Eutrophication is the nutrient enrichment of a body of water. Eutrophic bodies of water are characterized by abundant bottom vegetation, algal blooms, and a decreased fish population due to oxygen depletion. Nitrogen and Phosphorous are two important nutrients that lead to eutrophication.  According to the chemical composition of algae, balanced algal growth needs a ratio of Nitrogen to Phosphorous to be 7:1.  Since N/P < 7 in most natural waters, algal growth is usually limited by phosphorous. Due to this, the measurement of phosphorous in a body of water is a good indicator of water quality. The purpose of this experiment is to measure the phosphorous content of Lake Carnegie and determine whether or not it is eutrophic.

There are three main types of phosphates that were tested: total phophates, orthophosphates, and total inorganic phosphates. This was quantified by the optical absorption using a HACH spectrophotometer. Knowing the level of phophorous, the total phosphorous loading as a function of mean depth/hydraulic retention time was determined using the Vollenweider model. From this data, it was possible to determine the level of eutrophication of Lake Carnegie.

The table below shows the phosphate level of the standard sample and 3 lake samples.

Due to the lack of the data on the physical dimension of Lake Carnegie, we assumed a hypothetical lake whose volume is similar to that of Lake Carnegie. From this data, the total phosphorous load (TPL) was calculated to be 0.64 gP/m²/year and the mean depth/hydraulic residence time was calculated to be 0.86 m/yr.  Using Vollenweider's model, the x value (mean depth/hydraulic residence time) and the y value (TPL) showed that the lake was in fact eutrophic.  

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