Extraction of persistent lagrangian coherent structures for the pollutant transport prediction in the Bay of Bengal

Lagrangian Coherent Structures (LCS) are the hidden fluid flow skeletons that provide meaningful information about the Lagrangian circulation. In this study, we computed the monthly climatological LCSs (cLCS) maps utilizing 24 years (1994-2017) of HYbrid Coordinate Ocean Model (HYCOM) currents and ECMWF re-analysis winds in the Bay of Bengal (BoB). The seasonal reversal of winds and associated reversal of currents makes the BoB dynamic. Therefore, we primarily aim to reveal the cLCSs associated with seasonal monsoon currents and mesoscale (eddies) processes over BoB. The simulated cLCS were augmented with the complex empirical orthogonal functions to confirm the dominant lagrangian transport pattern features better. The constructed cLCS patterns show a seasonal accumulation zone and the transport pattern of freshwater plumes along the coastal region of the BoB. We further validated with the satellite imagery of real-time oil spill dispersion and modelled oil spill trajectories that match well with the LCS patterns. In addition, the application of cLCSs to study the transport of hypothetical oil spills occurring at one of the active oil exploration sites (Krishna-Godavari basin) was described. Thus, demonstrated the accumulation zones in the BoB and confirmed that the persistent monthly cLCS maps are reasonably performing well for the trajectory prediction of pollutants such as oil spills. These maps will help to initiate mitigation measures in case of any occurrence of oil spills in the future.

The consequences of reduced anthropogenic activities during the COVID-19 pandemic on microplastic abundance in a tropical estuarine region: Goa, India

Plastic pollution is pervasive, as it has infiltrated every corner of the planet and the COVID-19 pandemic has caused a depletion in the production, consumption, and disposal of plastics. To find out the effect of the COVID-19 pandemic, a comparative assessment of microplastics (MPs) observed before and after the pandemic was evaluated in surface water and sediment from the major rivers of Goa, i.e. Mandovi and Zuari. To comprehend the relative difference in the abundance, characteristics, and source of MPs, samples were examined in both the dry and wet seasons. We found a sharp decrease in the concentration of MPs immediately after the isolated pandemic. During the dry and wet seasons, two to seven times less concentration of MPs was recorded for water and sediments after the pandemic period compared to the prior pandemic. MPs size, >300 μm were relatively abundant after the pandemic period in contrast to the prior pandemic (<300 μm sized MPs were more). Polyamide (PA), polyvinyl alcohol (PVAL), and polyvinyl chloride (PVC) were the dominant polymers after the pandemic whereas earlier the dominant polymers were polyacetylene, polyacrylamide (PAM), and polyvinyl pyrrolidone (PVP). The risk assessment of MPs in sediments (Polymer load index) was higher prior to the pandemic. The water quality parameters also indicated an improvement in the water quality during the pandemic. The present study clearly exhibited that due to the reduction of overall anthropogenic activities during the COVID-19 pandemic period, a sharp decline of plastic waste and MP abundance in the coastal water body in Goa, west coast of India was found. This study unveils the controlling factors (such as total solid waste generation, plastic waste, tourism activities, and the effect of monsoon) which influence the abundance and distribution of macro- and microplastics.

Microplastics in the sediments along the eastern Arabian Sea shelf: Distribution, governing factors and risk assessment

Despite the omnipresence of microplastics (MPs), the studies around the western continental shelf of Indian Ocean (Eastern Arabian Sea-EAS) are uncovered and understudied. Thus, the present study was focused to understand the spatial distribution, characterization and risk assessment of MPs in sediment across seven coastal transects (10 to 50 m) all along the EAS shelf. The highest MPs concentration (MPs/kg d.w.) was detected in the northern EAS (NEAS; 2260 ± 1050) followed by central (CEAS; 1550 ± 1012) and southern (SEAS; 1300 ± 513) shelves. Among all distinct locations, the highest concentration of MPs (2500 ± 1042) was detected in the north coastal sediments off Mumbai, followed by off Mangalore (1480 ± 1169) in the center and off Kochi (1350 ± 212) in the south. MPs were found in the form of fibres, fragments and films with a predominance of fibres (~70-80 %). Approximately 74.6 % of the total MPs were in the size range of 300 μm to 5 mm. The surface of detected MPs was rough, irregular, and mechanical weathering features such as pits, grooves also observed and spotted with bacterial community structures. Polypropylene (PP; 34 %), polyisoprene (PIP; 19 %), butyl rubber (18 %), and low-density polyethylene (LDPE; 13 %) were dominant polymers. The pollution load index highlighted minor risk while the polymer hazard index exhibited a hazard level of V. Litter discharge, fishing activities, and active marine navigation are among the many high-risk sources of plastic contamination in this region. Due to the prevailing winds, currents, low sea surface height, and high precipitation, the conditions in the EAS are favorable for the accumulation of both sea-based and land-based particles. Hence, this study provides novel insights into the potential risks posed by MP to the IO rim and associated marine ecosystem which will enhance our knowledge of the ecological implications and consequences of MP pollution, ultimately aiding in developing effective management and mitigation strategies.

Microplastic intrusion into the zooplankton, the base of the marine food chain: Evidence from the Arabian Sea, Indian Ocean

Microplastics (MPs) are ubiquitous in the marine environment, yet information regarding their occurrence in the food web is limited. We investigated the concentration and composition of MPs in water and diverse zooplankton groups from the Arabian Sea basin. Forty-one zooplankton tows were collected with a bongo net (330 μm mesh) from the Arabian Sea in January 2019. MPs in the surface water varied between 0 and 0.055 particles/m³, with a relatively higher concentration (0.013 ± 0.002 particles/m³) in the central Arabian Sea. Though fibrous MPs were most abundant in the seawater (77.14 %), zooplankton prefers small fragments (55.3 %). The size of MPs was distinctly smaller (277.1 ± 46.74 μm) in zooplankton than that in seawater (864.32 ± 73.72 μm), and MPs bioaccumulation was observed in almost all the zooplankton functional groups. Polymer composition revealed polyamide, polyethylene, polypropylene, and PVC were abundant in water and zooplankton, suggesting that the textile, fishing, shipping, and packaging industries are significant sources. The prevailing northeasterly winds, strong West India Coastal Current, and conducive westward radiated Rossby wave during January 2019 have carried the microplastic contaminated water mass away from the coast, posing a threat to the open ocean ecosystems. These results demand further attention to investigate the state of plastic pollution in the Arabian Sea basin.

Year-to-year variability of oil pollution along the Eastern Arabian Sea: The impact of COVID-19 imposed lock-downs

This study investigated the year-to-year variability in the occurrence, abundance and sources of oil spills in the Eastern Arabian Sea (EAS) using sentinel-1 imagery and identified the potential oil spills vulnerable zones. The four consecutive year's data acquired from 2017 to 2020 (March-May) reveal three oil spill hot spot zones. The ship-based oil spills were dominant over zone's-1 (off Gujarat) and 3 (off Karnataka and Kerala), and the oil field based over zone-2 (off Maharashtra). The abundance of oil spills was significantly low in zone-1, only 14.30km² (1.2%) during lock-down due to the covid-19 pandemic. Whereas, the year-to-year oil spills over zone's 2 and 3 are not significantly varied (170.29 km² and 195.01 km²), further suggesting the influence of oil exploration and international tanker traffic are in operation during the lock-down. This study further recommends that manual clustering is the best method to study the distribution of unknown oil spills.

Fate of MV Wakashio oil spill off Mauritius coast through modelling and remote sensing observations

This study aims at assessing the fate of MV Wakashio oil spill, and the driving forces responsible for possible environmental consequences of polluted coastal region. GNOME simulations were performed, considering various meteo-oceanographic forcings such as (i) winds and currents, (ii) only winds, and (iii) only winds with different diffusion coefficients, and validated with the satellite images. The results revealed that the simulations performed with 'only winds' reasonably match with the satellite observations, indicating that winds are the primary driving forces. The conducive stokes drift is an added contribution to the predominant northwestward drift of the spill. The oil budget analysis suggests that beaching and evaporation together accounted for a significant portion of the spilled oil (1000 tons), in which ~60% of the oil was accounted only for beaching. Our results depict that the diffusion coefficient of 100,000 cm²/s and 3% windages are optimal for oil-spill simulations off the southeastern Mauritius coast.

Spatial and seasonal variation of microplastics and possible sources in the estuarine system from central west coast of India

The versatile use of various synthetic polymers, including plastics, generates a large volume of non-degradable waste, which is eventually responsible for forming microplastics (MPs) in aquatic environments. The present study describes the significant spatial and seasonal variation on the abundance of MPs and their physiochemical nature along the Mandovi-Zuari estuarine system of Goa, west coast of India. During the wet season (September), the average abundance of MPs was found relatively higher in water (0.107 particles/m³) and sediment (7314 particles/kg) than those found in the dry season (April) (0.099 particles/m³ in water and 4873 particles/kg in sediment). During the wet season, heavy rain and excessive riverine freshwater influx carry more terrestrial plastic debris in the estuarine system which causes higher averages MPs density in surface water and sediment. <300 μm sized particles and black colored MPs were predominant equally in water and sediment during both seasons. MPs of different shapes like fragments, fibres, films and beads accounted for most collected samples. The Micro-Fourier Transform Infrared Spectroscopy (μ-FTIR) based compositional analysis identified approximately 33 types of polymers, of which polyacrylamide (PAM), polyacetylene, polyamide (PA), polyvinyl pyrrolidone (PVP), polyvinyl chloride (PVC), and polyimide (PI) were abundant. Fragmentation of larger plastic particles due to mismanaged treated and untreated STPs and washing machine effluents are the primary sources of these MPs in the estuarine system. Moreover, these estuaries also receive a variety of domestic, industrial and other wastes from local cities, ports, and fishing jetties. Thus the present study enlightens the current distribution of MPs and their sources in the Mandovi-Zuari estuarine system and thus provides very useful information to the stakeholder and concerned departments for initiating the mitigation measures.

Formation and weathering assessment of oil-suspended sediment aggregates through a laboratory investigation

Formation of oil-suspended sediment aggregates (OSAs) is believed to be one of the natural cleaning processes in the marine environment. In this study, we have investigated the formation processes of OSAs under different mixing periods (continuous mixing and with the addition of sediments in between), oil-sediment ratios (1:1, 1:2 and 2:1) and crude oils (Arabian Light (AL), Kuwait (KW) and Murban (MB)). The results revealed that size of OSAs significantly increased (up to ≈ 1.41 mm) with the addition of sediments. Aggregates (total 36) were extracted for n-alkanes and polycyclic aromatic hydrocarbons to quantify and assess their weathering and toxic levels. The maximum n-alkane depletion was 84% (111-02), 94% (212-02) and 84% (321-02) and PAH depletion was ≈ 72% (111-02), 79% (212-02) and 81% (311-03) for the OSAs of AL, KW and MB crude oils, respectively, for the different samples considered, indicating that n-alkanes were depleted relatively higher than the PAHs. The highest depletion of both n-alkane and PAHs has occurred in OSAs of 10-h continuous mixing. The depletion of both n-alkane and PAHs reduced after the addition of sediments, however, escalated the growth of OSAs, resulting in bigger size OSAs. The concentration of PAHs of all 36 OSAs is greater than 5000 ng/g, indicating very high PAH pollution. Though the formation of OSAs helps in cleaning the spill sites, the carcinogenic threat to the marine ecosystem caused by these OSAs cannot be ignored.

Degradation of tarballs using associated bacterial consortia

Tarballs are semi-solid blobs of crude-oil formed in marine environment. Microbial degradation of tarballs is poorly understood, though there are indications that tarball-associated microbes can degrade recalcitrant hydrocarbons present in tarballs. In this study, 38 tarball-associated bacteria from Betul beach, Goa, India were initially screened for crude oil degradation. Based on preliminary studies and literature survey, four bacterial strains, Alcanivorax sp. Betul-O, Marinobacter sp. Betul-26, Pseudomonas sp. Betul-14, and Pseudomonas sp. Betul-M were selected for bacterial consortia preparation. Eleven bacterial consortia were prepared and studied for degradation of n-alkanes and polycyclic aromatic hydrocarbon compounds (PAHs) of tarballs based on gravimetric and GC-MS-MS analyses. The bacterial consortia depleted 53.69-97.78% and 22.78-61.98% of n-alkanes and PAH compounds, respectively, within 45 days. Bacterial consortium comprising Pseudomonas sp. Betul-14, Pseudomonas sp. Betul-M, and Alcanivorax sp. Betul-O exhibited promising tarball degradation abilities with 97.78% and 61.98% degradation of n-alkanes and PAH, respectively, within 45 days. Further research is required to obtain insights into degradation products and possible pathways involved.

Oil pollution in the Eastern Arabian Sea from invisible sources: A multi-technique approach

The Eastern Arabian Sea (EAS) is affected by oil pollution, as often evidenced by the presence of tarballs along the West Coast of India (WCI). Tarball samples collected during May 2017 along the Goa coast were subject to biomarker fingerprints, and the results matched with Bombay High (BH) oil fingerprints. The present study primarily aims at identifying the potential minor spill areas using Sentinel-imagery. Interestingly, repeated occurrence of oil spills detected at two locations, perfectly matched with BH platforms. The simulated Lagrangian trajectories also depict that tarball particles have originated from those detected locations. In 2017 alone, the quantity of spilled oil was estimated to be 129,392 l. However, spills detected offshore regions of Kachchh and Mangalore were found to be caused by ships. This is the first comprehensive study, tracking the oil pollution sources in the EAS through multi-technique approach - chemical, remote sensing and numerical modeling.

Assessing the source of oil deposited in the surface sediment of Mormugao Port, Goa - A case study of MV Qing incident

In June 2016, a cruise vessel was grounded in the Mormugao Port, resulting in unnoticed oil spill. The surface water and sediment samples were collected from the vicinity of the ship, and also an oil sample from the ship (OIL). These samples were subject to petroleum biomarker such as pentacyclic triterpenes (hopanes) and compound specific carbon isotopic (δ¹³C) analyses to assess the source of hydrocarbon pollution in the Mormugao Port. While no clear trend was observed in water samples, the bottom surface sediments did show an identical pattern of hopanes with the oil. The chemometric analyses of hopane Diagnostic Ratios (DRs) and δ¹³C ratios confirmed the ship oil as the source of oil pollution in sediments. Whereas the water is comparatively more dynamic than the sediment, the physical processes arising out of winds, waves, tides and currents might have dispersed the oil away from the grounded ship.

Diversity of bacteria and fungi associated with tarballs: Recent developments and future prospects

Tarballs are formed by weathering of crude oil in marine environment. They are transported from open ocean to the shores by sea currents and waves. Tarball pollution is a major concern to global marine ecosystem. Microbes such as bacteria and fungi are known to be associated with tarballs. They presumably play an important role in tarball degradation and some are potential human and animal pathogens. This paper highlights the recent studies on tarball-associated bacteria and fungi. Future perspectives on diversity, ecology and possible applications of tarball-associated microbes in bioremediation of beached tarballs have been discussed.

Backtrack modeling to locate the origin of tar balls depositing along the west coast of India

Tar ball (TB) deposition along the West Coast of India (WCI) is a common phenomenon during the southwest monsoon season, particularly along the coast of Goa and Gujarat, and it is a major concern to the stake holders. Our earlier studies showed that the source oil for the TBs deposited on the Goa coast in August 2010 is the tanker wash, and the source for subsequent TBs deposited on the Gujarat coast during July 2012 and June 2013 and Goa coast in May 2013 is from Bombay High (BH) oil fields. In the present study, the TBs that were deposited during May 2013 and May 2014 on the Goa coast were backtracked through a trajectory model, primarily to simulate their pathways and identify the reason for the occurrence of TBs only in May, and eventually to identify the origin and the source. The backtracking results re-confirmed that the TBs deposited in 2010 were originated from the tanker routes and that of both 2013 and 2014 TBs from the BH oil fields. The climatology of wind and surface circulation showed that the TBs deposited on the Goa coast during May/June only are from the oil fields and those during August from the tanker route. The results of backtracking simulations showed that the residence time of the oil residues/TBs is approximately 22days for August 2010 TBs, ≈30days for May 2013 TBs and 65days for May 2014 TBs. The residence time (in water) of TBs that deposit (on the coast) in the month of May could be as much as 7months, and could be around one month if deposit in August, primarily because of winds and hydrodynamic conditions of the Arabian Sea.

Characteristics, seasonal distribution and surface degradation features of microplastic pellets along the Goa coast, India

Microplastic pellets (MPPs) are ubiquitous contaminants, recognised as a serious threat to the biota in coastal, estuarine and marine environment. The distribution, abundance, weathering and chemical characteristics of MPPs on the beaches of Goa, and their transport to the coast during the southwest (SW) monsoon are discussed in this paper. MPP samples collected from six sandy beaches were categorised based on colour and polymer types using Stereoscope microscope and FTIR-ATR spectroscopy, respectively. White colour MPPs were the most abundant, and Polyethylene (PE) and Polypropylene (PP) were the dominant polymer types of MPPs deposited on all the beaches. Carbonyl index values showed that MPPs collected in June 2015 (representing SW monsoon) were 'new', whereas the MPPs collected in January 2015 were 'aged', showing that MPPs are arriving at Goa coast only during SW monsoon due to conducive hydrodynamic conditions. Characteristics of MPPs suggest that they could be originated primarily from ocean-based sources. The winds and surface currents during SW monsoon are the driving forces for the transportation and deposition of MPPs on the Goa beaches. The results of this study will be useful to the National 'Clean India' program for effective plastic debris removal management.

Identifying the source of tar balls deposited along the beaches of Goa in 2013 and comparing with historical data collected along the West Coast of India

Deposition of oil residues, also known as tar balls, is a seasonal phenomenon, and it occurs only in the southwest monsoon season along the west coast of India. This has become a serious environmental issue, as Goa is a global tourist destination. The present work aims at identifying the source oil of the tar balls that consistently depositing along the Goa coast using multi-marker fingerprint technique. In this context, the tar ball samples collected in May 2013 from 9 beaches of Goa coast and crude oils from different oil fields and grounded ship were subject to multi-marker analyses such as n-alkanes, pentacyclic terpanes, regular steranes, compound specific isotope analysis (CSIA) and principle component analysis (PCA). The n-alkane weathering index shows that samples have been weathered to various degrees, and the status of weathering is moderate. Since the international tanker route passes closer to the west coast of India (WCI), it is generally presumed that tanker wash is the source of the tar balls. We found that 2010/2011 tar balls are as tanker wash, but the present study demonstrates that the Bombay High (BH) oil fields can also contribute to oil contamination (tar balls) along ≈ 650 km stretch of the WCI, running from Gujarat in the north to Goa in the south. The simulated trajectories show that all the particles released in April traveled in the southeast direction, and by May, they reached the Goa coast with the influence of circulation of Indian monsoon system.

Source investigation of the tar balls deposited along the Gujarat coast, India, using chemical fingerprinting and transport modeling techniques

Deposition of tar balls (TBs) along the south Gujarat coast, situated on the west coast of India (WCI), commonly occurs during the southwest monsoon season. Several offshore oil fields off the Mumbai-Gujarat coast, and refineries along the coast might be sources of oil spills/leakages and lead to the formation of TBs. To identify the sources, we collected 12 TB samples from the beaches of Gujarat (Tithal, Maroli, Umbergam, and Nargol) during 15-17 July 2012 as well as samples of crude oils, namely, Cairn, NIKO, MSC Chitra, and two at Bombay High (BH). These TBs were subject to the following multimarker approach for source identification: Diagnostic Ratios of n-alkanes, polycyclic aromatic hydrocarbons, pentacyclic triterpanes, compound specific isotope analysis, Principle Component Analysis and numerical simulations (hydrodynamic model coupled with particle trajectories). The chemical fingerprint results reveal that the source of the TBs is BH crude oils, and the model results confirm that the source location is BH north oil fields. This is the first study of its kind in India to use fingerprinting and transport modeling techniques for source identification of TBs.

Identification of sources of tar balls deposited along the Goa coast, India, using fingerprinting techniques

Deposition of tar balls along the coast of Goa, India is a common phenomenon during the southwest monsoon. Representative tar ball samples collected from various beaches of Goa and one Bombay High (BH) crude oil sample were subjected to fingerprint analysis based on diagnostic ratios of n-alkane, biomarkers of pentacyclic tri-terpanes and compound specific stable carbon isotope (δ¹³C) analysis to confirm the source. The results were compared with the published data of Middle East Crude Oil (MECO) and South East Asian Crude Oil (SEACO). The results revealed that the tar balls were from tanker-wash derived spills. The study also confirmed that the source is not the BH, but SEACO. The present study suggests that the biomarkers of alkanes and hopanes coupled with stable carbon isotope analysis act as a powerful tool for tracing the source of tar balls, particularly when the source specific biomarkers fail to distinguish the source.