N:P Ratios and Uptake Dynamics in Intermittent Antarctic Streams
The intermittent streams of the Taylor Valley [TV], Antarctica have relatively simple ecology and hydrology. They are bounded by permafrost and fed only by glacial melt. There are no vascular plants or higher animals; benthic and hyporheic microbial communities drive stream ecosystem productivity and function. Background N:P stoichiometry varies along a spatial gradient, with low N:P at the coast and higher N:P inland. Our goal was to examine nutrient uptake dynamics across the TV in relation to the background N:P gradient. We conducted NO3-N, PO4-P, and NH4-N pulse addition experiments in six streams across the TV and analyzed the results with both breakthrough curve and TASCC-style analyses. For each nutrient, we expected uptake rates to be higher where ambient concentrations were lower. Results indicate that the uptake dynamics of these short, oligotrophic polar desert streams are comparable to those of temperate stream systems. However, the TV uptake patterns do not vary by geographic location or nutrient type. Instead, we see three general uptake patterns: 1) Increasing spiraling length (Sw) as nutrient concentration increases, possibly indicating nutrient saturation at higher concentrations; 2) Hysteresis, with shorter Sw on the falling limb than the rising limb, which may indicate a lag in biotic response; and 3) Decreasing Sw as nutrient concentration increases, which may indicate that the biota are able to quickly assimilate far more than the ambient nutrient levels. These findings shed new light on the spatiotemporal dynamics of nutrient demand across these intermittent Antarctic streams.
Christa.Torrens@colorado.edu
Environmental Studies Graduate Student, University of Colorado - Boulder