IS VERMONT LOSING ITS OLIGOTROPHIC LAKES?

Results from EPA’s National Lake Assessments suggest that phosphorus is increasing in lakes and ponds in the United States on a continental scale. Particularly troubling is the suggestion that the number of oligotrophic lakes decreased dramatically during the study period 2007-2012. The State of Vermont has been monitoring spring turnover total phosphorus in lakes over 20 acres for the past 40 years. We used linear mixed effects models to examine change in spring phosphorus concentration in 153 lakes, and to compare rates of change in lakes with different initial trophic status. The results suggest that while eutrophic lakes as a group have declined slightly in total phosphorus, mesotrophic and oligotrophic lakes have increased in total phosphorus. We estimate that spring total phosphorus has increased significantly in nearly all oligotrophic lakes in the state.