Water clarity in Lake Itasca: Bottom-up vs. Top-down theory

Abstract

Lake Itasca is clearer than normal for spring and expected to become less clear as the summer progresses, due to algal growth. Our research investigated the main factor that controls water clarity in Lake Itasca based on two different theoretical concepts: Bottom-up versus Top-down effects. Ultimately, we inferred that the top-down theory was the main influence, in which food web interactions were the largest driver of water clarity. We examined the abundance of zooplankton, hatching of yellow perch larvae, and algal levels in conjunction with nutrient levels to support our hypothesis. The zooplankton population declined in correlation to the presence of larval yellow perch, along with growth in the amount of chlorophyll at each site, presented evidence in food web change. Nitrate levels showed consistency and no pattern of change, further providing support towards our hypothesis. These results of our research supported our hypothesis in that the Top-down theory was the main controller on water clarity in Lake Itasca.