Effect of a monolayer on water quality at the air-water interface

Abstract

Water quality in an irrigation storage in Southeast Queensland was monitored on a fortnightly basis, for 18 months prior to monolayer application. Monitoring continued during the eight weeks of intermittent application, when 840 L of an experimental product was applied to the surface of the 16 ha storage. Indicators of water chemistry and biology were monitored on surface (microlayer), immediate subsurface and water column samples. Application of the monolayer compound was immediately detected as an increase in surface tension across the storage. There was no detectable increase above pre-application variation in dissolved oxygen, temperature, pH, conductivity, COD or BOD. Populations of phenol-degrading bacteria and phytoplankton peaked during the application period, indicating that the monolayer compound and/or climatic conditions prevailing during the selected application dates stimulated growth. Monolayer application to this storage appears relatively benign, but results should only be extrapolated to other less agriculturally impacted water storages with caution.