GROUNDWATER FLOW PATTERNS AND SOURCES OF WATER TO A CALCAREOUS FEN

Edinboro Lake is one of eight kettle lakes in northwestern Pennsylvania formed during Late Wisconsinan glaciation. The lake occurs within a complex package (up to 30 m thick) of glacial sediments that record multiple depositional events from glacial advance and retreat. On the northeastern lakeshore is a calcareous lake edge fen (terminology of Amon et al., 2002) with more than 15 threatened or endangered plant species. We conducted a field investigation to determine the sources of groundwater to the fen. Borehole lithologic data indicate that there are three unconsolidated aquifers present at the site: a surficial unconfined aquifer; a laterally continuous confined aquifer; and a deeper confined aquifer present only in the south. Each aquifer is between 3-7 m thick and consists of sand and gravel outwash deposits. Hydraulic head data collected from nine monitoring wells document lateral groundwater flow to the south (towards the lake) in each aquifer. Vertical groundwater gradients change direction and magnitude across the site over relatively short distances (< 300 m) and suggest a localized flow system of recharge and discharge. The fen occurs in topographic lows within the unconfined surficial aquifer; lateral seeps and discharge from this aquifer are definitive sources of water to the fen system. Vertical groundwater discharge from the deeper aquifers may also feed this system. We are collecting water samples from the fen and wells to characterize hydrochemistry and discern if deeper, vertical groundwater discharge is an additional source of water to the system.

Reference

Amon, J. P., C.A. Thompson, Q.J. Carpenter, and J. Miner, 2002, Temperate zone fens of the glaciated Midwestern USA: Wetlands, v. 22, no. 2, p. 301-317.