M. T. Moore

Transport and fate of atrazine and lambda-cyhalothrin in an agricultural drainage ditch in the Mississippi Delta, USA

Drainage ditches are integral components of agricultural production landscape, yet their contaminant mitigation capacity has been scarcely examined. If ditches are indeed capable of contaminant mitigation, then their use may serve as an alternative agricultural best management practice (BMP). A 50 m portion of an agricultural drainage ditch, located in the Mississippi Delta Management Systems Evaluation Area (MDMSEA), USA, was amended with a mixture of water, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) (herbicide) and lambda-cyhalothrin (-cyano-3-phenoxybenzyl-3-(2chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethyl cyclopropanecarboxylate) (insecticide), simulating a storm runoff event. Pesticide amendment was achieved using a diffuser to disperse the mixture at an inflow point along the ditch (designated as “0 m”). Pesticide concentrations in water, sediment, and plants were monitored for 28 days. One hour following initiation of simulated runoff, mean percentages of atrazine concentrations measured in water and sediment were 37 and 2%, respectively, while mean percentages of lambda-cyhalothrin concentrations in water and sediment were 12 and 1%, respectively. Atrazine and lambda-cyhalothrin mean percentage concentrations in plants (Polygonum(water smartweed), Leersia(cutgrass), and Sporobolus (smutgrass)) were 61 and 87%, respectively. Therefore, plants serve as an important site for pesticide sorption during runoff events. Aqueous concentrations of both pesticides decreased to levels which would not elicit non-target toxicological effects by the end of the 50 m portion of the drainage ditch. This research provides fundamental answers concerning the capability of vegetated agricultural drainage ditches to mitigate pesticide-associated storm water runoff. Published by Elsevier Science B.V.

Constructed wetlands for mitigation of atrazine-associated agricultural runoff

Atrazine was amended into constructed wetlands (59-73x14x0.3 m) for the purpose of monitoring transport and fate of the pesticide to obtain information necessary to provide future design parameters for constructed wetlands mitigation of agricultural runoff. Following pesticide amendment, a simulated storm and runoff event equal to three volume additions was imposed on each wetland. Targeted atrazine concentrations were 0 microg/l (unamended control), 73 microg/l, and 147 microg/l. Water, sediment, and plant samples were collected weekly for 35 days from transects longitudinally distributed throughout each wetland and were analyzed for atrazine using gas chromatography. Between 17 and 42% of measured atrazine mass was within the first 30-36 m of wetlands. Atrazine was below detection limits (0.05 microg/kg) in all sediment and plant samples collected throughout the duration of this study. Aqueous half lives ranged from 16 to 48 days. According to these data, conservative buffer travel distances of 100-280 m would be necessary for effective runoff mitigation.

Nutrient mitigation capacity in Mississippi Delta, USA drainage ditches

Eutrophication and hypoxia within aquatic systems are a serious international concern. Various management practices have been proposed to help alleviate nutrient loads transported to the Gulf of Mexico and other high-profile aquatic systems. The current study examined the nutrient mitigation capacity of a vegetated (V) and non-vegetated (NV) agricultural drainage ditch of similar size and landform in the Mississippi Delta. While no statistically significant differences in ammonium, nitrate, or dissolved inorganic phosphorus mitigation between the two ditches existed, there were significant differences in total inorganic phosphorus percent load reductions (V: 36% +/- 4; NV: 71% +/- 4). However, both agricultural drainage ditches were able to mitigate nutrients, thus reducing the load reaching downstream aquatic receiving systems. Further studies examining ecosystem dynamics within drainage ditches such as sediment and plant nutrient partitioning, as well as microbial processes involved, are needed to provide a better understanding of natural nutrient variability, seasonality and flux.

Agricultural Drainage Ditches Mitigate Phosphorus Loads as a Function of Hydrological Variability

Phosphorus (P) loading from nonpoint sources, such as agricultural landscapes, contributes to downstream aquatic ecosystem degradation. Specifically, within the Mississippi watershed, enriched runoff contributions have far-reaching consequences for coastal water eutrophication and Gulf of Mexico hypoxia. Through storm events, the P mitigation capacity of agricultural drainage ditches under no-till cotton was determined for natural and variable rainfall conditions in north Mississippi. Over 2 yr, two experimental ditches were sampled monthly for total inorganic P concentrations in baseflow and on an event-driven basis for stormflows. Phosphorus concentrations, Mannings equations with a range of roughness coefficients for changes in vegetative densities within the ditches, and discharge volumes from Natural Resources Conservation Service dimensionless hydrographs combined to determine ranges in maximum and outflow storm P loads from the farms. Baseflow regressions and percentage reductions with P concentrations illustrated that the ditches alternated between being a sink and source for dissolved inorganic P and particulate P concentrations throughout the year. Storm event loads resulted in 5.5% of the annual applied fertilizer to be transported into the drainage ditches. The ditches annually reduced 43.92 +/- 3.12% of the maximum inorganic effluent P load before receiving waters. Agricultural drainage ditches exhibited a fair potential for P mitigation and thus warrant future work on controlled drainage to improve mitigation capacity.

Mitigation assessment of vegetated drainage ditches for collecting irrigation runoff in California.

Widespread contamination of California water bodies by the organophosphate insecticides diazinon and chlorpyrifos is well documented. While their usage has decreased over the last few years, a concomitant increase in pyrethroid usage (e.g., permethrin) (replacement insecticides) has occurred. Vegetated agricultural drainage ditches (VADD) have been proposed as a potential economical and environmentally efficient management practice to mitigate the effects of pesticides in irrigation and storm runoff. Three ditches were constructed in Yolo County, California for a field trial. A U-shaped vegetated ditch, a V-shaped vegetated ditch, and a V-shaped unvegetated ditch were each amended for 8 h with a mixture of diazinon, permethrin, and suspended sediment simulating an irrigation runoff event. Water, sediment, and plant samples were collected spatially and temporally and analyzed for diazinon and permethrin concentrations. Pesticide half-lives were similar between ditches and pesticides, ranging from 2.4 to 6.4 h. Differences in half-distances (distance required to reduce initial pesticide concentration by 50%) among pesticides and ditches were present, indicating importance of vegetation in mitigation. Cis-permethrin half-distances in V ditches ranged from 22 m (V-vegetated) to 50 m (V-unvegetated). Half-distances for trans-permethrin were similar, ranging from 21 m (V-vegetated) to 55 m (V-unvegetated). Diazinon half-distances demonstrated the greatest differences (55 m for V-vegetated and 158 m for V-unvegetated). Such economical and environmentally successful management practices will offer farmers, ranchers, and landowners a viable alternative to more conventional (and sometimes expensive) practices.

Mitigation of metolachlor-associated agricultural runoff using constructed wetlands in Mississippi, USA☆

Abstract A loss of marginal wetland acreage adjoining agricultural fields has created a potential problem with water quality enhancement of agricultural runoff via wetlands. Current research is investigating the utility of constructed wetlands for pesticide mitigation purposes, thereby restoring water quality enhancement capability to the area. Constructed wetland mesocosms (59–73xa0m×14xa0m), located at the University of Mississippi Field Station (Lafayette County, MS), were amended with metolachlor to simulate a cropland runoff event. Target concentrations for wetlands were 73 and 147xa0μg/l metolachlor in addition to an unamended control (0xa0μg/l). Water, sediment, and plant samples were collected weekly for 35 days following metolachlor amendment. Samples were collected from sites, longitudinally distributed within each wetland, and analyzed for metolachlor using gas chromatography. Between 7 and 25% of measured metolachlor mass was in the first 30–36xa0m (from inflow) of wetlands immediately following application and simulated rainfall. Approximately 10% of measured metolachlor mass was in plant samples. Suggested wetland travel distances for effective mitigation of metolachlor runoff ranged from 100 to 400xa0m. According to the results from this research, aquatic receiving system impacts due to metolachlor runoff could be mitigated by using constructed wetlands as buffers. Landowners and government agencies can integrate this information into a water management plan, allowing for better control of both quantity and quality of runoff water from individual agricultural fields.

Mitigation of two pyrethroid insecticides in a Mississippi Delta constructed wetland

Constructed wetlands are a suggested best management practice to help mitigate agricultural runoff before entering receiving aquatic ecosystems. A constructed wetland system (180 m x 30 m), comprising a sediment retention basin and two treatment cells, was used to determine the fate and transport of simulated runoff containing the pyrethroid insecticides lambda-cyhalothrin and cyfluthrin, as well as suspended sediment. Wetland water, sediment, and plant samples were collected spatially and temporally over 55 d. Results showed 49 and 76% of the studys measured lambda-cyhalothrin and cyfluthrin masses were associated with vegetation, respectively. Based on conservative effects concentrations for invertebrates and regression analyses of maximum observed wetland aqueous concentrations, a wetland length of 215 m x 30 m width would be required to adequately mitigate 1% pesticide runoff from a 14 ha contributing area. Results of this experiment can be used to model future design specifications for constructed wetland mitigation of pyrethroid insecticides.

Effect of Three Insecticides and Two Herbicides on Rice (Oryza sativa) Seedling Germination and Growth

Rice (Oryza sativa L.) is one of the most important food crops worldwide. However, it is also a valuable tool in assessing toxicity of organic and inorganic compounds. For more than 20xa0years, it has been an approved species for standardized phytotoxicity experiments. The objective of this study is to determine germination and radicle (root) and coleoptile (shoot) growth of rice seeds exposed to three insecticides and two herbicides, commonly used in the agricultural production landscape. Although no germination effects of pesticide exposure were observed, significant growth effects were noted between pesticide treatments. Coleoptile growth was significantly (pxa0≤xa00.05) lowered in metolachlor/atrazine mixture, diazinon, and lambda-cyhalothrin exposures when compared with controls. Radicles of fipronil-exposed seeds were significantly larger (pxa0≤xa00.05) when compared with controls. This research contributes to the phytotoxicity assessment database, in addition to laying the foundation for the use of rice as a phytoremediation tool for agricultural pesticide runoff.

Ability of Four Emergent Macrophytes to Remediate Permethrin in Mesocosm Experiments

Increased focus is being placed on the ability of native vegetation to mitigate potential harmful effects of agricultural runoff, especially pyrethroid insecticides. Replicate 379xa0L Rubbermaid tubs (1.25xa0m [l]xa0×xa00.6xa0m [w]xa0×xa00.8xa0m [h]) were planted with individual species of cutgrass (Leersia oryzoides), cattails (Typha latifolia), bur-reed (Sparganium americanum), and powdery alligator-flag (Thalia dealbata), all common wetland macrophytes found in the Mississippi Delta, USA, agricultural region. Permethrin-enriched water (target concentration, 5xa0μg L−1) was pumped in at a 4-h hydraulic retention time at one end of the tub and discharged at the far end. Water samples were collected from discharge at 1-h intervals for 12xa0h and analyzed for permethrin concentrations. Permethrin removal rates were compared for the four different plant treatments and nonvegetated sediment-water controls. Results indicated that no particular single plant species was more effective at removing permethrin in water relative to unplanted controls. Overall mass reductions (from inflow to outflow) for cis-permethrin ranged from 67%xa0±xa06% in T. latifolia to 71%xa0±xa02% in L. oryzoides. The trans-permethrin overall mass reductions ranged from 76%xa0±xa04% in S. americanum to 82%xa0±xa02% in the unplanted control. Sediment and plant samples collected at the study conclusion indicated that 77%–95% of measured permethrin mass was associated with sediment for mesocosms planted with L. oryzoides, T. latifolia, and T. dealbata. Conversely, mesocosms planted with S. americanum had 83% of measured mass associated with the plant material. Specific plant-pesticide retention studies can lead to improved planning for best management practices and remediation techniques such as constructed wetlands and vegetated agricultural drainage ditches.

Contrasting Nutrient Mitigation and Denitrification Potential of Agricultural Drainage Environments with Different Emergent Aquatic Macrophytes.

Remediation of excess nitrogen (N) in agricultural runoff can be enhanced by establishing wetland vegetation, but the role of denitrification in N removal is not well understood in drainage ditches. We quantified differences in N retention during experimental runoff events followed by stagnant periods in mesocosms planted in three different vegetation treatments: unvegetated, cutgrass [ (L.) Sw.], and common cattail ( L.). We also quantified denitrification rates using membrane inlet mass spectrometry from intact cores extracted from each mesocosm treatment. All treatments retained 60% or more of NO-N loads during the 6-h experimental runoff event, but mesocosms planted with cutgrass had significantly higher (68%) retention than the cattail (60%) or unvegetated (61%) treatments. After the runoff event, mesocosms planted in cattail reduced NO-N concentrations by >95% within 24 h and cutgrass achieved similar reductions within 48 h, whereas reductions in the unvegetated mesocosms were significantly less (65%). Cores from cutgrass mesocosms had significantly higher average denitrification rates (5.93 mg m h), accounting for as much as 56% of the immobilized NO-N within 48 h, whereas denitrification rates were minimal in cores from the unvegetated (-0.19 mg m h) and cattail (0.2 mg m h) mesocosms. Our findings have implications for mitigating excess NO-N in agricultural runoff. While vegetated treatments removed excess NO-N from the water column at similar and significantly higher rates than unvegetated treatments, the high denitrification rates observed for cutgrass highlight the potential for permanent removal of excess N from agricultural runoff in vegetated ditches and wetlands.