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The targeting of critical surface runoff-producing zones should account for the influence of subsurface soil characteristics. In this study we assessed the runoff response of contrasting colluvial and residual soils. The study was conducted along two hillslopes within a 39.5-ha mixed land use watershed in Pennsylvania. Six sites (four colluvial, two residual) were monitored for runoff, hydraulic head, water table depth, and soil water content. A total of 111 rainfall events were monitored during the periods of July to December 2000, April to December 2001, and April to December 2002. Two high-intensity (5-min peak > 8 cm [h.sup.-1]) events had return periods of 2.5 and 4 yr. The colluvial soils are somewhat poorly and moderately well drained with fragipans and high clay content (37-14%) argillic horizons (fine, mixed, semiactive, mesic Aquic Fragiudalfs); the residual soils are well drained with moderate clay content (24%) argillic horizons (fine--loamy, mixed, semiactive, mesic Typic Hapludults). Across all events, overall runoff yields averaged 2.4% from the four colluvial sites and 0.01% from the two residual sites. The two colluvial sites with the greatest runoff production were located at the base of a primarily colluvial hillslope. The largest events at these sites occurred during periods of surface saturation (soil surface to a depth of at least 30 cm). These results suggest that nonwinter P management for these residual soils should focus on rare, large events. Nutrient management planning could be improved if runoff estimation methods were to better integrate information on subsurface and upslope soil hydrologic properties.

Model ground water ages based on chlorofluorocarbons (CFCs) and tritium/helium-3 ([H.sup.3]/[He.sup.3]) data were obtained from two arrays of nested piezometers located on the north limb of an anticline in fractured sedimentary rocks in the Valley and Ridge geologic province of Pennsylvania. The fracture geometry of the gently east plunging fold is very regular and consists predominately of south dipping to subhorizontal to north dipping bedding-plane parting and east striking, steeply dipping axial-plane spaced cleavage. In the area of the piezometer arrays, which trend north-south on the north limb of the fold, north dipping bedding-plane parting is a more dominant fracture set than is steeply south dipping axial-plane cleavage. The dating of ground water from the piezometer arrays reveals that ground water traveling along paths parallel to the dip direction of bedding-plane parting has younger [H.sup.3]/[He.sup.3] and CFC model ages, or a greater component of young water, than does ground w ater traveling along paths opposite to the dip direction. In predominantly unmixed samples there is a strong positive correlation between age of the young fraction of water and dissolved sodium concentration. The travel times inferred from the model ages are significantly longer than those previously calculated by a ground water flow model, which assumed isotropically fractured layers parallel to topography. A revised model factors in the directional anisotropy to produce longer travel times. Ground water travel times in the watershed therefore appear to be more influenced by anisotropic fracture geometry than previously realized. This could have significant implications for ground water models in other areas underlain by similarly tilted or folded sedimentary rock, such as elsewhere in the Valley and Ridge or the early Mesozoic basins., Introduction Purpose of This Study The U.S. Geological Survey (USGS) is investigating the ground water flux of dissolved nitrogen into Chesapeake Bay as a part of an investigation to determine [...]

The mapping of soil P concentration is necessary to assess the risk of P loss in runoff. We modeled the distribution of Mehlich-3 extractable soil P (M3P) in an east-central Pennsylvania 39.5-ha watershed (FD-36) with an average field size of 1.0 ha. Three interpolation models were used: (i) the field classification model--simple field means, (ii) the global model--ordinary kriging across the watershed, and (iii) the within-field model--ordinary kriging within fields with a pooled within-stratum variogram. Soils were sampled on a 30-m grid, resulting in an average of 14 samples per field. Multiple validation runs were used to compare the models. Overall, the mean absolute errors (MAEs) of the models were 76, 71, and 66 mg [kg.sup.-1] M3P for the field classification, global, and within-field models, respectively. The field classification model performed substantially worse than did the kriging models in five fields; these fields exhibited strong spatial autocorrelation. The within-field model performed substantially better than did the global model in three fields where autocorrelation was confined by the field boundary. However, no differences in P index classification were observed between the three prediction surfaces. The field classification model is simpler and less expensive to implement than the kriging models and should be adequate for applications that are not sensitive to small errors in soil P concentration estimates.

BSTRACT The problems encountered in estimating scale parameters in interdisciplinary watershed research are discussed. Meteorology, hydrology, geology and water quality are discussed with respect to their individual strengths and weaknesses when applied to different scale problems. Areas where incompatibilities exist are pointed out and suggestions are made for effecting compromise. A watershed scale of roughly a hundred acres may be the scale at which all disciplines can effect optimum interaction. [ABSTRACT FROM AUTHOR]

We considered hydrologic and chemical factors controlling P export from a 39.5-ha mixed land use watershed in east-central Pennsylvania, focusing our evaluation on watershed vulnerability to P loss. The spatial variations of P source factors, soil P, and P inputs from fertilizer and manure were evaluated. Distribution of Mehlich-3 soil P on a30-m grid over the watershed showed that soil P varied with land use. Soils in wooded areas had low Mehlich-3 P (<30 mg kg-1),grazed pasture had Mehlich-3 P values between 100 and 200 mg kg-1 and cropped fields receiving manure and fertilizer applications were mostly >200 mg kg-1. Phosphorus sources and transport controls on P loss were evaluated by examining in-stream P concentrations during storm hydrographs. Phosphorus concentrations decreased 50% downstream from headwaters to watershed outlet, and were more closely related to near-stream (within 60 m) distribution of high-P soils than to that of the whole watershed. This suggests that near-stream surface runoff and soil P are controlling P export from the watershed. Based on these findings, we modified the Phosphorus Index (PI),a user-oriented tool developed by the NRCS-USDA to identify criticalsource areas controlling P export from agricultural watersheds. The modification separately evaluates P source and transport factors, andincorporates the hydrologic return period to describe contributing areas. The modified PI was applied to the watershed to illustrate interactions between P source and transport processes controlling P export, and approaches for managing P loss. [ABSTRACT FROM AUTHOR]

Delaware County and the Cornell Cooperative Extension of Delaware County of New York State have initiated's farm-scale precision feed management (PFM) program to reduce soil-phosphorus build-up and phosphorus (P) losses to the Cannonsville Reservoir, a major supply source of New York City drinking water. The PFM program includes strategies that more precisely balance dairy cattle dietary P requirements with actual P intake and that improve on-farm forage production and utilization in the animal diet. The goal of the PFM program is to reduce manure P concentration, feed nutrients importation, P imbalance problems, and soil-P build-up while maintaining farm profitability. In this study, several PFM strategies were evaluated with respect to controlling P losses and soil-P build-up at both field and watershed scales using the Sail and Water Assessment Tool (SWAT) model. Using the SWAT model, manure with reduced P concentration was applied to cropland while grass forage clop productivity was increased through N fertilizer application. The SWAT model simulation revealed decreased particulate phosphorus and soluble phosphorus lows by 22% and 13%, respectively. Predicted reductions of average particulate phosphorus and soluble phosphorus loses at the watershed outlet were 16% and 13% respectively. over a three-year period. compared to the baseline (conditions before changes were implemented). Model results ah demonstrated an appreciable decrease in field-level mil-P during the growing season, indicating increased soil-P uptake by the improved grass-forage. For the growing season, reductions for predicted active and labile P pools were 11 and 5 mg kg-1 (0.02 and 0.01 lb tn-1), respectively, compared to the baseline. The corresponding reductions in field-level soil P were equivalent to 8% and 7% for labile and active P pods. respectively Overall, the PFM strategies were found to haw a potential for reducing soil-P build-up and P losses both at field and watershed levels. Performing a model-based environmental evaluation of farm management strategies at a watershed level helps to integrate farm management planning (the smallest management unit) into watershed level planning. Also, evaluating farm management strategies at a watershed scale provides valuable and comprehensive information for messing the potential for long-term, cost-effective, and permanent reduction of P loss from dairy agriculture to the Cannonsville Reservoir. [ABSTRACT FROM AUTHOR]