Temperature Dependence of Hydraulic Conductivity Decrease due to Biological Clogging under Ponded Infiltration

Abstract

Decrease in hydraulic conductivity due to microbial biomass accumulation in soil pore, i.e., biological clogging or bioclogging, was studied in laboratory repacked sand columns, and temperature dependence of the bioclogging was observed. Glucose solution of 100 ppm was percolated continuously to laboratory sand columns in ponded condition, and hydraulic conductivity was measured every day. The temperature conditions were 15, 20, 25 and 30°C, and the experimental period was 4, 7 and 10 days. After each experiment, numbers of bacteria and fungi were counted by dilute plate counting method, and the amount of soil organic matter was estimated from the measurement of loss on ignition. Hydraulic conductivity did not change in 15°C column, while it decreased exponentially with time in 20, 25 and 30°C columns, and the rate of the decrease was largest at 25°C. Loss on ignition increased with time for all columns, and the rate of the organic accumulation was smallest at 15°C and largest at 25°C. Exponential relationship was found between the loss on ignition and the relative hydraulic conductivity, which suggests that slime material observed at the inlet of the columns was a primary cause of biological clogging. Increase in the numbers of bacteria was highest at 30°C, while increase in the numbers of fungi was highest at 25°C. This suggests that clogging of soil pore by fungal hyphae also plays important role in biological clogging, although in many'studies fungal clogging tends to be neglected and only bacterial clogging has been studied.