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

摘要

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 (NO3-) 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 NO3- uptake velocity among biomes. Across 69 study watersheds in North America, dissolved organic carbon: NO3- ratios and photosynthetically active radiation were identified as the two most important predictor variables in explaining NO3- uptake velocity. However, within a specific biome the predictor variables of NO3- uptake velocity varied and included various physical, chemical, and biological attributes. Our analysis demonstrates the broad control of elemental stoichiometry on NO3- 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 NO3-, as well as for development of spatially explicit global models that describe N dynamics in streams and rivers.