The Effects of Fish Presence and Mixing Patterns on Water Clarity in Lakes: Arco, Deming, and Itasca

Abstract

In the summer of 2009, in Itasca State Park, MN, samples of zooplankton, chlorophyll a concentrations, and Secchi disk readings were studied in three lakes with differing characteristics. Our study sites were Deming Lake (fish, meromictic), Arco Lake (fishless, meromictic), and Lake Itasca (fish, dimictic). Our variables of interest were the presence or absence of fish, and whether the lake was dimictic or meromictic. Our study showed that Arco Lake, a small meromictic fishless lake, had the highest Secchi disk reading. Along with a high level of water clarity there was an abundance of large zooplankton. We contributed this high level of clarity with the absence of fish, and its meromictic stratification. Lake Itasca showed its true dimictic characteristics in our data, showing relatively low fluctuations in temperature and dissolved oxygen levels.