RELATIONSHIP BETWEEN CHANGES IN URBAN LAND COVER AND TRENDS IN WATER CLARITY IN FOUR TIME PERIODS FOR MAINE'S GREAT PONDS

Current studies have shown the importance of past land uses on current water quality. More information is needed to understand the relationship between water clarity and urban land cover. Changes in land use is one potential driver of changes in water clarity. Recent increases in seasonal, lakeshore development have sparked concerns regarding the management of lakeshore development and the impacts of such development on water clarity. Secchi disk trends for 2065 Maine Great Ponds, lakes greater than 10 ha, are analyzed using Seasonal Kendall tau for 4 time periods (1975-2007, 1975-1986, 1987-1996, 1997-2007). Secchi trends for lakes in all time periods are mapped using ARCGIS to investigate spatial trends across broader spatial extents. We used the Retrofit Change Layer (1992-2001) NLCD to characterize changes in residential development in drainage areas surrounding the Great Ponds. Results indicated that Secchi data over 30 years may impede finding significant changes to trends because of shifting trends over time. Decade Secchi data was able to find more significant trends. Most drainage areas surrounding the Great Ponds showed no change or increases in percent urban land cover over the nine years. To better understand the importance of lagged affects of urban land cover on water clarity, the change in urban land cover is used to explain Secchi trends in different time periods. This dynamic view of water clarity integrated with changing urban land cover complements more static views of lake water quality and may provide useful tools for management.