LAND-USE CHANGE AND WATERSHED DYNAMICS IN TWO LAKES OF COASTAL MAINE

The purpose of this study is to quantify the erosional response to land-use change in two adjacent coastal New England watersheds using lake-core analysis, orthorectified historic aerial imagery, and data from the National Land Cover Database (NCLD). We examine cores from Sennebec and Medomak ponds that record >800 years and >1600 years, respectively. This time frame spans from the era of indigenous populations, through the period of EuroAmerican settlement, and into the modern day, to provide insight into the dynamic relationship between humans and watershed processes through time. Preliminary results from lake-core analysis show changes in mass accumulation rates (MARs) and corresponding suspended sediment yields (SSYs) for Sennebec Pond in the early-19^th century, which coincides with a period of population growth and its associated land-use changes in Maine. This change is less evident over the same time frame in Medomak Pond. In Sennebec Pond, average MAR over the most recent 200-year interval was 0.07 g/cm²/yr (5.2 Mg/km²/yr) compared with 0.06 g/cm²/year (4.3 Mg/km²/yr) over the previous ~670 years. In Medomak Pond, the average MAR over the most recent 200 years was 0.04 g/cm²/yr (2.95 Mg/km²/yr) compared to an average of 0.04 g/cm²/yr (2.91 Mg/km²/yr) over the previous ~670 years. Compared to results from similar studies of lakes in more mountainous regions of New England (e.g., Cook et al., 2020), the recent changes in MAR and SSY appear more muted. With a relatively high percentage of open water and wetlands (17% in Sennebec and 19% in Medomak), the capacity of these low-relief coastal watersheds to trap sediment could potentially mute or lessen the signal visible in lake cores. Further investigations will quantify more recent land-use change through GIS analysis of historic orthoimagery compared with 2016 NLCD, as well as explore how differences in the watershed structures and histories that may account for the variations in the patterns of mass accumulation and SSY.