Date Approved
12-17-2025
Graduate Degree Type
Thesis
Degree Name
Biology (M.S.)
Degree Program
Annis Water Resources Institute
First Advisor
Bopaiah Biddanda
Second Advisor
Eric Snyder
Third Advisor
Steve Ruberg
Fourth Advisor
Anthony Weinke
Academic Year
2025/2026
Abstract
Metabolism is the sum of primary production (photosynthesis; PP) and respiration (R) and determines whether an ecosystem functions as a carbon sink or source. Inland waters are warming faster than the atmosphere and oceans. However, their contribution remains poorly quantified within the context of the global carbon budget. Muskegon Lake, Michigan, USA, a drowned river mouth, model Great Lakes estuary, and recently delisted Area of Concern (AOC), has been the subject of two decades of seasonal pelagic (2004-2024) and recent high-frequency littoral (2023-2024) metabolic sampling. This study examined long-term and spatial patterns of metabolism in surface waters, as well as environmental and nutrient drivers, including temperature, dissolved oxygen (DO), chlorophyll-a, pH, nitrate (NO3), ammonia (NH3), and total phosphorus (TP). Pelagic sites exhibited significant seasonal variability but were spatially consistent in rates of net primary production (NPP), R, and gross primary production (GPP), suggesting a well-mixed surface layer offshore. Average pelagic rates of NPP, R, and GPP, were 3318, 1890, and 5208 mgCm-2day-1, respectively, while littoral averages were 400, 348, and 748 mgCm-2day-1. The pelagic GPP:R ratio was lowest in spring (2.76) and highest in fall (6.52), whereas the littoral zone showed the opposite pattern, with the highest GPP:R in spring (6.03). These differences indicate a state of annual net autotrophy throughout with contrasting metabolic dynamics between zones. Long-term declines in NO3, and TP and increases in DO and pH in surface waters were also observed. Within the littoral zone, DO, chlorophyll-a, and pH varied significantly by site, and nutrients were seasonally dynamic in both lake zones, where NO3 peaked in spring while TP rose through the growing season. Multivariate analyses showed pelagic PP correlated strongly with TP, pH, and chlorophyll-a, while littoral PP was highly correlated with temperature and DO, reflecting possible differences in ecosystem processes across zones. Bacterial secondary production amounted to ~8% of GPP over the years, emphasizing the role of the microbial loop in carbon cycling. Overall, Muskegon Lake’s surface waters remain a significant carbon sink, though long-term warming and other anthropogenic stressors could change this metabolic balance, highlighting implications for Great Lakes estuaries under climate change.
ScholarWorks Citation
Dennis, Kaylynne Olivia, "Trends, Drivers, and Implications: Measurements of Production and Respiration Reveal Net Autotrophy in a Great Lakes Estuary" (2025). Masters Theses. 1173.
https://scholarworks.gvsu.edu/theses/1173
