Environmental Studies IDC3O3 Ms. Nguyen

* Amount of oxygen dissolved in water is a good indicator of water quality and the kinds of life it will support * Oxygen with a water content above 6 parts per million (ppm) will support many forms of aquatic life * Less than 2ppm, oxygen will only support worms, bacteria, fungi and other detritus feeders and decomposers

* Oxygen is added to water by diffusion from the air, especially when turbulence and mixing rates are high * By photosynthesis of green plants, algae and cyanobacteria (blue –green bacteria) * Oxygen is removed from water by respiration and chemical processes that consume oxygen

* Organic waste such as sewage, paper pulp or food waste rich in nutrients, especially nitrogen or phosphorus * Stimulates the growth of oxygen demanding decomposing bacteria * Biochemical oxygen demand (BOD) * The affects of oxygen-demanding wastes on rivers depends to a great extent on the volume, flow and temperature of the river water

* Oxygen decline downstream is called the oxygen sag

* Phosphates and nitrates are generally present in very limited amount in unpolluted freshwater and algae * Limited factor is a necessary material that is in short supply, and because of the lack of it, an organism cannot reach its full potential growth) * the excessive growth of algae and aquatic plants due to added nutrients is called eutrophication * As the organic matter decays, oxygen levels decreases, and fish and other aquatic species die

* Creates Dead Zones * E.g. seasonal hypoxia occurring at the outflows of the Mississippi River. *

* the sources of groundwater pollution span from every facet of social, agricultural and industrial activities * Once groundwater pollution have occurred, it is extremely difficult to treat * Very slow and costly * Difficult to know when all of the contaminated water has been removed

* Agricultural products: seventy three different pesticides have been detected in groundwater in Canada and the United States * Accidental spills or leaks of pesticides * Animal-feeding operations * Fertilizer applications * Irrigation practices

* Underground storage tanks: in the past, a large number of underground storage tanks containing gasoline and other hazardous substance have leaked * Four liters (1 gallon) of gasoline can contaminate the water supply of a community of people * Landfills: 90% of landfills in North America have no liners to stop leaks of underlying groundwater * 96% have no system to collect the leachate that seeps from the landfills * 60% of landfills place no restrictions on the waste accepted * Many are not inspected

* Septic tanks: Poorly designed and inadequately maintained septic systems leak nitrates, bacteria and toxic cleaning agents * over 20 millions used in the United States and up to a third have been found to be operating improperly * Surface impoundments: over 225,000 pits, ponds and lagoons used to store or treat waste * 71% are unlined and only 1 percent use a plastic or other synthetic, nonsoil liner * 99% of these do not have leak detention systems * 73% have no restriction on the waste placed in the impoundment * 60% are not inspected annually * Located near groundwater supplies

* Other sources of groundwater contamination: * mining waste * salting for controlling road ice * land application of treated wastewater * open dumps * cemeteries * radioactive disposal sites * urban runoff * construction excavation * fallout from atmosphere * animal feedlots