Delta Center for Agricultural Water Quality

EPA Grant Number: EM832968
Center: Delta Center for Agricultural Water Quality
Center Director: Farris, Jerry L.
Title: Delta Center for Agricultural Water Quality
Investigators: Farris, Jerry L. , Bouldin, Jennifer L. , Phillips, Greg , Green, V.Steven
Institution: Arkansas State University - Main Campus
EPA Project Officer: Packard, Benjamin H
Project Period: June 15, 2006 through June 14, 2009
Project Amount: $193,400
RFA: Targeted Research Center (2004) Recipients Lists
Research Category: Targeted Research


Historic agricultural practices, increasing population, and economic activity present unique water use challenges within the Mississippi Delta Ecoregion. The improvement of scientific basis for the development, implementation, and evaluation of sustainable water use practices and the shift in supply and demand of such a valuable resource peaks policy as well as scientific interests. Surface water retention and reuse, and groundwater utilization demand an increasingly complex scientific basis for environmental decision-making that is not being met by current approaches. Scientific assessments, tool development, communication, and outreach provide a basis for water-use forecasting. The need exists to develop an effective forecasting network to help assess not only water-use requirements, but also to measure ecosystem risks associated with such changes in water management.

Arkansas State University has established research facilities with unique capabilities to address critical questions relating vegetated edge-of-field flow pathways to reduction of contaminants. These facilities provide easily accessible infrastructure, laboratory space, venues for information dissemination, and access to science-based decision making for researchers, as well as public demonstrations of innovative techniques. Such efforts seek to provide a better understanding and measurement of the efficiency of contaminant removal by constructed wetlands, vegetated ditches, and other low-cost management practices. While focusing on physical and biological responses, projects attempt to define system impairments attributable to agriculture and measure the positive effects of potential best management practices.

In this proposal, we describe projects that have been prioritized for the Center’s mission toward assessment and evaluation and which gain an increased likelihood of success as a result of the EPA’s interest and funding. The project objectives are: 1) Compare soil enzyme activities and soil C, N, and P at different depths in an agricultural ditch under constant wetting and periodic wet/dry cycles with and without exposure to herbicide; 2) Characterization of the fate and effect of chemical mixtures in agricultural receiving systems measuring toxicity from the edge of field through conveyance systems; and 3) Measurement of the uptake, movement, and fate of pesticides within aquatic macrophytes from these edge of field systems. Although there is an increasing reliance upon decision aid models to implement chemical management related to water runoff, very little information is available on residues and secondary products or interactions among these substances in aquatic systems under conditions of actual use. The project results will be utilized to identify system impairment within constructed wetlands and vegetated ditches and measure the effects of management practices in improving water quality.

  1. Compare soil enzyme activities and soil C, N, and P at different depths in an agricultural ditch under constant wetting and periodic wet/dry cycles with and without exposure to herbicide.
  2. Characterize the fate and effect of chemical mixtures in agricultural receiving systems measuring toxicity from the edge of field through conveyance systems.
  3. Measure the uptake, movement, and fate of pesticides within aquatic macrophytes from edge of field systems.


  1. To quantify the effect of wetting and pesticide dosage on soil enzyme activities of constructed wetlands and vegetated agricultural drainage ditches, soil samples will be taken from the profile side of the wetland and ditch at different levels below the field surface as well as at the bottom of each system. Samples will be also be taken along the longitudinal transect of the wetland/ditch to quantify the effect of the distance from water inflow to determine spatial distribution. Samples will be taken periodically during the growing season and soil enzyme activities will be measured according to Tabatabai (1994) and Green et al. (2006a) using biochemical assays and response measured on a spectrophotometer at enzyme specific wavelengths.
  2. Mesocosm studies will utilize eight 379-L Rubbermaid ® containers and sediment with overlying water and ditch vegetation will be planted in half of the containers. Mesocosms will equilibrate in a greenhouse environment for ~ 2 months. Vegetated mesocosms will be allowed to develop a mixed vegetative community. Pesticide treatments will be prepared at recommended field dose of atrazine as Aatrex® [2.23 kg active ingredient (a.i.)/hectare] and lambda -cyhalothrin as Karate® (0.028 kg a.i./hectare). Treatments will be introduced to overlying water to simulate a 0.64 cm precipitation event from a 2.03 ha contributing area. Four treatments will be introduced into vegetated and unvegetated mesocosms to include control (untreated, receiving no pesticide application and atrazine combined with lambda -cyhalothrin at the same application rates.

    Collections will include 0, 3, 8, 24 h, and 7, 14, 28 and 56 d for the following parameters: total sediment microbes by colony enumeration for fungi/yeast (Potato Dextrose Agar) and aerobic bacteria (R2A Agar) , s ediment redox potential utilizing in-place platinum electrodes according to Faulkner et al. (1989), sediment particle size composition according to Gee and Bauder (1986) , water quality parameters (water and sediment temp, pH, DO, alkalinity, hardness, conductivity, nitrate, nitrite, phosphorus as orthophosphate) will follow American Public Health Association (1998). Nitrate (NO 3 -) determinations will follow the cadmium reduction and diazotization method with a 0.01 mg/L detection limit. Nitrite (NO 2 -) determinations will follow the diazotization method with a 0.005 mg/L detection limit. Soluble reactive phosphorus (PO 4 3-) determinations will follow the ascorbic acid method with a 0.05 mg/L detection limit.

    Water, sediment, and plants will be composited from at least three areas of the mesocosm, and water samples will be extracted on site with ethyl acetate and KCl. Sediments will be collected from the upper three cm for toxicity and pesticide analyses, while plant tissue will be include composited tissue from vegetative community. Chemical analyses will be conducted on unfiltered water, sediments, and plants to determine pesticide concentrations as described by gas chromatograph equipped with a 30-m DB-1MS column. Forty-eight hour acute toxicity in aqueous samples will be assessed with Ceriodaphnia dubia and Pimphales promelas following methods outlined by US EPA (2002). Inhibition of Chironomus tentans survival and growth will be assessed in solid-phase 10-d sediment tests (US EPA, 2000).

  3. Pesticide treatments for hydroponic exposure will be calculated using the recommended field dose of atrazine in 250-mL flask. E xposure will occurred in a Conviron ® growth chamber (Model 8507) and sample collection will include each of the following: remaining pesticide solution, adsorbed, roots, and upper biomass. Sample collection will include three replicates at 8 h, 24 h, 48 h, 5 d and 8 d and will follow techniques provided by Bouldin et al. (in press) and Dayan et al. (1997). Isotope measurements will use a Beckman Coulter LS 6500 Scintillation System featuring a Motorola 68000 Series microprocessor and a 32,768 channel Multichannel analyzer.

Expected Results:

  1. Agricultural ditch and wetland systems differ in that ditches generally undergo wet/dry cycles while constructed wetlands usually remain wetted for longer periods of time. A better understanding of the wetting and drying effects on microbial activity, as measured by soil enzyme activities, will enable better prediction of the functioning of agricultural ditches and constructed wetlands to improve water quality of runoff.
  2. E cological testing of pesticide mixtures to predict effects to aquatic ecosystems receiving agricultural runoff includes the presence of pesticide combinations with differing modes of toxic action, recently described in literature as across-class mixtures, and result in varying toxic responses challenging their predictability (Lydy et al, 2004). This field investigation will enhance the understanding of the transformation of pesticide mixtures within agricultural receiving systems as well as the benefits of resident vegetative communities.
  3. The distinction between macrophyte degradation and remediation through associated pathways (e.g. rhizodegradation) will aid in the optimization of vegetated receiving systems to alleviate agricultural runoff. Hydroponic exposures to commonly used pesticides will investigate these individual pathways and enable a better understanding of the phytoremediation capabilities of constructed wetlands and agricultural ditches.

Supplemental Keywords:

water management, ecosystem risks, ecosystem optimization, conveyance structures, conditions of actual use,

Progress and Final Reports:

  • 2006
  • 2007
  • Final