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bio155_Lecture_7_Nitrogen_Phosphorus

bio155_Lecture_7_Nitrogen_Phosphorus - BIOE 155 Fall 2009...

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BIOE 155, Fall 2009 CHEMICAL: NITROGEN AND PHOSPHORUS (read pp239-250 in Dodson) BACKGROUND Lakes are often classified according to trophic status, specifically how much energy or food is available for the lake food web. Oligotrophic—Low rates of primary productivity. These lakes usually have few nutrients and are relatively “pristine”. These lakes are generally characterized by having low light attenuation, low nutrients, and orthograde oxygen curves. Mesotrophic—Intermediate rates of primary productivity. Eutrophic—high rates of primary productivity. This is generally caused by high levels of nutrient loading. Eutrophic lakes are generally characterized by having high nutrients, rapid light attenuation, and clinograde oxygen curves. Cultural eutrophication —One of the major human perturbations of freshwaters is eutrophication. Eutrophication refers to a lake becoming more productive and exhibiting characteristics of this type of lake (rapid light attenuation, high rates of primary productivity). Excess nutrient inputs (generally P) drive eutrophication. PHOSPHORUS Phosphorus is usually the limiting nutrient in freshwaters. Thus, understanding the Phosphorus cycle has proved critical in management and conservation of freshwater systems. Excess phosphorus is the leading driver of eutrophication. There are several lines of evidence that demonstrated that P is the main driver of lake productivity. o Whole-lake experiment by D.W. Schindler (1977). o Surveys of many lakes that found strong relationships between TP and lake production.
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