Brackish Water Lagoon Research Articles

Spatiotemporal patterns and impact of a cyclone on the zooplankton community structure in a brackish coastal lagoon

Zooplankton communities in response to hydrological (salinity, turbidity, water temperature, nitrate, phosphate, silicate) and biological (phytoplankton density) variables were studied in the Asia’s largest brackish water lagoon, Chilika (India). Water samples were collected from 13 stations on a monthly frequency between July 2014–June 2015. A total of 141 species of holoplankton including Ciliophora, Foraminifera, Rotifera, Rhizopoda, Gastropoda, Cladocera, Copepoda, Ostracoda, Malacostraca, Chaetognatha, Chordata, Nematoda, and 18 types of planktonic larvae were identified. Copepods were the most dominant and diverse zooplankton in terms of their species richness, numerical abundance, and widespread distribution in the lagoon. The major holoplanktonic taxa were Acartia sp., Acrocalanus gibber, Acrocalanus gracilis, Acrocalanus longicornis, Euterpina acutifrons, Lecane sp., Oithona sp., Pseudodiaptomus serricaudatus, and Tintinnopsis tubulosa. The dominant planktonic larvae were bivalve veliger, copepod nauplii, cyphonautes larvae, gastropod veliger, and protozoea of lucifer. Canonical correspondence analysis showed that distribution of zooplankton assemblages was influenced by salinity, turbidity, and phytoplankton density. Indicator analysis demarcated 26 indicator zooplankton taxa. Of these, the most prominent indicator zooplankton such as Belzebub hanseni, Mesopodopsis orientalis, Chydorus sphaericus, and Corycaeus catus were characteristic to salinity gradient in southern sector, sediment resuspension in central sector, eutrophic conditions in northern sector, and tide-induced intrusion of marine forms in outer channel, respectively. Hudhud, a category 4 cyclone resulted decline in the abundances of zooplankton population. Copepod nauplii and copepodites were dominant during post-Hudhud and their succession was linked to the increased phytoplankton density due to an upsurge in the nutrient level in the northern sector of the lagoon. The present study provided a comprehensive detail on the zooplankton composition and their environmental drivers including the impact of a tropical cyclone from a tropical coastal lagoon system.

Phosphorus sorption behaviour of the largest brackish water lagoon, South Asia

The Chilika Lagoon is the largest brackish water ecosystem in the Asian continent and is a Ramsar site. Here, the sorption–desorption study was standardized simulating the environmental condition of the Chilika, to ascertain whether phosphorus (P) is the source or sink for sediments of the coastal ecosystem. The sorption behaviour of sediment phosphorus was better fitting into the modified Langmuir model. The effects of salinity, pH, and temperature on phosphorus sorption were found to be better understood by nonlinear relationships. The sorption was recorded to increase at its lower concentrations with increasing of mentioned parameters, when it decreased beyond some threshold values. The maximum phosphorus sorption capacity (Qmax) was more (258 mg/kg) in the freshwater stretch of the lagoon; Northern Sector compared to the relatively saline stretches, i.e., Outer Channel (219 mg/kg) and Southern Sector (237 mg/kg) (p < 0.05). This study will help to control eutrophication by increasing P sorption.

Landfall season is critical to the impact of a cyclone on a monsoon-regulated tropical coastal lagoon

Cyclones can produce a wide variety of short-term and long-term ecological impacts on coastal lagoons depending on cyclone's physical-meteorological characteristics and the lagoon's geographic, geomorphic, and bathymetric characteristics. Here, we theorized that in monsoon regulated tropical coastal lagoons, another important factor that could determine the impact of a cyclone is the landfall season or time of the year with reference to the monsoon season. We analyzed the impact of two cyclones which made landfall near Chilika, Asia's largest brackish water lagoon in different seasons, Cyclone Fani and Titli before and after the monsoon season. We compared field measured and satellite-derived water quality parameters including nutrient, salinity, water temperature, transparency, Chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) before and after the cyclones. We found that although both the cyclones were of similar intensities, after their land interaction, their impact on the lagoon's water quality was contrasting. The post-monsoon cyclone produced a substantial increase in total nitrogen (TN) and total phosphorous (TP), a large drop in salinity, CDOM, and Chl-a. In contrast, after the pre-monsoon cyclone, TN and TP did not show any such hike, no substantial change in salinity and CDOM either, and only a slight increase in Chl-a was observed. We found that the controlling factor in determining the impact of a cyclone is the rate and duration of freshwater discharge to the lagoon, which is normally a strong pulse for pre-monsoon and a continued high flow for post-monsoon cyclones. We conclude that the antecedent conditions of the lagoon and the watershed at the time of a cyclone's landfall is a key criterion in determining the impact. The combined use of satellite data and field data was proved critical to capture the overall impact of cyclones on the hydrological characteristics of the monsoon-regulated coastal lagoon.

Implementation of Smart Buoys and Satellite-Based Systems for the Remote Monitoring of Harmful Algae Bloom in Inland Waters

The deployment of Remote Monitoring Systems (RMS) based on Internet of Things (IoT) technologies and data management in the cloud is a cutting-edge solution for water management agencies to track harmful algae blooms (HABs). However, each environment presents different intrinsic characteristics, hence the reliability and representativeness of collected data may vary according to the selected RMS architecture. This study aims to implement the same RMS in two different water bodies in Spain: the freshwater As Conchas reservoir and the shallow L’Albufera brackish water lagoon. We firstly evaluate the pros and cons of current technologies available on the market and then we select an RMS based on a combination of plug-and-play (YSI-based) and customisable solutions (Libelium-based). The deployment of nodes on buoys allows big data collection from different areas of water bodies, their continuous transfer and storage on a web server, and their subsequent visualisation on the web interface in real time. Secondly, in order to know whether the selected RMS architecture and monitored environment influence the representativeness of the collected data, we perform a Pearson correlation test between the deployed nodes and satellite images. The results point out that the more heterogeneous the environment is, the more nodes must be deployed in different areas for a longer time to obtain a realistic view of the water body status. Therefore, this study provides critical and empirical data to implement a profitable and effective real-time monitoring system in other HAB-affected areas.

Migration, residency and habitat utilisation by wild and cultured Japanese eels (Anguilla japonica) in a shallow brackish lagoon and inflowing rivers using acoustic telemetry

This study monitored post-release movements of 20 wild Japanese eels (Anguilla japonica) [mean ± S.D. 520.8 ± 92.3 mm total length (TL), 217.9 ± 146.3 g body mass (BM)] in a brackish water lagoon in northeastern Japan using acoustic telemetry to elucidate how wild Japanese eels use different river, estuary and marine environments. In addition, 12 cultured Japanese eels (TL = 578.9 ± 18.0 mm, BM = 344.9 ± 25.5 g) were released to understand the comparative behaviours of wild and cultured eels. Both types of eels were simultaneously released in the southern inner part of the lagoon in September 2016 where there are freshwater influences from a river. Following release, eight of the wild eels (40%) were largely sedentary near the released point (river mouth) and stayed at the site for overwinter. Nonetheless, several individuals showed behavioural plasticity of habitat use: three wild eels moved towards the northern part of the lagoon with stronger influence from the sea during May-July 2017. Two wild eels showed clear repeated movements from the lagoon to a river at night and returned to the lagoon by dawn for more than a week every day, and one wild eel migrated upstream for overwintering. Signals from 55% of the wild eels could be detected for more than 6 months, whereas those from all of the cultured eels were lost by December 2016, indicating a short resident time of large cultured eels (BM > 200 g) released in a brackish water area. One wild silver eel migrated to the outer sea during the ebb tide at night in November 2016, probably triggered by the decrease in water temperature (from c. 20°C to c. 13°C), and seven cultured eels similarly moved to the outer sea during October-November 2016. The results revealed the similarities (e.g., nocturnal movements) and differences (e.g., stay period and seasonal movements) in the behavioural characteristics of wild and cultured eels and indicated that habitat connectivity among river, estuary and coastal waters is crucial for enabling eels to efficiently utilise these productive habitats through their behavioural plasticity.

Allometric relationships in morphological traits associated with foraging, swimming ability, and predator defense reveal adaptations toward brackish and freshwater environments in the threespine stickleback.

Freshwater colonization by threespine stickleback has led to divergence in morphology between ancestral marine and derived freshwater populations, making them ideal for studying natural selection on phenotypes. In an open brackish–freshwater system, we previously discovered two genetically distinct stickleback populations that also differ in geometric shape: one mainly found in the brackish water lagoon and one throughout the freshwater system. As shape and size are not perfectly correlated, the aim of this study was to identify the morphological trait(s) that separated the populations in geometric shape. We measured 23 phenotypes likely to be important for foraging, swimming capacity, and defense against predation. The lateral plate morphs in freshwater displayed few significant changes in trait sizes, but the low plated expressed feeding traits more associated with benthic habitats. When comparing the completely plated genetically assigned populations, the freshwater, the hybrids, the migrants and the lagoon fish, many of the linear traits had different slopes and intercepts in trait‐size regressions, precluding our ability to directly compare all traits simultaneously, which most likely results from low variation in body length for the lagoon and migrant population. We found the lagoon stickleback population to be more specialized toward the littoral zone, displaying benthic traits such as large, deep bodies with smaller eyes compared to the freshwater completely plated morph. Further, the lagoon and migrant fish had an overall higher body coverage of lateral plates compared to freshwater fish, and the dorsal and pelvic spines were longer. Evolutionary constraints due to allometric scaling relationships could explain the observed, overall restricted, differences in morphology between the sticklebacks in this study, as most traits have diversified in common allometric trajectories. The observed differences in foraging and antipredation traits between the fish with a lagoon and freshwater genetic signature are likely a result of genetic or plastic adaptations toward brackish and freshwater environments.

Assessing the vulnerability of small-scale fishery communities in the estuarine areas of Central Vietnam in the context of increasing climate risks

Although Vietnam's coastal and estuarine areas are most vulnerable to the impact of climate shocks, very few studies have closely evaluated this vulnerability. This research applied the Livelihood Vulnerability Index (LVI) and the United Nations Intergovernmental Panel on Climate Change vulnerability framework (LVI-IPCC) to estimate the climate vulnerability of small-scale fisheries in the Tam Giang – Cau Hai lagoon, Central Vietnam - recognised as the biggest brackish water lagoon in South East Asia. Mixed methods, including key informant interviews, group discussions and questionnaire surveys (N = 181), were applied to collect empirical data in two estuarine fishery communities of Loc Binh and Huong Phong communes, Thua Thien Hue province. Two important findings emerge from this analysis, (1) the overall results of this study indicate that livelihood strategies and availability of food are the most critical factors in determining livelihood vulnerability for the two surveyed communes in the TG-CH lagoon and (2) the LVI and LVI-IPCC are effective tools to assessing vulnerability at the community level. It is expected that the lessons learnt from this study will assist in designing future studies and help devise intervention strategies to reduce the vulnerability of small-scale fishery communities in developing countries.

Foraging behavior of yellow-phase Japanese eels between connected fresh- and brackish water habitats

Japanese eels (Anguilla japonica) utilize a broad range of habitats along the marine-freshwater ecotone during their growth phase in inland waters. This study aimed to analyze the foraging behavior of yellow-phase Japanese eels in connected fresh- and brackish water habitats and to connect foraging behavior and habitat use through the analysis of carbon (δ13C) and nitrogen (δ15N) stable isotopes. Stomach contents of eels collected in fresh- and brackish waters were analyzed to identify food sources. Values of δ13C and δ15N were analyzed in eels and their potential food sources, and used to predict the recent foraging patterns of eels in the Matsukawa-ura, a brackish water lagoon, and in three freshwater tributaries. Eels preyed on the benthic river community and the mudflat community of the lagoon. Gobiid fishes were found to be an important food source for eels in fresh- and brackish water habitats, while Japanese mitten crabs (Eriocheir japonica) and shore crabs (Hemigrapsus spp.) were major prey in fresh- and brackish waters respectively. δ13C values of potential eel prey differed significantly between fresh- and brackish waters and were used to classify three recent patterns of foraging by the 73 eels included in this study: 1) freshwater foraging, 2) brackish water foraging, and 3) multiple-habitat foraging. The data suggested that some eels recently or frequently moved between fresh- and brackish water habitats while others demonstrated a higher fidelity to either fresh- or brackish waters. Isotopic characteristics of prey in the respective foraging habitats revealed the plasticity of habitat use of yellow eels in the study area. This study demonstrates an integrated approach to study habitat use and foraging behavior of eels. Furthermore, the study underlines the need to consider freshwater and estuarine habitats and the connectivity between them for eel management and conservation.

Rapid impact assessment of extremely severe cyclonic storm Fani on morpho-dynamics &amp; ecology of Chilika Lake, Odisha, India

This article evaluates the impacts of ‘Fani’, a category four cyclone on the shoreline and ecology of the largest brackish water lagoon of Asia, Chilika, on the East Coast of India. The cyclone forced open two New Tidal Inlets (NTI) along the northern shore of the lagoon’s outer channel leading to erosion of the embankments and spits. The average rate of change due to cyclonic storm ‘Fani’ was – 6.12 m while 66.03% of the total transects registered symbol of erosion along the shoreline of Chilika lagoon. Post Fani the information made available on its impact on Chilika was minimal which made us to look into published news articles, online news channels,past published scientific literature to corroborate the likely impact of such erosion and new tidal inlets on the lake ecosystem. Experts differed on their opinions on how the plankton, fish, seagrass and critically endangered Irrawaddy Dolphin would respond to the salinity changes in the lake aftermath of the cyclone. Some of the impacts of ‘Fani’ on the lake shoreline and ecosystem were imminent, such as the opening of tidal inlets and spot death of three Irrawaddy dolphins; whereas, long-term impacts such as changes in the biomass and composition of plankton communities, fish and bird population in the lake are primarily unknown and warrants further detailed investigation. Nevertheless, the study asserts that cyclone driven shoreline damage can impact lagoon ecosystem by bringing in a rapid change in the salinity field

Seasonal and spatial variations in elemental distributions in surface sediments of Chilika Lake in response to change in salinity and grain size distribution

Chilika lake, the largest brackish water lagoon in Asia, has a unique setting, where the north-eastern part receives freshwater from the terrestrial runoff, and the south-eastern part receives seawater from the Bay of Bengal. The seasonal variability in the quantity of inflowing water and their mixing in the lake controls the mobilization and precipitation of various elements. Seasonal sediment samples were collected from both the river and seawater influenced regions of the lake to understand the spatio-seasonal distributions of various elements along the salinity gradient. The major elements present in the sediments are mostly derived from the parent rock weathering in the source region and subsequently transported into the lake by the rivers. Seasonal variations in trace element concentrations are more prominent in the north-eastern part of the lake (i.e., low salinity region), and their higher concentrations have been observed during the post-rainy period. The affinity of the elements (Al, Fe, Mn, Li, V, Co, Cr, Cu, Th, and Zn) towards fine-grain sediments suggests that the size distribution pattern controls their accumulation, retention, and remobilization. The concentrations of Cr, Cu, and Pb exceeded the effects range low, and effects range median benchmarks indicating the potential biological risk in the low salinity region as compared to the high salinity region. The statistical analysis indicated that the concentrations of elements in the region proximal to the sea mouth are controlled by grain size and physicochemical condition of the lake water. In contrast, the element concentrations in the interior region are associated with anthropogenic activities and weathering processes. Continuous monitoring and assessment of element concentrations of the lake sediments can help to protect the lake ecology from the harmful element contaminations.

Submarine groundwater discharge to a tropical coastal lagoon (Chilika lagoon, India): An estimation using Sr isotopes

Submarine groundwater discharge (SGD) is an important component of the marine 87Sr/86Sr budget, which is currently in an imbalance with a missing source. In this contribution, dissolved Sr concentrations and 87Sr/86Sr of the Chilika lagoon (India), the largest brackish-water lagoon in Asia, have been investigated for three different seasons (pre-monsoon (May 2017), monsoon (Aug., 2017) and post-monsoon (Jan., 2018)) to infer coastal behavior of Sr and estimate the SGD fluxes to the coastal ocean. Major source waters (groundwater, river and seawater) and suspended sediments from the lagoon system have also been analyzed for source characterization. Salinity and Sr concentrations of the Chilika samples show wide variations during pre-monsoon (0.2–35.8; 1–93 μmol/kg), monsoon (0.1–20.1; 0.8–55 μmol/kg) and post-monsoon (0.3–7.7; 1–20 μmol/kg) seasons. Despite of these variations, salinity and Sr concentrations of the lagoon co-vary linearly as expected for conservative mixing between river and seawater. In contrast, the mixing plot between 1/Sr and 87Sr/86Sr during the monsoon and pre-monsoon seasons deviate from the river-seawater mixing trend, indicating an additional source/sink of 87Sr to this lagoon. The non-conservative behavior of 87Sr/86Sr during monsoon has largely been restricted to low salinity (< ~2) regime, which could be attributed to subsurface ion-exchange process. During the pre-monsoon, the SGD can explain the non-conservative isotopic behavior that requires additional water supply with higher 87Sr/86Sr ratios. The SGD fluxes have been estimated using two separate approaches, (i) using an inverse model with fixed SGD composition and (ii) using a source-mixing computation using variable SGD compositions within the lagoon. These computations estimate that the SGD contributes ~20% of total water supplied to the Chilika lagoon during the pre-monsoon season. This SGD contribution corresponds to a flux of 1.51 × 106 m3/d to the lagoon. Data from this and earlier studies indicate that the 87Sr/86Sr ratios of the SGD to the western Bay of Bengal, which receives water from several large rivers from the Himalaya and Peninsular Indian regions, are relatively higher (~0.715) than the seawater value (0.7092). The SGD flux to the east coast of India, therefore, would not contribute in reducing the oceanic imbalance, which requires a less-radiogenic source.

Temporal dynamics of species associations in the parasite community of European eels, Anguilla anguilla, from a coastal lagoon.

The resilience of biological communities is of central importance in ecology, but is difficult to investigate in nature. Parasite communities in individual hosts provide good model systems, as they allow a level of replication usually not possible with free-living communities. Here, using temporal data (2005–2017) on the communities of endohelminth parasites in European eels, Anguilla anguilla, from brackish-water lagoons in Italy, we test the resilience of interspecific associations to changes in the abundance of some parasite species and the disappearance of others. While most parasite species displayed changes in abundance over time, three trematodes that were present in the early years, two of which at high abundance, completely disappeared from the parasite community by the end of the study period. Possibly other host species required for the completion of their life cycles have declined in abundance, perhaps due to environmental changes. However, despite these marked changes to the overall community, pairwise correlations in abundance among the three most common parasite species (all trematodes) were stable over time and remained mostly unaffected by what happened to other species. We explore possible reasons for these resilient species associations within a temporally unstable parasite community inhabiting a mostly stable host population.

Morphological and physiological traits of Mediterranean sticklebacks living in the Camargue wetland (Rhone river delta).

Three-spined sticklebacks (Gasterosteus aculeatus L.) living at the southern limit of the species distribution range could possess specific morphological and physiological traits that enable these fish to live at the threshold of their physiological capacities. Morphological analysis was carried out on samples of sticklebacks living in different saline habitats of the Camargue area (Rhone delta, northern Mediterranean coast) obtained from 1993 to 2017. Salinity acclimation capacities were also investigated using individuals from freshwater-low salinity drainage canals and from mesohaline-euryhaline lagoons. Fish were maintained in laboratory conditions at salinity values close to those of their respective habitats: low salinity (LS, 5‰) or seawater (SW, 30‰). Fish obtained from a mesohaline brackish water lagoon (BW, 15‰) were acclimated to SW or LS. Oxygen consumption rates and branchial Na+ /K+ -ATPase (NKA) activity (indicator of fish osmoregulatory capacity) were measured in these LS or SW control fish and in individuals subjected to abrupt SW or LS transfers. At all the studied locations, only the low-plated "leiurus" morphotype showed no spatial or temporal variations in their body morphology. Gill rakers were only longer and denser in fish sampled from the LS-freshwater (FW) drainage canals. All fish presented similar physiological capacities. Oxygen consumption rates were not influenced by salinity challenge except in SW fish transferred to LS immediately and 1 h after transfer. However, and as expected, gill NKA activity was salinity dependent. Sticklebacks of the Camargue area sampled from habitats with contrasted saline conditions are homogenously euryhaline, have low oxygen consumption rates and do not appear to experience significantly greater metabolic costs when challenged with salinity. However, an observed difference in gill raker length and density is most probably related to the nutritional condition of their habitat, indicating that individuals can rapidly acclimatize to different diets.

WATER QUALITY INDEX AS A CRITICAL TOOL FOR AN ASSESSMENT OF BIODIVERSITY OF INLAND WATER ECOSYSTEM

The importance of brackish water lagoon, Chilika for hotspot of biodiversity in Asian continent was studied vigorously to value the water quality for conservation of biodiversity. The water quality index for biodiversity (WQIB) is the measurement tool used for assessment of biodiversity. The study covers 16 sampling locations for the selected parameters to monitor monthly during the period (2011- 2015). The individual sectors of the lagoon possess unique characteristics. The water quality of northern sector highly deteriorated compared to other sectors. Water quality of the outer channel is least infected. The study highlighted that the summer season is the best period for enrichment of biodiversity and monsoon is the worst period for the biodiversity conservation.

Spatial analysis of bacteria in brackish lake sediment

The spatial distribution of bacterial communities inhabiting sediment is heterogeneous at different spatial scales, but mostly unexplored. Here, it is postulated that the heterogeneity of the bacterial community composition varies at the same scale of the heterogeneity of sediment chemical properties. The large spatial scale (km) diversity in sediment from a brackish water lagoon (Chilika Lake, India) is studied, considering the large scale physical and chemical characteristics of land cover, climate, pH, and salinity. Seventy-two samples (24 stations, 3 seasons: winter, rainy, and summer) of sediment from Chilika Lake were analyzed by 16S ribosomal ribonucleic acid (rRNA) gene sequencing, and the relations with land cover and other physico-chemical parameters are discussed. More samples were collected after a severe cyclonic storm (Phailin) passed near the lagoon in 2013, to see the impact of the tropical storm on the spatial and temporal distribution of bacteria in the sediment. The results demonstrate clear spatial relations between physico-chemical parameters (e.g., salinity), land surfaces (e.g., drainage area), and the distribution of sediment microbial communities.

Characterization of dredged soil collected from island of Chilika lake

Chilika lake, the second largest brackish water lagoon in the world, is situated at the east coast of India. It is an estuarine lake connected with the Bay of Bengal. Hydrology of Chilika depends on Mahanadi River in the north side, 52 channels of water in the western side and Bay of Bengal in eastern side. Various rivers dispose their water into the lake causing siltation, which ultimately results in decrease in depth of water body leading to ecological imbalance of the lake and the surrounding area. This necessitates dredging to be carried out in Chilika and presently the dredged material is dumped inside the lake creating islands. Proper utilization of the dredged material rather than treating it as a waste material is the need of the hour. In the present study an attempt has been made to explore the utilization potential of dredged material through its characterization. This is achieved through X-Ray Diffraction test, scanning electron microscope test, Fourier transform infrared test, geotechnical and agronomical characterization tests on the soil collected from dredged island of Chilika lake. For this purpose, representative samples were collected from two dredged islands situated in the central sector of the lake. In this investigation presence of Quartz as the main component with some amount of Phengite, Sanidine etc. are found. Based on the characterization, some suggestions regarding the potential utilization of the dredged soil are also discussed.

Correction to: Post-release behaviors and movements of cultured and wild Japanese eels (Anguilla japonica) in a shallow brackish water lagoon in northeastern Japan

Correction to: Post-release behaviors and movements of cultured and wild Japanese eels (Anguilla japonica) in a shallow brackish water lagoon in northeastern Japan

Post-release behaviors and movements of cultured and wild Japanese eels (Anguilla japonica) in a shallow brackish water lagoon in northeastern Japan

A total of 30 cultured [610.6 ± 24.0 mm total length (TL)] and six wild Japanese eels Anguilla japonica collected on site (622.2 ± 133.1 mm TL) were tagged with acoustic transmitters and released into a shallow brackish water lagoon in northeastern Japan in June 2014 and July–October 2014, respectively; their post-release movements in the entire lagoon were monitored by acoustic receivers. We found that the cultured and wild eels had some common features, such as nocturnal activity and the exploitation of a wide range of brackish environments and occasionally river excursions at night from the lagoon. However, the total periods of detection and seaward movement behaviors differed between the cultured and wild eels, with 26 cultured eels no longer being detected within 6 months, whereas four wild eels were detected for >6 months. In total, 12 cultured eels moved into the outer ocean (potentially seaward migration) in October after typhoons passed and in November after the water temperature decreased (13.8 ± 1.2 °C), as opposed to the wild eels. While the contribution of the cultured eels to reproduction after the seaward movement remains unknown, these findings showed that they remained in the lagoon only for a limited time.

Influence of geochemical properties on natural radionuclides in the sediment of Asia’s largest brackish water lagoon, Chilika-East Coast of India: evaluation through geo-statistical applications

The study signifies the first work on natural radioactivity and to identify the associations as well as influence of geochemical properties on it. The determination of the natural radioactivity such as: 226Ra, 232Th, and 40K were carried out by gamma spectrometer and the median activities were found to be 26.27, 81.61, and 620.09 Bq kg−1, respectively. The geochemical parameters are pH, sand, silt, clay, organic carbon (OC), calcium carbonate (CaCO3), magnesium (Mg), potassium (K), calcium (Ca), sodium (Na), iron (Fe), phosphorus (P) and nitrogen (N) has been determined. The lagoon was mostly dominated by muddy-type sediment which is nearly 60% of the total sample and the high pH noticed in the NS (7.58) of Chilika, which is due to the presence of grass and weeds, by their photosynthesis process, which may cause the lake slighter alkaline. The high Fe concentration (2.53%) in the NS may be due to rapid relies of iron, whereas the enrichment of Ca in CS (1.02%) in the sediment may be from land runoff. The influence and relations between geochemical and natural radionuclides of the sediment were evaluated through geo-statistics, such as correlation matrices, factor analysis, and cluster analysis.

Dissolved boron in a brackish-water lagoon system (Chilika lagoon, India): Spatial distribution and coastal behavior

Boron is a bio-essential metalloid and its concentrations as well as isotopic compositions are useful tracers for various environmental processes; however, its oceanic budget is not yet well-constrained. In this contribution, spatial and seasonal distribution of dissolved boron of the Chilika lagoon, India (Asia's largest brackish-water lagoon) and its possible source waters have been investigated to constrain its coastal behavior and chemical budget. Further, oxygen isotopic analyses of selected samples were carried out to quantify the evaporation process. The boron concentrations show significant spatial variations (0.6–246 μmol/kg; for monsoon (Aug., 2017) season), with the lower values being observed in the river-dominated northern sector of the lagoon. The area-weighted boron concentration of the Chilika during monsoon (128 μmol/kg) is found intermediate to that of the riverine (1.7 ± 0.8 μmol/kg), groundwater (25 ± 38 μmol/kg) and oceanic (406 ± 13 μmol/kg) water sources. In contrast to boron, the average δ18O value (2.2 ± 0.7‰) for the lagoon samples is significantly enriched than their source waters. Calculations based on the δ18O and salinity data estimate about 40% loss of surface water via evaporation. Co-variation between boron and salinity of the samples establishes conservative behavior during onset of the monsoon (June) and also, in the monsoon (Aug) seasons. The boron-salinity trend and boron/salinity ratios of pre-monsoon (May) samples, however, point to its non-conservative behavior with significant boron removal at low-saline regime through ion-exchange (adsorption) processes. Removal of boron is mostly limited to salinity <15 psu and the intensity (in %) of removal increases steadily with decrease in salinity. These adsorptive losses of boron during pre-monsoon period are mostly dependent on the water residence time; higher residence time allows efficient particulate-water interaction, which possibly intensifies the removal. Further, the boron concentrations show significant changes on diurnal and fortnightly timescales due to tide/ebb cycles. However, the coastal behavior of boron, despite of large concentration changes, remains invariant due to tidal forcing. Outcomes of this study underscore adsorptive removal of boron from coastal regimes and its importance in understanding authigenic boron distribution in clay-rich sedimentary archives from near-shore settings.