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1.
Submarine groundwater discharge (SGD) is a global phenomenon that carries large volumes of groundwater and dissolved chemical species such as nutrient, metals, and organic compounds to coastal zones. We report the influence of SGD on the coastal waters of Jeju Island, Korea, using high‐resolution aerial thermal infrared (TIR) mapping techniques and field investigations. An aircraft‐based system was implemented using a cost‐effective TIR camera for aerial TIR mapping. Ground‐based calibrations and system integration with GPS/IMU (global positioning system/inertial measurement unit) were performed for the aerial systems. The aerial surveys showed distinct low‐temperature signatures of SGD along the coasts of Jeju Island, revealing large groundwater inputs from the coastal aquifers to the ocean. Multiple aerial surveys over a range of seasons and tidal stages revealed that SGD rates dynamically affect the sea surface temperature (SST) of the coastal zone. The in‐situ measurements supported that SGD has a substantial influence on the coastal water chemistry as well as SST. Our observations highlight the extent to which aerial‐based TIR mapping can serve as a powerful tool for studying SGD and other coastal processes. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

2.
Fluxes of submarine groundwater discharge (SGD) were investigated into two tidal rivers on the north and south shore of Long Island, NY, during July 2015. Ground‐based handheld thermal infrared (TIR) imagery, combined with direct push‐point piezometer sampling, documented spatially heterogeneous small‐scale intertidal seepage zones. Pore waters were relatively fresh and enriched in nitrogen (N) within these small‐scale seeps. Pore waters sampled just 20 cm away, outside the boundary of the ground‐based TIR‐located seepage zone, were more saline and lower in N. These ground‐based TIR‐identified seeps geochemically represented the terrestrial fresh groundwater endmember, whereas N in pore waters sampled outside of the TIR‐identified seeps was derived from the remineralization of organic matter introduced into the sediment by tidal seawater infiltration. A 222Rn (radon‐222) time‐series was used to quantify fresh SGD‐associated N fluxes using the N endmembers sampled from the ground‐based TIR pore water profiles. N fluxes were up‐scaled to groundwater seepage zones identified from high‐resolution airborne TIR imagery using the two‐dimensional size of the airborne TIR surface water anomalies, relative to the N flux from the time‐series sampling location. Results suggest that the N load from the north‐shore tidal river to Long Island Sound is underrepresented by at least 1.6–3.6%, whereas the N load from SGD to a south‐shore tidal river may be up to 9% higher than previous estimates. These results demonstrate the importance of SGD in supplying nutrients to the lower reaches of tidal rivers and suggest that N loads in other tidal river environments may be underestimated if SGD is not accounted for.  相似文献   

3.
Nutrient fluxes from developed catchments are often a significant factor in the declining water quality and ecological functioning in estuaries. Determining the relative contributions of surface water and groundwater discharge to nutrient‐sensitive estuaries is required because these two pathways may be characterized by different nutrient concentrations and temporal variability, and may thus require different remedial actions. Quantifying the volumetric discharge of groundwater, which may occur via diffuse seepage or springs, remains a significant challenge. In this contribution, the total discharge of freshwater, including groundwater, to two small nutrient‐sensitive estuaries in Prince Edward Island (Canada) is assessed using a unique combination of airborne thermal infrared imaging, direct discharge measurements in streams and shoreline springs, and numerical simulation of groundwater flow. The results of the thermal infrared surveys indicate that groundwater discharge occurs at discrete locations (springs) along the shoreline of both estuaries, which can be attributed to the fractured sandstone bedrock aquifer. The discharge measured at a sub‐set of the springs correlates well with the area of the thermal signal attributed to each discharge location and this information was used to determine the total spring discharge to each estuary. Stream discharge is shown to be the largest volumetric contribution of freshwater to both estuaries (83% for Trout River estuary and 78% for McIntyre Creek estuary); however, groundwater discharge is significant at between 13% and 18% of the total discharge. Comparison of the results from catchment‐scale groundwater flow models and the analysis of spring discharge suggest that diffuse seepage to both estuaries comprises only about 25% of the total groundwater discharge. The methods employed in this research provide a useful framework for determining the relative volumetric contributions of surface water and groundwater to small estuaries and the findings are expected to be relevant to other fractured sandstone coastal catchments in Atlantic Canada. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

4.
Coastal lagoons are significant wetland environments found on coastlines throughout the world. Groundwater seepage may be a key component of lagoon water balances, though only a few studies have investigated large (>100 km2) coastal lagoons. In this study, we combined airborne thermal infrared imagery with continuous measurements of radon (222Rn—a natural groundwater tracer), conductivity, water temperature and dissolved oxygen to map groundwater seepage to a large coastal lagoon in New Zealand. We found evidence of seepage along the margins of the lagoon but not away from the margins. Our findings confirmed previously known seepage zones and identified new potential locations of groundwater inflow. Both point source and diffuse seepage occurred on the western and northwestern margins of the lagoon and parallel to the barrier between the lagoon and sea. These observations imply geologic controls on seepage. The combination of remote sensing and in-situ radon measurements allowed us to effectively map groundwater discharge areas across the entire lagoon. Combined, broad-scale qualitative methods built confidence in our interpretation of groundwater discharge locations in a large, dynamic coastal lagoon.  相似文献   

5.
Along the tropical coastline of the Great Barrier Reef (GBR) region, little is known to date about submarine groundwater discharge (SGD) into the near-shore ocean. In an oceanographic sense, SGD consists of freshwater flow from land as well as seawater circulated through sediments. Recent radiochemical and geophysical studies, using the tracer (222)Rn and apparent ground conductivity respectively, provide evidence for SGD to occur in a variety of hydrogeological settings. In this paper, a non-quantitative overview of different settings of SGD in the region is presented: (1) recirculation of seawater through animal burrows in mangrove forests, (2) freshwater SGD from unconfined aquifers as a narrow coastal fringe of freshwater along Wet Tropics beaches, (3) SGD from coastal dune systems in form of localised freshwater springs in the intertidal zone, (4) inner-shelf SGD from confined submarine aquifer systems comprised of riverine paleochannels incised into the shelf.  相似文献   

6.
Evaluation of time-space distributions of submarine ground water discharge   总被引：2，自引：0，他引：2  
Submarine ground water discharge (SGD) rates were measured continuously by automated seepage meters to evaluate the process of ground water discharge to the ocean in the coastal zone of Suruga Bay, Japan. The ratio of terrestrial fresh SGD to total SGD was estimated to be at most 9% by continuous measurements of electrical conductivity of SGD. Semidiurnal changes of SGD due to tidal effects and an inverse relation between SGD and barometric pressure were observed. Power spectrum density analyses of SGD, sea level, and ground water level show that SGD near shore correlated to ground water level changes and SGD offshore correlated to sea level changes. SGD rates near the mouth of the Abe River are smaller than those elsewhere, possibly showing the effect of the river on SGD. The ratio of terrestrial ground water discharge to the total discharge to the ocean was estimated to be 14.7% using a water balance method.  相似文献   

7.
Ground‐based handheld thermal infrared imagery was used for the detection of small‐scale groundwater springs at the northwestern beach of Spiekeroog Island (northwest Germany). The surveys and in situ measurements of electric conductivity were carried out from shortly before to shortly after low tide along the low water line. Several brackish groundwater discharge springs with a diameter of 1–2 cm were observed along the beach at a distance of 2–3 m above the low water line. The high fresh water portion in the discharging water derives from the fresh water lens in the center of the island. During cold weather, the springs were identified by a significantly increased temperature (3–5 °C higher) and a lower electric conductivity (<10 mS/cm) in contrast to the surrounding sea water (1–2 °C, >30 mS/cm). During warmer weather conditions, an inverse temperature contrast was observed. The measurements confirm the applicability of thermal imagery for the detection of small‐scale groundwater discharge locations as an extension to the established method of aerial thermal scans and prove the existence of submarine groundwater seeps in porous systems. A ground‐based handheld thermal infrared imagery survey enables a precise installation of sampling devices as, for example, seepage meters.  相似文献   

8.
Three intrusive systems of detection and quantification of coastal erosion events (using thermocouples and thermal pins) were developed and tested from 2005 to 2008 in different regions of the Gulf and maritime estuary of the St Lawrence (Quebec, Canada). The 3‐m‐long thermal pins inserted inside unconsolidated deposits allow the monitoring of erosion for a time period sometimes extending over several seasons. The thermocouple or thermocable method allows not only the instrumentation of unconsolidated deposits but also of rocky and cohesive substrate to a depth of 85 cm. An autonomous microclimatic station located near the experimental sites simultaneously samples temperature parameters, precipitation, snow cover, wind speed and direction as well as global radiation. The differential analysis of cliff thermal regime performed simultaneously with an analysis of air temperature makes it possible to determine the activation periods of coastal erosion processes. The results also make it possible to establish with precision the actual influence of rapid variations of certain climatic and microclimatic parameters (radiation, presence of snow cover, precipitation, etc.) on the physical state of surfaces and also on the activation of certain physical processes connected to coastal erosion events. The automated thermal erosion pin system (ATEPS) allows high temporal resolution (i.e. continuous) monitoring, enabling a real coupling of coastal erosion rates and climatic parameters. Preliminary results with the ATEPS system indicate that mild winter temperature and direct solar radiation are significant factors controlling cliff retreat rates. Moreover, the melting of segregation ice during the spring thaw contributed for more than 70% of cliff retreat against only 30% for frost shattering. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.
Phytoplankton community structure in coastal areas is a result of various environmental factors such as nutrients, light, grazing, temperature, and salinity. The Yucatan Peninsula is a karstic tropical region that is strongly influenced by submerged groundwater discharge (SGD) into the coastal zone. Phytoplankton community structure and its relationship with regional and local water quality variables were studied in four ports of the northwestern Yucatan Peninsula. Water quality was strongly related to SGD, and variations in phytoplankton community structure were related to local nutrient loading and hydrographic conditions, turbulence, and human impacts. Our study provides an ecological baseline for the Yucatan Peninsula and serves as a basis for establishing monitoring programs to predict changes at sites with high hydrological variation and in developing an early alert system for harmful toxic algal blooms.  相似文献   

10.
Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra‐enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra‐rich groundwater have induced high activities of Ra isotopes and 222Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (224Ra, 222Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater‐fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

11.
There are many factors affecting submarine groundwater discharge (SGD). However, systematic study of the influences of these factors is still limited. In this study, numerical modeling is performed to quantitatively explore the influences of various factors on SGD in a coastal aquifer. In such locations, tidal and terrestrial hydraulic gradients are the primary forces driving fresh and salt water movement. Unlike steady-state flow, dynamic fresh and salt water mixing at the near-shore seafloor may form an intertidal mixing zone (IMZ) near the surface. By constructing a general SGD model, the effects of various model components such as boundary conditions, model geometry and hydraulic parameters are systematically studied. Several important findings are obtained from the study results: (1) Previous studies have indicated there will be a freshwater discharge tube between the classic transition zone and the IMZ. However, this phenomenon may become unclear with the increase of heterogeneity and anisotropy of the medium’s conductivity field. (2) SGD and IMZ are both more sensitive to the vertical anisotropy ratio of hydraulic conductivity (Kx/Kz) than to the horizontal ratio (Kx/Ky). (3) Heterogeneity of effective porosity significantly affects SGD and IMZ. (4) Increase of the storage coefficient decreases fresh water discharge but increases mixing salt water discharge and total SGD. The increase will also change the shape of the IMZ. (5) Variation of dispersivities does not affect SGD, but significantly changes the distributions of the IMZ and the whole mixing zone. These findings will be helpful to the sampling design of field studies of SGD and to the application of dynamic SGD models to field sites for model development and calibration.  相似文献   

12.
Traditional methods for studying surface water and groundwater interactions have usually been limited to point measurements, such as geochemical sampling and seepage measurement. A new methodology is presented for quantifying groundwater discharge to a river, by using river surface temperature data obtained from airborne thermal infrared remote sensing technology. The Hot Spot Analysis toolkit in ArcGIS was used to calculate the percentage of groundwater discharge to a river relative to the total flow of the river. This methodology was evaluated in the midstream of the Heihe River in the arid and semiarid northwest China. The results show that the percentage of groundwater discharge relative to the total streamflow was as high as 28%, which is in good agreement with the results from previous geochemical studies. The data analysis methodology used in this study is based on the assumption that the river water is fully mixed except in the areas of extremely low flow velocity, which could lead to underestimation of the amount of groundwater discharge. Despite this limitation, this remote sensing‐based approach provides an efficient means of quantifying the surface water and groundwater interactions on a regional scale.  相似文献   

13.
Seasonal variations in sea level are often neglected in studies of coastal aquifers; however, they may have important controls on processes such as submarine groundwater discharge, sea water intrusion, and groundwater discharge to coastal springs and wetlands. We investigated seasonal variations in salinity in a groundwater‐fed coastal wetland (the RAMSAR listed Piccaninnie Ponds in South Australia) and found that salinity peaked during winter, coincident with seasonal sea level peaks. Closer examination of salinity variations revealed a relationship between changes in sea level and changes in salinity, indicating that sea level–driven movement of the fresh water‐sea water interface influences the salinity of discharging groundwater in the wetland. Moreover, the seasonal control of sea level on wetland salinity seems to override the influence of seasonal recharge. A two‐dimensional variable density model helped validate this conceptual model of coastal groundwater discharge by showing that fluctuations in groundwater salinity in a coastal aquifer can be driven by a seasonal coastal boundary condition in spite of seasonal recharge/discharge dynamics. Because seasonal variations in sea level and coastal wetlands are ubiquitous throughout the world, these findings have important implications for monitoring and management of coastal groundwater–dependent ecosystems.  相似文献   

14.
Groundwater can be important in regulating stream thermal regimes in cold, temperate regions, and as such, it can be a significant factor for aquatic biota habits and habitats. Groundwater typically remains at a constant temperature through time; that is, it is warmer than surface water in winter and cooler in summer. Further, small tributaries are often dominated by groundwater during low flows of winter and summer. We exploit these thermal patterns to identify and delineate tributary/groundwater inputs along a frozen river (ice‐on) using publically available satellite data, and we tested the findings against airborne, thermal infrared (TIR) data. We utilize a supervised maximum likelihood classification (sMLC) to identify possible groundwater inputs while the river is in a frozen state (kappa coefficient of 96.77 when compared with visually delineated possible groundwater inputs). We then compare sMLC‐identified possible groundwater inputs with TIR‐classified groundwater inputs, which confirmed that there was no statistical difference (χ2 = .78), that is, confirming that groundwater inputs can be delineated in north temperate river systems using available satellite imagery of the system's frozen state. Our results also established the spatial extent and influence of possible groundwater inputs in two seasons. The thermal plumes were longer and narrower in winter; this is likely related to seasonal differences in dispersion regimes. We hypothesize that differences between summer and winter is related to either (a) tributaries that are modulated by shading in summer or (b) aquifer disconnection from the river in winter owing to frozen ground conditions and lack of aquifer recharge. This method of establishing tributary/groundwater inputs and contributions to surface water thermal regimes is relatively simple and can be useful for science and management as long as “ice cover exists”; that is, the system can achieve a frozen state.  相似文献   

15.
Exposure from groundwater contamination to aquatic receptors residing in receiving surface water is dependent upon the rate of contaminated groundwater discharge. Characterization of groundwater fluxes is challenging, especially in coastal environments where tidal fluctuations result in transient groundwater flows towards these receptors. This can also be further complicated by the high spatial heterogeneity of subsurface deposits enhanced by anthropogenic influences such as the mixing of natural sediments and backfill materials, the presence of subsurface built structures such as sheet pile walls or even occurrence of other sources of contaminant discharge. In this study, the finite volume point dilution method (FVPDM) was successfully used to characterize highly transient groundwater flows and contaminant mass fluxes within a coastal groundwater flow system influenced by marked tides. FVPDM tests were undertaken continuously for more than 48 h at six groundwater monitoring wells, in order to evaluate groundwater flow dynamics during several tide cycles. Contaminant concentrations were measured simultaneously which allowed calculating contaminant mass fluxes. The study highlighted the importance of the aquifer heterogeneity, with groundwater fluxes ranging from 10−7 to 10−3 m/s. Groundwater flux monitoring enabled a significant refinement of the conceptual site model, including the fact that inversion of groundwater fluxes was not observed at high tide. Results indicated that contaminant mass fluxes were particularly higher at a specific monitoring well, by more than three orders of magnitude, than at other wells of the investigated aquifer. This study provided crucial information for optimizing further field investigations and risk mitigation measures.  相似文献   

16.
Hypoxic conditions (dissolved oxygen (DO)<2 mg l−1) have been documented in the nearshore coastal waters of Long Bay, South Carolina, United States of America, during summer months over the past several years. Hypoxia was documented in August 2009 in the nearshore (<500 m offshore) for ten consecutive days and four days in September 2009 corresponding with spring tides. This study measured radon activities of shallow beachface groundwater and nearshore bottom waters to estimate mixing rates and submarine groundwater discharge (SGD) in the nearshore waters of central Long Bay. Statistical analyses demonstrate significant correlations between high bottom water radon activities, low DO, and cooler bottom water temperatures during hypoxic conditions. Elevated radon activities during hypoxia were significantly influenced by upwelling favorable conditions which severely limited cross-shelf mixing. Model results indicate mixing of nearshore and offshore waters was limited by up to 93% (range: 43-100%) relative to non-hypoxic conditions. Data suggests previously overlooked natural phenomena including limited cross-shelf mixing and SGD can significantly influence nearshore water quality.  相似文献   

17.
地震预报尤其是临震预报,是当今国内外公认的世界性难题,对于这个复杂的问题,需要改变思维模式和探测手段来寻找突破口。笔者认为,在诸多的地震前兆信息中,震前地温突升是比较容易捕捉到的前兆信息之一。依据震前有关地温突升的一些观测事实和卫星热红外遥感能够探测到大震前有热红外异常现象,以及有地温突升必然就伴有地热信息释放的理念,笔者阐述了组建地温观测与卫星热红外观测相结合的新型立体化地热观测系统的必要性和可行性,我国目前现有气象台站2800多个,地震台站1400多个,共计4200多个台站,要统一增设80cm及以下地温观测并纳入到地震观测网。当发现某一地点地温有突升现象时,立刻对该地区上空的卫星热红外遥感资料进行重点分析和研究,从中提取可能的地热异常信息及其分布状况。一是地温观测基本摆脱了地表以上复杂多变的天气变化等干扰信息的影响,二是从周围复杂多变的卫星热红外遥感图像中摆脱出来,转移到有地温突升地区上空的图像中来。  相似文献   

18.
A large quantity of submarine groundwater discharge (SGD) of about 1000 m3 day?1 m?1 of the 600‐km‐long shoreline of South Atlantic Bight has been estimated by Moore (Global Biogeochemical Cycles, 2010b, 24, GB4005, doi: 10.1029/2009GB003747 ). However, there is great uncertainty in estimating the percentage of net, land‐originated groundwater recharge of SGD. Moreover, most previous studies considered the homogeneous case for the coastal superficial aquifers. Here, we investigated the terrestrial‐originated SGD through a multilayered submarine aquifer system, which comprises two confined aquifers and two semi‐permeable layers. The inland recharge includes a constant part representing the annual average and a periodical part representing its seasonal variation. An analytical solution was derived and used to analyse the distributions of the terrestrial‐originated SGD from the multilayered aquifers along the Winyah Bay transect, South Atlantic Bight. It is found that the width of the zone of SGD from the upper aquifer ranges from ~0.8 to ~8.0 km depending on the leakance of the seabed semi‐permeable layer. A head of the upper aquifer at a coastline 1.0 m higher than the mean sea level will cause a SGD of 1.82– 18.3 m3 day?1 m?1 from that aquifer as the seabed semi‐permeable layer's leakance varies from 0.001 to 0.1 day?1, providing considerable possibility for considerable land‐originated SGD. Seasonal terrestrial‐originated SGD variations predicted by the analytical model provide consistent explanation of the seasonal variation of 226Ra observed by Moore (Journal of Geophysics, 2007, 112, C10013, doi: 10.1029/2007JC004199 ). The contribution of the lower aquifer to SGD is only 1.2–12% of that of the upper aquifer. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

19.
The National Survey and Cadastre - Denmark (KMS) has for several years produced gravity anomaly maps over the oceans derived from satellite altimetry. During the last four years, KMS has also conducted airborne gravity surveys along the coast of Greenland dedicated to complement the existing onshore gravity coverage and fill in new data in the very-near coastal area, where altimetry data may contain gross errors. The airborne surveys extend from the coastline to approximately 100 km offshore, along 6000 km of coastline. An adequate merging of these different data sources is important for the use of gravity data especially, when computing geoid models in coastal regions.The presence of reliable marine gravity data for independent control offers an opportunity to study procedures for the merging of airborne and satellite data around Greenland. Two different merging techniques, both based on collocation, are investigated in this paper. Collocation offers a way of combining the individual airborne gravity observation with either the residual geoid observations derived from satellite altimetry or with gravity derived from these data using the inverse Stokes method implemented by Fast Fourier Transform (FFT).  相似文献   

20.
Ecohydrological processes are a key element to consider in functional river restorations. In the framework of a LIFE+ European restoration program, we have investigated the potential for airborne thermal‐infrared remote sensing to map surface water–groundwater exchanges and to identify their driving factors. We focused our attention on anastomosing channels on an artificial island of the Upper Rhine River (Rohrschollen), where a new channel was excavated from the floodplain to reconnect an older channel in its upstream part. These hydraulic engineering works led to an increased inflow from the Rhine Canal. Here, we propose an original data treatment chain to (a) georeference the thermal‐infrared images in geographic information system based on visible images, (b) detect and correct data errors, and (c) identify and locate thermal anomalies attributed to groundwater inputs and hyporheic upwellings. Our results, which have been compared to morpho‐sedimentary data, show that groundwater upwelling in the new channel is controlled by riffle–pool sequences and bars. This channel is characterized by large bedload transport and morphodynamic activity, forming riffles and bars. In the old channel, where riffle–pool sequences no longer exist, due to impacts of engineering works and insufficient morphodynamic effects of the restoration, thermal anomalies appeared to be less pronounced. Groundwater inputs seem to be controlled by former gravel bars outcropping on the banks, as well as by local thinning of the low‐permeability clogging layer on the channel bed.  相似文献   

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