Aquatic macrophyte community shifts in five shallow lakes in Sibley County, Minnesota

Aquatic macrophyte communities play a key role in shaping the structure and function of freshwater systems. This study examined the understudied shallow lakes of Sibley County, Minnesota, to characterize their aquatic macrophyte communities and document seasonal shifts in community structure, particularly in lakes with invasive species. Full-lake surveys using the point-intercept method were conducted during both early and late growing seasons in 2019 across all five lakes. The dominant native species across most lakes was sago pondweed (Stuckenia pectinata), though Schilling Lake was an exception, being dominated by the invasive curlyleaf pondweed (Potamogeton crispus) in the early season. Significant seasonal shifts in macrophyte communities occurred in nearly every lake, with patterns varying based on species composition and the presence of invasive plants. Schilling Lake exhibited the most pronounced change, with mean species richness increasing from 0.69 (early season) to 1.11 (late season). The invasive curlyleaf pondweed was a major driver of this shift—its frequency declined from 44.4% (early season) to 13.9% (late season), while native sago pondweed increased from 6.3% to 63.9% over the same period. Compared to larger southern Minnesota lakes, all five study lakes had relatively low species richness. The findings highlight how invasive species like curlyleaf pondweed can alter seasonal community dynamics, with implications for lake management and conservation efforts in these understudied systems.