279-12 Groundwater Flow Models Show Esker Deposits Enhance Groundwater Circulation in a Maine Peatland

Session: The Current Understanding of the Role of Wetland Hydrology in the Cycling of Elements and other Substances: A Technical Session in Memory of Paul H. Glaser

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Peatlands are complex wetlands that play an important part in the global carbon budget. Northern peatlands have played a significant role in storing carbon since the last ice age, containing over 80% of all terrestrial peat carbon. Hydrology influences many biogeochemical processes within peatland ecosystems; notably, the position of the water table in a peatland directly impacts carbon sequestration or emission and water circulation within a peat basin will influence nutrient distribution and availability. Traditional models of peatland hydrology show downward flow during normal or wet periods while during dry periods flow reversal occurs and water moves upward from mid-depths, driven primarily by evapotranspiration at the peat surface. Hydro-geophysical studies of northern peatlands in Maine, USA, over the last two decades have identified the presence of eskers buried beneath some peat deposits and hypothesized that these esker deposits allow for increased vertical groundwater flow that does not follow the expected flow patterns described by established literature and may act as a conduit between the peatland and regional groundwater system. Additionally, this increased groundwater movement may facilitate transport of labile carbon and create hot spots of methanogenesis. Using the results from these studies along with new hydrologic and geophysical datasets, a USGS MODFLOW 6 groundwater flow model was developed for Caribou Bog near Bangor, ME. Caribou Bog is a multi-unit, ombrotrophic, domed peatland with a patterned pool system. Groundwater flow models were created by inserting a local-scale model encompassing the peatland into a coarser-gridded regional model. Simulations were then run at the regional (watershed) scale and calibrated using the PEST parameter estimation package. Initial results show that the areas overlying the esker have increased vertical movement particularly after large rain events rather than during dry periods, supporting the concept that the peat is hydraulically connected to the underlying aquifer. These results challenge the traditional hydrologic models of peatlands as well as the viewpoint that ombrotrophic peat systems are completely disconnected from groundwater flow. These results may also provide insights about future carbon cycling within the peatland as climate change primarily impacts precipitation patterns and increased temperatures.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7837

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