Mandovi Estuary Research Articles

Investigating the evolution of sand bars and natural channel formation in the Mandovi estuary along the central west coast of India

Coastal formations, such as sandbars, play a vital role in shaping the environment and maintaining local and regional coastal morphology. This study deals with two noteworthy sandbars, namely Aguada and Reis Magos which are in the Mandovi estuary of the Goa region in the central west coast of India. They have attracted great attention because of their dynamics and their role in shaping the adjoining coast. This study employs a comprehensive approach, incorporating in-situ observations and remote sensing methods, to investigate the mechanisms underlying the emergence and dissipation of these sandbars and their linkage with adjoining navigational channels and coastline. During the intense wave conditions of the southwest monsoon (June to September), these sandbars undergo a temporary phase of dispersion. This phenomenon results in the accumulation of sand from both the sandbars and the neighbouring Miramar beach within the navigational channel. As a consequence, it obstructs maritime traffic and forms a unified shallow bar, obstructing maritime navigation in the area. However, following the attenuation of monsoon waves in October to November, the sandbar and beach initiate a gradual replenishment process, aimed at compensating for the sediment loss incurred during the monsoon season. This recurring trend has demonstrated persistent characteristics over an extended period. The presence of the sandbar may pose navigational challenges for large barges, cruise ships, and fishing boats but on the other hand, it serves as an effective barrier against incoming high-energy waves into the inner parts of the Mandovi estuary. Results revealed notable variations in the extent of the sandbar over the study period. The maximum recorded extent of the sandbar was 82.48 ha and 32.59 ha on May 04, 2021, while the minimum extent was measured at 36.68 ha and 7.14 ha on February 14, 2019, for Reis Magos and Aguada bar respectively. The sandbar promotes a calm environment along the shoreline and reduces erosion susceptibility by dissipating the wave energy before reaching the riverbanks. The absence of this protective sandbar would have significantly impacted the parts of the Goa region. Notably, the maximum erosion of 107 m was observed at the right bank of the estuary, while the maximum accretion of 141 m was recorded in the Caranzalem from 1975 to 2023. This study contributes valuable insights into the formation, dissipation, and environmental implications of sandbars within the estuary in Goa. The integration of in-situ observations and remote sensing data affords a comprehensive understanding of sandbar dynamics, highlighting the essential role that they play in coastal protection, navigation and the preservation of the local environment.

A halophilic Chromohalobacter species from estuarine coastal waters as a detoxifier of manganese, as well as a novel bio-catalyst for synthesis of n-butyl acetate.

Anthropogenic pollution due to ferro-manganese ore transport by barges through the Mandovi estuary in Goa, India is a major environmental concern. In this study a manganese (Mn) tolerant, moderately halophilic Chromohalobacter sp. belonging to the family Halomonadaceae was isolated from the sediments of a solar saltern adjacent to this Mandovi estuary. Using techniques of Atomic absorption spectroscopy, Scanning electron microscopy-Energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy and Atomic Force Microscopy, the Chromohalobacter sp. was explored for its ability to tolerate and immobilize Mn in amended and unamended media with 20% natural salt concentration (w/v). In aqueous media supplemented with 0.1 mM Mn, the Chromohalobacter sp. was capable of sequestering up to 76% Mn with an average immobilization rate of 8 mg Mn /g /day. Growth rate kinetic analysis using Gompertz mathematical functions was found to model the experimental data well. The model inferred that the maximum growth rate of Chromohalobacter sp. was at 10% natural salt concentration (w/v). The Chromohalobacter sp. was further found to be multimetal tolerant showing high tolerance to Iron (Fe), Nickel (Ni) and Cobalt (Co), (each at 4 mM), and tolerated Manganese (Mn) up to 6 mM. Morphologically, the Chromohalobacter sp. was a non-spore forming, Gram negative motile rod (0.726 μ× 1.33 μ). The adaptative mechanism of Chromohalobacter sp. to elevated Mn concentrations (1 mM) resulted in the reduction of its cell size to 0.339 μ× 0.997 μ and the synthesis of an extracellular slime, immobilizing Mn from the liquid phase forming Manganese oxide, as confirmed by Scanning Electron Microscopy. The expression of Mnx genes for manganese oxidation further substantiated the finding. This bacterial synthesized manganese oxide also displayed catalytic activity (∼50% conversion) for the esterification of butan-1-ol with CH3COOH to yield n-butyl acetate. This Chromohalobacter sp. being indigenous to marine salterns, has adapted to high concentrations of heavy metals and high salinities and can withstand this extremely stressed environment, and thus holds a tremendous potential as an environmentally friendly "green bioremediator" of Mn from euryhaline environments. The study also adds to the limited knowledge about metal-microbe interactions in extreme environments. Further, since Chromohalobacter sp. exhibits commendable catalytic activity for the synthesis of n-butyl acetate, it would have several potential industrial applications.

Occurrence, distribution and sources of phthalates and petroleum hydrocarbons in tropical estuarine sediments (Mandovi and Ashtamudi) of western Peninsular India

The present study provides baseline information on the concentration levels, distribution characteristics and pollution sources of environmental contaminants, such as phthalic acid esters (PAEs or phthalates) and petroleum hydrocarbons in surface sediments of the tropical estuaries (Mandovi and Ashtamudi) from western Peninsular India. Total PAEs (∑5PAEs), hopanes, steranes and diasteranes concentrations from Ashtamudi estuary ranged from 7.77 to 1478.2 ng/g, n.d.-363.2 ng/g, n.d.-121.5 ng/g and n.d.-116.6 ng/g, respectively. Likewise, PAEs (∑6PAEs), steranes and diasteranes concentrations from Mandovi estuary ranged from 60.1 to 271.9 ng/g, 2.33–40.1 ng/g and 2.28–23.0 ng/g, respectively. The PAEs comprising di-isobutyl phthalate (DIBP), dibutyl phthalate (DBP), an isomer peak for DBP, di(2-ethylhexyl) phthalate (DEHP), di-isononyl phthalate were dominant in Ashtamudi estuary sediments, while PAEs including diethyl phthalate, DIBP, DBP and its isomer, DEHP, di(2-ethylhexyl) terephthalate were detected in the Mandovi sediment samples. The results of this study show an insignificant correlation of TOC with PAEs, and indicates that the varying spatial distributions of the PAEs in both the estuaries can be the result of discharge sources. The higher concentration of PAE congeners was noticed in Ashtamudi, a Ramsar wetland site, that can be attributed to land-based plastic waste. The petroleum biomarkers were abundantly present in Mandovi estuary due to anthropogenic activities such as boating and spillage from oil tankers. The findings of the present study will serve as a reference point for future investigation of organic contaminants in Indian estuaries, and calls for attention towards implementing effective measures in controlling the pervasion of the PAEs and petroleum biomarkers.

Biogenesis of selenium nanospheres using Halomonas venusta strain GUSDM4 exhibiting potent environmental applications.

Selenite reducing bacterial strain (GUSDM4) isolated from Mandovi estuary of Goa, India was identified as Halomonas venusta based on 16S rRNA gene sequence analysis. Its maximum tolerance level for sodium selenite (Na2SeO3) was 100mM. The 2, 3-diaminonaphthalene-based spectroscopic analysis demonstrated 96 and 93% reduction of 2 and 4mM Na2SeO3 respectively to elemental selenium (Se0) during the late stationary growth phase. Biosynthesis of Se nanoparticles (SeNPs) commenced within 4h during the log phase, which was evident from the brick red color in the growth medium and a characteristic peak at 265nm revealed by UV-Vis spectrophotometry. The intracellular periplasmic synthesis of SeNPs in GUSDM4 was confirmed by transmission electron microscopy (TEM). Characterization of SeNPs by X-ray crystallography, TEM and energy-dispersive X-ray analysis(EDAX) clearly demonstrated spherical SeNPs of 20-80nm diameter with hexagonal crystal lattice. SeNPs (0.8 and 1mg/L) primed seeds under arsenate [As(V)] stress showed increase in shoot length, root length and biomass by 1.4-, 1.5- and 1.1-fold respectively, as compared to As(V) primed seeds alone. The proline and phenolic content in seeds primed with SeNPs under arsenate stress showed alleviated levels proving its ameliorative potential. SeNPs also demonstrated anti-biofilm activity at 20µg/mL against human pathogens which was evident by scanning electron microscopic (SEM) analysis. SeNPs interestingly revealed mosquito larvicidal activity also. Therefore, these studies have clearly demonstrated amazing potential of the marine bacterium, Halomonas venusta in biosynthesis of SeNPs and their applications as ameliorative, anti-biofilm and mosquito larvicidal agents which is the first report of its kind.

Spatio-Temporal Dynamics of Phytoplankton in the Mandovi Estuary, on the Central West Coast of India During Post Monsoon

Spatio-Temporal Dynamics of Phytoplankton in the Mandovi Estuary, on the Central West Coast of India During Post Monsoon

Metal enrichment and toxicity assessment through total and speciation of metals in lower and middle regions of tropical (Mandovi) Estuary, western coast of India.

The study aimed to understand the metal enrichment and toxicity in lower and middle regions of a tropical Mandovi Estuary, revealed metals dilution by coarser intertidal mudflat sediments in the lower estuary (downstream of the fishing jetty-core S). A relatively calm depositional environment prevailed at the middle estuary (core M) and also at the upstream of the jetty of the lower estuary (core L) facilitating deposition and enrichment of Mn and Zn in cores M and Mn, Cu and Co in core L. The distribution of trace metals in sediments was regulated by grain size, total organic carbon and Fe-Mn oxides. The potential contamination index indicated a moderate degree of metal contamination in sediments while the anthropogenic factor showed the signatures of human-induced activities in the enrichment of metals. The sequential extraction of metals showed bioavailability of Mn, Cu, Zn and Co. Fe-Mn oxide and organic/sulphide were key phases for the retention of bioavailable metals. The elevated level of these metals suggested possible toxicity to benthic biota, particularly from Mn (cores L and M) and Co (core L) according to the screening quick reference table.

Seasonal variability in environmental parameters influence bacterial communities in mangrove sediments along an estuarine gradient

Mangrove ecosystems are repositories of divergent microbial communities which respond differently to environmental characteristics. Hence, it is important to understand the community structure with respect to pertinent controlling environmental factors. Seasonal down-core variations in bacterial communities were investigated at 3 mangrove sites at upstream, mid-stream and mouth region along the economically-important Mandovi estuary, west coast of India. Genomic DNA extracted from 45 sediment samples were analyzed by 454 pyrosequencing. A total of 15008 operational taxonomic units (OTUs) were assigned to 54 phyla and 127 classes re-affirming mangroves to be biodiversity hotspots. Members of class Alphaproteobacteria constituted up to 35% of the tag sequences and showed marked seasonal variability at all locations (Kruskal-Wallis test, p < 0.05). Occurrence of other abundant phyla like Bacteroidetes, Firmicutes, Actinobacteria, Chloroflexi and Acidobacteria at the study sites indicated their participation in biogeochemical cycling. Seasonal fluctuations in the environmental variables influenced the bacterial communities. Statistical analysis revealed that during the monsoon, bacterial communities proximal to the mouth region were largely influenced by pore water NH4+ concentrations due to its accumulation in the sub-surface sediments. At the upstream site, elevated organic carbon and NO2− content during the post-monsoon caused variations in the bacterial community.

Influence of seasonal and environmental variables on the emission of methane from the mangrove sediments of Goa.

Mangrove sediments are known sources for methane emission that has a very high global warming potential. The spatio-temporal emission of methane in the mangrove sediments was quantified in the present study using the static closed chamber technique. Besides, the effects of environmental parameters on methane emission were estimated at Betim (mouth), Chorão (midstream), and Volvoi (upstream) stations along the tropical Mandovi estuary. On an average, the methane emission at the upstream estuarine station at Volvoi was maximum (1268.68 ± 176nMcm-2h-1) compared to the other two stations. Annually, the methane emission was significantly influenced by physicochemical parameters like salinity at Betim and Volvoi and, the redox potential at the midstream station at Chorão. The variation of methane emission between the 3 stations (P < 0.001) is attributed to the variation in methanotrophy (P < 0.05) and methanogenesis (P < 0.05) influenced by differences in the concentration of nutrients (P < 0.05) and organic carbon (P < 0.05). Seasonally, the highest methane emission at Chorão was during the post-monsoon, at Betim was during the monsoon season (1305.34 ± 108.58nMcm-2h-1), and at the upstream station at Volvoi, the emission of methane was highest during the pre-monsoon season (1514.68 ± 130.94nMcm-2h-1). The influence of environmental parameters was more prominent on methane emission at the 3 stations during the monsoon season. Spearman's correlation analysis indicated that seasonal changes in methane emissionare not only attributed to the influence of seasonal rainfall that leads to the fresh water input, but also to the variation in biogeochemical parameters.

Inventory of fishery resources using participatory research approach in Mandovi Estuary in Central western coast of India

Aim: The fisheries resources of Mandovi Estuary, along the central west coast of India were analysed for taxonomic, functional, feeding and population aspects and also to record and prepare an inventory on fish and shellfish species. Methodology: Finfish and shellfish taxa were monitored for four years (2016 to 2020) through surveys in small and regional markets, fishermen surveys, fishing gear samplings, telephonic interviews and photographs. Results: A total of 318 taxa are counted comprising of 169 (53.1%) demersal, 71 (22.3%) pelagic fish, 37 (11.6%), molluscan and 41 (12.9%) crustacean species. The community was dominated by marine immigrants and the freshwater types contributed least to the composition. In the inventory, majority of the resources were of commercial value and this category contributed 70% of total documented species. Even though detailed analyses were required, nearly 2% of the fauna appeared to be endemic to the region. Further, more than 30% species listed were data deficient. Out of 318 species, 10% were unknown in the Mandovi estuary. Interpretation: This data set comprehensively documents the finfish and shellfish diversity of Mandovi estuary from 2016 to 2020. The type of fish assemblage is briefly discussed focusing on the management of these resources in the estuary.

Benthic exchange along a tropical estuarine salinity gradient during dry season: Biogeochemical and ecological implications

Benthic biogeochemistry and its coupling with pelagic ecology are less understood in tropical than in temperate estuaries, which have significant implications for global carbon and nutrient cycling. In dry season, the Mandovi Estuary of Western India develops a prominent salinity gradient (0–35 psu), and remains nutrient-limited but most productive, which stands in contrast to wet season. To understand the role of benthic exchange in the sustenance of estuarine biogeochemistry and ecosystem, we carried out biogeochemical measurements in the water column and a series of intact-core incubations along the estuarine salinity gradient, during the dry season of 2014. We observed that the lower estuary was nitrogen (N)-limited whereas the middle and upper estuary were phosphorus (P)-limited. The benthic respiration (38.6–82.87 mmol O2 m−2 d−1), organic carbon (Corg) mineralization (34.3–79.8 mmol C m−2 d−1) and nutrient exchange rates considerably varied along the salinity gradient. Variability in benthic respiration was apparently controlled by labile Corg content and faunal abundance in the sediments. Benthic exchange of NH4+ and NOx− were mainly controlled by salinity and NOx− of the water column, respectively. Benthic PO43− exchange was predominantly controlled by sedimentary Fe content and bottom water O2, whereas benthic SiO44− exchange was primarily controlled by sediment-water SiO44− gradient. Abiotic processes accounted for 37-79% of sediment O2 consumption (SOC). Benthic metabolism accounted for 34–60% of total community respiration and mineralized 43–145% equivalent of C fixed through primary production (PP). Of dissolved inorganic nitrogen (DIN) efflux (0.67–2.59 mmol m−2 d−1), NH4+ comprised 91% in the lower estuary but NOx− (NO3− + NO2−) comprised 97% in the upper estuary, and benthic nitrification apparently determined the dominant N species released from the sediments. Coupled nitrification-denitrification apparently caused the loss of 30–69% of NH4+ diffusing from the deeper sediments. The estuarine sediments were a net source of DIN and SiO44−, potentially meeting up to 31% of N and 40% of Si demand of the phytoplankton, but acted as a net PO43− sink owing to high sedimentary Fe and normoxia, and tended to buffer the estuarine water PO43− to 0.05–0.19 μM. Benthic PO43− influx (0.006–0.026 mmol m−2 d−1) apparently caused the P-limiting condition in the middle and upper estuary. Particularly, the role benthic DIN supply was crucial for the sustenance of estuarine PP as the estuary receives some PO43− from the sea and sufficient SiO44− from the river but not sufficient DIN. The sediments potentially immobilized up to 25% and 20% of riverine DIN and PO43− load, respectively. Overall, the study revealed an efficient benthic carbon recycling and a tight benthic-pelagic coupling in the estuary during the dry season.

Processes and metal enrichment of adjacent mudflat and mangrove environments in the middle estuarine regions of tropical Mandovi Estuary, Goa, west coast of India

Processes and metal enrichment of adjacent mudflat and mangrove environments in the middle estuarine regions of tropical Mandovi Estuary, Goa, west coast of India

Characterization of sedimentary organic matter and depositional processes in the Mandovi estuary, western India: An integrated lipid biomarker, sedimentological and stable isotope approach

A multiproxy study involving bulk (TOC, δ13Corg, grain size) and molecular (n-alkane biomarkers) analyses is used to investigate surface sediments from the Mandovi estuary in Goa, west coast of India to determine the origin, distribution and composition of organic matter (OM). The δ13Corg and n-alkane based indices (terrigenous/aquatic ratio (TAR) and Paq) indicate higher terrigenous OM accumulation in the river dominated upper reaches of the estuary. The presence of unresolved complex mixture (UCM), n-alkane indices (carbon preference index (CPI), average chain length (ACL), natural n-alkanes ratio (NAR)) and diagnostic isoprenoid ratios (pristane/phytane (Pr/Ph), Pr/n-C17, Ph/n-C18) helped to characterise intense human activity in the lower estuary. This conclusion is further supported by relatively high concentration of hopanes indicating petroleum contamination in the lower estuary. Furthermore, the study also highlights the important role of grain size on the distribution of OM along coastal margins, and provides detailed understanding of the variations in OM distribution/accumulation forced by natural processes and anthropogenic activities. The results of this study have significant implications for identifying natural and anthropogenic OM sources in estuarine systems especially in the context of increasing anthropogenic activities.

Assessment of metal enrichment and contamination in surface sediment of Mandovi estuary, Goa, West coast of India

Assessment of metal enrichment and contamination in surface sediment of Mandovi estuary, Goa, West coast of India

Variations of Colored Dissolved Organic Matter in the Mandovi Estuary, Goa, During Spring Inter-Monsoon: A Comparison With COVID-19 Outbreak Imposed Lockdown Period

Colored dissolved organic matter (CDOM) is one of the important fractions of dissolved organic matter (DOM) that controls the availability of light in water and plays a crucial role in the cycling of carbon. High CDOM absorption in the Mandovi Estuary (Goa) during spring inter-monsoon (SIM) is largely driven by both in-situ production and anthropogenic activities. Here we have presented the CDOM variation in the estuary during SIM of 2014–2018 and compared it with that of 2020 when the COVID-19 outbreak imposed lockdown was implemented. During 2020, low CDOM absorption was observed at the mid-stream of the estuary as compared to the previous years, which could be attributed to low autochthonous production and less input from anthropogenic activities. On the other hand, high CDOM observed at the mouth during 2020 is linked to autochthonous production, as seen from the high concentrations of chlorophyll a. High CDOM in the upstream region could be due to both autochthonous production and terrestrially derived organic matter. Sentinel-2 satellite data was also used to look at the variations of CDOM in the study region which is consistent with in-situ observations. Apart from this, the concentration of nutrients (NO3–, NH4+, and SiO44–) in 2020 was also low compared to the previous reports. Hence, our study clearly showed the impact of anthropogenic activities on CDOM build-up and nutrients, as the COVID-19 imposed lockdown drastically controlled such activities in the estuary.

Variations of Colored Dissolved Organic Matter in the Mandovi Estuary, Goa, During Spring Inter-Monsoon: A Comparison With COVID-19 Outbreak Imposed Lockdown Period

Colored dissolved organic matter (CDOM) is one of the important fractions of dissolved organic matter (DOM) that controls the availability of light in water and plays a crucial role in the cycling of carbon. High CDOM absorption in the Mandovi Estuary (Goa) during spring inter-monsoon (SIM) is largely driven by both in-situ production and anthropogenic activities. Here we presented the CDOM variation in the estuary during SIM of 2014 to 2018 and compared it with that of 2020 when the COVID-19 outbreak imposed lockdown was implemented. During 2020, low CDOM absorption was observed at the mid-stream of the estuary as compared to the previous years, which could be attributed to low autochthonous production and less input from anthropogenic activities. On the other hand, high CDOM observed at the mouth during 2020 is linked to the autochthonous production, as seen from the high concentrations of chlorophyll a. High CDOM in the upstream region could be due to both autochthonous production and terrestrially derived organic matter. Sentinel- 2 satellite data was also used to look at the variations of CDOM in the study region which is consistent with in-situ observations. Apart from this, the concentration of nutrients (NO3-, NH4+ and SiO44-) in 2020 was also low compared to the previous reports. Hence, our study clearly showed the impact of anthropogenic activities on CDOM build-up and nutrients, as the COVID-19 imposed lockdown drastically controlled such activities in the estuary.

A comparative study on microzooplankton communities in two tropical monsoonal estuaries

We studied on microzooplankton (MZP) communities from two major rivers, the Mandovi and the Zuari estuarine system of Goa on central west coast India. Despite both estuaries having a common point of discharge (eastern part of the Arabian Sea) and origin (in the Western Ghats), the Zuari estuary retains its marine condition; in contrast, the Mandovi estuary becomes a nearly freshwater condition for most parts of the year. The essential components of the marine food web, the MZP showed substantial seasonal variation driven by hydrographical parameters. Canonical correspondence analysis (CCA) depicts that prevailing differential environmental variables such as salinity, chlorophyll a, and dissolved oxygen influence the MZP assemblages in the tropical estuarine systems, which lead to the dominance of heterotrophic dinoflagellates (~80%) in the Zuari estuary for most parts of the year and dominance of loricate ciliates (~67%) in the Mandovi estuary. During monsoon, the seasonal intrusion of low oxygen water from the coastal region directs the dominance of heterotrophic dinoflagellates (22 to 80%) in these estuarine systems, particularly in the Zuari estuary. Whereas, prevailing high saline waters during the pre-monsoon (23 to 62%) and the post-monsoon (34 to 55%) supported the loricate ciliates dominated MZP community. The higher abundance of MZP in the upstream during the pre-monsoon and euhaline region of the downstream compared to the upstream (oligohaline) during monsoon and post-monsoon seems to be supported by microbial food (pico and nano-plankton), which warrants further investigation.

Copper dynamics in a tropical estuarine system during dry season

This is the first study to comprehend copper (Cu)-dynamics in a monsoon fed Indian estuarine system (the Mandovi estuary from the central west coast of India). Distribution and speciation of Cu in estuarine sediment, pore water, suspended particulate matter (SPM) and water column was used to understand geochemical cycling of Cu in the estuary. Geochemical fractionation study reveals that sedimentary organic carbon (Corg) was the major hosting phase for non-residual Cu in the sediments. Experimental analysis and chemical speciation modelling suggests that leaching of sedimentary Cu2+, CuCO3 and a fraction of Cu-Corg complexes increased Cu-concentrations in the pore water towards the downstream of the estuary. Dissolved Cu concentration in overlying water column was observed to increase with increasing Cu concentrations in the pore water. This study suggests that chemical speciation of sedimentary Cu play key role in controlling its distribution and dynamics in the tropical estuarine system during dry period.

Seasonal production of nitrous oxide in a tropical estuary, off western India

Estuaries are highly productive ecosystems, and estuarine emission of N2O contributes significantly to the global nitrogen (N) budget. Presented here are the spatio-temporal distribution and water–air flux of N2O from a monsoonal, tropical estuary, the Mandovi located off Goa, during three consecutive years of 2011, 2012 and 2013. Despite substantial input from various sources, the estuary was moderately enriched with nitrogenous nutrients (≤30μM). However, the N transformations do not seem to contribute towards considerable emissions of N2O. Nonetheless, the seasonal upwelling along the west coast of India influences the water column chemistry at the estuarine mouth, as the upwelled water intrudes ∼13 km inside the estuary, leading to significant changes in terms of N2O cycling. A high build-up of N2O in the bottom waters was observed annually during peak southwest monsoon (SWM). The highest concentrations of N2O ∼164 nM (∼2459 %, August 2011), 106 nM (∼1566 %, September 2012), and 156 nM (∼2320 %, August 2013) were recorded at the estuarine mouth that was associated with a coastally-derived upwelled water mass. However, the average concentrations of N2O during pre- and post-monsoon were 10.88 ± 2.07 nM and 11.07 ± 2.85 nM, respectively, for the three years.The water–air flux of N2O was highest during SWM and was lowest during pre- and post-monsoons. The average flux by the estuary varied from ∼3.98 - 48.46μmol m−2d−1. The average annual emission from the Mandovi estuary was estimated to be ∼5.5 × 106 g N2O y−1, which seems to be a smaller fraction when compared to coastal emissions. Our study suggests that while the Mandovi estuary remains in saturation with respect to N2O, it acts as a modest source of N2O to the atmosphere, especially during SWM.

Characterizing three shallow-water locations off Goa, India, using passive acoustic data.

In this study, an analysis of the passive acoustic data is carried out for the quantitative characterization of shallow-water acoustic environments from three major estuarine systems of Goa during the months of March and April. The identification of fish sounds was carried out using waveform and peak power spectral densities (PSDs) of the individual fish calls. Fish sound data showed that the toadfish of the Batrachoididae family (Colletteichthys dussumieri species) produced a spectral level 112.27 ± 4.48 dB re 1 μPa2 /Hz at 448.96 ± 40.30 Hz frequency from the mangrove-dominated tidally influenced Mandovi estuary. Similarly, in a coral reef area near Grande Island in the Zuari estuary, Tiger Perch fish from the Terapontidae family (Terapon threaps species) were identified, having spectral levels 106.91 ± 3.08 dB re 1 μPa2 /Hz at 1791.56 ± 106.55 Hz frequency. From the Sal estuary, PSD levels were found to be around 98.24 ± 2.98 dB re 1 μPa2/Hz at 1796.95 ± 72.76 Hz frequency for Tiger Perch of the Terapontidae family (T. threaps species). To characterize the contributions of biophony (fish), geophony (wind and flow, etc.), and anthrophony (boats, etc.), cluster analysis is employed. In the Mandovi estuary, the root-mean-square sound pressure level (SPLrms) of broadband toadfish was a function of the water flow and temperature. In the Zuari estuary, SPLrms was a function of the water temperature and wind, whereas in the Sal estuary, wind mainly influenced the SPLrms.

Chromate detoxification potential of Staphylococcus sp. isolates from an estuary.

Chromium (Cr) pollution is an emerging environmental problem. The present study was carried out to isolate Cr-resistant bacteria and characterize their Cr detoxification and resistance ability. Bacteria screened by exposure to chromate (Cr6+) were isolated from Mandovi estuary Goa, India. Two isolates expressed high resistance to Cr6+ (MIC ≥ 300 µg mL-1), Cr3+ (MIC ≥ 900 µg mL-1), other toxic heavy metals and displayed a pattern of resistance to cephalosporins and ß-lactams. Biochemical and 16 S rRNA gene sequence analysis indicated that both isolates tested belonged to the Staphylococcus genus and were closely related to S. saprophyticus and S. arlettae. Designated as strains NIOER176 and NIOER324, batch experiments demonstrated that both removed 100% of 20 and 50 µg mL-1 Cr6+ within 4 and 10 days, respectively. The rate of reduction in both peaked at 0.260 µg mL-1 h-1. ATP-binding cassette (ABC) transporter gene involved in transport of a variety of substrates including efflux of toxicants was present in strain NIOER176. Through SDS-PAGE analysis, whole-cell proteins extracted from both strains indicated chromium-induced specific induction and up-regulation of 24 and 40 kDa proteins. Since bacterial ability to ameliorate Cr6+ is of practical significance, these findings demonstrate strong potential of some estuarine bacteria to detoxify Cr6+ even when its concentrations far exceed the concentrations reported from many hazardous effluents and chromium contaminated natural habitats. Such potential of salt tolerant bacteria would help in Cr6+ bioremediation efforts.