Low-salinity Groundwater Research Articles

ENVIRONMENTAL PRESSURES INFLUENCING LIVING STROMATOLITES IN HAMELIN POOL, SHARK BAY, WESTERN AUSTRALIA

Environmental parameters in Hamelin Pool, Shark Bay were investigated to characterize extrinsic factors that may be affecting stromatolite morphogenesis. Hamelin Pool, which evolved into a restricted environment during the last few millennia, sustains the world's most extensive and diverse assemblage of modern marine stromatolites. These stromatolites occur in a shallow nearshore facies belt covering over 100 km of coast. Temperature, salinity, water level, and current data collected between 2012 and 2014 have revealed previously undocumented regional and seasonal trends. Regional trends include increasing salinity, greater temperature range, and decreasing energy moving southward from Faure Sill and to the Nilemah Embayment. Seasonal trends reveal paradoxically increased salinities in wet winter months and decreased salinity in dry summer months. When paired with annual tidal cycles, these trends suggest the influx of low salinity groundwater along the Hamelin Pool shelf. Speculation on how the documented environmental parameters may affect stromatolite growth suggests potential impact on morphology, internal fabric, and stromatolite-building microbial communities. These insights into environmental pressures within a living stromatolite system provide a framework for understanding extrinsic factors affecting microbial communities and stromatolite development throughout Earth history.

Tracking tidal inundation in a coastal salt marsh with Helikite airphotos: Influence of hydrology on ecological zonation at Crab Haul Creek, South Carolina

Abstract Ecological zones in a salt marsh are influenced by many factors, including hydroperiod, soil salinity, groundwater flow, and nutrient/oxygen availability. In this project, high-resolution aerial images taken by a Helikite helium balloon-kite at 100 m altitude were used to develop a detailed flooding model and derive a spatially comprehensive map of ecological zones at the headwaters of a small tidal marsh creek at a forest-marsh boundary in North Inlet estuary, South Carolina. We constructed photomosaics from Helikite imagery over a 150 × 100 m area to identify ecological zones using an automated, maximum likelihood classification. In the same area, we developed a digital terrain model with ± 2 cm overall vertical accuracy, primarily from waterlines at known tide height tracked by Helikite imagery and GPS. These are low-cost, easily implemented methods for studying marsh processes where access is often challenging. Quantifying frequency of inundation, an approximation of hydroperiod, using our terrain model and comparing it to ecological zones revealed that there is not a linear relationship between elevation and inundation above mean high tide. Ecological zones exhibit complex spatial patterns that neither elevation nor hydroperiod alone can explain. In the northwestern basin, adjacent to a forest-marsh boundary, inflow of low salinity groundwater from a large freshwater lens beneath the forest prevents the development of Salicornia virginica zones and allows the high-marsh plant Juncus roemarianus to be present at middle-to-low marsh elevations. Conversely, in the southwestern portion of the basin adjacent to a relict beach ridge underlain by a smaller freshwater lens, saltwater infiltration during spring tides and evapotranspiration during neap tides allows Salicornia virginica zones to develop in hypersaline soils. Many of the current numerical models for predicting salt marsh ecological zonation consider hydroperiod as the main factor; however, the asymmetry of the basin in both ecological zones and freshened groundwater discharge imply groundwater and surface-water inundation should both be considered in the distribution of ecological zones in a coastal salt marsh.

Investigation of fluoride removal from low-salinity groundwater by single-pass constant-voltage capacitive deionization

Capacitive deionization (CDI) is attracting increasing attention as an emerging technology for the facile removal of ionic species from water. In this work, the feasibility of fluoride removal from low-salinity groundwaters by single-pass constant-voltage CDI was investigated and a model developed to describe the dynamic fluoride electrosorption behavior. Effects of operating parameters including charging voltage and pump flow rate as well as impact of fluoride and chloride feed concentrations on the effluent fluoride concentration and equilibrium fluoride adsorption capacity were studied and the obtained data used to validate the model. Using the validated model, the effects of various design parameters, including arrangement of multiple CDI cells, on fluoride removal were assessed. Single-pass constant-voltage CDI was found to be effective in removing fluoride from low-salinity groundwaters but, as expected, removal efficiency was compromised in waters of high salinity. The relatively simple electrosorption model developed here provided a satisfactory description of both fluoride removal and current evolution and would appear to be a useful tool for prediction of CDI performance over a range of operating conditions, cell arrangements and feed water compositions though scope for model improvement exists.

Detection of Low Salinity Groundwater Seeping into the Eastern Laizhou Bay (China) with the Aid of Landsat Thermal Data

Xing, Q. G.; Braga, F.; Tosi, L.; Lou, M. J.; Zaggia, L.; Teatini, P.; Gao, X. L.; Yu, L. J.; Wen, X. H., and Shi, P., 2016. Detection of low salinity groundwater seeping into the Eastern Laizhou Bay (China) with the aid of Landsat Thermal Data. Low-salinity groundwater storages beneath the sea bottom and submarine groundwater discharges (SGD) are of great importance in environmental management and the use of coastal water resources. A preliminary hydro-morpho- geologic analysis allows for considering the presence of low-salinity groundwater in the offshore of the Laizhou Bay (Southern Bohai Sea, China). In order to detect the potential SGD, the analysis of the Sea Surface Temperature (SST) anomalies was carried out using Landsat thermal images acquired in the seasons characterised by the largest difference in temperature between seawater and groundwater. At the nearshore scale, patchy cold water anomalies occur approximately in the same positions along the intertidal zone of the Southern bay, where the unconfined aquifer discharges, independently of tide conditions. At the embayment scale, cold water anomalies spread out in the Eastern Laizhou Bay where the confined aquifer is likely exposed. Salinity and temperature measured in surficial waters of the eastern Laizhou Bay support the hypothesis of SGD, which can be derived from remote sensing images; the occurrence of macroalgal blooms might also be the consequence of the SGD-enhanced nutrient supply. This work pointed out the need of future oceanographic and groundwater flow modeling along with long-term monitoring of processes associated with the suspected SGD. The outcomes of this preliminary study will be of great help to direct effective in-situ investigations aimed at quantifying the volumes of SGD and to simulate coupled groundwater/surface-water flow.

The formation of shallow fresh groundwater in the north of Yanchi county, Ningxia, China: main influencing factors and mechanism

Shallow fresh groundwater is not common in the middle of basins in arid and semiarid areas with strong evaporation where shallow groundwater is often brackish water or saline water. In this study, the shallow fresh groundwater in the north area of Yanchi county, China was investigated for the main influencing factors and mechanisms of its formation. The results showed that freshwater of HCO3 and SO4 types with mean salinity of 0.78 g/L formed in the north of the study area while brackish and saline water of SO4·Cl–Na type with mean salinity of 2.28 g/L formed in the west and south of the study area. The fresh groundwater formed owing to the special physico-chemical properties of the aeolian sand which has the good permeation of atmospheric precipitation, the weak evaporation of the groundwater, the low salt contents in the vadose zone and aquifer medium, the weak water–rock interaction and the good hydrodynamic condition. The lateral recharge of low salinity groundwater also played a mixing and diluting role in the formation of the fresh groundwater. The findings should provide a scientific basis for the exploitation and utilization of local groundwater resources and be of significance in the exploration and exploitation of fresh groundwater in arid and semiarid regions.

Influence of seawater intrusion on microbial communities in groundwater

Groundwater is the sole source of potable water on Jeju Island in the Republic of (South) Korea. Groundwater is also used for irrigation and industrial purposes, and it is severely impacted by seawater intrusion in coastal areas. Consequently, monitoring the intrusion of seawater into groundwater on Jeju is very important for health and environmental reasons. A number of studies have used hydrological models to predict the deterioration of groundwater quality caused by seawater intrusion. However, there is conflicting evidence of intrusion due to complicated environmental influences on groundwater quality. Here we investigated the use of next generation sequencing (NGS)-based microbial community analysis as a way to monitor groundwater quality and detect seawater intrusion. Pristine groundwater, groundwater from three coastal areas, and seawater were compared. Analysis of the distribution of bacterial species clearly indicated that the high and low salinity groundwater differed significantly with respect to microbial composition. While members of the family Parvularculaceae were only identified in high salinity water samples, a greater percentage of the phylum Actinobacteria was predominantly observed in pristine groundwater. In addition, we identified 48 shared operational taxonomic units (OTUs) with seawater, among which the high salinity groundwater sample shared a greater number of bacterial species with seawater (6.7%). In contrast, other groundwater samples shared less than 0.5%. Our results suggest that NGS-based microbial community analysis of groundwater may be a useful tool for monitoring groundwater quality and detect seawater intrusion. This technology may also provide additional insights in understanding hydrological dynamics.

Detection of Sinkhole Formation by Strain Profile Measurements Using BOTDR: Simulation Study

AbstractThe sudden collapse of sinkholes in the Dead Sea area represents a serious threat to infrastructure in the area. The formation of these sinkholes has been shown to be directly correlated with the drop in the Dead Sea water level which is accompanied by a corresponding lowering of the groundwater level and permits the penetration of low-salinity groundwater into coastal areas. This water causes dissolution of the salt layers which results in the formation of subsurface voids that develop into collapse sinkholes. Various tools and measurement methods have been investigated in order to attempt to detect the formation of sinkholes, but to date, there is no method capable of providing early warning of possible collapse. This paper investigates the use of fiber-optic Brillouin optical time-domain reflectometry (BOTDR) or Brillouin optical time-domain analysis (BOTDA) for such detection. Brillouin optical time-domain reflectometry or analysis (BOTDR/A) is an optical measurement technique that provides di...

Evaluation of the possible use of a Bulgarian clinoptilolite for removing strontium from water media

AbstractThe sorption of Sr2+ ions by natural clinoptilolite was investigated using the batch method. The effects of pH, contact time and strontium concentrations were tested and the optimal conditions for sorption were determined. The process was very fast initially and equilibrium was reached within 24 h. Kinetic sorption data were fitted to pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The simple pseudo-second-order rate model provides good agreement with the experimental data for Sr2+ uptake. The respective rate constants, k2, calculated at different initial Sr2+ concentrations, were obtained. The equilibrium data were analysed by applying the Langmuir, Freundlich and Dubinin–Raduchkevich isotherm models. The Langmuir model describes the observed Sr2+ uptake most accurately and the value of the monolayer sorption capacity is 32.81 mg Sr2+/g. The effect of Na+ ions and the effectiveness of uptake from low saline groundwater simulated solutions were also studied and discussed.

Fluoride and Arsenic Removal by Nanofiltration Technology from Groundwater in Rural Areas of China: Performances with Membrane Optimization

Nanofiltration (NF) membrane configuration for fluoride and arsenic removal from groundwater has a key role in controlling operation performances and membrane fouling. Some bench-scale contrast experiments using commercial NF membranes were done to obtain the optimum arrangement performances. The NF membrane arrays included one-stage, two-stage, and three-stage systems. The NF membrane surface was negatively charged above its isoelectric point (approximately at pH 5.9–6.4). Accordingly, the raw groundwater was initially adjusted to a neutral or alkaline pH to enhance the effect of electrical charge repulsion and improve the ion removal efficiencies by NF. The encouraging results indicated that a membrane in a parallel-linear arrangement with staging 2:1 was the preferable arrangement to remove fluoride and arsenic from low-salinity groundwater in rural areas of China. With this optimal arrangement, the NF system obtained fluoride and arsenic removal efficiencies of 70˜73% and 92˜94% respectively, a preferable permeate flux of 73.37 L h−1 m2 and acceptable water flux recovery rate of 65% at 16°C. This optimal arrangement can further limit the potential membrane fouling by lowering the interstage Reynolds number. Moreover, the water product cost was lowest by the NF system with this optimal arrangement.

Microbiological Investigation of Persistent Mortalities in Litopenaeus vannamei Grown in Low Saline Waters in India

Abstract Microbial diseases are a serious hindrance to successful shrimp aquaculture. The Pacific white shrimp Litopenaeus vannamei is an exotic species recently introduced in India to supplement the failing aquaculture of the Asian tiger shrimp Penaeus monodon due to viral diseases. However, after a brief initial success, the aquaculture of L. vannamei is also experiencing serious problems due to microbial diseases. In this study, we conducted a microbiological investigation into the problem of persistent mortalities in selected L. vannamei farms on the southeastern coast of India. The infected shrimps were positive for the white spot syndrome virus (WSSV) by a nested PCR, though no visible white spots were present on the animals. The shrimps were heavily colonized by Vibrio parahemolyticus, which were isolated from the hepatopancreas, gills, and the body surface. The pond water, despite being low saline groundwater, harbored large numbers of V. parahemolyticus and other Vibrio species, and V. parahemolyticus isolated from L. vannamei were resistant to β-lactam antibiotics and cephalosporins. Our results strongly suggest that the persistent mortalities of L. vannamei were due to a co-infection by V. parahemolyticus and WSSV. Received December 16, 2013; accepted February 14, 2014.

Elucidating the sources and mechanisms of groundwater salinization in the Ziz Basin of southeastern Morocco

In the Ziz Basin, located in arid area in southeastern Morocco, surface waters are scarce and local populations are entirely dependent on groundwater resources for drinking and irrigation. In order to evaluate the main factors controlling the origin and salinization of groundwater resources, we have investigated the chemical and stable isotope compositions of groundwater and surface water in different areas in the Ziz basin, upstream and downstream from the Hassan Addakhil dam, which is the major man-made reservoir in the basin. A large variation in water quality was observed, specifically an increase in salinity from north (upstream to the reservoir with TDS ~ 460 mg/L) to south (downstream; TDS ~ 16,000 mg/L). In the northern portion of the basin, the low saline groundwater is composed primarily of Ca2+ and Mg2+ due to dissolution of carbonate formations in the High Atlas Mountains. In contrast, the major dissolved consequents of saline waters are Cl−, SO4 2− and Na+, apparently due to dissolution of evaporite minerals (gypsum and halite). In some areas elevated nitrate contents imply anthropogenic contamination derived from local agriculture. The stable isotopes data (δ18O = −8.6 to −8.3 ‰ and δ2H = −55.7 to −53.8 ‰) indicate that the High Atlas Mountains, upstream of the reservoir constitute the major source of water to the Ziz Basin. Given that this arid basin is entirely dependent on groundwater resources, long-term salinization of groundwater in the Ziz Basin could lead to negative effects and reduction of the local agricultural productivity in addition to the degradation of drinking water quality in this region.

Coastal aquifer system in late Pleistocene to Holocene deposits at Horonobe in Hokkaido, Japan

The groundwater flow systems and chemistry in the deep part of the coastal area of Japan have attracted attention over recent decades due to government projects such as geological disposal of radioactive waste. However, the continuous groundwater flow system moving from the shallow to deep parts of the sedimentary soft rock has not yet been characterized. Therefore, the Cl–, δD and δ18O values of the pore water in the Horonobe coastal area in Hokkaido, Japan, were measured to 1,000 m below the ground surface, and a vertical profile of the pore-water chemistry was constructed to assist in elucidating groundwater circulation patterns in the coastal area. The results show that the groundwater flow regime may be divided into five categories based on groundwater age and origin: (1) fresh groundwater recharged by modern rainwater, (2) fresh groundwater recharged by paleo rainwater during the last glacial age, (3) low-salinity groundwater recharged during the last interglacial period, (4) mixed water in a diffusion zone, and (5) connate water consisting of paleo seawater. These results suggest that the appearance of hydrological units is not controlled by the boundaries of geological formations and that paleo seawater is stored in younger Quaternary sediments.

Mass balances of nitrogen and phosphorus in an integrated culture of shrimp (Litopenaeus vannamei) and tomato (Lycopersicon esculentum Mill) with low salinity groundwater: A short communication

This study re-examines the performance of an integrated shrimp-tomato system using the nutrients mass balance approach. A budget was calculated based on nutrients analysis, water management, feeding, fertilization, stocking, harvest and sludge removal. Nitrogen and P content in the input water (groundwater) were low, contributing 33.5% and 0.5%, of the total inputs, respectively. Most of the N (43.6%) and P (98.8%) entered to the system as shrimp food. Likewise, 15.2% and 2.5% of the input N, and 8.9% and 4.3% of the input P, were converted to harvested shrimp and tomato plants, respectively; 4.1% N and 24.6% P remained in the organic sludge, while the environmental losses expressed per unit of production were relatively low, 57kgNton−1 and 7.1kgPton−1 of product harvested. About 13.4% of input N was unaccounted for, and was assumed to be lost to the atmosphere via denitrification and volatilization. Comparison between these results and previous studies indicate that the shrimp-tomato system produces a relatively low recovery of N and P as harvested products, however, the main progress reached with this system is the reduction of the environmental losses of N and P in terms of kg of each nutrient per ton of the product harvested.

Offshore fresh groundwater reserves as a global phenomenon

The flow of terrestrial groundwater to the sea is an important natural component of the hydrological cycle. This process, however, does not explain the large volumes of low-salinity groundwater that are found below continental shelves. There is mounting evidence for the global occurrence of offshore fresh and brackish groundwater reserves. The potential use of these non-renewable reserves as a freshwater resource provides a clear incentive for future research. But the scope for continental shelf hydrogeology is broader and we envisage that it can contribute to the advancement of other scientific disciplines, in particular sedimentology and marine geochemistry.

Submarine groundwater discharge to the Baltic coastal zone: Impacts on the meiofaunal community

The discharge of groundwater into the sea affects surrounding environments by changing the salinity, temperature and nutrient regimes. This work reports the spatial effects of a submarine groundwater discharge (SGD) on the abundance and structure of the meiofaunal community in the shallow area of Puck Bay (Baltic Sea). Several field expeditions in the years 2009 and 2010 found that low-saline groundwater escapes into the bay from permeable, sandy, near-shore sediments. The SGD literature has grown rapidly during the current decade; however, the effects of this type of disturbance on the shallow sandy bottom fauna have thus far been little studied. We provide evidence that the discharge of groundwater has a clear effect on meiofaunal assemblages in the research area. This effect was reflected in a significant decline of certain meiofaunal taxa, mainly nematodes and harpacticoids, as well as in altered patterns of temporal distribution and small-scale (vertical) zonation of meiofaunal assemblages. Overlooking submarine groundwater discharge processes may lead to serious misinterpretations of ecological data. It is clear that groundwater discharge phenomena should be considered in future scientific studies.

Geologic effects on groundwater salinity and discharge into an estuary

Summary Submarine groundwater discharge (SGD) can be an important pathway for transport of nutrients and contaminants to estuaries. A better understanding of the geologic and hydrologic controls on these fluxes is critical for their estimation and management. We examined geologic features, porewater salinity, and SGD rates and patterns at an estuarine study site. Seismic data showed the existence of paleovalleys infilled with estuarine mud and peat that extend hundreds of meters offshore. A low-salinity groundwater plume beneath this low-permeability fill was mapped with continuous resistivity profiling. Extensive direct SGD measurements with seepage meters (n = 551) showed fresh groundwater discharge patterns that correlated well with shallow porewater salinity and the hydrogeophysical framework. Small-scale variability in fresh and saline discharge indicates influence of meter-scale geologic heterogeneity, while site-scale discharge patterns are evidence of the influence of the paleovalley feature. Beneath the paleovalley fill, fresh groundwater flows offshore and mixes with saltwater before discharging along paleovalley flanks. On the adjacent drowned interfluve where low-permeability fill is absent, fresh groundwater discharge is focused at the shoreline. Shallow saltwater exchange was greatest across sandy sediments and where fresh SGD was low. The geologic control of groundwater flowpaths and discharge salinity demonstrated in this work are likely to affect geochemical reactions and the chemical loads delivered by SGD to coastal surface waters. Because similar processes are likely to exist in other estuaries where drowned paleovalleys commonly cross modern shorelines, the existence and implications of complex hydrogeology are important considerations for studies of groundwater fluxes and related management decisions.

Karstic groundwater discharge and seawater recirculation through sediments in shallow coastal Mediterranean lagoons, determined from water, salt and radon budgets

Groundwater discharge to coastal water bodies is increasingly recognised to contribute significantly to coastal water and solute budgets. In order to evaluate the discharge of low-salinity groundwater of karstic origin and of recirculation of seawater through sediments into Mediterranean lagoons, a study was carried out in La Palme, Salses-Leucate and Thau lagoons on the French Mediterranean coastline in the dry summer months 2009, using radon and salinity as tracers.Whereas Salses-Leucate lagoon receives significant fluxes of karstic low-salinity groundwater, in La Palme and Thau lagoons, karstic groundwater fluxes are small, and have little effect on the lagoons' radon balance. A simultaneous water, salt and radon budget of the small La Palme lagoon (ca 50ha surface area and 0.6m mean depth) was used to simulate average salt and radon concentration over a one month period. The results indicate that despite its small flux (0.8–1.2% of lagoon volume per day) the discharge of low-salinity karstic groundwater contributes significantly to maintaining salinity lower than seawater in the seasonally closed lagoon, but makes only a minor contribution (7–18%) to the radon budget.Wind-driven seawater recirculation through sediments on the other hand is a major contributor, estimated at 22–60% of total radon fluxes to the lagoon, equivalent to a water flux of 1.4–7.0% of lagoon volume day−1. The remaining balance of Radon is supplied by diffusion and in-water production from decay of its parent nuclide. Using a stand-alone radon model without considering a water and salt balance would have considerably overestimated the flux of groundwater of karstic origin.Radon can be regarded as a proxy for other dissolved solutes such as nutrients and contaminants transported with groundwater and seawater recirculation fluxes. Nutrient and contaminant enrichment of sediments in Mediterranean lagoons is well documented. Wind-driven seawater recirculation through these sediments as documented in this study may remobilise these nutrients and contaminants. It may thus play a considerable role in lagoonal biogeochemical budgets, and may require consideration in water quality management in Mediterranean coastal lagoons.

Integration of geochemical and isotopic tracers for elucidating water sources and salinization of shallow aquifers in the sub-Saharan Drâa Basin, Morocco

In the arid sub-Saharan of southern Morocco, groundwater salinization poses a direct threat for agricultural production in six oases’ basins that are irrigated by water imported from the High Atlas Mountains. Here the geospatial distribution of salinity is evaluated in shallow groundwater, springs and surface waters in the Drâa Basin, integrating major and trace element geochemistry and isotopic tracers (O, H, Sr and B). The data show that water discharge from the High Atlas Mountains to the Upper section of the Drâa Basin is characterized by both low and high salinity, a distinctive low δ18O and δ2H composition (as low as −9‰ and −66‰, respectively), typical for meteoric water from high elevation, a 87Sr/86Sr range of 0.7078–0.7094, and δ11B of 12–17‰. The Ca–Mg–HCO3, Na–Cl–SO4, and Ca–SO4 compositions as well as the Br/Cl, 87Sr/86Sr, and δ11B values of the saline water suggest dissolution of Lower Jurassic carbonates and evaporite rocks in the High Atlas Mountain catchment. Storage and evaporation of the imported water in a man-made open reservoir causes an enrichment of the stable isotope ratios with a δ18O/δ2H slope of <8 but no change in the Sr and B isotope fingerprints. Downstream from the reservoir, large salinity variations were documented in the shallow groundwater from the six Drâa oases, with systematically higher salinity in the three southern oases, up to 12,000mg/L. The increase of the salinity is systematically associated with a decrease of the Br/Cl ratio, indicating that the main mechanism of groundwater salinization in the shallow aquifers in the Drâa oases is via salt dissolution (gypsum, halite) in the unsaturated zone. Investigation of shallow groundwater that flows to the northern Drâa oases revealed lower salinity (TDS of 500–4225) water that is characterized by depleted 18O and 2H (as low as −9‰ and −66‰, respectively) and higher 87Sr/86Sr ratios (∼0.7107–0.7115) relative to irrigation water and groundwater flow from the Upper Drâa Basin. This newly-discovered low-saline groundwater with a different isotopic imprint flows from the northeastern Anti-Atlas Jabel Saghro Mountains to the northern oases of the Lower Drâa Basin. This adjacent subsurface flow results in a wide range of Sr isotope ratios in the shallow oases groundwater (0.7084–0.7131) and appears to mitigate salinization in the three northern Drâa oases. In contrast, in the southern oases, the higher salinity suggests that this mitigation is not as affective and increasing salinization through cycles of water irrigation and salt dissolution appears inevitable.

Aquaculture of Marine Fish in Inland Low Salinity Well Water: Potassium Is Not the Only Limiting Element

Inland saline groundwater is abundant in various areas of the world but is not suitable for traditional agriculture irrigation and is also not suitable for marine aquaculture mainly because of potassium deficiencies. In the present work, we used marbled spinefoot rabbitfish Siganus rivulatus, as a model organism to investigate whether varying levels of aqueous K+ affect survival and growth, and whether ambient K+ has an effect on fish osmoregulation and haemolymph osmolality. A ten-week growth experiment was conducted where fish were reared in reconstituted inland saline water containing K+ concentrations equivalent to 15%, 40% and 100% (denoted as: Trt15, Trt40, and Trt100, respectively) of potassium in 15 ppt seawater. A 15 ppt seawater treatment (CSW) was used as a control. Fish weight, length, survival, Fulton-type condition index, blood and water osmolality, and serum Na+ and K+ concentrations were evaluated. Gill NKA activity was also estimated. Fish reared in Trt15 died during week 8. At the end of the experiment (week 10), no differences were observed in fish survival and total length among treatments Trt40 and Trt100 and control (P>0.05). Final weight was less in Trt40 and Trt100 than in CSW. Fulton-type condition index results showed that Trt100 was more suitable for fish than Trt40, but still not as suitable as 15 ppt sea water. Sodium (Na+) in serum was not affected by aqueous K+ levels, whereas serum K+ varied congruently with aqueous K+. Rabbitfish reared in Trt40 and Trt100 had greater blood osmolality than those reared in control seawater. Gill NKA activity also increased by 50% in Trt40 and Trt100 as compared to control. The present study shows that potassium-deficient 15 ppt inland well water is not suitable for long-term culture of Siganus rivulatus. Results suggest that inland saline well waters greatly increase activity of NKA and consequently energy expenditure. Furthermore, K+ does not appear to be the only limiting mineral in inland low salinity groundwater that affects fish osmoregulation.

Integrated culture of white shrimp (Litopenaeus vannamei) and tomato (Lycopersicon esculentum Mill) with low salinity groundwater: Management and production

The optimal utilization of water in arid and semi-arid regions is pivotal for resource sustainability. The integration of aquaculture with traditional agriculture may be a solution to achieve more efficient water use, maximizing farm production without increasing water consumption, avoiding disposition of aquaculture effluents and supplementing additional fertilizer to the agricultural crop. The objective of this study was to test the feasibility of an integrated shrimp (Litopenaeus vannamei) -tomato (Lycopersicon esculentum Mill) culture and evaluating the effects of the irrigation with shrimp farm effluent on tomato yield and to describe shrimp production. A field experiment was carried out in a randomized complete block design to evaluate the effects of three different water types on the growth of tomatoes: effluent water from shrimp culture tanks, nutritive solution prepared for tomatoes, and water directly from the well. Groundwater (0.65gL−1 of salinity) supplemented with KCl and MgNO3 was used with a shrimp stocking density of 50 postlarvae shrimp per m2. Evaluations for shrimp (mean weight, growth rate, survival and yield) and for tomato plants (fruit number, mean fruit weight and yield) were performed. Daily monitoring included temperature, conductivity, pH and dissolved oxygen in shrimp tank waters. Chemical analysis in a weekly monitoring included major ions and nutrients. The shrimp yield was 11.1±0.2kg per tank (3.9±2.0tha−1) with a mean survival of 56.3±1.1%, a mean weight of 13.9±0.4g, and a feed conversion rate of 1.60±0.03. The yield of tomatoes irrigated with shrimp effluent (33.3±2.1kg per 45 plants) was comparable to those irrigated with nutritive solution (35.7±1.7kg), and significantly (P<0.05) higher than those irrigated with groundwater (25.5±2.4kg). The budget evidenced that most of the N (43.6%) and P (99.4%) entered to the shrimp–tomato system as shrimp food. Within the system, 13.2% and 2.1% of the input N were converted to harvested shrimp and tomato plants; similarly, 8.9% and 4.3% of the input P, were converted to harvested shrimp and tomato plants. From this work, it is demonstrated that the shrimp–tomato culture system is feasible, with a water consumption rate of 2.1m3 per kg of harvested products. However, more research is needed to adjust the shrimp–tomato culture system in regards to the precise integration of the number of tomato plants per shrimp culture area and to optimize the composition of water used in terms of the major ions (concentration and ratio) and salinity.