Abiotic factors that affect the distribution of aquatic macrophytes in shallow north temperate Minnesota lakes: a spatial modeling approach

Macrophytes are an integral component of lake communities; therefore, understanding the factors that affect macrophyte community structure is important for conservation and management of lakes. In Sibley County, Minnesota, USA, five of the largest and most recreationally important lakes were surveyed using the point-intercept method. At each point the presence of macrophytes were recorded, water depth was measured, and a sediment sample was collected. Sediment samples were partitioned by determining sand, silt, clay, and organic matter fractions. The richness of macrophytes in all lakes were modeled via generalized linear regression with six explanatory variables: water depth, distance from shore, percent sand, percent silt, percent clay, and percent sediment organic matter. If model residuals were spatially autocorrelated, then a geographically weighted regression was used. Mean species richness (N point−1) was negatively related to depth and distance from shore and either positively or negatively related to silt depending on the lake and which macrophytes were present. All species richness models had pseudo-R2 values between 0.25 and 0.40. Curlyleaf pondweed (Potamogeton crispus) was found at 44% of all sampling points in one lake, and its presence was related to water depth, percent silt, and percent sediment organic matter during early season surveys. Results from this study exhibit the inhibitory relationship between water depth and macrophyte growth. The results from these models suggest interactions are complex between macrophytes, environmental factors, and sediment texture; and that these interactions are species and site specific. A single landscape scale model would not be appropriate to capture the in-lake processes driving macrophyte distribution and abundance; and management strategies will need to be developed on a lake-by-lake basis.