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Title: Evidence for a regime shift in nitrogen export from a forested watershed

Author: Webster, J. R.; Knoepp, Jennifer; Swank, Wayne; Miniat, Chelcy;

Date: 2016

Source: Ecosystems

Publication Series: Scientific Journal (JRNL)

Description:

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.

Keywords: Watershed, nitrogen, budget, regime shift, cleacutting stream

Publication Notes:

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  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

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Citation:


Webster, J. R.; Knoepp, J. D.; Swank, W. T.; Miniat, C. F. 2016. Evidence for a regime shift in nitrogen export from a forested watershed. Ecosystems 19: 881-895. 15 p.  10.1007/s10021-016-9974-1

 


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