UMD researchers reveal data from wetland studies in the Northland
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2 | Why so polluted?
Under the belief that water could dilute any substance, industries and individuals during the 18th and 19th centuries often used rivers and lakes as garbage cans. Industrial effluent, raw sewage and animal carcasses would often be dumped into waterways, without much thought of contamination and downstream neighbors.
This practice started changing in the 20th century as people became aware of the importance of clean water to health. However, as more industries and people moved into the Great Lakes region, the more the rivers and lakes became polluted. Today, pollutants enter the Great Lakes in many different ways, but the main three entryways of pollutants are point source, nonpoint source and atmospheric pollution.Point source pollution
When pollutants enter the waterway though a specific entry point, such as a drainpipe draining directly into a river, it's called point source pollution. Industrial water discharges and sewage treatment plants are the main culprits of this type of pollution. Point source pollutants can include many different organic and inorganic substances, including human waste and toxic metals.
Point source pollution can be traced to a specific discharge point and owner; therefore, it has been the easiest source of pollution to control and regulate. Since the Clean Water Act of 1972, nearly 100 percent of all industrial plants use control measures to reduce their toxic discharge, and the number of sewage treatment facilities has doubled.Nonpoint source pollution
In contrast to point source pollution, nonpoint source (or NPS) pollution comes from many different diffuse sources and is extremely difficult to regulate and control; therefore, many experts believe that NPS pollution is the top hazard facing the Great Lakes today.
NPS pollution is mainly caused by runoff, when rain and snowmelt move over the land, picking up pollutants along the way and eventually dumping the pollutants into rivers and lakes. Some common NPS pollutants include fertilizers and pesticides from agricultural lands and homeowners; oil, grease and salt from highways; sediment from construction sites and eroding shorelines; and animal and human waste.Atmospheric pollution
Atmospheric pollution (or air deposition) is another form of nonpoint source pollution, though instead of polluting via runoff, the pollution falls from the sky. As water moves through the hydrologic cycle, it falls as rain or snow and then evaporates into the air from land and surface water. Pollutants emitted into the air, such as through smoke stacks, follow this same path, and can be carried through the atmosphere and deposited into waterways hundreds of miles away from its source. Acid rain is the most well-known form of atmospheric pollution.
The major sources of atmospheric pollution include coal-burning energy plants and waste incinerators. The combustion of fossil fuels and waste (such as from hospitals) produces large amounts of mercury in the air, a toxic chemical that is fatal to humans and animals in large quantities. Phosphorus and polychlorinated biphenyls (PCBs) are also transported to waterways via air deposition.
Graphics: Industrial pollution in Green Bay, Wis.; power plant along Lake Michigan.