Transport Of Agrichemicals Research Articles

Atrazine fate and transport within the coastal zone in southeastern Puerto Rico

Agrichemical transport to coastal waters may have adverse ecological impact. This work examined atrazine fate and transport in a field adjacent to Puerto Rico’s Jobos Bay National Estuarine Research Reserve. The herbicide’s use was linked to residue detection in shallow groundwater and movement toward the estuary; however, data indicated that transport via this pathway was small. In contrast, surface runoff as tropical storm systems moved through the area appeared to have high potential for atrazine transport. In this case, transport to the estuary was limited by runoff event timing relative to atrazine application and very rapid atrazine dissipation (DT50=1–3days) in field soil. Soil incubation studies showed that accelerated degradation conditions had developed in the field due to repeated atrazine treatment. To improve weed management, atrazine replacement with other herbicide(s) is recommended. Use of products that have greater soil persistence may increase runoff risk.

Dissipation of Sulfamethazine and Tetracycline in the Root Zone of Grass and Tree Species

The detection of veterinary antibiotics (VAs) in drinking water resources resulting from manure disposal operations has raised public health concerns. Previous studies have demonstrated the benefits of using multispecies vegetated buffer strips (VBS) to reduce agrichemical transport from agroecosystems. However, VA fate and subsequent effects of VAs on microbial activities in the root zone ofVBS have not been well documented. A growth chamber study was conducted to investigate dissipation of two commonly administered VAs, sulfamethazine (SMZ) and tetracycline (TC), and the relationship between VA dissipation and soil enzyme activities in the root zone of selected plant species. Switchgrass, eastern gammagrass, orchardgrass, and a hybrid poplar tree were grown in pots containing a Mexico silt loam/sand mixture for 3 mo, followed by plant biomass removal and collection of root zone soil. Radiolabeled (3H) SMZ or TC was applied to the soils and samples were incubated in the dark for 5 wk. Among the plant species studied, hybrid poplar showed enhanced capability for promoting SMZ dissipation. The half-lives of SMZ in soil planted to the poplar tree were significantly reduced by the enhanced enzymatic activity. Comparison of soil enzymatic activities between the antibiotic treatments revealed that fluorescein diacetate hydrolytic and glucosaminidase enzyme activities were significantly lower in TC-treated soils than in SMZ-treated soils. The beta-glucosidase activities were similar between the two VA treatments. Correlation analyses showed that the half-life of SMZ in the soil was negatively correlated with enzymatic activity. Enhanced SMZ dissipation in soil planted to hybrid poplar suggests that incorporation of this plant species in VBS may mitigate deleterious effects of SMZ in the environment.

Chlorothalonil and 2,4-D losses in surface water discharge from a managed turf watershed

Managed turf sites (golf courses) are the most intensively managed landscapes in the urban environment. Yet, long-term watershed scale studies documenting the environmental transport of agrichemicals applied to these systems are rare. The objective of this study was to quantify the surface discharge losses of two commonly applied pesticides (chlorothalonil and 2,4-D) resulting from prevailing practices on a managed golf course. Inflow and outflow discharge waters on a subarea of Northland Country Club located in Duluth, MN were measured for both quantity and quality from April through November from 2003 to 2008. The median chlorothalonil outflow concentration (0.58 microg L(-1)) was significantly greater (p < 0.05) than the inflow concentration, which was below the detection limit (0.07 microg L(-1)). Similarly, the median outflow 2,4-D concentration (0.85 microg L(-1)) was significantly greater (p < 0.05) than the inflow concentration (0.31 microg L(-1)). Chlorothalonil concentrations occasionally exceeded acute toxicity levels (7.6 microg L(-1)) reported for rainbow trout. No 2,4-D concentrations exceeded any human or aquatic species published toxicity level; however, the maximum measured 2,4-D concentration (67.1 microg L(-1)), which rarely occurred, did approach the 70 microg L(-1) maximum contaminant level (MCL) for that compound. Losses of both pesticides were detectable throughout the annual sampling period. Mean annual chlorothalonil loading was 10.5 g ha(-1) or 0.3% of applied, while mean annual 2,4-D loading was 4.9 g ha(-1) or 0.5% of applied. The findings of this study provide quantifiable evidence of agrichemical transport resulting from typical turfgrass management and highlight the need for implementation of best management practices to combat the offsite transport of agrichemicals used in professional turf management.

AGRICHEMICAL TRANSPORT TO GROUNDWATER THROUGH COASTAL PLAIN SOILS

A 1ha field with Pine Flat loamy sand (coarseloamy, siliceous, thermic Typic Paleudult) and Troup loamy sand(loamy, siliceous, thermic Grossarenic Kandiudult) surface soils, located near Plains, Georgia, was studied for four years(1993 to 1996) to evaluate potential agrichemical transport to groundwater. The field was managed to produce summer cornand winter wheat. Commercial fertilizer, the herbicide atrazine, and the insecticide carbofuran were applied to the field in1993, 1994, and 1995. Average annual application rates were 266 kg nitrogen ha1, 2.5 kg atrazine ha1, and 2.4 kgcarbofuran ha1. Monthly soilwater and groundwater samples were collected. The samples were analyzed for nitratenitrogen (NO3N), chloride, atrazine, carbofuran, and deethylatrazine (DEA). Soilwater and groundwater samplesindicated elevated NO3N concentrations (>5 ppm) in the vadose zone at 4.3 m and in the aquifer at 10 m (>4 ppm). Of thestudied pesticides, carbofuran and DEA were observed at the greatest concentrations in groundwater.<br><br>Both NO3N and pesticides were transported during groundwater recharge following periods of excess precipitation.Peak pesticide concentrations in groundwater were observed in late 1994, driven by a large precipitation event in July of 1994when 565 mm of rain fell over a 4day period. Atrazine and carbofuran concentrations in groundwater did not exceed theEPA maximum contaminant levels of 3 ppb and 40 ppb, respectively. Spatially averaged concentrations observed in monthlygroundwater collected directly below the field were well below these standards. Concentrations of NO3N, atrazine, DEA,and carbofuran observed in groundwater from the onfield wells were significantly different from upgradient anddowngradient concentrations (p = 0.05). These data indicate a significant impact to the local groundwater. Nitrate N wastransported downgradient from the field at the largest concentrations. Peak concentrations of atrazine and DEA weresimultaneously observed in the groundwater, indicating similar transport rates for both compounds and rapid transformationfrom atrazine into DEA in the rootzone.

Soil characteristics and agrichemicals in groundwater of the Midwestern United States

A comprehensive set of soil characteristics were examined to determine the effect of soil on the transport of agrichemicals to groundwater. This paper examines the relation of soil characteristics to concentrations and occurrence nitrate, atrazine, and atrazine residue from 99 wells completed in unconsolidated aquifers across the Midwestern United States. Soil characteristics that determine the rate of water movement were directly related to the occurrence and concentrations of nitrate and atrazine in groundwater. The substantial differences in the relations found among soil characteristics and nitrate and atrazine in groundwater suggest that different processes affect the transformation, adsorption, and transport of these contaminants. A multi-variable analysis determined that the soil characteristics examined explained the amount of variability in concentrations for nitrate (19%), atrazine (33%), and atrazine residue (29%). These results document that, although soils do affect the transport of agrichemicals to groundwater, other factors such as hydrology, land use, and climate must also be considered to understand the occurrence of agrichemicals in groundwater.

Agrichemicals in Ground Water of the Midwestern USA: Relations to Soil Characteristics

AbstractA comprehensive set of soil characteristics were examined to determine the effect of soil on the transport of agrichemicals to ground water. This paper examines the relation of local soil characteristics to concentrations and occurrence of nitrate, atrazine (2‐chloro‐4 ethylamino‐6‐isopropylamino‐s‐trazine), and atrazine residue [atrazine + deethylatrazine (2‐amino‐4‐chloro‐6‐isopropylamino‐s‐triazine) + deisopropylatrazine (2‐amino‐4‐chloro‐6‐ethylamino‐s‐triazine)] from 99 wells completed in unconsolidated aquifers across the midwestern USA. The occurrence and concentrations of nitrate and atrazine in ground water were directly related to soil characteristics that determine the rate of water movement. The substantial differences in the relations found among soil characteristics and nitrate and atrazine in ground water suggest that different processes affect the transformation, adsorption, and transport of these contaminants. A multivariate analysis determined that the soil characteristics examined explained the amount of variability in concentrations for nitrate (19.0%), atrazine (33.4%), and atrazine residue (28.6%). These results document that, although soils do affect the transport of agrichemicals to ground water, other factors such as hydrology, land use, and climate must also be considered to understand the occurrence of agrichemicals in ground water.

TRACER STUDIES OF SUBSURFACE FLOW PATTERNS IN A SANDY LOAM PROFILE

A study designed to provide a better understanding of the mechanisms of agrichemical transport togroundwater was conducted on a 0.81-ha agricultural corn field near Plains, Georgia. The objectives were to: (1)characterize vadose zone flow paths of water and agrichemicals under normal climatic and management conditions andevaluate their spatial and temporal variability; and (2) relate spatial and temporal transport patterns to geophysicalproperties of the soil and climatic conditions. Agrichemical transport was assessed over a five-year period from 1989 to1994 through analysis of collected soil and groundwater samples. A bromide (Br ) tracer was applied at 78 kg ha1 in1989 and at 105 kg ha1 in 1991. Chloride (Cl) and nitrogen were applied with fertilizer each year except 1994. Soilcharacterization tests indicated a dramatic decrease in the saturated hydraulic conductivity associated with a largeincrease in clay content in a zone from 1 to 4 m below the soil surface. As a result of this soil feature, Br concentrationsin the vadose zone below 4 m were normally less than 2 mg kg1 throughout the study. Aquifer chemical concentrationsindicated nitrate nitrogen (NO3 N) and Cl applied to the soil surface in the spring were transported to the groundwaterat 9 m by that same fall. Bromide concentrations in ground water peaked at 0.65 mg L1 while NO3 N concentrationspeaked at 6.9 mg L1 and Cl at 4.0 mg L1. Agrichemical transport and variability were controlled by climatic patternsand soil hydraulic characteristics. Transport to groundwater increased when precipitation and irrigation volumes in thefirst 30 days after spring fertilization and planting exceeded twice the normal precipitation. If large spring thunderstormsoccur soon after chemical application, the likelihood of groundwater contamination by agrichemicals is substantiallyincreased. These data provide the means to relate transport of agrichemicals in and through the vadose zone togeophysical characteristics and irrigation and precipitation inputs.

Transport of Agrichemicals to Ground and Surface Water in a Small Central Indiana Watershed

AbstractThe occurrence, distribution, concentrations, and pathways of agrichemicals in water were investigated in the Sugar Creek watershed, a poorly drained agricultural watershed typical of many watersheds in the midwestern USA. Water samples from Sugar Creek, two tile drains, and 11 wells along a groundwater flowpath to Sugar Creek were collected between May 1992 and August 1996 and analyzed for N and pesticide compounds. Nitrate was the principal N species and pesticides were common in alluvial water‐bearing units in the Sugar Creek floodplain. In the confined stratified drift aquifers, ammonia was the principal N species and pesticides were rare. Tile drains directly affected the water quality in Sugar Creek by transporting soil pore water and shallow groundwater containing high concentrations of nitrate (NO3) and pesticides to the creek. When tile drains were flowing (typically December through July), elevated NO3 concentrations (2–10 mg/L NO3N) in the creek correlated with high NO3 concentrations (2–23 mg/L NO3N) in tile drains discharging to the creek. Likewise, with concentrations of atrazine and atrazine metabolites, seasonal trends in the tile‐drain effluent were similar to seasonal trends in Sugar Creek. When tile drains went dry, NO3 concentrations in the creek were low, indicating most groundwater discharge to the creek consisted of old or denitrified water. Trace levels of pesticides in the creek at low flow probably were the result of seepage from alluvial water‐bearing units.

Solute Transport in Seasonal Perched Water Tables in Loess‐Derived Soilscapes

AbstractHydraulically restrictive fragipans and argillic horizons are a common feature of loessial soils in the Palouse region of northern Idaho, resulting in perched water development during the winter and early spring. The high relief of the region may result in lateral flow of perched water and solutes. This study was initiated to quantify the rates of solute movement through perched water at three sites receiving 610, 700, and 830 mm of annual precipitation. Three transects, perpendicular to slope contours, consisting of seven, nine, and seven sampling wells, were installed at each site. Five kilograms of KBr tracer were applied in a trench upslope from the transects. Water samples were drawn biweekly to test for Br‐. Rate of Br‐ movement and saturated hydraulic conductivity (Ksat) of soil horizons were used to quantify flow of perched water. Results indicate that maximum observed Br‐ transport decreased with annual precipitation and was 86, 50, and 35 cm d‐1 at the 830, 700, and 610‐mm sites, respectively. Depth profiles for Ksat are similar among sites; values range from 63 to 129 cm d‐1 in the Ap horizons and decrease with depth to 0.10 to 0.21 cm d‐1 in the restrictive horizons. The E horizons immediately above the argillic‐fragipan horizons have Ksat values from 1.2 to 5.2 cm d‐1 suggesting that much of the rapid solute transport via perched water tables occurs in the more permeable horizons overlying the E horizons. Our results demonstrate that perched water flow through these landscapes may enhance agrichemical transport, thereby impacting both nutrient‐use efficiency and local water quality.

SIZE OF POINTERS FOR RESIDUE COVER MEASUREMENT

Comprehensive models for agrichemical transport necessarily include runoff predictions to partition rainfallbetween infiltration and runoff, as this ability is fundamental to predictions of chemical runoff and leaching. We compared GLEAMS, Opus, and PRZM-2 model runoff predictions with runoff measured in a precisely controlled field site used for chemical runoff studies. In 1992 and 1993, two 14.5 m 42.9 m corn (Zea mays, L.) field plots with 3% slope on Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) received six severe, artificial rainfall events over the growing season with each event consisting of a 25 mm hC1 rainfall for 2 h. Runoff was monitored continuously using a collector and flume. Model performance criteria included sensitivity analysis, graphical comparison and statistical analysis including mean, ratio of means, root mean square error (RMSE), and a paired difference t-test. Observed runoff averaged 20% of added rainfall. Lowest values occurred with freshly plowed soil or full canopy cover, while 24 to 34% runoff occurred when nearly bare soils had crusted over. Using an initial moisture condition-II curve number (CN) of 85, GLEAMS and Opus predicted runoff within 10%, overall, and produced a pattern of high and low runoff that closely followed observed. PRZM-2 overpredicted runoff by 90%, overall, and predicted its highest runoff when observed runoffwas lowest. Paired difference t-tests indicated a significant difference between measured and predicted runoff for PRZM-2 (p<0.001 at = 0.05), but none for GLEAMS (p = 0.761) or Opus (p = 0.194). Mean, ratio of means, and RMSE showed that GLEAMS and Opus performed better than PRZM-2. All three models were very sensitive to CN values which were empirical and subjective, but less sensitive to measurable soil physical properties. With careful parameterization, GLEAMS and Opus could be used to simulate runoff from similar row-crop and soil conditions.

GLEAMS*, OPUS, AND PRZM-2 MODEL PREDICTED VERSUS MEASURED RUNOFF FROM A COASTAL PLAIN LOAMY SAND

Comprehensive models for agrichemical transport necessarily include runoff predictions to partition rainfallbetween infiltration and runoff, as this ability is fundamental to predictions of chemical runoff and leaching. We compared GLEAMS, Opus, and PRZM-2 model runoff predictions with runoff measured in a precisely controlled field site used for chemical runoff studies. In 1992 and 1993, two 14.5 m 42.9 m corn (Zea mays, L.) field plots with 3% slope on Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudult) received six severe, artificial rainfall events over the growing season with each event consisting of a 25 mm hC1 rainfall for 2 h. Runoff was monitored continuously using a collector and flume. Model performance criteria included sensitivity analysis, graphical comparison and statistical analysis including mean, ratio of means, root mean square error (RMSE), and a paired difference t-test. Observed runoff averaged 20% of added rainfall. Lowest values occurred with freshly plowed soil or full canopy cover, while 24 to 34% runoff occurred when nearly bare soils had crusted over. Using an initial moisture condition-II curve number (CN) of 85, GLEAMS and Opus predicted runoff within 10%, overall, and produced a pattern of high and low runoff that closely followed observed. PRZM-2 overpredicted runoff by 90%, overall, and predicted its highest runoff when observed runoffwas lowest. Paired difference t-tests indicated a significant difference between measured and predicted runoff for PRZM-2 (p<0.001 at = 0.05), but none for GLEAMS (p = 0.761) or Opus (p = 0.194). Mean, ratio of means, and RMSE showed that GLEAMS and Opus performed better than PRZM-2. All three models were very sensitive to CN values which were empirical and subjective, but less sensitive to measurable soil physical properties. With careful parameterization, GLEAMS and Opus could be used to simulate runoff from similar row-crop and soil conditions.

Observed and Simulated Transport of a Conservative Tracer under Line‐Source Irrigation

AbstractAlthough a number of solute transport models are currently available to predict the transport of agrichemicals in the vadose zone, validation of these models under field conditions has been limited. This study monitored the transport of a conservative tracer (Br−) under three water regimes (high, medium, and low) imposed by a line‐source irrigation system and tested the validity of the simulation model, LEACHM, to predict Br− transport. In July 1990, RbBr was surface applied to 12 uncropped columns at 56 kg Br− ha−1. Four columns (0.203‐m diam., 1.2‐m length) were positioned in each water regime and equipped with soil solution samplers at 0.36‐, 0.66‐, and 0.96‐m depths. Soil solution samples were taken 20 times over 80 d to monitor Br− transport. Cumulative water applied to each water regime, by irrigation and precipitation, ranged between 251 and 458 mm. Results indicated dramatic differences in Br− transport among water regimes. Complete Br− breakthrough curves (with apex concentrations of approximately 60 mg Br− L−1) were observed under high water regime at all depths whereas the majority of Br− applied to the low water regime remained at or near the 0.36‐m depth. Inputs used to predict Br− transport in LEACHM simulations were either measured directly or estimated from experimental conditions. To simulate Br− transport for each water regime, we used three LEACHM input files, which reflected the variability of the soil profile water release retention coefficients. Results indicated that LEACHM's predictions of Br− concentration (at all depths and under all water regimes) differed from observed means by an average (n = 180) of 9.0 to 9.4 mg Br− L−1 (approximately 15–16% of the average apex concentrations). These results indicate that under the experimental system studied, LEACHM adequately predicted the transport of a conservative tracer in the vadose zone.

Device for Collecting Large-diameter, Undisturbed Soil Cores

Soil columns are used in research to characterize agrichemical transport and fate. The purpose of this project was to design, fabricate, and test a free-standing, light-weight, easy-to-operate, and low-cost device for collecting undisturbed, large-diameter soil cores for use in column studies. The design uses hydraulic power to insert hollow sample cylinders into the soil profile. The device provides a reliable and relatively quick sampling process with minimal labor requirements, and employs a precision hydraulic control circuit which allows the operator to regulate the insertion process to minimize compressional disturbances of the sample. Helical earth anchors, installed hydraulically, are used to stabilize the frame during the insertion process.