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Field and Laboratory Setup to Determine Preferential Flow in Volcanic Soils
Authors: C.M. Regalado, R. Muñoz-Carpena, J. Álvarez-Benedí, A.R. Socorro, and J.M. Hernández-Moreno
Keywords: volcanic soils, hydrology, water capacity, water and solute transport, large undisturbed columns
Previous studies in the unsaturated zone of a terraced transported volcanic soil in the Canary Islands showed the presence of non-mobile (highly adsorbed and degradable) glyphosate, and its transformation product AMPA (aminomethylphosphonic acid), in the deeper soil layers (>60 cm depth). This provides evidence of a rapid by-pass flow in this kind of soils. In this paper we present the set-up used to study the preferential flow under these conditions. Firstly, a bimodal water capacity curve with two distinct water release regions (micro- and macropore) was detected in this kind of soils. Then we discuss the exchange-resin technique used in soil texture characterisation, in support of the bimodal capacity trend. Thirdly we describe field and laboratory work with large undisturbed soil columns (85 cm long x 50 cm diameter). These columns were instrumented under controlled laboratory conditions with TDR, digital tensiometers, soil solution extractors, and a controlled bottom boundary condition including drainage collection, to study the water flow and solute transport when a solution of a tracer is homogeneously applied to the top of the column. Finally a field set-up is described which consists on a 400x 100x 90 cm (LxWxD) trench within a greenhouse drip irrigated banana plantation monitoring the same experimental variables than in the laboratory scenario. Experimental factors related to the sampling of undisturbed soil monoliths and in situ monitoring of preferential flow are discussed. Textural characteristics (strong aggregation due to Fe-oxyhydroxides content), bimodal water capacity curves (which distinguish between a 0.2 mm macropore phase and a micropore region), and moisture content regime (drying and wetting spells which produces swelling and cracking) are proposed as responsible factors for preferential flow.(Download PDF) (Export to EndNotes)