Acid mine drainage and remediation impacts on biofilm structure and extracellular enzyme activities during succession

To improve assessment and restoration efforts, this research characterized acid mine drainage (AMD), with high concentrations of metals and acidic pH, and CaO doser treatment impacts on the structure and function of lotic biofilms.  We documented algal diversity, biomass, bacterial abundances, and extracellular enzyme activity (EEA) during biofilm succession on tiles over 5 weeks in eight streams (3 AMD, 3 downstream of a doser, 1 control recovered from AMD, and 1 control with no AMD).  Biomass accrual was greatest in the non-AMD control, least in sites downstream of the doser, and intermediate in non-treated AMD sites.  Phosphatase was greatest throughout succession in AMD sites, likely responding to P limitation due to non-organically bound P.  Leucine-amino peptidase and β-glucosidase were greatest in control streams.  β-glucosidase was related to biomass, probably because algal exudates are the dominant source of polysaccharides in biofilms.  β-xylosidase was consistent among streams, indicating similar roles of allochthonous carbon.  PCA of week 5 EEAs showed AMD streams clustered together, doser sites similar to moderate AMD impairment, and control streams isolated from others in the ordination.  The doser treatment gradually improved biofilms downstream, but complete recovery is likely impossible within the 4.8 km reach sampled due to metal precipitates.