Journal
ECOSYSTEMS
Volume 19, Issue 5, Pages 881-895Publisher
SPRINGER
DOI: 10.1007/s10021-016-9974-1
Keywords
watershed; nitrogen; budget; regime shift; clearcutting; stream
Categories
Funding
- USDA Forest Service
- Southern Research Station
- Coweeta Hydrologic Laboratory
- National Science Foundation
- NSF [DEB0823293]
- Division Of Environmental Biology
- Direct For Biological Sciences [1440485] Funding Source: National Science Foundation
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In this study, we document a functional regime shift in stream inorganic nitrogen (N) processing indicated by a major change in N export from a forested watershed. Evidence from 36 years of data following experimental clearcut logging at Coweeta Hydrologic Laboratory, NC, suggests that forest disturbance in this area can cause elevation of dissolved inorganic N (DIN) loss lasting decades or perhaps longer. This elevation of N export was apparently caused by an initial pulse of organic matter input, reduced vegetation uptake, increased mineralization of soil organic N, and N fixation by black locust-associated bacteria following clearcut logging. In forested reference watersheds at Coweeta, maximum DIN concentration occurs in summer when base flow is low, but the clearcut watershed shifted to a pattern of maximum winter DIN concentration. The seasonal pattern of DIN concentration and export from reference watersheds can be explained by terrestrial and in-stream processes, but following clearcutting, elevated DIN availability saturated both terrestrial and in-stream uptake, and the N export regime became dominated by hydrologic transport. We suggest that the long-term elevation of stream DIN concentration and export along with the changes in seasonality of DIN export and the relationship between concentration and discharge represent a functional regime shift initiated by forest disturbance.
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