Saline Groundwater Discharge Research Articles

Dynamics of submarine groundwater discharge and freshwater‐seawater interface

Relationships between submarine groundwater discharge (SGD) and the freshwater‐saltwater interface are evaluated by continuous measurements of SGD rates, conductivity and temperature of SGD, and resistivity measurements across the coastal aquifer. Our measurements show that the processes of SGD differ between the offshore and nearshore environments. SGD and submarine fresh groundwater discharge (SFGD) rates were largest just landward of the saltwater‐freshwater interface. SGD variations landward the saltwater‐freshwater interface had negative correlations with tidal variations, because of the connections of terrestrial groundwater in the land and the ocean. SGD in the nearshore can be explained mainly by connections of terrestrial groundwater, while offshore SGD rate is controlled mostly by oceanic process such as recirculated saline groundwater discharge.

Submarine groundwater discharge to a small estuary estimated from radon and salinity measurements and a box model

Abstract. Submarine groundwater discharge was quantified by a variety of methods for a 4-day period during the early summer of 2004, in Salt Pond, adjacent to Nauset Marsh, on Cape Cod, USA. Discharge estimates based on radon and salinity took advantage of the presence of the narrow channel connecting Salt Pond to Nauset Marsh, which allowed constructing whole-pond mass balances as water flowed in and out due to tidal fluctuations. The data suggest that less than one quarter of the discharge in the vicinity of Salt Pond happened within the pond itself, while three quarters or more of the discharge occurred immediately seaward of the pond, either in the channel or in adjacent regions of Nauset Marsh. Much of this discharge, which maintains high radon activities and low salinity, is carried into the pond during each incoming tide. A box model was used as an aid to understand both the rates and the locations of discharge in the vicinity of Salt Pond. The model achieves a reasonable fit to both the salinity and radon data assuming submarine groundwater discharge is fresh and that most of it occurs either in the channel or in adjacent regions of Nauset Marsh. Salinity and radon data, together with seepage meter results, do not rule out discharge of saline groundwater, but suggest either that the saline discharge is at most comparable in volume to the fresh discharge or that it is depleted in radon. The estimated rate of fresh groundwater discharge in the vicinity of Salt Pond is 3000-7000 m3 d-1. This groundwater flux estimated from the radon and salinity data is comparable to a value of 3200-4500 m3 d-1 predicted by a recent hydrologic model (Masterson, 2004; Colman and Masterson, 2004), although the model predicts this rate of discharge to the pond whereas our data suggest most of the groundwater bypasses the pond prior to discharge. Additional work is needed to determine if the measured rate of discharge is representative of the long-term average, and to better constrain the rate of groundwater discharge seaward of Salt Pond.

Fresh and saline groundwater discharge to the ocean: A regional perspective

Studies of groundwater flow in coastal aquifers often focus strongly on freshwater and investigate flow in a narrow (<5 km) zone surrounding the coastline. This work was designed to place coastal flow in a regional context and to compare fresh and saline submarine groundwater discharge (SGD) for regional flow systems. Numerical flow and transport models were developed to estimate SGD associated with topography‐driven flow, seawater recirculation, and geothermal convection in a passive margin setting. Simulations were based on two cross sections of North Carolina, and sensitivity studies were used to explore the impact of varying hydraulic and transport parameters. Results suggest that saline flow associated with seawater recirculation and geothermal convection should be considered in studies of SGD. Studies limited to shallow topography‐driven flow may be justified in using small study areas, but flow systems contributing to SGD may span at least 20 km surrounding the coast and continental slope.

Sources of salinity and boron in the Gaza strip: Natural contaminant flow in the southern Mediterranean coastal aquifer

Salinization in coastal aquifers is a global phenomenon resulting from the overexploitation of scarce water resources. The Gaza Strip is one of the most severe cases of salinization, as accelerated degradation of the water quality endangers the present and future water supply for over 1 million people. We investigate the chemical and isotopic (87Sr/86Sr, δ11B, δ18O, δ2H, and δ34SSO4) compositions of groundwater from the southern Mediterranean coastal aquifer (Israel) and the Gaza Strip in order to elucidate the origin of salinity and boron contamination. The original salinity in the eastern part of the aquifer is derived from discharge of saline groundwater from the adjacent Avedat aquitard (Na/Cl < 1, 87Sr/86Sr ∼ 0.7079, and δ11B ∼ 40‰). As the groundwater flows to the central part of the aquifer, a dramatic change in its composition occurs (Na/Cl > 1, high B/Cl, SO4/Cl, and HCO3, 87Sr/86Sr ∼ 0.7083; δ11B ∼ 48‰), although the δ18O‐δ2H slope is identical to that of the Avedat aquitard. The geochemical data suggest that dissolution of pedogenic carbonate and gypsum minerals in the overlying loessial sequence generated the Ca‐rich solution that triggered base exchange reactions and produced Na‐ and B‐rich groundwater. The geochemical data show that most of the salinization process in the Gaza Strip is derived from the lateral flow of the Na‐rich saline groundwater, superimposed with seawater intrusion and anthropogenic nitrate pollution. The methodology of identification of multiple salinity sources can be used to establish a long‐term management plan for the Gaza Strip and can also be implemented to understand complex salinization processes in other similarly stressed coastal aquifers.

Dryland salinity in Western Australia: managing a changing water cycle

Clearing of agricultural land has resulted in significant changes to the surface and groundwater hydrology. Currently about 10% of agricultural land in Western Australia is affected by dryland salinity and between a quarter and a third of the area is predicted to be lost to salinity before a new hydrological equilibrium is reached. This paper develops a general statement describing the changes to the surface and groundwater hydrology of the wheatbelt of Western Australia between preclearing, the year 2000 and into the future. For typical catchments in the wheatbelt it is estimated that average groundwater recharge and surface runoff have increased about tenfold when comparing the current hydrology to that preclearing. Saline groundwater discharge and flood volumes have also increased significantly. Saline groundwater discharge and associated salt load will probably double in the future in line with the predicted increase in the area of dryland salinity. In addition, future increases in the area of dryland salinity/permanent waterlogging will probably double the volumes in flood events and further increase surface runoff in average years. The outcomes of surface and groundwater management trials have been briefly described to estimate how the hydrology would be modified if the trials were implemented at a catchment scale. These results have been used to formulate possible integrated revegetation and drainage management strategies. The future hydrology and impacts with and without integrated management strategies have been compared.

Formation processes at the Ohalo II submerged prehistoric campsite, Israel, inferred from soil micromorphology and magnetic susceptibility studies

AbstractSoil‐geomorphic analysis coupled with micromorphology, SEM/EDS, magnetic susceptibility, and conventional sedimentological studies allowed us to reconstruct the site formation history and validate the archaeologically observed variability of human activities in the prehistoric camp of Ohalo II (19.5 ka B.P.), Sea of Galilee, Israel. The cultural layers rest upon the Late Pleistocene Lake Lisan deposits that accumulated under conditions of changing water supply and increasing rate of sedimentation from deep‐water varvelike deposits to basalt‐derived, near‐shore sandy lacustrine deposits. Intermittent occupation is recorded in some localities, indicating short‐term inundation episodes, which led to partial truncation and deformation of the sediments, primarily in the eastern lakeward part of the site. On the elevated, landward positions, incipient soils with strongly bioturbated profiles formed. Micromorphology demonstrates that intentional flooring was applied within the remains of brush huts, where millimeter‐sized, horizontally organized burnt and unheated vegetal tissues were likely to have been placed upon the compacted ground. In fireplaces, the cultural deposits in thin sections are composed of strongly mixed, abundant wood charcoal, ashes, and fishbone remains. Post‐depositional alterations were controlled by intermittent inundation of the site and salinization, which induced gypsum and pyrite deposition, primarily along decayed roots, and eventual pyrite oxidation. Accumulation of sodium and chlorine in the post‐occupation deposits is likely to have occurred because of discharge of saline groundwater. Although only suggestive at this stage of research, the conclusions drawn from magnetic susceptibility parameters of archaeologically related deposits at Ohalo II fit well with the micromorphological reconstructions and provide new information on the Late Pleistocene evolution of the Lake Lisan/Sea of Galilee fluctuating system. © 2003 Wiley Periodicals, Inc.

Evaluating improvements in irrigation efficiency as a salinity mitigation option in the South Australian Riverland

A modelling framework incorporating relationships between agricultural production and groundwater hydrology was developed to estimate the benefits of improved irrigation efficiency in the Riverland of South Australia. Increased irrigation efficiency can generate external benefits to downstream users through reduced discharge of saline groundwater. In the Riverland these benefits are large in comparison to the direct value of the irrigation water. However, the non‐exclusive and site‐specific nature of these benefits makes it difficult to fully internalise them through market instruments such as salinity credits. Achieving optimal irrigation efficiency is likely to require institutional arrangements that promote collective investment and public expenditure.

Fate of Benzene in a Stratified Lake Receiving Contaminated Groundwater Discharges from a Superfund Site

Predicting the fate of benzene in aquatic environments, and estimating corresponding human exposures, is critically dependent on knowledge of this carcinogen's biodegradation rate under the site-specific conditions. We used three approaches for quantifying this key fate process: (1) short-term (hours) observations of benzene loss in laboratory incubations of representative water samples, (2) whole-lake benzene mass balance studies, and (3) modeling of the temporal evolution of benzene vertical profiles in the lake. Our field site, the Halls Brook Holding Area (HBHA), continuously receives benzene input (about 20 μM or 1.5 ppm) into its anoxic hypolimnion via discharge of saline groundwater from an adjacent Superfund site (Industri-Plex in Eastern Massachusetts.) Using summertime, lake water samples in the laboratory, we found benzene was degraded in three metalimnion samples at rates between 1 and 2.5 d-1. An epilimnion sample yielded a similar result, but no degradation was observed in another epilimnio...

A METHOD FOR DETERMINING SALT SOURCES IN SURFACE WATERS'

ABSTRACT: This paper presents a method for determining the causes of salinization of surface waters, in this case the upper Colorado River and its tributaries in Texas. The analysis, which includes a combination of statistical analysis and graphical methods, indicates that among the sources of salt (e.g., saline ground water discharge into surface waters and storm runoff, both surface and shallow subsurface, and washing minerals into surface waters) the major contributor is saline ground water, which discharges into the river and streams. Data also points to salt plume intrusion into the river and streams from sources of salt in the aquifers.

Geophagy: who eats soil and where do possible contaminants go?

Geophagy describes both purposeful and inadvertent ingestion of soil. It has long been recognized as a source of essential trace metals for wild animals and livestock, and soil ingestion by humans has also been associated with nutritional disorders. The amounts ingested purposefully by some people are large, up to 50 g/day. The amounts ingested inadvertently are much smaller and very difficult to quantify. The pathways include dust adhering to plants and to hands that ultimately is transferred to the mouth and ingested. Recently, this phenomenon has been highlighted because it can be the dominant pathway for ingestion of environmentally immobile soil contaminants. Three things must be known to estimate health impacts: how much soil is ingested, are the contaminant concentrations enriched on the soil particles ingested, and how bioavailable are the soil bound contaminants in the gut? Two hypothetical scenarios are examined in detail, one is the exposure of a child playing in lead (Pb)-contaminated sand, and the other is the exposure of a hunter consuming a deer that ingested soil at a surface discharge of deep saline groundwater in the vicinity of an underground nuclear waste repository.

Balneology, mineral water, and spas in historical perspective

Saline springs within intracratonic basins are a common, but rarely studied phenomena. Derived primarily from the mixing of basin brines (evaporated seawater) with shallow groundwater and/or freshwater recharge, there are many saline springs within the Illinois Basin. These include free-flowing springs, bedrock seeps into otherwise freshwater aquifers, and salt licks. In this study, a total of 44 saline springs, seeps, licks and wells were sampled. The chemical compositions of the saline springs of the Illinois Basin are dominated by Na and Cl- with a combined concentration as high as 60,000 mg/L. Some of the springs are enriched in H2S supporting populations of white filamentous, sulfide-oxidizing bacteria. Because the spring water contains a component of basin brines, and because basin brines of the Illinois Basin have been well characterized by others, ion mass ratios were used to identify the geologic period of the source formation(s).In general and on a basin-wide scale, saline groundwater discharge occurred along geologic structures and from strata along the margins of the Illinois Basin, originating from every period of the basin’s geologic strata (Cambrian through Pennsylvanian). The greatest number of saline springs occurred where geologic structures intersect large streams or major aquifers. Saline springs were often found in clusters that may extend over many square kilometers. The occurrence of saline springs are a reflection of the geology, geologic structure, geologic history including continental glaciation, surface water-groundwater interactions, groundwater flow regimes, and overall groundwater chemistry within the Illinois Basin. In parts of the Illinois Basin, our data suggest that brines within strata of older geologic periods have migrated upward along geologic structures, infiltrated strata of younger geologic periods, and mixed with, and in some cases, replaced brines within those strata. The source of salinity in springs within the center of the Illinois Basin is typically brines from geologic strata that outcrops and subcrops along structures associated with the LaSalle Anticlinorium. Salt licks that occur near the southeastern boundary of the Illinois Basin in Kentucky constitute points of discharge for regional groundwater flow from the basin. The Cl/Br and K/Cl mass ratios of the salt licks in Kentucky suggest that the saline groundwater is a mixture of brines from Cambrian and Ordovician strata.

Saline groundwater in Mono Basin, California: 1. Distribution

Mono Lake, California is a perennial, closed‐basin saline lake. Up to 2 km of sediments have accumulated below the lake, and a well log shows that saline groundwater of concentration > 18,000 ppm extends to the bottom of the basin fill. We investigated the groundwater system with the variable‐density flow and solute transport code SUTRA to determine if the basin's recharge and inferred groundwater salinity are consistent with observational data. Steady state model predictions of the position and shape of the interface separating saline from fresh groundwater are consistent with the salinity profile derived from the spontaneous‐potential (SP) log of a geothermal well on the lake's shoreline. We also inferred the basin‐wide saline groundwater distribution and concentration from experiments with a steady state model of the entire basin groundwater system. Hydrologic variations around the lake determine the position of the saline‐fresh groundwater interface: Higher recharge rates characteristic of the Sierra Nevada shoreline push the interface far beneath the lake. The interface probably lies below the shoreline around much of the rest of the lake. On the low‐recharge northeastern shoreline the interface top may lie outside the lake edge. This positions the saline groundwater discharge zone just below the playa surface and contributes to development of salt flats on the recently exposed former lake bed. Simulations suggest that the basin fill permeability may not have significant anisotropy, possibly owing to extensive faulting which increases vertical permeability. For an anisotropic basin fill, the resultant increased channeling of recharge beneath the lake readily overcomes the opposing force of the saline groundwater density, and it is flushed out of the basin sediments. A simple permeability representation of the basin lithology, with low permeability below the lake and an anisotropic transition to higher permeability outside the lake, reasonably represents the well and spring water salinity observations.

Management Of Saline Groundwater Discharge By Long-term Windmill Pumping In The Wheatbelt, Western Australia

Land and stream salinization in the Western Australian wheatbelt developed as a result of clearing of native vegetation. This caused a shift in the hydrological balance and a 10- to 30-fold increase in recharge. Rising water levels rejuvenated groundwater flow through paleao channels and increased baseflow to drainage lines. An increase in saline groundwater ascension (TDS 5000–30 000 mgl−1) to the near-surface, induced by rising pressure heads in the deeper semi-confined aquifer system, advanced land and stream salinization. Areas in a catchment where groundwater flow is channelled upwards by subsurface geological strctures are especially susceptible to salinization and water logging.

Combining measurements of transpiration and stable isotopes of water to determine groundwater discharge from forests

Discharge of saline groundwater from Eucalyptus forests on a semi-arid floodplain was directly determined by first measuring transpiration rates from the forests, and then partitioning the transpiration flux into groundwater discharge and soil water depletion. This partitioning was achieved by identifying the source of the transpired water with naturally occurring stable isotopes of water. Transpiration rates were low, being about 0.3 mm day −1 from three E. largiflorens sites and up to 2 mm day −1 from an E. camaldulensis site. There was no significant variation in transpiration across seasons, indicating that transpiration was limited by environmental factors other than evaporative demand. Despite its salinity (electrical conductivities of 11–33 dS m −1), the groundwater was used by the forests at all sites and all times, and made up 100% of transpiration in more than half of the measurements, and 40–80% in the remainder. There was some consistency in water uptake patterns. E. camaldulensis tended to take up shallow soil water and groundwater simultaneously, as did trees at one of the E. largiflorens sites. At the driest sampling time, however, groundwater was the only source of water for trees at both of these sites. Trees at the remaining two E. largiflorens sites generally relied solely on the groundwater. The tree water source results indicate that groundwater discharge fluxes were between 40 and 100% of the transpiration fluxes at these sites. These groundwater discharge fluxes were small in terms of regional groundwater balances, but would be important in the salinisation of the soils. Additionally, uptake of water from the soil profile by the trees substantially increased groundwater discharge compared with discharge from the soils had they been bare of vegetation.

Monitoring Saline Discharge Areas: Farrell Flat, a Case Study

By monitoring saline groundwater discharge areas, an indication of the extent of dryland salinisation processes occurring in an area may be determined. Processed remotely sensed data (SPOT MS and aerial photography) has been analysed within a geographic information system database to identify the dynamic relationship between changing vegetation cover and increasing salt levels on a saline groundwater discharge area. Temporal analysis of this database was conducted for a saline discharge area on a wheat/sheep property in South Australia from the period 1966 to 1990. The results provide a directional and quantitative assessment of the change in salt affected areas during the study period. Information of this type benefits land managers at the regional scale by quantifying salinisation trends.

Reclaiming sandplain seeps by intercepting perched groundwater with eucalypts

AbstractAt a sandplain seep at East Belka in the Western Australian Wheatbelt, saline groundwater discharge occurs from a shallow (approx. 2 m) perched aquifer of moderate permeability (0.15 m day−1). Groundwater qualities range from over 2,500 mS m−1 in the saline area, to between 660 and 1,700 mS m−1 in the plantation. In 1986 five varieties of eucalypts (E. globulus, E. cladocalyx var. nana and three provenances of E. camaldulensis) were planted across the contour upslope from the seep on about 1.0 per cent of the catchment. By 1989 the seedlings had grown to heights of up to 6.5 m. Despite above‐average rainfall over the study period, perched water‐tables under the plantation and seep were progressively lowered (approx. 0.5‐1.0 m) until the area was dry at the start of the 1989‐1990 summer. Wheat (Triticum aestivum) established on the seep and adjacent paddock in May 1989, provided a yield of over 1.0 t ha−1 on a site that had been unproductive for 20 years.The method has the potential to reclaim much of the existing eastern and northern wheatbelt where there are salinity problems caused by perched groundwater, and could prevent recharge of the regional aquifer beneath the sandplain seep. However, additional techniques will be required to prevent deep aquifer discharge caused by steadily rising (approx. 0.15 m yr−1) regional water‐tables. Discharge and associated dryland salinity from the regional system are expected to be major problems during the next 40 years at the site investigated.

Effect of groundwater interception and irrigation on salinity and piezometric levels of an aquifer

AbstractThe major strategy used to prevent the discharge of highly saline groundwater to the River Murray in southeastern Australia is groundwater interception and disposal. The basic design principle assumes that the extraction of groundwater from an aquifer hydraulically connected to the river, using a line of pumps positioned close and roughly parallel to the river, will decrease piezometric heads thereby reducing the discharge of saline groundwater to the river. The paper considers one of these schemes which was designed for the Mildura area on the basis of a hydrogeological investigation. It analyses the effects on piezometric head and groundwater salinity due to the groundwater interception scheme and adjacent irrigation activity over a period of several years from January 1980. It is shown that piezometric heads have decreased significantly in the stretch close to the river. A slight reduction in groundwater salinity is also apparent in this stretch except for an area between the river and a holding basin used for disposal of the saline effluents emanating from the groundwater interception scheme. This general reduction in groundwater salinity is mainly caused by pumping from the groundwater interception scheme and recharge from irrigation. The exception in the trend in groundwater salinity is due to the movement of a highly saline body of groundwater from the holding basin towards the River Murray. Results of this Australian experience should be helpful to the designers of similar salinity mitigation schemes elsewhere.

Environmental isotope hydrology of salinized experimental catchments

Deuterium, oxygen-18, tritium and chloride concentrations were used in three salinized experimental catchments to gain insight into the mechanism of solute concentration and flow processes in the saturated and unsaturated zones. The three experimental catchments were studied because of their location in different rainfall regions, their status with respect to clearing of native vegetation and with respect to secondary salinization. Two uncleared catchments have average annual rainfalls of approximately 820 and 1220 mm, respectively. The third cleared catchment has an annual rainfall of 650–750 mm. This catchment was in an advanced state of secondary salinization and displayed large areas of saline groundwater discharge with halite encrustation at the ground surface. The stable isotope compositions of the solution phase in solute bulge profiles in the unsaturated zone showed a close agreement with the amount-weighted mean isotopic composition of rainfall and only surficial evidence of isotopic enrichment due to evaporation. Evaporation from the soil surface plays a minor role as a mechanism of solute concentration in the unsaturated zone. The dominant process of solute concentration in the unsaturated zone was ion exclusion during uptake of water by tree roots which was evidently a solute but not isotope fractionating process. Tritium analyses of unsaturated zone water and grondwater indicated movement of recent recharge to 7–10 m depth at the low rainfall site but over the full depth of the 15 m unsaturated zone at the higher rainfall site. The variability in δ 18O and δ 2H values of groundwaters was used in association with chloride concentrations to provide information on mixing characteristics of groundwaters within the catchments.

Response of input and output of water and chloride to clearing for agriculture

Five small forested catchments in the Collie River Basin in southwest Western Australia were instrumented to quantify the changes in the input and output of salt and water when land use changed from forest to agriculture. The paired catchment approach was used with two adjacent catchments located in high rainfall (1200 mm yr −1) and a group of three located in a lower (800 mm yr −1) rainfall area. The treatment of complete clearing was applied to one catchment in the high rainfall zone, and to about half of one catchment in the lower rainfall zone after three years of calibration with the uncleared control catchments. Strategies of partial clearing were applied to the third catchment in the lower rainfall zone. The catchment pairs were found to be well matched. The yield of water and salt increased immediately after clearing. In the higher rainfall catchment streamflow increased about four times to 48% of rainfall, salt load increased to fifteen times the mean saltfall (measured as chloride ion) of 7 g m −2 yr −1. Direct runoff increased fourfold to 16% of yearly streamflow, due partly to the progressive increase in the area of soil saturated to the surface. The perched groundwater system was the major source (77% in 1983) of streamflow though it was the route rather than the source of increased salt to the stream. The mottled and pallid clay profile was the dominant source of salt transported by the deep groundwater system into the perched aquifer. Streamflow became perennial in the first postclearing year. Absolute increases in streamwater and salt output from partially cleared catchments in the lower rainfall location were about an order of magnitude less than for the higher rainfall catchment though the relative increases were similar. The three catchments were found to be accumulating salt. In the cleared catchments the rising potentiometric surface would establish a saline groundwater discharge zone in the valley and a net export of salt. In all treated catchments reduced interception results in increased water availability at the soil surface for stormflow and infiltration. The reduction in transpiration had an added effect in increasing recharge to groundwater. A new equlibrium for water had not been achieved eight years after clearing, but was estimated to precede the new salt equilibrium.