STILL WATERS, SILENT WITNESSES: USING LAKE SEDIMENT RECORDS IN THE CLASSROOM

A lake’s calm still surface masks a remarkably dynamic system whose sedimentary record reflects processes across its drainage basin. Lake sediment cores provide excellent records of local and regional environmental change over time and are widely used in research. However, these cores are also powerful pedagogical tools. While Upper Midwest students are familiar with lakes, they seldom consider lakes’ sedimentary processes. Consequently, lake sediment cores provide students with a novel and engaging perspective that builds on prior knowledge to explore interactions between human activities and lake systems.

This fall is the debut of a lake sediment core lab in the University of Minnesota’s introductory earth science program. The lab is based on research data from the University’s LacCore Facility and the Science Museum of Minnesota’s St. Croix Watershed Research Station. Much of the lab involves the study of digital images and physical samples of lake sediment cores from Lake McCarrons, located in the Twin Cities metropolitan area. Lake McCarrons has a relatively small drainage basin with a well-documented history. Students will use physical samples and research data to explore how lake sedimentation responded to changes in the lake’s drainage basin. Significant human impacts began with early agricultural activities that drained wetlands areas and increased soil erosion. Increased nutrient runoff caused persistent stratification and made the lake vulnerable to algal blooms. Stratification also led to varve deposition, which allows students to date changes over the last century as Lake McCarrons became increasingly urban. Creation of a recreational beach, housing divisions, urban sewage, and salt used to deice roads all left identifiable changes in the lake’s sedimentary record.

This lab will also explore effects on large scale water systems. Students will examine how human activities increased Lake Pepin sedimentation rates and led to the creation of the Gulf of Mexico dead zone. Since students should have opportunities to explore solutions as well as problems, the lab ends by returning to Lake McCarrons to examine the lake’s response to remediation efforts including the establishment of a sanitary sewer system, wetlands restoration, sediment catchment basins, and alum treatment.