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1.
A preliminary study shows that the submarine groundwater discharge(SGD) exists around Taiwan even though groundwater overdrawing on the island is serious. Fifteen of the 20 sites studied for major anions and cations recorded a clear SGD signal with freshwater outflow. A total of 278 salinity and major ion measurements were made. Sixteen nearly freshwater SGD(salinity≤1.0) samples were obtained, providing strong and direct evidence for the existence of fresh meteoric groundwater entering the ocean from Taiwan. The total SGD flux is estimated to be 1.07×1010 t/a which is about 14% of the annual river output. The freshwater component of the SGD is3.85×109 t which is about 5.2% of the annual river discharge in Taiwan. The collected SGD has a composition similar to seawater with an addition of Ca, CO_3 and HCO_3 due to dissolution of calcareous rocks. Some samples with high Cl/(Na+K) may indicate pollution.  相似文献   

2.
Measurements of electric resistivity of the seabed and of the electric conductivity of submarine groundwater discharge (SGD) collected in seepage meters have been made to evaluate temporal variability of the origin and quality of submarine groundwater discharge in Ubatuba, Brazil. A diurnal variation of SGD conductivity was found under the condition of semi-diurnal tidal changes over a period of 4 days. Both the ground resistivity and the conductivity of the discharged groundwater indicated that the freshwater–saltwater interface moved towards offshore at high tide, i.e. in the direction opposite to commonly made observations. SGD comprised a combination of Submarine Fresh Groundwater Discharge (SFGD) of terrestrial origin, and of Recirculated Saline Groundwater Discharge (RSGD) of marine origin. The maximum of the terrestrially derived fraction SFGD/SGD was found at a distance of 50 m offshore. A lower SFGD/SGD ratio was found closer to shore, where the highest SGD flux was measured. SGD conductivity and ground resistivity displayed a diurnal cyclicity at semi-diurnal tidal water level variations, indicating that tidal water level fluctuations may not be the primary driver of SGD flux, but preferential flow in volcanic hydrogeologic setting at Ubatuba.  相似文献   

3.
New perspectives on radium behavior within a subterranean estuary   总被引：2，自引：0，他引：2  
Over the past decade, radium isotopes have been frequently applied as tracers of submarine groundwater discharge (SGD). The unique radium signature of SGD is acquired within the subterranean estuary, a mixing zone between fresh groundwater and seawater in coastal aquifers, yet little is known about what controls Ra cycling in this system. The focus of this study was to examine controls on sediment and groundwater radium activities within permeable aquifer sands (Waquoit Bay, MA, USA) through a combination of field and laboratory studies. In the field, a series of sediment cores and corresponding groundwater profiles were collected for analysis of the four radium isotopes, as well as dissolved and sediment associated manganese, iron, and barium. We found that in addition to greater desorption at increasing salinity, radium was also closely tied to manganese and iron redox cycling within these sediments. A series of laboratory adsorption/desorption experiments helped elucidate the importance of 1) contact time between sediment and water, 2) salinity of water in contact with sediment, 3) redox conditions of water in contact with sediment, and 4) the chemical characteristics of sediment on radium adsorption/desorption. We found that these reactions are rapid (on the order of hours), desorption increases with increasing salinity and decreasing pH, and the presence of Fe and Mn (hydr)oxides on the sediment inhibit the release of radium. These sediments have a large capacity to sorb radium from fresh water. Combined with these experimental results, we present evidence from time series groundwater sampling that within this subterranean estuary there are cyclic periods of Ra accumulation and release controlled by changing salinity and redox conditions.  相似文献   

4.
The inflow of terrestrial groundwater into the ocean is increasingly recognized as an important local source of nutrients and pollutants to coastal ecosystems. Although there is evidence of a link between fresh submarine groundwater discharge (SGD)-derived nutrients and primary producer and primary consumer abundances, the effects of fresh SGD on the productivity of higher trophic levels such as ichthyofaunal communities remain unclear. To further investigate this relationship, we sampled three sites inside a coral reef lagoon in Mauritius: One site entailing six distinct groundwater springs, a site highly influenced by freshwater influx through the springs, and a strictly marine control site. Using remote underwater video surveys, we found that fish abundances were significantly higher at the groundwater springs than at the other two sampling sites.Principal component analyses showed that the springs and the spring-influenced part of the lagoon were best described by elevated water nutrient loadings, whereas the control site was characterized by higher water salinity and pH. Macroalgae cover was highest at the control site and the springs. Herbivores and invertivores dominated the fish community at the springs, in contrast to generalists at the control site. At the spring-influenced site, we mainly encountered high coral/turf algae cover and high abundances of associated fish feeding groups (territorial farmers, corallivores). Our results provide evidence of a fresh SGD-driven relationship between altered hydrography and distinct fish communities with elevated abundances at groundwater springs in a coral reef lagoon. These findings suggest that the management and assessment of secondary consumer productivity in tropical lagoons should take into account the effects of groundwater springs.  相似文献   

5.
We measured the time-series variations in 222Rn activity at a fixed station in the Yeongsan River Estuary (YRE), Korea, where the upstream water is obstructed by an artificial dam, during November 18–24, 2008, and conducted a horizontal 222Rn survey in the Seomjin River Estuary (SRE), Korea, during December 16–18, 2008. In the YRE, we observed constantly low levels of 222Rn activity over the sampling period, relative to the summer in 2008. The 222Rn variations and 222Rn mass-balance modeling results indicate that the submarine groundwater discharge (SGD) in the YRE was relatively low and constant over the sampling period and that the temporal SGD variations were not related to tides or to the water elevation in the dam upstream. This low and constant SGD appears to be due to the lower water level in the dam relative to the local sea level during the study period, resulting in the SGD mostly from the surrounding land areas rather than from the dam. In the SRE, higher 222Rn activities were observed at upstream stations of the river (salinity: <5) and decreased as the salinity increased, but there were marked increases of 222Rn, together with dissolved inorganic silicate (DSi), at stations close to the river mouth (salinity: ～33). This suggests that the river has major groundwater inputs from the two extreme upstream and downstream areas. Because most chemical flux estimations via river discharge do not account for groundwater inputs from the downstream high-salinity zone, our results suggest that there is an important unaccounted source of river-driven chemical fluxes. Overall, our study shows that the continuous 222Rn monitoring system provides high-resolution information on SGD over different locations and times.  相似文献   

6.
The distributions of dissolved organic carbon (DOC), Ba, U, and a suite of naturally occurring radionuclides in the U/Th decay series (222Rn, 223,224,226,228Ra) were studied during high- and low-discharge conditions in the Loxahatchee River estuary, Florida to examine the role of submarine groundwater discharge in estuarine transport. The fresh water endmember of this still relatively pristine estuary may reflect not only river-borne constituents, but also those advected during active groundwater/surface water (hyporheic) exchange. During both discharge conditions, Ba concentrations indicated slight non-conservative mixing. Such Ba excesses could be attributed either to submarine groundwater discharge or particle desorption processes. Estuarine dissolved organic carbon concentrations were highest at salinities closest to zero. Uranium distributions were lowest in the fresh water sites and mixed mostly conservatively with an increase in salinity. Suspended particulate matter (SPM) concentrations were generally lowest (< 5 mg L− 1) close to zero salinity and increased several-fold ( 18 mg L− 1; low discharge) toward the seaward endmember, which may be attributed to dynamic resuspension of bottom sediments within Jupiter Inlet.Surface water-column 222Rn activities were most elevated (> 28 dpm L− 1) at the freshwater endmember of the estuary and appear to identify regions of the river most influenced by the discharge of fresh groundwater. Activities of four naturally occurring isotopes of Ra (223,224,226,228Ra) in this estuary and select adjacent shallow groundwater wells yield mean estuarine water-mass transit times of less than 1 day; these values are in close agreement to those calculated by tidal prism and tidal frequency. Submarine groundwater discharge rates to the Loxahatchee River estuary were calculated using a tidal prism approach, an excess 226Ra mass balance, and an electromagnetic seepage meter. Average SGD rates ranged from 1.0 to 3.8 × 105 m3 d− 1 (20–74 L m− 2 d− 1), depending on river-discharge stage. Such calculated SGD estimates, which must include both a recirculated as well as fresh water component, are in close agreement with results obtained from a first-order watershed mass balance. Average submarine groundwater discharge rates yield NH4+ and PO4− 3 flux estimates to the Loxahatchee River estuary that range from 62.7 to 1063.1 and 69.2 to 378.5 μmol m− 2 d− 1, respectively, depending on river stage. SGD-derived nutrient flux rates are compared to yearly computed riverine total N and total P load estimates.  相似文献   

7.
The four naturally-occurring radium isotopes (223Ra, 224Ra, 226Ra and 228Ra) were used to estimate the submarine groundwater discharge (SGD) in the Isola La Cura marsh area in the northern Venice Lagoon (Italy). By determining the radium contributors to the study area (river, coastal ocean and sediments) the radium excess in the lagoon water was quantified through a mass balance model. This radium excess is attributed to a submarine groundwater discharge source and represents the most important input of radium. Possible endmembers were considered from analysis of groundwater samples (subtidal and marsh piezometers, marsh wells and seepage meters) that were enriched in Ra by one to two orders of magnitude relative to surface waters. In particular, a permeable layer at 80 cm depth in the surrounding marsh is considered to be representative of the most likely SGD source, although similar radium activities were measured in other subtidal porewater samples collected in the Isola La Cura area. The estimated SGD flux to the study area ranged from 1 · 109 to 6 · 109 L·d− 1, the same order of magnitude as the overall riverine input to the lagoon (3 · 109 L·d− 1). A major fraction of this SGD flux is likely recirculated seawater, as evidenced by the endmember salinity. The water residence time of 2 days was estimated by both using the shortest-lived radium isotope and estimating the volume of water exchanged between the lagoon and the open sea during a tidal cycle (tidal prism approach). This SGD flux could be used to estimate the input of other chemical species (metals, nutrients, etc.) via SGD which might affect the Venice Lagoon ecosystem.  相似文献   

8.
Stable isotopes, tritium, radium isotopes, radon, trace elements and nutrients data were collected during two sampling campaigns in the Ubatuba coastal area (south-eastern Brazil) with the aim of investigating submarine groundwater discharge (SGD) in the region. The isotopic composition (δD, δ18O, 3H) of submarine waters was characterised by significant variability and heavy isotope enrichment. The stable isotopes and tritium data showed good separation of groundwater and seawater groups. The contribution of groundwater in submarine waters varied from a few % to 17%. Spatial distribution of 222Rn activity concentration in surface seawater revealed changes between 50 and 200 Bq m−3 which were in opposite relationship with observed salinities. Time series measurements of 222Rn activity concentration in Flamengo Bay (from 1 to 5 kBq m−3), obtained by in situ underwater gamma-spectrometry showed a negative correlation between the 222Rn activity concentration and tide/salinity. This may be caused by sea level changes as tide effects induce variations of hydraulic gradients, which increase 222Rn concentration during lower sea level, and opposite, during high tides where the 222Rn activity concentration is smaller. The estimated SGD fluxes varied during 22–26 November between 8 and 40 cm d−1, with an average value of 21 cm d−1 (the unit is cm3/cm2 per day). The radium isotopes and nutrient data showed scattered distributions with offshore distance and salinity, which implies that in a complex coast with many small bays and islands, the area has been influenced by local currents and groundwater–seawater mixing. SGD in the Ubatuba area is fed by coastal contaminated groundwater and re-circulated seawater (with small admixtures of groundwater), which claims for potential environmental concern with implications on the management of freshwater resources in the region.  相似文献   

9.
海底地下水排放对典型红树林蓝碳收支的影响   总被引：1，自引：0，他引：1  
海底地下水排放(Submarine Groundwater Discharge，SGD)是陆海相互作用的重要表现形式之一，其携带的物质对近岸海域生源要素的收支有重要影响。本文利用222Rn示踪技术估算了我国典型红树林海湾—广西珍珠湾在2019年枯季(1月)SGD携带的碳通量。调查发现，地下水中222Rn活度、溶解无机碳(DIC)和溶解有机碳(DOC)的平均浓度均高于河水和湾内表层海水。利用222Rn质量平衡模型估算得到珍珠湾SGD速率为(0.36±0.36) m/d，SGD输入到珍珠湾的DIC和DOC通量分别为(2.41±2.63)×107 mol/d和(1.96±2.20)×106 mol/d。珍珠湾溶解碳的源汇收支表明，SGD携带的DIC和DOC分别占珍珠湾总DIC和总DOC来源的91%和89%。因此，SGD携带的DIC和DOC是珍珠湾DIC和DOC的主要来源，是海岸带蓝碳收支和生物地球化学循环过程中的重要组成。  相似文献   

10.
Measurements of submarine groundwater discharge (SGD) along the South American coast and over fractured rock aquifers are rare. The rate and distribution of SGD was measured using three types of vented benthic chambers on the floor of Flamengo Bay located at the southeast coast of Brazil. Discharge rates were found up to almost 400 cm day−1, although typically less than 100 cm d−1. Large variations in SGD rates were seen over distances of a few meters which are attributed to the geomorphologic features of the fracture rock aquifer underlying a thin blanket of coastal sediments; clustering of fractures and the topography of the rock–sediment interface might be focusing or dispersing the discharge of groundwater. SGD was modulated by the tides with the highest values occurring at times of low tide, but the interaction was non-linear and, the correlation was weak at tidal ranges less than 1 m. The effect was masked by devices that integrated the SGD, but detected on continuously recording devices.  相似文献   

11.
The influence of submarine groundwater discharges (SGD) on the dynamics of coastal ecosystems is receiving increasing scientific attention, although our knowledge of this issue still remains insufficient. Understanding the ecological response of coastal ecosystems to SGD dynamics is important in order to evaluate and predict changes in coastal communities. The aim of the present study was to characterize the effect of groundwater discharge on subtidal soft‐bottom macrofaunal assemblages in the south coast of Portugal (Algarve) at different times of the year and under different discharge regimes. Sediment macrofauna was sampled twice per season in spring and summer 2011 in two locations: one under influence of SGD (Olhos de Água) and one not under that influence (Arrifes). The results showed that differences in community structure between locations occurred mainly during spring, when the magnitude of groundwater discharge was higher. Several individual taxa were strongly associated with the SGD, particularly during spring: the polychaete families Magelonidae and Oweniidae; the isopod Cyathura carinata; and the bivalves Tellimya ferruginosa and Tellina fabula. Some of these taxa are already considered indicators of SGD, whereas others merit further investigation. The average similarity among samples was consistently larger in the location with SGD and the average similarity between the two locations was generally higher during spring, indicating that SGD promote stability in macrobenthic communities across time and space. SGD were also associated with higher values of Chlorophyll a (Chl a), fine sediments and total abundance of organisms (particularly suspension feeders). This suggests that differences between locations are associated with SGD and mediated by nutrient fluxes and sediment transport, or their interaction.  相似文献   

12.
Driven by the hydraulic gradient, terrestrial groundwater can be discharged directly into the coastal ocean where heads are above sea level, a phenomenon known as submarine groundwater discharge (SGD). Although long overlooked, in recent years SGD has received increasing attention due largely to its potential importance in the transport of chemical constituents to the sea. Indeed, SGD occurrence and control mechanisms are still poorly understood. Submarine discharge often represents only a minor component of regional total water budgets, but because estimated fluxes are highly variable and quantification remains challenging, the process deserves to be carefully evaluated when investigating marine ecosystems and/or the safety of geological repositories in coastal areas, notably for the underground storage of CO2. In view of the focus the topic is gaining, reflected in the large amount of information continuously being published in this field, here we present a selected review of our current knowledge of key mechanisms determining submarine groundwater discharge, and an updated compilation of most recent advances in research both in Japan and other regions of the world. In addition, we identify some potential pitfalls that need to be borne in mind in future work on SGD. Particularly in view of globally increasing urbanization and climate change, this contribution should prove useful also to local governmental authorities and scientists involved in groundwater coastal ecosystem management.  相似文献   

13.
Submarine groundwater discharge (SGD) into a coastal lagoon off Perth, Western Australia, contains nitrate and silicate in concentrations two orders of magnitude higher than those of the receiving waters. This discharge delivers enough nitrate to replace that dissolved in the lagoon water mass about every eight days and enough silicate to replace the lagoon silicate in about 48 days. The delivery rate of nitrate nitrogen by SGD is equal to about 48% of that required for observed growth rates of lagoon macrophytes. Surface salinity is lower close to the shore as a result of SGD. During calm conditions a salinity front was observed in the lagoon, with a nearshore pool of nutrient-enriched water floating above the more saline ocean water.  相似文献   

14.
为评价胶州湾水体表观年龄和地下水入海通量,2011年9—10月在胶州湾地区分别采集地下水、河水和海水样品,对水样的224Ra和226Ra活度进行测量。基于224Ra和226Ra半衰期的差异,运用224Ra与226Ra的活度比值计算了胶州湾水体表观年龄;采用三端元混合模型计算了胶州湾海水中地下水、河水与湾外海水的混合比例;在水体表观年龄和混合比例的基础上,计算了地下水入海通量。结果表明:研究期间胶州湾水体表观年龄分布范围为3.2—39.4d,平均值为14.7d,呈现从湾顶到湾口年龄逐渐增大的趋势,地下水的平均混合比例是11.0%,地下水的入海通量为7.29×106m3/d,海底地下水排泄速率为3.8cm/d。  相似文献   

15.
There is increasing evidence that submarine groundwater discharge (SGD) in many areas represents a major source of dissolved chemical constituents to the coastal ocean. In Great South Bay, NY, previous studies have shown that the discharge of nutrients with SGD may cause harmful algal blooms. This study estimates SGD to Great South Bay during August 2006 by performing a mass balance for each of the dissolved Ra isotopes (224Ra, 223Ra, 228Ra, 226Ra). The budget indicates a major unknown source (between 30 and 60% of the total input) of Ra to the bay. This imbalance can be resolved by a flux of Ra-enriched groundwater on the order of 3.5–4.5 × 109 L d− 1, depending on the Ra isotope. The Ra-estimated SGD rates compare well with those previously estimated by models of flow that decreases exponentially away from shore. Compared to previous reports of fresh groundwater discharge to the bay, the Ra-estimated discharge must comprise approximately 90% recirculated seawater. The good agreement between Ra- and model-estimated flow rates indicates that the primary SGD endmember may be best sampled at shallow depths in the sediments a short distance bayward of the low tide line.  相似文献   

16.
Radium isotopes (223Ra, 224Ra, 226Ra, and 228Ra) and water chemistry were used to identify two chemically distinct sources of submarine groundwater discharge (SGD) in Celestún Lagoon, Yucatán, Mexico. Low salinity groundwater discharging from springs within the lagoon has previously been identified and extensively sampled for nutrient concentrations. However, a second type of groundwater discharging into the lagoon was detected during this study using radium isotope activity measurements. This second type of groundwater is characterized by moderate salinities (within the range of lagoon salinities) and very elevated radium activities in comparison to the low salinity groundwater, mixed lagoon water, and seawater. Further analysis showed that the two types of groundwater also have distinct chloride, strontium, and sulfate ratios, along with slightly different nutrient concentrations. Groundwater discharge occurs through large and small springs scattered throughout the lagoon, and both types of groundwater were detected discharging from one of the larger springs. The relative proportions of low salinity groundwater and brackish high radium groundwater varied over the tidal cycle. In order to better understand the relative contributions of each type of groundwater to the lagoon, a three end-member mixing model based on the distinct chemical and isotopic compositions of both types of groundwater and of seawater was used to estimate the distribution of each water type throughout the lagoon in different seasons. This study suggests that substantial groundwater discharge to the lagoon can occur during both dry and rainy seasons. The presence of two groundwater sources has implications for monitoring and protection of the Celestún Lagoon Biosphere Reserve, since the two sources may have different susceptibilities to anthropogenic contamination depending on their respective recharge area and recharge rates.  相似文献   

17.
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   

18.
Submarine groundwater discharge (SGD) is delivered into the oceans at various hydrogeological settings. Where coastal aquifers have spatial heterogeneous properties such as preferential flowpaths, SGD is also commonly heterogeneously distributed along the coast. SGD from a heterogeneous, fractured rock aquifer on the Ubatuba coast, Brazil has been investigated by depth profiling of ground conductivity. On spatial scales of <10 m, a significant variation in sub-surface conductivity and associated discharge rate is documented. These geophysical observations were used to identify preferential flowpaths, and to explain significant differences in average discharge rates observed in seepage meter records placed only a few metres apart from each other. This paper illustrates the utility of sub-surface conductivity measurements for accurate investigations of SGD fluxes.  相似文献   

19.
钦州湾河流沉积物中镭的解吸行为   总被引：1，自引：0，他引：1  
放射性镭同位素在海底地下水排放（SGD）等海洋物质变化过程的研究中具有优良的示踪作用，估算SGD通量时需要计算河流悬浮颗粒物的解吸通量。因此，对河流沉积物/悬浮颗粒物中镭同位素解吸行为的研究不可或缺，而目前对于粒度较小范围内镭同位素的解吸特征及其机理的研究依然不足。本文选用钦州湾河流沉积物，通过室内实验探究粒度和盐度对沉积物中镭同位素解吸行为的影响。结果表明，在沉积物平均粒径0.9~136.0 μm范围内，随着粒径增大，沉积物中镭同位素在海水（盐度为33.9）中解吸活度逐渐减小，且变化趋势也逐渐变缓，平均粒径大于43.7 μm后，解吸量几乎不变；在海水盐度4.9~33.9范围内，随着盐度增大，沉积物中镭同位素解吸活度逐渐增大，盐度大于24.9后，解吸量趋于不变。本文创新性地建立了沉积物表面分形结构的镭解吸理论模型，拟合得到钦州湾河流沉积物表面最大可交换态224Ra、226Ra和228Ra活度分别为1.13 dpm/g、0.17 dpm/g和0.85 dpm/g，以干重计；沉积物中224Ra、226Ra和228Ra最大解吸比分别为30%、7%和18%。钦州湾河流沉积物颗粒表面最大可交换态224Ra和226Ra活度分别处于全球中等水平和较低水平，而其最大解吸比分别处于全球较高水平和较低水平。本研究结果有助于更好地理解镭同位素的解吸行为，以帮助更准确地估算SGD通量。  相似文献   

20.
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   

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