Land-based Sources of Pollution

Located downstream from land, the sea inevitably becomes the ultimate sink of human-generated pollutants via runoff or through direct dumping. This host of pollutants includes sewage, persistent organic pollutants (POPs), radioactive substances, heavy metals, excess nutrients (fertilizers, nitrogenous compounds, etc), halogenated hydrocarbons (pesticide, PCBs, dioxins, etc), litter, or simply excessive amounts of sediment. Each of these pollutants independently, or in combination contributes to the degradation or destruction of marine habitats.

Many of these pollutants pose direct human-health risks. Heavy metals, such as arsenic, cadmium, chromium, copper, nickel, lead and mercury, concentrate in the tissues of many marine species, becoming highly contaminated in the process. Persistent organic pollutants and hydrocarbons are commonly found in land-based runoff and ultimately accumulate in harvested species.

Currently, the most widespread threat of land-based pollutants to marine and coastal habitats is posed by a combination of municipal sewage, solid waste, fertilizers, urban run-off and other nitrogenous compounds. Human activities now add at least as much fixed nitrogen to terrestrial ecosystems as do all natural sources combined and the oceans receive this nitrogenous pollution from both coastal runoff and atmospheric deposition. The nutrients cause an over-production of algae in coastal regions. When the algae die, an over-production of micro bacteria occurs, including some highly toxic species. As these bacteria decompose the algal remains, they consume much of the oxygen dissolved in the water, causing mass mortality of fish and invertebrates. In coastal marine habitats, areas affected by anthropogenic eutrophication are particularly widespread, persistent and increasing.