Review on the Sundarbans delta oil spill: effects on wildlife and habitats

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REVIEW ON THE SUNDARBANS DELTA OIL SPILL: EFFECTS ON WILDLIFE AND HABITATS

Bautista H., Rahman K.M.M.

Аннотация

В последнее время водные системы дельты Сундарбана подвергаются возрастающему воздействию, вызванному разливом нефти. Гидрологическая возможность соединения водных экосистем в дельте Сундарбана делает их высокочувствительными к широкому диапазону антропогенных действий. 9 декабря 2014 приблизительно 94,000 галлонов (78,271 Имперских галлонов) тяжелого дистиллятного топлива было пролито в реку Шела, которая проходит через Сундарбан. Мангровые растения, речные травы, морские водоросли и связанные с ними беспозвоночные были покрыты нефтью; некоторые из них погибли вскоре после этого происшествия. Гибель таких видов, как дельфин Иравади (Orcaella brevirostris), Восточная бескоготная выдра (Amblonyx cinereus), по сообщениям, также вызвана разливом нефти. Присутствие Бенгальского грифа (Gyps bengalensis) в небе над Сундарбаном указало на крупномасштабную гибель дикой фауны.

Ключевые слова: нефть, влияние, Сундарбан, экосистемы, дикая природа, среда обитания.

Abstract

Recently, Sundarbans aquatic ecosystems are suffering escalating impacts caused by oil spill. The hydrological connectivity of aquatic ecosystems in the Sundarbans Delta makes them highly sensitive to a broad range of anthropogenic activities. On December 9, 2014 approximately 94,000 gallons (78,271 Imperial gallons) of heavy furnace oil spilled into Shela River, which runs through the Sundarbans. Intertidal mangroves plants, river grasses, algae, and associated invertebrates were badly covered by oil and some of them died soon after. The death of Irrawaddy dolphin (Orcaella brevirostris), Oriental samll-clawed otter (Amblonyx cinereus) has been reported because of oil spill. The presence of White rumped vulture (Gyps bengalensis) over the Sundarbans sky also indicated the large scale death of wild fauna.

Keywords: Oil, effects, Sundarbans, ecosystems, wildlife, habitats

Introduction

Sundarbans is the world's largest tidal mangrove forest is one of the most bio-diverse places on Earth, a UNESCO declared world heritage site [1], is the last home of Bengal tigers (Panthera tigris) and many others important wildlife fauna including riverine Irrawaddy (Orcaella brevirostris) and Ganges dolphins (Platanista gangetica) [2]. The area of Sundarbans is approximately 10,000 square kilometres (3,900 sq mi) most of which is in Bangladesh and rest of its situated in India [3]. Sundarbans backings a total of 334 species of plants [4]. The most familiar flora of Sundarbans are Sundari (Heritiera fomes), Gewa (Excoecaria agallocha), Goran (Ceriops decandra) and Keora (Sonneratia apetala). Sundarbans is the address of 150 spеcies of fish, 270 speсies of birds, 42 sрecies of mаmmals, 35 reptiles inсluding Estuаrine Crocоdile (Crocodylus porosus) and 8 amphibiаn species [5].

The Dеlta of Sundаrbаns are always noticеd for its immеnse oil tаnker trаffic that's why here in the cоastal water the risk of oil spill is also so high. On December 9, 2014, approximately 94,000 gallоns (78,271 Imperial gallons) of heavy fuel oil spilled out of a downed tanker and into the Sundarbans Delta (Shеla River) strаddling Bangladesh and India [6]. Most of the aquatic animal in the Sundarbаn Delta of Bangladesh and India, from riverine dolphins, salt water crocodiles and aquatic birds to single called plankton, could be affected by the oil contamination in the Delta. Spilled oil always have great negative effects on the mangrove ecosystem on the basis of its compоsition and concеntration. Sometimes, it causes the transformаtions of the chеmical comрosition of the environment and alterаtion in it's physical propеrties that lead to the dеstruction of the nutritiоnal capital of the mangrove biomass which is so harmful for the human health and as well as for the balance of biological environment.

Effects of Oil Spill

In general, sрilled oil can affесts animals and plants in twо ways: dirесt from the oil and from the respоnsе or cleаnup process. There is no clear relаtionship between the amount of oil in the aquatic ecosystems and the likely impасts on its wildlife populations. A lesser spill at the inaccurate time or wrong season and in a responsive ecosystem may prove much more catastrophic than a greater spill at another time of the year in another or even the same ecosystems [7].

Fig 1 Geographical location of Sundarbans Reserved Forest (Bangladesh), coordinates 21°56?59?N 89°10?59.988?E

Even little spills can have very adverse effects [8]. Thus, one should not simply compаre figures -- the size of an oil spill is exactly not the only ingredient of importance in terms of what ecological disturbance can be caused by the oil.

Oil is lethal to roughly all creatures. The lethal impact depends on the content and concentration of the oil, and the reactivity of the species affected [9]. Actually, spilled oil can harm to wildlife populations in two major ways: i) Physical junction and ii) Toxic infection.

In this review study, we focused mainly on the effects of oil spill on cetaceans (dolphins), otters, birds, fishes, coastal wetlands and intertidal zones, and the overall ecosystems.

The impact of oil on Cetaceans

sundarban delta oil spill

Sundarbans Delta is the habitat of two globally vulnerable dolphins' species: Irrawaddy river dolphins (Orcaella brevirostris) and Ganges dolphins (Platanista gangetica) [10]. For breathing purposes when dolphins, come to the outward of water, oily water can be coating their blowholes and get in their lungs, making respiration difficult. Oil can enter into the animals' eyes, possibly causing harm to vision. It can also get in their jaws, where it can be ingested, and potentially damaging interior structures. Oil pollutions like to have detrimental impacts on cetacean reproduction and long term health [11]. After Oil spill in Sundarbans Delta, the reported death of Irrawaddy river dolphin is documented.

Impacts of oil on Otters

Oriental small-clawed otter (Amblonyx cinereus) aquatic carnivore animal lives in the aquatic ecosystem of Sundarbans [10]. Otters spend a lot of their time on the water surface and are totally relying on their fur coat for isolation and for the ability to swim. As a result, otters are considered as being very susceptible to oil pollution as oil can result in the fur losing its capacity to insulate the animals. Nonetheless, inhaling petroleum products or ingesting oil when they groom themselves can blow their lungs, cause ulcers, and result in liver and kidney disturbance. Habitat loss and declining food resources create indirect impacts on the otters [11]. The Sundarbans oil spill incident is believed to have led to the death of several otters, mainly as a result of ingestion of oil [12].

The effect of oil on Birds

Aquatic birds are very sensitive to oil pollution in several ways. Primarily, oil soaks into the plumage and damages insulation and floating ability causing low body temperature, starvation and die through inhalation of water [13]. The oil damages the water resistance of feathers by unsettle the actual orderly adjustment of feather barbules and barbicels [13, 14].

The birds sometimes sniff or consume oil. As lot of the materials in oil are lethal in character, this may cause severe damage/health impacts such as lung inflammation, glutted lungs, intestinal or pulmonary hemorrhage, liver and kidney damage [15]. This effects are sometime as lethal as hypothermia, although the effects may not manifest themselves as rapidly. Oil can also affect the reproductive potentiality of the birds as oil from feathers of a bird that is laying on eggs can cross through the opening in the eggshells and either kill the embryos or lead to abnormal offspring.

Impacts of oil spill on fish

Much less is known about the effects of oil on fish, fish eggs and larvae. The huge percentage of fish died after Sundarbans oil spill indicate that the effects can be serious and long-term. Oil may disturb fish in many approach. Fish readily take up oil ingredients into their tissues after exposure to oil in water, food or sediment. Fish may inhale large contents of oil over their gills [9]. Fish that have been exposed to oil may suffer from alter in heart and inhaling rate, extended livers, lowered growth, gradual destruction of fin and scale, and a diverse of impacts at biochemical and nuclear levels. If this does not kill them more or less directly, the oil may affect the reproductive potentiality negatively and/or result in deformed spine [16].

Fish eggs and larvae are commonly more responsive to oil pollution than adult fish. Lethal effects (LC50) of water-soluble petroleum ingredients on larvae have been predicted to be in the range 0.1 - 1 mg/kg [17]. Heintz et al. (1999) found a greater reactivity of herring and pink salmon embryos during long-term exposure to weathered Exxon Valdez fuel oil. Lowest observed effective concentrations (LOECs) were about 1 µg/kg (ppb) total PAH from very weathered oil. Total PAH from less weathered oil was less lethal demonstrating that toxicity in the very weathered oil was basically related with the larger PAHs [18].

Effects on Vegetation

Oil spill always have important short and long-term effects on coastal area ecosyastems. Chemical toxicity of the crude oil disturb the plant water conjunction, hamper metabolism, become lethal to cell, retard the photosynthesis of aquatic flora, and prevent with oxigen intake from environment and soils.

During heavy tide, spilled oil enter into the center of the Sundarbans, and plants leaves and stem become covered by oil which will block the stomata, reduced oxygen diffussion to the roots, result will hamper the plant growth. Oil already mixed with soil has reduced oxygen resulting to anaerobic condition that in effect increases plant stress. Laboratory result showed that Plants with blocked leaves are more severely affected as compared to plants in contaminated soils[19]. It is reported that the floating objects like water hyacinth (Eichhornia crassipes) is spreading thin layer of oil in the whole river. This floating object with oil coating is helping in oil spread too. By visual observation it's noted that most of the plants of the Sundarbans are covered by oil including two of most famous plants named Sundari (Heritiera fomes) and Nipa palm (Nypa fruticans) (Table 1). While some apparent acute effects of oil exposure (i.e., loss of leaves from some young mangrove trees at the low tide margin) were observed along two creeks, resource experts from the Bangladesh Forest Research Institute and the Department of Forest also noted that new growth had already begun to appear on the plants [12]. Though in naked eyes, effect of oil spill on the Sundarbans vegetation is not strongly reported but it has long term effect on it without any doubt. In addition, clean-up process of the oil causes physical disturbance and compaction of the vegetation and soil [20].

Table 1

IUCN Red list of mangrove species from Bangladesh?s Sundarbans region with their status, updated in 2015. Not evaluated (ne), Least concern(lc), Near threatened (NT), Endangered (EN), Critically endangered (CR), Extinct (EX) [21].

Conclusions

Mangroves are very sensitive to oil contact; result includes a loss of canopy cover, elevated percentage of mutation and acuteness to other stresses. Oil-affected mangroves can experience yellowed leaves, defoliation, and even death of the trees within a few weeks to several months.

Oil spill incident in the Shela River of the Sundarban wildlife sanctuary, considered as a severe oil spill accident from ecological point of view. From microorganisms to large wildlife fauna affected by oil pollution very badly. Oil will likely reduce the amount and health of all prey species, reducing the food available for aquatic mammals, birds and crocodile. Plankton is the foundation for nearly all life in the Delta of Sundarbans and they will most likely be affected. Contaminants from the spill and the dispersants are likely to concentrate in the upper food chain, affecting dolphins, otters, birds and fishes.

References

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