Katie Knapp defends her thesis measuring carbon cycling in Muskegon Lake
On June 12, 2019, graduate student Katie Knapp successfully defended her Master’s thesis titled “Dynamic Carbon Cycling in Muskegon Lake – a Great Lakes Estuary”. Her thesis committee members included: Bopi Biddanda, and Eric Snyder (GVSU), and Steven Ruberg (NOAA).
In her thesis, Katie argued Muskegon Lake is annually net autotrophic, meaning more oxygen production via photosynthesis is happening in the lake than is being used via respiration. Katie used time-series data from the Muskegon Lake Observatory (www.gvsu.edu/buoy/) with additional buoys to estimate metabolism across Muskegon Lake and found significant differences across the sub-basins of Muskegon Lake. The deepest area of the lake, furthest from the Muskegon River, had higher rates of metabolism compared to other sites. This increased activity in the deeper part of the lake was likely due to the deeper thermocline (a layer of water with a temperature gradient that becomes colder as depth increases) depth and higher residence time associated with this site. A traditional testing method (enclosing water in light and dark bottles and measuring O2 changes over time) was compared to the more modern buoy method (sensors measuring O2 in open water over time) and were found to have significantly different results. Both methods had pros and cons; however, the buoy method typically over-estimated metabolism rates compared to the traditional method. When compared globally, Muskegon Lake ranked in the middle of the range of metabolism rates of other inland waters. If Muskegon Lake represented the average inland waters covering 3% of Earth’s surface, the metabolism of the world’s freshwater ecosystems would be comparable to each of the following biomes: upwelling zones in the ocean, Mediterranean shrubland, and tundra. Thus, it is important to include the inland water biome into global carbon budgets because it can contribute a significant portion of carbon cycling.
Katie will be teaching this fall in the Life Sciences department at Muskegon Community College in Muskegon, MI.