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Background
Human caused nutrient loading of aquatic ecosystems is a widespread problem. The addition of factors, which would normally limit the growth of organisms, can result in altered biomass, abundance and species diversity
of communities (Scrimgeour, 1997). Two nutrients commonly released into streams are phosphorus in the form of phosphate ion and nitrogen in the form of the nitrate ion. Phosphate and nitrate are commonly the
limiting factors for algae growth in lakes (Fairchild, 1985).
The major sources of nitrates released into the environment in the United States are fertilizers, animal manure, and atmospheric sources as nonpoint sources and sewage treatment and various industries as point
sources (Puckett, 1994). The use of nitrate fertilizers in the U.S. increased twenty-fold increase between 1945 and 1985 (Alexander, 1990).
Major phosphorus sources are sewage treatment plants and food processing plants as point sources and the nonpoint sources of agricultural and urban runoff as well as natural weathering of phosphate containing
minerals. The amount of phosphates released into the environment by human causes has been reduced through its removal from detergents in 1971, as well as a decrease in phosphate fertilizers (Smith,
1994).
This procedure will serve as a model for the effect of nutrient loading (nitrogen, phosphate, and nitrogen and phosphate) on periphyton algal growth. Specifically, the biomass of algae in response to the
addition of nutrient-diffusing substratum will be measured
Ordinarily periphytic algal growth may be limited by a number of factors including suitable attachment sites. By providing a standardized platform for attachment the levels of two key nutrients may be
manipulated and the growth of the algae determined by increase in biomass.
Terra cotta flowerpots are sealed and filled with 1.5 % agar solution containing salts of nitrate and/or phosphate ions. The pots are then placed in an aquatic environment. Over a period of weeks the
nutrients in the agar salt medium diffuse through the surface of the pot and release into the immediate environment. The amount of biomass that accumulates on the pots can be measured and interpreted as
a means of finding the limiting factor in the system.
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