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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Periphyton
NUTRIENT CONCENTRATIONS IN A BOREAL RIVER: THRESHOLDS FOR PERIPHYTON GROWTH.
S.L. Depoe1, P.A. Chambers2, and K.J. Devito1. 1Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, 2National Water Research Institute, Canada Centre for Inland Waters, Burlington, Ontario, Canada, L7R 4A6
Nutrient limitation was assessed during the 2000 open-water season at four sites with varying nutrient supply along a 70 km reach of a 5th order boreal river (Wapiti River, Alberta, Canada). Three direct measures of nutrient status (alkaline phosphatase activity, periphyton tissue N:P, nutrient diffusing substrata ) were used to determine the primary nutrient limiting growth, assess shifts in periphyton nutrient status along the study reach, and identify ambient concentrations associated with a shift in nutrient status. The uppermost, low-impact site consistently showed N and P co-limitation whereas the two midstream sites showed a transition to N-limitation, with the lowermost, heavily impacted site showing evidence of N and P saturation. Alkaline phosphatase assays indicated phosphorus sufficiency when SRP concentrations were > 1.5 ug L-1. Nutrient diffusing pots indicated nutrient surfeit conditions at SRP > 5 ug L-1 and DIN > 32 ug L-1 while tissue N:P ratios where indicative of N deficiency (< 10 molar ratio) when DIN < 40 ug L-1. Thus, in this N and/or P limited system, concentrations greater than 1.5 - 5 ug L-1 SRP and 32 – 40 ug L-1 DIN were sufficient to saturate periphyton growth.
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