Streambank erosion and phosphorus loading to surface waters: Knowns, unknowns, and implications for nutrient loss reduction research and policy.

To monitor and meet water quality objectives, it is necessary to understand and quantify the contribution of nonpoint sources to total phosphorus (P) loading to surface waters. However, the contribution of streambank erosion to surface water P loads remains unclear and is typically unaccounted for in many nutrient loading assessments and policies. As a result, agricultural contributions of P are overestimated, and a potentially manageable nonpoint source of P is missed in strategies to reduce loads.

Incorporating the benefits of vegetative filter strips into risk assessment and risk management of pesticides.

The pesticide registration process in North America, including the USA and Canada, involves conducting a risk assessment based on relatively conservative modeling to predict pesticide concentrations in receiving waterbodies. The modeling framework does not consider some commonly adopted best management practices that can reduce the amount of pesticide that may reach a waterbody, such as vegetative filter strips (VFS). Currently, VFS are being used by growers as an effective way to reduce off-site movement of pesticides, and they are being required or recommended on pesticide labels as a mitigation measure.

Comparison of empirical and mechanistic equations for vegetative filter strip pesticide mitigation in long-term environmental exposure assessments.

Recent advances in mechanistic modeling of vegetated filter strips (VFS) have made it possible to incorporate VFS mitigation into environmental exposure assessments (EEAs). However, outside of fixed efficiency approaches, there are no widely adopted and standardized procedures for incorporating VFS quantitative mitigation into long-term, higher-tier EEAs. A source of hesitation involves the use of empirical equations for predicting pesticide trapping by the VFS.

Effect of vegetative filter strip pesticide residue degradation assumptions for environmental exposure assessments.

Understanding and simulating the fate and transport of pesticides from a field to adjacent receiving water bodies is critical for estimating long-term environmental exposure concentrations (EECs) in regulatory higher-tier environmental exposure assessments (EEA). The potential of field mitigation practices like vegetative filter strips (VFS) to reduce pesticide pollution is receiving increasing attention. Previous research has proposed a modeling framework that links the US Environmental Protection Agency's (US-EPA) PRZM/EXAMS higher-tier EEA with a process-based VFS model (VFSMOD).

Hydrologic cost-effectiveness ratio favors switchgrass production on marginal croplands over existing grasslands.

Switchgrass (Panicum virgatum L.) has attracted attention as a promising second generation biofuel feedstock. Both existing grasslands and marginal croplands have been suggested as targets for conversion to switchgrass, but the resulting production potentials and hydrologic impacts are not clear.

Streambanks: A net source of sediment and phosphorus to streams and rivers.

Sediment and phosphorus (P) are two primary pollutants of surface waters. Many studies have investigated loadings from upland sources or even streambed sediment, but in many cases, limited to no data exist to determine sediment and P loading from streambanks on a watershed scale. The objectives of this paper are to review the current knowledge base on streambank erosion and failure mechanisms, streambank P concentrations, and streambanks as P loading sources and then also to identify future research needs on this topic.

Evaluation of a universal flow-through model for predicting and designing phosphorus removal structures.

Phosphorus (P) removal structures have been shown to decrease dissolved P loss from agricultural and urban areas which may reduce the threat of eutrophication. In order to design or quantify performance of these structures, the relationship between discrete and cumulative removal with cumulative P loading must be determined, either by individual flow-through experiments or model prediction. A model was previously developed for predicting P removal with P sorption materials (PSMs) under flow-through conditions, as a function of inflow P concentration, retention time (RT), and PSM characteristics.

Does mechanistic modeling of filter strip pesticide mass balance and degradation processes affect environmental exposure assessments?

Vegetative filter strips (VFS) are a widely adopted practice for limiting pesticide transport from adjacent fields to receiving waterbodies. The efficacy of VFS depends on site-specific input factors. To elucidate the complex and non-linear relationships among these factors requires a process-based modeling framework.

Validation of a quantitative phosphorus loss assessment tool.

Pasture Phosphorus Management Plus (PPM Plus) is a tool that allows nutrient management and conservation planners to evaluate phosphorus (P) loss from agricultural fields. This tool uses a modified version of the widely used Soil and Water Assessment Tool model with a vastly simplified interface. The development of PPM Plus has been fully described in previous publications; in this article we evaluate the accuracy of PPM Plus using 286 field-years of runoff, sediment, and P validation data from runoff studies at various locations in Oklahoma, Texas, Arkansas, and Georgia.

Distinct influence of filter strips on acute and chronic pesticide aquatic environmental exposure assessments across U.S. EPA scenarios.

Vegetative filter strips (VFS) are proposed for protection of receiving water bodies and aquatic organisms from pesticides in runoff, but there is debate regarding the efficiency and filter size requirements. This debate is largely due to the belief that no quantitative methodology exists for predicting runoff buffer efficiency when conducting acute and/or chronic environmental exposure assessments. Previous research has proposed a modeling approach that links the U.

Trapping phosphorus in runoff with a phosphorus removal structure.

Reduction of phosphorus (P) inputs to surface waters may decrease eutrophication. Some researchers have proposed filtering dissolved P in runoff with P-sorptive byproducts in structures placed in hydrologically active areas with high soil P concentrations. The objectives of this study were to construct and monitor a P removal structure in a suburban watershed and test the ability of empirically developed flow-through equations to predict structure performance.

Escherichia coli load reduction from runoff by vegetative filter strips: a laboratory-scale study.

Vegetative filter strips (VFS) are commonly used best management practices for removing contaminants from runoff. Additional research is warranted to determine their efficiency and the most appropriate metrics for predicting fecal bacteria reductions. The objective of this research was to determine VFS effectiveness in removing from runoff relative to inflow rate, infiltration capacity, and flow concentration.

Design and application of a direct-push vadose zone gravel permeameter.

A borehole permeameter is well suited for testing saturated hydraulic conductivity (K(sat)) at specific depths in the vadose zone. Most applications of the method involve fine-grained soils that allow hand auguring of test holes and require a small water reservoir to maintain a constant head. In non-cohesive gravels, hand-dug test holes are difficult to excavate, holes are prone to collapse, and large volumes of water are necessary to maintain a constant head for the duration of the test.

Revised framework for pesticide aquatic environmental exposure assessment that accounts for vegetative filter strips.

For pesticides that do not pass higher-level environmental exposure assessments, vegetated filter strips (VFS) are often mandated for use of the compound. However, VFS physiographic characteristics (i.e.

Parameter importance and uncertainty in predicting runoff pesticide reduction with filter strips.

Vegetative filter strips (VFS) are an environmental management tool used to reduce sediment and pesticide transport from surface runoff. Numerical models of VFS such as the Vegetative Filter Strip Modeling System (VFSMOD-W) are capable of predicting runoff, sediment, and pesticide reduction and can be useful tools to understand the effectiveness of VFS and environmental conditions under which they may be ineffective. However, as part of the modeling process, it is critical to identify input factor importance and quantify uncertainty in predicted runoff, sediment, and pesticide reductions.

Escherichia coli transport from surface-applied manure to subsurface drains through artificial biopores.

Bacteria transport in soils primarily occurs through soil mesopores and macropores (e.g., biopores and cracks).

Subsurface transport of phosphorus in riparian floodplains: influence of preferential flow paths.

For phosphorus (P) transport from upland areas to surface water systems, the primary transport mechanism is typically considered to be surface runoff with subsurface transport assumed negligible. However, certain local conditions can lead to an environment where subsurface transport may be significant. The objective of this research was to determine the potential of subsurface transport of P along streams characterized by cherty or gravel subsoils, especially the impact of preferential flow paths on P transport.

Uncalibrated modelling of conservative tracer and pesticide leaching to groundwater: comparison of potential Tier II exposure assessment models.

The Root Zone Water Quality Model (RZWQM) and Pesticide Root Zone Model (PRZM) are currently being considered by the Office of Pesticide Programs (OPP) in the United States Environmental Protection Agency (US EPA) for Tier II screening of pesticide leaching to groundwater (November 2005). The objective of the present research was to compare RZWQM and PRZM based on observed conservative tracer and pesticide pore water and soil concentrations collected in two unique groundwater leaching studies in North Carolina and Georgia. These two sites had been used previously by the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) Environmental Model Validation Task Force (EMVTF) in the validation of PRZM.

Evaluating factors affecting the permeability of emulsions used to stabilize radioactive contamination from a radiological dispersal device.

Present strategies for alleviating radioactive contamination from a radiological dispersal device (RDD) or dirty bomb involve either demolishing and removing radioactive surfaces or abandoning portions of the area near the release point. In both cases, it is imperative to eliminate or reduce migration of the radioisotopes until the cleanup is complete or until the radiation has decayed back to acceptable levels. This research investigated an alternative strategy of using emulsions to stabilize radioactive particulate contamination.

Interrelationship of macropores and subsurface drainage for conservative tracer and pesticide transport.

Macropore flow results in the rapid movement of pesticides to subsurface drains, which may be caused in part by a small portion of macropores directly connected to drains. However, current models fail to account for this direct connection. This research investigated the interrelationship between macropore flow and subsurface drainage on conservative solute and pesticide transport using the Root Zone Water Quality Model (RZWQM).

Analytical model for aquifer response incorporating distributed stream leakage.

An analytical model of stream/aquifer interaction is proposed that predicts drawdown in an aquifer with leakage from a finite-width stream induced by pumping from a well. The model is formulated based on the assumptions of stream partial penetration, a semipervious streambed, and distributed recharge across a finite-width stream. Advantages of the analytical solution include its simple structure, consisting of the Theis well function with integral modifications.