Properties of natural microlayers on Australian freshwater storages and their potential to interact with artificial monolayers

Abstract

Microlayers are natural surface films derived from hydrophobic organic compounds that form on most lakes and streams. Holarctic brown-water lakes have been most commonly studied, with Australian research limited to marine microlayers. Artificial monolayers based on long-chain fatty alcohols have been applied to freshwater storages to reduce evaporative loss. As a water conservation strategy, monolayer technology was not widely adopted because of variable field performance. However, the role of natural microlayers in reducing monolayer performance has not previously been investigated. In the present study, microlayer and subsurface samples from six water storages in Queensland were characterised for water-quality indices, including biochemical oxygen demand, permanganate index and ultraviolet light absorbance. Microlayer enrichment in south-eastern Queensland is comparable to or higher than that in holarctic lakes. The results indicated that microlayer compounds have the potential to disrupt monolayers in at least the following three ways: as substrates for microbes capable of degrading monolayer compounds, as chromophores accelerating photodegradation, and as impurities disrupting the molecular packing required to reduce evaporative loss. The knowledge gained from studying natural microlayers can also be used to benchmark novel monolayer compounds, to minimise their environmental impact on freshwater ecosystems.