Nonpoint Source Pollution and Coastal Environments
Unlike point source pollution, which involves a relatively constant pollutant discharge from a fixed point, non-point
source (NPS) or diffuse pollution is characterised by the wide distribution of a pollution source and by
highly irregular rates of delivery. NPS pollution can be transported into coastal environments via ground-water,
streams and rivers, the atmosphere, combined sewage overflows, storm drains and flood control
channels, as discharges from boats, and as the release of toxic chemicals from contaminated sediments,
among other pathways.
NPS pollution encompasses the spectrum of pollutant types--including animal waste and human
pathogens, soil and sediment, construction debris, industrial chemicals, pesticides and mine tailings, nutri-ents,
oil and grease, trash, and many others. The sources and amount of NPS pollution vary from region
to region depending on such factors as land-use, population density, local and regional hydrology, water-shed
alteration, and management practices.
While significant improvements have been made in the U.S. in reducing point sources of environmental
contamination, NPS pollution has proven extremely difficult to regulate and control. In fact, until recently,
it had been generally overlooked as an important factor in water quality.
- The Environmental Protection Agency (EPA) now considers NPS pollution to be the major cause of
water quality issues in the U.S. Its ultimate impacts range from human illness and death to the dramatic
alteration of natural environments and is the reason that approximately 40% of monitored U.S. rivers,
lakes, and estuaries are not clean enough for fishing or swimming.
- The effects of NPS pollution on coastal environments include, but are not limited to: human illness
through the contamination of beachwater and seafood with pathogens; the stimulation of harmful algal
blooms from enhanced nutrification; shellfish bed closures; the degradation or destruction of coral reefs
and seagrass beds via siltation, eutrophication, and increased turbidity; the contamination of marine
food webs with toxic chemicals; and the loss of biodiversity as a result of eutrophication and reduced
water column oxygen levels.
- According to the National Estuarine Eutrophication Assessment (1999), nutrient-related water quality
problems--in large part due to NPS pollution--can be found in at least 60% of the Nation's estuaries.
Furthermore, the Assessment warned that over the next 20 years the severity and extent of nutrient
enrichment problems is likely to worsen in tandem with coastal population growth.
The main sources of NPS pollution include:
- Agriculture: Over 12 million metric tons of nitrogen and phosphorus as commercial fertilizers are applied
to agricultural lands each year in the U.S.--an amount considered to be between 24 and 38% in excess
of crop needs--and is a major cause of the nutrient pollution of the nation's surface waters. Other NPS
pollutants associated with agriculture include sediments, salts, organic matter, and pesticides. In terms of
the latter, it has been estimated by the National Oceanographic and Atmospheric Administration
(NOAA) (1992) that over 29 million pounds of 35 commonly used pesticides are applied annually to
agricultural lands in U.S. coastal watersheds. These enter rivers and estuaries via surface runoff and the
atmosphere where they may contaminate or kill aquatic organisms and alter the function and structure of
local aquatic communities.
- Atmospheric deposition: Approximately 3 million metric tons of nitrogen are deposited from the atmosphere
onto U.S. lands and waters each year. Over 50% of these emissions come from coal- and oil-burning
facilities while some 40% originate from automobiles, trucks and other forms of transportation.
Agricultural fertilizers (primarily via the volatilization of ammonia) and other sources make up the
remainder.
- Livestock farms: It is estimated that domestic livestock operations in the U.S. produce 1.37 billion tons of
manure each year--equivalent to 5 tons for each U.S. citizen. Though well-known as a major source of
nutrient pollution, there is now substantial concern over the human health impacts of waterborne dis-ease-
causing agents (e.g., E. coli O157:H7, Cryptosporidium, Salmonella) emanating from livestock operations.
Less than 1% of farms with livestock are currently required to control their animal wastes.
- Septic tank systems: Malfunctioning or inadequate septic tank systems can introduce nutrients and disease-causing
microorganisms to coastal waters via ground or surface waters. In the U.S. overall there are an
estimated 25 million septic tanks receiving 175 billion gallons of wastewater.
- Timber cultivation (silviculture) and logging: Forest-related operations can produce sediment (from accelerated
erosion), pesticides and fertilizers, and organic debris. NPS pollution from forestry and its effects on
streamflow and spawning habitat has been an important factor in the decline, endangerment, or extinc-tion
of numerous sea trout and salmon populations throughout the Pacific Northwest.
- Urban runoff: All wastes deposited on impervious surfaces (e.g., pavement) and not removed by street
cleaning, the wind, or decomposition will ultimately end up as surface or storm-water run-off. This
includes the spectrum of pollutants emanating from such sources as: motor vehicles (e.g., hydrocarbons,
metals, oils and fluids); residential areas (e.g., lawn chemicals, nutrients from plant debris and fertilizers);
construction sites (e.g., soil, debris); and commercial and industrial facilities (e.g., atmospheric deposi-tion
of metals, organic chemicals, and nutrients); as well as a range of other materials associated with
urban life (e.g., animal wastes, plastics, and other litter).
- Water-based sources: While the majority of NPS pollution affecting marine and estuarine environments
originates on land, the operational discharges, spills, and leaching of pollutants from boats, ships, boat-yards
and marinas can have substantial local impacts. Pollutants include oily bilge water, human sewage,
debris and litter, and toxic chemicals (e.g., tributyltin, hydrocarbons) associated with boat hull paints and
wood pilings.
- Approximately 53% of the total U.S. population--about 139 million people--lives along the coast.
Population growth in coastal counties is projected to increase by an average of 3,600 people per day and
reach 165 million by 2015. As a result, pressures on coastal watersheds, shorelines, and nearshore waters
will continue to be substantial. For example, the EPA has estimated that, each day, some 21.3 billion gal-lons
of spent cooling water and treated domestic sewage and industrial effluent is discharged directly
into U.S. coastal waters. Combined with NPS pollution, oil and chemical spills, discharges into rivers
upstream of coastal areas, and the atmospheric deposition of contaminants, a vast mixture of chemicals,
nutrients, particulates, and pathogens are degrading water quality and threatening public health.
- A wide variety of management programs and legislative requirements are needed to adequately address
the range of NPS pollution sources. Foremost among these include stricter and enforceable water quality
standards, changes in agricultural practices leading to reductions in pesticide use and excess nutrient flow,
reductions in fossil fuel use, and the protection and/or restoration of wetlands and riparian vegetation.
- While NPS pollution is a major contributor to the degradation of the Nation's marine environments, its
impacts do not occur in isolation. Indeed, there is widespread scientific consensus that the full range of
stresses--also including, for example, fisheries, introduced species, coastal land-use change and urbaniza-tion,
point source pollution, reduction of freshwater inputs, and a projected change in climate--need to
be taken into account when watershed and coastal protection strategies are being revised or developed.
Bricker, S.B. et al. 1999. National Estuarine Eutrophication Assessment: Effects of Nutrient Enrichment in the Nation's
Estuaries. National Ocean Service, NOAA: Silver Spring, MD.
Carpenter, S.R. et al. 1998. Nonpoint pollution of surface waters with phosphorus and nitrogen. Issues in
Ecology No. 3. Ecological Society of America: Washington, D.C.
Pait, A.S. et al. 1992. Agricultural Pesticide Use in Coastal Areas: A National Summary. National Ocean Service,
NOAA: Silver Spring, MD.
Rose, J.B. et al. 1999. Microbial Pollutants in Our Nation's Water. American Society for Microbiology:
Washington, D.C.
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