Synopsis:
This study summarized results of a comparative 15N-tracer study from a wide variety of sites throughout the United States, to derive general principles related to headwater streams and nitrogen dynamics. Standardized protocols were applied in 12 headwater streams representing a wide diversity of biomes throughout the United States. These sites were part of the Lotic Intersite Nitrogen eXperiment (LINX). The most rapid uptake and transformation of inorganic nitrogen occurred in the smallest streams. Ammonium entering these streams was removed within a few tens to hundreds of meters, primarily through assimilation by microorganisms, sorption to sediments, and nitrification. Nitrate was also removed from stream water but traveled a distance 5 to 10 times as long, on average, as ammonium. Nitrate was removed by biological assimilation and denitrification processes. During seasons of high biological activity, the reaches of headwater streams retain and transform important amounts of inorganic N, frequently more than 50% of the inputs from their watersheds.
O2 Interpretation of study context: Conclusions indicate that small streams are the most important at regulating water chemistry in large drainages, because their large surface-to-volume ratios favour rapid nitrogen uptake and processing. Yet small streams are often the most vulnerable to diversion, channelization, and elimination in urban and agricultural environments. Therefore, restoration and preservation of small stream ecosystems should be a central focus of management strategies to ensure maximum N processing in watersheds, which in turn will improve the quality of water delivered to downstream aquatic systems.
Conclusions:
Small streams are the most important at regulating water chemistry in large drainages, because their large surface-to-volume ratios favour rapid nitrogen uptake and processing. Yet small streams are often the most vulnerable to diversion, channelization, and elimination in urban and agricultural environments.
Thresholds/Learnings: