Phosphates and Dissolved Oxygen

Phosphates are present in many natural waters, such as lakes and streams. Phosphates are essential to aquatic plant growth, but too much phosphate can lead to the growth of algae and results in an algae bloom. Too much algae can cause a decrease in the amount in dissolved oxygen in the water. Oxygen in water is affected in many different ways by phosphates

Phosphorus is usually present in natural waters as phosphate(Mcwelsh and Raintree, 1998). Phosphates are present in fertilizers and laundry detergents and can enter the water from agricultural runoff, industrial waste, and sewage discharge (Outwater,1996) . Phosphates, like nitrates, are plant nutrients (Phosphates, 1997). When too much phosphate enters a water, plant growth flourishes (Phosphates). Phosphates also stimulate the growth of algae which can result in an algae bloom(World Book Encyclopedia,1999). . Algae blooms are easily recognized as layers of green slime, and can eventually cover the water's surface. As the plants and algae grow, they choke out other organisms. These large plant populations produce oxygen in the upper layers of the water but when the plants die and fall to the bottom, they are decomposed by bacteria which use a lot of the dissolved oxygen in the lower layers (Phosphates). Bodies of water with high levels of phosphates usually have high biological oxygen demand (BOD) levels due to the bacteria consuming the organic plant waste and subsequent low dissolved oxygen levels(Hooper,1998).

The addition of large quantities of phosphates to waterways accelerates algae and plant growth in natural waters (Hooper), enhancing eutrophication and depleting the water body of oxygen. This can lead to fish kills and the degradation of habitat with loss

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of species. Large mats of algae can form and in severe cases can completely cover small lakes. Dying plants and algae will create phosphates while decaying, as a result, water can become putrid from decaying organic matter (World Book Encyclopedia). When the concentration of phosphates rises above 100 mg/liter the coagulation processes in drinking water treatment plants may be adversely affected (World Book Encyclopedia). Manmade sources of phosphate include human sewage, agricultural run-off from crops, sewage from animal feedlots, pulp and paper industry, vegetable and fruit processing, chemical and fertilizer manufacturing, and detergents.

Dissolved oxygen is one of the best indicators of the health of a water ecosystem. Dissolved oxygen can range from 0-18 parts per million (ppm), but most natural water systems require 5-6 parts per million to support a diverse population (Phosphates). Dissolved oxygen levels change and vary according to the time of day, the weather and the temperature. If yearly comparisons are made on dissolved oxygen levels, they should be done at the same time of day, during the same season and on a day with a temperature variation of only 10 degrees Celsius from the previous reading (Phosphates). A decrease in the dissolved oxygen levels is usually an indication of an influx of some type of organic pollutant (Phosphates).