A novel method to assess effects of chemical stressors on natural biofilm structure and function

The regulation and management of chemical contaminants rarely use community- and ecosystem-level endpoints, partly due to a lack of suitable methods. To overcome this limitation, we propose contaminant exposure substrata (CES), an adaptation of the widely used nutrient-diffusing substratum method, to assess responses of biofilm communities to chemical contaminants in situ. We describe methods for using CES to assess effects on biofilm biomass, community structure, process rates, biofilm–consumer interactions and biofilm chemistry. We also provide equations to calculate the flux of soluble chemicals from CES and describe an approach to compare contaminant dose in CES assays to the contaminant dose encountered by biofilms in polluted surface waters. Data from four case studies demonstrate that CES can detect impairment of biofilm structure and function. The adaptability, simplicity and cost-effectiveness of CES make them valuable tools to assess community- and ecosystem-level responses to contaminants, suggesting potential for routine use and incorporation of data generated from such assays into contaminant regulation and management.