Landscape based assessment of human disturbance for Michigan lakes

We describe a process for assessing lake impairment and identifying key disturbances that had the greatest impact on each lake for all lakes 5 acres or bigger in Michigan using available natural and human disturbance databases. Using statistical relationships between in-lake indicators for a subset of lakes and landscape natural and human-induced measures for all lakes, we assessed lake health status for all lakes. Approximately 92% of the lakes were least to marginally impacted and 8% were moderately to heavily impacted.  Among the heavily impacted lakes, more inline lakes (92%) were impacted than disconnected (6%) or headwater lakes (2%), and more small lakes were impacted than medium to large lakes.  For inline lakes, 83% of the heavily impacted lakes were < 100 acres, 8% between 100-1,000 acres, and 1% > 1,000 acres.  For disconnected and headwater lakes, all heavily impacted lakes were < 100 acres.  Among the key disturbances, nutrient yields and farm animal density affected the highest, agriculture affected moderate, and point source and road measures affected least number of lakes.  Our process permits evaluation of lake health across large regions, and yields a disturbance index that is a physicochemical and biological indicator weighted sum of multiple disturbance factors.