Factors influencing groundwater seepage in a large, mesotrophic lake in New York

Groundwater seepage is gaining recognition as a critical feature of lake shoreline environments, yet our understanding of this process is complicated by the considerable spatial heterogeneity observed in flow rates within and among lakes. This research investigated spatial patterns in groundwater seepage around the shoreline of Oneida Lake, a 207 km2 lake located in central New York, USA. Replicated, shielded seepage meters, with associated controls, were used to quantify rates and directions of groundwater flow along a 120 m stretch of shoreline throughout the summers of 1997-1999. These reference meters exhibited an average flow rate of 72 ml m−2 h−1 (n=840; SE=5) with individual flow rates as high as 1200 ml m−2 h−1. Additional meters, monitored in 1998, indicated that seepage patterns were highly synchronous but increased in magnitude of flow rate with increasing distances offshore up to 100 m from shore. In 1999, private landowners assisted in weekly monitoring of seepage meters at 28 additional sites distributed around the 88 km perimeter of Oneida Lake. The highest groundwater flow rates, averaging 100 ml m−2 h−1, consistently occurred along the northern and eastern shorelines; lowest flow rates, including areas of groundwater recharge, occurred along the western and southwestern shorelines, proximal to the lake's outlet. Spatial patterns in groundwater flow were surprisingly unrelated to substrate texture despite wide variability observed around the lake edge, from silty-clays, to sands, gravels and boulders. Broad-scale factors of underlying bedrock geology and regional precipitation patterns appear to be driving the observed spatial patterns in Oneida Lake's groundwater contributions.