 Background
The East Mahantango Creek Watershed in east-central Pennsylvania is the primary experimental venue for hydrology and nutrient transport research programs of the Pasture Systems and Watershed Management Research Unit, USDA-ARS. The main ARS office is located on the campus of the Pennsylvania State University, University Park, PA; a field office servicing the Watershed is located at Klingerstown, PA and is staffed by five technicians.
Watershed statistics
Size: 420 km2
Land use: Predominantly forested ridgetops with agriculture dominating the valley floors. Total area is 45% cropland or pasture; 55% forested, and 1% urban and residential.
Population: Approximately 9,000 interspersed between farmsteads and small towns; population growth is stable to slightly declining (-0.2%/yr).
Geology/Soils: The Watershed is located in the Valley and Ridge Physiographic Province of central Pennsylvania. It is underlain by folded and fractured, interbedded shales, siltstones, and sandstones. No limestone or karst geology occurs within the basin. Soils are typically shallow (<1.5m) and predominantly well-drained silt loams.
Water resources: Ground water supplies 100% of the drinking water for the basin population.
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Hydrology
Average annual precipitation is approximately 1090 mm. Average annual streamflow is approximately 650 mm, with a major portion (60%-80%) being supplied by ground water. Subsurface flow controlled by an unconfined aquifer in highly fractured, shallow bedrock with high transmissivity and low storativity. Overland flow occurs primarily from expanding and contracting ground water discharge zones (seep areas) and from areas underlain by low-permeability clay (fragipan) layers.
Major issues in the Watershed
Nutrients: Nitrate concentrations in ground water and lower-order streams are correlated with upgradient land use. Consequently, surface and subsurface nitrate concentrations around high-density poultry and swine operations and intensively cropped fields are usually elevated above acceptable limits. High soil test phosphorus (P) levels in fields susceptible to surface runoff can result in significant amounts of P being exported to adjacent streams.
Soil erosion: Lack of stream bank stabilization and some cropping practices lead to localized soil erosion problems and sediment-laden discharges to streams. However, watershed-wide sediment loss is not considered to be a problem.
Sewage discharge: Sewage from the entire population is handled by on-lot septic systems. Sewage discharge does not appear to be a major problem within the watershed.
Development: Development is not a major issue in the watershed.
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Current monitoring
Stream gages: A USGS gaging station (420 km2 with over 70 yrs of record) located near Malta, PA defines the East Mahantango Creek Watershed. ARS has operated gages on two subwatersheds (116 and 7.2 km2) within the Basin since 1967.
Wells: ARS has monitored water levels in 11 observation wells continuously since 1973. These wells are used solely for research purposes and are located within the 7.2-km2 subwatershed of the Mahantango Watershed known as WE-38.
Weather stations: ARS operates two climate stations; one near Klingerstown, PA has been in operation since 1967, while a second station near Leck Kill, PA has been in existence since 1978. Continuous data for some parameters, such as temperature, do not exist for the time prior to the conversion from analog to digital monitoring equipment in 1996.
GIS: ARS, the Susquehanna River Basin Commission, the State, and Pennsylvania State University have a variety of GIS databases for the Watershed.
Geochemical labs: ARS at University Park maintains its own analytical facilities, capable of providing most inorganic analyses.
Experimental sites: ARS has had a presence in the Mahantango Watershed since 1966, with the majority of its monitoring and research being conducted within the 7.2 km2 subwatershed WE-38. Currently active research activities focus on ground water recharge, overland flow generation, and nutrient losses from agriculture, with an emphasis on phosphorus. USGS and ARS have recently initiated a joint effort to conduct cross-hole tracer tests to better quantify ground water travel times within the fractured bedrock characteristic of the region.
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Agencies and cooperators USDA-ARS (lead)
USGS (cooperator)
Logistics
The East Mahantango Creek Watershed (see figure on next page) is located about 50 km north of Harrisburg, PA, midway between Interstate 80 to the north and the Pennsylvania Turnpike to the south. Interstate 81 passes close to the eastern boundary of the Watershed. The Watershed is between Penn State University and Temple University (and others in Philadelphia, PA). Bucknell University in Lewisburg, PA is located roughly 30 km to the northwest.
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Future work
Since 1966, ARS has invested a considerable amount of time and equipment and expects to conduct research within the watershed for years to come. Primary research objectives will include more precise determinations of surface runoff generation mechanisms, subsurface pathways and travel times, and better estimations of nutrient losses and associated controlling mechanisms. More recently, USGS has had an increasing presence on the Watershed, being concerned with ground water age-dating and travel times in context of impacts of nitrate remediation.
Selected references describing available data and watershed performance (this is a small selection of many available)
Pionke, H.B., W.J. Gburek, and G.J. Folmar. Quantifying stormflow components in a Pennsylvania watershed when 18O input and storm conditions vary. J. Hydrol. 148:169-187. 1993.
Pionke, H.B., W.J. Gburek, A.N. Sharpley, and R.R. Schnabel. Flow and nutrient export patterns for an agricultural hill-land watershed. Water Resour. Res. 32(6):1795-1804. 1996.
Pionke, H.B., W.J. Gburek, A.N. Sharpley, and J.A. Zollweg. Hydrological and chemical controls on phosphorus losses from catchments. In: Phosphorus Loss from Soil to Water, H. Tunney, O.T. Carton, P.C. Brookes, and A.E. Johnston, eds., CAB International Press, Cambridge, England, pp. 225-242. 1997. (Refereed Chapter)
Gburek, W.J., and A.N. Sharpley. Hydrologic controls on phosphorus loss from upland
agricultural watersheds. J. Environ. Qual. 27(2)267-277. 1998.
Gburek, W.J., G.J. Folmar, and J.B. Urban. Field data and ground water modeling in a layered fractured aquifer. Ground Water 37(3):175-184. 1999.
Gburek, W.J., and G.F. Folmar. Patterns of contaminant transport in a layered fractured aquifer. J. Contaminant Hydrol. 37(1999):87-109. 1999.
Gburek, W.J., and G.F. Folmar. Flow and chemical contributions to streamflow in an upland watershed: a baseflow survey. J. Hydrol. 217(1999):1-18. 1999.
Pionke, H.B., W.J. Gburek, R.R. Schnabel. A.N. Sharpley, and G.F. Elwinger. Seasonal flow, nutrient concentrations and loading patterns in stream flow draining an agricultural hill-land watershed. J. Hydrol. 220(1999):62-73. 1999.
Gburek, W.J., and G.F. Folmar. A ground water recharge field study: Site characterization and initial results. Hydrol. Process. 13:2813-2831. 1999.
Yu, Zhongbo, W.J. Gburek, and F.W. Schwartz. Evaluating the spatial distribution of water balance in a small watershed, Pennsylvania. Hydrol. Processes 14:941-956. 2000.
Lindsey, B.D., W.J. Gburek, and G.J. Folmar. Watershed scaling effect on base flow nitrate, Valley and Ridge Physiographic Province. J. Amer. Water Resour. Assn. 37: 1103-1117. 2001.
Srinivasan, M.S., W.J. Gburek, and J.M. Hamlett. Dynamics of stormflow generation - A field study in east-central Pennsylvania. Hydrol. Process. 16:649-665. 2002.
McGuire, K.J., D.R. DeWalle, and W.J. Gburek. Evaluation of mean residence time in subsurface waters using oxygen-18 fluctuations during drought conditions in the mid-Appalachians. J. Hydrol. 261:132-149. 2002.
Burton, W.C., L.N. Plummer, E. Busenberg, B.D. Lindsey, and W.J. Gburek. Influence of fracture anisotropy on ground water ages and chemistry, Valley and Ridge Province, Pennsylvania. Ground Water 40:242-257. 2002.
Needelman, B.A., W.J. Gburek, G.W. Petersen, A.N. Sharpley, and P.J.A. Kleinman. 2004. Surface Runoff along Two Agricultural Hillslopes with Contrasting Soils. Soil Sci. Soc. Am. J. 68:914-923. 2004.
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