Vegetated Treatment Systems for Removing Contaminants Associated with Surface Water Toxicity in Agriculture and Urban Runoff

The overall goal of these procedures is to combine chemical analysis with freshwater invertebrate toxicity tests to evaluate how well vegetated treatment systems remove current-use pesticides from urban storm water, and agriculture irrigation runoff. This approach is intended to answer whether standard remediation practices are effective at protecting surface water quality from contaminants. And to determine the appropriate monitoring components for evaluating effectiveness of management practices.

The main advantage of these procedures is that they couple toxicity test protocols with chemical monitoring of in-field remediation techniques, designed to reduce loading of pesticides in surface waters. Bryn Phillips and Michael Cahn will demonstrate components of an integrated vegetated treatment system, designed to remove pesticides and other contaminants from agricultural runoff. Jennifer Voorhees will demonstrate three toxicity test protocols, used to monitor the treatment system.

The vegetated drainage ditch, used in the current example, is 152 meters long, and has a semi V-shaped cross-section width of five meters at the top, and one meter depth. The ditch vegetation is a combination of native grass species, primarily seeded with red fescue. The vegetated ditch is augmented with compost filters and carbon filters.

Filters are constructed from tubular mesh sleeves that are two meters long and twenty centimeters in diameter. Fill each carbon sleeve with 30 liters of granulated, activated carbon. And fill each compost sleeve with 15 kilograms each of partially decomposed yard waste from any clean source, such as a local landfill.

Install the filters in different sections of the vegetated ditch, as displayed in the text protocol. Anchor the sleeves to the ditch bottom with wire stakes on the upstream edge. Then, place a 2.5 meter long, six inch wide, section of pine board on the downstream edge of each of the sleeves.

Dig the pine boards into the two sides, and bottom of the channel, to minimize water bypassing and undercutting the carbon sleeves. The boards will also provide vertical support to maximize the water contact time with the carbon. The efficacy of the integrated ditch system can be tested by creating simulated agricultural runoff, using groundwater mixed with suspended sediment and spiked with a model pesticide.

Since neurotoxic pesticides, such as organophosphates, pyrethroids, and neonicotinoids, have recently been linked to surface water toxicity, treatment systems and monitoring programs should emphasize these pesticide classes. Monitor the inlet flow rate with a digital meter, and data logger. Use the data to quantify total volume of the runoff water applied to the ditch inlet.

Construct a weir at the outlet of the ditch, and plumb it with an outlet pipe connected to a digital flow meter and data logger. Program the data loggers to activate peristaltic pumps located at the inlet, and at various stations below the inlet of the ditch, to collect composite subsamples of runoff into stainless steel containers at five minute intervals. Transfer composite samples of runoff water from trials into amber glass bottles at the end of each runoff trial.

Maintain the samples on ice at four degrees Celsius for later toxicity and chemical analysis, as described in the text protocol. Due to time constraints, we have emphasized an integrated vegetated ditch for treating pesticides and agricultural runoff. The design and monitoring principles applied to this system also apply to urban storm water treatment using bioswales, as discussed in the manuscript.

Prepare composited inlet and outlet vegetated ditch water samples for conducting toxicity tests using three test species, following modified US Environmental Protection Agency acute and chronic test protocols. Prior to setting up exposures, measure the dissolved oxygen, PH, and conductivity of a subsample of each sample, using appropriate meters and electrodes. Also, measure unionized ammonia using a spectrophotometer.

Next, conduct acute 96 hour survival tests, with the cladoceran Ce.dubia. Expose five Ce.dubia neonates in each of five replicates of inlet and outlet stormwater samples. Replicates consist of 20 milliliter scintillation vials containing 15 milliliters of test solution.

Renew the Ce.dubia test daily by feeding neonates a mixture of yeast, Cerophyll, trout chow, and Selenastrum algae two hours prior to renewal. Then, transfer the organisms to a fresh sample. Record the total number of surviving neonates daily.

Also, conduct acute 10 day survival tests with the amphipod H.azteca. Expose 10 seven day-to 14 day-old amphipods to each of five replicates. Replicates consist of 300 milliliter glass beakers, containing 100 milliliters of test solution.

Count the number of surviving amphipods daily, and renew 50%of the test solution every 48 hours. Feed each beaker every 48 hours with 1.5 milliliters of YCT after the renewal. To conduct chronic 10 day survival and growth tests with the midge C.dilutus, expose 12 seven day-old animals in each of four replicates.

Replicates consist of 300 milliliter glass beakers, containing 200 milliliters of test solution, and five milliliters of sand, as the substrate for tube-building by the larvae. Renew 50%of the test solution every 48 hours. Feed each beaker daily with an increasing amount of fish food slurry, from four grams per liter of fish food slurry.

After counting the final survival of C.dilutus, measure the growth of the surviving organisms as ash-free dry weight. Compare final Ce.dubia survival after 96 hours of exposure to inlet and outlet vegetated ditch samples to their survival in moderately-hard control water, using a t-test. Use the same procedures to compare final survival of H.azteca, and the final survival and growth of C.Dilutus.

Representative results of the vegetated treatment of agriculture irrigation runoff, showed that this system is effective at reducing pesticide and toxicity. The average chlorpyrifos loading was reduced by 98%at a flow rate of 3.2, and by 94%at a flow rate of 6.3 liters per second. Toxicity was eliminated in two of the three trials at the lower flow rate, and one of the three trials at the higher flow rate.

Reductions of toxicity and pesticides and other contaminants were also observed in bioswale treatment of storm water. Pyrethroid pesticides were greatly reduced in storm water, and associated toxicity to the amphipod, H.azteca, was also reduced. Conversely, the concentration of fipronil sulfone was not reduced by bioswale treatment, and neither was toxicity to the midge, C.Dilutus.

Water quality regulators and researchers use aquatic toxicity testing to evaluate the capacity of surface waters to support aquatic life. Data generated through decades of monitoring in California has shown that most toxicity to invertebrates is caused by pesticides. Environmental regulators in California are implementing policies to reduce loading of pesticides from storm water, and agriculture runoff.

These include the promotion of treatment systems, designed to reduce loading of current-use pesticides from these sources. Visual demonstration of the toxicity test protocols should reinforce the concept that monitoring the efficacy of these treatment systems needs to use test species and protocols that are sensitive to current-use pesticides. We have shown that vegetated systems are a cost-effective solution for treating pesticides in agricultural runoff.

Addition of granulated, activated carbon to these systems has been shown to remove residual pesticides not removed by vegetation. Monitoring the effectiveness of these systems using targeted chemical analysis, and appropriate toxicity test protocols, will ensure that these practices are protecting aquatic ecosystems.