Paper No. 239-4
Presentation Time: 9:00 AM-6:30 PM
LAND USE CHANGES OVER THE PAST 200 YEARS IN NORTHEAST OHIO RECOGNIZED IN LAKE CORES FROM BROWN’S LAKE BOG, NORTHEAST OHIO
Northeast Ohio has undergone a marked land use change over the past 200 years. Studying lakes from the area can help us determine landscape response to deforestation, draining wetlands, and intensive agriculture. A 1 meter core extracted from Browns Lake dated using Pb-210 shows an abrupt transition from organic-rich muds to several 10s of centimeters of a bright loess layer, then near the top of the core a recovery back to more organic-rich sediments. Loss on ignition, magnetic susceptibility, x-ray diffraction, and grain-size analysis characterize the transition that occurred during the early decades of the 19th century. Pb-210 dating determined that at about 45cm depth, the core dates to 1846 CE. Downward extrapolation put land clearing and the increased flux of quartz and clay into the lake about 1820 CE. Magnetics, grain size and mineralogy support a wind-blown hypothesis for the sediment associated with land clearing and agriculture. The magnetics are inverse to the organic content determined from loss on ignition that shows a decrease in magnetics and a gradual return to organics in the upper 30 cm of the core. This return to organic-rich sediments is consistent with the abandonment of farmland, changes in agriculture, including conservation tillage and a wetter climate, all consistent with less windblown flux and more organics in the system. Comparisons with climate proxy records based on tree-rings and with observational climate records suggest that the early land clearing may have occurred during a relatively dry and cool interval and that the return to organic-rich sediments that occurred over the last several decades is associated with wetter and warmer conditions. The role of land use change and its effect on the regional energy balance (i.e. change in albedo via atmospheric dust and surface reflectivity) and the hydrologic cycle (observed drying) are unknown but being investigated.