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Notes:
I used nutrient diffusing substrata also know as (NDS) to measure nutrient limitation
Each NDS consisted of a 50mL centrifuge tube filled with 2% agar solution
This was combined with either nitrogen, phosphorus or N and P together, or a control wither neither N or P.
Each tub was topped with either a porous glass disc or a sponge so the nutrients diffused through the top (Substrate) when the tubes were submerged in the stream.
The glass discs selected for autotrophs
The sponges selected for heterotrophs.
Each NDS combination was replicated 3X for each stream and the same tests were conducted in the summer and in the fall.
After 3-4 weeks I returned the NDS to the laboratory where I measured biofilm response to the nutrient diffusion by measuring oxygen change in the light and dark to calculate the primary production and the respiration.
Additionally I measured algal biomass accumulation on the glass discs