Hydraulic conductivity and pore-size distribution in small microcosms with and without enchytraeids (Oligochaeta)

Abstract

Enchytraeids can influence pore structure by enlargement of pores, reduction of pore-size and formation of new pores. The distribution of enchytraeids through soil is strongly related to the placement of plant residues which is, therefore, expected to influence their effect on porosity and pore-size distribution. Fifteen cm soil columns with a bulk density of ca. 1.4 g/cm 3 were built using 3 metal rings each 5 cm high. Two types of columns were created: buried litter (BL) with organic matter mixed through the whole column and surface litter (SL), where the litter was added onto the surface of the column. To half of the columns of each treatment 45 enchytraeids were added. Saturated hydraulic conductivity was determined at time 0 and then after 4, 8 and 12 weeks. After the hydraulic conductivity measurements, the columns were separated into 3 depths and soil moisture retention was measured at a range of low suction pressures (0.5–20 kPa). Hydraulic conductivity decreased with time in the BL columns. At each time interval, K sat was higher in the BL columns containing enchytraeids compared to columns without enchytraeids. Presence and distribution of organic matter, the number of enchytraeids present and the duration of the experiment, influenced the impact of enchytraeids on hydraulic conductivity. Frequent ingestion and egestion of soil reduced its stability, especially in the SL columns, thereby decreasing pore size and continuity.