Graduate Thesis Or Dissertation
 

WarrenKristina2003.pdf

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/7h149s228

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  • Tile drainage increases aeration in the root zone of poorly drained soils by accelerating water movement from the subsurface. Water movement is the main agent of chemical transport, either transporting soluble materials directly (e.g., nitrate) or by transporting the soil particles that bind adsorptive compounds (e.g., pesticides). The detection frequency of field-applied chemicals in surface water and groundwater near agricultural lands prompts the study of chemical fate on tile-drained fields. Tile effluent was monitored on four Willamette Valley fields from October 2000- May 2002. All fields were planted in perennial grass seed, except corn was planted in one field in 2000, and in another field in 1999. Field areas were 30, 20, 2.86, and 2.86 acres. At the outlet of each tile system, effluent flux was monitored and samples were frequently collected for analysis of nitrate, tracer, and selected pesticides. A transect of piezometers was installed to monitor water table dynamics. Field-scale saturated hydraulic conductivity (Ks) was estimated by inputting tile flux data into the Polubarinova-Kochina solution to the Boussinesq equation for tile drains, and these values were compared to core-scale K values for each field. Two fields had a peak drainage rate of over 25 mm day⁻¹. Because of the rapid tile response, the water table never reached within 0.5 m of the soil surface, and dropped below the depth of the tiles (about 1 m) within a day, causing tile flow to be intermittent. The tile drains on these two fields intercepted 4% and 10% of the precipitation. The two other fields had slower drainage (5-9 mm day⁻¹) and tile-drained 28% and 33% of the precipitation. The water table reached within 10 cm of the soil surface and took 7-14 days to drop below the level of the tile drains. Flow-weighted average nitrate concentrations ranged from 1 mg NO₃-N L⁻¹ on the well-established tall fescue field to 14 mg NO₃-N L⁻¹ on the first-year tall fescue field that had been in corn the previous year. Mass losses ranged from 1-6.7% of applied nitrate. Concentrations peaked during periods of low flow, while mass losses peaked during high-flow periods. Diuron, metolachior, and chlorpyrifos losses through the tile lines were less than 0.25% of that applied pesticide, and never exceeded EPA drinking water advisory limits. Concentrations of metolachior and chlorpyrifos were similar in tile effluent and surface runoff. The highly adsorptive pesticide diuron lost 3% of the applied mass through surface runoff and exceeded EPA drinking water advisory limits for diuron for three months. Average soil core and field-scale K values on each field were within a factor of two. The soil core data varied over several orders of magnitude, and the model data varied over one order of magnitude for each field. A tracer study verified that preferential flow accounts for less than 0.5% of solute transport to tile drains. On perennial grass seed fields in the Willamette Valley, the loss of highly adsorptive pesticides through surface runoff may be the greatest environmental concern. By reducing surface runoff, tile drains could improve surface water quality in the Willamette Valley. Tiles could also be diverting nitrate from groundwater, and delivering it to surface water during peak flow periods when it is most diluted. Because the water table dropped slowly and nitrate losses followed EPA standards after the first year of grass stand establishment, Water Table Management (WTM) is not advised at this time.
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file details WarrenKristina2003.pdf 2017-08-08 Öffentlich Herunterladen