共查询到20条相似文献，搜索用时 218 毫秒
1.
June A. Oberdorfer Matthew Charette Matthew Allen Jonathan B. Martin Jaye E. Cable 《Estuarine, Coastal and Shelf Science》2008
Near-shore discharge of fresh groundwater from the fractured granitic rock at Flamengo Bay, Ubatuba, Brazil, is strongly controlled by the local geology. Freshwater flows primarily through a zone of weathered granite to a distance of 24 m offshore. In the nearshore environment this weathered granite is covered by about 0.5 m of well-sorted, coarse sands containing pore water with sea water salinity, with an abrupt transition to much lower salinity once the weathered granite is penetrated. Further offshore, low-permeability marine sediments contain saline porewater, marking the limit of offshore migration of freshwater. Freshwater flux rates based on tidal signal and hydraulic gradient analysis indicate a fresh submarine groundwater discharge of 0.17–1.6 m3/day per m of shoreline. Dissolved inorganic nitrogen and silicate are elevated in the porewater relative to seawater, and appeared to be a net source of nutrients to the overlying water column. The major ion concentrations suggest that the freshwater within the aquifer has a short residence time. Major element concentrations do not reflect in situ alteration of the granitic rocks, possibly because the alteration occurred prior to development of the current discharge zones, or because of large volumes of water discharge in this high rainfall region. 相似文献
2.
Field observation was conducted to monitor phosphate concentrations in groundwater and seawater mixing at two sandy beaches in Futtsu and Miura in Tokyo Bay, Japan. Dissolved phosphate concentrations were measured along transects from fresh groundwater aquifer to seawater adjacent the beaches. The concentrations were often high (up to 46 µM) in fresh groundwater samples (Cl– < 0.2). Coastal seawater, on the other hand, exhibited low phosphate concentrations (1.5 µM or less). Along the transects, phosphate generally displayed non-conservative behavior during mixing of fresh and saline waters in the aquifer; concentrations as high as 100 µM were found around the upper limit of seawater intrusion (Cl– = 2). Laboratory experiments were executed to identify the processes that control the phosphate behavior in the mixing processes. The results revealed that adsorption-desorption processes by the aquifer sand particles could significantly control the phosphate concentrations in the groundwater. Furthermore, the adsorption and/or desorption was found to be a function of salinity; the equilibrium concentration of dissolved phosphate in slurry of sand and water was the highest in freshwater and decreased considerably in saline water. The extreme concentration of phosphate may be caused by release from sand particles coinciding with the rapid change in salinity with tide. 相似文献
3.
Multiple tracers of groundwater input (salinity, Si, 223Ra, 224Ra, and 226Ra) were used together to determine the magnitude, character (meteoric versus seawater), and nutrient contribution associated with submarine groundwater discharge across the leeward shores of the Hawai'ian Islands Maui, Moloka'i, and Hawai'i. Tracer abundances were elevated in the unconfined coastal aquifer and the nearshore zone, decreasing to low levels offshore, indicative of groundwater discharge (near-fresh, brackish, or saline) at all locations. At several sites, we detected evidence of fresh and saline SGD occurring simultaneously. Conservative estimates of SGD fluxes ranged widely, from 0.02–0.65 m3 m− 2 d− 1at the various sites. Groundwater nutrient fluxes of 0.04–40 mmol N m− 2 d− 1 and 0.01–1.6 mmol P m− 2 d− 1 represent a major source of new nutrients to coastal ecosystems along these coasts. Nutrient additions were typically greatest at locations with a substantial meteoric component in groundwater, but the recirculation of seawater through the aquifer may provide a means of transferring terrestrially-derived nutrients to the coastal zone at several sites. 相似文献
4.
作者采用水化学演化图（hydrochemical facies evolution diagram,HFE-D）和海水入侵地下水质量指数（GQISWI）对山东威海文登区地下水的化学演化和海水入侵情况进行了分析。Piper图的结果表明文登区从北到南地下水的化学组成分别是Ca-HCO3、Ca-Mg-Cl、Na-Cl。HFE-D表明沿海地区的含水层中海水占主导地位,并且地下淡水补给不足,无明显淡化趋势;内陆地区含水层中的淡水多数处于海水侵入期,有咸化趋势。运用GQISWI、地理信息系统和空间插值法结合,得到了文登区浅层海水入侵现状图。另外,作者考虑渗透系数对离子浓度的影响,运用反距离加权插值算法并结合渗透系数分析了文登区浅层地下水海水入侵程度。结果表明文登沿海地区已经发生了极其严重的海水入侵现象,结合HFED可知咸水有向内陆继续扩散的趋势。研究结果对文登区地下水资源的利用和海水入侵的防治具有重要意义。另外本文是HFE-D和GQISWI在国内文献中的首次应用,为国内其他地区的海水入侵评价提供了参考。 相似文献
5.
Miguel Rodríguez-Rodríguez José Benavente Francisco J. Alcalá Mariano Paracuellos 《Estuarine, Coastal and Shelf Science》2011,91(3):400-410
During recent historical times the Adra river delta, a detrital coastal aquifer of nearly 32 km2 located in a semi-arid, mountainous area of SE Spain, has undergone different changes caused by human activity. Within this context, both the river dynamics in the plain and the geomorphology of the coastline have at various times resulted in the formation of small lagoons. At present only two small (<0.5 km2) lagoons exist, at the eastern edge of the aquifer, which, although closely surrounded by commercial market-garden greenhouses, are protected under international agreements. During the last 30 years of the twentieth century traditional agricultural irrigation techniques have undergone significant changes to improve their efficiency. Surface-water resources in the Adra river basin are regulated via the Beninar reservoir. In addition, the use of groundwater is increasing progressively. Both these factors affect the recharge of the coastal aquifer. To monitor these changes measurements of electrical conductivity and water level fluctuations have been recorded in these lagoons for the last 35 years (1975–2010). A comparison of the hydrochemical characteristics of the water in the lagoons and of the surrounding groundwater from 2003 to 2010 shows marked differences induced by the different hydrological dynamics in each lagoon, as well as by the hydrogeological impact of changes in land use in the delta. The increase in water demand is a consequence of the extension of irrigated areas from the fluvio-deltaic plain to its slopes, originally occupied by unirrigated crops. A reduction in irrigation return-flow is linked to the use of new irrigation techniques. These modifications affect both the recharge regime of the aquifer and its water quality. Moreover, extreme precipitation events, which are characteristic of Mediterranean semi-arid environments, can affect the lagoons’ hydrological dynamics to a considerable extent. One such example is the unusually rainy period from January to March 2010 (>600 mm). This event, along with other effects, has dramatically lowered the salinity of the water in both lagoons. This case study reveals the extreme vulnerability of deltaic environments and also how lagoons can reflect anthropogenic changes over the whole river basin. 相似文献
6.
《Estuarine, Coastal and Shelf Science》2006,66(1-2):6-12
Unconfined aquifers beneath the south sector of the Venice Lagoon are characterized by the presence of saline water. The results of this study allow the determination of the superficial extension of the salt water contamination in the direction of the mainland and the relationship between chemical analysis and conductivity, which reveals a complex lateral and vertical variability in both the permeability and textural pattern. Moreover, geophysical data validated by log data together with other physical and chemical results show a dislocation of the aquifer basement. This fact allows for the presumption that the salt groundwater distribution is affected by a regional tectonic lineament which extends towards the SE. Therefore salt contamination may be due to saline intrusion from the sea and the lagoon, and also from fossil brines mobilised by the combined action of tectonics and infiltration of fresh groundwater. 相似文献
7.
莱州湾南岸海水入侵变化趋势及成因分析 总被引：3，自引：2，他引：1
为了探讨滨海经济快速发展形势下莱州湾南岸海水入侵范围变化及其控制因素,利用2011—2015年4月份(枯水期)莱州湾南岸地下水潜水层TDS(可溶性固体总量)、Cl–质量浓度连续监测数据,结合历史资料,分析莱州湾南岸海水入侵分布特征。结果表明,近5年来研究区地下水Cl–质量浓度均值为13.4 g/L,呈由岸向内陆快速减小趋势;研究区海水入侵呈带状分布,2015年入侵线向内陆伸入超过45 km,入侵范围较1980年向陆扩张约11~30 km。通过对比分析得出,研究区年均降雨量、地下水位埋深及地下水超采面积与海水入侵面积呈显著线性相关,发现持续干旱气候、地下淡水超采是导致海水入侵扩张的主要因素,卤水开发、海水养殖及莱州湾沿岸河流拦蓄工程进一步导致海水入侵的加剧。 相似文献
8.
9.
利用三门湾海岸带最近施工完成的水文地质孔、工程地质孔和地下水碳（14C）测年以及前人的分析研究资料,对三门湾海岸带第四系分布、第四系承压含水层富水性和咸淡水资源分布、承压水年龄和可更新能力进行了深入研究。三门湾海岸带蛇盘滩涂围垦区第一承压含水层（组）富水性较好,绝大部分地区为淡水;宁海县长街镇区域承压水淡水资源总体呈“人”字型分布,北部的大湖?车岙港区域淡水主要分布在第一承压含水层（组）中,在大湖?下洋涂区域淡水主要分布在第二承压含水层（组）中。三门湾海岸带第四系承压水年龄普遍较老。蛇盘滩涂围垦区第一承压含水层地下水年龄为21 642～22 012 cal a BP,未受到后期海侵作用影响;长街下洋涂滩涂围垦区第二承压含水层地下水的年龄为35 052～45 439 cal a BP,部分地段受到后期海侵影响。在目前未开采利用条件下,承压水补给条件差、水资源更新性差。对于拟作为应急供水水源地靶区,应加强地下水资源管理。 相似文献
10.
L. Felipe H. Niencheski Herbert L. Windom Willard S. Moore Richard A. Jahnke 《Marine Chemistry》2007,106(3-4):546-561
The Patos–Mirim Lagoon system along the southern coast of Brazil is linked to the coastal ocean by a narrow mouth and by groundwater transport through a Holocene barrier. Although other groundwater systems are apparently active in this region, the hydraulic head of the lagoon, the largest in South America, drives groundwater transport to the coast. Water levels in wells placed in the barrier respond to changing water level in the lagoon. The wells also provide a measure of the nutrient concentrations of groundwater flowing toward the ocean. Additionally, temporary well points were used to obtain nutrient samples in groundwater on the beach face of the barrier. These samples revealed a subterranean freshwater–seawater mixing zone over a ca. 240 km shoreline. Previously published results of radium isotopic analyses of groundwater and of surface water from cross-shelf transects were used to estimate a water flux of submarine groundwater discharge (SGD) to nearshore surface waters of 8.5 × 107 m3/day. Using this SGD and the nutrient concentrations in different compartments, nutrient fluxes between groundwater and surface water were estimated. Fluxes were computed using both average and median reservoir (i.e. groundwater and surface water) nutrient concentrations. The SGD total dissolved inorganic nitrogen, phosphate and silicate fluxes (2.42, 0.52, 5.92 × 106 mol day− 1, respectively) may represent as much as 55% (total N) to 10% (Si) of the nutrient fluxes to the adjacent shelf environment. Assuming nitrogen limitation, SGD may be capable of supporting a production rate of ca. 3000 g C m2 year− 1in the nearshore surf zone in this region. 相似文献
11.
Patrick Ollivier Christelle Claude Olivier Radakovitch Bruno Hamelin 《Marine Chemistry》2008,109(3-4):337
Submarine groundwater discharge (SGD) is now recognized as an important pathway for water and chemical species fluxes to the coastal ocean. In order to determinate SGD to the Gulf of Lion (France), we measured the activities of 226Ra and 228Ra by thermal ionization mass spectrometry (TIMS) in coastal waters and in the deep aquifer waters of the Rhone deltaic plain after pre-concentration of radium by MnO2. Compared to conventional counting techniques, TIMS requires lower quantities of water for the analyses, and leads to higher analytical precision. Radium isotopes were thus measured on 0.25–2 L water samples containing as little as 20 fg of 226Ra and 0.2–0.4 fg of 228Ra with precision equal to 2%. We demonstrate that coastal surface waters samples are enriched in 226Ra and 228Ra compared to the samples further offshore. The high precision radium measurements display a small but significant 226Ra and 228Ra enrichment within a strip of circa 30 km from the coast. Radium activities decrease beyond this region, entrained in the northern current along the shelf break or controlled by eddy diffusion. The radium excess in the first 30 km cannot be accounted for by the river nor by the early diagenesis. The primary source of the radium enrichment must therefore be ascribed to the discharge of submarine groundwater. Using a mass-balance model, we estimated the advective fluxes of 226Ra and 228Ra through SGD to be 5.2 × 1010 and 21 × 1010 dpm/d respectively. The 226Ra activities measured in the groundwater from the Rhone deltaic plain aquifer are comparable to those from other coastal groundwater studies throughout the world. By contrast, 228Ra activities are higher by up to one order of magnitude. Taking those groundwater radium activities as typical of the submarine groundwater end-member, a minimum volume of 0.24–4.5 × 1010 l/d is required to support the excess radium isotopes on the inner shelf. This has to be compared with the average rivers water runoff of 15.4 × 1010 l/d during the study period (1.6 to 29% of the river flow). 相似文献
12.
海水入侵和土壤盐渍化是重要的海洋灾害类型。文章选取3个土壤采样点和3个地下水采样点,以地下水氯离子浓度和矿化度以及土壤氯离子含量、硫酸根离子含量和全盐量为监测项目,首次对惠州市大亚湾淡澳河入海口沿岸区域的海水入侵和土壤盐渍化状况进行研究。研究表明:研究区2个采样点未受海水入侵,1个采样点海水入侵程度为轻度;1个采样点为氯化物-硫酸盐型和中盐渍化土,2个采样点为氯化物型和盐土;海水入侵程度以及土壤盐渍化类型和程度与离岸距离均无相关性,但受与河口距离的影响。今后将进一步加强监测和研究,为沿海环境风险管控和海岸带整治修复提供科学依据。 相似文献
13.
Coastal groundwater systems can have a considerable impact on sediment transport and foreshore evolution in the surf and swash zones. Process-based modeling of wave motion on a permeable beach taking into account wave-aquifer interactions was conducted to investigate the effects of the unconfined coastal aquifer on beach profile evolution, and wave shoaling on the water table. The simulation first dealt with wave breaking and wave runup/rundown in the surf and swash zones. Nearshore hydrodynamics and wave propagation in the cross-shore direction were simulated by solving numerically the two-dimensional Navier–Stokes equations with a k–ε turbulence closure model and the Volume-Of-Fluid technique. The hydrodynamic model was coupled to a groundwater flow model based on SEAWAT-2000, the latter describing groundwater flow in the unconfined coastal aquifer. The combined model enables the simulation of wave-induced water table fluctuations and the effects of infiltration/exfiltration on nearshore sediment transport. Numerical results of the coupled ocean/aquifer simulations were found to compare well with experimental measurements. Wave breaking and infiltration/exfiltration increase the hydraulic gradient across the beachface and enhance groundwater circulation inside the porous medium. The large hydraulic head gradient in the surf zone leads to infiltration across the beachface before the breaking point, with exfiltration taking place below the breaking point. In the swash zone, infiltration occurs at the upper part of the beach and exfiltration at the lower part. The simulations confirm that beaches with a low water table tend to be accreted while those with a high water table tend to be eroded. 相似文献
14.
John F. Bratton John Karl Böhlke David E. Krantz Craig R. Tobias 《Marine Chemistry》2009,113(1-2):78-92
To better understand large-scale interactions between fresh and saline groundwater beneath an Atlantic coastal estuary, an offshore drilling and sampling study was performed in a large barrier-bounded lagoon, Chincoteague Bay, Maryland, USA. Groundwater that was significantly fresher than overlying bay water was found in shallow plumes up to 8 m thick extending more than 1700 m offshore. Groundwater saltier than bay surface water was found locally beneath the lagoon and the barrier island, indicating recharge by saline water concentrated by evaporation prior to infiltration. Steep salinity and nutrient gradients occur within a few meters of the sediment surface in most locations studied, with buried peats and estuarine muds acting as confining units. Groundwater ages were generally more than 50 years in both fresh and brackish waters as deep as 23 m below the bay bottom. Water chemistry and isotopic data indicate that freshened plumes beneath the estuary are mixtures of water originally recharged on land and varying amounts of estuarine surface water that circulated through the bay floor, possibly at some distance from the sampling location. Ammonium is the dominant fixed nitrogen species in saline groundwater beneath the estuary at the locations sampled. Isotopic and dissolved-gas data from one location indicate that denitrification within the subsurface flow system removed terrestrial nitrate from fresh groundwater prior to discharge along the western side of the estuary. Similar situations, with one or more shallow semi-confined flow systems where groundwater geochemistry is strongly influenced by circulation of surface estuary water through organic-rich sediments, may be common on the Atlantic margin and elsewhere. 相似文献
15.
随着全球气候变暖,风暴潮在沿海地区的频率和强度均可能增长,由此引发的海水垂向入侵可能会造成大面积的含水层淡水咸化。同时,由人类活动引起的沿海虾塘咸水养殖规模日益增长,由此引发的咸水垂向入侵可能会导致沿海地区地下水水质及生态环境的恶化。虽然已有一部分学者在海水(咸水)垂向入侵的研究中取得了成果,但由于海水(咸水)垂向入侵过程复杂,其对地下水咸化及恢复规律依然有待深入研究。文章阐述了海水垂向入侵的危害及前人的研究办法,总结了他们的研究成果并得出了海水垂向入侵的影响因子,指出了洪水和养殖活动对沿海地区含水层的威胁。得出的结果如下:研究海水垂向入侵常用的方法包括室内试验和数值模拟;海水垂向入侵主要与地形地貌、含水层性质和水文气象条件有关;虾塘养殖等人类活动可能会成为垂向咸水入侵的潜在来源。建议未来在海水垂向入侵研究中将多种现场观测实验方法结合起来。数值模拟应注重与现场观测实验数据相互验证,模型简化的方式有必要仔细考虑。虾塘养殖等人类活动可能造成的垂向咸水入侵问题应更多地受到关注。 相似文献
16.
17.
18.
Global climate change has resulted in a gradual sea-level rise. Sea-level rise can cause saline water to migrate upstream in estuaries and rivers, thereby threatening freshwater habitat and drinking water supplies. On the other hand, sea-level rise, resulting from thermal expansion of ocean waters and increased melting of glaciers and ice caps, is one of the most apparent and widespread consequences of climate change. This phenomenon has been taken into account in all the Assessment Reports published by the Intergovernmental Panel on Climate Change (IPCC). In this paper, salinity intrusion and intrusion length due to possible sea-level rise in the Sebou estuary (Morocco) was investigated. A one-dimensional hydrodynamic-salinity transport model was used for the simulation of the salinity intrusion and associated water quality, with observed field data being used for model calibration and validation. Additionally, the model validation process showed that the model results fit the observed data fairly well. A coupled gas-cycle/climate model was used to generate the climate change scenarios in the studied area that showed sea-level rises varying from 0.3 to 0.9 m for 2100. The models were then combined to assess the impact of future sea-level rise on the salinity distribution and intrusion length in the Sebou estuary. The response of salt intrusion length to changes in important dimensional parameters are presented, showing that the salinity intrusion length is inversely correlated with the river discharge, i.e., a high river discharge results in a reduced salt intrusion and vice versa, and directly with the sea-level rise. Additionally, the magnitude and frequency of the salinity standard violations at the two pump stations were predicted for 2100, showing that the salinity violations under climate change effects can increase to ～45–48% of the times at these locations. Finally, the main objective of this simulation method is to accelerate and facilitate of systems' behavior learning in the current and future situation. 相似文献
19.
黄河三角洲浅层地下水化学特征与演化 总被引：1，自引：0，他引：1
2009年4月~2010年3月连续2年对黄河三角洲19口地下水监测井进行观测并对地下水离子化学成分分析,探讨了该区域浅层地下水化学成分、水化学类型及演化规律,为揭示区域地下水环境特征和演化具有现实意义。结果表明,黄河三角洲地区地下水p H值变化较小,地下水埋深较浅且年内变化幅度为1.0~3.0 m,但矿化度和各离子差异明显,地下水以Na+、Cl–占绝对优势;矿化度较低的测井的离子浓度变幅较小,反之,矿化度高的测井离子浓度变幅较大;地下水化学类型分为氯化物型、重碳酸盐氯化物型、重碳酸盐氯化物硫酸盐型和硫酸盐重碳酸盐型四大类型,主要包括Na+-Cl–、Na+-Cl–.3HCO?、Na+-Cl–.3HCO?、Na+-Cl–.3HCO?.24SO?、Na+-3HCO?.Cl–.24SO?和Na+-24SO?.3HCO?六种子类型,氯化物型主要分布于广饶县咸水入侵区和滨海区域,重碳酸盐氯化物型主要分布于黄河三角洲保护区内,重碳酸盐氯化物硫酸盐型分布在广饶县咸水入侵区,硫酸盐重碳酸盐型主要分布在靠近黄河流路附近;根据黄河三角洲流路变迁和Gibbs模型,黄河三角洲地区水样化学组成均落在Gibbs提出的Boomerang Envelope模型右上翼,表明研究区水样化学组成主要受蒸发和沉淀作用,海水控制起次要作用,土地利用变化、灌溉、施肥等人为活动的影响亦不能忽视。 相似文献
20.
海底承压含水层排泄是海底地下水排泄的一种主要形式。由于这一过程发生在海水层下部，探测难度较大。为探讨海洋多电极电阻率法对该过程的探测能力，根据典型海底承压含水层地质模型构建不同排泄阶段地电模型，模拟海面和海床面两种探测情形分别进行多电极电阻率法理论探测结果计算和物理模拟，并对所得电阻率剖面进行对比分析。研究结果表明，水面多电极电阻率探测剖面能够清晰刻画出排泄入海的淡水体在海水中迁移、混合过程，但剖面异常特征和分辨率受探测装置形式、电极极距、海水深度影响；海床面探测则对沉积层中咸淡水交换过程反映能力更强，沉积层中的锲形海水侵入体可得到良好反映。 相似文献