Quantification of drain-connected macroporous flow pathways by smoke injection

TY - JOUR

T1 - Quantification of drain-connected macroporous flow pathways by smoke injection

AU - Petersen, Jens Carsten Tilbæk

AU - Nielsen, Marie Habekost

AU - Hansen, Søren

PY - 2012

Y1 - 2012

N2 - Macropores forming continuous pathways from the soil surface to subsurface drains favor the loss of many contaminants to surface waters. Few techniques are available to quantify such pathways at the fi eld scale. A previously introduced smoke injection technique remains to be tested and refi ned. Four times during the spring of 2010 we investigated the effects of injected air pressure, water table depth, and soil moisture on the number of smokeemitting macropores (SEMs) connected to 120-cm-deep tile drains established in 1965 in a sandy loam soil near Copenhagen, Denmark. The investigated technique worked, basically. Spatial distributions of SEMs were analyzed for two 35-m-long drain sections. The number of SEMs increased dramatically in 12 d when the water table dropped from about 0 cm to 20 to 50 cm below drain depth. Reproducible distributions were obtained with air pressures in the range 0.38 to 0.93 kPa, and with the water table 20 to 50 cm below drain depth. Between 65 and 96 SEMs were mapped along each drain section under such conditions, all (except three) being distributed within a 1.0-m band centered above the drain. The hypothesis that detected fl ow-active macropores were randomly distributed along the drains, i.e., that the macropores were distributed according to a Poisson process, was rejected in all cases (P > 0.05%). The observed uneven distribution of continuous macropores suggest that transport of many surface-applied contaminants to drainage could also be unevenly distributed along drain lines, and it calls for attention toward scale effects in studies on leaching losses to subsurface drains.

AB - Macropores forming continuous pathways from the soil surface to subsurface drains favor the loss of many contaminants to surface waters. Few techniques are available to quantify such pathways at the fi eld scale. A previously introduced smoke injection technique remains to be tested and refi ned. Four times during the spring of 2010 we investigated the effects of injected air pressure, water table depth, and soil moisture on the number of smokeemitting macropores (SEMs) connected to 120-cm-deep tile drains established in 1965 in a sandy loam soil near Copenhagen, Denmark. The investigated technique worked, basically. Spatial distributions of SEMs were analyzed for two 35-m-long drain sections. The number of SEMs increased dramatically in 12 d when the water table dropped from about 0 cm to 20 to 50 cm below drain depth. Reproducible distributions were obtained with air pressures in the range 0.38 to 0.93 kPa, and with the water table 20 to 50 cm below drain depth. Between 65 and 96 SEMs were mapped along each drain section under such conditions, all (except three) being distributed within a 1.0-m band centered above the drain. The hypothesis that detected fl ow-active macropores were randomly distributed along the drains, i.e., that the macropores were distributed according to a Poisson process, was rejected in all cases (P > 0.05%). The observed uneven distribution of continuous macropores suggest that transport of many surface-applied contaminants to drainage could also be unevenly distributed along drain lines, and it calls for attention toward scale effects in studies on leaching losses to subsurface drains.

U2 - 10.2136/sssaj2011.0163

DO - 10.2136/sssaj2011.0163

M3 - Journal article

SN - 0361-5995

VL - 76

SP - 331

EP - 341

JO - Soil Science Society of America Journal

JF - Soil Science Society of America Journal

IS - 2

ER -