PHYSICAL AND CHEMICAL LIMNOLOGY


OBJECTIVE

There are many physical and chemical parameters of potential interest to limnologists, but one can infer much about aquatic ecosystems from a relatively few measurements. This exercise will introduce you to various physical and chemical measures that are used routinely in limnological analyses.

Physical/chemical parameters do not differ between Lake Winona and the lentic backwaters of the Mississippi River during September.

You will collect numerous water samples from east Lake Winona and from Sam Gordy Slough, a lentic backwater of the Mississippi River, for use in determining a wide variety of physical and chemical parameters. In the "field" you will determine water temperature, dissolved oxygen, conductivity, pH, and turbidity with the appropriate battery-operated instruments (meters). You also will use various kits to determine nitrate concentrations and total hardness. As conditions permit, you also will 1) measure dissolved oxygen, pH, conductivity, and water temperature at 1-m intervals from surface to bottom, 2) determine Secchi disc transparency and light transmittance, and 3) collect water samples from several depths with a Kemmerer water bottle for analysis (nitrate, hardness, turbidity) and comparison to the surface samples.
The use of the various instruments will be explained to you during the lab.

Once all data are collected, calculate means and standard deviations (where appropriate) for each water body and parameter and construct a data table. Use the simple statistical software (e.g., VassarStats) available on the internet to determine whether or not any of the parameters differ between the lake and backwaters. The instructor will demonstrate, if needed, the use of the software either to individuals or to small groups.
Construct a series of figures (graphs) depicting any changes in the parameters measured (e.g., temperature, DO, pH, etc.) with depth for your lake and backwater data. Remember, limnologists like to plot depth along the vertical axis, with surface readings at the top of the figure (0 in upper left) and increasing depths extending downward. Changes in water temperature and dissolved oxygen with depth often are presented (graphed) on the same figure.

Return to Limnology Lab

Neal D. Mundahl
Winona State University
Winona, MN 55987-5838