Effectiveness of Vegetative Filter Strips for Mitigation in Higher-Tier Pesticide Exposure Assessments: Mechanistic Analysis with VFSMOD

2020 ◽  
Author(s):  
Rafael Muñoz-Carpena ◽  
Garey Fox ◽  
Amy Ritter
Keyword(s):  
Pesticide Exposure ◽  
Regulatory Compliance ◽  
Model Parameters ◽  
Shallow Water Table ◽  
Modeling Framework ◽  
Vegetative Filter Strips ◽  
Filter Strips ◽  
Pesticide Transport ◽  
Mechanistic Analysis ◽  
The Right

<p>Pesticides high-tier, long-term environmental risk assessments (ERA) are based on the combination of complicated mechanistic models to evaluate regulatory compliance. The modeling framework often involves large sets of input factors (model parameters, initial and boundary conditions, and other model structure options). How can we identify the relative importance of human, chemical, physical and biological drivers on the assessment results? Is there a case for “the right answers for the right reasons”? For the case of pesticide mitigation practices like vegetative filter strips (VFS) for runoff mitigation, what are the important factors controlling or limiting their efficiency under different field settings? We evaluate the combination of the current ERA frameworks (US EPA PWC and EU FOCUS SWAN) in combination with VFSMOD, an established and commonly used numerical model for the analysis of runoff, sediment, and pesticide transport in VFS. We present a systematic study of the importance of different field conditions that have been proposed in the past as limiting the efficiency of VFS in realistic settings: flow concentration (channelization) through the filter, timing of pesticide application compared to other drivers, assumptions about the degradation and remobilization of pesticide trapped in the filter between runoff events, seasonal presence of a shallow water table near the receiving water body. We identify instances in which the importance commonly assigned to these factors is not supported by the mechanistic analysis, where other factors different than those proposed largely control the results of the assessments.</p>

Effect of Remobilization of Pesticide Residues in Vegetative Filter Strips for Mitigation in Higher-Tier Pesticide Exposure Assessments with VFSMOD

2020 ◽  
Author(s):  
Rafael Muñoz-Carpena ◽  
Stefan Reichenberger ◽  
Robin Sur
Keyword(s):  
Pesticide Residue ◽  
Pesticide Exposure ◽  
Mixing Layer ◽  
Soil Surface ◽  
Vegetative Filter Strips ◽  
Filter Strips ◽  
Pesticide Transport ◽  
Runoff Event ◽  
High Tier

<p>Vegetative filter strips (VFS) are commonly implemented in the field to mitigate runoff pesticide inputs into surface waters and protect aquatic ecosystems. The efficiency of this mitigation practice can be evaluated within the current regulatory high-tier, long-term environmental risk assessments (ERA) in combination with VFSMOD, an established and commonly used numerical model for the analysis of runoff, sediment, and pesticide transport in VFS. For every rainfall/runoff event in the long-term time series, VFSMOD takes the PRZM calculated edge-of-the-field surface runoff, eroded sediment yield, and dissolved and particle-bound pesticide load.  It then calculates infiltration, sedimentation and pesticide trapping in the VFS during the event, and the outflow into the downslope aquatic body for further calculations and risk analysis. Importantly, at the end of each event, VFSMOD calculates the amount of pesticide residue retained in the filter (sediment-bound and infiltrated in the liquid phase), its degradation until the next event in the series, and the fraction of pesticide residue that is remobilized and added to the next runoff event. In earlier VFSMOD versions, full remobilization of the pesticide residue sorbed to sediment and that dissolved in the soil surface mixing layer (typically the top 0.5-5 cm) was calculated conservatively. Recent VFSMOD ERA applications for very highly-sorbed (i.e. pyrethroids) or persistent pesticides indicate that the full remobilization scheme might be too conservative in some cases. In this work, we evaluate new alternative partial remobilization schemes in VFSMOD, i.e. no remobilization of adsorbed residues, but full remobilization of dissolved residues in the mixing layer, or alternatively just a fraction of the mixing layer by diffusive exchange with the runoff. We evaluate the effects of the alternative remobilization schemes on observed total VFS pesticide reductions from available field data. In addition, employing global sensitivity analysis, we assess the relative importance of the alternative remobilization model structures in the context of the expected field variability of other known drivers of VFS efficiency (hydrology, soils, vegetation, pesticide chemical characteristics). The study provides science-based recommendations for future high-tier pesticide ERA with VFS mitigation.</p>

scholarly journals Shallow water table effects on water, sediment, and pesticide transport in vegetative filter strips – Part 2: model coupling, application, factor importance, and uncertainty

2018 ◽  
Vol 22 (1) ◽  
pp. 71-87 ◽  
Author(s):  
Claire Lauvernet ◽  
Rafael Muñoz-Carpena
Keyword(s):  
Hydraulic Conductivity ◽  
Shallow Water ◽  
Water Table ◽  
Overland Flow ◽  
Silty Clay ◽  
Relative Importance ◽  
Shallow Water Table ◽  
Vegetative Filter Strips ◽  
Filter Strips ◽  
Pesticide Transport

Abstract. Vegetative filter strips are often used for protecting surface waters from pollution transferred by surface runoff in agricultural watersheds. In Europe, they are often prescribed along the stream banks, where a seasonal shallow water table (WT) could decrease the buffer zone efficiency. In spite of this potentially important effect, there are no systematic experimental or theoretical studies on the effect of this soil boundary condition on the VFS efficiency. In the companion paper (Muñoz-Carpena et al., 2018), we developed a physically based numerical algorithm (SWINGO) that allows the representation of soil infiltration with a shallow water table. Here we present the dynamic coupling of SWINGO with VFSMOD, an overland flow and transport mathematical model to study the WT influence on VFS efficiency in terms of reductions of overland flow, sediment, and pesticide transport. This new version of VFSMOD was applied to two contrasted benchmark field studies in France (sandy-loam soil in a Mediterranean semicontinental climate, and silty clay in a temperate oceanic climate), where limited testing of the model with field data on one of the sites showed promising results. The application showed that for the conditions of the studies, VFS efficiency decreases markedly when the water table is 0 to 1.5 m from the surface. In order to evaluate the relative importance of WT among other input factors controlling VFS efficiency, global sensitivity and uncertainty analysis (GSA) was applied on the benchmark studies. The most important factors found for VFS overland flow reduction were saturated hydraulic conductivity and WT depth, added to sediment characteristics and VFS dimensions for sediment and pesticide reductions. The relative importance of WT varied as a function of soil type (most important at the silty-clay soil) and hydraulic loading (rainfall + incoming runoff) at each site. The presence of WT introduced more complex responses dominated by strong interactions in the modeled system response, reducing the typical predominance of saturated hydraulic conductivity on infiltration under deep water table conditions. This study demonstrates that when present, the WT should be considered as a key hydrologic factor in buffer design and evaluation as a water quality mitigation practice.

scholarly journals Shallow water table effects on water, sediment and pesticide transport in vegetative filter strips: Part B. model coupling, application, factor importance and uncertainty

2017 ◽  
Author(s):  
Claire Lauvernet ◽  
Rafael Muñoz-Carpena
Keyword(s):  
Hydraulic Conductivity ◽  
Shallow Water ◽  
Water Table ◽  
Overland Flow ◽  
Silty Clay ◽  
Relative Importance ◽  
Shallow Water Table ◽  
Vegetative Filter Strips ◽  
Filter Strips ◽  
Pesticide Transport

Abstract. Vegetative filter strips are often used for protecting surface waters from pollution transferred by surface runoff in agricultural watersheds. In Europe, they are often prescribed along the stream banks, where a seasonal shallow water table (WT) could decrease the buffer zone efficiency. In spite of this potentially important effect, there are no systematic experimental or theoretical studies on the effect of this soil boundary condition on the VFS efficiency. In the companion paper, we developed a physically-based numerical algorithm (SWINGO) that allows representing soil infiltration with a shallow water table. Here we present the dynamic coupling of SWINGO with VFSMOD, an overland flow and transport mathematical model to study the WT influence on VFS efficiency in terms of reductions of overland flow, sediment and pesticide transport. This new version of VFSMOD was evaluated with two contrasted benchmark field studies in France (sandy-loam soil under Mediterranean semi-continental climate, and silty-clay under temperate Oceanic climate), where testing of the model with field data showed promising results. The analysis showed that for the conditions of the studies, VFS efficiency decreases markedly when the water table is 0 to 1.5 m from the surface. In order to evaluate the relative importance of WT among other input factors controlling VFS efficiency, two global sensitivity and uncertainty analysis (GSA) methods, Morris and eFAST, were applied on the benchmark studies. The most important factors found for VFS overland flow reduction were saturated hydraulic conductivity and WT, added to sediment characteristics and VFS dimensions for sediment and pesticide reductions. The relative importance of WT varied as a function of soil type (most important at the silty-clay soil) and hydraulic loading (rainfall + incoming runoff) at each site. The presence of WT introduced more complex responses dominated by strong interactions in the modelled system response, reducing the predominance of saturated hydraulic conductivity on infiltration under typical deep water table conditions. This study demonstrates that when present, WT should be considered as a key hydrologic factor in buffer design and evaluation as a water quality mitigation practice.

scholarly journals Shallow water table effects on water, sediment, and pesticide transport in vegetative filter strips – Part 1: nonuniform infiltration and soil water redistribution

2018 ◽  
Vol 22 (1) ◽  
pp. 53-70 ◽  
Author(s):  
Rafael Muñoz-Carpena ◽  
Claire Lauvernet ◽  
Nadia Carluer
Keyword(s):  
Shallow Water ◽  
Water Table ◽  
Surface Runoff ◽  
Rainfall Intensity ◽  
Initial Conditions ◽  
Companion Paper ◽  
Soil Infiltration ◽  
Shallow Water Table ◽  
Vegetative Filter Strips ◽  
Filter Strips

Abstract. Vegetation buffers like vegetative filter strips (VFSs) are often used to protect water bodies from surface runoff pollution from disturbed areas. Their typical placement in floodplains often results in the presence of a seasonal shallow water table (WT) that can decrease soil infiltration and increase surface pollutant transport during a rainfall-runoff event. Simple and robust components of hydrological models are needed to analyze the impacts of WT in the landscape. To simulate VFS infiltration under realistic rainfall conditions with WT, we propose a generic infiltration solution (Shallow Water table INfiltration algorithm: SWINGO) based on a combination of approaches by Salvucci and Entekhabi (1995) and Chu (1997) with new integral formulae to calculate singular times (time of ponding, shift time, and time to soil profile saturation). The algorithm was tested successfully on five distinct soils, both against Richards's numerical solution and experimental data in terms of infiltration and soil moisture redistribution predictions, and applied to study the combined effects of varying WT depth, soil type, and rainfall intensity and duration. The results show the robustness of the algorithm and its ability to handle various soil hydraulic functions and initial nonponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found to be effectively decoupled from surface infiltration and excess runoff processes for depths larger than 1.2 to 2 m, being shallower for fine soils and shorter events. For nonponded initial conditions, the influence of WT depth also varies with rainfall intensity. Also, we observed that soils with a marked air entry (bubbling pressure) exhibit a distinct behavior with WT near the surface. The good performance, robustness, and flexibility of SWINGO supports its broader use to study WT effects on surface runoff, infiltration, flooding, transport, ecological, and land use processes. SWINGO is coupled with an existing VFS model in the companion paper (Lauvernet and Muñoz-Carpena, 2018), where the potential effects of seasonal or permanent WTs on VFS sediment and pesticide trapping are studied.

Sign in / Sign up

Export Citation Format

Share Document