Abstract
Paired watershed studies are used around the world to evaluate and quantify effects of forest and water management practices on hydrology and water quality. The basic concept uses two neighboring watersheds (one as a control and another as a treatment), which are concurrently monitored during calibration (pre-treatment) and post-treatment periods. A statistically significant relationship between the control and treatment watersheds is established during calibration period such that any significant shift detected in the relationship during treatment is attributed to the treatment effects. The approach assumes that there is a consistent, quantifiable, and predictable relationship between watershed response variables. This study tests the hypothesis that the hydrologic relationships between control and treatment watersheds for daily water table elevation (WTE) and daily flow data were similar without any statistically significant difference during two different calibration (1988-1989 and 2007-2008) and treatment periods (1995-1996 and 2009), when the control and treatment watersheds were interchanged. The watersheds are two artificially drained loblolly pine forests (D1: 24.7 haand D2: 23.6 ha) located in coastal North Carolina. Results depicted significantly similar WTE regression relationships during the two calibration periods but significantly different WTE relationships during the two treatment periods with reversed control and treatment watersheds. Calibration and treatment flow relationships, and the mean treatment effects on WTE and flow, before and after treatment reversal were significantly different (α = 0.05). The study also discusses causes of differences in hydrologic relationships and treatment effects for such reversal of treatments during a 21-year span of the study on these two similar and adjacent watersheds. The observed differences in the hydrologic relationships between control and treatment watersheds before and after treatment reversal may be attributed to climate or hydrologic non-stationarity which may affect the reliability of paired watershed approach especially when the calibration periods are short.
Highlights
Much of the existing knowledge and science on effects of forest management and silvicultural practices on water yield, peak flows, and water quality are in great part based on results from experimental watersheds at sites such as Hubbard Brook (New Hampshire), Coweeta Hydrological Laboratory (North Carolina), H
A statistically significant relationship between the control and treatment watersheds is established during calibration period such that any significant shift detected in the relationship during treatment is attributed to the treatment effects
Ends: December 22, 2009 this study addresses is whether the hydrologic relationships and treatment effects during the first calibration and treatment periods, remain the same in the second calibration and treatment periods where similar watersheds were interchanged for treatment
Summary
Much of the existing knowledge and science on effects of forest management and silvicultural practices on water yield, peak flows, and water quality are in great part based on results from experimental watersheds at sites such as Hubbard Brook (New Hampshire), Coweeta Hydrological Laboratory (North Carolina), H. The experiments used a paired watershed approach to quantify effects of various forest management activities on the above hydrological variables [2,3,4,5,6,7,8,9,10,11]. The basic concept of a paired watershed method involves use of two neighboring watersheds (one as a control and another as a treatment), which are concurrently monitored during calibration (pre-treatment) and post-treatment periods [12]. A statistically significant relationship between the control and treatment watersheds is established during calibration period such that any significant shift detected in the relationship during treatment is attributed to the treatment effects. The approach has been extended to other fields of study to assess effectiveness of conser-
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