AUTHOR=Wymore Adam S. , Rodríguez-Cardona Bianca M. , Herreid Allison , McDowell William H. 

TITLE=LINX I and II: Lessons Learned and Emerging Questions

JOURNAL=Frontiers in Environmental Science

VOLUME=Volume 7 - 2019

YEAR=2019

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2019.00181

DOI=10.3389/fenvs.2019.00181

ISSN=2296-665X

ABSTRACT=Anthropogenic nitrogen (N) loading has had widespread effects on the integrity of aquatic ecosystems. Headwater streams play a central role in controlling watershed N budgets by serving as a final environmental filter for excess nutrient inputs before they are exported to downstream receiving waters. Understanding the controls on in-stream N cycling has direct implications for water quality; however, in-stream nitrogen cycling is also a source of greenhouse gas production including nitrous oxide (N2O). Here we review some lessons learned from the Lotic Intersite Nitrogen eXperiments (LINX I and II), which were a series of replicated 15N in situ manipulations across biomes and land-uses designed to provide insight into the controls and fate of inorganic nitrogen in stream ecosystems. We highlight six unique insights gained from these continental- scale projects and discuss their implications for predicting fluxes and concentrations of N2O through a series of emerging questions to motivate future work. Our objective in this review is to present both retrospective and forward-looking perspectives on the N cycle in headwater streams and river networks.