Timber harvest and flood impacts on sediment yield in a postglacial, mixed-forest watershed, Maine, USA

Abstract

Abstract The impact of human activities on sediment yield is poorly constrained in the northeastern United States, as in other northern hemisphere forested landscapes previously occupied by Pleistocene ice sheets. This study examines changes in sedimentation in Little Kennebago Lake (LKL), Maine, in relation to extreme hydrologic events and land-use change. Historical records indicate minimal disturbance before the onset of commercial logging after 1891. Sediment cores record >1,200 years of sedimentation and allow comparison of prehistoric and anthropogenic conditions. Variations in sediment yield are evaluated in the context of hydrologic records and reconstructions of road density and timber harvest derived from historical topographic maps and aerial photographs. Cores collected before and after a highly erosive, localized extreme rainfall event in July 2018 provide a template for interpreting clastic layers found earlier in the record. The frequency of these events increased around 1900, with five layers in the previous ∼1100 years and 12 layers from 1900-2018. This timing corresponds to an increase in suspended sediment yield from 2.0 Mg/km2/yr to 6.4 Mg/km2/yr and increased abundance of pollen taxa associated with forest disturbance. A relative lack of discrete erosion events since ∼1970, in spite of increasing timber harvest, suggests that modern best management practices may be effective in reducing erosion. The 2018 event is a reminder, however, that ongoing reevaluation of management practices is necessary in light of changing hydrology, in this region and elsewhere.