High Salinity Areas Research Articles

Harmful Microalgae Exhibit Broad Environmental Adaptability in High-Salinity Area Across the Dafengjiang River Estuary.

Harmful algal blooms (HABs) often occur in estuaries due to their unique environmental heterogeneity, posing significant environmental and human health risks. However, there is limited understanding of the community composition and community-level change points (thresholds) of harmful microalgae in subtropical estuaries. This study explored harmful microalgae community structure and thresholds in the Dafengjiang River estuary using a metabarcoding approach. The results revealed 63 harmful microalgae species, and major species included Guinardia flaccida, Prorocentrum cordatum, Thalassiosira punctigera, Pseudo-nitzschia galaxiae and T. gravida. Nonparametric change-point analysis and threshold indicator taxa analysis (TITAN) showed threshold responses of harmful microalgae community structure to ammonium (57.5-60 μg·L-1), total phosphorus (27.8-28.5 μg·L-1) and dissolved inorganic phosphorus (14.5-28 μg·L-1) along the salinity gradient. Wider environmental thresholds were also found in hypersaline areas. Additionally, Pyrodinium bahamense, Pfiesteria piscicida, Skeletonema tropicum and T. punctigera were sensitive to environmental changes and thus could be used as bioindicators. Overall, our study unveiled diverse abrupt transitions of harmful microalgal communities, providing a risk assessment for human health and ecological safety in subtropical estuary ecosystems.

Tracking the invasive and euryhaline pikeperch Sander lucioperca in the lower River Thames using acoustic telemetry indicates no movements into areas of relatively high salinity.

Native to Central and Eastern Europe, the euryhaline pikeperch Sander lucioperca can acclimatize to elevated salinity levels (e.g., up to 30‰), but it remains unknown whether their invasive populations use this ability to inhabit and/or disperse through brackish waters, such as estuaries and inshore areas. To test whether invasive pikeperch show a propensity to move into areas of relatively high salinity, their spatial use and movement patterns (e.g., home range, distances moved, and movement rates) were assessed using acoustic telemetry in the upper River Thames estuary, southeast England. Analyses revealed that individual pikeperch were capable of moving relatively long distances in a short time (e.g., speeds up to 70 m min-1), with movement patterns associated more with tidal state and elevation at the water surface (both assumed to relate to changes in salinity) than diurnal changes. There were no recorded movements of any pikeperch into the more saline, downstream waters of the estuary where salinity levels were recorded to over 40‰, with the mean salinity in the most downstream area where pikeperch were detected being 1.39‰ (range of logger: 1.22-1.71). The results suggest that these pikeperch did not use high salinity waters when less saline waters were available, and thus the risk that they will use to move through high salinity areas to expand their invasive range appears low. Accordingly, efforts to minimize risks of the further dispersal of invasive pikeperch populations can focus on control and containment programmes within fresh waters.

Spatial Prediction and Influencing Factors Analysis of Soil Salinization in Coastal Area Based on MGWR

Quantitative analysis of the spatial non-stationary characteristics of soil salinization influencing factors and the prediction of its spatial distribution are of great significance for the rational use of coastal saline soil resources and the formulation of local prevention and control measures. In this study, the Hekou District of Dongying City, Shandong Province, was used as the study area, and the descriptive statistics of soil salinization status were conducted using classical statistical methods. Spatial autocorrelation theory was used to explore the characteristics of global and local spatial structure of soil salinization in the study area. Influential factors related to soil salinity were selected, and multivariate linear regression （MLR）, geographically weighted regression （GWR）, and multi-scale geographically weighted regression （MGWR） methods were used to model and predict the spatial distribution of soil salinity in the study area and to analyze the spatial heterogeneity of the effects of different influencing factors on soil salinity. The results showed that： ① The mean value of soil salinity in the study area was 5.84 g·kg-1, indicating severe salinization, with a global Moran's I index of 0.19 （P<0.00） and obvious spatial aggregation characteristics. ② Among the three models, the MGWR model had the highest modeling accuracy. Compared with that of the MLR model, the Radj2 of GWR and MGWR improved by 0.05 and 0.07, respectively, and the RSS decreased by 210.13 and 179.95, respectively. ③ The results of MGWR regression showed that the spatial distribution of soil salinity appeared to be mainly affected by the middle soil salinity, soil clay content, and vegetation cover from the mean values of standardized regression coefficients of different influencing factors. Different influencing factors had significant spatial non-stationary characteristics on soil salinization. ④ The results of the spatial distribution prediction of soil salinity in MGWR showed that the areas of high soil salinity （≥6 g·kg-1） were mainly distributed in the northern part of the study area, with an overall spatial trend of decreasing from the coast to the interior. The results of the study can be used as a reference for the analysis and predictive mapping of factors affecting soil salinization in the county and on a larger scale using MGWR.

Effects of N application methods on cotton yield and fertilizer N recovery efficiency in salinity fields with drip irrigation under mulch film using 15N tracing technique.

Drip irrigation under mulch film promotes a non-uniform salinity distribution in salt fields. The effect of different N application methods on the growth and yield of cotton under drip irrigation under mulch film conditions in eastern coastal saline-alkaline soils in China remain remained unclear. A randomized complete block design was used in the experiment. Three N application methods were assigned: N applied under mulch film (low-salinity area; UM), N applied between mulch films (high-salinity area; BM), and half N applied under mulch film and half between mulch films (HUHB). Plant height, photosynthesis, Chl content, boll load, biomass, boll weight and boll density under UM were all significantly higher than those under the other two treatments. The N absorption of UM was higher than in the other two treatments, which might be attributed to the expression of GHNRT1.5 and GHNRT2.1. The net NO3- influx in the roots in UM increased significantly compared with that in BM. The yield and FNRE of UM were 3.9% and 9.1%, respectively, and were 26.52% and 90.36% higher than under HUHB and BM treatments. UM not only improved cotton yield but also alleviated the pollution of N residue on drip irrigation under mulch film conditions in salt areas.

Plant growth-promoting rhizobacteria Pseudomonas aeruginosa HG28-5 improves salt tolerance by regulating Na+/K+ homeostasis and ABA signaling pathway in tomato

Salinity stress badly restricts the growth, yield and quality of vegetable crops. Plant growth-promoting rhizobacteria (PGPR) is a friendly and effective mean to enhance plant growth and salt tolerance. However, information on the regulatory mechanism of PGPR on vegetable crops in response to salt stress is still incomplete. Here, we screened a novel salt-tolerant PGPR strain Pseudomonas aeruginosa HG28–5 by evaluating the tomatoes growth performance, chlorophyll fluorescence index, and relative electrolyte leakage (REL) under normal and salinity conditions. Results showed that HG28–5 colonization improved seedling growth parameters by increasing the plant height (23.7%), stem diameter (14.6%), fresh and dry weight in the shoot (60.3%, 91.1%) and root (70.1%, 92.5%), compared to salt-stressed plants without colonization. Likewise, HG28–5 increased levels of maximum photochemical efficiency of PSII (Fv/Fm) (99.3%), the antioxidant enzyme activities as superoxide dismutase (SOD, 85.5%), peroxidase (POD, 35.2%), catalase (CAT, 20.6%), and reduced the REL (48.2%), MDA content (41.3%) and ROS accumulation in leaves of WT tomatoes under salt stress in comparison with the plants treated with NaCl alone. Importantly, Na+ content of HG28–5 colonized salt-stressed WT plants were decreased by15.5% in the leaves and 26.6% in the roots in the corresponding non-colonized salt-stressed plants, which may be attributed to the higher K+ concentration and SOS1, SOS2, HKT1;2, NHX1 transcript levels in leaves of colonized plants under saline condition. Interestingly, increased abscisic acid (ABA) content and upregulation of ABA pathway genes (ABA synthesis-related genes NCED1, NCED2, NCED4, NECD6 and signal genes ABF4, ABI5, and AREB) were observed in HG28–5 inoculated salt-stressed WT plants. ABA-deficient mutant (not) with NCED1 deficiency abolishes the effect of HG28–5 on alleviating salt stress in tomato, as exhibited by the substantial rise of REL and ROS accumulation and sharp drop of Fv/Fm in the leaves of not mutant plants. Notably, HG28–5 colonization enhances tomatoes fruit yield by 54.9% and 52.4% under normal and saline water irrigation, respectively. Overall, our study shows that HG28–5 colonization can significantly enhance salt tolerance and improved fruit yield by a variety of plant protection mechanism, including reducing oxidative stress, regulating plant growth, Na+/K+ homeostasis and ABA signaling pathways in tomato. The findings not only deepen our understanding of PGPR regulation plant growth and salt tolerance but also allow us to apply HG28–5 as a microbial fertilizer for agricultural production in high-salinity areas.

Salinity tolerance of two critically endangered endemic species and its implications for distribution and conservation of model microinsular Mediterranean species

Medicago citrina and Euphorbia margalidiana are two microinsular species from the Western Mediterranean which are amongst the top 50 most threatened species of the Mediterranean. Conservation plans for both taxa involve translocation and ex situ seedling growth, yet salinity tolerance remains unknown for both species. The main objective of this work was to analyse how germination is modulated by salinity and to evaluate the seed buoyancy of both species to give light to their sea-dispersal capabilities. Salinity tolerance tests were performed using increasing concentrations (100, 200, 300, and 400 mM) solutions of different salts (NaCl, MgCl2, MgSO4, and Na2SO4). Recovery tests were carried out to analyse the potential ionic toxicity of salts. Seed buoyancy was also evaluated in sea and distilled water for each species. M. citrina was the most salt tolerant, germinating at values below 35.6 mS/cm, whilst E. margalidiana only germinated below 21.4 mS/cm. Na2SO4 and MgCl2 are the salts with the strongest inhibitory effect, whilst MgSO4 is the least inhibitory salt. In both species, buoyancy is very limited, being higher in M. citrina (up to 15 days) compared to E. margalidiana (4 days). The higher salinity tolerance and buoyancy allows M. citrina to colonise a broader range of islets than E. margalidiana, which requires moderate altitudes to keep populations away from salt impact. Both species cannot be considered as halophytes and so in situ and ex situ conservation measures should be carried out avoiding high salinity areas to ensure seedling development.

Seasonal and spatial variability of CO2 emissions in a large tropical mangrove‐dominated delta

AbstractThis study quantified the seasonal and spatial variability of partial pressure of CO2 (pCO2) and water‐atmosphere CO2 fluxes in the Parnaíba River Delta, the largest delta in the Americas. It is a pristine equatorial, mangrove‐dominated environment located in a transitional between humid and semi‐arid climates, with marked seasonality in rainfall and river discharge. Major channels and bays were sampled during dry and wet seasons, with continuous measurements of pCO2, temperature, salinity, and wind velocity. Subsurface water samples were collected in discrete stations for pH, total alkalinity (TA), dissolved inorganic carbon (DIC), dissolved oxygen and chlorophyll a quantification. A significant positive correlation between carbonate system parameters with salinity was found in both periods, with salinity significantly higher in the dry season. Strong deviations of pCO2, TA, and DIC from two endmembers conservative mixing were found, particularly in mangrove‐dominated waters, due to organic matter degradation. The Delta showed high spatial variability of pCO2, with the highest values in mangrove‐dominated waters, moderate in the river‐dominated regions, and lowest in the high salinity areas, suggesting that pCO2 variability is likely controlled by a combination of river‐ocean mixing and biological processes (respiration and photosynthesis). The Delta outgasses about 20 times less CO2 in the dry season (9.06 ± 11.09 mmol m−2.d−1) than in the rainy season (209.68 ± 250.87 mmol m−2 d−1). Our results indicate this large mangrove‐dominated tropical delta is an important source of CO2 to the atmosphere, but a sharp decrease was observed during dry periods.

La familia Amaranthaceae en la colección de referencia herbario de La Guajira (HG) “Wunü'ülia”, La Guajira, Colombia

Colombia is considered a country of great biological diversity, in which its wide variety of flora stands out. The department of La Guajira is located in the northernmost part of the country and has recently been highlighted by the presence of numerous initiatives aimed at characterizing its biodiversity, since much of the existing information on its vegetation cover is incipient. This means that any research on its biological richness has an impact on national biodiversity records. Amaranthaceae is a plant family with a pantropical distribution and numerous species records in the neotropics, including arid environments, disturbed and high salinity areas, among others. This study is the first report on the ecology and distribution of the family Amaranthaceae in the department of La Guajira through a review of the collection belonging to the Herbarium of La Guajira (HG) "Wunü'Ülia. A review of the specimens belonging to the family in the collection was carried out, determining eight genera and nine species.

SALINITY AND PARENT-OF-ORIGINS AFFECT LEAF NEOGENESIS OF Avicennia officinalis L. IN THE SUNDARBANS, BANGLADESH

Photosynthetic efficiency as well as growth of mangroves are closely associated with its new leaf production and leaf area. Avicennia officinalis L. is one of the exclusive and ecologically significant mangrove pioneer tree species in the Bangladesh portion of the Sundarbans. The effect of salinity and parent-of-origins on the new leaf production and leaf area of the mangrove A. officinalis in the less salinity zone (LSZ), moderate salinity zone (MSZ) and high salinity zone (HSZ) of the Sundarbans were studied under experimental conditions in a randomized block design. The results of the experiment highlighted that the number of new leaf production and leaf area of A. officinalis from the less, moderate and high salinity zones were reduced significantly (p&lt;0.05) with the increase in salinities. Yet, new leaf numbers as well as leaf area of this species did not differ significantly (p&lt;0.05) between and among the three salinity zones from 0 to 20 ppt salinities. However, from 25 ppt and above salinities, the new leaf numbers and leaf area of the moderate and high salinity zones were significantly higher (p&lt;0.05) compared to less salinity zone. Hence, saline environments and parental origins affected leaf neogenesis, and thereby influence the growth of this species. Therefore, the seedlings of A. officinalis of moderate and strong salinity zones origin can sustain in the increasing saline environments, and thereby contribute to the sustainable vegetation cover of the Sundarbans. Further, A. officinalis seedlings generating from the MSZ and HSZ can be used for mangrove plantation establishment in the high salinity areas of Bangladesh.

Assessing the application of the revised Remane Model to fish species in a fluvially dominated cool-temperate southern African coastal system

Estuaries are ecologically important areas which support a variety of aquatic species, particularly marine and estuarine fish species. This study represents a case study of the Orange River and Estuary (ORE) to understand patterns in fish assemblages and diversity trends that were compared to the revised Remane Model predictions in an estuary with poor marine fish species richness. A total of 30 species were recorded in the River continuum that comprised 14 freshwater, 10 marine and six estuarine species. Species diversity revealed seasonal variation in fish assemblages during the high-flow and low-flow seasons but not inter-annually. The results revealed that species diversity is lower in higher salinity areas when compared to low salinity areas. These patterns are consistent with the biogeographical trend of decreasing species richness along the South African coast from east to west, however, inconsistent with Remane predictions. The extremely low marine fish richness at its lower end and the extremely large freshwater influx at its upper end are the primary causes of the inconsistency. This may reflects the unsuitability of the Remane model for the Orange Estuary. In comparison to similar river-dominated South African estuaries, the ORE has a low marine species richness. When compared to more conventional South African estuaries, the ORE has a unique biotic environment with low fish species richness of estuarine-associated marine species adjacent to the Benguela upwelling zone and therefore the region does not offer suitable habitat for such species. As a result, the ORE is not a good candidate to test the Remane Model. The data does, however, confirm the left-hand part of the Remane model, which shows a decline in the fish species richness of freshwater fish species as salinity rises towards mesohaline and polyhaline levels.

Factors affecting the micronutrient status of adolescent girls living in complex agro-aquatic ecological zones of Bangladesh

Inadequate intake of both macro and micronutrients is the major determinant of micronutrient deficiencies in adolescent girls. This study assessed multiple micronutrient status including vitamin D, iron, vitamin A, and urinary iodine concentration among adolescent girls through two seasonal cross-sectional surveys conducted during dry and wet seasons. Mixed-effects linear and logistic regression analysis were conducted to assess associations between micronutrient status, salinity and seasonality. The mean age of the girls was 14 years. Vitamin (OH)D insufficiency was significantly higher in freshwater areas in wet season compared to dry season (wet season: 58% and dry season: 30%, P < 0.001). In wet season, risk of vitamin (OH)D insufficiency was three times higher compared to dry season (AOR: 3.03, 95% CI 1.71, 5.37, P < 0.001). The odds of vitamin (OH)D insufficiency was 11 times higher in fresh water areas compared to high saline areas (AOR: 11.51, 95% CI 3.40, 38.93, P < 0.001). The girls had higher risk of iron deficiency in wet season. Despite the environment being enriched with micronutrient-contained aquatic food, adolescent girls in coastal areas experience different micronutrient deficiencies. The high prevalence of vitamin (OH)D insufficiency in freshwater locations and seasonal iron deficiency in high saline areas needs attention.

Groundwater salinity in the Horn of Africa: Spatial prediction modeling and estimated people at risk

BackgroundChanges in climate and anthropogenic activities have made water salinization a significant threat worldwide, affecting biodiversity, crop productivity and contributing to water insecurity. The Horn of Africa, which includes eastern Ethiopia, northeast Kenya, Eritrea, Djibouti, and Somalia, has natural characteristics that favor high groundwater salinity. Excess salinity has been linked to infrastructure and health problems, including increased infant mortality. This region has suffered successive droughts that have limited the availability of safe drinking water resources, leading to a humanitarian crisis for which little spatially explicit information about groundwater salinity is available. MethodsMachine learning (random forest) is used to make spatial predictions of salinity levels at three electrical conductivity (EC) thresholds using data from 8646 boreholes and wells along with environmental predictor variables. Attention is paid to understanding the input data, balancing classes, performing many iterations, specifying cut-off values, employing spatial cross-validation, and identifying spatial uncertainties. ResultsEstimates are made for this transboundary region of the population potentially exposed to hazardous salinity levels. The findings indicate that about 11.6 million people (∼7% of the total population), including 400,000 infants and half a million pregnant women, rely on groundwater for drinking and live in areas of high groundwater salinity (EC > 1500 µS/cm). Somalia is the most affected and has the largest number of people potentially exposed. Around 50% of the Somali population (5 million people) may be exposed to unsafe salinity levels in their drinking water. In only five of Somalia's 18 regions are less than 50% of infants potentially exposed to unsafe salinity levels. The main drivers of high salinity include precipitation, groundwater recharge, evaporation, ocean proximity, and fractured rocks. The combined overall accuracy and area under the curve of multiple runs is ∼ 82%. ConclusionsThe modelled groundwater salinity maps for three different salinity thresholds in the Horn of Africa highlight the uneven spatial distribution of salinity in the studied countries and the large area affected, which is mainly arid flat lowlands. The results of this study provide the first detailed mapping of groundwater salinity in the region, providing essential information for water and health scientists along with decision-makers to identify and prioritize areas and populations in need of assistance.

Mangrove tree growth is size-dependent across a large-scale salinity gradient

Salinity-influenced ecosystems are projected to face a tree to stand level growth reduction as a response to climate change. Although large and mature trees play a central role in defining carbon dynamics and site conditions, their eco-physiological and functional responses to increasing salinity remain poorly understood. Therefore, we test our hypotheses, i.e., large-diameter trees are predominantly contributing to above-ground biomass (AGB) stocks, whilst small-diameter trees are mainly contributing to AGB growth or gain (biomass changes over time) in higher salinity areas of the Sundarbans mangrove forest, Bangladesh. It can further be expressed by a growth dominance coefficient (GDC) that turns negative (a negative GDC indicates small trees proportionately contribute more to growth) in high-salinity areas while remaining positive in lower-salinity areas. We also hypothesized that species and structural diversity positively influence AGB stocks and gain. To test our hypotheses, we employed data from 60 permanent sample plots installed in the Sundarbans mangrove forest to estimate size-dependent functions by examining tree size, diversity, and growth dominance patterns to salinity gradients. Trees in higher salinity areas showed negative or reverse growth dominance patterns, indicating large trees contributed less to forest growth, which means smaller trees were disproportionately responsible for growth within the stand. Across the salinity zones, large-diameter (>20 cm in diameter at breast height, DBH) trees contributed primarily to AGB stocks, while small-diameter (<20 cm in DBH) trees contributed more to forest growth. We observed species diversity had no significant influence, whilst vertical diversity (height diversity) had a significant positive influence on AGB stocks and gain. Forest functioning (e.g., biomass accumulation rate) is more asymmetric (higher growth of small trees vs. low growth of large trees) in poor sites (i.e., high salinity), as poor site quality favors small trees to grow but not the large-diameter trees, which indicates large trees are more sensitive to high salinity as they lose growth. Our results indicate the size-dependent tree functions also depend on biotic and abiotic factors in mangroves. Increased structural diversity and removing mature trees to allow small trees to grow may benefit mangrove forest functioning (biomass stocks and growth), but species diversity may not.

Impacts of climate change on vicennial spatial behaviors of Trichiurus japonicus in the East China Sea

Understanding fish's spatial behaviors are important for conservation biology under global warming, as one of the direct responses of fish to climate change is the alterations in distribution. We chose Trichiurus japonicus, which is an ecologically and economically important species in the East China Sea (ECS), to study the vicennial responses of demersal fish to climate change. Eight environmental variables (sea bottom temperature, sea bottom salinity, chlorophyll-a concentration, sea surface height, bathymetry, distance to the coast, slope data, and Terrain ruggedness index) combined with the annual survey data were fitted using integrated nested Laplace approximations and stochastic partial differential equations approach under the Bayesian framework to investigate its distribution shifts in spring during 1999–2019. Based on the distribution model, three spatial behavior indicators (center of gravity, Inertia, and Isotropy) were calculated and correlated with six regional climate indicators (Kuroshio index, Taiwan Warm Current Water index, meridional wind, zonal wind, Pacific Decadal Oscillation, and El Niño/Southern Oscillation) to study the potential cause of its spatial behaviors. During the study periods, the biomass of T. japonicus declined gradually, with a brief increase in 2003, 2007–2008, and 2015–2017. T. japonicus preferred high salinity, warm and deep-water area. The relatively persistent hotspots of T. japonicus in spring were in the offshore waters of eastern Zhejiang Province. The change in the center of gravity during the study periods was not obvious, which implied that the distribution shifts were not necessarily vulnerable for T. japonicus in response to climate change and it has strong adaptability to the environment. We also found that strong Kuroshio Current and Taiwan Warm Current Water as well as cold phased of El Niño/Southern Oscillation were accompanied by weakened spatial aggregation of T. japonicus. Overall, for these types of fish with relatively persistent hotspots, the establishment of seasonally protected areas will contribute to the sustainable utilization of the species.

Chemical processes and sustainability of rice-shrimp farming on saline acid sulfate soils in mekong delta

In the history of rice-shrimp farming (RSF) in the Mekong Delta, in saline acid sulfate soils (ASS), RSF has proved its sustainability as there is no long-term accumulation of acidity and salinity that adversely affect RSF production. However, the soil processes involved in this phenomenon are not well understood. This study aimed to determine the significant changes in soil and water chemical indicators associated with soil processes during different stages of RSF. Sampling was conducted in six stages to determine the pH and electrical conductivity (EC) of canal and field water, and the pHe, ECe, and sodium-soluble saturated extract (Na-sol) of surface soil (surS) and subsurface soil (subS) in the low-salinity area (LSA) and high salinity area (HSA) of Bac Lieu province. Putative exchange (exch.) Na+ hydrolysis occurs at the beginning of the rainy season when excess salts are leached. This drastically increases the pH of the field water by 0.6 pH units, from 8.2 to 8.8 in stages 1 to 2, respectively. Putative sulfurization has been shown to occur in subS in both LSAs and HSAs, with a significant decrease of 0.5 pH units from stages 4 to 5, leading to a decrease in the Na-sol of subS through exch. Na+ transformation. Simultaneously, with active soil preparation and liming for RSF, chemical processes such as exch. Na+ hydrolysis, sulfurization, and Na+ transformation are the main factors promoting exch. Na+ desorption, which help to reduce the long-term build-up of salinity and acidity that adversely affect RSF production. Although gypsum is considered an effective material in improving saline soils, in Vietnam, gypsum is the liming material of CaSO4; however, it is not commonly used in agriculture because of its high cost. By using CaCO3 or dolomite as a liming material in saline ASS, the dissolution of lime by sulfuric acid can provide a good opportunity for soil improvement and rice growth in RSF.

Population of Halocnemum strobilaceum (Pall.)M.Bieb in a Dry Salt Lake of the Central Kyzylkum

Halocnemum strobilaceum (Pall.) M. Bieb. is a halophytic desert plant. This plant population is widespread in areas of high salinity of the world, including a Dry Salt Lake of the Central Kyzylkum. Analyzing the environment of the plant root system and the inorganic and organic composition of the soil of dried salt marshes using modern methods is of great importance in explaining the mechanisms of rapid growth and development of H. strobilaceum in areas affected by the stress factor. In the researches, with the help of IR spectroscopic and agrochemical methods, the amount of inorganic salts and organic substances in the soil around the root system of the H. strobilaceum plant was shown to be closer to the standard indicators than the amount of these substances in the soil of dry saline areas. The obtained results serve to explain the importance of H. strobilaceum and similar dominant species in the formation of plant populations in arid and saline areas.

Effect of selected environmental factors on the seed germination of the invasive species Polygala myrtifolia (Polygalaceae) in Australia

Context Polygala myrtifolia L. has become a significant environmental weed in Australia, where it has invaded coastal ecosystems in temperate regions and there is a high risk of extensive further spread. Knowledge of seed-germination behaviour is essential to understand the potential future impact of this species. Aims We investigated the effects of selected environmental factors and dormancy on P. myrtifolia seed germination and emergence to improve management strategies. Methods Seeds were exposed to light, temperature, pH, salinity, osmotic potential and burial depth treatments to assess germination responses, dormancy and viability. Key results Non-dormant seeds readily germinated to high percentages (93.0–95.0%) under specific day–night temperatures of 25°C–15°C regardless of light conditions and across all soil pH (75.0–100.0%). Salinities were tolerated up to 100 mM NaCl (70.0% germination) before sharply declining. Germination reduced from 98.3% to 40.0% at osmotic potentials of −0.4 MPa and −0.6 MPa respectively. Emergence was greatest on the soil surface (48.33%) and absent from depths of 8 cm. Conclusions Germination was high during autumn, winter and spring conditions and across soils of any pH. The species is unlikely to invade areas of high salinity; however, it is moderately tolerant of low soil moisture during germination. Implications There is high risk of P. myrtifolia further invading sensitive ecosystems because of its high germination success. Preventing seed dispersal and ensuring seedlings are controlled on emergence are critical to reducing its impact. We recommend that the cultivation and sale of this species should be prohibited across Australia to prevent further spread.

Abundant and rare bacteria in anthropogenic estuary: Community co-occurrence and assembly patterns

In estuary, bacteria are critically vital to ecosystem function and sustainability. However, the effect of geographic distance and its related factors (i.e., salinity and nutrients) on bacterial diversity, co-occurrence, as well as community assembly on the abundant and rare species scale remained to be discussed. In this study, we deciphered the bacterial dynamics and ecological processes in the anthropogenic estuary of the Haihe River, in China. The results revealed that salinity was the major abiotic factor to shape bacterial community composition, diversity, and network complexity, and the role of biotic cytometric characteristics was considerable as well. Furthermore, the salinity gradient tended to select bacteria with low nucleic acid (LNA) such as Candidatus Pelagibacter and Longivirga, and abundant bacteria were more sensitive to the salinity gradient in comparison with rare ones. The similar keystone number and network topology values indicated that both abundant and rare bacteria played important ecological functions in degrading pollutants, developing co-occurrence networks, and maintaining compositional stability and complexity. In addition, drift and dispersion limitation dominated the ecological processes in the community assembly, suggesting that although salinity caused the migration of species, its ecological role was still weaker than that of stochastic processes. Further, niche differentiation contributed to different stochastic components of abundant and rare species. In high-salinity areas, rare bacteria with small population sizes but high diversity were enriched, which made the bacterial community more affected by ecological drift. Our study illustrated the different responses of abundant and rare bacteria to salinity and the assembly process of bacterial communities in anthropogenic estuary, deepening the understanding of their ecological processes in the estuarine ecosystem.

Effects of precipitation, irrigation, and exploitation on groundwater geochemical evolution in the people’s victory canal irrigation area, China

The People's Victory Canal Irrigation Area is a large gravity irrigation area in the middle and lower reaches of the Yellow River. Groundwater hydrochemistry is controlled by geochemical weathering, precipitation, irrigation from the Yellow River diversion, and artificial exploitation. The Piper diagram, hierarchical cluster analysis, Gibbs diagram, and ion proportion coefficient were applied to improve our understanding of the hydrogeochemical evolution. Our results indicated that groundwater ion concentration has prominent spatial zonation characteristics in the study area. The groundwater ion components in the low salinity area are mainly a result of silicate and carbonate weathering, with the major hydrochemical type being HCO3·Cl–Na·Mg and HCO3–Na·Ca. The soil salt content in the low salinity area is low. The main effect of precipitation on groundwater chemical composition is a reduction in groundwater ion concentration by recharge. The groundwater ion concentration near the canal is similar to the Yellow River water. The groundwater ionic components in the high salinity area are mainly affected by weathering, silicate dissolution, and evaporative salt rocks. The water chemical type is SO4·Cl–Na·Mg. Expectedly, the soil salt content is high in the high salinity area. The Yellow River recharge decreased the ion concentration of groundwater near the canal. In addition, the groundwater exploitation increase results in a change in the flow field, affecting the local groundwater chemistry. The groundwater ion concentration increases as the groundwater flow from the high salinity area to the low salinity area. In contrast, the groundwater ion concentration in the high salinity area decreases. We further discuss these results in the context of the complex influence of precipitation, Yellow River diversion irrigation, and artificial exploitation on the hydrogeochemical evolution.

Risks and adaptation dynamics in shrimp and prawn-based farming systems in southwest coastal Bangladesh

The shrimp industry in Bangladesh is an important economic sector with growing demand, export potential, and employment opportunities. However, the industry is threatened by external and local production and market risks. Risk management strategies can be implemented through farming systems modification developing of different types of shrimp and prawn-based systems, although the adaptive capacity and economic and socio-ecological impacts are unclear. This study evaluated risks, adaptation strategies, profitability, and socio-ecological dynamics in two shrimp-based (shrimp/shrimp/shrimp and wet season (WS) rice/shrimp/shrimp) and two prawn-based (prawn/dry season (DS) rice/prawn and prawn/DS rice/prawn/dike crops) farming systems. Data was collected using focus group discussions (n = 45), household case studies (n = 18), household surveys (n = 120), and key informant interviews (n = 20). Major risks identified included disease outbreaks, lack of tidal water, salinisation, heat extremes, irregular and reduced rainfall, and price fluctuations. Agronomic management (modifying production systems, adjusting farming operations, input applications, dike cropping) was the dominant adaptation strategy in addition to financial mechanisms (market update, selling live stocks and inputs credits), gher management (water management, excavation, dike management) and water management. Adverse socio-ecological impacts of shrimp farming included salinisation, biodiversity loss, soil and water contamination, and reduced crop and livestock production. In contrast, positive impacts of prawn farming included crop diversification and livestock production and decreased salinisation, soil degradation, and biodiversity loss. Despite higher production costs, prawn-based systems generated net income nearly three times higher (USD 3410 to 4470) as compared to shrimp-based systems (USD 1570 to 1790) because dike crops added about 25% extra income. A critical insight of the research is that the prawn-based systems (prawn/DS rice/prawn/dike crop and prawn/DS rice/prawn) were economically more viable (profitable and less risky) than the shrimp-based system. However, neither the shrimp nor prawn system is feasible in all locations. Improved and semi-intensive shrimp farming in high salinity areas with available tidal water and an integrated prawn-based farming system in low to moderate salinity areas can be a viable agricultural land use planning in southwest coastal Bangladesh. This research can contribute to sustainable land use planning for brackish water shrimp and fresh water prawns, and planning to increase the profitability, risk resilience and competitiveness of the shrimp- and prawn-based farming systems with less socioecological impacts.