Trace metal interactions with epilithic biofilms in small acidic mountain streams

Abstract

This study examined trace metal binding in epilithic biofilms in small acidic streams in the Duddon Valley, Cumbria, UK. Streams were chosen to include a range of pH values and biofilms with and without Fe and Mn oxyhydroxide deposits in order to assess these factors in biofilm accumulation of trace metals (Cd, Cr, Cu). Artificial sandpaper substrata were placed into three streams over a period of one year, with sample removal each month. At each sampling, temperature, photosynthetically active radiation (PAR), stream flow, dissolved organic carbon (DOC) concentration, dissolved metal concentrations (Cd, Cr, Cu, Fe and Mn), pH and alkalinity of the stream water were measured. Biofilm dry weights, concentrations of autotrophic organisms and bacteria were measured, as were the concentrations of Cd, Cr, Cu, Fe and Mn in the biofilm material (μg/g biofilm dry weight). Highest concentrations of metals in both the water column and the biofilm occurred between June and November. Correlation analysis revealed that microorganisms in the biofilm had strong relationships with biofilm-bound trace metal concentrations that may have had a significant impact on trace metal dynamics in the biofilm. However, ultimately the results indicated that trace metal concentrations in the biofilms could not be determined by single factors. Rather, changes in trace metal concentrations (including Fe and Mn) were attributed to complex interactions between meteorological, hydrological and biological factors, the relative contributions of which altered through the year.