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How Does Human Activity in Watersheds Affect the Water Quality of Lakes?

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How does human activity in watersheds affect the water

quality of lakes?

Water is a vital resource that sustains all living things. In Michigan, people value this

abundant resource and are attractive to the thousands of inland lakes which provide aesthetic, as

well as recreational opportunities throughout the year. The health of our lakes is directly

impacted by the amount of recreational use they receive, shoreline development, and water

quality. Water quality covers many aspects of lake chemistry and biology. Both natural and man-

made features of watersheds impact the quality of aquatic habitats. Examining the relationship

between land use and water clarity in lakes can help us to understand what negatively impacts

the health of our lakes. This in turn will lead us to finding solutions to improve and maintain the

quality of our lakes and waterways.

I expect aquatic habitats in watersheds with more man-made features to have lower water

quality and clarity. I expect this because runoff from man-made features will contain chemicals

and particles that reduce clarity through biological and physical processes.

Begin the lab by saving the 12 maps of the six lakes (six color coded by land use and the

same six in grayscale) along with a Legend file on the website. The Legend file explains the

color coding of land uses in the map files. Open up each map and Legend in the ImageJ program

and move the mouse cursor over the different areas of the grayscale image and looking in the Menu window, a numerical value (between 0 and 255) for each level of gray can be determined.

A list of numerical values was obtained for each color image by comparing the numerical value

in the grayscale image with the corresponding color image. By using the Legend. it was possible

to match the numerical values to each land use type and then determine the area of each land use

type in the grayscale image. Take the maps that are in black and white and have ImageJ analyze

the pixels into a histogram. Take the histogram and turn it into a list so that you know how many

pixels are to each land use. Then take that data and put it in excel so that you can determined

which land uses are most prevalent in each of the lakes. To do these take only the land uses that

occur prevalently on the graphs and use those to find the percentages of each, for each watershed

(leave out 255 because that is the white area around the map). Also, you should not include

water in the estimate of total watershed area because a watershed is the area of land that catches

rain and drains into the lake. You need to add up the total pixels to get an estimate of total

watershed area in order to determine the percentage of each land use type.

Water quality data for these lakes can be obtained from the Michigan Department of

Environmental Quality website. For this analysis of water clarity, parameters of Secchi disk,

total Phosphorous (Spring data), and Chlorophyll (mean) were used. Data can then be analyzed

in terms of water quality and how the percentage of surrounding watershed may have impacted

the data that was given. The six lakes can then grouped according to two categories: high water

quality or low water quality.

Moon, Indian, and Margrethe Lakes were determined to be of high quality and Devils,

Christina, and Pleasant Lakes were determined to be of low quality. The Secchi Disk readings


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