Towards a Biophysical Understanding of Observed Performance of Evaporation Suppressant Films Applied to Agricultural Water Storages - First Analyses

The potential utility of monomolecular layers ('monolayers') and other surface film materials for the reduction of open water evaporation has long been argued. However, outside the laboratory, trials to quantify the effectiveness of artificial surface films have produced highly variable results after application to water surfaces, whether natural water bodies or managed farm storages. This paper briefly reviews the physical mechanisms involved in evaporation suppression and the biophysical literature on aquatic surface microlayers. The wide-ranging results from sixteen months of outdoor trough-scale and (simultaneous) replicated bucket-scale evaporation reduction trials are interpreted using biophysical measurements made on microlayer and immediate subsurface water samples taken from the experimental troughs. When the prevailing environmental conditions and other ancillary measurements are taken into account, plausible hypotheses arise to account for at least some of the observed trial-to-trial differences in evaporation reduction and surface film performance. These results have implications for both small-scale trailing of evaporation suppressants and the deployment and management of artificial surface film materials on agricultural water storages.