Monday, 7 November 2005
17

Lateral Transport of Solutes through the Capillary Fringe: Field Evaluation.

Sergio M. Abit Jr., Aziz Amoozegar, Michael Vepraskas, and Christopher Niewoehner. Department of Soil Science, North Carolina State University, College of Agriculture and Life Sciences, Campus Box 7619, Raleigh, NC 27695-7619

Contrary to the common assumption that water and solutes applied to soil predominantly move downward in the vadose zone, laboratory studies have shown that transport of solute through the capillary fringe (CF) above a water table generally occurs in the horizontal direction. This study was conducted to: a) characterize the transport of chemicals in the CF and shallow groundwater (SGW) in a sandy soil, and b) to evaluate rainfall and water table fluctuation effects on subsurface lateral migration of solutes in the CF and SGW. The study was conducted at Juniper Bay, a Carolina Bay, in Robeson Co., NC in soils of the Leon series (Aeric Alaquods). Ten liters of a solution containing 75 mM potassium bromide and 75 mM magnesium nitrate were applied to the bottom of an auger hole that was dug to within 15 cm of the projected CF. Nests of tension samplers, installed at 0.45, 0.60, 0.75, 0.90 and 1.05 m below the soil surface at distances of 0.6, 1.2, 2.2 and 3.2 m from the auger hole were used to extract soil solution or ground water samples twice weekly for 84 days. Samples were analyzed for bromide (Br) and nitrate concentration. The tracer solutes stayed in the CF until enough percolation arising from rain events partially leached it below the water table. Nitrates were observed to retain its chemical integrity while moving horizontally along with Br in the CF. When pushed into the SGW, relative nitrate concentrations had been significantly reduced.

Handout (.pdf format, 99.0 kb)

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