Читать книгу Plastics Process Analysis, Instrumentation, and Control - Группа авторов - Страница 44

Plastic debris in the marine environment is widely documented, but the quantity of plastic entering the ocean from waste generated on land is unknown. The mass of land-based plastic waste entering the ocean was estimated (65).

Waste estimates for 2010 for the top 20 countries ranked by the mass of mismanaged plastic are collected in Table 1.3.

Table 1.3 Plastic waste from various countries (65).

Country	Mismanaged plastic waste /[%]	Plastic marine debris /[Mt y–1]
China	27.7	1.32—3.53
Indonesia	10.1	0.48—1.29
Philippines	5.9	0.28—0.75
Vietnam	5.8	0.28—0.73
Sri Lanka	5.0	0.24—0.64
Thailand	3.2	0.15—0.41
Egypt	3.0	0.15—0.39
Malaysia	2.9	0.14—0.37
Nigeria	2.7	0.13—0.34
Bangladesh	2.5	0.12—0.31
South Africa	2.0	0.09—0.25
India	1.9	0.09—0.24
Algeria	1.6	0.08—0.21
Turkey	1.5	0.07—0.19
Pakistan	1.5	0.07—0.19
Brazil	1.5	0.07—0.19
Burma	1.4	0.07—0.18
Morocco	1.0	0.05—0.12
North Korea	1.0	0.05—0.12
United States	0.9	0.04—0.11

It was calculated that 275 Mt of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 million Mt entering the ocean. The population size and the quality of the waste management systems largely determine which countries contribute the greatest mass of uncaptured waste available to become plastic marine debris. Without waste management infrastructure improvements, the cumulative quantity of plastic waste available to enter the ocean from land is predicted to increase by an order of magnitude by 2025 (65).

Marine plastic debris floating on the ocean surface is a major environmental problem (66). However, its distribution in the ocean is poorly mapped out and most of the plastic waste estimated to have entered the ocean from land is unaccounted for.

A better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surf zone (66).

The Ekman layer is the layer in a fluid where there is a force balance between pressure gradient force, Coriolis force and turbulent drag (67). It was first described by Vagn Walfrid Ekman (68). Ekman layers occur both in the atmosphere and in the ocean. There are two types of Ekman layers. The first type occurs at the surface of the ocean and is forced by surface winds, which act as a drag on the surface of the ocean. The second type occurs at the bottom of the atmosphere and ocean, where frictional forces are associated with flow over rough surfaces (67).

A review comprehensively discussed what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones (66). The study was based on the published literature and refers to insights from neighboring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and other issues.

Floating debris may occur through events that are collected in Table 1.4.

Also discussed was how measurements of marine plastics (both in-situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales (66).

Table 1.4 Floating debris (66).

Reason	References
Internal tides	(70, 71)
Direct wind force	(72, 73)
Langmuir circulation	(74)
Vertical transport and mixing	(75, 76)
Ice formation, melting and drift	(77)
River plumes	(78)
Surface waves and beaching	(79)
Storms	(80)
Tsunamis	(81)
Transport by seabirds	(82, 83)
Transport by plankton	(84)