value during the period of identification and validation. The total recharge of groundwater resources was 22.02×10~4 m~3/d, and the total drainage was 21.95×10~4 m~3/d at present. The Yuqia River leakage is the main supply source of groundwater. There is no significant effect on area of wetland when water source place exploited by 2.5×10~4 m~3/d at alluvial-diluvial fan of Yuqia River. After long-term exploitation, the spring flow reduces from 1.42×10~4 m~3/d to 1.01×10~4 m~3/d and wetland area reduces by 32.7% of original area. The calculation of water balance shows that it is safe to the Yuqia Basin, Da Qiadam Lake, the Mahai Basin at downstream of Yuqia River and wetland under the condition of water source place exploited by 2.5×10~4 m~3/d.     

Slow arsenic poisoning of the contaminated groundwater users

This paper gives impact of Arsenic contaminated water on human health as well as overview of the extent and severity of groundwater arsenic contamination in Bangladesh. Scalp hair is the most important part of the human body to monitor the accumulation of this type of poison. Therefore, an experiment has been carried out by Neutron Activation Analysis (NAA) at Atomic Energy Research Establishment (AERE), Savar, Dhaka, Bangladesh on human hair of corresponding tube well water users of these areas to determine the total accumulation of arsenic to their body. Hair samples collected from the region where the groundwater was found highly contaminated with arsenic. The obtained results of arsenic concentration in the lower age (Hb) categories of users (below 12 years of age users) is in the range of 0.33 to 3.29 /gmg/g (ppm) and that in the Hu categories (upper 12 years of age users) is 0.47 to 6.64 μg/g (ppm). Where as maximum permissible range is 1 ppm certified from WHO. Results show that the peoples are highly affected where the groundwater is highly contaminated with arsenic and acts as the primary source of arsenic poisoning among the peoples of those areas. The results indicate that human population is affected with arsenic locally using the contaminated water for a long time.     

Application of tritium in precipitation and in groundwater of the Kouris catchment (Cyprus) for description of the regional groundwater flow

The Kouris catchment is located in the south of the Troodos massif in Cyprus. It constitutes one of the biggest catchments of the island with important freshwater resources. Geologically, the catchment includes an ophiolitic complex outcropping in the north which is overlaid by sedimentary rocks in the south. The hydrology is driven by a Mediterranean climate, a mountainous topography, and a complex distribution of the hydrogeological properties resulting from the complex geology.To improve the understanding of groundwater hydrology of the Kouris catchment, 176 groundwater and precipitation samples were collected and their ³H contents were analyzed. The three-dimensional ³H transport in the groundwater was simulated by the PMPATH code. For numerical modelling, a regional input function of ³H in precipitation was constructed from a linear regression between data for Cyprus and for neighboring meteorological stations. The calculated residence times for the groundwaters in the sedimentary aquifer and Pillow Lavas were greater than 48 a and were considerably greater than those of the ophiolitic complex (14–30 a). The calibrated aquifer porosities were in a range of 0.05–0.06. The PMPATH model was applied for delineation of spring catchments that were represented by quite narrow zones of lengths up to 5 km.Another contribution resulting from the ³H analysis was a better understanding of the river–aquifer interactions. In most of the southern part, the lithified sediments received only negligible amounts of water from the rivers, while the alluvial aquifer contained mostly water infiltrated from rivers. The largest springs in the southern part, associated with the alluvial aquifer, also discharged water identical to that in the rivers.     

某石油化工污染场地地下水中挥发性有机物污染特征及成因分析

为了解典型污染场地浅层地下水微量有机污染特征,对西北某省会城市石油化工场地地下水中的挥发性有机污染物（VOCs）污染情况进行了调查。结果表明,污染场地地下水样品中挥发性有机污染物检出率为100%;检出率较高的是氯代烃和苯系物,检出率分别为60%和40%。超标组分为苯和1,2-二氯丙烷,苯超标率为30%,1,2-二氯丙烷超标率10%,苯最大检出浓度达1515μg/L。场地内的原油储存罐、污水隔油池的渗漏以及石油冶炼、机械加工过程工业废水不合理排放均为该场地地下水VOCs的重要来源;VOCs的理化性质以及污染场地地下水防污性能差是影响该场地地下水环境中VOCs归宿的主要因素。     

Water–rock interaction induced by contaminated groundwater in a karst aquifer, Greece

The karst system of SW Trifilia is composed of a thick sequence of carbonate sediments, which have experienced two types of dolomitization and dedolomitization processes and comprise an extended aquifer. The application of fertilizers in the region have not only caused the degradation of the groundwater quality but also induced hydrochemical changes exerting major control on dolomitization processes. Factor analysis indicates high correlation coefficient between NH ₄ ⁺ , NO ₃ ⁻ , Ca²⁺ and Mg²⁺, which can be attributed to cation-exchange processes involving clay minerals. The application of a conservative mixing model showed that the calculated groundwater types indicate a cation-exchange process between NH ₄ ⁺ , derived from fertilizers, and between Ca²⁺ and Mg²⁺. Mg²⁺ released from smectite interlayers, exchanged for NH ₄ ⁺ in the groundwater and favor a dolomitization process through the partial replacement of Ca²⁺ in the lattice of calcite (dedolomite) contained in precursor dolomites. This recent stage dolomitization occurred near the water level and within the phreatic zone only and had not influenced the whole karst massif; it also resulted in low Mg/Ca values found in the zone characterized by intensive application of nitrogen-based fertilizers and the absence of overlying impermeable strata.     

石油污染地下水中细菌分子生态学研究

采集了某废弃炼油厂的石油污染地下水样品,提取水中微生物总DNA,构建细菌16S rDNA克隆文库,并通过16S rDNA序列的系统发育分析,对样品中的细菌种群多样性以及群落结构进行了研究。结果表明,文库中阳性克隆的16S rDNA序列分属11个细菌类群,分别为Betaproteobacteria(381％),Alphaproteobacteria(353％),Gamaproteobacteria(51％),Deltaroteobacteria(52％),Bacteroidetes(40％),Verrucomicrobia(25％),Epsilonproteobacteria(19％),Nitrospira(13％),Planctomycetes(13％),Candidate Division OD1(13％),Unclassified Bacteria(38％)。在这一生态系统中,Betaproteobacteria和Alphaproteobacteria类细菌占据主导地位,二者所占比例均在三分之一以上。群落中最主要的降解菌是噬氢菌属(Hydrogenophaga)和鞘氨醇单胞菌属(Sphingomonas)细菌,它们在文库中所占比例达239％和195％。该石油污染地下水样品中细菌与许多其他已知的降解菌亲缘关系较近,如Sulfuricurvum kujiense、Trichlorobacter thiogenes、Rhodoferax ferrireducens以及红细菌属(Rhodobacter)、甲基单胞菌属(Methylomonas)和涅瓦菌属(Nevskia)细菌等。此外,文库中克隆的16S rDNA序列与许多类似的污染场地中发现的环境克隆相似性很高,如煤焦油污染的地下水、苯污染的地下水、原油污染的土壤、溴甲烷和氯甲烷污染的土壤、抗生素生产废水以及活性污泥等,证明该石油污染地下水中有大量降解菌群的存在。石油污染物的种类对降解菌群的组成有一定的选择作用。     

Selenium mobilization during a flood experiment in a contaminated wetland: Stewart Lake Waterfowl Management Area,Utah

Constructed and natural wetlands can accumulate elevated levels of Se; however, few data are available on cost-effective methods for remobilization and removal of Se from these areas. A field experiment was conducted to assess the effectiveness of flooding on the removal of Se from dry surface sediments. The 83-m² flood-experiment plot contained 10 monitoring wells, a water-quality minimonitor (continuous measurement of pH, specific conductance, water temperature, and dissolved O₂), a down-hole Br electrode, and 2 pressure transducers. Flooding was initiated on August 27, 2002, and a Br tracer was added to water delivered through a pipeline to the flood plot during the first 1.2 h. Standing water depth in the flood plot was maintained at 0.3 m through September 1, 2002. The Br tracer data indicate a dual porosity system that includes fracture (mud cracks) and matrix flow components. Mean vertical water velocities for the matrix flow component were estimated to range from 0.002 to 0.012 m/h. Dissolved (less than 0.45 μm) Se increased from pre-flood concentrations of less than 10 μg/L to greater than 800 μg/L during flooding in samples from deep (2.0 m below land surface) ground water. Selenium concentrations exceeded 5500 μg/L in samples from shallow (0.8 m below land surface) ground water. Ratios of Se to Br in water samples indicate that Se moved conservatively during the experiment and was derived from leaching of near-surface sediments. Cumulative Se flux to the deep ground water during the experiment ranged from 9.0 to 170 mg/m². Pre- and post-flood surface soil sampling indicated a mean Se flux of 720 mg/m² through the top 15 cm of soil. Ground-water samples collected 8 months after termination of the flood experiment contained Se concentrations of less than 20 μg/L. The minimonitor data indicate a rapid return to chemically reducing conditions in the deep ground water, limiting the mobility of the Se dissolved in the water pulse introduced during the flood experiment. Ratios of Se to Br in deep ground-water samples collected 8 months after the experiment confirmed the removal of Se from the aqueous phase. Based on the median Se flux rate estimated during the experiment of 0.65 mg/h/m² (n = 52), 7 flooding cycles would be required to meet the 4 μg/g remediation goal in surface soils from the SLWMA wetland.     

Evaluation of remedial alternatives for a petroleum contaminated unconfined aquifer with fluctuating groundwater level

This study evaluated remedial alternatives for a petroleum-contaminated site where an unconfined aquifer composed of a sandy layer of about 3–3.5 m thickness is covered by alluvial deposits and reclaimed soil of about 1.5 m thickness. Precambrian gneiss, of low permeability, lies below the sandy layer. The shallow water table is about 3 m below the surface, but shows high fluctuations of up to 1.5 m in response to precipitation events. The unsaturated soil near the water table and the groundwater are highly contaminated with petroleum hydrocarbons, especially toluene, which have apparently leaked from storage tanks. Selection of the remedial alternatives required consideration of the relevant laws on soil and groundwater conservation in Korea, the results of risk analysis and the hydrogeological conditions. The contaminated area has been divided into zones in which different remediation goals are set based on risk analysis and the degree of natural attenuation. It is estimated that the clean-up goal can be achieved in two years by the combined use of a trench drain and well point pumping to collect the contaminated groundwater for treatment, and a dual air injection system for the contaminated soil.     

Numerical modeling assessment of three-gate structures for capturing contaminated groundwater

This modeling study evaluated the capability of alternative funnel-and-gate structures with three gates for capturing contaminated groundwater in a hypothetical unconfined aquifer. Simulated interceptor structures were linear and 45 m wide, consisting of three gates and two funnels (walls). One gate occupied the center and two gates occupied the ends of the interceptor structures. The structures, positioned perpendicular to regional groundwater flow, traversed the entire thickness of the aquifer. A total of four structures were evaluated (numbers designate widths of end, center, and end gates, respectively, in meters): 3-3-3, 2-5-2, 1-7-1, and 4-1-4. Particle tracking and zonal water budgets identified shapes of capture zones and discharge patterns for each interceptor structure. A mass transport model, accounting for advection and hydrodynamic dispersion, tested the capability of each structure for capturing a contaminant plume. Results suggest that: time-dependent capture zones underestimate the amount of time to capture a contaminant plume, wide center gates facilitate plume capture, and wide end gates facilitate lateral containment of contaminants. Of the structures simulated, the 2-5-2 configuration was relatively efficient at processing and containing the simulated contaminant plume.     

Conflicts between wetland conservation and groundwater exploitation: Two case histories in Spain

The problems in two Spanish national parks located on wetlands are analyzed. The hydrogeological and ecological characteristics of the two parks are somewhat different as are their respective degrees of deterioration. The Tablas de Daimiel National Park is located on the Central Plateau of Spain. It used to consist of a marshy area of about 20 km² around the confluence of two relatively small rivers. The area was marshy mainly because it was the natural discharge zone for a Tertiary aquifer system about 100 m thick extending over an area of some 5,000 km², composed of calcareous and detrital material of continental origin. The average annual recharge has been estimated at approximately 350 hm³/yr. Current groundwater withdrawal is around 450 hm³/yr, mainly used to irrigate a surface area of some 1,000 km². This overdevelopment has led to a continuous depletion of the regional water table and eventually to the drying out of the marshy area. Spontaneous combustion or fires caused by man have occurred in about 10 km² of the desiccated areas since the spring of 1986. The Doñana National Park is located on the estuary of the River Guadalquivir. The aquifer system of the Lower Guadalquivir estuary consists essentially of a permeable formation of unconsolidated Plioquaternary materials with an area of some 3,000 km². Under the marshy area (about 1,800 km²) the aquifer system is confined below low-permeability estuary deposits which can be over 100 m thick. Around most of the marshland the aquifer crops out and is recharged by rain. The Doñana National Park is over 700 km² in size, part of which is in the marshland and part in the recharge area where the aquifer is phreatic. In the 1970s Spain's largest irrigation project using groundwater, covering a surface area of 240 km², was planned in an area bordering on the national park. The initial project has been scaled down considerably as a result of protests by conservation groups. However, it seems likely that the water table depletion as a result of pumpage for irrigation could cause a large part of the ecotone situated at the contact-line between the marshland and the phreatic aquifer to disappear. This ecotone exists because it is a natural groundwater dischange area.