Vegetative Filter Research Articles

Local-scale dynamics of plant-pesticide interactions in a northern Brittany agricultural landscape

Soil pollution by anthropogenic chemicals is a major concern for sustainability of crop production and of ecosystem functions mediated by natural plant biodiversity. Understanding the complex effects of soil pollution requires multi-level and multi-scale approaches. Non-target and agri-environmental plant communities of field margins and vegetative filter strips are confronted with agricultural xenobiotics through soil contamination, drift, run-off and leaching events that result from chemical applications. Plant-pesticide dynamics in vegetative filter strips was studied at field scale in the agricultural landscape of a long-term ecological research network in northern Brittany (France). Vegetative filter strips effected significant pesticide abatement between the field and riparian compartments. However, comparison of pesticide usage modalities and soil chemical analysis revealed the extent and complexity of pesticide persistence in fields and vegetative filter strips, and suggested the contribution of multiple sources (yearly carry-over, interannual persistence, landscape-scale contamination). In order to determine the impact of such persistence, plant dynamics was followed in experimentally-designed vegetative filter strips of identical initial composition (Agrostis stolonifera, Anthemis tinctoria/Cota tinctoria, Centaurea cyanus, Fagopyrum esculentum, Festuca rubra, Lolium perenne, Lotus corniculatus, Phleum pratense, Trifolium pratense). After homogeneous vegetation establishment, experimental vegetative filter strips underwent rapid changes within the following two years, with Agrostis stolonifera, Festuca rubra, Lolium perenne and Phleum pratense becoming dominant and with the establishment of spontaneous vegetation. Co-inertia analysis showed that plant dynamics and soil residual pesticides could be significantly correlated, with the triazole fungicide epoxiconazole, the imidazole fungicide prochloraz and the neonicotinoid insecticide thiamethoxam as strong drivers of the correlation. However, the correlation was vegetative-filter-strip-specific, thus showing that correlation between plant dynamics and soil pesticides likely involved additional factors, such as threshold levels of residual pesticides. This situation of complex interactions between plants and soil contamination is further discussed in terms of agronomical, environmental and health issues.

Metamodeling methods that incorporate qualitative variables for improved design of vegetative filter strips

Significant amounts of pollutant are measured in surface water, their presence due in part to the use of pesticides in agriculture. One solution to limit pesticide transfer by surface runoff is to implement vegetative filter strips. The sizing of VFSs is a major issue, with influencing factors that include local conditions (climate, soil, vegetation). The BUVARD modeling toolkit was developed to design VFSs throughout France according to these properties. This toolkit includes the numerical model VFSMOD, which quantifies dynamic effects of VFS on site-specific pesticide mitigation efficiency. In this paper, a metamodeling, or model dimension reduction, approach is proposed to ease the use of BUVARD and to help users design VFSs that are adapted to specific contexts. Three different reduced models, or surrogates, are compared: a linear model, GAM, and kriging. It is shown that kriging, implemented with a covariance kernel for a mixture of qualitative and quantitative inputs, outperforms the other metamodels. The metamodel is a way of providing a relevant first approximation to help design the pollution reduction device. In addition, it is a relevant tool to visualize the impact that lack of knowledge of some field parameters can have when performing pollution risk analysis and management.

The Allocation Method of Vegetation Types in the Green Belt of the Bay City Landscape Park

Pan, Z., 2020. The allocation method of vegetation types in the green belt of the bay city landscape park. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 1093–1097. Coconut Creek (Florida), ISSN 0749-0208.In view of the low utilization rate of resources in most of the green belt vegetation allocation methods used in the bay city landscape park, this paper puts forward the research on the allocation methods of green belt vegetation in the bay city landscape park. Analyze the ecological efficiency of the green belt, calculate the value of the direct green service function according to the geographical location of the vegetation filter belt and the river bank buffer belt, establish the regression model, enrich the level of plant community, stabilize the structure of plant community, and realize the allocation of vegetation types in the green belt of the bay city landscape park. The experimental results show that compared with the conventional allocation method, the resource consumption of the proposed method is lower and the resource utilization rate is greatly improved.

Sediment Yield Estimation and Effect of Management Options on Sediment Yield of Kesem Dam Watershed, Awash Basin, Ethiopia

Assessing sediment yield and identifying hotspot areas play a significant role for watershed management. Watershed models can be used for such processes. Therefore, this study aims to develop watershed model and estimate sediment yield, including mapping the spatial distribution of sediment yield for the Kesem Dam watershed (Ethiopia), which had experienced intensive agricultural activities and high sediment loadings problems. The study also aims to evaluate the effect of implementing management options on sediment reduction especially in high sediment yielding areas. The most widely used Soil and Water Assessment Tool (SWAT) model was used for sediment yield modeling and management options implementation. We developed the SWAT model of the Kesem Dam watershed for the period 1994-2010 based on available geo-spatial and hydro-meteorological data of the watershed. Using observed streamflow and sediment yield data of the watershed, the model was calibrated for the period 2000-2006 and validated for the period 2007-2010. Parameters used for the model calibration were identified based on sensitivity analysis. The performance of the model was evaluated by coefficient of determinations (R2), Nash-Sutcliffe efficiency (NSE), and percent bias (PBIAS). SWAT adequately reproduced the observed daily flows and sediment loads temporal evolution with R2 and NSE ≥ 0.7 and PBIAS < 15% both for the calibration and validation periods. The mean annual sediment yield of the watershed was 11.43 t/ha/yr. The model also identified areas with the highest sediment yields of 24 to 29 ton/ha/yr, indicating the suitability of the model to implement and assess the impacts of management options. However, treating those areas with different sediment management options reduced the annual average sediment yield by 80% under vegetative filter strips. These findings can be used as inputs for reducing sediment loadings to the Kesem dam watershed and implementing sustainable watershed management of the watershed and other similar areas.

Modeling study on the time-varying process of sediment trapping in vegetative filter strips

Vegetative filter strips (VFS) play an important role in reducing erosion, retaining runoff, and trapping sediment. The bed surface of a VFS is dynamic during continuous sediment deposition, which makes it difficult to determine the sediment transport capacity of overland flow in real time. This study described this process from a systematic perspective. Based on self-feedback theory, an ordinary differential equation was established with a self-inhibition correction factor and its analytical solution was obtained. A sediment-trapping-process model of VFS (STPMOD-VFS) was proposed. Then, the sediment trapping processes of three experiments under different conditions were predicted using the STPMOD-VFS, and the prediction was considered highly satisfactory. The uncertainty estimation results showed the STPMOD-VFS had significant ‘equifinality’ performance. The sensitivity of different parameters of the STPMOD-VFS was found significantly different. The parameters related to the sediment delivery rate of silt-laden inflow and those that control the attenuation coefficients of the instantaneous sediment trapping efficiency of the VFS were sensitive, while those parameters that control the initial sediment outflow rate were less sensitive. Finally, an equation describing the sediment trapping process by a VFS under a dynamic sediment inflow rate was built and solved, and a general expression for the VFS sediment trapping time-varying process was given. The findings of this study could help in evaluation of sediment processes on grassed hillslopes.

Sustainable soil amendments to improve nature-based solutions for wastewater treatment and resource recovery

Vegetation Filters (VFs) can be a sustainable solution to treat wastewater and to recover resources such as nutrients, water and biomass from small municipalities and isolated dwellings. However, under certain conditions, the leakage of nutrients, especially of nitrate, can represent a limitation. The addition of two sustainable soil amendments, woodchips and biochar, has been tested as a strategy to improve nutrient attenuation in VFs increasing sorption sites and microbial activity.To this end, unsaturated infiltration and batch experiments have been carried out at laboratory scale. The systems for infiltration experiments contain natural soil, natural soil amended with woodchips and natural soil amended with biochar. To determine the sorption capacity of NH4+, batch tests were performed using an amendment/SWW ratio of 1:20 and an NH4+ initial concentration ranging from 30 to 600 mg L−1.Results from the infiltration experiments show a high attenuation (~95%) of total phosphorous (TP) independently of the amendments. Different behaviour is observed for total nitrogen (TN). The removal of this species is obtained only in the soil amended with woodchips (>85%) whereas the natural soil alone and the soil with biochar have no impact on TN attenuation. In these two porous media, all the NH4+ input concentration is transformed to NO3− that infiltrates without further reactions. According to batch experiment results, the potential role of biochar in the nutrient attenuation is limited to sorption processes (Kd (NH4+) = 21.37–193.18 L kg−1). Woodchips act primarily as a labile source of carbon promoting biodegradation, being more effective for nutrient attenuation than the sorption capacity of biochar.

Using ArcGIS hydrologic modeling and LiDAR digital elevation data to evaluate surface runoff interception performance of riparian vegetative filter strip buffers in central Iowa

The Midwest is well known for agriculture, and Iowa is a leader in corn (Zea mays L.) and soybean (Glycine max [L.] Merr.) production. Fertilizers and chemical pesticides used to increase crop production can adversely affect the soil and water health. Midwest farmers also produce livestock and graze cattle on pastureland that can lead to excessive surface runoff and soil erosion. Establishing vegetative filter strips (VFSs) along the edge of farmland is one of the best management practices (BMPs) to reduce nutrient and sediment loss. However, studies have revealed that the classic VFS design along the length of an agricultural field does not adequately address nonuniform flow through the buffer. New designs are being researched to increase the efficiency of the VFS. In order to accurately implement new design strategies, the runoff flowpaths into the VFS need to be accurately modeled. This research assesses the performance of existing established VFS buffers of selected sites by modeling and analyzing the flow accumulation from the field into the VFS using geographic information system (GIS) and light detection and ranging (LiDAR) derived digital elevation model (DEM) 5 × 5 m data. This study also employed the new coefficient of flow interception (CFI) approach that improves the process of identifying areas where flow is concentrated and designing more efficient filter strips to account for concentrated runoff. In this study, the performance of VFS in three sites was evaluated by developing and using the CFI. Among the three sites, site 1 had very poor efficiency and no flow passes through the VFS, site 2 had low efficiency, and site 3 had excellent efficiency.

Evaluation of Sediment Trapping Efficiency of Vegetative Filter Strips Using Machine Learning Models

The South Korean government has recently focused on environmental protection efforts to improve water quality which has been degraded by nonpoint sources of water pollution from runoff. In order to take care of environmental issues, many physically-based models have been used. However, the physically-based models take a large amount of work to carry out site simulations, and there is a need to find faster and more efficient approaches. For an alternative approach for sediment management using the physically-based models, the machine learning-based models were used for estimating sediment trapping efficiency of vegetative filter strips. The seven nonlinear regression algorithms of machine learning models (e.g., decision tree, multilayer perceptron, k-nearest neighbors, support vector machine, random forest, AdaBoost and gradient boosting) were applied to select the model which best estimates the sediment trapping efficiency of vegetative filter strips. The sediment trapping efficiencies calculated by the machine learning models showed similar results as those of vegetative filter strip modeling system (VFSMOD-W) model. As a result of the accuracy evaluation among the seven machine learning models, the multilayer perceptron model-derived the best fit with VFSMOD-W model. It is expected that the sediment trapping efficiency of the vegetative filter strips in various cases in agricultural fields in South Korea can be predicted easier, faster and accurately by the machine learning models developed in this study. Machine learning models can be used to evaluate sediment trapping efficiency without complicated physically-based model design and high computational cost. Therefore, decision makers can maximize the quality of their outputs by minimizing their efforts in the decision-making process.

Irrigating Nursery Crops with Recycled Run-off: A Review of the Potential Impact of Pesticides on Plant Growth and Physiology

Interest in capturing and reusing runoff from irrigation and rainfall in container nurseries is increasing due to water scarcity and water use regulations. However, grower concerns related to contaminants in runoff water and other issues related to water safety are potential barriers to the adoption of water capture and reuse technologies. In this review, we discuss some of the key concerns associated with potential phytotoxicity from irrigating container nursery crops with recycled runoff. The concentration of pesticides in runoff water and retention ponds is orders of magnitude lower than that of typical crop application rates; therefore, the risk of pesticide phytotoxicity from irrigation with runoff water is relatively low. Nonetheless, some pesticides, particularly certain herbicides and insecticides, can potentially affect crops due to prolonged chronic exposure. Pesticides with high solubility, low organic adsorption coefficients, and long persistence have the greatest potential for crop impact because they are the most likely to be transported with runoff from container pads. The potential impact on plant growth or disruption of physiological processes differs among pesticides and sensitivity of individual crop plants. Growers can reduce risks associated with residual pesticides in recycled irrigation water by adopting best management practices (e.g., managing irrigation to reduce pesticide runoff, reducing pots spacing during pesticide application, use of vegetative filter strips) that reduce the contaminant load reaching containment basins as well as adopting remediation strategies that can reduce pesticide concentrations in recycled water.

Identification of Study Sites for Placement of Sediment Traps in Vegetated Buffer Strips

Abstract The aim of this contribution was to outline the decision procedure for selecting potential sites suitable for installing sediment traps in vegetation buffer strips in the Fugnitz catchment, Austria. The selection procedure consisted of GIS data processing where the contributing areas of specific sites were specified according to the selected criteria (i.e. slope above 2°, vegetation strip in between agriculturally used land and river network, contributing area of at least 300 m2). Available landuse maps were updated with formerly not-digitized structures potentially influencing connectivity (e.g. ephemeral streams and road ditches) which were mapped in the field. From 31 pre-defined sites 15 were selected, taking into account as additional selection criteria the slope angle, soil erodibility and size of the contributing area. Two sites were selected for further investigations – i.e. installation of the sediment traps in vegetation filter strips collecting event-based sediment yields from adjacent arable fields. We conclude that GIS analysis has shown to be useful for the first step-delineation of potential sites of interest on the catchment scale. However, field-based surveys have been shown to be inevitable to obtain on-site information on vegetation characteristics and fine-scale topographic and management information.

Best management practices for agricultural nonpoint source pollution: Policy interventions and way forward

AbstractBest management practices (BMPs) are the tools which are adopted to run any activity while inflicting least negative impacts on the surrounding environment. Since, water pollution is one of the most important issues in today's world; it is indispensable to discuss the activities which are deteriorating its quality. Although, a number of treatment technologies and methods are in place for treating the point sources of pollution, there is a need to address nonpoint sources of pollution. There are many successful practices which are capable of curtailing the impacts of nonpoint source pollution, if adopted. In this paper an attempt has been made to evaluate the performance and trade‐offs of various management practices to address the issues of agricultural nonpoint source pollution. Nevertheless, there is a dearth of guiding principles which can pave a way for adoption of these practices. Therefore, an attempt has also been made to explore the aspects of policy formulations along with emphasizing the factors which can lead to adoption/ non‐adoption of such practices.

Treatment of horizontal silage bunker runoff using biochar amended vegetative filter strips

Horizontal silage bunkers produce leachate that contains contaminants that can be detrimental to the environment if released untreated. Vegetated filter strips are used to treat silage bunker runoff to prevent contamination of surface waters via infiltration, however increased infiltration poses risks to groundwater, particularly for nitrate (NO3−). Vegetated filter strip plots with a sandy loam soil, half of which are amended with biochar, were investigated to assess the treatment of silage bunker runoff over 20 application events. The subsurface effluent biological oxygen demand (BOD5), chemical oxygen demand (COD), and total phosphorus (TP) were reduced on average by 40%, 46%, and 75%, respectively, and there was no statistical difference between treatments. The total nitrogen (TN) was reduced by 49 and 64% for control and biochar plots, respectively, which was significantly different between treatments. Biochar significantly reduced nitrate nitrogen (NO3−-N) leaching by 40% compared to the control, however, the NO3−-N concentration in leachate was still high ranging from 0.19 to 191.04 mg NO3−-N L−1 and 0.18–108.89 mg NO3−-N L−1 for control and biochar plots, respectively. A mass balance suggests the primary mechanism for a decrease in TN and NO3−-N leaching from biochar amended plots was greater retention of NO3−-N and organic N (ORG-N) within the soil/biochar matrix. The development of oxygenated functional groups and/or formation of organomineral layer on the biochar surface likely enhanced N retention.

A Multicriteria Index System for the Selection of Best Management Practices at the Watershed Scale

The selection of Best Management Practices (BMPs) is the key of nonpoint source pollution control at a watershed scale. To date, there are no comprehensive methods or corresponding tools for the selection of BMPs by considering the operation constraints on local spatial conditions, especially for those large-scale watersheds. In this study, a new method was developed to provide economically, ecologically and operationally effective solutions, which integrates the Geographic Information System-based multicriteria index analysis with a watershed model. Land use, area, soil type and slope were used as potential constraints for selection system. This method helps identify the potential placements for BMPs at the watershed scale and reduce the work of an accurate algorithm-based optimization of BMPs placement in watershed. The system was validated with Soil and Water Assessment Tool in Daning River watershed, the Three Gorges Reservoir Region, China. Based on the results, the new approach provides more specific potential sites for BMPs than traditional methods at a watershed scale. Within the new framework, the vegetative filter strip was suggested as the most widespread practice, while the constructed wetland is the least effective option. The area with relatively flat agricultural plains was suitable for most practices, suggesting a more operationally effective scheme if the new method was used. The system developed in this study could easily extend to other watersheds to provide an objective selection method and the potentialsite of BMPs.

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. A recent study evaluated existing empirical equations and a mechanistic mass-balance approach using the most extensive field database available of VFS pesticide efficiency from single-event storms. That study concluded that an updated empirical equation (Sabbagh equation) and a mechanistic mass-balance approach performed reasonably well. The objective of this research was to study the effect of upscaling the VFS trapping equations from single events into long-term EEAs. The U.S. EPA Pesticide in Water Calculator (PWC) model linked with the Vegetative Filter Strip MODeling system (VFSMOD) long-term EEA modeling framework (30 yr) was updated to incorporate the alternative trapping equations and tested VFS mitigation results under contrasting agroecological settings with varying erosion/sediment transport conditions. Differences in both acute and chronic 90th percentile estimated environmental exposure concentrations (EECs) were relatively small when comparing predictions using the four pesticide trapping equations. A global sensitivity analysis (GSA) also indicated that selection of a specific trapping equation for predicting EECs was less important than other important input factors such as the VFS length and pesticide properties. However, in terms of the percent reductions in EECs, the choice of pesticide trapping equation was as important as the VFS length. This research builds upon the conclusion of previous single-event studies that the mechanistic mass-balance and refit Sabbagh empirical equation were both valid for EEAs. The mass balance approach represents a reasonable option for regulatory agencies that prefer mechanistic approaches.

Species- and organ-specific responses of agri-environmental plants to residual agricultural pollutants

Soil pollution by anthropogenic chemicals is a major concern for sustainability of crop production and of ecosystem functions mediated by natural plant biodiversity. The complex effects on plants are however difficult to apprehend. Plant communities of field margins, vegetative filter strips or rotational fallows are confronted with agricultural pollutants through residual soil contamination and/or through drift, run-off and leaching events that result from chemical applications. Exposure to xenobiotics and heavy metals causes biochemical, physiological and developmental effects. However, the range of doses, modalities of exposure, metabolization of contaminants into derived xenobiotics, and combinations of contaminants result in variable and multi-level effects. Understanding these complex plant-pollutant interactions cannot directly rely on toxicological or agronomical approaches that focus on the effects of field-rate pesticide applications. It must take into account exposure at root level, sublethal concentrations of bioactive compounds and functional biodiversity of the plant species that are affected. The present study deals with agri-environmental plant species of field margins, vegetative filter strips or rotational fallows in European agricultural landscapes. Root and shoot physiological and growth responses were compared under controlled conditions that were optimally adjusted for each plant species. Contrasted responses of growth inhibition, no adverse effect or growth enhancement depended on species, organ and nature of contaminant. However, all of the agricultural contaminants under study (pesticides, pesticide metabolites, heavy metals, polycyclic aromatic hydrocarbons) had significant effects under conditions of sublethal exposure on at least some of the plant species. The fungicide tebuconazole and polycyclic aromatic hydrocarbon fluoranthene, which gave highest levels of responses, induced both activation or inhibition effects, in different plant species or in different organs of the same plant species. These complex effects are discussed in terms of dynamics of agri-environmental plants and of ecological consequences of differential root-shoot growth under conditions of soil contamination.

Comparing Filtering Techniques for Removing Vegetation from UAV-Based Photogrammetric Point Clouds

Digital Elevation Models (DEMs) are 3D representations of the Earth’s surface and have numerous applications in geomorphology, hydrology and ecology. Structure-from-Motion (SfM) photogrammetry using photographs obtained by unmanned aerial vehicles (UAVs) have been increasingly used for obtaining high resolution DEMs. These DEMs are interpolated from point clouds representing entire landscapes, including points of terrain, vegetation and infrastructure. Up to date, there has not been any study clearly comparing different algorithms for filtering of vegetation. The objective in this study was, therefore, to assess the performance of various vegetation filter algorithms for SfM-obtained point clouds. The comparison was done for a Mediterranean area in Murcia, Spain with heterogeneous vegetation cover. The filter methods that were compared were: color-based filtering using an excessive greenness vegetation index (VI), Triangulated Irregular Networks (TIN) densification from LAStools, the standard method in Agisoft Photoscan (PS), iterative surface lowering (ISL), and a combination of iterative surface lowering and the VI method (ISL_VI). Results showed that for bare areas there was little to no difference between the filtering methods, which is to be expected because there is little to no vegetation present to filter. For areas with shrubs and trees, the ISL_VI and TIN method performed best. These results show that different filtering techniques have various degrees of success in different use cases. A default filter in commercial software such as Photoscan may not always be the best way to remove unwanted vegetation from a point cloud, but instead alternative methods such as a TIN densification algorithm should be used to obtain a vegetation-less Digital Terrain Model (DTM).

Willow evapotranspiration beds without discharge for handling of household wastewater &amp; biomass short rotation willow coppice fertilised with nutrient from human urine mixture

Storstmm County and A &amp; B Backlund ApS have been co-operating in a project collectingexperiences and making investigations regarding the oldest evapotranspiration bed withoutoutlet in Denmark situated in Storstmm County. Results from the project Danish EPA M226-0025 "EXPERIENCES AND EXAMINATIONS FROM A EVAPOTRANSTIRATION BEDWITHOUT DISCHARGE AT TAPPERN0JE" are presented in this paper. The bed hasworked very stable since 1992. A water balance has been calculated estimating theevapotranspiration of the bed. Contents of nutrients in the wastewater and nutrients, heavymetal and organic compounds in the soil have been analysed. Steam production of thewillows has been estimated. A &amp; B Backlund ApS is engaged in further development of thesystems.A small part ofan international project FAIR5-CT97-3947 (1998-2002) "BIOMASS SHORTROTATION WILLOW COPPICE FERTILISED WITH NUTRIENT FROM MUNICIPALWASTEWATER (BWCW) is dedicated fertilising willows with human urine mixtures. Theexperiences has up to now been very positive and efforts are made to prolong the project andestablish further demonstration projects.Willow evapotranspiration beds, willow vegetation filter, wastewater treatment, human urinefertiliser, no-mixing toilets, diverting toilets, separation toilets, ecological engineering,ecological sanitation

Willow coppice plantations as wastewater treatment systems

Short rotation willow coppice (Salix) can be used as vegetation filter to treat industrialand municipal wastewater. In May 1998 a EU-FAIR project, "Biomass short rotationwillow coppice fertilized with nutrient from municipal wastewater (BWCW)" wasstarted to investigate the consequences to establish willow plantations to treatwastewater in some European countries with varying climatic conditions. The aims ofthis research project were to evaluate the positive effects of irrigation of willow-toenergy plantations with wastewater, but also to find the negative consequences and todevelop strategies to deal with them. The project comprises comparable pilot plantationslocated in four different climatic regions in the four European countries: France, Greece,Unite Kingdom and Sweden. In this paper the experiences from this EU research projectBWCW, which will be finished off in 2002, are briefly described.

Can willow roots oxygenate leachate in vegetation filter beds?¬ a mass spectrometer investigation in Wales

Membrane inlet mass spectrometry (MIMS) was used to monitor dissolved gas concentrationsin-situ in laboratory microcosms and in a constructed willow vegetation filter bed in Walesused to treat leachate. A mini-rhizotron digital camera system was developed for use incombination with MIMS studies of gas dynamics. The major results of the studies are:-• Diurnal cycles in the concentrations of 02, CO2 and C� were shown to occur with arooted willow cutting in a stirred microcosm.• Willow beds show considerable sub-surface spatial diversity. Generally, oxygen decreaseswith depth whereas methane and carbon dioxide increase with depth. Small pockets ofgases were seen. Oxygen occurred throughout the profile.• Microbial processes follow diurnal cycles. Oxygen is released from willow roots duringdaylight. Methane and carbon dioxide accumulate during the dark.• The high degree of mixing distributes oxygenated water throughout the bed. Stopping theflow of leachate allowed conditions to become anaerobic, except in local micro-sites.These techniques appear to offer considerable potential for direct measurement of sub-surfaceenvironments in constructed wetlands, particularly in respect of the microbial processesoccurring in the bed, and the oxygenation capacity of willow vegetation filters.

Retention Efficiency of Vegetative Filter Strips for Nitrogen in Danjiangkou Reservoir Area, Central China

Abstract To investigate the retention efficiency and mechanism of nitrogen of Vegetative filter strips (VFSs) in the Danjiangkou Reservoir area, simulated runoff discharging experiments were carried out in a new-established Bermuda VFS. The results showed that the Bermuda VFS reduced 73.1-86.1 % of surface runoff through infiltration. The outflow rate of runoff increased first and then became stable with time. The concentration reduction rates (CRRs) and load reduction rates (LRRs) of NH3-N increased initially and then decreased with the increase of inflow concentration. The average CRRs and LRRs of NH3-N in three treatments ranged 66.1-90.3 % and 90.0-96.7 %, respectively. The concentration reduction of NH3-N was primarily achieved by soil adsorption. The optimal inflow concentration of NH3-N for the optimum CRR was between 0.65 and 3.52 mg/dm3. The CRRs and LRRs of NO3-N fluctuated between 6.8-14.0 % and 72.0-77.9 % in three treatments. The concentration reduction of NO3-N was primarily achieved by plant uptake and soil microbe assimilation. The optimal inflow concentration of NO3-N for optimum CRR exceeded 6.78 mg/dm3. The CRRs and LRRs of TN increased with the increase of inflow concentrations. The average CRRs in the low, moderate and high treatments reached 9.7, 14.8 and 27.4 %, respectively, and the average LRRs reached 72.1, 74.3 and 81.2 %, respectively. The optimal inflow concentration of TN for optimum CRR exceeded 10.21 mg/dm3. The study showed that Bermuda grass can retain nitrogen in runoff efficiently and should be promoted around the Danjiangkou reservoir.