Investigations of freshwater surface microlayers: comparisons of methods for sampling various microlayer thicknesses with observations on select chemical and microbiological features of microlayers of three aquatic ecosystems relative to the bulk of subsurface water

Abstract

The first part of this thesis reports the comparison of four surface microlayer sampling devices. The objective of this comparison was to determine the relative sampling efficiencies, and depth of water collected by each sampler. The results showed that the plate and drum samplers were far superior to the screen and tray samplers in sampling efficiency and in collecting a thin surface microlayer. This is the first reported comparison of surface microlayer samplers. The second aspect of this thesis is the comparison of freshwater surface microlayers to the subsurface water from 10 cm depth. Several parameters were studied to determine differences between the surface microlayers and the subsurface water of three aquatic environments with different trophic levels. The parameters studied were: (1) particulate matter, (2) major inorganic ions, (3) select metals, (4) fungal populations, (5) bacterial populations, (6) most probable numbers of coliform bacteria, and (7) algal populations and distributions. The results showed that surface microlayers were often microbiologically and chemically enriched relative to the subsurface water. Frequently, fungi and bacteria (including coliforms) were found in significantly higher concentrations in surface microlayer samples than in samples collected via routine sampling techniques. Freshwater surface microlayers have received little or no study prior to this project. However, it was shown that these thin layers of water may have major roles in the recycling of nutrients, incorporation of toxicants into food chains, and in the creation of aerosols containing coliform and pathogenic bacteria. Furthermore, the study of surface microlayers offers a more sensitive technique of monitoring aquatic environments for certain pollution parameters such as coliform bacteria, heavy metals, and many pesticides.