Can uptake length in strams be determined by nutrient addition experiments? Results from an interbiome comparison study

Abstract

Nutrient uptake length is an important parnmeter tor quantifying nutrient cycling in streams. Although nutrient tracer additions are the preierred method for measuring uptake length under ambient nutrient concentrations, short-term nutrient addition experiments have more irequently been used to estimate uptake length in streams. Theoretical analysis of the relationship between uptake length determined by nutrient addition experiments (S_w') and uptake length determined by tracer additions (S_w)predicted that S_w' should be consistently longer than 5,", and that the overestimate of uptake length by S_w( should be related to the level of nutrient addition above ambient concentrations and the degree of nutrient limitation. To test these predictions, we used data irom an interbiorne study of NH,- uptake length in which ¹⁵NH,- tracer and short-term NH,-a ddition experiments were performed in 10 streams using a uniform experimental approach. The experimental results largely contirmed the theoretical predictions: s_w' was consistently longer than S_w and S_w':S_w ratios were directly related to the level of NH,- addition and to indicatvrs of N limitation. The experimentally derived S_w':S_w, ratios were used with the theoretical results to infer the N limitation status of each stream. Together, the theoretical and experimental results showed the tracer experiments should be used whenever possible to determine nutrient uptake length in streams. Nutrient addition experiments may be useful for comparing uptake lengths between different streams or cliiferent times in the same stream. however, provided that nutrient additions are kept as low as possible and of similar miagnitude.

Keywords

Stream, ammonium, uptake length, nutrient cycling, nutrient spiraling, nitrogen limitation.

Citation

Mulholland, P. J; Tanks, J. L.; Webster, J. R.; Bowden, W. B.; Dodds, W. K; Gregory, S. V.; Grimm, N. B; Meriam, J. L.; Meyer, J. L.; Peterson, B. J.; Valett, H. M.; Wollheim, W. M. 2002. Can uptake length in strams be determined by nutrient addition experiments? Results from an interbiome comparison study. J. N. Am. Bethol. Soc. 2002, 21(4): 544-560