SIMULATING THE HYDROGEOLOGIC SETTING OF PEATLANDS IN THE KENAI PENINSULA LOWLANDS, ALASKA A. S. Reeve 1 and Mike Gracz 2 1 Department of Earth Sciences University of Maine Orono, Maine, USA 04469 E-mail: asreeve@maine.edu 2 P.O. Box 15301, Fritz Creek, Alaska, USA 99603 Abstract: Ground-water flow simulations were constructed to evaluate the interaction between ground water and wetlands systems, focusing on peatlands in the Kenai Peninsula Lowlands, south-central Alaska. Peatland systems occur in both recharge and discharge zones along transects simulated in computer models, whereas toe slope wetlands occurred in discharge zones. Sensitivity analysis indicates that hydraulic conductance of subsurface units has a strong influence on the rates and directions of ground-water flow exchanged between peatland systems and the surrounding mineral sediments, and needs to be further characterized to assess the hydrologic function of wetlands in the Kenai Lowlands. Perching of the water table was simulated in several modeling scenarios, altering ground-water flux rates to wetlands and shifting recharge zones to topographically lower areas. Runoff (saturated surface flow and shallow interflow) was the dominant flux in all simulations. Our exploratory simulations suggest three avenues for future research using computer modeling to evaluate wetland hydrologic function in the Kenai Peninsula: 1) improved simulation methods to better characterize ground-water perching and overland flow, 2) better characterization of the distribution and hydrogeologic parameters of geologic units, and 3) collection of hydraulic head data in and near representative wetland systems to calibrate computer simulations. Key Words: geology, ground water, simulation modeling INTRODUCTION The Kenai Lowlands occupy about 9,400 km 2 on the western side of the Kenai Peninsula, along the coastline of south-central Alaska. The broad low- land platform is 41% wetland, ranging from extensive peatland complexes to riparian wetlands. These wetlands were mapped in detail outside the boundaries of the Kenai National Wildlife Refuge to characterize areas that are subject to development. Human activities, including residential development in rural areas, urbanization, and extraction of natural resources, may degrade these relatively undisturbed wetlands, altering their hydrologic and ecologic value. In addition to these local environ- mental factors, regional changes in climate may be altering the hydrologic cycle across the Kenai Peninsula (Klein et al. 2005). The location of wetlands within a landscape is an important control on the hydrologic function of wetlands (Winter 1988, Winter et al. 2001, Godwin et al. 2002). Understanding the hydrologic function of wetlands is important if these wetlands are to be properly managed and to understand the important linkages between wetlands and other ecosystems. Wetlands account for about 43% of Alaska’s landscape (Hall et al. 1994), but surprisingly little has been published regarding the hydrologic function of Alaskan wetland systems. Siegel (1988a, 1988b) collected hydrogeologic data on several wetland systems in southern Alaska, and concluded that bogs and fens near Juneau, Alaska act as recharge zones, whereas forested wetlands act as discharge zones. While the hydrologic assessment of wetlands within the Kenai Lowlands has been identified by local environmental groups as an important step in evaluating these systems, little readily available hydrologic information is available to characterize these wetland systems. Furthermore, while hydrol- ogy is clearly an important functional process within all wetland systems, it is not clear what hydrologic processes are important in the Kenai Lowlands. To better understand the broad hydrologic and geologic factors influencing the wetlands of the Kenai Lowlands: 1) landscape-level topographic and geo- logic profiles were constructed illustrating the WETLANDS, Vol. 28, No. 1, March 2008, pp. 92–106 ’ 2008, The Society of Wetland Scientists 92