Sedimentation patterns in the three basins of Walden Pond, Concord, Massachusetts, U.S.A.: a multiproxy approach to decipher environmental trends, anthropogenic impacts, and regional events of the last 800 years

Abstract Multiproxy analysis of sedimentary records retrieved from the three basins of Walden Pond, Concord, Massachusetts, reveals distinct sedimentary processes characterizing each basin configuration. It also allows reconstruction of a comprehensive landscape history that explores a wide range of questions from climate change to regional anthropogenic and natural events. Here, we present an 800-year-long sedimentary record of the three basins of Walden Pond, a closed kettle lake, that has been affected by changes to the landscape since European settlement in the early 17th century and during later transition to a popular tourist destination. Separate age models were developed for each basin using pollen stratigraphy, onset of industrial contaminants, and radiocarbon dating, which allow robust correlation between the three basins. Using a combination of geophysical, sedimentological, geochemical, and palynological proxies we were able to define four time periods of landscape change: a mostly forested landscape before the early 17th century, an early European era characterized by logging and shoreline use, an industrial period with peak concentrations of air pollutants such as coal and Pb, and the youngest period of widespread recreational activities marked by soil erosion, high nutrient input, and high productivity. While all three basins show the main trends, the shallowest basin is most affected by shoreline processes. The deepest and largest basin has the highest sedimentation rate, likely because of sediment focusing and more effective preservation of organic matter due to partial lake-bottom anoxia. Suspended sediments and airborne pollutants are more equally distributed throughout all basins but can be diluted in larger basins. In addition to long-term trends, we were able to identify sudden-onset sedimentation events, likely caused by mass wasting along the steep-sided slopes of all three basins. Three of these horizons are evident in more than one basin and perhaps are linked to a strong historic earthquake in 1755 CE and two prehistoric earthquakes.