Excerpts from the 2015 report of the UN Ad Hoc Working Group on the Regular Process for Global Reporting and Assessment of the State of the Marine Environment Including Socioeconomic Aspects:
Increasing Inputs of Harmful Material
The agricultural revolution of the last part of the twentieth century, which has largely enabled the world to feed its rapidly growing population, has also brought with it problems for the ocean in the form of enhanced run-off of both agricultural nutrients and pesticides, as well as airborne and waterborne inputs of nutrients from waste from agricultural stock. (The use of fertilizers) is rapidly growing in parts of the world where only limited use had occurred in the past. That growth has the potential to lead to increased nutrient run-off to the ocean if the increased use of fertilizers is not managed well. . . In the case of pesticides, the issues are analogous to those of industrial development. Newer pesticides are less polluting than older ones, but there are gaps in the capacity to ensure that these less-polluting pesticides are used, in terms of educating farmers, enabling them to afford the newer pesticides, supervising the distribution systems and monitoring what is happening in the ocean.
Eutrophication resulting from excess inputs of nutrients from both agriculture and sewage causes algal blooms. Those can generate toxins that can make fish and other seafood unfit for human consumption. Algal blooms can also lead to anoxic areas (i.e. dead zones) and hypoxic zones. Such zones have serious consequences from environmental, economic and social aspects. The anoxic and hypoxic zones drive fish away and kill the benthic wildlife. Where these zones are seasonal, any regeneration that happens is usually at a lower trophic level, and the ecosystems are therefore degraded. This seriously affects the maritime economy, both for fishermen and, where tourism depends on the attractiveness of the ecosystem (for example around coral reefs), for the tourist industry. Social consequences are then easy to see, both through the economic effects on the fishing and tourist industries and in depriving the local human populations of food.
Marine debris is present in all marine habitats, from densely populated regions to remote points far from human activities, from beaches and shallow waters to the deepest ocean trenches. It has been estimated that the average density of marine debris varies between 13,000 and 18,000 pieces per square kilometer. However, data on plastic accumulation in the North Atlantic and Caribbean from 1986 to 2008 showed that the highest concentrations (more than 200,000 pieces per square kilometer) occurred in the convergence zones between two or more ocean currents. Computer model simulations from data from 12,000 satellite-tracked floats deployed since the early 1990s as part of the Global Ocean Drifter Program, confirm that debris will be transported by ocean currents and will tend to accumulate in a limited number of subtropical convergence zones or gyres.
Plastics are by far the most prevalent debris item recorded, contributing an estimated 60 to 80 per cent of all marine debris. Plastic debris continues to accumulate in the marine environment. The density of microplastics within the North Pacific Central Gyre has increased by two orders of magnitude in the past four decades. Marine debris commonly stems from shoreline and recreational activities, commercial shipping and fishing, and dumping at sea. The majority of marine debris (approximately 80 per cent) entering the sea is considered to originate from land-based sources. – (Excerpted by SU Research and Environmental News Service)