Nitrate uptake across biomes and the influence of elemental stoichiometry: A new look at LINX II

Abstract

Abstract Considering recent increases in anthropogenic N loading, it is essential to identify the controls on N removal and retention in aquatic ecosystems because the fate of N has consequences for water quality in streams and downstream ecosystems. Biological uptake of nitrate (NO 3 − ) is a major pathway by which N is removed from these ecosystems. Here we used data from the second Lotic Intersite Nitrogen eXperiment (LINX II) in a multivariate analysis to identify the primary drivers of variation in NO 3 − uptake velocity among biomes. Across 69 study watersheds in North America, dissolved organic carbon:NO 3 − ratios and photosynthetically active radiation were identified as the two most important predictor variables in explaining NO 3 − uptake velocity. However, within a specific biome the predictor variables of NO 3 − uptake velocity varied and included various physical, chemical, and biological attributes. Our analysis demonstrates the broad control of elemental stoichiometry on NO 3 − uptake velocity as well as the importance of biome‐specific predictors. Understanding this spatial variation has important implications for biome‐specific watershed management and the downstream export of NO 3 − , as well as for development of spatially explicit global models that describe N dynamics in streams and rivers.