image: Martin Creek, which flows into Martin Bay of Big Bay de Noc in Lake Michigan. view more
Credit: Image credit: Robert J. Mooney.
A study uncovers the contribution of nutrients to Lake Michigan by small tributaries. In rivers, lakes, and marine coastlines worldwide, excessive inputs of nutrients such as nitrogen and phosphorus cause eutrophication, a condition favorable to the growth of harmful algal blooms that reduces water quality and alters ecosystem functions. Monitoring and regulation of eutrophication commonly focuses on the largest tributaries. Robert J. Mooney and colleagues monitored 235 tributaries to Lake Michigan, the world's fifth-largest freshwater lake, for nutrient loads and the concentration of nutrients in each tributary over 6 days. The six largest tributaries accounted for around 70% of the daily nitrogen and phosphorus, but small and abundant tributaries also played a significant role. The authors report that nutrient loads in small tributaries were high for their size, and the nutrients were biased toward dissolved inorganic forms. Further, because plumes of nutrients released by small tributaries become trapped and overlap with each other in coastal areas, they likely have outsize impacts and fuel algal blooms. According to the authors, the results suggest that small tributaries may be an underappreciated source of nutrients to water bodies and could be a target for eutrophication mitigation.
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Article #20-01376: "Outsized nutrient contributions from small tributaries to a Great Lake," by Robert J. Mooney et al.
MEDIA CONTACT: Robert J. Mooney, University of Wisconsin-Madison, WI; tel: 608-669-4016; e-mail: <rjmooney@wisc.edu>
Journal
Proceedings of the National Academy of Sciences