A RECORD OF ANTHROPOGENICALLY-DRIVEN LANDSCAPE CHANGE AND PRELIMINARY FIRE HISTORY OVER THE HISTORICAL PERIOD, BROWNS LAKE, OHIO

Few late Holocene paleolimnological archives from Ohio have been published. Brown’s Lake, a kettle lake in northeast Ohio, represents an opportunity to fill this gap. Formed during deglaciation about 14.5 ka, the sediment record includes the Younger Dryas and the 8.2 ka event. Despite its apparent climate sensitivity, the late Holocene paleoclimate record has not yet been established. Here, we describe the lithology and changes in sedimentation rates for the upper ~1.5 m of the core record, which can be divided into three discrete lithologic units: 1) a pre-settlement unit that spans from the bottom of the core to ~56 cm from the top, 2) a lighter-colored unit that records disturbance by European settlement practices, and 3) a third unit that consists of a darker, organic-rich sediment in the uppermost ~15 cm. Unit 1 is a dark brown sapropel, with abundant plant macrofossils and sponge spicules, common charcoal, and rare clastic minerals. An abrupt transition marks the onset of unit 2, whose sediments are lighter in color, consistent with a higher silt content observed in smear slides. This unit is also depleted in plant macrofossils and charcoal compared with unit 1; this difference may be due to a more rapid sedimentation rate, which would serve to dilute the charcoal signal, or it may record suppression of fire after settlement. This is supported by bulk radiocarbon dates from units 1 and 2, which record uncalibrated ages of 400 +/- 30 BP at 58 cm and 1490 +/- 30 BP at 140 cm, respectively. These preliminarily dates suggest a faster sedimentation rate for unit 2, which is consistent with extensive anthropogenic landscape disturbance and the resultant increased denudation rates. Pending radiocarbon ages will better quantify the sedimentation rates. Until then, Pb-210 dates from the uppermost part of a second core from the lake are used to correlate the cores and add age control. This second core records similar lithologic transitions, including a switch from darker, organic-rich sediments (unit 1) to lighter sediments with higher magnetic susceptibility (unit 2). This transition has been dated at ~1820 CE, which supports our hypothesis that unit 2 represents a time of anthropogenic disturbance and possibly fire suppression.