Arsenic Concentrations in Surface Runoff from Small Watersheds in Texas1
- C. W. Richardson,
- J. D. Price and
- Earl Burnett2
This study was conducted to determine the movement of arsenic by surface runoff after application of arsenic acid for desiccation of cotton (Gossypium hirsutum [L.]). Arsenic acid was applied at 6.6 kg/ha during the cotton year of a cotton-grain sorghum (Sorghum bicolor [L.])-oats (Avena sativa [L.]) rotation.
The concentration of arsenic dissolved in the runoff water was highest during the first runoff event after application and decreased during subsequent events. Arsenic concentrations in the first runoff after treatment ranged from 250 to 18 ppb, depending on time and tillage after application. Tillage that incorporated treated plant material into the soil reduced arsenic concentration in runoff water. After two or three runoff events, the arsenic concentration decreased to 10 to 20 ppb and remained essentially constant until the next application 3 years later.
The arsenic concentration of the sediment from the watersheds averaged 20 ppm and appeared to be related more to the arsenic content of the soil than to the length of time or the tillage between arsenic acid application and first runoff. Assuming average annual runoff and sediment yield, the amount of arsenic that would be transported from a watershed by runoff and erosion is about 7% of the amount applied. Part of the arsenic that moves from a watershed may be arsenic that occurs naturally in the soil. Of the total arsenic moved from a watershed, 38% would be in solution and 62% would be attached to the sediment.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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