Artificial substrate exposure times for periphyton biomass estimates in rivers

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Abstract
The time for periphyton biomass to accrue to approximately natural levels on a new artificial substrate sampler, designed for use in harsh river environments, was investigated. Six 8‐week experiments were attempted in 9 New Zealand rivers of differing nutrient status. Accrual rates were highly variable and results between experiments were inconsistent within rivers. The colonisation stage, and the low biomass communities, were dominated by heterotrophic organisms and/or detritus. In unenriched and enriched rivers, biomass on the artificial substrates approximated natural substrate communities after 4 weeks. In moderately enriched rivers results were highly variable and artificial substrate biomass gave only a fair representation of natural substrate levels after 8 weeks of accrual. Because of variability in accural rates, adopting standard accrual times for artificial substrate sampling of New Zealand's shallow, swift rivers is not recommended. Samplers should be checked regularly and removed just before sloughing starts at the most productive site, to avoid comparing sloughed and non‐sloughed communities.