Tracing Nitrate Sources in the Saginaw Bay watershed, MI: Implication for Harmful Algal Blooms
Harmful Algal Blooms (HABs) have become more prevalent in recent decades due to increased anthropogenic nutrient input and warmer water temperatures associated with climate change. Nutrient (nitrogen) inputs include loading from the expansion of urban centers (wastewater discharge) and agricultural intensification (inorganic fertilizers and animal waste). In this study, water samples from Saginaw Bay and its watershed were analyzed using a combination of water chemistry, stable water isotopes (δD and δ18O), and nitrate stable isotopes (δ15N and δ18O). The purpose of this study was to evaluate sources, processes, and spatial patterns of nitrate in Saginaw Bay and its watershed causing HABs. We collected water samples from 23 streams and rivers across the watershed and 9 sites from the Bay. The result shows that: 1) the mean nitrate concentration tends to be higher (1.79 mg/l, nitrate-N) in streams that drain from areas with high agricultural land use and concentrated animal feeding operations, 2) the mean nitrate concentration in the Saginaw Bay is relatively low (0.41 mg/l, nitrate-N) and uniformly distributed throughout the water column, 3) the average δ15N value for river samples was 10.69‰ and the average δ18O value was 3.48‰. The dual-isotope analysis result suggests that manure and septic waste are the main sources of contaminants in the watershed. The relative nitrate contribution from manure and septic waste ranged from 35% to 86%. The second-largest nitrate source was typically inorganic fertilizer and its contribution ranged from 3% to 49%. In addition, nitrification sources contribute 7% to 15% of nitrate contamination in the watershed. Ultimately, the outcome of the study provides vital information for effective nutrient management in the Saginaw Bay watershed to prevent future expansion of HABs and further deterioration of water quality in the Great Lakes Region.
Zelalem K. Bedaso
Primary Advisor's Department
Stander Symposium project, College of Arts and Sciences
United Nations Sustainable Development Goals
Clean Water and Sanitation
"Tracing Nitrate Sources in the Saginaw Bay watershed, MI: Implication for Harmful Algal Blooms" (2022). Stander Symposium Projects. 2513.