UNRAVELING THE EFFECTS OF CLIMATE CHANGE AND FOREST MANAGEMENT ACTIONS ON AN IMPORTANT AND DYNAMIC GROUNDWATER-SURFACE WATER SYSTEM IN MANISTEE NATIONAL FOREST, MICHIGAN

The Pines Point Semi-Primitive Area of Manistee National Forest, Michigan is underlain by a thick sequence of well-sorted, med-grained outwash sand which supports a dynamic, linked groundwater-surface water system along the White River. The White River is a designated Michigan State Natural River and candidate Federal Wild and Scenic River. Pines Point is also a site of active Savanna Ecosystem restoration efforts. Three drilled monitoring wells (PPW1, PPW2, PPW3) were instrumented to collect high-resolution groundwater levels at the onset of savanna restoration efforts, including canopy reduction, by the US Forest service in Pines Point. Long-term data suggest ground water in this system is responding to both the reduction of canopy and climate-change induced trends in monthly and annual precipitation.

Pines Point wells generally record an annual hydrograph dominated by a single, large groundwater recharge event. Over the period of record, inter-annual variability, resulting from interactions among precipitation, antecedent conditions, and now, forest management efforts, is evident in the magnitude, timing, and duration of recharge events. Notably in 2021, with the lowest annual precipitation in our period of record, evidence of typical groundwater recharge events were absent in wells PPW1 and PPW2. Groundwater at PPW3, adjacent to an area of forest canopy reduction, showed a recharge event despite the low annual precipitation.

Monthly precipitation for the period 2011 – 2022 displays a trend of + 0.89 cm/year in August, and + 0.31 cm/year in October, and prior to the 2021 recharge anomaly, all wells displayed trends of rising groundwater levels. Changes in seasonality of precipitation and snowmelt patterns may also be the driver of observed increases in groundwater temperatures on the scale of +0.4 deg C over the last decade. The increase in precipitation during summer and fall seasons is consistent with larger scale observations of seasonal precipitation trends throughout the Midwest. This work ultimately seeks to distinguish the impact of distinct hydrologic drivers to this groundwater system and how that may alter the linked White River surface-water system.