BIOFILM-MEDIATED SEDIMENT TRAPPING INCREASES MICROPLASTIC DENSITY AND THEREBY ENHANCE VERTICAL FLUX OF PLASTICS IN THE OCEAN

Our previous work showed that microbial organisms alone cannot induce sinking of buoyant microplastic particles larger than 40 µm. Here we experimentally examine whether biofilm-facilitated sediment accumulation can induce sinking in larger plastics. HDPE shopping bags and LDPE cling wrap were incubated in a tidal subestuary for 15 days during summer. The plastics were subsampled every two days to measure microbial biomass, photosynthetic pigments, silica, sediment mass, size, and plastic density using Percoll density gradient columns. Initially, the plastic bag material had a density of ~1.065 g/cm³, while the cling wrap was buoyant (<1.005 g/cm3). Both plastics showed minimal density change over the first 5 days but became strongly negatively buoyant (>1.1 g/cm³) by day 7. Silica accumulation was negligible until day 3, increased by day 9, and then remained invariable. Photosynthetic pigments followed a similar pattern, becoming detectable on day 3 and peaking between days 9-11. Sediment mass increased significantly from day 5, peaked on day 9, and then declined. Acid-soluble components of sediments (i.e., primarily carbonates) remained low until day 7, after which they increased steadily. In contrast, acid-insoluble sediments (i.e., primarily silica) trapped in the biofilm matrix were mostly responsible for the increased density of larger microplastics, facilitating their transport to deeper waters. The observed plateau in all variables at approximately day 7 into the incubation indicates that if plastics do not sink by then they may remain at the surface until denser, shell-bearing metazoans achieve dominance of the biofouling community.

Presentation Preference: Poster

Primary Presenter: Gregory Joern, Old Dominion University (gjoer001@odu.edu)

Authors:

Gregory Joern, Old Dominion University  (gjoer001@odu.edu)

Alexander Bochdansky, Old Dominion University  (ABochdan@odu.edu)