Mahantango Creek Watershed, Pennsylvania Characteristics The 420-km2 Mahantango Creek Watershed was selected in 1966 as an USDA-ARS experimental watershed in part because of the presence of a USGS stream gauge, which was established at the watershed outlet (USGS 01555500 East Mahantango Creek near Dalmatia, PA) in 1930 (Gburek, 1977). Mahantango Creek is a tributary of the Susquehanna River, which contributes 50% of the streamflow input to the Chesapeake Bay. Mahantango Creek Watershed is typical of upland agricultural watersheds within the nonglaciated, folded and faulted Appalachian Valley and Ridge Physiographic Province. However, no limestone or karst geology occurs within the basin. Resistant sandstones and conglomerate bedrock primarily comprise Mahantango Creek Watershed's ridge crests (350 to 500 m elevation), while valleys (125 to 300 m elevation) are underlain by less resistant shales and siltstones (Bryant et al., 2011). Mature forest covers the dominant ridge to the north, while cropland and pasture dominate the rolling hills of the watershed interior. Total area is approximately 44% cropland or pasture, 55% forested, and 1% urban and residential. Climate is temperate and humid with the largest average monthly precipitation occurring in June and the smallest in February (Buda et al., 2011b). Average precipitation is approximately 1080 mm yr-1 and streamflow about 500 mm yr-1, with baseflow comprising approximately 70% of total streamflow. Subsurface flow is controlled by an unconfined, highly transmissive, highly fractured, shallow bedrock layer with low storativity. Overland flow occurs primarily on expanding and contracting areas of ground water discharge and on areas underlain by low-permeability clay (fragipan) layers. Typically the highest stream flows occur near March when vegetative transpiration is minimal and the lowest flows occur in August (Buda et al., 2011a). Nearly 70% of the water soluble phosphorus exported in stream flow occurs during the 10% that is defined as storm flow, whereas 60% of the nitrate export occurs during non-storm periods (Church et al., 2011). From 1967 to 1976, a network of up to 43 rain gauges, eight meteorological sites, and six stream gauging stations provided uniform coverage across Mahantango Creek Watershed. In response to the 1976 reorganization of ARS, research objectives in Mahantango Creek Watershed became more sharply focused on water quality and the decision was made to cease monitoring the entire watershed and to focus resources on a 7.3-km2 intensive-study subwatershed designated WE-38. This subwatershed is located on the north flank of the major anticline underlying Mahantango Creek Valley, so all strata dip to the north with a general east-west strike. Tributary 17302 to Little Mahantango Creek drains WE-38 from the crest of the northern ridge (475 m elevation) southward to a compound weir (215 m elevation) at 40.704 degrees N, 76.588 degrees W. The physiography and land use are representative of the larger Mahantango Creek Watershed. Agricultural land use dominates the Susquehanna River basin and most tributaries including the Mahantango Creek watershed. Agricultural land use has also been identified as a major source of nutrients to the Chesapeake Bay. Specifically, within the Mahantango Creek Watershed the following issues are of concern: Nutrients: Ground water and first-order stream nitrate concentrations in the basin are correlated to adjacent land use. Consequently surface and subsurface water concentrations around high-density poultry and swine operations and intensively cropped fields are usually elevated above acceptable limits. High soil phosphorus levels in fields susceptible to surface runoff often result in significant amounts of the nutrient being exported to adjacent water bodies. Soil erosion: Lack of stream bank stabilization and heavy agriculture has led to soil erosion and sediment-laden discharge in streams. ARS has had a presence in the Mahantango Creek Watershed since 1966. However, the majority of the research and monitoring has been conducted within WE-38. Primary research objectives in the past have included determination of subsurface pathways and travel times and an estimation of runoff generation and nutrient export mechanisms. Future research objectives in the basin include further refinement of both subsurface and surface transport mechanisms, impacts of frozen soil and snow on nutrient transport, and BMP assessment. Daily precipitation, streamflow, and water quality data records are included in the STEWARDS database along with basic GIS shapefiles for the three rain gauges, weir, water quality sampling site, stream network, and watershed boundary. A 5-m DEM is included through the ftp direct download or as an additional option during a "specific query." These data are described more fully in Bryant et al. (2011), Buda et al. (2011a, 2011b), and Church et al. (2011). Land cover, soils, additional DEMs, orthophotoimagery, and special interest databases for the watershed are publically available through USDA-NRCS Geospatial Data Gateway and Pennsylvania Spatial Data Access (PASDA). References (there are many relevant publications, only a small selection is presented here) Gburek, W.J., 1977, The Mahantango Creek Watershed - General hydrology and research results, in Proc. Smithsonian Watershed Research Workshop, edited by D. L. Correll, Chesapeake Bay Center for Environmental Studies, Edgewater, Maryland, p. 227-250. Gburek, W.J. and Folmar, G.J, 1999a, A ground water recharge field study: site characterization and initial results, Hydrological Processes, v. 13, p. 2813-2831. Gburek, W.J., and Folmar, G.J., 1999b, Flow and chemical contributions to streamflow in an upland watershed: a baseflow survey, Journal of Hydrology, v. 217, no. 1-2, p. 1-18. Gburek, W.J., Folmar, G.J., and Urban, J.B., 1999, Field data and ground water modeling in a layered fractured aquifer, Ground Water, v. 37, no. 2 p. 175-184. Gburek, W.J., and Urban, J.B., 1990, The shallow weathered fracture layer in the near-stream zone, Ground Water, v. 28, p. 875-883. Gburek, W.J., Urban, J.B., and Schnabel, R.R., 1986, Nitrate contamination of ground water in an upland Pennsylvania watershed, Proceedings of Agricultural Impacts on Ground Water - A Conference. NWWA, Omaha, Nebraska, p. 352-380. Lindsey, B.D., Gburek, W.J., and Folmar, G.J., 2001, Watershed scaling effect on base flow nitrate, Valley and Ridge Physiographic Province, Journal American Water Resources Association, v. 37, no. 5, p. 1103-1117. Pionke, H.B., W.J. Gburek, A.N. Sharpley, and R.R. Schnabel, 1996, Flow and nutrient export patterns for an agricultural hill-land watershed, Water Resources Research, v. 32, no. 6, pp. 1795-1804. Collaborators and Cooperating Agencies and Groups |
