GEOPHYSICAL SURVEYING OF AN INLAND LAKE IN OHIO FOR THE FIRST TIME: TACKLING INVASIVE AQUATIC VEGETATION AT INDIAN LAKE

Indian Lake in central-western Ohio was originally a small, 640-acre kettle lake formed by glaciers. In the 1850s, the arrival of the Miami-Erie Canal brought on the expansion of Indian Lake into a reservoir of more than 5,000-acres. Acquired by the state of Ohio in 1898, Indian Lake became a thriving state park, supporting a variety of outdoor recreation and tourism activities. During the summers of 2022 and 2023, explosive growth of three dominant species of invasive aquatic vegetation drastically impacted the lake, making it almost impassable and affecting not only fishing and boating, but also tourism. To better understand how to tackle the invasive vegetation problem and improve overall lake quality, the Ohio Department of Natural Resources (ODNR) began researching causes for the prevalent vegetation growth, including the muddy, organic-rich bottom sediments into which the plants root. Removal of excess sediment helps to restrict growth of the aquatic plants by reducing their substrate, removing seed-infused sediment, and increasing the lake depth thereby reducing the potential for the plants to obstruct the upper water column. With a sediment dredging program already in place at Indian Lake, ODNR needed an optimized plan-of-action to focus dredging efforts; understanding where and how the bottom sediments are distributed became a key to tackling the problem. Using a research vessel outfitted with advanced geophysical tools, the Ohio Geological Survey (OGS) collected over 42 miles of highly accurate data providing information on bathymetry, side-scan sonar, and sub-bottom profiles of bottom sediments for a large portion of the lake. New key items created for Indian Lake include maps for bathymetry, muddy-sediment thickness models, mud volumetrics, and a mosaic image of the lake bottom. In addition, the sub-bottom profiler data provided a unique look at underlying sediment layers that existed prior to the filling of the lake, indicative of the area’s past glacial geologic history. The OGS was able to provide ODNR with valuable insight to address the invasive aquatic plant dilemma, while also providing geophysical data for the first time for an inland lake in Ohio, gaining a better understanding of the current state of the lake as well as a view into its past.