Freshwater Research Articles

Antimicrobial Pattern of Foodborne Bacterial Hazards Isolated from Vegetables in Dhaka City

The prevalence of undesirable microbial contaminants in fresh vegetables, often consumed raw as salad vegetables, is a concern for the global public health community. In this study, samples from different local markets in Dhaka were collected to evaluate the microbiological quality and safety of four raw salad vegetables, namely, lettuce, tomato, cucumber, and coriander leaves. Microbiological analyses revealed a higher total aerobic bacterial count (3.10 to 8.71 log CFU/g) and coliform count (non-detectable to 7.61 log CFU/g) regardless of RSV type. In all of the examined shop types, foodborne pathogens like Escherichia coli and Salmonella spp. were found in more than 60% of the analyzed vegetable samples, and the isolated E. coli and Salmonella spp. were found to be completely resistant to 3 different antibiotics (Amoxicillin, Erythromycin, and Rifampicin) and intermediately resistant to 2 other antibiotics (Bacitracin and Novobiocin). Therefore, the study findings revealed that the presence of multidrug-resistant E. coli and Salmonella spp. in fresh vegetable samples is a cause for worry when consumed raw. Controlled environment production approaches, such as indoor farming of vegetables and washing with plenty of fresh water before consumption, can help to reduce pathogen and antimicrobial resistance bacteria. J. of Sci. and Tech. Res. 6(1): 45-51, 2024

Congo River: Analysis of suspended sediment flux in a multichannel megasystem in Central Africa

Tropical mega rivers play a crucial role in transferring water and sediment to the oceans. The Congo River is the second largest in the world by volume of water, playing a significant role in the export of fresh water and sediment from the continent to the Atlantic Ocean. This paper aims to analyze the variability of the suspended sediment flux of the Congo River between 2005 and 2018. Suspended Sediment Concentration (SSC), water discharge and water level data were used at the Brazzaville station, which represents 97% of the basin area, and precipitation data for the entire basin. Solid discharge, specific sediment yield and denudation rate of the basin were estimated. The estimated water discharge was 41 268 m³.s-1 for the period between 1947 and 2023, with a bimodal river regime with a flood peak in December and a secondary peak in May. The mean annual SSC estimated for the Congo River was 27.20 mg.L-1. A moderate (r = 0.48) and weak (r = -0.26) correlation was observed between SSC and precipitation, and SSC and water level, respectively, possibly influenced by the basin's terrain characteristics. During the year, the Congo River transfers 33.66 × 106 ton.year-1 of sediment to the ocean, has a specific sediment yield of 9.62 ton.km-2.year-1 and a very low denudation rate (3.37 mm.ky-1).

South Atlantic meridional overturning circulation and its respective heat and freshwater transports from sustained observations near 34.5°S

The Atlantic Meridional Overturning Circulation (AMOC) drives northward Meridional Heat Transport (MHT) and affects climate and weather patterns, regional sea levels, and ecosystems. This study uses a methodology recently applied in 22.5°S to estimate the strength and structure of the AMOC, MHT and freshwater (FWT) transports at 34.5°S since 2005. For this, temperature and salinity profiles from sustained observations were used in conjunction with satellite and reanalysis data under two mapping methodologies: (i) an optimized mapping and (ii) a two-layer feed-forward neural network approach. There is strong agreement between both methods for AMOC, MHT and FWT estimates, thus showing the mapping methodologies are robust. In addition, the AMOC variability estimate is significantly correlated with the monthly SAMBA array data (correlation of 0.41). The mean AMOC transport of 17.0 ± 1.6 Sv, a MHT of 0.6 ± 0.1 PW, and a FWT of -0.02 ± 0.01 Sv are estimated between January 2005 and May 2023 at 34.5°S. The MHT and FWT are analyzed in terms of their horizontal (Hhor and Fhor) and overturning contributions (Hov and Fov), and vertical structures. The MHT is dominated by the overturning contribution (correlation of 0.92), while the FWT is controlled by the overturning contribution driven by the wind via Ekman transport at seasonal timescale, and by horizontal contribution at longer timescales. Both horizontal heat (Hhor) and freshwater (Fhor) components are mostly confined to the upper 500 m, with the geostrophic Fov and Fhor offsetting each other between 50 m and 500 m, and the Ekman Fov in the upper 50 m determining the negative FWT. Finally, the estimated mean Fov of -0.15 Sv agrees with previous estimates that the AMOC exports freshwater in the South Atlantic, and suggests that the AMOC is unstable. Although a long-term trend in the Fov was not detected in the past 20 years, there is a salinification trend (0.05 ± 0.01 PSU/decade) in the upper 300 m near 34.5°S since 2005.

Numerical Analysis of the Influence of 2D Dispersion Parameters on the Spread of Pollutants in the Coastal Zone

The transport of pollutants with flowing waters is one of the most common processes in the natural environment. In general, this process is described by a system of differential equations, including the continuity equation, dynamic equations, pollutant transport equations and equations of state. For the analyzed problem of pollutant migration in wide rivers and the coastal zone, a two-dimensional model is particularly useful because the velocity and mass concentration profile is vertically averaged. In this model, taking into account the dispersion flux leads to appropriate equations, and the dispersion process is described by the dispersion tensor. Due to the transverse isotropy of the dispersion process, the coordinates of this tensor are expressed in terms of local dispersion coefficients along the direction of the velocity and in the direction perpendicular to it. Commonly used methods for determining mass dispersion coefficients refer to a gradient velocity profile, typical for rivers. However, in the coastal zone, the velocity profile changes from gradient to drift when shear stresses on the surface caused by the wind begin to dominate. The drift profile also occurs in estuaries, where there is a difference in the density of fresh and salt water. This paper analyzes the numerical solution of the two-dimensional dispersion equations in the coastal zone for the dispersion coefficients adopted for the gradient and drift velocity profiles and then assesses how this affects the final result. Four typical scenarios of pollutant migration in the coastal zone of the Bay of Puck are presented. The calculated dispersion coefficients differ significantly depending on the adopted velocity profile: for the gradient, DLG = 0.17 [m2/s], and for the drift, DLD = 89.94 [m2/s].

Phylospecies in the Mexican marine algal diversity and the problem of morphospecies

Algae constitute a non-natural group of organisms that share morphological, physiological and ecological characteristics due to a complex shared evolutionary history. They live attached to a substrate or floating in a column of fresh or marine water. These latter are classified into macro and microalgae, whose current diversity recorded in Mexico is represented by approximately 1,700 species of macroalgae and 1,500 of microalgae. However, this diversity is based on morphological attributes. The problem of the morphospecies is that it depends on the expression of the genotype in response to the environmental heterogeneity in which these organisms establish themselves, resulting in phenotypic plasticity or morphological monotony, with the consequent overlapping of characters, generating misidentifications with several taxonomical problems associated and unstable classification systems. The molecular characterization of species has generated great taxonomic changes and more robust classifications. Currently, the diversity of Mexican phylospecies is reduced, with only 250 macro and microalgae, representing 12.5 and 2.3 % of the diversity, respectively. However, of the 142 works associated with phylospecies, 82 have led to taxonomic changes and proposals with important implications in the construction of more stable classification systems and a better understanding of Mexican phycofloristic diversity in all groups.

Strength and Durability of Paving Block with Seawater and POFA (Palm Oil Fuel Ash)

Seawater has the potential to replace fresh water in the production of concrete. Given the restricted availability of freshwater sources and the high cost of transportation, it is crucial to optimize this scenario. On the other hand, agricultural residue is a potential material that can replace cement-based materials, thereby reducing CO2 emissions. Sustainability in the concrete sector is important, hence, research on using alternative renewable resources such as palm oil fuel ash (POFA) for concrete production is necessary. POFA is an agricultural byproduct and industrial waste that is potentially used as a partial substitution for cement due to the presence of pozzolan. The objective of this study is to examine the impact of icluding POFA (Palm Oil Fuel Ash) as a substitute in the paving block, while also considering the influence of seawater mixing and curing water. Further, POFA is used as a supplementary binder for paving blocks at 0%, 10%, 20%, 30%, 40%, and 50% for Portland Composite Cement replacement. The paving blocks properties, such as workability, density, compressive strength, water absorption, and resistance to sulfate attack, were evaluated. The results of the tests confirmed that 10% POFA mixed with seawater and cured with freshwater met the minimum necessity for Class B, as specified by the Indonesian National Standard for parking park applications. As a result of incorporating POFA as a cement replacement, a more environmentally friendly paving block could be established.

USE OF GEO-INFORMATION SYSTEMS FOR GROUNDWATER MONITORING

Abstract . The article is devoted to the study of the possibilities of using geographic information systems (GIS) for monitoring the state of groundwater, which is important for ensuring environmental safety and sustainable management of water resources. Groundwater is an important source of fresh water for the population, industry and agriculture, but it is vulnerable to various pollutions caused by both natural and anthropogenic factors. Therefore, the implementation of reliable monitoring systems that allow timely detection, assessment and forecasting of changes in water quality is necessary to prevent the deterioration of the ecological situation and prevent the spread of pollution. Geographic information systems (GIS ) offer significant opportunities for the collection and integration of large volumes of spatial data, including satellite images, remote sensing results, automated sensor data, and field observations. GIS allow creating multi-layered maps reflecting the ecological state of underground aquifers, modeling pollution processes and predicting their possible impact on nearby ecosystems and water sources. Thanks to the use of GIS, it is possible to combine data from different sources in a single interactive system, which simplifies analysis and provides the ability to quickly respond to any detected deviations. The article examines in detail the key methods used within GIS for groundwater monitoring, including satellite sounding to analyze changes in the earth's surface, spectral indices to assess the state of vegetation and soil salinity, and radar methods to determine soil electrical conductivity. Particular attention is paid to the application of three-dimensional modeling, which allows visualization of the spread of pollution in underground aquifers, which facilitates decision-making regarding the optimal location of monitoring stations and the design of protective structures. In combination with automated sensors recording water parameters in real time, GIS provides continuous monitoring of the physico-chemical indicators of groundwater and allows for prompt assessment of their condition. The article also analyzes the possibilities of using predictive modeling in GIS to assess the further spread of pollution and develop environmental risk management measures. It is described how mathematical models in GIS can help predict the impact of anthropogenic and natural factors on groundwater, which ensures the development of scientifically based solutions to reduce pollution and maintain water quality at a safe level. The implementation of GIS in groundwater monitoring is an important step towards increasing the efficiency of water resources management, ensuring their protection from pollution and preserving the ecological stability of the regions.

Polyanionic Electrolyte Ionization Desalination Empowers Continuous Solar Evaporation Performance.

Solar evaporation contributes to sustainable and environmentally friendly production of fresh water from seawater and wastewater. However, poor salt resistance and high degree of corrosion of traditional evaporators in brine make their implementation in real applications scarce. To overcome such deficiency, a polyanionic electrolyte functionalization strategy empowering excellent uniform desalination performance over extended periods of time is exploited. This 3D superhydrophilic graphene oxide solar evaporator design ensures stable water supply by the enhanced self-driving liquid capillarity and absorption at the evaporation interface as well as efficient vapor diffusion. Meanwhile, the polyanionic electrolyte functionalization implemented via layer-by-layer static deposition of polystyrene sodium sulfonate effectively regulates/minimizes the flux of salt ions by exploiting the Donnan equilibrium effect, which eventually hinders local salt crystallization during long-term operation. Stable evaporation rates in line with the literature of up to 1.68kg m-2 h-1 are achieved for up to 10 days in brine (15‰ salinity) and for up to 3 days in seawater from Hangzhou Bay in the East China Sea (9‰ salinity); while, maintaining evaporation efficiencies of ≈90%. This work demonstrates the excellent benefits of polyanionic electrolyte functionalization as salt resistance strategy for the development of high-performance solar powered seawater desalination technology and others.

LI-FI Performance Analysis in Various Aquatic Environments for Reliable Underwater Communication

The ability to communicate reliably and quickly underwater has been one of the driving forces behind the development of alternative technologies to conventional radio frequency systems. This study explores the performance of Light Fidelity (Li-Fi), a high-speed optical wireless communication technology, in diverse aquatic environments like fresh water, salt water, and turbid water. It evaluates key parameters like signal attenuation, data rate, bit error rate, and transmission range. Results show that Li-Fi offers significant advantages in bandwidth and data rate over traditional methods, but its efficiency is highly dependent on environmental conditions. The study recommends optimizing Li-Fi systems for reliable underwater communication, paving the way for enhanced underwater networking and data transmission applications.

Low Evaporation Enthalpy Ionic Covalent Organic Frameworks for Efficient Atmospheric Water Harvesting at Low Humidity

Herein, we introduce a series of ionic covalent organic frameworks (iCOFs) with a focus on addressing the challenge of water collection at low relative humidity levels below 25%. These iCOFs are characterized by numerous hydrophilic sites and high water stability, enabling efficient water vapor adsorption even at relatively low humidity levels. Through the use of various hygroscopic salt cations and precise control of ion concentration within the pores, the water state within the iCOFs pores can be effectively managed. Among the iCOFs, TB‐COF‐Li stands out with an impressive adsorption capacity of 0.24 g g‐1 from 0 to 22% RH. Notably, due to its ionic porous structure, TB‐COF‐Li exhibits a significantly lower enthalpy of evaporation, measured at 967.04 J g‐1, compared to bulk water with an enthalpy of 2387.4 J g‐1. Moreover, under simulated conditions of 1.5 solar intensity at 60 °C, the majority of the adsorbed water can be rapidly desorbed without the need for additional energy input. This efficient desorption process contributes to a high water collection rate of 0.092 g g‐1 h‐1 in the final atmospheric water harvesting device. The development of these iCOFs offers a promising and cost‐effective solution for obtaining fresh water in arid regions.

The Problem of the Shortage of Fresh Water in Egypt and the Possibilities of Its Solution

The population growth rates that increased after the 1952 revolution accelerated the decline in the supply of fresh water to Egyptians due to the exhaustion of its traditional sources. As a result, at the turn of the 1980s – 1990s, Egypt has overcome the water deficit limit of 1000 m3 per person per year. In order to reduce water stress, the Government of the country in the second half of the twentieth century pursued a policy of birth control and reduction of cultivation of moisture-loving crops. Since the beginning of the 21st century, with the slow introduction of modern irrigation methods, it has focused on increasing the reuse of treated drainage waters in agriculture and the construction of seawater desalination plants to meet the needs of industry and public utilities. The Egyptian Government sees prospects for solving the problem of water scarcity, the growth rate of demand for which in the 21st century will decrease as population growth and economic development slow down, in the achievements of scientific and technological progress and the widespread use of cheap water treatment technologies.

A new rainbow gudgeon of Sarcocheilichthys (Teleostei: Cyprinidae) from Fujian Province, China with redescriptions of S. hainanensis

The teleostean family Cyprinidae is a megadiverse fish taxon that occupies most of the freshwater biomes of the world. The cyprinid genus Sarcocheilichthys of the subfamily Gobioninae is represented by a total of 14 nominal species, most of which are distributed in the vast continent of China. Our recent field collections and surveys in river systems of Fujian Province, southern China, had discovered a cyprinid fish that was recognized herein as a Sarcocheilichthys species new to science. The undescribed species, temporarily known as the Hanjiang rainbow gudgeon, is most similar to S. nigripinnis but can be well distinguished by differences in meristic counts, dorsal fin blotch patterns, and the morphology of oromandibular structures and genital organs. A detailed redescription of the valid Hainan rainbow gudgeon, S. hainanensis, is also provided herein.

Assessing scientific knowledge on Ecuadorian bony fishes from a scientometric perspective.

Bony fishes play a pivotal role in Ecuador's social, economic, and ecological aspects. However, the current state of scientific knowledge on this group remains poorly understood. This study aims to assess the scientific output related to Ecuadorian bony fishes, identifying both well-researched and understudied areas. A scientometric analysis was conducted using the Scopus database, evaluating 265 peer-reviewed publications on marine and freshwater bony fishes. The results revealed that 55.5% of studies focused on marine environments, 41.9% on freshwater ecosystems, and 2.6% on mixed environments. The earliest study was published more than 130 years ago, with a marked increase in research output since 2018. Geographic and regional disparities in research efforts were evident, with the Galapagos Islands hosting the highest number of studies at the provincial level and the coastal region leading in regional publications. Additionally, there has been a notable increase in the participation of women in research over time; however, it remains significantly below parity. English was the dominant language in these publications. On average, the delay between data collection and publication was 8.43 years, which may lead to outdated or ineffective management decisions. This underscores the importance of continually updating data to ensure the accuracy of conservation status assessments. Both marine and freshwater species that were endemic have been less studied compared to non-endemic species. Most of the studied species were categorized as "least concern," although a significant proportion of species classified as "data deficient" have started to be investigated by Ecuadorian researchers. The categories "endangered" and "near threatened" were the least studied, highlighting the urgent need for conservation initiatives targeting these vulnerable taxa. Biases in the number of studies among families, species, and geographic distribution indicate the need to expand research efforts to underrepresented taxa and regions. This analysis underscores the necessity of diversifying methodologies and broadening the research focus to more comprehensively address the challenges associated with the conservation and management of bony fishes in Ecuador.

Gill Health in Fish Farmed in Recirculating Aquaculture Systems (RAS): A Review.

Recirculating Aquaculture Systems (RAS) have been proposed as the future of aquaculture, because they can be used anywhere regardless of access to water, they offer high level of control over farming environment, including biosecurity, and are considered to be sustainable. However, despite of continuous development, there can be still issues with water quality affecting gill health of fish farmed in these systems. This review provides an overview of fish gill structure and gill immune response, and discusses the known impacts of RAS on gill health. Several experimental studies have inadequately reported conditions, particularly water quality, making it difficult to determine if the observed effects were due to water quality issues or RAS system itself. It is crucial for studies investigating the impact of RAS on fish to report water quality during the study. Furthermore, assessments of RAS effects on gill health should include sufficient independent replicates and flow through controls using a common water source. Various methods have been used to assess gill health in RAS, including gill histology, presence of pathogens, gene expression in the gills and gill microbiome analysis. Differences in gill health in fish from RAS and a flow through system have been shown for a number of freshwater and marine fish species. However, these results have been inconsistent across studies, and some results have been challenging to interpret as indicators of gill health. Holistic studies including a number of different methods to assess fish gills would give more conclusive results. More research is needed, in particular, on brackish and marine RAS, to fully understand their impacts on gill health.

Dependence of water radiation on temperature at microwaves

Abstract Additional experimental and calculated data for the previously published work are presented. Fresh water radiation-temperature dependence at wavelength 8 mm in the temperature range of 30-85 °C has been experimentally investigated. Measurements were made with the microwave radiometer with central frequency 37.5 GHz (wavelength 8 mm).The absolute method of measuring the intensities of distributed radiation was used. A horn with a 30x30 mm opening was used as an antenna. Calibration of the intensity of the received radiation was carried out by its own radiation of a black body at different temperatures. The equipment had a sensitivity (fluctuation threshold) 0.2 K at a time constant τ = 1 sec. An increment of the radio-brightness contrast is about 3 K in temperature range of 30 50 °C and approximately 25 K in the temperature range- of 55-85 °C. The water radio emission depends non-linearly on the kinetic temperature. It was determined that the radio brightness temperature of the surface increases from 0.28 to 1 K per 1 °C of water heating. It was shown, that the radiation temperature of the water surface for the 8 mm waves and temperature range 30-85 °C is determined not by the bulk kinetic water temperature, but by the effective temperature of the skin-depth layer formed under the influence of heat exchange with atmosphere.atmosphere.

In situ infestation of sea trout Salmo trutta with salmon louse Lepeophtheirus salmonis reveals parasite-induced behavioral modifications.

In areas with high densities of salmon farming, spillover of the ectoparasitic salmon louse Lepeophtheirus salmonis poses a major threat to wild anadromous salmonids. By combining experimentally salmon louse infestation (mean ± standard deviation = 0.25 ± 0.25 lice g-1 fish) with acoustic telemetry, we studied the behavior of wild first-time migrating sea trout Salmo trutta (n = 58, fork length = 138-204 mm) from late June to September in a marine area with naturally low infestation pressure. We observed that a similar proportion of sea trout from the control and exposed groups returned to fresh water both temporarily and permanently. However, sea trout from the control group spent nearly twice the amount of time in the fjord before first freshwater detection compared to exposed individuals (32 vs. 17 days), and statistical models indicated a dose-response of louse burden on the timing of freshwater return. This effect was combined with evidence of negative impacts of salmon louse burden on overall marine residency. Sea trout predominantly utilized waters within their natal fjord during the marine migration, with exposed fish spending significantly more time close to their home river than sea trout from the control group. In summary, the behavioral modifications caused by salmon lice could reduce individual marine growth, increase long-term mortality, and ultimately harm recruitment at the population level.

Climate warming drives population trajectories of freshwater fish

Climate change has emerged as a key threat to biodiversity, leading to broad-scale shifts in distributions of marine and terrestrial species as they attempt to track thermally suitable habitat. By contrast, our understanding of climate responses of freshwater species is relatively undeveloped, limiting our knowledge of whether projected warming will lead to freshwater biodiversity loss. Here, we linked a multicontinental database of riverine fish population abundance time series collected from 1958 to 2019 to temperature data from the same period. Across the sampled localities, waters warmed by 0.21 °C per decade (annual maximum of monthly temperatures). We tested whether fish responded to this change by i) increasing abundance at the cooler poleward limit of species distributions-predicted if warming has opened new opportunities-and ii) decreasing abundance toward the equatorward limit of distributions-predicted if temperatures have exceeded tolerance thresholds. We found that observed population trends were consistent with both of these expected patterns from climatic warming and that the trends were more pronounced in time series covering the longer time periods of 30+ y. The responses consistent with climate change were most evident in species with larger body sizes, higher trophic levels, river-sea migratory behavior, and more widespread distributions. Moreover, positive abundance responses to warming were more likely at higher altitudes where conditions tend to be cooler. These findings indicate that projected future warming will likely lead to widespread shifts in riverine community structure, including abundance declines at the trailing edge of species distributions.

Integrated management of lakes, reservoirs, and their basins is critical for a climate-resilient planet: an urgent wake-up call from collective amnesia

ABSTRACT Integrated management of lakes and reservoirs and their basins is vital for preserving their significant socioeconomic and ecological benefits, which are essential for climate resilience. Lakes and reservoirs store 88% of the Earth's fresh surface water, providing water, food, energy security, flood protection, drought mitigation, and ecosystem services. This article highlights the rapid depletion and deterioration of these Lentic (standing) waters and the consequent loss of valuable benefits, threatening the global water supply and exacerbating environmental and climate crises. It discusses the evolution of lake management practices and contrasts these with strategies for managing lotic (flowing) waters. It summarizes collaborative best practices for Lake Basin Governance developed through a multiagency partnership. It reviews recent global initiatives to sustainably manage lakes, integrate storage, address aging dams, and foster partnerships and cooperation. It highlights the widespread failures across international water and environmental policies and institutions. The article calls on the global water and environmental community to awaken from collective amnesia, act, and implement best practices for governing lakes, reservoirs, and basins. Our companion article examines the institutional inertia hindering integrated action and offers collaborative opportunities for integrating land and water management in lake and reservoir basins to enhance climate resilience.

The role of habitat preference and feeding strategy on exposure to microplastic pollution in freshwater fish species.

Microplastic (MP) pollution has been observed in a variety of ecosystems, but there is a limited number of studies on reservoir ecosystems. The aim of this study was to determine the levels of MP contamination in sediment, water and commercially important fish species (Cyprinus carpio, Perca fluviatilis, Atherina boyeri and Sander lucioperca) collected from the Yamula Reservoir in Türkiye. Water samples were collected at five stations. Four sediment samples were collected from the lake. As sediments from the lake represent a vital element of the lake ecosystem, they function as a historical archive that reflects alterations in land use and the characteristics of the lake over time. The average amounts of MPs observed in sediment and water samples were 0.12 MP/g and 0.58 MP/m3 respectively. The digestive systems of 30 individuals of each fish species were examined. The highest amount of MP was observed for C. carpio (6 ± 5.9 MP/individual), while the lowest amount of MP was observed for A. boyeri (1.8 ± 1.7 MP/individual). MP abundance in S. lucioperca and P. fluviatilis was 2 ± 2.8 and 4.6 ± 6.3 MP per individual. The most commonly observed polymer types were polypropylene (67%), polyvinyl alcohol (13%), polyethylene resin (13%) and high-density polyethylene (7%). The pollution load indexes determined for each fish species from the highest to the lowest were as follows: 1.83 (C. carpio) 1.6 (S. lucioperca) 1.05 (P. fluviatilis) and, 1 (A. boyeri). The findings of the study indicate that all sampling stations, including both sediment and water, are contaminated with MPs. Furthermore, the results demonstrate that all examined fish species ingest MPs. Additionally, the results indicate that fish inhabiting a wide range of habitats and consuming diverse diets are more susceptible to MP contamination.

Effects of Mixed Saline and Fresh Water Sprinkler Irrigation on the Rhizosphere Soil Microbial Community of Summer Maize

Mixing saline and fresh water can help to increase the agricultural water utilization rate and solve the water shortage situation, but its role on rhizosphere microbes is unknown. This study revealed the effects of mixed saline and freshwater sprinkler irrigation at different proportions on the rhizosphere soil microbial community of summer maize. Compared to freshwater sprinkler irrigation, sprinkler irrigation with 2 g·L−1 of mixed saline and fresh water significantly increased the bacterial α-diversity and significantly affected the structure and composition of bacterial communities, increasing the number of OTUs, the ACE index, and the Shannon index in the rhizosphere soils, whereas sprinkler irrigation with 3 g·L−1 did not lead to significant changes. In addition, there was a significant difference in β-diversity between the mixed saline and freshwater sprinkler irrigation and the freshwater sprinkler irrigation. Principal coordinate analysis revealed that the 2 g·L−1 and 3 g·L−1 sprinkler irrigation treatments were closer to each other, but both were at a greater distance from the freshwater sprinkler irrigation, indicating that mixed saline and freshwater irrigation significantly affected the structure of rhizosphere soil bacterial communities. Ammonium nitrogen, alkaline dissolved nitrogen, and total nitrogen all affected the soil bacterial community structure by more than 10%, with ammonium nitrogen being the most influential environmental factor. The relative abundance of most microbes in the mixed saline and freshwater sprinkler treatments was positively correlated with ammonium nitrogen, especially in the 2 g·L−1 treatment, while that of most microbes in the freshwater sprinkler treatment was negatively correlated with ammonium nitrogen. In conclusion, selecting a sprinkler irrigation model with a mineralization level of mixed saline and freshwater not exceeding 2 g·L−1 could enhance the rhizosphere soil microbial community while conserving water resources.