URBAN POND ARCHIVES OF CLIMATE AND ANTHROPOGENIC ACTIVITIES: A CASE STUDY ON SLUICE POND, LYNN, MA

New England lake sediments preserve a rich history of post-glacial environmental and climate conditions as well as human overprints. Sluice Pond is a relatively deep (z_max=19.8m) and small (18.0ha) lake located in the urban center of Lynn, MA. The central basin is currently well stratified, with the thermocline base occurring at ~10m. The analysis of sediment cores and sub-bottom geophysical data reveal that lake level has changed as a result of Holocene hydroclimate variability, with pronounced low stands prior to 8,200 cal BP, from 5,100 – 3,500 cal BP, and from 2,000 – 1,300 cal BP. Such lake level changes have affected sedimentation patterns and the thermal structure of the pond. Long sediment cores (~5m) from the deep basin have also revealed anomalous isotopic, magnetic, and density data in the upper sediments, presumably due to anthropogenic activity. To focus on the time period of enhanced anthropogenic activity, additional short sediment cores (~1m) from the deep basin were collected. Age constraints on these upper sediments are afforded by radioisotopes (²¹⁰Pb, ¹⁴C) and well established chronostratigraphic markers (Ambrosia, ¹³⁷Cs, Pb, V). Core stratigraphy, proxy time series and principle components analysis provide evidence of three distinct periods of human impact. During Colonial time a modest increase in the flux of terrigenous matter is evident, presumably due to agricultural activities in the watershed. By the early 19^th Century, we observe increased fluxes of terrigenous matter as the watershed became more developed, and Mn/Fe suggests a shift to more reducing conditions in the sediment. Much of the evidence at this time suggests a rather abrupt shift, likely associated with the manufacturing boom in Lynn in the 19^th century. From the early 20^th Century to present sediments are laminated black muds, with low Mn/Fe, negative δ³⁴S, and low magnetic susceptibility, all of which provide evidence of permanent anoxia in the deep basin. The limnologic evidence of meromixis in the modern water column concurs with paleo redox conditions becoming reducing as a result of increasing and changing land use patterns. A focus on urban lacustrine systems can simultaneously provide climate records and patterns of anthropogenic activities and are a rich archive for examining abrupt shifts in sedimentation patterns.