LATE HOLOCENE CHANGES IN THE NITROGEN ISOTOPE COMPOSITION OF A SEDIMENT CORE FROM NEQUASSET LAKE, WOOLWICH, ME

The nitrogen input of anadromous fish into fresh water bodies can be tracked through the stable isotopic signal of freshwater foodwebs (Post and Walters, 2009; Walters et al., 2009) and sedimentary records (Finney et al, 2002; Kline et al, 1993). The marine derived nitrogen input excreted by anadromous fish is consumed by the phytoplankton, which then gets incorporated into the foodweb, or settles out and becomes part of the sedimentary record. Thus, stable nitrogen isotopes of sediment cores provide a useful tool for evaluating the changes in anadromous fish runs through time. The purpose of this study is to examine the nitrogen isotope composition of a sediment core collected from Nequasset Lake, in Woolwich Maine. This lake is dammed but currently has a fish ladder and provides spawning habitat for the anadromous alewife (Alosa pseudoharengus). This study seeks to quantify the baseline fish runs that have occurred in the watershed. Stable carbon isotope composition, C/N ratios, grain size analysis and magnetic susceptibility analysis will be done to provide information on environmental changes in the watershed that may have impacted the baseline fish runs and/or the nitrogen isotope signal in the lake sediments. This study provides insight into the ecological potential of restoring the Nequasset Lake fish ladder to its prehistoric capacity.