Marine debris
Marine debris, also known as marine litter, is human-created solid material that has deliberately or accidentally been released in seas or the ocean. Floating oceanic debris tends to accumulate at the center of gyres and on coastlines, frequently washing aground, when it is known as beach litter or tidewrack. Deliberate disposal of wastes at sea is called ocean dumping. Naturally occurring debris, such as driftwood and drift seeds, are also present. With the increasing use of plastic, human influence has become an issue as many types of plastics do not biodegrade quickly, as would natural or organic materials. The largest single type of plastic pollution and majority of large plastic in the oceans is discarded and lost nets from the fishing industry. Waterborne plastic poses a serious threat to fish, seabirds, marine reptiles, and marine mammals, as well as to boats and coasts.
Dumping, container spillages, litter washed into storm drains and waterways and wind-blown landfill waste all contribute to this problem. This increased water pollution has caused serious negative effects such as discarded fishing nets capturing animals, concentration of plastic debris in massive marine garbage patches, and increasing concentrations of contaminants in the food chain.
In efforts to prevent and mediate marine debris and pollutants, laws and policies have been adopted internationally, with the UN including reduced marine pollution in Sustainable Development Goal 14 "Life Below Water". Depending on relevance to the issues and various levels of contribution, some countries have introduced more specified protection policies. Moreover, some non-profits, NGOs, and government organizations are developing programs to collect and remove plastics from the ocean. However, in 2017 the UN estimated that by 2050 there will be more plastic than fish in the oceans if substantial measures are not taken.
Types
Researchers classify debris as either land- or ocean-based; in 1991, the United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution estimated that up to 80% of the pollution was land-based, with the remaining 20% originating from catastrophic events or maritime sources. More recent studies have found that more than half of plastic debris found on Korean shores is ocean-based.A wide variety of man-made objects can become marine debris; plastic bags, balloons, buoys, rope, medical waste, glass and plastic bottles, cigarette stubs, cigarette lighters, beverage cans, polystyrene, lost fishing line and nets, and various wastes from cruise ships and oil rigs are among the items commonly found to have washed ashore. Six-pack rings, in particular, are considered emblematic of the problem.
The U.S. military used ocean dumping for unused weapons and bombs, including ordinary bombs, Unexploded ordnance, landmines and chemical weapons from at least 1919 until 1970. Millions of pounds of ordnance were disposed of in the Gulf of Mexico and off the coasts of at least 16 states, from New Jersey to Hawaii.
Eighty percent of marine debris is plastic. Plastics accumulate because they typically do not biodegrade as many other substances do. They photodegrade on exposure to sunlight, although they do so only under dry conditions, as water inhibits photolysis. In a 2014 study using computer models, scientists from the group 5 Gyres, estimated 5.25 trillion pieces of plastic weighing 269,000 tons were dispersed in oceans in similar amount in the Northern and Southern Hemispheres.
Persistent industrial marine debris
Some materials and activities used in industrial activities that do not readily degrade, that persist in the environment, and tend to accumulate over time. The activities can include fishing, boating, and aquaculture industries that harvest or use resources in the marine environment and may lose or discard gear, materials, machinery or solid wastes from industrial processes into the water or onto shorelines. This can include anything as large as a fishing boat or as small as particle from a Styrofoam lobster float. In 2003, a study was conducted to identify types, amounts, sources, and effects of persistent industrial marine debris in the coastal waters and along the shores of Charlotte County, New Brunswick, and examine any relationship between the amount and types of persistent industrial marine debris, and the types and numbers of industrial operations nearby. Materials like plastic or foam can break down into smaller particles and may look like small sea creatures to wildlife such as birds, cetaceans, and fish, and they may eat these particles. Indigestible material may accumulate in the gut creating blockages or a false sense of fullness and eventually death from lack of appropriate nutrient intake.Ghost nets
Macroplastic
Microplastics
Deep-sea debris
Marine debris is found on the floor of the Arctic ocean. Although an increasing number of studies have been focused on plastic debris accumulation on the coasts, in off-shore surface waters, and that ingested by marine organisms that live in the upper levels of the water column, there is limited information on debris in the mesopelagic and deeper layers. Studies that have been done have conducted research through bottom sampling, video observation via remotely operated vehicles, and submersibles. They are also mostly limited to one-off projects that do not extend long enough to show significant effects of deep-sea debris over time. Research thus far has shown that debris in the deep-ocean is in fact impacted by anthropogenic activities, and plastic has been frequently observed in the deep-sea, especially in areas off-shore of heavily populated regions, such as the Mediterranean.Litter, made from diverse materials that are lighter than surface water, have been found to spread over the floor of seas and open oceans, where it can become entangled in corals and interfere with other sea-floor life, or even become buried under sediment, making clean-up extremely difficult, especially due to the wide area of its dispersal compared to shipwrecks. Plastics that are usually negatively buoyant can sink with the adherence of phytoplankton and the aggregation of other organic particles. Other oceanic processes that affect circulation, such as coastal storms and offshore convection, play a part in transferring large volumes of particles and debris. Submarine topographic features can also augment downwelling currents, leading to the retention of microplastics at certain locations.
A Deep-sea Debris database by the Global Oceanographic Data Center of the Japan Agency for Marine-Earth Science and Technology, showing thirty years of photos and samples of marine debris since 1983, was made public in 2017. From the 5,010 dives in the database, using both ROVs and deep-sea submersibles, 3,425 man-made debris items were counted. The two most significant types of debris were macro-plastic, making up 33% of the debris found – 89% of which was single-use – and metal, making up 26%. Plastic debris was found at the bottom of the Mariana Trench, at a depth of 10,898m, and plastic bags were found entangled in hydrothermal vent and cold seep communities.
Garbage patches (gyres)
Environmental impacts
Not all anthropogenic artifacts placed in the oceans are harmful. Iron and concrete structures typically do little damage to the environment because they generally sink to the bottom and become immobile, and at shallow depths they can even provide scaffolding for artificial reefs. Ships and subway cars have been deliberately sunk for that purpose.Additionally, hermit crabs have been known to use pieces of beach litter as a shell when they cannot find an actual seashell of the size they need.
Impacts from plastic pollution
Many animals that live on or in the sea consume flotsam by mistake, as it often looks similar to their natural prey. Overall, 1288 marine species are known to ingest plastic debris, with fish making up the largest fraction. Bulky plastic debris may become permanently lodged in the digestive tracts of these animals, blocking the passage of food and causing death through starvation or infection. Tiny floating plastic particles also resemble zooplankton, which can lead filter feeders to consume them and cause them to enter the ocean food chain. In addition, plastic in the marine environment that contaminates the food chain can have repercussions on the viability of fish and shellfish species.COVID-19 pandemic impacts
In Kenya, the COVID-19 pandemic has impacted the amount of marine debris found on beaches with around 55% being a pandemic-related trash items. Although the pandemic-related trash has shown up along the beaches of Kenya, it has not made its way into the water. The reduction of litter in the ocean could be a result of the closing of beaches and lack of movement during the pandemic, so less trash was likely to end up in the ocean. Additional impacts of the COVID-19 pandemic have been seen in Hong Kong, where disposable masks have ended up along the beaches of Soko's islands. This may be attributed to the increased production of medical products during the pandemic, leading to a rise in unconventional disposal of these products.Removal
Coastal and river clean ups
Techniques for collecting and removing marine debris include the use of debris skimmer boats . Devices such as these can be used where floating debris presents a danger to navigation. For example, the US Army Corps of Engineers removes 90 tons of "drifting material" from San Francisco Bay every month. The Corps has been doing this work since 1942, when a seaplane carrying Admiral Chester W. Nimitz collided with a piece of floating debris and sank, costing the life of its pilot. The Ocean cleanup has also created a vessel for cleaning up riverine debris, called Interceptor. Once debris becomes "beach litter", collection by hand and specialized beach-cleaning machines are used to gather the debris.There are also projects that stimulate fishing boats to remove any litter they accidentally fish up while fishing for fish.
Elsewhere, "trash traps" are installed on small rivers to capture waterborne debris before it reaches the sea. For example, South Australia's Adelaide operates a number of such traps, known as "trash racks" or "gross pollutant traps" on the Torrens River, which flows into Gulf St Vincent.
In lakes or near the coast, manual removal can also be used. Project AWARE for example promotes the idea of letting dive clubs clean up litter, for example as a diving exercise.
Once a year there is a diving marine debris removal operation in Scapa Flow in Orkney, run by Ghost Fishing UK, funded by World Animal Protection and Fat Face Foundation.
Cleanup of marine debris can be stymied by inadequate collaboration across levels of government, and a patchwork of regulatory authorities. For example, there are an estimated 1600 abandoned and derelict boats in the waters of British Columbia. In 2019 Canada's federal government passed legislation to make it illegal to abandon a vessel but enforcement is hampered because it is often difficult to determine who owns an abandoned boat since owners are not required to have a license – licensing is a provincial government responsibility. The Victoria-based non-profit Dead Boats Disposal Society notes that lack of enforcement means abandoned boats are often left to sink, which increases the cleanup cost and compounds the environmental hazard.