The Great Lakes and the streams draining to them provide an abundance of ecosystem services, including habitat, water resources, and recreational opportunities. The success and wellbeing of these water bodies are impacted by a variety of factors, including invasive species and septic systems. Along the shoreline of the Great Lakes, invasive species, such as Phragmites and Typha, are a major concern to the coastal wetlands. Within the inland river systems, near-shore septic systems can create elevated levels of nutrients that can have a collection of negative impacts. Both of these threats ultimately relate back to the presence and application of nutrients such as nitrogen and phosphorus. We first address the landscape conditions that allow for coastal wetland invasion. Using machine learning algorithms, we were able to quantify relationships between the presence of invasive species in coastland wetlands, and a variety of landscape scale variables - primarily the nutrient loads of nitrogen and phosphorus. We determined that high invasion is most strongly associated with nitrogen loading above 118 kg/ha/yr within the watersheds derived from the invaded wetlands. We then address how septic systems could be contributing to nutrient loads within the Manistee and Au Sable Rivers of Michigan. We modeled groundwater flow and the transport of nutrients to assess how competently septic systems are retaining nutrients. On average, septic systems allow 88% of introduced nitrogen, and 49% of phosphorus, to enter groundwater. These findings will inform watershed management and provide a better understanding of the effectiveness of septic systems.
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