Nutrient limitation in phytoplankton has been a primary area of research in marine and aquatic sciences for decades. Phytoplankton play a large role in nutrient cycling, carbon sequestration, and determining oxygen concentrations in wetlands, as well as serving as an important food source for zooplankton and, in turn, larval fish. However, the factors that contribute to wetland phytoplankton growth, such as nutrient concentrations, are often overlooked. Here, we look at long-term nutrients in Old Woman Creek, a 0.6 km^2 flow through wetland on the southern shore of Lake Erie in Huron, OH. Water quality monitoring at Old Woman Creek dates back to 1980 and presents a unique opportunity to examine temporal patterns in nutrient limitation status in wetland phytoplankton. Using long-term nutrient data, we examine both seasonal and historical trends in the nitrogen to phosphorus ratio (N:P) to determine how nutrient limitation may be changing over time. Additionally, in 2023 we performed bimonthly nutrient debt experiments to complement our long-term analyses. We spiked in situ containers with phosphate, ammonium, and phosphate + ammonium to determine which nutrient was deficient in the phytoplankton community. While wetland phytoplankton appear to be phosphorus deficient most of the time, nitrogen deficiency often persists throughout the summer and seems to occur more frequently in Old Woman Creek than in lakes. While unsuitable for determining true nutrient limitation, our long-term analyses and in situ experiments present a compelling assessment of nutrient deficiency in wetland phytoplankton, suggesting that nitrogen may be more important in wetlands than was previously thought. A better understanding of which nutrient limits phytoplankton growth in wetlands, and when, will inform nutrient management on the landscape to ensure that management strategies achieve their intended goals.
