Impacts of freeze-thaw cycles on runoff and sediment yield of slope land

Abstract

Although freeze-thaw cycles can alter soil physical properties and microbial activity, their overall impact on soil functioning remains unclear. Soil experiencing freeze-thaw is more vulnerable to become erosion material source of erosion, thereby increasing the severity of a variety of soil erosion. In order to reveal the influence of freeze-thaw effects on soil erosion by water, in this paper we quantitatively tested the hypothesis that soil freeze-thaw processes significantly increase the potential for soil erosion by water during rainfall-runoff events. The freeze-thaw cycles detection system and simulated rainfall equipment were used for the experiment. Control test was designed as an unfrozen soil with air-dried. The experimental design involved four simulated rainfall intensities (25, 50, 75 and 100 mm/h), two freeze-thaw cycles (FTC=3 and 6) and two kinds of soil moisture mass fraction (10% and 20%) on four 0.5-m-long, 0.2-m-wide, and 0.1-m-deep soil boxes set at 5% slope. Experiments were conducted at the USDA-ARS National Soil Erosion Research Lab. Surface soil (0-10 cm) materials from a Crosby-Miami complex alfisol with 20% clay, 66% silt and 14% sand from the Purdue Animal Science Research and Education Center in West Lafayette, Indiana. The test soil was air-dried, crushed and passed through an 8-mm sieve, and then experienced the designed freeze-thaw pattern. A 100-min continuous rainstorm was applied. The storm consisted of four intensity sequences: 50 mm/h for 60 min, 25 mm/h for 20 min, 75 mm/h for 10 min and 100 mm/h for 10 min. Runoff samples were collected in 1-L HDPE bottles every 5 min during the two lower intensity rains and every 3 min during the two higher intensity rains. Time to fill the runoff bottle was recorded. After each run, the sample bottles were weighed immediately to obtain the runoff rate. Approximately 5 mL of saturated alum solution was added to the sample bottles to flocculate the suspended sediment. After settling overnight, the excess water was poured off the bottles. The bottles were placed in the oven set at 105 °C for at least 24 h or until the sediments were dried. Dry weights were then taken to calculate the sediment delivery rate and concentration. The results showed that all kinds of experimental treatments could increase runoff and sediment yield intensity under the same rainfall intensity compared with the control test, and sediment yield intensity increased significantly greater than runoff generation intensity. Runoff generation intensity and sediment yield intensity increased with increasing soil moisture mass fraction when freeze-thaw cycles and rainfall intensities were same. The variation of runoff generation intensity and sediment yield intensity with freeze-thaw cycles were relatively complex. Runoff generation intensity and sediment yield intensity increased with increasing freeze-thaw cycles when soil moisture mass fraction was 10%. When soil moisture mass fraction was 20%, runoff generation intensity and sediment yield intensity decreased with increasing freeze-thaw cycles. When soil moisture mass fraction was 10%, and the freeze-thaw cycles both were 3 and 6, total runoff generation amount increase were 3.52% and 4.71%, respectively, total sediment yield amount increase were 6.13% and 16.95%, respectively. When soil moisture mass fraction was 20%, and the freezing and thawing cycles both were 3 and 6, total runoff generation amount increase percentage were 10.24% and 5.01%, respectively, total sediment yield amount increase were 81.99% and 53.07%, respectively. Under the same rainfall intensity, impact of soil moisture mass fraction on runoff generation intensity and sediment yield intensity was big, and the impact of freeze-thaw cycles on runoff generation intensity and sediment yield intensity was relatively small. This paper can provide an insight for the mechanism of freeze-thaw erosion. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved.