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Copenhagen, Denmark

Nielsen M.H.,Copenhagen University | Styczen M.,Copenhagen University | Ernstsen V.,Dep. of Geochemistry | Petersen C.T.,Copenhagen University | Hansen S.,Copenhagen University
Vadose Zone Journal | Year: 2011

Transport and retention of colloids are important issues when addressing the risk of contamination of the aquatic environment. A field study tracer experiment was performed allowing a quantification of solutes and colloids along macropores in a sandy loam soil with a tile drain located at 1.2 m depth. Using a field sprayer, a 6-m 2 plot was irrigated with 50 mm of water containing a mixture of 1-μm imfluorescent microspheres (1.34 x 10 10 melamine-resin microspheres [MS] L -1), bromide (0.14 g Br L -1), and the dye Brilliant Blue (2.2 g BB L -1) during a 4-h period. Before irrigation, the groundwater table was more than 0.7 m below drain depth. The tracer concentrations were measured in drain water and in soil collected along 15 stained preferential flow paths located in the drain trench and the adjacent till. It was found that the tracer concentration along biopores do not necessarily reflect the concentration of tracers transported through the biopore. Furthermore, it was recognized that at drain depth the proportion of soil samples from the drain trench with concentrations of Br and MS greater than two times the detection limit was significantly higher than in samples from the till. This implies that substances can accumulate along the drain pipe during heavy precipitation events. Finally, water transported through a few biopores well connected to the drain pipe resulted in drainage. Compared with the concentrations in the added tracer solution, the sampled drain water showed undiluted concentrations of BB and Br, whereas MS was reduced 150 times. © Soil Science Society of America.

Nielsen M.H.,Copenhagen University | Styczen M.,Copenhagen University | Ernstsen V.,Dep. of Geochemistry | Petersen C.T.,Dep. of Geochemistry | Hansen S.,Dep. of Geochemistry
Vadose Zone Journal | Year: 2010

This study examined the number, distribution, and connectivity of biopores (>1 mm) in a sandy loam till with tile drains located at 1.2-m depth. Two areas (6.5 by 1 m, 10 m apart) were irrigated within 6 to 8 h with 50 mm of water containing the dye Brilliant Blue (2.2 g L-1using a field sprayer. Groundwater was initially below drain depth. The distribution of stained and unstained biopores was examined in 15- and 30-cm-wide horizontal terraces in 0.5-m-long sections along the 6.5-m irrigated transect at up to eight depths (15-175 cm), for a total investigated area of 14 m 2. This extensive data set showed that the number of biopores were of similar magnitude at both study sites in and outside the drain trench, ranging from 0 to 1114 m -2 in the 14-m 2 examined section. The number of stained biopores (0-833 m -2) was unevenly distributed in the horizontal direction and seemed unaffected by distance to the drain trench (0-5.5 m), while in vertical sections with numerous dyed biopores at 150-cm depth, staining continued farther down in fractures. Staining in the drain trench was associated with biopores, voids, fractures, and the soil along the pipe, which may indicate that the tile drain took over the role of fractures in the till. Consequently, the connectivity of biopores with fractures or drains may have an important impact on staining patterns and on preferential flow phenomena. © Soil Science Society of America.

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