Effect of turfgrass cover and irrigation on soil mobility and dissipation of mefenoxam and propiconazole

Irrigation effects on pesticide mobility have been studied, but few direct comparisons of pesticide mobility or persistence have been conducted on turfgrass versus bare soil. The interaction of irrigation practices and the presence of turfgrass on the mobility and dissipation of mefenoxam [N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-D-alanine methyl ester] and propiconazole (1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole) was studied. Sampling cylinders (20-cm diam.) were placed in either creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.) Farw.] or bare soil. Mefenoxam was applied at 770 g a.i. ha(-1) and propiconazole was applied at 1540 g a.i. ha(-1) on 14 June 1999. Sampling cylinders were removed 2 h after treatment and 4,8,16, 32, and 64 days after treatment (DAT) and the cores were sectioned by depth. Dissipation of mefenoxam was rapid, regardless of the amount of surface organic matter or irrigation. The half-life (t1/2) of mefenoxam was 5 to 6 d in turf and 7 to 8 d in bare soil. Most mefenoxam residues found in soil under turfgrass were in the 0- to 1-cm section at 0, 4, and 8 DAT. Residues were found in the 15- to 30-cm section at 4, 8, 16, 32, and 64 DAT, regardless of turf cover or irrigation. The t1/2 of propiconazole was 12 to 15 d in turfgrass and 29 d in bare soil. Little movement of propiconazole was observed in either bare soil or turf.     

Risk assessment of pesticide runoff from turf

The TurfPQ model was used to simulate the runoff of 15 pesticides commonly applied to creeping bentgrass (Agrostis stolonifera L.) fairways and greens on golf courses in the northeastern USA. Simulations produced 100-yr daily records of water runoff, pesticide runoff, and pesticide concentration in runoff for three locations: Boston, MA, Philadelphia, PA, and Rochester, NY. Results were summarized as annual and monthly means and annual maximum daily loads (AMDLs) corresponding to 10- and 20-yr return periods. Mean annual pesticide runoff loads did not exceed 3% of annual applications for any pesticide or site, and most losses were substantially less than 1% of application. However, annual or monthly mean concentrations of chlorothalonil, iprodione, and PCNB in fairway runoff often exceeded concentrations that result in 50% mortality of the affected species (LC50) for aquatic organisms. Concentrations of azoxystrobin, bensulide, cyfluthrin, and trichlorfon in extreme (1 in 10 yr or 1 in 20 yr) events often approached or exceeded LC50 levels. Concentrations of halofenozide, mancozeb, MCPP, oxadiazon, propiconazole, thiophanate-methyl, triadimefon, and trinexapac-ethyl were well below LC50 levels, and turf runoff of these chemicals does not appear to be hazardous to aquatic life in surface waters.     

Selection of plants for optimization of vegetative filter strips treating runoff from turfgrass

Runoff from turf environments, such as golf courses, is of increasing concern due to the associated chemical contamination of lakes, reservoirs, rivers, and ground water. Pesticide runoff due to fungicides, herbicides, and insecticides used to maintain golf courses in acceptable playing condition is a particular concern. One possible approach to mitigate such contamination is through the implementation of effective vegetative filter strips (VFS) on golf courses and other recreational turf environments. The objective of the current study was to screen ten aesthetically acceptable plant species for their ability to remove four commonly-used and degradable pesticides: chlorpyrifos (CP), chlorothalonil (CT), pendimethalin (PE), and propiconazole (PR) from soil in a greenhouse setting, thus providing invaluable information as to the species composition that would be most efficacious for use in VFS surrounding turf environments. Our results revealed that blue flag iris (Iris versicolor) (76% CP, 94% CT, 48% PE, and 33% PR were lost from soil after 3 mo of plant growth), eastern gama grass (Tripsacum dactyloides) (47% CP, 95% CT, 17% PE, and 22% PR were lost from soil after 3 mo of plant growth), and big blue stem (Andropogon gerardii) (52% CP, 91% CT, 19% PE, and 30% PR were lost from soil after 3 mo of plant growth) were excellent candidates for the optimization of VFS as buffer zones abutting turf environments. Blue flag iris was most effective at removing selected pesticides from soil and had the highest aesthetic value of the plants tested.     

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.     

Nutrient load generated by storm event runoff from a golf course watershed

Turf, including home lawns, roadsides, golf courses, parks, etc., is often the most intensively managed land use in the urban landscape. Substantial inputs of fertilizers and water to maintain turf systems have led to a perception that turf systems are a major contributor to nonpoint source water pollution. The primary objective of this study was to quantify nutrient (NO(3)-N, NH(4)-N, and PO(4)-P) transport in storm-generated surface runoff from a golf course. Storm event samples were collected for 5 yr (1 Apr. 1998-31 Mar. 2003) from the Morris Williams Municipal Golf Course in Austin, TX. Inflow and outflow samples were collected from a stream that transected the golf course. One hundred fifteen runoff-producing precipitation events were measured. Median NO(3)-N and PO(4)-P concentrations at the outflow location were significantly (p < 0.05) greater than like concentrations measured at the inflow location; however, median outflow NH(4)-N concentration was significantly less than the median inflow concentration. Storm water runoff transported 1.2 kg NO(3)-N ha(-1) yr(-1), 0.23 kg NH(4)-N ha(-1) yr(-1), and 0.51 kg PO(4)-P ha(-1) yr(-1) from the course. These amounts represent approximately 3.3% of applied N and 6.2% of applied P over the contributing area for the same period. NO(3)-N transport in storm water runoff from this course does not pose a substantial environmental risk; however, the median PO(4)-P concentration exiting the course exceeded the USEPA recommendation of 0.1 mg L(-1) for streams not discharging into lakes. The PO(4)-P load measured in this study was comparable to soluble P rates measured from agricultural lands. The findings of this study emphasize the need to balance golf course fertility management with environmental risks, especially with respect to phosphorus.     

Fungicide leaching from golf greens: effects of root zone composition and surfactant use

Soil water repellency in golf putting greens may induce preferential "finger flow," leading to enhanced leaching of surface applied fungicides. We examined the effects of root zone composition, treatment with a non-ionic surfactant, and the use of the fungicide iprodion or a combination of azoxystrobin and propiconazole on soil water repellency, soil water content distributions, fungicide leaching, and turf quality during 1 yr. Soil water repellency was measured using the water drop penetration time (WDPT) test and tension infiltrometers. Our study was made on a 3-yr-old experimental green seeded with creeping bentgrass (Agrostis stolonifera L.) 'Penn A-4' at Landvik in southeast Norway. The facility consists of 16 lysimeters with two different root zone materials: (i) straight sand (1% gravel, 96% sand, 3% silt and clay, 4 g kg(-1) organic matter) (SS) and (ii) straight sand mixed with garden compost to an organic matter content of 21 g kg(-1) (Green Mix [GM]). Surfactant treatment resulted in 96% lower average WDPTs at 1 cm depth, three times higher water infiltration rates at the soil surface, and reduced spatial variation in soil water contents. Fungicide leaching was close to zero for the GM lysimeters probably due to stronger sorption. Concentrations in the drainage water from SS lysimeters often exceeded surface water guideline values for all three fungicides, but surfactant treatment dramatically reduced fungicide leaching from these lysimeters. In autumn and winter, surfactant-treated plots were more infected with fungal diseases probably because of higher water content in the turfgrass thatch layer.     

Size distribution of organic matter and associated propiconazole in agricultural runoff material

Sorption and desorption characteristics of propiconazole (1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole) to different particle/aggregate-size fractions of agricultural runoff material were investigated. Emphasis was put on clay and colloidal size fractions to evaluate their role as potential sorbents and carriers for this pesticide. The runoff material was separated into size fractions ranging from 2 mm to ca. 15 nm by wet sieving, sedimentation, centrifugation, and membrane ultrafiltration. Each fraction was characterized by its organic C content and C/N ratio. Distinctive sorption properties of clay-sized particles and colloids were investigated. The obtained size fractions differed significantly in their organic C concentration, C/N ratio, and sorption properties to propiconazole. Organic matter was mainly associated in aggregates >2 microm. Binding of propiconazole to this coarse fraction made up 80% of the sorbed propiconazole. The distribution coefficient between solid and aqueous phases increased with decreasing particle size. The colloidal fraction (<0.16 microm) exhibited the highest sorbtivity, with a distribution coefficient of 113 L kg(-1), which was more than four times higher than that in the bulk sample (27 L kg(-1)). The fraction <2 microm represented 8% of the total sample weight, but contributed to 20% of the sorbed propiconazole. Strong hysteresis was observed for the sorption-desorption of propiconazole on the runoff material. Under dilution very little sorbed propiconazole will be released into the water phase. Due to its high sorbtivity and mobility and the strong sorption-desorption hysteresis, particles in the fraction <2 microm can be important carriers of propiconazole in runoff suspensions with high sediment load.     

Estimating Watershed Level Nonagricultural Pesticide Use From Golf Courses Using Geospatial Methods1

Abstract: Limited information exists on pesticide use for nonagricultural purposes, making it difficult to estimate pesticide loadings from nonagricultural sources to surface water and to conduct environmental risk assessments. A method was developed to estimate the amount of pesticide use on recreational turf grasses, specifically golf course turf grasses, for watersheds located throughout the conterminous United States (U.S.). The approach estimates pesticide use: (1) based on the area of recreational turf grasses (used as a surrogate for turf associated with golf courses) within the watershed, which was derived from maps of land cover, and (2) from data on the location and average treatable area of golf courses. The area of golf course turf grasses determined from these two methods was used to calculate the percentage of each watershed planted in golf course turf grass (percent crop area, or PCA). Turf‐grass PCAs derived from the two methods were used with recommended application rates provided on pesticide labels to estimate total pesticide use on recreational turf within 1,606 watersheds associated with surface‐water sources of drinking water. These pesticide use estimates made from label rates and PCAs were compared to use estimates from industry sales data on the amount of each pesticide sold for use within the watershed. The PCAs derived from the land‐cover data had an average value of 0.4% of a watershed with minimum of 0.01% and a maximum of 9.8%, whereas the PCA values that are based on the number of golf courses in a watershed had an average of 0.3% of a watershed with a minimum of <0.01% and a maximum of 14.2%. Both the land‐cover method and the number of golf courses method produced similar PCA distributions, suggesting that either technique may be used to provide a PCA estimate for recreational turf. The average and maximum PCAs generally correlated to watershed size, with the highest PCAs estimated for small watersheds. Using watershed specific PCAs, combined with label rates, resulted in greater than two orders of magnitude over‐estimation of the pesticide use compared to estimates from sales data.     

Removal of selenate from water by zerovalent iron

Zerovalent iron (ZVI) has been widely used in the removal of environmental contaminants from water. In this study, ZVI was used to remove selenate [Se(VI)] at a level of 1000 microg L(-1) in the presence of varying concentrations of Cl-, SO(2-)4, NO(-)3, HCO(-)3, and PO(3-)4. Results showed that Se(VI) was rapidly removed during the corrosion of ZVI to iron oxyhydroxides (Fe(OH)). During the 16 h of the experiments, 100 and 56% of the added Se(VI) was removed in 10 mM Cl- and SO(2-)4 solutions under a closed contained system, respectively. Under an open condition, 100 and 93% of the added Se(VI) were removed in the Cl- and SO(2-)4 solutions, respectively. Analysis of Se species in ZVI-Fe(OH) revealed that selenite [Se(IV)] and nonextractable Se increased during the first 2 to 4 h of reaction, with a decrease of Se(VI) in the Cl- experiment and no detection of Se(VI) in the SO(2-)4 experiment. Two mechanisms can be attributed to the rapid removal of Se(VI) from the solutions. One is the reduction of Se(VI) to Se(IV), followed by rapid adsorption of Se(IV) to Fe(OH). The other is the adsorption of Se(VI) directly to Fe(OH), followed by its reduction to Se(IV). The results also show that there was little effect on Se(VI) removal in the presence of Cl- (5, 50, and 100 mM), NO(-)3 (1, 5, and 10 mM), SO(2-)4 (5 mM), HCO(-)3 (1 and 5 mM), or PO(3-)4 (1 mM) and only a slight effect in the presence of SO(2-)4 (50 and 100 mM), HCO(-)3 (10 mM), and PO(3-)4 (5 mM) during a 2-d experiment, whereas 10 mM PO(3-)4 significantly inhibited Se(VI) removal. This work suggests that ZVI may be an effective agent to remove Se from Se-contaminated agricultural drainage water.     

流动注射—光度法联用测定海水中PO4-P

本法针对海水分析时严重的盐度和基体干扰,以监测的海水试样为载流,并在流动注射进样阀前流路上首次引入自制全容量阴离子交换柱,去除载流中的磷酸盐,使进入系统的载流盐度与试样一致,消除了基体干扰,并通过阴柱在线再生条件试验和工作曲线优化试验,建立了流动注射磷锑钼蓝(还原剂为抗坏血酸)光度法直接测定PO4-P浓度为Ⅰ类～Ⅳ类海水的新方法,能分辨海水类别。结果表明,在最适合条件下,该方法在PO4-P浓度5～80μg/L范围内峰高与浓度成线性关系,方法检出限为0.73μg/L,空白海水加10μg/L、30μg/L和60μg/L PO4-P标准物质连续进样,RSD分别为4.57%(n=5)、4.72%(n=4)和5.76%(n=4)。进行实际样品分析时,加标回收率为101%～102%,具有很好的准确性,与国家标准方法———磷钼蓝分光光度法比对,结果吻合,令人满意。     

Transport and fate of nitrate and pesticides: hydrogeology and riparian zone processes

There is continuing concern over potential impacts of widespread application of nutrients and pesticides on ground- and surface-water quality. Transport and fate of nitrate and pesticides were investigated in a shallow aquifer and adjacent stream, Cow Castle Creek, in Orangeburg County, South Carolina. Pesticide and pesticide degradate concentrations were detected in ground water with greatest frequency and largest concentrations directly beneath and downgradient from the corn (Zea mays L.) field where they were applied. In almost all samples in which they were detected, concentrations of pesticide degradates greatly exceeded those of parent compounds, and were still present in ground waters that were recharged during the previous 18 yr. The absence of both parent and degradate compounds in samples collected from deeper in the aquifer suggests that this persistence is limited or that the ground water had recharged before use of the pesticide. Concentrations of NO(-)(3) in ground water decreased with increasing depth and age, but denitrification was not a dominant controlling factor. Hydrologic and chemical data indicated that ground water discharges to the creek and chemical exchange takes place within the upper 0.7 m of the streambed. Ground water had its greatest influence on surface-water chemistry during low-flow periods, causing a decrease in concentrations of Cl(-), NO(-)(3), pesticides, and pesticide degradates. Conversely, shallow subsurface drainage dominates stream chemistry during high-flow periods, increasing stream concentrations of Cl(-), NO(-)(3), pesticides, and pesticide degradates. These results point out the importance of understanding the hydrogeologic setting when investigating transport and fate of contaminants in ground water and surface water.     

EVALUATION OF SELECTED PESTICIDES IN NORTH CAROLINA SURFACE WATER SUPPLIES: INTAKE STUDY1

ABSTRACT: Studies were conducted to analyze the presence of 11 selected pesticides in 12 surface water supply intakes in the Piedmont and coastal plain regions of North Carolina. Samples were assayed using enzyme linked immunosorbent assays (ELISAs). Samples with pesticide detection of 1 μg/L or greater were extracted and confirmed using gas chromatography/mass spectrometry (GC/MS). Detection limits of the immunosorbent assays for pesticide residues were generally an order of magnitude higher than GC/MS. Atrazine was detected in approximately 45 percent of the samples, and on two occasions was at or above the lifetime Maximum Contaminant Level of 3.0 μg/L set by the Environmental Protection Agency for an annual average in finished drinking water. Metolachlor was detected in 58 percent of the samples. Of the remaining nine pesticides, including carbaryl, aldicarb, 2,4‐D, chiorpyrifos, acetochlor, methomyl, carbofuran, alachlor, and chlorothalonil, only aldicarb, 2,4‐D, and chlorpyrifos were detected in less than 9 percent of the samples for each pesticide.     

WATER QUALITY CHARACTERISTICS OF STORM WATER FROM MAJOR LAND USES IN SOUTH FLORIDA1

ABSTRACT: Starting in 1998, a study was conducted to characterize storm water quality from predominant land use types in a coastal watershed along the south central coast of Florida, namely citrus, pasture, urban, natural wetland, row crop, dairy, and golf courses. Sixty‐three sampling sites were located at strategic points on drainage conveyances for each of seven specific land use areas. Runoff samples were collected following storm events that met defined rainfall criteria for a period of 30 months. Nitrogen (N), phosphorus (P), heavy metals, pesticides, and other water quality parameters were determined, and the results were analyzed to compare and characterize land uses as relative sources for these constituents in runoff. Results showed that runoff from most land use types had low dissolved oxygen concentration and that sediment and nutrient concentrations were closely related to land use, particularly to the amount of fertilizer applied in each land use. Among the eight heavy metals tested, copper was the most frequently detected and was mostly associated with runoff from citrus and golf course land uses. High levels of arsenic were also detected in golf course runoff. The most frequently detected pesticide was simazine from citrus. The information and methodologies presented may facilitate pollution source characterization and ecological restoration efforts.     

Use of spent substrate after Pleurotus pulmonarius cultivation for the treatment of chlorothalonil containing wastewater

Lignocellulosic materials are used as substrate for the cultivation of the edible mushroom Pleurotus pulmonarius. After two or three flushes of mushrooms, the spent substrate is discarded although it still has an important enzymatic activity that can be used for several purposes. In this study, we sought to determine the technical feasibility of using spent substrate from P. pulmonarius to degrade chlorothalonil. Reaction mixture was prepared with 6 ml of pesticide aqueous solution (2 mg active ingredient/l) and 3 ml of enzymatic extract obtained from spent P. pulmonarius substrate. The enzymatic reaction (27 °C, pH 7.4) was conducted for 1 h with sampling at 15 min intervals. The effect of storage time and temperature (freezing or refrigerating) of spent substrate and enzymatic extract, respectively, on the activity over chlorothalonil was determined. Freshly obtained spent substrate extract was able to reduce 100% of the initial concentration of chlorothalonil (2 mg/l) after 45 min of reaction. Storage time had a negative effect on the stability of the enzymatic activity: with spent substrate stored for a week, chlorothalonil concentration was reduced in 49.5% after 1 h reaction and with substrate stored for two and three weeks, the degradation efficiency decreased to 9.15% and 0%, respectively. Cooling and freezing the spent substrate extract also had a negative effect on chlorothalonil degradation.     

Simulating nitrate drainage losses from a Walnut Creek watershed field

This study was designed to evaluate the improved version of the Root Zone Water Quality Model (RZWQM) using 6 yr (1992-1997) of field-measured data from a field within Walnut Creek watershed located in central Iowa. Measured data included subsurface drainage flows, NO3-N concentrations and loads in subsurface drainage water, and corn (Zea mays L.) and soybean [Glycine mar (L.) Merr.] yields. The dominant soil within this field was Webster (fine-loamy, mixed, superactive, mesic Typic Endoaquolls) and cropping system was corn-soybean rotation. The model was calibrated with 1992 data and was validated with 1993 to 1997 data. Simulations of subsurface drainage flow closely matched observed data showing model efficiency of 99% (EF = 0.99), and difference (D) of 1% between measured and predicted data. The model simulated NO3-N losses with subsurface drainage water reasonably well with EF = 0.8 and D = 13%. The simulated corn grain yields were in close agreement with measured data with D < 10%. Nitrogen-scenario simulations demonstrated that corn yield response function reached a plateau when N-application rate exceeded 90 kg ha(-1). Fraction of applied N lost with subsurface drainage water varied from 7 to 16% when N-application rate varied from 30 to 180 kg ha(-1) after accounting for the nitrate loss with no-fertilizer application. These results indicate that the RZWQM has the potential to simulate the impact of N application rates on corn yields and NO3-N losses with subsurface drainage flows for agricultural fields in central Iowa.     

Prairie strips reduce fecal indicator bacteria concentrations in simulated runoff

Vegetative filter strips (VFS) have shown promising results in reducing the downstream transport of many agroecosystem contaminants. A recently developed type of VFS, prairie strips, has been shown to significantly reduce the impact of corn and soybean production systems on water quality in terms of sediment, nitrogen, and phosphorus losses. This study assessed potential additional benefits of prairie strips to include the reduction of pathogens. To assess the impact of prairie strips on manure-laden agricultural runoff, we utilized a physical model of prairie strips in a laboratory flume to conduct highly controlled overland flow experiments. Escherichia coli and Enterococcus concentration reductions of up to 45% and 65% were observed for runoff and infiltration flows, respectively, while mass load reductions of up to 65% were observed for surficial runoff flows. The degree of concentration or mass load reductions was dependent on the residence time of the flow within the strip and the partitioning of overland flow running onto the strip to infiltration and runoff flows. Based on our results and a review of the literature, we developed a design method to provide guidance on the width of prairie strip buffer needed to achieve a user-defined reduction of fecal bacteria concentration.     

Fate of colloidal-particulate elemental selenium in aquatic systems

Bacterial reduction of selenate [Se(VI)] to elemental Se [Se(0)] is considered an effective bioremediation technique to remove selenium (Se) from agricultural drainage water. However, the fate of the newly formed Se(0) in aquatic systems is not known when it flows out of the treatment system. A set of laboratory experiments was conducted to determine the fate of the colloidal-particulate Se(0) in a water column and in a water-sediment system. Results showed that the newly formed colloidal-particulate Se(0) followed two removal pathways in aquatic systems: (i) flocculation-sedimentation to the bottom of the water and (ii) oxidation to selenite [Se(IV)] and Se(VI). During 58 d of the experiments, 51% of the added Se(0) was precipitated to the bottom of the water and 47% was oxidized to Se(IV) in the water column. In the water-sediment system, Se(IV) in the water accounted for 21 to 25% of the added Se(0). Adsorption of Se(IV) to the bottom sediment resulted in a relatively low amount of Se(IV) in the water. This study indicates that the newly formed Se(0) may be an available form of Se for uptake by organisms if it flows to aquatic systems from a treatment site. Therefore, an effective bioremediation system for removing Se from drainage water must reduce Se(VI) to Se(0) and remove Se(0) directly from the drainage water.     

Pesticide removal from container nursery runoff in constructed wetland cells

The increased use of pesticides by container nurseries demands that practices for removal of these potential contaminants from runoff water be examined. Constructed wetlands may be designed to clean runoff water from agricultural production sites, including container nurseries. This study evaluated 14 constructed wetlands cells (1.2 by 4.9 m or 2.4 by 4.9 m, and 30 or 45 cm deep) that collected pesticide runoff from a 465-m2 gravel bed containerized nursery in Baxter, TN. One-half of the cells were vegetated with bulrush, Scirpus validus. The cells were loaded at three rates or flows of 0.240, 0.120, and 0.060 m3 d(-1). Herbicides-simazine (Princep) [2-chloro-4,6-bis(ethylamino)-s-triazine] and metolachlor (Pennant) [2-chloro-N-(2-ethyl-6-methylphenyl)-N-2-methoxy-1-methylethyl-acetamide] -were applied to the gravel portion of the container nursery at rates of 4.78 and 239 kg ha(-1), respectively, 9 July 1998, and at rates of 2.39 and 1.19 kg ha(-1), respectively, 17 May 1999. Pesticides entering the wetland and wetland cell water samples were analyzed daily to determine pesticide removal. At the slower flow rate, which corresponds to lower mass loading and greater hydraulic retention times (HRTs), a greater percentage of pesticides was removed. During the 2-yr period, cells with plants removed 82.4% metolachlor and 77.1% simazine compared with cells without plants, which removed 63.2% metolachlor and 64.3% simazine. At the lowest flow rate and mass loading, wetland cells removed 90.2% metolachlor and 83% simazine. Gravel subsurface flow constructed wetlands removed most of the pesticides in runoff water with the greatest removal occurring at lower flow rates in vegetated cells.     

Runoff loss of pesticides and soil: a comparison between vegetative mulch and plastic mulch in vegetable production systems

Current vegetable production systems use polyethylene (plastic) mulch and require multiple applications of agrochemicals. During rain events, runoff from vegetable production is enhanced because 50 to 75% of the field is covered with an impervious surface. This study was conducted to quantify off-site movement of soil and pesticides with runoff from tomato (Lycopersicon esculentum Mill.) plots containing polyethylene mulch and a vegetative mulch, hairy vetch (Vicia villosa Roth). Side-by-side field plots were instrumented with automated flow meters and samplers to measure and collect runoff, which was filtered, extracted, and analyzed to determine soil and pesticide loss. Seasonal losses of two to four times more water and at least three times as much sediment were observed from plots with polyethvlene mulch (55.4 to 146 L m(-2) and 247 to 535 g m(-2), respectively) versus plots with hairy vetch residue (13.7 to 75.7 L m(-2) and 32.8 to 118 g m(-2), respectively). Geometric means (+/-standard deviation) of total pesticide loads for chlorothalonil (tetrachloroisophthalonitrile) and alpha-and beta-endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro6,9-methano-2,4,3-benzodioxathiepin 3-oxide) for a runoff event were 19, 6, and 9 times greater from polyethylene (800+/-4.6, 17.6+/-3.9, and 39.1+/-4.9 microg m(-2), respectively) than from hairy vetch mulch plots (42+/-6.0, 2.8+/-5.0, and 4.3+/-4.6 microg m(-2), respectively) due to greater concentrations and larger runoff volumes. The increased runoff volume, soil loss, and off-site loading of pesticides measured in runoff from the polyethylene mulch suggests that this management practice is less sustainable and may have a harmful effect on the environment.     

Removal of organic matter and nitrogen from river water in a model floodplain

A significant improvement in river water quality cannot be expected unless nonpoint-source contaminants are treated in addition to the further treatment of point-source contaminants. If river water is sprayed over a floodplain, the consequent water filtration through the sediment profile can simultaneously remove organic matter and nitrogen in the water through aerobic and denitrifying reactions. This hypothesis was tested using lysimeters constructed from polyvinyl chloride (PVC) pipe (150 cm long, 15 cm in diameter) packed with loamy sand floodplain sediment. Water was applied to the top of the lysimeters at three different flow rates (48, 54, and 68 mm d(-1)). Concentrations of NO3 and dissolved oxygen (DO), chemical oxygen demand (COD), and redox potential (Eh) in the water were measured as functions of depth after the system reached steady states for both water flow and reactions. At the rate of 68.0 mm d(-1), a reducing condition for denitrification developed below the 5-cm depth due to the depletion of O2 by organic matter degradation in the surface oxidizing layer; Eh and DO were below 205 mV and 0.4 mg L(-1), respectively. At a depth of 70 cm, COD and NO3-N concentration decreased to 5.2 and 3.8 mg L(-1) from the respective influent concentrations of 17.1 and 6.2 mg L(-1). Most biodegradable organic matter was removed during flow and further removal of NO3 was limited by the lack of an electron donor (i.e., organic matter). These results indicate that the floodplain filtration technique has great promise for treatment of contaminated river water.