The coastal shorelines of the Great Lakes host unique habitats for the flora and fauna that are rare or endangered. Phosphorus (P) is an essential element for biological metabolisms and can be a limiting nutrient in the lakes shoreline biota. In this study, we measured the distribution and relative abundance of P and dissolved organic matter (DOM) in the east shoreline of Lake Michigan, which represents one of the largest freshwater sand dune systems on Earth. We examined the mineral effects on DOM degradation and P adsorption in the shoreline ecosystem, and the interactions between DOM, P, and minerals were also investigated. The findings suggest a potential role of minerals in controlling DOM decomposition and P storage in coastal environments, which may help to further understand the biogeochemical cycles of C and P in large inland water bodies.