Rivers, carriers of plastic

Plastic pollution in oceans and rivers is growing and its accumulation on riverbanks, deltas, coastlines and the ocean surfaces is rapidly increasing. Plastic pollution poses a threat not only to aquatic life, and ecosystems, but also affects human health. Recent studies show that land-based plastics are one of the main sources of marine plastic pollution either by direct emission from coastal zones or more importantly- by transport through rivers.

And rivers have indeed been found to be major carriers of plastic! A recent study finds that of the total 100,887 outlets of rivers and streams observed globally, 31,904 locations emit plastic waste into the ocean, leaking in 1.0 (0.8 to 2.7) million MT into the marine environment.

More than 1000 rivers account for 80 percent of global annual plastic emissions, which range between 0.8 million and 2.7 million metric tons per year, with small urban rivers among the most polluting.

India, a top riverine plastic polluter

India appears second among the top twenty countries that have a high contribution of riverine plastic emissions nationally as well as globally.

Studies show that the Indus, Brahmaputra and the Ganges are the top plastic carrying rivers in the country among the ten rivers that drain over 90 percent of the total plastic debris into the sea globally.

While the Indus carries the second highest amount of plastic to the sea, the Brahmaputra and Ganga together carry the sixth highest. These plastic wastes are not only from cities but also from villages along these rivers.

Plastic and the mighty Ganges

The Ganges originates in the Himalayas and the 2500 km river is of high religious, cultural, socio-economic and ecological significance for India and supports the livelihoods of over 655million people living on its banks.

The paper titled 'Riverine plastic pollution from fisheries: Insights from the Ganges river system' published in the journal Science of Total Environment informs that the Ganges River system has been identified as one of 14 continental rivers into which over a quarter of global waste is discarded. It is the second largest plastic polluting catchment in the world (0.12 million tonnes plastic discharged per year), after the Yangtze River in China (0.33 million tonnes).

Inland fisheries provide an important source of livelihood and nutrition for a large section of the population residing in the lower parts of the Ganges. The region is an important biodiversity spot hosting a large number of endemic aquatic species, many of which are under pressure due to anthropogenic factors such as dam construction, habitat degradation, pollution and fisheries bycatch.

Abandoned, lost or otherwise discarded fishing gear represents a substantial proportion of global  plastic pollution and can cause significant environmental and socio-economic impacts. However, little is known on the kinds of plastic debris and its distribution, factors influencing distribution of plastic waste and the associated risks to biodiversity in the vicinity of the Ganges, which can later be deposited in the oceans.

The paper discusses the findings of a study that explores the extent and the kinds of fishing gear related plastic wastes found on the riverbanks of the Ganga and its impact on the environment.

The study finds that:

Most of the discarded fishing gear is made of plastic

A large amount of abandoned, lost or otherwise discarded fishing gear (ALDFG) is found on the Ganges riverbank. The most commonly occurring plastic wastes include strings (41.2 percent) followed by nets (40.2 percent), ropes (10.1 percent), floats and lines.

Almost half of the nets are made up of nylon while the rest are made from PCT (23.1 percent), polyethylene (15.4 percent), high-density polyethylene and polypropylene.

Ropes are predominantly made from polypropylene (46.2 percent) followed by regular and high-density polyethylene (both 23.1 percent) while floats are mainly made of of polyethylene (68.8 percent) followed by high-density polyethylene (18.8 percent) and polystyrene. Strings are mainly made from polypropylene (47.2 percent) and high-density and regular polyethylene.

Small mesh sizes of the nets increases risk to aquatic animals

A range of fishing techniques are used by fisherfolk living along the banks of the Ganges and thus  a wide-range of net mesh-sizes right from 1 mm mosquito net to 130 mm monofilament gill nets can be found along the banks of the Ganges.

The small mesh size of the nets increases the risk of high capture rates of juvenile fish, thus affecting the sustainability of fisheries. Small mesh size also increases the risk of entanglement of aquatic species especially those like the Ganges river dolphin.

Poor disposal mechanisms and regulatory practices lead to piling of plastic waste

Majority of the fisherfolk change or replace their nets every six months depending on the quality, durability and cost. While some of the gears are converted into other useful items, many of them are discarded into the environment and thrown into a river or left at the riverbank. Some fisherfolk also say that they either sell, burn or bury old gear.

Lack of information on regulations among the fisherfolk and ineffective regulations further worsen the situation leading to piling up of unused fishing gears on the river shore or into the river.

Biodiversity threat to animals increases due to plastic waste

A number of fisherfolk report of crabs, crocodiles, dolphins, frogs, lizards, otters, rays, sawfish, sharks, snails, snakes, turtles and domestic animals being caught in the nets alive.

Of the five amphibian species assessed, the Indian bullfrog and marbled toad are the most vulnerable to being caught in the nets followed by Jerdon's bullfrog, Tytler's pond frog and Nepal Paa frog.

Of the freshwater turtle species, the three-striped roofed turtle is the most vulnerable of all animals to being entangled in the nets followed by black spotted turtles, northern river terrapin and red-crowned roofed turtles.

Marsh crocodiles, gharials and salt water crocodiles and a range of birds including black-bellied terns, river terns, sarus cranes, Indian skimmer and river lapwing and otters species such as the smooth-coated otter, small-clawed otter and Eurasian otter are vulnerable to getting caught/entangled in the nets.

The species with the highest risk of entanglement in the nets include the threatened freshwater turtles and otters, and the endangered Ganges river dolphins.

The study calls for an urgent need to design targeted and practical interventions to limit the input of fisheries-related plastic pollution into the Ganga that ultimately reaches the ocean, posing a risk to biodiversity and freshwater as well as marine health.