GEOGRAPHIC VARIATION OF NUTRIENT SPIRALING IN STREAMS IN MINNESOTA, NORTHERN CALIFORNIA, AND EASTERN SIBERIA

Clear evidence exists that streams actively regulate fluxes of carbon, nitrogen, and phosphorus from upland terrestrial ecosystems to downstream aquatic environments. Knowledge of functional characteristics of streams across a range of environments is paramount to our ability to predict changes in these ecosystems as climate changes. We used nutrient spiraling metrics to infer nutrient limitation in small streams in Minnesota, California, and the Siberian Arctic. We quantified these metrics using solute addition experiments in which nitrogen and phosphorus were added simultaneously with chloride as a conservative tracer. We found significant geographical variation in nutrient uptake by streams, suggesting variation in nutrient limitation. Siberian streams exhibited high spatial variation in uptake with some streams exhibiting N limitation and others P limitation depending on their landscape position. California streams varied in degree of autotrophy and had low background nutrient concentrations, but were strongly nitrogen limited. Minnesota streams had high background nitrate concentrations from agricultural runoff, but high rates of ammonium uptake indicating nitrogen limitation. These results suggest that streams in different landscapes will respond differently to changes in nutrient and organic matter inputs.