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Introduction: Salinity of water and soil resources is one of the most basic agricultural problems, especially in arid and semi-arid regions. Identifying and domesticating salinity-resistant plant (halophytes) species with economic value is an important strategy for these regions. Materials and methods: This research aimed to investigate the amount of elements and the quality of fodder in several Salicornia species under the influence of water salinity in a factorial experiment with a completely randomized design in pot culture conditions in Bojnourd (North Khorasan province) in 2018. Irrigation treatment was applied at two levels (brackish water and normal water), and Salicornia species treatment included four species (Salicornia persica, S. sinus persica, S. europaea, and S. bigelovii) and Salicornia var Markazi. The source of salty water was the Kal-Shoor river in Esfrain and the source of normal water was the well located in Research and Education of Agriculture and Natural Resurces Center in Bojnourd. Due to the high salinity of Kal-Shoor river, normal water was used to adjust the salinity to the treatment limit of 45 dSm-1. To produce seedlings, Salicornia seeds were planted in plastic combs for seedling production in April 2018. After 60 days, seedlings (10-15 cm) were transferred to pots. The irrigation circuit varied in different growth stages according to weather conditions, and irrigation was done by the weight method with the 80% moisture index of the pots. Results and discussion: The results showed that the amount of nitrogen, phosphorus, potassium, magnesium, sodium and chlorine increased with the increase in irrigation water salinity in all species. The highest accumulations of sodium (11%) and chlorine (23.5%) were observed in S. sinus persica and the lowest amount of sodium (8.6%) and chlorine (21%) were observed in S. persica. Among the Salicornia species, the lowest amount of elements is related to potassium and phosphorus ions, which is mostly due to the limitation of the absorption of these elements under the influence of sodium ions, and as mentioned in the sources, the process of absorption of these elements increases gradually with the growth stages. Maintaining a more negative potential of the membrane is an important factor for salinity tolerance, considering that in saline soils, chlorine and sodium are the most common solutes, the absorption of sodium and chlorine ions is important for regulating osmotic pressure and cytoplasmic concentration. In this experiment, in both irrigation treatments, the most elements in all species were related to chlorine and sodium ions. Based on the measurement of quality variables of fodder, the percentages of protein, crude fat, and ash in salty water treatment were higher than those in normal water. The highest percentage of crude fat (1.32%) in S. var. Markazi was affected by saltwater treatment, which was significantly different from the other species. The highest percentages of protein in S. bigelovii and S. europaea under the influence of saltwater treatment were 6.06% and 6.31%, respectively, which were significantly different from the other species. The highest amounts of ash belonged to S. europaea (63%) and S. bigelovii (62%) in saltwater treatment, and S. sinus persica contained the least ash (49%) in normal water treatment. Although the increase in protein increases the quality of fodder, the increase in the amount of ash and crude fat causes limitations in animal nutrition and digestibility. Therefore, the increase of water salinity has a negative effect on the quality of fodder. Conclusion: Brackish water treatment increased the amount of ash in all species to different proportions, which is a limiting factor for the pure consumption of salicornia in animal feed. Therefore, the relative reduction of water salinity and the selection of suitable species are effective in increasing the quality of fodder.On the other hand, the great ability of Salicornia species to absorb and store salts in their aerial parts provides the basis for the exploitation of their vegetative organs for the production of vegetable salt. Moreover, it is economically important along with other applications of Salicornia (production of fodder, oil, medicines, and protection). [ABSTRACT FROM AUTHOR]

Human activities are not only increasing salinization of rivers, they might also be altering the temporal dynamics of salinity. Here, we assess the effect of human activities on the temporal dynamics of electrical conductivity (EC) in 91 Spanish rivers using daily measures of EC from 2007 to 2011. We expected rivers weakly affected by human activities to have low and constant ECs, whereas rivers strongly affected by human activities should have high and variable ECs throughout the year. We collected information on land use, climate, and geology that could explain the spatiotemporal variation in EC. We identified four groups of rivers with differences in EC trends that covered a gradient of anthropogenic pressure. According to Random Forest analysis, temporal EC patterns were mainly driven by agriculture, but de-icing roads, mining, and wastewater discharges were also important to some extent. Linear regressions showed a moderate relationship between EC variability and precipitation, and a weak relationship to geology. Overall, our results show strong evidence that human activities disrupt the temporal dynamics of EC. This could have strong effects on aquatic biodiversity (e.g., aquatic organisms might not adapt to frequent and unpredictable salinity peaks) and should be incorporated into monitoring and management plans. [ABSTRACT FROM AUTHOR]

Simple Summary: Climate-related salinization of inland waters is observed in many regions of the world as a major environmental problem affecting natural processes in aquatic ecosystems. In order to better predict and control these changes, it is important to study the responses of aquatic fauna to increasing salinity. Macrozoobenthic fauna, which includes mollusks, small crustaceans, and insect larvae, constitutes the main food base for fish and water birds. Due to their relatively short life cycles, large species diversity, and high abundance, macrozoobenthos are the best indicators of changing water salinity. To determine the species richness, distribution, and salinity tolerance of macrozoobenthos, we investigated 17 small rivers with different water salinity in the southern arid region of the East European Plain. The study shows that the species richness gradually decreases with an increase in water salinity in the rivers. In freshwater rivers, the macrozoobenthos fauna includes more than 100 species, whereas, in hypersaline rivers with salinity comparable to seawater, only 10 species were found. A total of 5 of the 156 invertebrate species can be used as indicators of water salinization in rivers of the arid regions of Europe. This study investigated the species composition, distribution, and salinity tolerance of macrozoobenthos in 17 small rivers in the southern arid region of the East European Plain, which are characterized by a small channel gradient, slow-flowing or stagnant water bodies, and a wide range of water salinity, varying between 0.18 and 30 g L−1. In total, 156 taxa were found, among which 66 were Diptera species. The study revealed that the formation of benthic communities in the rivers is influenced by natural factors of the catchment basins, including the flat landscape with sparsely developed relief differentiation, climate aridity, and the widespread occurrence of saline soils and groundwater, largely related to the sedimentation of the ancient Caspian Sea and modern climate changes. These conditions are favorable for the occurrence of lacustrine macrozoobenthic species in freshwater, euryhaline, and halophilic ecological groups. The investigation revealed a decrease in species richness in response to an increase in water salinity. The five identified halophilic species Tanytarsus kharaensis, Glyptotendipes salinus, Cricotopus salinophilus, Chironomus salinarius, and Palpomyia schmidti can be used as indicators of river ecosystem salinization. [ABSTRACT FROM AUTHOR]

Soil salinization is a widespread phenomenon leading to land degradation, particularly in regions with brackish inland aquaculture ponds. However, because of the high geographical and temporal fluctuation, monitoring vast areas provides substantial challenges. This study uses remote sensing data and machine learning techniques to predict soil salinity. Four linear models, namely linear regression, least absolute shrinkage and selection operator (LASSO), ridge, and elastic net regression, and three boosting algorithms, namely XGB regressor, LightGBM, and CatBoost regressor, were used to predict soil salinity. Cross-validation was performed by splitting the data into 30% for model testing and 70% for model training. Multiple metrics such as determination coefficient (R2), root mean square error (RMSE), mean square error (MSE), and mean absolute error (MAE) were used to compare the performances of these algorithms. By comparison, the CatBoost regressor model performed better than the other models in both testing (MAE = 0.42, MSE = 0.28, RMSE = 0.53, R2 = 0.92) and training (MAE = 0.49, MSE = 0.36, RMSE = 0.60, R2 = 0.90) phases. Hence, the CatBoost regressor model was recommended for monitoring soil salinity in India's massive inland aquaculture zone. [ABSTRACT FROM AUTHOR]

Freshwater salinization of rivers is occurring across the globe because of nonpoint source loading of salts from anthropogenic activities such as agriculture, urbanization, and resource extraction that accelerate weathering and release salts. Multidecadal trends in river salinity are well characterized, yet our understanding of annual regimes of salinity in rivers draining diverse central and western U.S. landscapes and their associated catchment attributes is limited. We classified annual salinity regimes in 242 stream locations through dynamic time warping and fuzzy c‐medoids clustering of salinity time series. We found two dominant regimes in salinity characterized by an annual summer–fall peak or spring decline. Using random forest regression, we found that precipitation amount, stream slope, and soil salinity were the most important predictors of salinity regime classification. Advancing our understanding of salinity regimes in rivers will improve our ability to predict and mitigate the effects of salinization in freshwater ecosystems through management interventions. [ABSTRACT FROM AUTHOR]

This study is to establish a new approach to estimate river salinity of semi‐arid agricultural watershed and identify drivers by using hydrologic modeling and machine learning. We augmented the limitations of the Soil and Water Assessment Tool (SWAT) to model salinity by coupling with eXtreme Gradient Boosting (XGBoost), a decision‐tree‐based ensemble machine learning algorithm. Streamflow, precipitation, elevation, main reach length, and dominant soil texture of the top two layers were used along with NO3, NO2, and total phosphorus (TP) output from a calibrated SWAT model are used as predictors to Total Dissolved Solids (TDS) in the XGBoost algorithm. Then, the SWAT model simulations of streamflow, NO3+NO2, and TP from 2000 to 2015 are used as inputs of the XGBoost model to predict monthly water TDS distribution along the river. The predicted river water TDS showed a higher concentration as going downstream from El Paso (inlet) through the Hudspeth canal to Fort Quitman (outlet). Finally, this study carried out cause analysis focusing on soil physical characteristics. The soil salinity level is directly affected by the soil permeability and irrigation water. As a result, the highest TDS is shown in sites with silt loam, whereas the lowest TDS was shown in sites with very cobbly soil. Silt soils can hold more water and are slower to drain than soils of a sand type. These analyses can be used to better understand the mitigation of water salinity. [ABSTRACT FROM AUTHOR]

Solute dynamics depend strongly on hydrologic flow paths and transit times within catchments. In this paper, we use a travel time tracking method to simulate stream salinity (as measured by electrical conductivity) in the Duck River catchment, NW Tasmania, Australia. The study couples storage selection function transit time modelling with two alternate approaches to model electrical conductivity (EC). The first approach assumes the catchment has a cyclic salt balance (i.e., rainfall source, stream flow sink) that is in dynamic equilibrium and evapoconcentration of salt is the only process changing concentration. The second approach assumes that the salinity of water in catchment storages is a function of water age in those stores, without explicitly simulating salt mass balance processes. The paper compares these alternate approaches in terms of EC simulation performance, simulated stream water age distributions, and simulated storage age distributions. A split sample calibration‐validation analysis was conducted using the 2008 and 2009 water years. Both EC simulation approaches reproduced stream EC variations very well under both calibration and validation. The simulations using the age‐related EC simulation approach produced less biased results and, consequently, higher model coefficient of efficiency for validation periods. This approach also produced more consistent model parameter estimates between periods. There were systematic differences in the resultant age distributions between models, particularly for the solute balance‐based simulations where parameters (catchment storage size) changed more between the two calibration periods. The effect of time varying versus static storage selection functions were compared, with clear evidence that time varying storage selection functions with parameters linked to catchment conditions (flow) are essential for adequate simulation of EC dynamics during flow events. [ABSTRACT FROM AUTHOR]

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Saltwater intrusion is a natural mixture process between watershed freshwater and seawater that frequently occurs in estuaries. Station-based monitoring of saltwater intrusion is time-consuming and labor-intensive. To enable quick monitoring of saltwater intrusion, this study developed new remote sensing algorithms for water surface salinity measurement using four decision tree-based machine learning models. These models were built based on simultaneously collected in-situ salinity data from a waterway in the Pearl River Delta and Unmanned Aerial Vehicle (UAV) hyperspectral images. A 10-fold cross-validation was applied to assess the performance of the models, with XGBoost outperforming the other three models (R 2 =0.93, RMSE = 0.88 psu). Then the developed model was employed for Sentinel-2 multispectral satellite images to invert the estuarine salinity distribution at a larger spatial scale. Results displayed the high performance of the machine learning models proposed in this study for mapping the salinity distribution in river channels, making it an efficient and practical technique for monitoring saltwater intrusion in river channels at a regional scale. [Display omitted] • We developed a ML method to predict estuary salinity from UAV data. • Model's versatility extends to large-scale monitoring with satellite images. • Feature importance enhances predictor selection, boosting model practicality. • Validation underscores high accuracy of the method in estuary salinity mapping. [ABSTRACT FROM AUTHOR]

Low-lying coastal environments are highly dynamic and sensitive to natural as well as anthropogenic perturbations. Climate change, sea level rise, storms and tsunamis are the natural phenomena that affect the deltaic coasts in Southeast Asia in general and Vietnam in particular. The effects of these phenomena can be exacerbated by human activities such as mangrove deforestation, aquaculture and infrastructure development. Conversely, the low-lying coastal areas are important in the economic development of Southeast Asian countries. In the Vietnamese Mekong Delta, coastal areas have been affected by a number of factors, such as climate change, sea level rise, aquaculture, pollution and tourism-related activities in recent decades. The present study investigated shoreline changes, expansion of aquaculture ponds, soil salinity changes and salinity intrusion in the river systems along the coastal areas of Ben Tre Province in the Vietnamese Mekong Delta between 1998 and 2020 using satellite imagery and field data. Variations in erosion and accretion were found to be not unique along the coast of Ben Tre. There was a rapid expansion of aquaculture ponds between 1998 and 2015 and a slight decline since then. Soil salinity has been increased between 1998 and 2020; it is seen from recent satellite data that soil is becoming more saline in the inland areas of Ben Tre. Saltwater intrusion into the rivers of Ben Tre is considered associated with El Niño-La Niña conditions. It is suggested that reforestation of abandoned shrimp ponds in Ben Tre by mangrove vegetation can be effective as a bioshield against coastal hazards, such as sea level rise and shoreline erosion. [ABSTRACT FROM AUTHOR]

Estuaries are dynamic environments which are driven by various natural processes like river discharge, tides, waves, influx of saline water and sediments, etc. These ecosystems are the most sensitive to sea level rise and fluctuations in river discharge associated with climate change. A direct response of sea level rise and river discharge can be observed in the water level of estuaries. However, existing models have not considered these parameters for forecasting water level. This paper focuses on developing a water level forecast model for the Chikugo River estuary in Japan using Nonlinear Autoregressive with Exogenous inputs (NARX Model). NARX neural network was used to do the one-step-ahead prediction of water level considering the various parameters that can very well be influenced by climate change: previous water level, river discharge, and salinity. Accordingly, three models were developed: (i) Model I considering previous water level; (ii) Model II additionally considering river discharge; and (iii) Model III additionally considering salinity. All the models showed appreciable performance in forecasting the water level. Model III had the best correlation with the water level with a cross-correlation value of 0.6030, while the river discharge had only a cross-correlation of 0.1113 indicating that the Chikugo River estuary is tide-dominated. The model was trained using different combinations of available data - previous water level, river discharge, and salinity. Cross-correlation results showed a better correlation between water level and salinity than various other combinations trained. Therefore, tidal intrusion influences the water level in the estuary, thereby depicting that sea level rise can affect the water level, and its influence can be well predicted by the developed model. The water level significantly affects the flora and fauna and the predictability of future estuarine floods can help in taking necessary mitigation strategies. • Water Level of Chikugo estuary forecasted using NARX model. • Analyzed the influence of previous water level, discharge and salinity. • Water level has more cross-correlation with salinity than discharge. • Forecasted the water level for various river discharge and salinity. • Model capable to analyse the influence of climate change on water level. [ABSTRACT FROM AUTHOR]

Benthic macroinvertebrate community assessments are used commonly to characterize aquatic systems and increasingly for identifying their impairment caused by myriad stressors. Yet sampling and enumeration methods vary, and research is needed to compare their abilities to detect macroinvertebrate community responses to specific water quality variables. A common assessment method, rapid bioassessment, uses subsampling procedures to identify a fixed number of individual organisms regardless of total sample abundance. In contrast, full-enumeration assessments typically allow for expanded community characterization resulting from higher numbers of identified organisms within a collected sample. Here, we compared these two sampling and enumeration methods and their abilities to detect benthic macroinvertebrate response to freshwater salinization, a common stressor of streams worldwide. We applied both methods in headwater streams along a salinity gradient within the coal-mining region of central Appalachia USA. Metrics of taxonomic richness, community composition, and trophic function differed between the methods, yet most metrics exhibiting significant response to SC for full-enumeration samples also did for rapid bioassessment samples. However, full-enumeration yielded taxonomic-based metrics consistently more responsive to the salinization gradient. Full-enumeration assessments may potentially provide more complete characterization of macroinvertebrate communities and their response to increased salinization, whereas the more cost-effective and widely employed rapid bioassessment method can detect community alterations along the full salinity gradient. These findings can inform decisions regarding such tradeoffs for assessments of freshwater salinization in headwater streams and highlight the need for similar research of sampling and enumeration methodology in other aquatic systems and for other stressors. [ABSTRACT FROM AUTHOR]

The Shapour River, with a catchment area of 4254 km2, is a major river system in southern Iran. While the upstream river flow (the upper Shapour River) is fresh, it becomes extremely salinized at the downstream confluence of the Shekastian saline tributary and the entering nearby Boushigan saline spring. Then, the river passes via the Khesht plain and finally discharges into Raeisali-Delvari storage dam which went into operation in 2009. Over the 2006–2019 period, reduced precipitation and over-utilization of freshwater resources resulted in ~ 72% streamflow reduction in the Shapour River. Due to not using the saline waters for irrigation, drinking, and industrial purposes, the ratio of saline-outflow of Shekastian tributary and Boushigan spring to fresh-outflow of upper Shapour River increased by ~ 3 times; consequently, river salinity fluctuation domain at the Khesht plain inlet dramatically increased from 2.1–4.0 dS m−1 to 3.7–26.0 dS m−1. It resulted in major economic damages to the agricultural sector of middle Shapour River. On the seasonal timescale, consecutive processes of salt accumulation during irrigation season of the Khesht plain date orchards and then salt drainage during the rainy season have adjusted salinity fluctuation domain from 3.7–26.0 dS m−1 at the plain inlet to 5.2–8.9 dS m−1 at the plain outlet. In the lower Shapour River, storage/mixing of fresh/saline inflow waters in the Raeisali-Delvari reservoir has adjusted strong river salinity fluctuation domain from 0.9–10.7 dS m−1 at the reservoir inlet to 3.6–5.5 dS m−1 at the reservoir outlet. The success of the Raeisali-Delvari reservoir for salinity adjustment is due to its suitable location on the Shapour River, by being situated downstream of all main river tributaries with natural saline/fresh sources of water. [ABSTRACT FROM AUTHOR]

Salinization of streams, rivers and other water sources threaten the civilizations, ecologies enduring constituent species that results in rendering the precious water unusable for human chores. Increase in salinity across the flow in streams and wet-lands have been mostly to raise a concern towards salt tolerance to various limits. Hence, it becomes important to monitor the acidity/alkalinity causing water parameters that can be referred to as salinity. The prime measure scale of salinity is the quality of potential-of-hydrogen (pH) present in river waters at two sample locations. Two locations that have been identified by CPCB as per the highly reported pollutants' level found, have been analysed through artificial-intelligence (AI) conjucted with Multivariate Adaptive Regression Spline (MARS). The hybrid of wavelet neuro-fuzzy inferences with that of MARS (WNF-MARS) predicted with more accuracy. Simulation of performance measures: root meant square error (RMSE); mean absolute error (MAE); goodness-of-fit (R2) together with their execution time for the three prototypes provided remarkable results. RMSE outcomes diminish on the whole on applying the training and validating data division in Wavelet conjucted MARS and WNF-MARS as compared to studying the data through MARS. Goodness-of-fit statistic analysed the concentration levels of salinity in the river at the identified sites. Thus, it is observed from this study that the pH levels provide future estimation of inapt quality of water at the source, so that it prohibits the further-decay of water consumed in the ecosystem. Thus, these predictors would be helpful towards formulation of strategies for protection of vegetation and other required purposes. [ABSTRACT FROM AUTHOR]

Phragmites australis is the dominant species in the Yellow River Delta and plays an important role in wetland ecosystems. In order to evaluate the relationship between phenotypic variation and environmental factors, explore how functional traits respond to changes in electrical conductivity and soil water content, and reveal the ecological strategies of P. australis, we investigated the ecological responses of P. australis to soil properties based on 96 plots along the coastal–inland regions in the Yellow River Delta of China. Within the range of soil water content (SWC, 9.39%–36.92%) and electrical conductivity (EC, 0.14–13.29 ms/cm), the results showed that (a) the effects of salinity were more important than the soil water content for the characterization of the morphological traits and that plant functional traits including leaf traits and stem traits responded more strongly to soil salinity than soil water content; (b) compared with morphological traits such as average height and internode number, physiological traits such as SPAD value, as well as morphological traits closely related to physiological traits such as specific leaf area and leaf thickness, showed stronger stability in response to soil water and salinity; and (c) under the condition of high electrical conductivity, P. australis improved its water acquisition ability by increasing indicators such as leaf water content and leaf thickness. In addition, with the increase in plant tolerance to stress, more resources were used to resist external stress, and the survival strategy was inclined toward the stress tolerator (S) strategy. Under low EC conditions, P. australis increased specific leaf area and leaf area for its growth in order to obtain resources rapidly, while its survival strategy gradually moved toward the competitor (C) strategy. [ABSTRACT FROM AUTHOR]

Salinity has become a major issue in most large scale irrigation schemes, assessing the extent of the spread has become daunting and laborious. Remote sensing techniques were used to map salinity and develop models for extracting and identifying salinity in soils. Sentinel-2B optical imaging satellite with 13 spectral bands and 10 m spatial resolution was used. SNAP Desktop, ERDAS Imagine, and ArcGIS 10.6 software were used as the main GIS packages for building models and running functions such as input, output, analysis, and processing. Stepwise Multiple Linear Regression (MLR) techniques were carried out for the assessment of the spatial distribution of ECe and to predict salinity level at different locations of the Kano River Irrigation Project (KRIP). Four models were developed, however, due to the lower Variance Inflation Factor (VIF), model 2 which is a combination of salinity Index and band 3 (Green band) was used in delineating the spatial extent of the salinity. Close monitoring of the salt development and application of reversal measures were recommended. [ABSTRACT FROM AUTHOR]

Regime shifts of major salinity constituents (Ca, Mg, Na, K, SO4, Cl, HCO3, and NO3) in the lower Salinas River, an agricultural ecosystem, can have major impacts on ecosystem services central to continued agricultural production in the region. Regime shifts are large, persistent, and often abrupt changes in the structure and dynamics of social-ecological systems that occur when there is a reorganization of the dominant feedbacks in the system. Monitoring information on changes in the system state, controlling variables, and feedbacks is a crucial contributor to applying sustainability and ecosystem resilience at an operational level. To better understand the factors driving salinization of the lower Salinas River on the central coast of California, we examined a 27-year record of concentrations of major salinity constituents in the river. Although limited in providing an understanding of solute flux behavior during storm events, long-term "grab sampling" datasets with accompanying stream discharges can be used to estimate the actual history of concentrations and fluxes. We developed new concentration–discharge relationships to evaluate the dynamics of chemical weathering, hydrological processes, and agricultural practices in the watershed. Examinations of long-term records of surface water and groundwater salinity are required to provide both understanding and perspective towards managing salinity in arid and semi-arid regions while also enabling determination of the influence of external climatic variability and internal drivers in the system. We found that rock weathering is the main source of Ca, Mg, Na, HCO3, and SO4 in the river that further enables ion exchange between Ca, Mg, and Na. River concentrations of K, NO3, and Cl were associated with human activities while agricultural practices were the major source of K and NO3. A more direct anthropogenic positive trend in NO3 that has persisted since the mid-1990s is associated with the lag or memory effects of field cropping and use of flood irrigation. Event to inter-year scale patterns in the lower Salinas River salinity are further controlled by antecedent hydrologic conditions. This study underscores the importance of obtaining long-term monitoring records towards understanding watershed changes-of-state and time constants on the range of driving processes. [ABSTRACT FROM AUTHOR]

Human-induced (i.e., secondary) salinization affects aquatic biodiversity and ecosystem functioning worldwide. While agriculture or resource extraction are the main drivers of secondary salinization in arid and semi-arid regions of the world, the application of deicing road salt in winter can be an important source of salts entering freshwaters in cold regions. Alpine rivers are probably affected by salinization, especially in highly populated mountain regions, although this remains to be explored. In this study, we analyzed multi-year conductance time series from four rivers in the European Alps and demonstrated that the application of deicing road salt is linked to peaking rivers' salinity levels during late winter/early spring. Especially in small catchments with more urban surfaces close to the rivers, conductance increased during constant low-flow periods in late winter and was less correlated with discharge than in summer. Thus, our results suggest that small rivers highly connected to urban infrastructures are prone to considerable salinity peaks during late winter/early spring. Given the low natural level of salinities in Alpine rivers, the aquatic biodiversity might be significantly affected by the recorded changes in conductance, with potential consequences on ecosystem functioning. Thereby, we urge the research community to assess the impact of secondary salinization in Alpine rivers and call for an implementation of management practices to prevent the degradation of these pristine and valuable ecosystems. [ABSTRACT FROM AUTHOR]

As the largest hydropower project in China, the impact of the Three Gorges Project (TGP) on the ecological environment has aroused public attention and has been studied from various aspects. After the TGP was operated, seasonably adjusted runof f by the Three Gorge Reservoir (TGR) might cause great changes of hydrological regime in the lower reaches of the Yangtze River, especially the estuarine areas where seawater intrusion is strong and salt-water environment is complicated. The salt-water dynamics in this region will be greatly influenced in response to the operation of TGP. In order to study the impact of the project on salt -water dynamics and soil salinity, a field experiment has been carried out in the Yangtze River Estuary (YRE). This paper seeks to investigate the influence of the TGR on salt-water dynamics and soil salinity in YRE through the analysis of the relationship between the impact factors of salt - water dynamics in the estuary area. Results showed that the estuarine runoff was closely related to the impoundment process, and the estuarine runoff was one of the most important factors that influenced salinity dynamics of water and soil in the estuary. Results showed that discharge of the TGR was affected by its water storage speed, and runoff at Datong station in the estuary was significantly correlated with the reservoir discharge. The reservoir discharge affected Datong runoff and the lag time of influence of the TGR on Datong discharge is about 8 to 9 days. Runoff at Datong station influenced the river water level in the estuary, and impact of the river runoff on the river water level was delayed around 13 days. The lag time of the influence of the impoundment process of the TGR on the estuarine water level is about 20 days. The discharge decrease of the reservoir reached 3600 m3/s during the impoundment period in 2011, and it would cause about 3500 m3/s flow decline at Datong station with 8 days lag. It will result in 15.6 cm drop in the water level and 4.26 mS/cm increase in river water electrical conductivity (EC) in the estuary, which indicated the increase risk of seawater intrusion intensity in the estuary. Significantly positive correlation between river water salinity and ground-water salinity was also observed, and influence of the river water salinity on groundwater salinity increased gradually from the river bank to the inland. Significant correlation existed between groundwater salinity and soil salinity in different soil layers, with the closest relation in the deep layers. Monitoring results showed that salinity of river water, groundwater and soil under impoundment process performed higher than that of non-impoundment process, and it could be inferred that the impoundment process has a certain impact on the salt-water dynamics and soil salinity in the estuary. In summary, soil and groundwater salinity were affected by the TGR, and risk of soil salinization increased. [ABSTRACT FROM AUTHOR]

Water salinity is a complex issue in coastal and estuarine areas. Currently, remote sensing techniques have been widely used to monitor water quality changes, ranging from river to oceans. The salinity of Karun River has been increasing due to some critical factors, therefore, This study aimed at building regression models to ascertain the water salinity through the relationship between the reflectance of the Landsat-8 OLI and In situ measurements. A total of 102 observed samples were divided into 70% training and 30% test from June 2013 to July 2018 along the Karun River. Spectral signature analysis showed that band 1 - Coastal/Aerosol (0.433–0.453 μm), band 2 - Blue (0.450–0.515 μm) and band 3 - Green (0.525–0.600 μm) are sensitive to salinity. Furthermore, to have a comprehensive investigation, the Support Vector Regression (SVR) method was applied. The outcomes related to the quality of the SVR depend on several factors e.g. proper setting of the SVR meta-parameters, therefore, to deal with this issue Genetic Algorithm (GA) was applied. The SVR model resulted in values of R2 and RMSE for test data which are respectively obtained to be 0.7 and 390 μs cm−1. Eventually, Karun water salinity maps were prepared by SVR method to demonstrate the Karun water salinity on 1 February 2015 and 5 September 2018. [ABSTRACT FROM AUTHOR]

Traditional monitoring methods often ignore the vegetation information, which has significantly indirect influence on the process of soil salinization. In this study, the vegetation indices-salinity indices (VI-SI) feature space was utilized to improve the inversion accuracy of soil salinity, while considering the bare soil and vegetation information. By fully considering the surface vegetation landscape in the Yellow River Delta, twelve VI-SI feature spaces were constructed, and two categories of soil salinization monitoring index were established. The experiment results showed that remote sensing monitoring index based on MSAVI-SI1 had the highest inversion accuracy (coefficient of determination (R2) = 0.912), while that based on the ENDVI-SI4 feature space had the lowest (R2 = 0.664). Therefore, the remote sensing monitoring index derived from MSAVI-SI can greatly improve the dynamic and periodical monitoring of soil salinity in the Yellow River Delta. [ABSTRACT FROM AUTHOR]

Salinity loading in the Upper Colorado River Basin (UCRB) costs local economies upward of $300 million U.S. dollars annually. Salinity source models have generally included coarse spatial data to represent nonagriculture sources. We developed new predictive soil property and cover maps at 30‐m resolution to improve source representation in salinity modeling. Salinity loading erosion risk indices were also created based on soil properties, remotely sensed bare ground exposure, and topographic factors to examine potential surface soil erosion drivers. These new maps and data from previous SPARROW models were related to recently updated records of salinity at 309 stream gauges in the UCRB using random forest regressions. Resulting salinity yield predictions indicate more diffuse salinity sources, with slightly higher yields in more arid portions of the UCRB, and less overall load coming from irrigated agricultural sources. Model simulations still indicate irrigation to be the major human source of salinity (661,000 Mg or 12%) and also suggest that 75,000 Mg (1.4%) of annual salinity in the UCRB is coming from areas with excessive exposed bare ground in high‐elevation mountain areas. Model inputs allow for field‐scale screening of locations that could be targeted for salinity control projects. Results confirm recent studies indicating limited surface erosional influence on salinity loading in UCRB surface waters, but impacts of monsoonal runoff events are still not fully understood, particularly in drylands. The study highlights the utility of new predictive soil maps and machine learning for environmental modeling. Key Points: A flexible random forest approach for salinity yield modeling is presentedField‐scale distribution characteristics of new soil property maps were the most important catchment salinity yield predictorsNew 30‐m soil cover maps highlight areas where salinity control projects may reduce loads by 1.4% or 76,051 Mg [ABSTRACT FROM AUTHOR]

Soil salinization is one of the most damaging environmental problems in coastal areas, including Indus River Delta (IRD). Due to the reduction of flow in the Indus basin, saline water from the Arabian Sea is intruding into the IRD and has degraded the agricultural lands drastically. Focusing on the gravity of the problem, the present study was designed to explore the spatial distribution of soil salinity in the IRD. Physicochemical analysis of 375 soil samples randomly collected from 125 different locations within the study area was used. Analysis revealed that for the top 0-20cm of soil, about 66.4% of the samples had electrical conductivity (EC) values, and 72.8% sodium content (ESP) values higher than the FAO guidelines. Similarly, for soil depth of 20-40cm, 60.8% of the EC values, and 72% of ESP exceeded the safe limits. Finally, for 40-60cm of soil depth, 56.8% of the EC values and 79.2% of the ESP values were higher than the safe limits. Spatial analysis revealed that more than 50% of the IRD samples were affected by soil salinity. Reduced freshwater flow and the entry of saline water into the delta may likely be the causes of soil salinity in the IRD. [ABSTRACT FROM AUTHOR]

• Impact of floods on salinity is examined across 259 rivers and streams. • Salinity during floods varies from a 100% decrease to 34% increase relative to mean. • In 6.1% of all events, floods lead to an increase in salinity relative to mean. • Intra-site variability is controlled by short-term antecedent conditions of salinity. • Aridity and anthropogenic factors lead to varying salinity response across sites. Salinity is an important water quality parameter that affects ecosystem health and the use of freshwaters for industrial, agricultural, and other beneficial purposes. Although a number of studies have investigated the variability and trends of salinity in rivers and streams, the effects of floods on salinity across a wide range of watersheds have not been determined. Here, we examine this question by utilizing long-term observational records of daily streamflow and specific conductance (SC ; a proxy for salinity) in addition to catchment characteristics for 259 United States Geological Survey (USGS) monitoring sites in the contiguous United States spanning a wide range of climatic, geologic and hydrologic conditions. We used a combination of statistical methods, random forest machine learning models, and information-theoretic causal inference algorithms to determine the response of SC to floods and the factors that impact salinity changes within sites (intra-site variability) and across sites (inter-site variability). Our results show that changes to SC during flood events exhibited substantial variability ranging from a 100% decrease to 34% increase relative to the long-term mean. We found that dilution is the prevailing mechanism that decreases SC levels during floods for most sites, but other mechanisms caused an increase of SC for 6.1% (n = 5521) of flood events. Our analysis revealed that antecedent conditions of SC in the few days preceding the flood are the most important factor in explaining intra-site variability. The response of salinity to floods also varied considerably across sites with different characteristics, with a notable effect of urbanization in temperate climates resulting in increased dilution of SC , and mining in arid climates, which adversely increases SC levels. Overall, we find that the combined effect of aridity and anthropogenic factors is of primary importance in determining how salinity responds to floods, and it bears strongly on water quality conditions in a future world — one in which floods are expected to increase in frequency and intensity, concurrent with shifting aridity patterns and increasing urbanization. [Display omitted] [ABSTRACT FROM AUTHOR]

Mesembryanthemum crystallinum (ice plant) exhibits extreme tolerance to salt. Epidermal bladder cells ( EBCs), developing on the surface of aerial tissues and specialized in sodium sequestration and other protective functions, are critical for the plant's stress adaptation. We present the first transcriptome analysis of EBCs isolated from intact plants, to investigate cell type-specific responses during plant salt adaptation., We developed a de novo assembled, nonredundant EBC reference transcriptome. Using RNAseq, we compared the expression patterns of the EBC-specific transcriptome between control and salt-treated plants., The EBC reference transcriptome consists of 37 341 transcript-contigs, of which 7% showed significantly different expression between salt-treated and control samples. We identified significant changes in ion transport, metabolism related to energy generation and osmolyte accumulation, stress signalling, and organelle functions, as well as a number of lineage-specific genes of unknown function, in response to salt treatment., The salinity-induced EBC transcriptome includes active transcript clusters, refuting the view of EBCs as passive storage compartments in the whole-plant stress response. EBC transcriptomes, differing from those of whole plants or leaf tissue, exemplify the importance of cell type-specific resolution in understanding stress adaptive mechanisms. [ABSTRACT FROM AUTHOR]

Summary Salinization is a global threat to the quality of streams and rivers, but it can have many causes. Oil and gas development were investigated as one of several potential causes of changes in the salinity of Muddy Creek, which drains 2470 km 2 of mostly public land in Wyoming, U.S.A. Stream discharge and salinity vary with seasonal snowmelt and define a primary salinity–discharge relationship. Salinity, measured by specific conductance, increased substantially in 2009 and was 53–71% higher at low discharge and 33–34% higher at high discharge for the years 2009–2012 compared to 2005–2008. Short-term processes (e.g., flushing of efflorescent salts) cause within-year deviations from the primary relation but do not obscure the overall increase in salinity. Dissolved elements associated with increased salinity include calcium, magnesium, and sulfate, a composition that points to native soil salts derived from marine shales as a likely source. Potential causes of the salinity increase were evaluated for consistency by using measured patterns in stream chemistry, slope of the salinity–discharge relationship, and inter-annual timing of the salinity increase. Potential causes that were inconsistent with one or more of those criteria included effects from precipitation, evapotranspiration, reservoirs, grazing, irrigation return flow, groundwater discharge, discharge of energy co-produced waters, and stream habitat restoration. In contrast, surface disturbance of naturally salt-rich soil by oil and gas development activities, such as pipeline, road, and well pad construction, is a reasonable candidate for explaining the salinity increase. As development continues to expand in semiarid lands worldwide, the potential for soil disturbance to increase stream salinity should be considered, particularly where soils host substantial quantities of native salts. [ABSTRACT FROM AUTHOR]

• Baseflow salinity comes from old Cl− in KCl and perhaps legacy Cl− from road salt. • Impact of KCl on salinity is underestimated if plant K+ uptake/removal is ignored. • Over 50 percent of baseflow comes from regional groundwater based on 87Sr/86Sr data. • The remaining baseflow comes from shallow aquifers based on 36Cl/Cl and NO 3 – data. • Multiple-isotope approaches improve identification of sources of salinity. Subsurface drainage modifications are a common practice in agricultural watersheds, especially in poorly drained soils of the American Midwest, yet our understanding of their impact on baseflow generation processes is incomplete. By extension, these same practices can make baseflow vulnerable to salinization. To address these knowledge gaps, a combined geochemical and multiple isotope approach was used to identify sources of baseflow and salinity in the Wabash River, draining Indiana, Ohio, and Illinois. Anomalously high salinity and high concentrations of F−, SO 4 2−, Na+, Sr2+, and K+ were measured in baseflow along the headwaters reach of the Wabash River from Fort Recovery, OH to Huntington, IN. Three river sites in the headwaters reach have low 36Cl/Cl ranging from 27.5 (x 10−15) to 33.4 (x 10−15) that do not fall within the 36Cl/Cl range for monthly precipitation. Their 36Cl/Cl are consistent with 36Cl dilution most likely due to the presence of old Cl− found in potash (KCl) fertilizers. However, the 87Sr/86Sr ratios of the headwaters reach range from 0.708530 to 0.708904 (+/- 0.000025) and are similar to Silurian bedrock samples (0.708292 +/- 0.000047) indicating a geologic source for some solutes. The δ18O of the headwaters reach are isotopically light and similar to cold-season recharge, whereas the δ18O of the downstream river samples are similar to summer precipitation. The Cl−, NO 3 –, Cl−/Br−, and 36Cl/Cl data point to an anthropogenic source of salinity, namely KCl and road salt, whereas the F−, Sr2+, SO 4 2−, and 87Sr/86Sr data point to a geologic source of solutes. We infer that shallow groundwater that is Cl− and NO 3 – rich mixes in the river with regional groundwater that is Cl− and NO 3 – poor. The contribution of regional groundwater to baseflow in the headwaters reach is not insignificant (>58 percent) and these interactions should be considered in future hydrologic models of the Upper Wabash River. Without the aid of multiple isotopic and geochemical tracers, baseflow generation processes and sources of salinity in the headwaters reach would remain masked by the elevated solute concentrations associated with the shallow aquifers. Further research is needed to better understand the impact of KCl fertilizers on the overall salinity budgets of agricultural watersheds. [ABSTRACT FROM AUTHOR]

Extensive field investigations allowed depiction of soil water salinity within two large representative regions of a river valley that has been irrigated for more than 120 years. The nature and severity of the salinity problem is captured by hundreds of field surveys, encompassing tens of thousands of measurements and spanning 9 years. Soil water extract salinity, averaged over all surveys and all measured locations, is 4.1 dS m-1 in the Upstream Study Region and 6.2 dS m-1 in the Downstream Study Region. Variability over the measurements is substantial, with a coefficient of variation of approximately 0.51 Upstream and 0.39 Downstream. Relationships to soil and groundwater conditions also were explored, providing field-based insights into major contributing factors and into the value of measuring those factors as part of a salinity reconnaissance. A broad survey, like that described herein, affords a sense of the magnitude of economic loss, in terms of crop-yield reduction, that is exacted by irrigation-induced salinity. Evaluation of the measurements in relation to an estimated average threshold for crop-yield reduction indicates that approximately 42% of the more than 122,000 locations surveyed over both regions had ECe values exceeding the corresponding threshold. Average yield reductions due to soil water salinity are approximately 6% over surveyed locations Upstream and 17% over locations Downstream. Moreover, survey results point toward general targets for irrigation and drainage planning and form a basis for the development of more detailed solutions using computational modeling. [ABSTRACT FROM AUTHOR]

The article discusses the study which examines the soil moisture and porewater salinity dynamics that could contribute to the understanding of river, floodplain, and vadose zone hydrology of the Loxahatchee River in Florida. It implies that soil moisture is predictable on the river stage and topographic elevation, while porewater salinity rarely exceeds tolerance thresholds for bald cypress upstream and downstream areas. The study indicates that floodplain monitoring depends on vadose zone hydrology and it provides proposals for the restoration and management systems of the Loxahatchee River.

We investigated changes in the global distribution of surface-layer salinity by comparing 2003–2007 Argo-float data with annual mean climatological surface-layer salinity data for 1960–1989 from the World Ocean Database 2005. The two datasets showed similar patterns, with low values in subpolar and tropical regions and higher values in the subtropics. The recent Argo data indicate that the contrast between low and high salinity has intensified in all areas except the subpolar North Atlantic. The intensified contrast of the surface layer salinity was maintaining for 2003–2007. Using a simple method, we attempted to estimate evaporation and precipitation changes on the basis of surface-layer salinity changes. The results show a high probability that the global hydrological cycle has increased in the past 30 years. [ABSTRACT FROM AUTHOR]

Soils down slope of roads have been affected over decades by road salting in the UK uplands. Salt additions to fresh soil facilitate dispersal of organic matter so there is a potential risk of release of DON and DOC to nearby rivers where these run parallel to roads. Over time, however, salting enhances soil pH of naturally acid soils, and thus organic matter degradation through to CO2, thereby, lowering soil organic matter content. In addition any relatively labile organic matter may have already been dispersed. Thus, it is hypothesised that enhanced DOC mobilisation should only be a potential problem if soils not previously exposed to salt become heavily exposed in the future. This paper combines data from field observations and laboratory simulations to elucidate mechanisms controlling organic matter mobilisation processes to determine what controls spatial and temporal trends in DOC concentrations in soil solutions down slope of roads. Organic matter solubilisation is dependent on the degree of road salt exposure soils have had. The laboratory experiment provided evidence that there are two competing effects upon which solubilisation is dependent (a) pH suppression and (b) sodium dispersion. Other organic matter solubility models, if correct, link quite well with the authors “when it’s gone, it’s gone” hypothesis. [ABSTRACT FROM AUTHOR]

This paper investigates the link between shrimp farming development and salination processes in the coastal Cai Nuoc district of Ca Mau province, Mekong delta, Vietnam. Surface water, groundwater, and soils were sampled for four consecutive seasons (2002-2004). Salinity in the surface water (40.04-44.78 ‰) was, during the dry season, higher than that of the oceans and remained high during the wet season (more than 8‰). Soils were highly affected by salinity (EC(1/5) 4.57 dS/m), even during the wet season (EC(1/5) 3.78-3.90 dS/m). Salinity levels in both surface water and soils were regulated by seasonal rainfall patterns. The groundwater seemed to be unaffected by shrimp farming development though its salinity level (1.04‰) was higher than the normal values acceptable for human consumption. As a result of shrimp farming development, soil and water salination is currently a serious environmental issue in the Cai Nước district. [ABSTRACT FROM AUTHOR]

Abstract  In keeping with the standard scientific methods, investigations of salinity processes focus on the collection and interpretation of contemporary scientific data. However, using multiple lines of evidence from non-hydrogeologic sources such as geomorphic, archaeological and historical records can substantially add value to the scientific investigations. By using such evidence, the validity of the assumptions about salinity processes in Australian landscapes is challenged, especially the assumption that the clearing of native vegetation has resulted in rising saline groundwater in all landscapes. In the Corangamite region of south-west Victoria, salinity has been an episodic feature of the landscapes throughout the Quaternary and was present at the time of the Aboriginal inhabitants and the first pastoral settlement by Europeans. Although surface-water salinity has increased in some waterways and the area of salinised land has expanded in some landscapes, there is no recorded evidence found which supports significant rises in groundwater following widespread land-use change. In many areas, salinity is an inherent component of the region’s landscapes, and sustains world-class environmental assets that require appropriate salinity levels for their ecological health. Managing salinity requires understanding the specific salinity processes in each landscape. [ABSTRACT FROM AUTHOR]

Catch per unit effort (CPUE) of estuarine push net (EPN) and abundance of Acetes shrimps in the coastal waters of Klebang Besar, Malacca were investigated based on the catch data from April 2006 to March 2007. The average monthly CPUE of the EPN observed was 3.53 (± 3.99) kg/fisherman/hour. The total catch comprised of three major categories namely: Acetes shrimps (90%), fish juveniles (9%) and other shrimps (1%). Amongst the Acetes shrimps, three species (A. indicus, 87%, A. japonicus, 12% and A. intermedius, 1%) were recorded from the investigated area. The peak catches were observed during the months of September, November and December. There was no significant correlation (p > 0.05) between monthly catches and environmental parameters (temperature, dissolved oxygen, salinity and pH). [ABSTRACT FROM AUTHOR]

This study aimed at evaluating the ploidy effects on growth performances of Chinese shrimp ( Fenneropenaeus chinensis Osbeck, 1765) reared in different salinities under laboratory conditions. In the acute salinity experiment, there was no difference ( P>0.05) in tolerance observed in triploid and diploid shrimp due to abrupt salinity changes. The lethal salinity for 50% of the individuals in 96 h at 23–25 °C was about 2 g L−1 in both triploids and diploids. While for the chronic salinity experiment, statistical analyses confirmed that the differences in growth performances including the specific growth rate (SGR), the feeding rate (FR), feed conversion efficiency (FCE) and intermoult period (IP) between triploid and diploid were related to salinity. Diploid shrimp reared in 20 g L−1 exhibited highest SGR ( P<0.05), while triploids performed well in 20 and 30 g L−1 salinities ( P<0.05). Based on the survival and growth data, the optimal salinity for the culture of diploid F. chinensis should be 20 g L−1 and for triploids it should be between 20 and 30 g L−1. [ABSTRACT FROM AUTHOR]

Abstract: The effect of low salinity on the survival of recently hatched veliger of the gastropod Nassarius reticulatus (L.) was studied under laboratory conditions at 17 °C±1 °C. Significant mortality occurred for salinities ≤17 psu and the LS50 (salinity that causes 50% mortality) varied from 14.5 psu to 17.2 psu for exposures between 1 h and 48 h, respectively. The results were included in a mathematical model in order to estimate the mortality of N. reticulatus veliger in Ria de Aveiro under different salinity scenarios determined by numerical simulation. The model predicts a massive mortality of veliger immediately after their eclosion (1 h) in Ria de Aveiro during spring tide when the river input reaches its expected maximum — a situation that has been observed occasionally and may overlap a massive eclosion of veliger in the water. Except in this extreme situation, the mortality in Ria de Aveiro is generally restricted to the upstream limits of the channels. The results indicate that N. reticulatus recruitment in estuaries may strongly depend on the prevailing salinity regime. [Copyright &y& Elsevier]

Abstract: Survival, haemolymph osmolality and the specific metabolic rate of the isopod Idotea chelipes from the brackish waters of the southern Baltic Sea (salinity 7 psu) were investigated after acclimation to different salinities in the range of 3–30 psu keeping other parameters constant (T =15 °C, full air saturation). Haemolymph osmolality of I. chelipes increased from 379±33 mmol kg−1 at 3 psu to 935±12 mmol kg−1 at 30 psu. In the salinity range of 3–11 psu I. chelipes exhibited a hyperosmotic pattern of haemolymph regulation, whereas from 14 to 25 it behaved like an osmoconformer. Isoosmosis occurred at 28.5 psu (920 mmol kg−1). The specific metabolic rate of I. chelipes was significantly (P <0.05) related to salinity, with maximum (2.4±0.8 J g−1 wm h−1) and minimum values (0.6±0.3 J g−1 wm h−1) at 7 and 20 psu, respectively. The changes in the specific metabolic rate and in the difference between the osmolality of haemolymph and external medium were significantly correlated for I. chelipes (P <0.05). Rates of change per salinity unit were, however, unequal varying according to salinity transition. These differences indicate that osmotic adjustment may be a more or less costly in terms of energy according to salinity. [Copyright &y& Elsevier]

Moderately saline soda lakes harbor extremely abundant and fast growing bacterial communities. An interesting phenomenon of an explosive bacterial growth in shallow soda lakes in Eastern Austria after dilution with rainwater, concomitantly with a significant decrease in temperature was observed in a former study. In the present study, we tried to identify the factors being responsible for this enhanced bacterial growth in laboratory batch cultures. Three experiments were performed with water taken from two different lakes at different seasons. Natural soda lake water was diluted with distilled water, artificial lake water, sterile filtered soda lake water, and grazer-free water to test (1) for the influence of compatible solutes released to the environment and reduced salt stress after osmotic down-shock, (2) for the influence of nutrients, which may be washed in from the dry areas of the lake bottom after rainfall and (3) for the decrease of grazing pressure due to dilution. The potential influence of (4) viruses was indirectly deduced. The response of the bacterial community to the manipulations was measured by changes in bacterial numbers, the incorporation of 3H-leucine and the concomitant determination of the amount of 3H-leucine uptaking bacteria by microautoradiography. The influence of the environmental factors enhancing bacterial growth after a simulated rainfall event showed variations between the lakes and over the seasons. The addition of nutrients was, in all experiments, the main factor triggering bacterial growth. The decrease in grazing pressure and viral lysis after dilution was of significant importance in two of three experiments. In the experiment with the highest salinity, we could show that either compatible solutes released after osmotic down-shock and used as a source of nutrients for the soda lake bacterial populations or reduced salt stress were most probably responsible for the observed marked enhancement of bacterial growth. [ABSTRACT FROM AUTHOR]

Abstract: Sediments from 28 saline and hypersaline (salinity 13.6–149.2) ponds on Christmas Island (Kiritimati), in the Central tropical Pacific Ocean, were investigated for the effect of salinity on the D/H ratios of lipid biomarkers. Hydrogen isotope ratios (expressed as δD values) of total lipid extracts, and individual hydrocarbons heptadecane, heptadecene, octadecane, octadecene, diploptene, and phytene from cyanobacteria, became increasingly enriched in deuterium as salinity increased, spanning a range of 100‰, while lake water δD values spanned a range of just 12‰. Net D/H fractionation between lipids and source water thus decreased as salinity increased. Isotope fractionation factors (α lipid–water) were strongly correlated with salinity, and increased in all compound classes studied by up to 0.0967 over a salinity range of 136. Differences in the hydrogen isotopic composition of lipids derived from three biosynthetic pathways (acetogenic, mevalonate, and non-mevalonate) remained similar irrespective of the salinity. This suggests that the mechanism responsible for the observed α lipid–water–salinity relationship originates prior to the last common biosynthetic branching point, the Calvin Cycle. We propose that a decrease in the exchange of intra- and extra-cellular (ambient) water resulting from down-regulation or closure of water channels (aquaporins) within cyanobacterial cell membranes, and subsequent isotopic enrichment of the intracellular water, likely resulting from metabolic reactions. These findings imply that caution must be exercised when attempting to reconstruct source water δD values using lipid δD values from environments that may have experienced salinity variations. On the other, hand our results can be used to establish a paleo-salinity proxy based on lipid δD, if additional constraints on source water δD values can be made. [Copyright &y& Elsevier]

The very salty water of the lakes from the studied areas, associated with the reduced capacities of basins and a change of water rather absent, is characterized by a specific variation in time and space of the physical and chemical parameters. In this study we appealed to selective analysis of the most representative parameters (salinity and temperature), which provide jarring feature in analogy with other lakes. No doubt, the variation of salinity establishes various forms of anomaly in the running of all physical and chemical parameters, generating spectacular vertical modifications (heliothermy, transition from acid ph to basic, high reduction of oxygen to the depth associated with the growth of the quantity of H2S etc.). The stimulation of an intense dynamics of water in the superficial strata the through or local contribution of fresh water comes to complicate even more the distribution on time and space of the salinity and temperature. [ABSTRACT FROM AUTHOR]

Abstract: Sea surface salinity (SSS) data in the Atlantic Ocean is investigated between 50°N and 30°S based on data collected mostly during the period 1977–2002. Monthly mapping of SSS is done to extract the large-scale variability. This mapped variability indicates fairly long (seasonal) time scales outside the equatorial region. The spatial scales of the seasonal anomalies are regional, but not basin-wide (typically 500–1000km). These seasonal SSS anomalies are found to respond with a 1–2 month lag to freshwater flux anomalies at the air–sea interface or to the horizontal Ekman advection. This relation presents a seasonal cycle in the northern subtropics and north-east Atlantic indicating that the late-boreal spring/summer season is less active than the boreal winter/early-spring season in forcing the seasonal SSS variability. In the north-eastern mid-latitude Atlantic, SSS is positively correlated to SST, with SSS slightly lagging SST. There are noticeable long-lasting larger-scale signals overlaid on this regional variability. Part of it is related to known climate signals, for example ENSO and NAO. A linear trend is present during the first half of the period in some parts of the basin (usually towards increasing salinities, at least between 20°N and 45°N). Based on a linear regression analysis, these signals combined can locally represent up to 20% of SSS variance (in particular near 30°N/60°W or 40°N/10–30°W), but usually represent less than 10% of the variance. [Copyright &y& Elsevier]

The numerical simulation of long-term large-scale (field to regional) variably saturated subsurface flow and transport remains a computational challenge, even with today's computing power. Therefore, it is appropriate to develop and use simplified models that focus on the main processes operating at the pertinent time and space scales, as long as the error introduced by the simpler model is small relative to the uncertainties associated with the spatial and temporal variation of boundary conditions and parameter values. This study investigates the effects of various model simplifications on the prediction of long-term soil salinity and salt transport in irrigated soils. Average root-zone salinity and cumulative annual drainage salt load were predicted for a 10-year period using a one-dimensional numerical flow and transport model (i.e. UNSATCHEM) that accounts for solute advection, dispersion and diffusion, and complex salt chemistry. The model uses daily values for rainfall, irrigation, and potential evapotranspiration rates. Model simulations consist of benchmark scenarios for different hypothetical cases that include shallow and deep water tables, different leaching fractions and soil gypsum content, and shallow groundwater salinity, with and without soil chemical reactions. These hypothetical benchmark simulations are compared with the results of various model simplifications that considered (i) annual average boundary conditions, (ii) coarser spatial discretization, and (iii) reducing the complexity of the salt-soil reaction system. Based on the 10-year simulation results, we conclude that salt transport modelling does not require daily boundary conditions, a fine spatial resolution, or complex salt chemistry. Instead, if the focus is on long-term salinity, then a simplified modelling approach can be used, using annually averaged boundary conditions, a coarse spatial discretization, and inclusion of soil chemistry that only accounts for cation exchange and gypsum dissolution–precipitation. We also demonstrate that prediction errors due to these model simplifications may be small, when compared with effects of parameter uncertainty on model predictions. The proposed model simpliflcations lead to larger time steps and reduced computer simulation times by a factor of 1000. [ABSTRACT FROM AUTHOR]

1. The influence of salinity, temperature and physiological development on habitat choice by juvenile salmon is poorly understood. We measured differences in the net energetic cost of habitats that differed in salinity or temperature using behavioural titration of juvenile salmon and correlated these costs with body size and osmoregulatory enzyme activity to quantify how costs change with physiological development. 2. Juvenile salmon showed a strong preference for saline water (27 or 15 vs 0) and for cold water (9 °C vs 14 °C). It was estimated to be 0·15 W and 0·11 W more costly for salmon to forage in fresh water than in 15 and 27 salt water, respectively, and 0·09 W more costly to forage in warm than in cold water. 3. We expected fish to prefer 15 salt water to fresh water regardless of enzyme activity because they are iso-osmotic with this salt concentration. In contrast, preference for higher salt concentrations should increase with enzyme activity. Consistent with our expectations, enzyme activity was not correlated with preference for 15 salt water, but was positively correlated with preference for 27 salt water. 4. The cost of changing salinity vs changing temperature were very similar, indicating that knowledge of both of these costs are necessary to understand juvenile salmon habitat choice. [ABSTRACT FROM AUTHOR]

Abstract: Low salinity (<35) surface waters (LSSW) at the southern entrance to the western English Channel (48.5°N, 5.1°W, near Ushant) were observed in late winter (March–April) in three successive years (2002–04) during near continuous ship of opportunity operations. The source of the LSSW is the northward spreading plumes from the Loire (47.5°N, 2.5°W) and Gironde (45.6°N, 1.2°W) along the French Atlantic coast. Fastest plume travel times were associated with northeasterly winds, consistent with Ekman theory. Differences between years in the mean winter (January–March) combined river discharges (D) was consistent with the minimum salinities (S min) of the LSSW (2004: D=4211m3 s−1, S min=33.68; 2003: D=3630m3 s−1, S min=33.90; 2002: D=1579m3 s−1, S min=34.53). Winter mean (1905–74) salinity is otherwise 35.33 near Ushant. The LSSW intruded into the western English Channel in each year, suggesting a common phenomenon. The low salinity intrusion was freshest (mean=35.11±0.21) and most penetrative (reaching 50.7°N, 1.0°W by the end of the year) in 2003 on account of (1) entering on a spring tide giving greater tidal excursion into the western English Channel and (2) intrusion favourable winds (southwesterly/southeasterly) acting on the longer term residual flow. Less penetration occurred in 2004 when the arrival of the LSSW coincided with a neap tide followed by intrusion-resistant northwesterly winds, resulting in a less saline (mean=35.20±0.23) intrusion. In 2004, transport tended to be offshore to at least 100km from the French Atlantic coast (47°N, 4.8°W–48°N, 4.7°W). In 2002, the lower volume of plume water relative to the other years produced a more saline intrusion (mean=35.25±0.12). Prevailing westerly winds may have pushed this intrusion northwards beyond the route of the ferry, making it difficult to assess the true extent of the intrusion in 2002. A link of the LSSW to phases of the winter North Atlantic Oscillation index from a literature search of the last 84 years was inconclusive. [Copyright &y& Elsevier]

The ability to predict stream alkalinity values over timescales shorter than monthly or annually is needed to understand the response of stream chemistry to acidic inputs which occur across short time scales (days). We develop and apply a coupled series of physically-based models which are able to predict daily stream alkalinity values by first calculating soil air CO2 concentrations. We apply the model to a 9 year record of discharge and stream chemistry from a small catchment in the Shenandoah National park of Virginia. We find that we are able to accurately predict the minimum daily stream alkalinity values for all years and we are able to accurately predict the entire annual cycle for 6 of the 9 years (Nash–Sutcliffe criterion equals 0.26). For the 3 years which we overpredict summer stream alkalinity, summer precipitation was greater than normal and much greater than the period for which the model was calibrated. [ABSTRACT FROM AUTHOR]

During the latest years medium-sized (15–30 μm), single-celled dinoflagellates have been reported to form blooms in the northern Baltic Proper and the Gulf of Finland in winter and spring. Recent studies (Kremp et al., . Proceedings of the 7th International conference of Modern and Fossil Dinoflagellates, September 21–25, Nagasaki, Japan, 66 pp.) indicate that those blooms are caused by two isomorphic species – Scrippsiella hangoei (Schiller) Larsen, and a new species, tentatively belonging to the genus Woloszynskia. Until now there has been no report on how widely distributed these phytoplankton species are in the Baltic Sea. In this study, the occurrence of Scrippsiella/Woloszynskia complex in the entire Baltic Sea was investigated, by using monitoring data from 1997 to 2003. The species occurred in a salinity range from 2 to 8 PSU. Highest concentrations were observed at salinity 4.5–6.5 PSU. Maximum cell densities of Scrippsiella/Woloszynskia complex in the water column were mainly obtained in April or in the beginning of May by the water temperature <3 °C prior to stratification was formed. In the central Gulf of Finland, the second maximum was found in 1999 and 2002 by the temperature >6 °C. Bloom formations in the Baltic Proper and in the Gulf of Finland may not only be explained by optimum temperature and salinity, but also with other factors e.g. high nutrient concentrations and good seeding conditions from the sediments. [ABSTRACT FROM AUTHOR]

Soil salt-water dynamics in the Yangtze River Estuary (YRE) is complex and soil salinity is an obstacle to regional agricultural production and the ecological environment in the YRE. Runoff into the sea is reduced during the impoundment period as the result of the water-storing process of the Three Gorges Reservoir (TGR) in the upper reaches of the Yangtze River, which causes serious seawater intrusion. Soil salinity is a problem due to shallow and saline groundwater under serious seawater intrusion in the YRE. In this research, we focused on the temporal variation and spatial distribution characteristics of soil salinity in the YRE using geostatistics combined with proximally sensed information obtained by an electromagnetic induction (EM) survey method in typical years under the impoundment of the TGR. The EM survey with proximal sensing method was applied to perform soil salinity survey in field in the Yangtze River Estuary, allowing quick determination and quantitative assessment of spatial and temporal variation of soil salinity from 2006 to 2017. We developed regional soil salinity survey and mapping by coupling limited laboratory data with proximal sensed data obtained from EM. We interpreted the soil electrical conductivity by constructing a linear model between the apparent electrical conductivity data measured by an EM 38 device and the soil electrical conductivity (EC) of soil samples measured in laboratory. Then, soil electrical conductivity was converted to soil salt content (soil salinity g kg−1) through established linear regression model based on the laboratory data of soil salinity and soil EC. Semivariograms of regional soil salinity in the survey years were fitted and ordinary kriging interpolation was applied in interpolation and mapping of regional soil salinity. The cross-validation results showed that the prediction results were acceptable. The soil salinity distribution under different survey years was presented and the area of salt affected soil was calculated using geostatistics method. The results of spatial distribution of soil salinity showed that soil salinity near the riverbanks and coastlines was higher than that of inland. The spatial distribution of groundwater depth and salinity revealed that shallow groundwater and high groundwater salinity influenced the spatial distribution characteristics of soil salinity. Under long-term impoundment of the Three Gorges Reservoir, the variation of soil salinity in different hydrological years was analyzed. Results showed that the area affected by soil salinity gradually increased in different hydrological year types under the impoundment of the TGR. [ABSTRACT FROM AUTHOR]