Hydrogeologic and geomorphic processes in a karst landscape and seasonably-cold climate: Linking spatial distribution and morphometric dynamics of closed depressions to bedrock fractures in a wastewater spray irrigated agricultural and forest system located at the site of the Living Filter in Central Pennsylvania, United States

Abstract

The Living Filter at Pennsylvania State University in Central Pennsylvania receives on average 1.5 million gallons per day (MGD) of secondary treated wastewater effluent year-round since 1962. The objective of this study was to identify and relate any bedrock fracture traces and surface depressions to any surficial or geomorphologic processes currently underway as a result of irrigation. The Living Filter is underlain by a massive dolomite with fractures trending near N-S that were previously documented using photogrammetry. A manual process was developed in order to determine the trend and location of several fracture traces within the Astronomy site section of the Living Filter. A semi-automated isolation scheme was next used to identify and correlate closed depressions to the location of fracture traces in the Living Filter. A predominant but slight NE-SW trend was observed among fractures at N5E in the area north of the Pennsylvania Furnace Anticline. A high occurrence of depressions was noted in the area of fractures compared to non-fractured bedrock. The depressions in this area were found to have a net gain of 8000 ft2, the result of which was from the net loss of 5000 ft2 within the agricultural portion of the site and a net gain of 13,000 ft2 within the forested portion of the site. Cross sections of several depressions within cropped areas indicated a lower angle slope corresponding to a V-shape while depressions within forested areas were characterized by a traditional U-shape and previously established steeper slope. These findings will enhance the current understanding of the different morphologic characteristics of both forested and agricultural depressions in karst topography. The workflows implemented here can be implemented in similar sites that display topographical variances from the bedrock fractures.