Date of Award

Winter 12-10-2017

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Andrew Reeve

Second Committee Member

Aram Calhoun

Third Committee Member

Aria Amirbahman

Abstract

Studies on New England vernal pools measured precipitation as the dominant source of water for vernal pools and evapotranspiration as the dominant pathway for water loss. More recent studies suggest groundwater plays a larger role in the hydrology of vernal pools, but have not quantified the amount. Additionally, hydrologic studies on vernal pools in New England are limited. This project investigated the hydrology of 6 vernal pools in central Maine by creating biweekly water budgets with a focus on quantifying groundwater flow. The field sites were divided into two major groups: (1) urban pools underlain by glaciomarine clay (Bangor pools) and (2) rural pools underlain by glaciofluvial influenced deposits (east pools). Our hydrologic assessment included volume changes calculated from pool-basin topography and continuous water level data, shallow hydraulic head piezometer data, processing of National Weather Service datasets to calculate precipitation rates, and evapotranspiration (ET) (McGuinness-Bordne Method). The vertical groundwater flux was calculated using two methods: (1) vertical specific discharge calculated using vertical temperature arrays analyzed in a one-dimensional (1D) heat-transport finite-difference model and (2) vertical specific discharge calculated using the Darcy flux equation.

Results from this study confirmed precipitation and evapotranspiration were the dominant hydrological components in vernal pool water budgets. Specific discharge calculated using vertical temperature arrays overestimated groundwater flow into the pools, thus producing larger error in water budget models than specific discharge calculated using the Darcy flux equation. The east pools had higher hydraulic conductivities and larger storage capacity than the Bangor pools. The east pools were suggested to have groundwater influence indicated from proximity of well and surface water levels (< 7 cm difference), suggesting hydraulic interconnectedness.

Although water budget errors were large, water budget models without groundwater exchange resulted in unbalanced water budgets for the east pools. For the Bangor pools, water budget models without groundwater exchange produced lower error than with groundwater influence. The direction of specific discharge calculated using the Darcy flux equation matched the direction of volume needed to create balanced water budgets for the east pools. The Bangor pools showed a similar trend during the wetting phase, but had balanced water budgets without groundwater exchange during the drying phase. Normalized hydrologic components suggested the Bangor pools had similar groundwater influence during the wetting phase as the east pools. But during the drying phase of the Bangor pools, ET was the dominant pathway for water loss and groundwater influence was minimal (< 0.01 m).

In this study, vernal pools with higher hydraulic conductivities, closeness of well and surface water levels, and larger storage capacities are suggested to be connected to the water table and thus, are hydraulically connected to other bodies of water via groundwater. Connectivity to other bodies of water suggests the need for more effective regulations protecting vernal pool water quality.

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