Vegetative Filter Research Articles

The role of willow roots in sub-surface oxygenation of vegetation filter beds — mass spectrometer investigations in Wales, U.K.

Membrane inlet mass spectrometry (MIMS) was used to monitor dissolved gas concentrations in-situ in laboratory microcosms and in a constructed willow vegetation filter bed used to treat leachate. Diurnal cycles in the concentrations of oxygen, carbon dioxide and methane were seen. O2 is released from willow roots during daylight. CO2 and CH4 accumulate during the dark. Results also demonstrate sub-surface spatial heterogeneity in the willow bed, with locally high concentrations of O2 within otherwise anoxic zones. This technique enables direct measurement of subsurface environments in constructed wetlands, and provides evidence of the oxygenation capacity of willow vegetation filters.

Global Sensitivity and Uncertainty Analyses of the Water Quality Model VFSMOD-W

This study presents the statistical evaluation of the vegetative filter strip modeling system VFSMOD-W as a tool to design vegetative filter strips to use in the mitigation plans required as a part of phosphate mining permitting process by the State of Florida. A two-step statistical evaluation framework using global techniques is presented based on: (1) a screening method (Morris) for qualitative ranking of parameters, and (2) a variance-based method (extended Fourier Analysis Sensitivity Test--extended FAST) for quantitative sensitivity and uncertainty analyses. Measured characteristics of the central Florida phosphate-mining region are used to construct the 16 probability distributions of input factors. Two design filter lengths (3 and 6 m) and two model structures (VFSM--the filter module alone, and UH/VFSM--combined filter and source area components) are considered and compared to previous local one-parameter-at-a-time (OAT) analyses. It was found that for this application the filter's saturated hydraulic conductivity (VKS) was the most important factor controlling the filter runoff response, explaining over 90% of total output variance irrespective of model structure. In the case of the VFSM structure, sediment-related outputs were mainly influenced by three parameters: sediment particle size diameter (DP), effective flow width of the strip (FWIDTH), and VKS. For UH/VFSM, there were six important parameters: DP, the source area erosion and runoff parameters (slope of the source area Y, USLE soil erodibility index K, and runoff curve number CN), FWIDTH, and VKS. The results show the model's additive nature for this specific application, i.e., there are no significant parameter interactions for all model outputs except sediment outflow concentration and sediment wedge geometry. The uncertainty analysis indicates that regardless of the model structure, the probability of meeting a minimum required 75% sediment reduction was acceptable at the 90% confidence level for the 6 m long filter, but not for the 3 m filter. In general the UH/VFSM model structure exhibited larger output uncertainty. Comparison with previous OAT analyses of the model indicates the importance of performing the global evaluation for each specific model application. The results illustrate four main products of the global analysis: ranking of importance of the VFSMOD-W parameters for different outputs, effect of changing modeling structure, type of influence of the important parameters, and assurance of the model's behavior.

Diagnosis of internal radionuclide contamination by mobile laboratories

To support patient management of possible radiation casualties in case of a radiological or a nuclear event, the Defence Radiation Protection Service (SPRA) is able, 24 h a day, to supply intervention means in France and overseas if requested by military authorities or civilian institutions. SPRA has developed mobile laboratories for the diagnosis of internal radionuclide contamination. The mission of this mobile unit is to study health and environment risks linked to radiological hazards for exposed people: workers, soldiers and also civilians. The mobile laboratories are able to be deployed in all types of nuclear or radiological events, and give the results of analysis to physicians and authorities in a short time. The vehicles are fully equipped to detect and to survey exposure to alpha, beta and gamma emitters for the supervision of people exposed to ionising radiation, by whole body counting or analysis of biological samples. Environmental survey by analysis of wipes, soil, water, vegetation or air filters can also be achieved.

Performance of Grass Barriers and Filter Strips under Interrill and Concentrated Flow

Effectiveness of grass barriers and vegetative filter strips (FS) for reducing transport of sediment and nutrients in runoff may depend on runoff flow conditions. We assessed the performance of (1) switchgrass (Panicum virgatum L.) barriers (0.7 m) planted above fescue (Festuca arundinacea Schreb.) filter strips under interrill (B-FS) and concentrated flow (CF-B-FS), and (2) fescue alone under interrill (FS) and concentrated flow (CF-FS) for reducing runoff, sediment, nitrogen (N), and phosphorus (P) loss from fallow plots on a Mexico silt loam. We compared exclusively the performance of barriers and filter strips separately under interrill and concentrated flow. Runoff and sediment were sampled at 1 m above and at 0.7, 4, and 8 m below the downslope edge of the sediment source area. Filter strips under interrill flow reduced 80% and those under concentrated flow reduced 72% of sediment at 0.7 m (P < 0.01). With the addition of supplemental runoff simulating runoff from a larger sediment source area, FS reduced 80%, but CF-FS reduced only 60% of sediment. The FS reduced organic N and NO(3)-N by an additional 50% (P < 0.01) more than CF-FS at 0.7 m. Although the effectiveness of both treatments increased with increasing width, CF-FS removed less sediment than FS alone at 8 m (P < 0.04). In contrast, barriers above filter strips under interrill and concentrated flow were equally effective at 8 m; decreasing runoff by 34%, sediment by 99%, and nutrients by 70%. Thus, barriers combined with FS can be an effective alternative to FS alone for sites where concentrated flows may occur.

COST EFFECTIVENESS OF VEGETATIVE FILTER STRIPS AND INSTREAM HALF‐LOGS FOR ECOLOGICAL RESTORATION1

ABSTRACT: This paper presents the results of cost effectiveness (CE) analysis of vegetative filter strips (VFS) and instream half‐logs as tools for recovering scores on a fish Index of Biotic Integrity (IBI) in the upper Wabash River watershed (UW) in Indiana. Three assumptions were made about recovery time for IBI scores (5,15, and 30 years) and social discount rates (1, 3, and 5 percent), which were tested for sensitivity of the estimated CE ratios. Effectiveness of VFS was estimated using fish IBIs and riparian forest cover from 49 first‐order to fifth‐order stream reaches. Half‐log structures had been installed for approximately two years in the UW prior to the study and provided a basis for estimates of cost and maintenance. Cost effectiveness ratios for VFS decreased from $387 to $277 per 100 m for a 1 percent increase in IBI scores from first‐to fifth‐order streams with 3 percent discount and 30‐year recovery. This cost weighted by proportion of stream orders was $360. The ratio decreased with decreasing time of recovery and discount rate. Based on installation costs and an assumption of equal recovery rates, half‐logs were two‐thirds to one‐half as cost‐effective as VFS. Half‐logs would be a cost‐effective supplement to VFS in low order streams if they can be proven to recover IBI scores faster than VFS do. This study provides baseline data and a framework for planning and determining the cost of stream restoration.

Effectiveness of Vegetative Filter Strips in Removal of Sediments from Overland Flow

Abstract Many forms of natural heritage manifested as streams, rivers, ponds, lakes and wetlands play an integral role in maintaining natural beauty, health and a high quality of life. Agricultural intensification in southern Ontario has contributed to elevated sediments, nutrient and bacteria levels in water bodies. Vegetative filter strips (VFS) are control measures that can partially remove sediments and pollutants adhered to sediments from overland runoff before entering water bodies. The objective of this study was to determine the effect of vegetation type, width of the filter strip, runoff flow rate and inflow sediment characteristics on effectiveness of the VFS in removing pollutants from runoff. The results show that sediment removal efficiency increased from 50 to 98% as the width of the filter increased from 2.5 to 20 m. In addition to the width of the filter strip, grass type and flow rate were also significant factors. This study indicates that the first five (5) metres of a filter strip are critical and effective in removal of suspended sediments. More than 95% of the aggregates larger than 40 µm in diameter were trapped within the first five metres of the filter strip.

Effectiveness of vegetative filter strips in attenuating nutrient and sediment runoff from irrigated pastures

Increasing concern about non-point source pollutants released from grazing livestock, a worldwide problem, motivated the present study on the effects of vegetative filter strips (VFS) for controlling pollutants (nutrients, micro-organisms and sediment loading) from grazed, irrigated pastures. Flood-irrigated pastures are an important source of forage for livestock during summer months in California, USA when the surrounding rangelands are dry and dormant. Significant amounts of runoff can be generated from these pastures during irrigation events.Nine plots on an irrigated pasture were assigned randomly to one of three treatments: Control (no VFS), Treatment VFS-1 (8·3×7 m, 0·0058 ha VFS) and Treatment VFS-2 (17·1×7 m, 0·012 ha VFS). In 2000, two grazing events (in April and June/July) occurred during the irrigation season prior to the experiment; further, the experimental plots were grazed between irrigations 2 and 3. Attenuation of runoff loads by VFS treatment was measured during four irrigation events (between 1 August and 3 October 2000) for total suspended solids (TSS), ortho-phosphate (Ortho-P), inorganic phosphate (Inorg-P), total phosphate (Total-P), organic phosphate (Org-P), polyphosphate (Poly-P), total Kjeldahl nitrogen (TKN), NH3, NO3 and presumptive faecal coliforms (FC).On average, approximately 0·43 of the applied water left the plots as runoff. Treatment effects approached significance for TSS and TKN and were significant (P&lt;0·05) for Poly-P and NH3. Irrigation number effects were significant for all but TSS, NO3 and FC. The effects of VFS treatments were not consistent. Treatment VFS-2, although representing the largest buffer strip, did not always produce the lowest pollutant loads in runoff. Slope, relatively high runoff volumes and some channelled flow were probably responsible for the limited effectiveness of VFS in the present study. These results suggest that effectiveness of VFS for reducing sediment and nutrient transport from irrigated pastures may be questionable.

Measurement of radionuclides in contaminated environmental matrices: Participation in Quality Assessment Programme (QAP) of U.S. Department of Energy's Environmental Monitoring Laboratory

A Quality Assessment Programme (QAP) was initiated by the U.S. Department of Energy (DOE) in 1998 to establish creditability in the measurements of radionuclides in contaminated environmental samples; soil, vegetation and air filters. For this purpose the Neutron Activation Analysis (NAA) Laboratory at the Pakistan Institute of Nuclear Science and Technology (PINSTECH), an IAEA Regional Resource Unit (IAEA-RRU), along with 76 other well-known and relevant international laboratories were invited to participate in a regular proficiency programme. The measurement procedures employed, the problems encountered and the improvements and experience gained by the NAA Laboratory throughout this exercise are presented.

Mineralisation of atrazine, metolachlor and their respective metabolites in vegetated filter strip and cultivated soil

In vegetated filter strips (VFS) the presence of perennial vegetation, rhizodeposition of labile organic substrates and the accumulation of an organic residue thatch layer may enhance microbial numbers and activity, thereby increasing the potential for mineralisation of herbicides and herbicide metabolites retained during run-off events. The objective of this laboratory experiment was to compare the mineralisation of atrazine and metolachlor with that of their respective metabolites in VFS and cultivated soil. With the exception of total bacteria, propagule density of the microbial groups, endogenous soil enzymes and microbial diversity were higher in the VFS soil. This correlated with increased mineralisation of metolachlor and its metabolites in the VFS soil and indicates potential for VFS to curtail the subsequent transport of these compounds. In contrast, the mineralisation of atrazine and the majority of its metabolites was substantially reduced in VFS soil relative to cultivated soil. Consequently, the potential for subsequent transport of atrazine and many of its metabolites may be greater in VFS soil than in cultivated soil if reduced mineralisation is not offset by increased sorption in the VFS.

Atrazine and Metolachlor Sorption to Switchgrass Residues

Herbicide retention by residue mulch in vegetative filter strips could be an effective attenuation mechanism for removing herbicides from runoff. Adsorption studies were conducted to quantify the amount of atrazine and metolachlor that can be adsorbed and removed from runoff by thatch or fresh switchgrass residue. Adsorption of C14‐atrazine and metolachlor on thatch or fresh switchgrass residue was conducted by using concentrations of 2.5, 7.5, 13.2, and 26.4 µmol L−1 and a 24‐h equilibration period. Adsorption coefficients (Kd) decreased in the order, atrazine sorption on fresh switchgrass residue (81.1 L−1 kg−1), metolachlor sorption on fresh residue (32.9 L−1 kg−1), atrazine sorption on thatch residue (21.4 L−1 kg−1), and metolachlor sorption on thatch switchgrass residue (15.1 L−1 kg−1). On a volumetric basis (Kd-vol), only atrazine showed a significantly greater Kd-vol value on fresh residue than on the thatch residue. Absorption through cut ends of the residues (especially the fresh residue) may have produced adsorption capacities that would not be observed under field conditions. Fresh or thatch switchgrass residue in vegetative filter strips can help abate atrazine and metolachlor by intercepting and sorbing some of the herbicides.

Overland flow modeling in a vegetative filter considering non-planar topography and spatial variability of soil hydraulic properties and vegetation density

Summary Vegetative filters are used to remove contaminants from overland flow. Little is known about the impacts of non-planar topography and spatially variable soil hydraulic properties and vegetation density on filter performance. In this study, we developed a protocol for modeling the effects of these quantities on overland flow features which influence greatly the filter efficiency. Two-dimensional overland flow was modeled using the physically based, distributed hydrologic model MIKE SHE. Soil hydraulic properties were represented using spatially variable saturated hydraulic conductivity and a spatially uniform soil–water retention curve. When field measured data and predictions from the uncalibrated model were compared, good agreement was found. The simulated volumetric outflow was within approximately 5% and 25% of the measured outflow at the two areas monitored within the study filter. Non-planar topography significantly impacted overland flow, but accounting for spatially variable roughness and variable soil hydraulic properties had a lesser impact on the two-dimensional overland flow. The volumetric outflow was affected by 36% and 20% because of non-planar topography, 14% and 18% due to variable roughness, and 15% and 16% because of variable soil hydraulic properties for the two grid areas, respectively.

Atrazine Tolerance of Grass Species with Potential for Use in Vegetated Filters in Australia

The response of introduced (Pennisetum clandestinum Hochst.) and native (Stipa aristiglumis F. Muell., Themeda australis (R. Br.) Stapf, Danthonia spp. (L.) grasses to the herbicide atrazine was studied in plants with the potential for use in vegetated filters (biofilters) designed to reduce chemical loads in agricultural runoff. The response was detected by photosynthetic inhibition using leaf chlorophyll fluorescence. With continuous short-term (14 days) dosing with atrazine in sand culture, P. clandestinum showed the greatest tolerance, regardless of the dose (20–500 μg/L). In a clay vertosol soil in the glasshouse, the four species were tolerant to longer-term (84 days) application of three successive doses of simulated run-on, each dose containing 100 μg/L atrazine, a concentration which is comparable to the highest reported in runoff from agricultural land in Australia. Even with a subsequent single atrazine dose at ∼ ∼5000 μg/L, established plants of the four species showed signs of quick recovery (7–21 days) to normal photosynthetic activity. In a field experiment with simulated run-on, applied to P. clandestinum pasture in sandy loam soil, repeated doses at concentrations up to 1000 μg/L gave no significant response; only a subsequent single dose of 5000 μg/L had significant effects, from which plants soon recovered. Although damage from atrazine can be demonstrated with continuous dosing in non-adsorbing media, in soil culture the tolerance of the four selected species to repeat doses of atrazine shows they may be used confidently for biofiltering purposes. P. clandestinum was especially tolerant.

The prospects for willow plantations for wastewater treatment in Sweden

The concept of willow vegetation filters for the treatment of nutrient-rich wastewater has the potential to address two of our most serious environmental problems today -water pollution and climate change- in a cost-efficient way. Despite several benefits, including high treatment efficiency, increased biomass yields, improved energy and resource efficiency, and cost savings, willow vegetation filters have so far only been implemented to a limited degree in Sweden. This is due to various kinds of barriers, which may be the result of current institutional, structural and technical/geographical conditions. This paper discusses the prospects of a more widespread utilisation of willow plantations for wastewater treatment in Sweden, including existing incentives and barriers, based on current knowledge and experience. © 2005 Elsevier Ltd. All rights reserved.

APEX FEEDLOT WATER QUALITY SIMULATION

A manure erosion equation was developed and added to the APEX model for use in estimating nutrient losses from feedlots and manure application fields. The modified APEX was validated with data from feedlots near Bushland, Texas, and Carrington, North Dakota. The model was used to investigate feedlot management options on a hypothetical feedlot with realistic data. Vegetative filter strip (VFS) characteristics including 10%, 25%, 50%, and 100% FLRs (flow length ratios, i.e., filter flow length/feedlot flow length) and slopes of 1%, 5%, and 10% were considered. Combinations of these VFS characteristics were compared on two soil types: clay loam and fine sandy loam. Management options included three stocking rates (10, 15, and 20 m2 head-1) and two clean-out intervals (90 and 180 d). Additionally, two climatic conditions (precipitation of 440 and 825 mm year-1) were simulated. Results from 50-year simulations indicate that a VFS downslope of the feedlot can greatly reduce nutrient loads. All three VFS characteristics (FLR, slope, and soil) were important in controlling organic N and P losses. The best organic N and P control was obtained from a VFS with maximum FLR (100%), minimum slope (1%), and a sandy loam soil. Results were similar for soluble N and P control except that VFS slope had little effect. The simulated management options (clean-out interval and stocking rate) were also effective in controlling nutrient losses. The climatic variable (annual precipitation) gave higher nutrient losses from the feedlot and the VFS with 825 mm than with 440 mm. Nutrient control efficiencies, CEs, 100.* (1.0 - nutrient loss from VFS / nutrient loss from feedlot) were calculated for all scenarios considered. The VFSs on sandy loam soil with FLRs equal to or greater than 50% gave the highest CEs for both soluble and organic nutrients. Other factors including VFS slope, clean-out interval, and stocking rate had marginal impacts on CE. For soluble nutrients, CE is inversely related to annual precipitation. Thus, it is important to locate feedlots in areas with low precipitation and to provide a well designed VFS. The APEX model with the new manure erosion equation provides a tool for designing VFSs for controlling nutrient losses from feedlots.

Precision riparian buffers for the control of nonpoint source pollutant loading into surface water: A review

Numerous studies have shown the effectiveness of riparian buffers in reducing sediment, pathogen, and nutrient loads into surface and groundwater in agricultural catchments. Reported retention rates of sediment, N, and P were as high as 97%, 85%, and 84%, respectively. Often, however, riparian buffers fail to perform their protective functions due to low adaptability of their designs to local settings. This is caused by our inadequate understanding of the conditions under which riparian buffers perform the best at field scale. Therefore, a precision oriented approach based on thorough analysis of spatially variable characteristics of landscape has to be undertaken in riparian buffer construction. Such an approach has a potential to improve the protective qualities and the economic viability of the riparian buffers. This paper gives an overview of the current level of research on riparian buffers and discusses the importance of spatial variability of local conditions on their performance. It presents the approaches for precision buffer design and its practical implementation and highlights the directions for future development of precision conservation. Key words: riparian buffer, vegetative filter, water quality, precision conservation.

Suspended Sediment Removal by Vegetative Filter Strip Treating Highway Runoff

Structural best management practices (BMPs) are often used to mitigate the impact of storm water runoff on receiving waters. Vegetative filter strips (VFS) are an example of a structural BMP that has been used to treat storm water and highway runoff. Physical factors affecting the performance of VFS include pollutant characteristics, vegetation composition and density, soil properties, and the physical dimensions of the filter strip. In this study, field-suspended sediment data were collected from an experimental VFS treating highway runoff in eastern North Carolina. Field data were used to test the design concepts of the VFS treatment train and to validate a simulation model for evaluating the impact of these physical factors on sediment removal as a function of filter strip length. It was concluded that the experimental filter strip was effective in removing more than 85% of the incoming total suspended sediment (TSS). Simulation results support field observations that a 10-m or longer filter strip can retain most of the medium and large particles (> 8 μ m) transported in runoff. Simulations also indicate infiltration loss is largely responsible for the retention of small-size sediment particles (< 8 μ m). Saturated hydraulic conductivity and initial water contents have little effects on TSS removal. The condition of vegetative coverage, in particular vegetation density, is another factor affecting the performance of filter strip.

Runoff transport of faecal coliforms and phosphorus released from manure in grass buffer conditions

To test the hypothesis that faecal coliform (FC) and phosphorus (P) are transported similarly in surface runoff through the vegetative filter strip after being released from land-applied manure. The Hagerstown soil was packed into boxes that were 10 cm deep, 30 cm wide and 100, 200 or 300 cm long. Grass was grown in boxes prior experiments. Same-length boxes were placed under rainfall simulator and tilted to have with either 2% or 4% slopes. Dairy manure was broadcast on the upper 30-cm section. Rainfall was simulated and runoff samples were collected and analysed for Cl, FC and total phosphorus (TP). Mass recovery, the concentration decrease rate k, and the ratio FC : TP showed that there was a consistent relationship between FC and TP in runoff. The FC and TP transport through simulated vegetated buffer strips were highly correlated. As a knowledge base on the effect of the environmental parameters on P transport in vegetated buffer strips is substantially larger than for manure-borne bacteria, the observed similarity may enhance ability to assess the efficiency of the vegetated buffer strips in retention of FC currently used as indicator organisms for manure-borne pathogens.

Economics of using wastewater irrigation of willow in Northern Ireland

Abstract The economics of growing short rotation willow coppice as an energy crop are marginal and highly dependent on the support for the conventional crops or enterprises they replace and on the maintenance of high yield levels. Consequently any value which can be added to the crop by giving it a dual function will greatly enhance its economic sustainability. In this context the additional use of short rotation willow coppice as a vegetation filter for wastewater (bioremediation) presents such a value added opportunity. This paper calculates the added value in terms of avoided costs for the chemical and or physical treatment of the wastewater, and the avoided costs for fertilisation of the coppice and yield improvements due to the fertilisation and irrigation effects of the application of the wastewater. In the calculated situation, the wastewater is applied to the coppice during the growing season and treatment reverts to the conventional in the dormant season. Calculations show that saved costs in the conventional treatment of wastewater are higher ( £ 5.8 – £ 14.83.5 kg N - 1 ) than the saved costs for fertiliser and higher coppice yields (equivalent to £ 0.7 kg N - 1 ). This added value that the bioremediation of wastewater confers on the energy produced from short rotation willow coppice has the potential to alter radically the economic sustainability of the crop even if, as is the likely case, not all of the avoided treatment costs will be passed on to the biomass producer.

Reducing herbicide runoff from agricultural fields with vegetative filter strips: a review

Although the effectiveness of vegetative filter strips (VFS) for reducing herbicide runoff is well documented, a comprehensive review of the literature does not exist. The objectives of this article are to denote the methods developed for evaluating herbicide retention in VFS; ascertain the efficacy of VFS regarding abating herbicide runoff; identify parameters that affect herbicide retention in VFS; review the environmental fate of herbicides retained by VFS; and identify future research needs. The retention of herbicide runoff by VFS has been evaluated in natural rainfall, simulated rainfall, and simulated run-on experiments. Parameters affecting herbicide retention in VFS include width of VFS, area ratio, species established in the VFS, time after establishment of the VFS, antecedent moisture content, nominal herbicide inflow concentration, and herbicide properties. Generally, subsequent transport of herbicides retained by VFS is reduced relative to adjacent cultivated soil because of enhanced sorption and degradation in the former.

Herbicide losses in runoff events from a field with a low slope: Role of a vegetative filter strip

Herbicide runoff and the effects of a narrow vegetative filter strip (VFS) were studied on an arable field in the low-lying plains of the Veneto Region (north-east Italy). Cultivated plots were compared with and without a 6 m wide VFS composed of trees, shrubs and grass. Natural and simulated runoff were monitored during 2000 and 2001. Herbicides applied on the field were: metolachlor (2184–2254 g ha −1), terbuthylazine (1000–1127 g ha −1) and isoproturon (1000 g ha −1). The VFS reduced both runoff depth (10.2–91.2%) and herbicide losses (85.7–97.9%) in the monitored rainfall events. Total herbicide loss with runoff was low (0.69–3.98 g ha −1 without VFS, less than 0.27 g ha −1 with VFS), but concentrations were sometimes very high, especially of terbuthylazine and isoproturon during the first events after treatment. In these events there was a high probability of exceeding the ecotoxicological endpoint for algae, but the VFS helped to reduce the potential risk. Two VFS effectiveness mechanisms were identified: (i) dilution, and (ii) a “sponge-like” effect, which temporarily trapped chemicals inside the VFS before releasing them.