A Statistical Examination of Water Quality in Two Iowa Lakes

Water quality has become and important issue in the state of Iowa as well as across the entire United States. Two Iowa Lakes, Silver Lake and Casey Lake were chosen for study by a team of biologists, chemists, earth scientists and statisticians from the University of Northern Iowa. Our goals are to statistically compare the water quality in the two lakes in each year and examine whether or not each lake has changed, in terms of water quality variables, from 1999 to 2000. In addition, we explore which variables most affect phosphorus levels in each lake in 2000. Lastly, we explore the spatial distribution of phosphorus in the sediment of each lake. Discriminant Analyses and ANCOVA show significant difference between the two lakes in both 1999 and 2000 as well as a change in Silver Lake's water quality data from 1999 to 2000. Regression Analyses show that, in Silver Lake, phosphorus levels increased during the summer of 2000 while they decreased with increasing levels of surface dissolved oxygen and decreased as the water became less clear. The analyses also show that phosphorus levels in Lake Casey decreased as the water became less clear. A significant relationship between phosphorus in the sediment and depth exists in Lake Casey. While a significant 2-dimensional spatial correlation cannot be shown in Silver Lake, spatial analyses do show the existence of a significant 3-dimensional spatial correlation in Lake Casey.