Water Quality of Alimagnet, Farquar, and Long Lakes in Apple Valley, Minnesota

Alimagnet, Farquar, and Long Lakes, in Apple Valley, Minnesota, were sampled from 1973-79 to determine their physical and chemical characteristics. A storm-sewer inlet to Alimagnet Lake was also sampled during two storms in 1978. All the lakes have at least one storm-sewer inlet draining residential areas. Alimagnet and Farquar Lakes have lift-station outlets and Long Lake is connected by a culvert to Farquar Lake. The 1976-77 drought caused a more noticeable effect on the quality of the lakes than any other factor. Chloride concentrations were 10 to 15 milligrams per liter before the drought, but increased 2 to 4 times during the drought. Dissolved solids reacted similarly. Dissolved oxygen and pH were governed mainly by biological activity. During the summer, dissolved oxygen was often above 100-percent saturation and pH was as high as 9.0. In February 1977, dissolved-oxygen concentration was less than 0.5 milligrams per liter in the three lakes. Ratios between mean total nitrogen and mean total phosphorus ranged from 22:1 to 26:1, indicating that nitrogen most likely was not limiting algal productivity in any of the lakes. Trophic-state indices indicate that the lakes are eutrophic. There was no evidence of long-term trends; however, increased trophic-state indices during the drought occurred in Alimagnet Lake. Blue-green algae dominated the phytoplankton populations. Aphanizomenon, Anacystis, and Oscillatoria were the most common genera in the samples. Storms sampled at a storm-sewer inlet to Alimagnet Lake showed higher concentrations of chromium, copper, nickel, and zinc than of lead, arsenic, cadmium, and mercury. Total phosphorus for the September 1978 storm had a concentration of 1.7 milligrams per liter, which means that approximately 29 pounds entered the lake during the 5.5-hour sampling period.