# Surface Texture of Macroplastic Pollution in Streams Alters the Physical Structure and Diversity of Biofilm Communities

## TL;DR

Plastic pollution in streams changes the structure and diversity of biofilm communities compared to natural surfaces like wood.

## Contribution

This study experimentally shows how plastic surfaces with different textures affect biofilm diversity and biomass in streams.

## Key findings

- Plastic surfaces reduced species richness compared to wood veneers.
- Rough plastic surfaces had the highest evenness of biofilm communities.
- Wood veneers had significantly more biofilm biomass than plastic surfaces.

## Abstract

Biofilms can develop on nearly any surface, and in aquatic ecosystems they are essential components of biogeochemical cycles and food webs. Plastic waste in waterways is a new type of surface for biofilm colonisation. To analyse the influence of plastic pollution on the development and diversity of microbial freshwater biofilms that colonised them, we incubated 388 cm2 veneers of high‐density polyethylene (HDPE) with two veneer textures, smooth and rough, and tulip tree wood (
Liriodendron tulipifera
), in three rural headwater streams at the Savannah River Site (Aiken, SC, USA). We collected biofilms from veneers after 14, 28 and 56 days of incubation and analysed 16S rRNA genes and biofilm properties. We found that plastic negatively affected species richness of biofilms compared with wood, but that evenness was greatest on rough textured HDPE. Beta diversity was primarily influenced by stream site. Beta diversity differed more between wood and plastic veneers than with plastic surface texture and became more different over time. Wood had nine times more biomass than rough HDPE and 40 times more biomass than smooth HDPE. Given the projected increase of macroplastic pollution in aquatic ecosystems, our findings emphasise the need to further understand its effects on biofilm characteristics.

Biofilms develop on natural surfaces in stream ecosystems, but increasingly unnatural surfaces such as plastic trash are also available. In a field experiment, biofilms on wood veneers or plastic veneers with a smooth or rough surface texture differed in bacterial alpha and beta diversity and biofilm biomass. These differences may have consequences for the functional contributions of biofilms to stream ecosystems.