Small streams can have a big impact on the water quality of the lakes they empty into. Inputs from small streams can contribute to nutrient loading, or when elements like nitrogen and phosphorous found in agricultural fertilizers run off the land and into downstream waters and larger lakes. These inputs can feed algal blooms that affect coastal waters by creating oxygen-starved dead zones that may lead to regional fish kills.  

A graduate student at the University of Wisconsin-Madison’ Center for Limnology and former Northeast CASC fellow Rob Mooney, along with UW-Madison peer Will Rosenthal sampled 235 tributaries that flow into Lake Michigan over a six day road trip to understand how small tributaries contribute to nutrient loading.  

They found that six of the largest tributaries sampled accounted for nearly 70 percent of the nutrients entering lake Michigan. “It’s hard to think of a Great Lake, like Lake Michigan, as a singular lake. It is just so massive and built up of all of these smaller segments of coastline that have different tributaries running in,” Mooney says. However, understanding the inputs from these tributaries can help resource managers better understand the potential impacts of nutrient loading for nearshore ecosystems and communities in the Great Lakes region. 

Rob Mooney was a former Northeast CASC fellow and current graduate student at University of Wisconsin – Madison. He is currently pursuing a PhD in Zoology while conducting research through the Center for Limnology.