Association of Chemical Aggregates and Fungal Moieties Affecting Native Environmental Films.

Fungi are prevalent microorganisms in environmental films. Their impacts on the film chemical environment and morphology remains poorly defined. Here we present microscopic and chemical analyses fungi impacts to environmental films over long- and short-time scales. We report bulk properties of films accumulated for 2 months (February and March 2019) and 12 months to contrast short and longer-term effects. Bright field microscopy results show that fungi and fungal-associated aggregates cover close to 14% of the surface after 12 months and include significant numbers of large (tens to hundreds of µm in diameter) particles aggregated with fungal colonies. Data acquired for films accumulated over shorter times (2 months) suggest mechanisms that contribute to these longer-term effects. This is important because the film's exposed surface will determine what additional material will accumulate over the ensuing weeks or months. A combination of scanning electron microscopy and energy dispersive X-ray spectroscopy provides spatially resolved maps of fugal hypha and nearby elements of interest. We also identify a "nutrient pool" associated with the fungal hypha which extend orthogonally to the growth direction to ca. 50 µm distances. We conclude that fungi have both short-term and long-term effects on the chemistry and morphology of environmental film surfaces. In short, the presence (or absence) of fungi will significantly alter the films' evolution and should be considered when analyzing environmental film impacts on local processes.

Host surface orientation impacts environmental film accumulations.

Two environmental films were passively collected in different orientations (vertical or horizontal) at the same location over two months. We characterized these films using bright field microscopy, total dissolved species analysis, pH analysis, vibrational interfacial spectroscopy, and contact angle goniometry. Results show that horizontal films have significantly higher surface coverage than the vertical samples (+50%). The vertical and horizontal films also show different particle morphologies but the particle size distributions are not statistically different. Vertical surfaces have smaller, less compact particulate suggesting particle adsorption depends on the surface area in contact with the parent substrate. Horizontal surfaces also generate more total dissolved solid material per unit area when washed with water (+61%). The dissolved solids from the vertical substrate are more acidic per unit mass, suggesting increased pH active species like nitrate, sulfate, or organic acids. Vibrational spectroscopy provides evidence of nitrates and sulfates in both films, but spectroscopic profiles show these ions are present in different forms. Contact angle goniometry measurements show horizontal films are more hydrophilic than vertical films, despite being deposited on the same substrate material. We also report significantly different hydrogen bonding environments for condensed water between the two films. Our results suggest that environmental films deposited on vertical vs horizontal surfaces will have significantly different characteristics, informing models for deposition and impacts to human and environmental health.