Response of small New England ponds to historic land use

Abstract

This palaeolimnological study addresses whether the timing, magnitude and nature of lake-ecosystem changes closely track changes in land-use intensity and forest cover in the watershed, and the extent to which lakes retuni to pre-disturbance states following the substantial long-term declinie in human activity that is typical for much of the rural eastern United States. Land-use intensity in the watersheds increased rapidly witlh European settleminent and forest clearance, peaked in the mid-nineteenth century when 60-80% of the land was cleared for agriculture, and then declined to the present as natural reforestation resulted in 65-90% forest cover. Land-use intensity in the three watersheds studied ranged from limited logging to extensive clearance for pasturing and to total clearance for pasture and tillage. In contrast to many studies in which human activity continues to increase throughout the settlement period, all three watersheds now support mature, growing forest and are in their most natural condition in the last 200 years. Dated cores from three ponds were analysed for pollen, fossil chironomids, percenit organic matter and sedimentation changes to compare lake and vegetation change among sites. Increased sedimenit-accumulation rates and small increases in productivity occurred in all lakes during the settlement period. Both tremain higher thani pre-settlement levels, indicating that despite lengthy periods without disturbance and a return to completely forested conditions, the systems and sediment records have not returned to pre-disturbance states. In contrast with results from many other palaeolimnological studies, the magnitude of lake response was slight, probably due to the low intensity of nineteenth-century agriculture and the small watershed sizes.