Effect of irrigation with municipal water or sewage effluent on the biology of soil cores

Abstract

Microbial populations and respiratory activity are reported for topsoils (0-10 cm) of 15 cm diameter cores (depth 50 cm) of 10 pasture soils representative of soils of North Island, New Zealand, after 15 months' irrigation with either municipal tapwater or unchlorinated sewage effiuent from a biological filtration plant. Respiratory activity in the unamended soil was low, with respiratory quotient (R.O.) less than 1. Addition of glucose produced about a four-fold increase in CO? production and the R.O. rose to 1. Total microbial populations were similar. There were few bacterial spores but more actinomycetes. Gram-negative bacteria comprised only a small proportion of the population. Coliform counts, both total and faecal, were low. A wide range of organisms were present; the moat numerous, other than bacteria and fungi, were flagellates, amoebae, and solitary green algae. Representatives of the fauna found in the filtration plant were recovered from the effiuent irrigated soils. All measurements showed greater oifferences among the different soils studied than between the two irrigation treatments.

Effect of irrigation with municipal water or sewage effluent on the biology of soil cores

“…As reported previously (Cairns et al 1978), nematodes, rotifers, gastrotrichs, and tardigrades also occurred in the dilution cultures. ;;s~i$…”

“…However, it seems possible that the concentrations are not appreciably higher than in normal field soils, since the respiratory activity was not significantly enhanced (Cairns et al 1978). Possibly most of the readily available nutrients are leached through the topsoil.…”

“…The ability of the protozoan population to adapt to the irrigation regime is partly explained by a comparable stability in the bacterial populations, and this in turn is probably due to the effective predation of the microfauna, particularly the protozoa, on the incoming microflora, particularly the coliform bacteria, which seldom reached large !lumbers in the soils (Cairns et al 1978). The stability of the populations would have ensured that pH, oxygen, and carbon dioxide tensions did not fluctuate greatly.…”

“…The design of the experiment, the soils studied, and the general methods of analysis are covered in Childs et al (1977), and Cairns et al (1978). For the examination of protozoa, plain agar (2%) plates were used for culture.…”

“…In a previous paper of this series (Cairns et al 1978), an indication was given of the overall level of protozoan populations of pasture topsoils subjected to an experimental regime of irrigation with either municipal tapwater or secondary sewage effluent from a biological treatment plant. The composition of the fauna and changes related to the irrigation regime were not considered.…”