A Micro-Bioassay for Epilithon using Nutrient-Diffusing Artificial Substrata

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Abstract
A modification of the nutrient-diffusing substrata method was used to evaluate nutrient and invertebrate grazer effects on attached epilithic algae in an arctic river. An acid-cleaned porcelain or fused silica disk was melted into the opening of a small plastic, agar-filled vial, supplemented with water soluble materials. These materials were such that they would have an impact on the biomass and/or productivity of the autotraphic and/or heterotrophic communities colonizing hard surfaces in rivets and lakes. The vials were independent replicates (3–6/treatment), providing many more treatments per unit cost and unit effort than other methods currently employed. After 3 week incubation periods in the river, we not only showed that this method works very well, we also were able to demonstrate that the river is limited by phosphorus and nitrogen, thereby confirming the results of previous assays. This method would also allow for the use of, nutrients, xenobiotics, antibiotics, and/or organic substrates to be used to enhance or minimize the effects on autotrophs or heterotrophs in complex communities.