Gordon J. Folmar

Phosphorus loss from an agricultural watershed as a function of storm size.

Phosphorus (P) loss from agricultural watersheds is generally greater in storm rather than base flow. Although fundamental to P-based risk assessment tools, few studies have quantified the effect of storm size on P loss. Thus, the loss of P as a function of flow type (base and storm flow) and size was quantified for a mixed-land use watershed (FD-36; 39.5 ha) from 1997 to 2006. Storm size was ranked by return period (<1, 1-3, 3-5, 5-10, and >10 yr), where increasing return period represents storms with greater peak and total flow. From 1997 to 2006, storm flow accounted for 32% of watershed discharge yet contributed 65% of dissolved reactive P (DP) (107 g ha(-1) yr(-1)) and 80% of total P (TP) exported (515 g ha(-1) yr(-1)). Of 248 storm flows during this period, 93% had a return period of <1 yr, contributing most of the 10-yr flow (6507 m(3) ha(-1); 63%) and export of DP (574 g ha(-1); 54%) and TP (2423 g ha(-1); 47%). Two 10-yr storms contributed 23% of P exported between 1997 and 2006. A significant increase in storm flow DP concentration with storm size (0.09-0.16 mg L(-1)) suggests that P release from soil and/or area of the watershed producing runoff increase with storm size. Thus, implementation of P-based Best Management Practice needs to consider what level of risk management is acceptable.

Using Flue Gas Desulfurization Gypsum to Remove Dissolved Phosphorus from Agricultural Drainage Waters

High levels of accumulated phosphorus (P) in soils of the Delmarva Peninsula are a major source of dissolved P entering drainage ditches that empty into the Chesapeake Bay. The objective of this study was to design, construct, and monitor a within-ditch filter to remove dissolved P, thereby protecting receiving waters against P losses from upstream areas. In April 2007, 110 Mg of flue gas desulfurization (FGD) gypsum, a low-cost coal combustion product, was used as the reactive ingredient in a ditch filter. The ditch filter was monitored from 2007 to 2010, during which time 29 storm-induced flow events were characterized. For storm-induced flow, the event mean concentration efficiency for total dissolved P (TDP) removal for water passing through the gypsum bed was 73 ± 27% confidence interval (α = 0.05). The removal efficiency for storm-induced flow by the summation of load method was 65 ± 27% confidence interval (α = 0.05). Although chemically effective, the maximum observed hydraulic conductivity of FGD gypsum was 4 L s(-1), but it decreased over time to <1 L s(-1). When bypass flow and base flow were taken into consideration, the ditch filter removed approximately 22% of the TDP load over the 3.6-yr monitoring period. Due to maintenance and clean-out requirements, we conclude that ditch filtration using FGD gypsum is not practical at a farm scale. However, we propose an alternate design consisting of FGD gypsum-filled trenches parallel to the ditch to intercept and treat groundwater before it enters the ditch.

Effect of direct incorporation of poultry litter on phosphorus leaching from coastal plain soils

Management of poultry litter on the Delmarva Peninsula is critical to reducing phosphorus losses to the Chesapeake Bay. New poultry litter incorporation technologies have shown promise at reducing phosphorus losses, but their effectiveness has not been tested in this environmentally sensitive region. This study evaluates subsurface leaching losses of three litter application methods, including surface broadcast, surface broadcast with disking, and subsurface litter incorporation with a novel litter incorporator developed by the USDA Agricultural Research Service. Cube-shaped soil lysimeters (61 × 61 × 61 cm [24 × 24 × 24 in]) were extracted from high phosphorus (P) (Mehlich-3 P is greater than 500 mg kg−1) agricultural soils on the University of Maryland Eastern Shore Research Farm near Princess Anne, Maryland, and were subjected to two rainfall simulation events that were separated by 11 semiweekly soaking-type irrigation events. The average cumulative total phosphorus loss was highest for the subsurface litter incorporation method (0.48 kg ha−1 [0.43 lb ac−1]) and was lowest for the no litter control (0.19 kg ha−1 [0.17 lb ac−1]). Particulate P loss among manure treatments ranged from 58% to 64% of total P loss. Total phosphorus losses were strongly correlated to total phosphorus concentration in the leachate (coefficient of determination [r2] ≥ 0.84), indicating availability of P in applied litter to be the primary control of P in leachate. Soil properties also impacted P leaching losses, with the soils possessing a higher sand content and having a shallower depth to the sandy subsoil, yielding higher cumulative total P losses (0.64 kg ha−1 [0.57 lb ac−1]). Although the subsurface litter incorporator increased total P leaching losses, a concern on the Delmarva Peninsula, opportunity exists to modify the subsurface incorporator design using zone tillage, potentially reducing the leaching losses.

Patterns of contaminant transport in a layered fractured aquifer

We investigated patterns of contaminant transport within the layered and fractured aquifer of a 7.3-km2 upland agricultural watershed in east-central Pennsylvania, USA. Geometry and hydraulic properties of the aquifer had been characterized by field testing and model calibration. These results were extended to simulate flow pathways and patterns of contaminant transport in both areal and cross-section formats within the watershed. The analyses indicated that the ground water flow system at the larger watershed scale is comprised of smaller units of subsurface flow which are self-contained at the scale of first- or second-order streams. For this scale subwatershed or larger, contaminant inputs to ground water from the mix of land use within the subwatershed should translate directly to the quality of nonstorm streamflow. For illustration, recharge water quality from typical land-use distributions were combined with a simple model of contaminant transport to simulate nitrate concentration patterns in ground water in a cross-section format. Land use in the vicinity of the drainage divides between streams was found to control ground water quality within the deeper layers of the aquifer, while land use over the remainder of the watershed area affected water quality only within the shallower layers of the aquifer. Streamflow nitrate data collected during a baseflow survey on the watershed were examined in context of these simulations and found to support the conclusions. Results of the study demonstrate the potential for localized contamination of ground water and nonstorm streamflow by agricultural land use, as well as the potential for managing stream quality and minimizing contamination within targeted zones of the ground water by controlling land use position.

Baseflow nitrate in relation to stream order and agricultural land use.

Management of agricultural nonpoint-source pollution continues to be a challenge because of spatial and temporal variability. Using stream order as an index, we explored the distribution of nitrate concentration and load along the stream network of a large agricultural watershed in Pennsylvania-the East Mahantango Creek Watershed and two of its sub-watersheds. To understand nitrate concentration variation in the stream water contributed from ground water, this study focused on baseflow. Impacts of agricultural land use area on baseflow nitrate in the stream network were investigated. Nitrate concentration showed a general decreasing trend with increasing stream order based on stream order averaged values; however, considerable spatial and temporal variability existed within each snapshot sampling. Nitrate loads increased with stream order in a power function because of the dominant effect of stream flow rate over the nitrate concentration. Within delineated sub-watersheds based on stream orders, positive linear functions were found between agricultural land use area percentage and the baseflow nitrate concentration and between agricultural drainage area and the nitrate load. The slope of the positive linear regression between the baseflow nitrate concentration and percent agricultural land area seems to be a valuable indicator of a watersheds water quality as influenced by agricultural practices, watershed size, and specific physiographic setting. Stream order seems to integrate, to a certain degree, the source and transport aspects of nonpoint-source pollution on a yearly averaged basis and thus might provide a quick estimate of the overall trend in baseflow nitrate concentration and load distribution along complex stream networks in agricultural watersheds.

Imaging Hydrological Processes in Headwater Riparian Seeps with Time-Lapse Electrical Resistivity

Delineating hydrologic and pedogenic factors influencing groundwater flow in riparian zones is central in understanding pathways of water and nutrient transport. In this study, we combined two-dimensional time-lapse electrical resistivity imaging (ERI) (depth of investigation approximately 2 m) with hydrometric monitoring to examine hydrological processes in the riparian area of FD-36, a small (0.4 km2 ) agricultural headwater basin in the Valley and Ridge region of east-central Pennsylvania. We selected two contrasting study sites, including a seep with groundwater discharge and an adjacent area lacking such seepage. Both sites were underlain by a fragipan at 0.6 m. We then monitored changes in electrical resistivity, shallow groundwater, and nitrate-N concentrations as a series of storms transitioned the landscape from dry to wet conditions. Time-lapse ERI revealed different resistivity patterns between seep and non-seep areas during the study period. Notably, the seep displayed strong resistivity reductions (∼60%) along a vertically aligned region of the soil profile, which coincided with strong upward hydraulic gradients recorded in a grid of nested piezometers (0.2- and 0.6-m depth). These patterns suggested a hydraulic connection between the seep and the nitrate-rich shallow groundwater system below the fragipan, which enabled groundwater and associated nitrate-N to discharge through the fragipan to the surface. In contrast, time-lapse ERI indicated no such connections in the non-seep area, with infiltrated rainwater presumably perched above the fragipan. Results highlight the value of pairing time-lapse ERI with hydrometric and water quality monitoring to illuminate possible groundwater and nutrient flow pathways to seeps in headwater riparian areas.

A Phosphorus Transport Study: Influence of Poultry Litter Application Method on Leaching

Phosphorus (P) transport to surface waters via subsurface pathways contributes to eutrophication. This study was conducted to compare the extent and mechanisms of vertical P translocation after application of poultry litter by broadcast, broadcast-then-disked, and subsurface incorporation methods to a Coastal Plain soil on the University of Maryland-Eastern Shore Research Farm near Princess Anne, MD. Treatment and unamended control replicates were collected in undisturbed soil blocks 61 by 61 by 61 cm and prepared for two rainfall simulation events that were separated by 11 semi-weekly soaking-type irrigation events. Then FD&C No. 2 blue food dye was applied to the soil surface and leached through the profile. The blocks were inverted and the soil was removed in 10-cm layers. Separate soil samples taken around the dye-stained surface of macropores and within the soil matrix were analyzed for P content. Calcium chloride-extractable P (CCEP) levels for the soil associated with macropores were significantly elevated over the soil matrix within treatment at the 30-cm depth for all manured treatments, but not for the control, confirming that macropores are a pathway for translocation of recently applied litter P. Among treatments, macropore CCEP levels at the 30 and 40-cm depths were greater for the broadcast treatment than for the other litter application treatments, whose methods involved soil disturbance. CCEP concentrations in the soil matrix at the 30-cm depth were significantly higher for the unamended control, suggesting that matrix flow P losses from these high-P content soils will continue after cessation of litter application.

EXPERIMENTAL SYSTEM FOR SIMULATING A NATURAL SOIL TEMPERATURE PROFILE DURING FREEZE-THAW CYCLES

In order to better assess the effects of freeze-thaw cycles on soil physical properties, water and pollutant transport, and microbial activity, a simple experimental soil thermal cycling system was developed. The system consisted of an insulated bin containing four cylindrical PVC lysimeters encased in sand, with a commercially-available heating cable located in the bottom of the sand mass. The heating cable created an upward heat flux representative of heat flow in soil under field conditions. In order to test the system, the sand-soil temperature at the bottom of the bin was set at a range of 0 to 5°C in 1°C increments. Observed hourly temperatures as well as soil temperature gradients and freezing and thawing rates are reported for three freeze-thaw cycles. The experimental system was successful in reproducing a natural vertical temperature profile in the soil and minimizing large fluctuations in subsurface soil temperatures relative to changes in air temperature.

Development of a Lysimeter System to Simultaneously Study Runoff and Leaching Dynamics

Better control of non-point source nutrient losses from soil spread with manure requires understanding of associated environmental processes. This study was conducted to develop a laboratory system for analysis of hydrologic and nutrient dynamics associated with manure application. The research objective was to identify a soil lysimeter size, a method of soil capture, and materials of construction to simultaneously study surface and subsurface processes. A steel lysimeter 60 cm wide and long by 60 cm deep was driven into the ground with a 2 – Mg drop hammer, excavated, and under girded with a 12.7 cm thick PVC plate to capture a block of soil. PVC spacer plates, temporarily situated between the steel lysimeter walls and the sample soil block, were removed after the lysimeter was excavated and bottomed. The remaining gap was filled with petrolatum (petroleum jelly) in order to prevent by-pass flow and potential chemical interaction of the soil solution with the steel lysimeter walls. An initial test of the design was conducted by excavating and preparing twenty lysimeters for rainfall simulation. The experimental method provided researchers opportunity to study both surface and subsurface processes in one assemblage.

Integrating Phosphorus and Nitrogen Management for Water Quality Protection

Demands on modern agriculture have resulted in feed and animal production operations becoming geographically fragmented. Phosphorus (P) and nitrogen (N) levels are increasing in surface and ground water where animal feeding operations are concentrated because of excessive amounts of manure being applied to the landscape. Consequently, researchers are attempting to develop and implement nutrient management plans that are both agronomically and environmentally effective. Currently, P management is being emphasized — variations of the Phosphorus Index (PI), a user-oriented tool developed by USDA-NRCS that ranks the risk of P loss from individual fields, are being implemented. Nitrogen Indices (NIs) have also been proposed, but they have not yet gained the visibility of the PI. Most versions of both indices are relatively sound in their representation of nutrient source-related factors because of the history of laboratory- and plot-scale soil chemistry and fertility research. Conversely, the indices are weak in their representation of nutrient transport processes. A fully integrated approach to nutrient management must consider not only the field-scale soil-water-plant-nutrient relationships, but also the differing transport-related behaviors of N and P at the watershed scale. Here, we present an integrated application of P and N indices to a mixed-land-use watershed in east-central PA that receives manure from animal operations. The indices contain transport factors reflecting probabilities (for P) and travel times (for N) of movement from where the nutrient is applied to the landscape to where it enters the stream. By formulating the two indices in a consistent space- and time-based manner, a fully integrated approach to nutrient management can be implemented to minimize nutrient impacts on both ground water and surface water resources.