solution

The Great Lakes Environmental Research Laboratory of the U.S. National Oceanic and Atmospheric Administration (NOAA-GLERL) routinely monitors the western basin of Lake Erie from May to October every year. The data file LakeErie1.csv includes all available data up to the end of 2014. Two variables are of particular interest in studying lake eutrophication. They are the total phosphorus (TP) and chlorophyll a (chla) concentrations. These are concentration variables and we often assume that their distributions are approximately normal.

• Read the data into R and use the graphics to evaluate whether TP and chla are normally distributed.

• Western Lake Erie’s nutrient concentrations are largely associated with Maumee River input, which varies from year to year due to variation in weather conditions. As a result, we expect that TP, as well as chla, concentration distributions vary by year. Use the function qqmath (from package lattice) to draw normal Q-Q plots of TP and chla concentrations by year. Are the annual concentration distributions closer to being normal?