Brackish Water Region Research Articles

Continuous year-round isolation of giant viruses from brackish shoreline soils.

Giant viruses, categorized under Nucleocytoviricota, are believed to exist ubiquitously in natural environments. However, comprehensive reports on isolated giant viruses remain scarce, with limited information available on unrecoverable strains, viral proliferation sites, and natural hosts. Previously, the author highlighted Pandoravirus hades, Pandoravirus persephone, and Mimivirus sp. styx, isolated from brackish water soil, as potential hotspots for giant virus multiplication. This study presents findings from nearly a year of monthly sampling within the same brackish water region after isolating the three aforementioned strains. This report details the recurrent isolation of a wide range of giant viruses. Each month, four soil samples were randomly collected from an approximately 5 × 10 m plot, comprising three soil samples and one water sample containing sediment from the riverbed. Acanthamoeba castellanii was used as a host for virus isolation. These efforts consistently yielded at least one viral species per month, culminating in a total of 55 giant virus isolates. The most frequently isolated species was Mimiviridae (24 isolates), followed by Marseilleviridae (23 isolates), Pandoravirus (6 isolates), and singular isolates of Pithovirus and Cedratvirus. Notably, viruses were not consistently isolated from any of the four samples every month, with certain sites yielding no viruses. Cluster analysis based on isolate numbers revealed that soil samples from May and water and sediment samples from January produced the highest number of viral strains. These findings underscore brackish coastal soil as a significant site for isolating numerous giant viruses, highlighting the non-uniform distribution along coastlines.

Coastal wetland restoration through the lens of Odum's theory of ecosystem development

Advancing ecological restoration assessments requires a more detailed consideration of species interactions and ecosystem processes. Most restoration projects rely on a few metrics not always directly linked with ecological theory. Here, we used Odum's theory of ecosystem development to assess and compare the ecosystem structure and services of created marshes (4–6 years old) with preexisting, reference marshes in a brackish water region of the Mississippi River Delta. We built ecosystem models for created and reference marshes that integrated large datasets of stomach contents, stable isotopes, and taxa abundances. Despite strong resemblance in community structure, created marshes were at an earlier succession stage compared to the reference marshes, having lower biomass (including exploited species), higher biomass turnover and production, less dependence on detritus, lower material cycling, and less energy flowing through specialist pathways. Although preserving preexisting marshes should be a priority, created marshes may still be an important tool for the restoration of coastal areas and their ecosystem services. In addition, our results show that comparisons of species biodiversity alone may fail to capture essential differences in ecosystem processes between habitats, which reinforces the importance of ecosystem modeling approaches to assess restoration projects.

Collective actions to support sustainable aquaculture: Evidence from brackish water ponds area in Aceh Tamiang

Our research focuses on establishing and improving farmers’ organization in areas with brackish water aquaculture. This research aims to promote sustainable aquaculture enterprises in Aceh Tamiang by engaging fish farmer organizations and promoting collective action. Managing a brackish water region covering a total land area of 3,624.5 hectares requires collective action measures. There is no local governing body that manages water resources or the environment and surroundings of the ponds. Farmers who require knowledge about pond waste and sediment management in the context of fish farming can better understand pond season planting techniques. We selected two villages from the four sub-districts of Aceh Tamiang to gather relevant data from April to May 2021. We comprehensively investigated the brackish aquaculture in Sungai Kuruk III, located in the Seruway sub-district. Our study recommends the formation of a collective entity called Gapokkan, where groups of brackish water fish producers from various villages in Aceh Tamiang can collaborate and unite. Gapokkan can effectively address various difficulties associated with brackish water pond areas to achieve sustainable aquaculture in Aceh Tamiang.

Ovarian and spawning reference, size at first maturity and fecundity of Glossogobius giuris caught along Vietnamese Mekong Delta

This study investigates the ovarian development, spawning patterns, maturity size and fecundity of the goby Glossogobius giuris–a commercial fish in the Vietnamese Mekong Delta–based on the data analysis of 659 individuals. Specimens were caught using trawl nets from four sites representing freshwater (Cai Rang, Can Tho) to salinized regions in the dry season (Long Phu, Soc Trang), and brackish water regions (Hoa Binh, Bac Lieu and Dam Doi, Ca Mau) over the 12 months of 2020. Histological analysis showed that it was a multi-spawner as different stages of oocytes appeared in mature ovaries. The fish could spawn throughout the year, with a peak in April at the freshwater region and in September at salinized and brackish areas as mature ovaries appeared monthly during the studied period and gonadosomatic index displayed the highest value in April and in September, respectively. This goby’s primary egg releasing time tended to be regulated by salinity changes over the four sampling sites. Likewise, size at first maturity of this species could be related to the salinity variation as this value was the longest in freshwater (6.14 ± 0.17) and the shortest in the salinization region (4.82 ± 0.66). Batch fecundity is measured at 5,118–100,003 eggs/female and related to fish length and weight (r2 > 0.76). Findings can be useful for the development of fish conservation strategies and artificial reproducing studies.

Stock assessment of two populations of Glossogobius sparsipapillus (Osteichthyes, Gobiidae) in the Mekong Delta

Glossogobius sparsipapillus is one of the gobies that inhabits brackish and freshwater regions in the Mekong Delta. However, data on the biological parameters of this species population are limited. Therefore, the present study aims to provide the necessary knowledge on the fishing status of this goby living in freshwater (Cai Rang, Can Tho: CR) and brackish water regions (Long Phu, Soc Trang: LP). Data analysis results of 1379 individuals showed that males outnumbered females in LP (374 males: 288 females); the reverse case was found in CR (351 males: 366 females). There were five-six classes of length frequency, with the highest values between 8 and 12 cm (1122 individuals, 81.36%). The von Bertalanffy curve was L = 15.75(1 − e−0.62(t + 0.30)) in CR and L = 15.85(1 − e−0.83(t + 0.23)) in LP. Its longevity was 4.84 yrs in CR and 3.61 yrs in LP. The growth performance was 2.19 in CR and 2.32 in LP. The total, natural, and fishing mortalities were 2.17 yr−1, 1.49 yr−1, and 0.68 yr−1 in CR; 3.46 yr−1, 1.68 yr−1, and 1.78 yr−1 in LP, respectively. The fish stock has not been overexploited as E (0.31 in CR and 0.51 in LP) were lower than E0.1 (0.465 in CR and 0.652 in LP) 0.3.46 yr−1, 1.68 yr−1, and 1.78 yr−1 in LP, respectively. The fish stock has not been overexploited as E (0.31 in CR and 0.51 in LP) were lower than E0.1 (0.465 in CR and 0.652 in LP).

In vitro Bioassay of Allelopathic Activities of a Mangrove Tree, Kandelia obovata, and Fast-growing Trees, Betula platyphylla and Populus alba, Using Protoplast Co-culture Method

Allelopathic activities of a salt-tolerant and low-temperature tolerant mangrove tree, Kandelia obovata, which grows in brackish water regions of sub-tropical areas, and two fast-growing trees, Betula platyphylla and Populus alba, which grow in the temperate area, were examined by two in vitro bioassay methods, the sandwich method using dried leaves and the protoplast co-culture method using leaf protoplasts. Lettuce root growth examined by the sandwich method, was inhibited 50% by 50 mg dried mature leaves of K. obovata. In the protoplast co-culture method, inhibition rates of cell division of lettuce protoplasts were 31% and 69% by leaf protoplasts of K. obovata at densities of 1 × 104 mL-1 and 5 × 104 mL-1, respectively. These results were compared with the inverse relationship between allelopathic activities and salt tolerance of mangrove plants of different families. B. platyphylla showed 37% inhibition by the sandwich method using dried young leaves, but only 10% inhibition at 5 × 104 mL-1 by the protoplast co-culture method using leaf protoplasts of B. platyphylla. Dried young leaves of P. alba showed 66% inhibition, but the leaf protoplasts at the density of 5 × 104 mL-1 showed highly stimulatory activity. Abscisic acid, of which contents in leaf protoplasts of three tree species varies from high to low in relation to salt tolerance and recalcitrance of tissue culture, was discussed as a putative allelochemical.

Metabarcoding analysis of harmful algal bloom species in the Changjiang Estuary, China

Harmful algal blooms (HABs) frequently occur in estuaries because of their unique environmental conditions, including strong salinity gradients, rich nutrients, and complex currents. Numerous HAB species have been identified and characterized in estuaries worldwide, however, their composition and distribution patterns are still poorly understood. In this study, the first metabarcoding analysis of HAB species was conducted in the Changjiang Estuary. This study identified 86 HAB species, including 45 Dinoflagellata, 37 Ochrophyta, 2 Cryptophyta, 1 Haptophyta, and 1 Chlorophyta species. Most HAB species showed similar distribution patterns in the Changjiang Estuary, with higher relative abundances in the sampling sites outside the estuary. The results indicate that, in addition to HAB species being distributed along salinity and temperature gradients, several other key environmental factors influenced their distribution. To our knowledge, many of the HAB species identified in this study, including those that are unique to brackish water regions, such as Katablepharis japonica and Skeletonema marinoi, have not been reported in previous studies on the Changjiang Estuary. Furthermore, rich Skeletonema diversity was observed, with Skeletonemamarinoi being the most abundant species. The richness of the HAB species identified in the Changjiang Estuary supports the existence of diverse HAB species, which could potentially form HABs under favorable environmental conditions. Overall, this study provides novel insights into the dynamics of HAB formation in estuaries.

Evolution and Structure of the Kuroshio Extension Front in Spring 2019

Satellite data products and high-resolution in situ observations were combined to investigate the evolution and structure of the Kuroshio Extension Front in Spring 2019. The former reveals the variation of the front is influenced by the northward movement of the Kuroshio Extension through transporting warm and saline water to a cold and brackish water region. The latter indicates steep upward slopes of the isopycnals, tilting northward in the frontal zone, as well as several ~300 m thick blobs of North Pacific Intermediate Water between 26.25 and 26.75 kg/m3, where conspicuous thermohaline intrusions occur. Further analysis indicates these thermohaline intrusions prefer to alternate salt fingering and diffusive convection interfaces, and are affected by strong shears.

Reverse electrodialysis for power generation using seawater/municipal wastewater: Effect of coagulation pretreatment

Reverse electrodialysis (RED) converts salinity gradient energy (SGE) into electrical energy. Seawater and river water are the most promising feed solutions for RED, but municipal wastewater instead of river water could be acceptable if the wastewater treatment plant is close to the sea because river water is often used for human demands, i.e., for drinking water and agricultural irrigation. In addition, the environmental impact at the mixing point (the brackish water region) must be considered. Wastewater pretreatment is necessary to prevent performance reduction in the subsequent RED process. In this study, the effect of pretreatment using polyaluminum chloride (PAC) as a coagulant on the RED performance was investigated using model and real municipal wastewater and seawater samples. The results reveal that the presence of PAC residue after coagulation negatively affected the subsequent RED process, especially because of the increased cation exchange membrane resistance, which resulted in a 40% reduction in power generation. However, the optimized PAC dosage (and lower amount of PAC residue) resulted in a 20% improvement in RED power generation because 50% of the wastewater organic content had been removed. Thus, coagulation pretreatment with the optimized PAC dose is useful before RED power generation when using municipal wastewater.

Biodiversity of cyanobacteria and other aquatic microorganisms across a freshwater to brackish water gradient determined by shotgun metagenomic sequencing analysis in the San Francisco Estuary, USA.

Blooms of Microcystis and other harmful cyanobacteria can degrade water quality by producing cyanotoxins or other toxic compounds. The goals of this study were (1) to facilitate understanding of community structure for various aquatic microorganisms in brackish water and freshwater regions with emphasis on cyanobacteria, and (2) to test a hypothesis that Microcystis genotypes that tolerate higher salinity were blooming in brackish water environments during the severe drought, 2014. Shotgun metagenomic analysis revealed that cyanobacteria dominated the brackish water region while bacteria dominated the freshwater region. A group of cyanobacteria (e.g., Aphanizomenon, Microcystis, Planktothrix, Pseudanabaena), bacteria (e.g., Bacillus, Porphyrobacter), and diatoms (Phaeodactylum and Thalassiosira) were abundant in the brackish water region. In contrast, Hassallia (cyanobacteria) and green algae (Nannochloropsis, Chlamydomonas, and Volvox) were abundant in the landward freshwater region. Station variation was also apparent. One landward sampling station located downstream of an urbanized area differed substantially from the other stations in terms of both water chemistry and community structure, with a higher percentage of arthropods, green algae, and eukaryotes. Screening of the Microcystis internal transcribed spacer region revealed six representative genotypes, and two of which were successfully quantified using qPCR (Genotypes I and VI). Both genotypes occurred predominantly in the freshwater region, so the data from this study did not support the hypothesis that salinity tolerant Microcystis genotypes bloomed in the brackish water region in 2014.

Feasibility study on formation of fresh water reservoir and impounding the surface runoff for urban water survival in a coastal brackish water region of Kollam, India

The paper presents the feasibility study on the formation of fresh water reservoir and impounding the surface runoff in a typical brackish water lake of southern India, Ashtamudi Lake for urban water survival of Coastal town, Kollam, India. The concept envisages of building a barrage at the outlet of Ashtamudi Lake at the mouth of the Arabian Sea to serve the purpose of preventing seawater intrusion into the lake, avoiding the contamination of the freshwater supply from sea water. To validate the concept, it is proposed to conduct a feasibility study which addresses the concerns about the availability of runoff from Kallada River. The paper also presents possible schemes for storing fresh water within Ashtamudi Lake by constructing dikes at appropriate locations. The length of dike and the volume of water that can be stored with proposed schemes are outlined in the paper.

Impact of rainfall on spatio-temporal distribution of sediment organic matter along the Chittagong Coast, Bangladesh

Sediment organic matter regulates the coastal biogeochemical cycle which is influenced by rainfall pattern and has potential relationship with organic carbon as well as mud characteristics. The objective of present research was to identify the impact of precipitation on the spatiotemporal variation inorganic features of intertidal mudflats. Three locations were selected in freshwater zone; two were in brackish water region and last three locations situated in marine waters from Halda to Salimpur coast. Two sites from each location were designated as the highest high tide level (onshore) and lowest low tide level (offshore) of the intertidal zone during winter (December to February) and monsoon (June to August) spanning between 2013 and 2014. Sediment organic matter and carbon were measured by combustion and Walkey-Black wet oxidation in turn. Average organic matter content in monsoon were found 4.5±0.03, 2.3±0.01 and 2.4 in freshwater, brackish and marine locations whereas 5.2±0.6, 3.9±0.14 and 5.4±0.04% investigated during winter. Precipitation pattern varies from different seasons and locations that have impact on land runoff, freshwater inflow, mixing and circulation. Mud dominated coastal intertidal zones represented high organic matter content than sand dominated coast. Furthermore, depositional pattern, transport, erosion-accretion processes, tidal action, wave characteristics and seasonal inconstancy control the organic matter characteristics in the coastal sediment. This research suggests the necessity of periodic observation of rainfall pattern and organic matter distribution to assess the intertidal deposits which support the stabilization of local geomorphology and biogeochemistry in Chittagong coastal region.Res. Agric., Livest. Fish.3(1): 175-186, April 2016

Biotic invasions can alter nutritional composition of zooplankton communities

Ecologists and ecosystem managers often base their understanding of trophic dynamics on consumer and resource biomass. However, the factors that alter the relative nutritional value of resources are often poorly understood, despite their potential to decouple trophic interactions. Recent population declines in pelagic fishes of the upper San Francisco Estuary were not accompanied by an equivalent decrease in zooplankton biomass, which are the main resource for the fish and their larvae. It was hypothesized that changes in zooplankton nutritional conditions following the establishment of invasive species caused food‐quality related limitations for these higher‐order consumers. Using stable isotopes, elemental stoichiometry and fatty acid analyses for all dominant invasive and native zooplankton taxa and seston, we characterized the plankton community structure in the estuary and demonstrated taxon‐specific differences in their nutritional value. We then quantified the temporal dynamics in meso‐zooplankton proportions of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), polyunsaturated fatty acids (PUFA), and ratio of n3:n6 fatty acids. We found temporal increase in the community‐level DHA, n3 to n6 fatty acid ratio, decrease in the community‐level EPA and PUFA in the brackish water region, but no change in the bulk PUFA proportions in the freshwater region of the estuary. These changes were caused mainly by declines of native cladocerans that are rich in EPA and by an increase in the dominance of invasive taxa with high DHA concentrations, similar to that of native taxa. Although we showed temporal shifts in individual fatty acid classes, the proportion of the essential fatty acids remained relatively high, suggesting that nutritional prey availability for fish remained unchanged with the shift in species composition. We argue that the nutritional content of resource communities should be considered when analyzing the long‐term trophic dynamics and designing effective management and restoration strategies.

Effects of salinity on survival, daily food intake and growth of juvenile round goby Neogobius melanostomus (Pallas, 1814) from a brackish water system

Summary The growth response of juvenile round gobies was tested in various salinities to assess the potential performance of the species in widely differing salinities in the Baltic Sea and adjacent waters. An experimental approach analysed the survival, daily food intake and growth of juvenile Neogobius melanostomus from the brackish water region of the Kiel Canal, Germany. Round gobies (TL = 61.5 ±5.3 mm; n = 40) were fed ad libitum (diet = mysid shrimp; energy content = 4.7 cal per mg dry weight) at salinity levels of 0.1, 7.5, 15 and 30 over 12 weeks. Two replicate tanks (125 × 30 × 30 cm; 100 L) were maintained for each salinity level, each holding five specimens at a mean temperature of 19.90°C (±0.64°C; n = 136). Survival at all levels was 100%, except for 0.1 with 90%. Mean daily food intake (% of body weight) increased from salinity level 0.1 to 15 (from 17.76% to 19.95%); specimens at level 30 showed a more diversified and lower mean food intake (18.44%). Mean cumulative body weight gain appeared greatest at a level of 7.5 (224.52%), closely followed by 0.1 (206.57%) and 15 (191.92%). In contrast, fish growth was significantly lower at a salinity level of 30 (100.57%). Results of the experiment indicate that salinity tolerance estimates of the round goby made by other authors are too low regarding specimens that stem from brackish habitats. Growth patterns of some specimens, even in the salinity 30 treatment, show that a further spread of this species into regions with higher salinities is quite possible.

Coexistence and Genetic Variability of Contracaecum rudolphii A and Contracaecum rudolphii B (Nematoda: Anisakidae) In Cormorants, Phalacrocorax carbo sinensis, In the Baltic Region

Although numerous genetically isolated entities within Contracaecum rudolphii sensu lato are presently defined, information on the distribution and ecology of these groups is nonetheless in demand. In the present study, information based upon DNA sequence data (restriction analysis and sequencing of rDNA) on the distribution of the species C. rudolphii A and C. rudolphii B in the cormorant Phalacrocorax carbo sinensis from the Baltic region (Poland and Finland) is provided. These data corroborate previous work that identified C. rudolphii A in brackish water regions and C. rudolphii B in fresh water sites, although mixed infections also occur. The 2 species may inhabit the same host specimen. One rare heterozygote of the species was recorded.

Migration history of Sakhalin taimen Hucho perryi captured in the Sea of Okhotsk, northern Japan, using otolith Sr:Ca ratios

Sakhalin taimen Hucho perryi populations have decreased drastically to near extinction. It is urgent to establish an effective conservation strategy based on an understanding of the characteristics of migration and habitat use of this species. We examined the migration history of anadromous Sakhalin taimen captured off the Sarufutsu coast, northern Hokkaido, Japan, using otolith Sr:Ca ratios and also examined the relationship between their otolith Sr:Ca ratios during freshwater and seawater residence in a rearing experiment. Otolith Sr:Ca ratios of some fish from the Sarufutsu coast showed freshwater levels (0.5–4.0 × 10−3) near the core, which thereafter increased to brackish water levels (4.0–6.0 × 10−3), and then to seawater levels (6.0–10.0 × 10−3) in the outermost regions. Those findings indicate that specimens from the Sarufutsu coast migrated to the brackish water region or the sea and spent most of their lives there. The anadromous migration pattern including the timing of downstream migration seems to be flexible among individuals in the species. They migrate between freshwater and seawater or brackish water several times during their lives, showing extensive habitat use. It is essential to secure the continuity among the freshwater, brackish water, and seawater areas for their effective conservation.

Modeling of Resuspension Mechanism of Deposited Organic Mud in the Tidal Estuary

The excess deposition of organic matter impacts to the eco-systems in brackish water regions. Improving the environment is necessary to understand the deposition and transportation characteristics of organic matter. In this study, salinity effect to resuspension characteristics of organic mud was examined. From these results, a resuspension model which can consider the qualities of organic mud and water salinity was estimated. It was clarified that the calculated resuspension flux and grain size distribution using this model extremely replicate the measured data. Additionally, this model can grasp the particle size selection by salinity.

FLEXIBLE CONTROL OF DENSITY CURRENT MIGRATION BY USING SLUICE GATE

Controlling adverse density currents has been an important issue on water quality and ecosystems of brackish water regions. This study proposes to apply sluice gate for flexible control of density current migration in open channels. Hydraulic characteristics of density flows around a sluice gate are investigated by flume experiments employing the Particle Image Velocimetry technique and numerical calculations by a Large Eddy Simulation model. The results show that the behavior of density front migration under a sluice gate is dominated by internal Froude number of both fresh water and salt water layers, and entrainment of salt water in a downstream region of a dike is influenced by evolution of instantaneous flow structures in a fresh water layer.

Deposition and Transportation Characterisrics of Organic Matter in Brackish Water Region

Observation and laboratory experiments were performed to understand the re-suspension mechanism of organic mud under salinity variation at an estuarine bed. The organic mud is transported upstream under the separation into different types of organic matter. The re-suspension flux of organic mud depends on not only the shear stresses and organic properties but also surface water salinity. The re-suspension flux of organic mud was separated into fresh water and saline water components. The re-suspension flux also depends on the content rate of POCs originated in oil and fat/primary production. The trend of turbidity in the Tenma River can be almost explained with the re-suspension formula of organic mud considering the salinity effect.

The influence of environmental conditions on the seasonal variation of Microcystis cell density and microcystins concentration in San Francisco Estuary

A bloom of the cyanobacteria Microcystisaeruginosa was sampled over the summer and fall in order to determine if the spatial and temporal patterns in cell density, chlorophyll a (chl a) concentration, total microcystins concentration, and percent microcystins composition varied with environmental conditions in San Francisco Estuary. It was hypothesized that the seasonal variation in Microcystis cell density and microcystin concentration was ecologically important because it could influence the transfer of toxic microcystins into the aquatic food web. Sampling for Microcystis cell density, chl a concentration, total microcystins concentration and a suite of environmental conditions was conducted biweekly at nine stations throughout the freshwater tidal and brackish water regions of the estuary between July and November 2004. Total microcystins in zooplankton and clam tissue was also sampled in August and October. Microcystis cell density, chl a concentration and total microcystins concentration varied by an order of magnitude and peaked during August and September when \( {\text{P}}^{{\text{B}}}_{{\text{m}}} \) and αB were high. Low streamflow and high water temperature were strongly correlated with the seasonal variation of Microcystis cell density, total microcystins concentration (cell)−1 and total microcystins concentration (chl a)−1 in canonical correlation analyses. Nutrient concentrations and ratios were of secondary importance in the analysis and may be of lesser importance to seasonal variation of the bloom in this nutrient rich estuary. The seasonal variation of Microcystis density and biomass was potentially important for the structure and function of the estuarine aquatic food web, because total microcystins concentration was high at the base of the food web in mesozooplankton, amphipod, clam, and worm tissue during the peak of the bloom.