Measuring anthropogenic disturbances in a hydrogeomorphic-based lake classification built using fish assemblages in 360 north-temperate lakes

Hydrogeomorphic features and anthropogenic disturbances affect fish assemblages but the relative importance of these variables is inadequately understood. Quantifying these linkages, across multiple spatial scales, is key to developing lake ecosystem assessment tools and management plans. Accordingly, I classified lakes with similar hydrogeomorphic features and within these lake groups, identified the most important anthropogenic influences on fish species richness. I used fish assemblage, hydrogeomorphic, and anthropogenic data from 360 lakes in Maine, New Hampshire, Iowa, Michigan, and Wisconsin. To build lake classes, I used classification and regression trees; lakes having similar fish species richness were best grouped by lake area, ecological drainage unit, and watershed area. Results indicated that in addition to positive associations of lake and watershed area with species richness, regionalization frameworks were useful tools in identifying unique areas of freshwater biodiversity. Within classes of naturally similar lakes, species richness generally had a negative association with fish stocking, dams, and urban and agricultural land cover/use. Species richness was positively associated with human population density and road density. The methodology of classifying lakes appears to be a tool that lake managers can utilize to better understand fish assemblages in inland lakes. Classifications were also useful in grouping naturally similar lakes to identify the effects of human disturbances.