An assessment methodology for successional systems. I. Null models and the regulatory framework |
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Authors: | Craig Loehle John Gladden Eric Smith |
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Institution: | (1) Environmental Sciences Division, Savannah River Laboratory Savannah River Site, 29808-0001 Aiken, South Carolina, USA;(2) Department of Statistics, Virginia Polytechnic Institute and State University, 24061 Blacksburg, Virginia, USA |
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Abstract: | Standard procedures for evaluating environmental impact involve comparison between before and after conditions or scenarios
or between treatment and control site pairs. In many cases, however, endogenous directional change (natural succession) is
expected to occur at a significant rate over the period of concern, particularly for manmade systems such as impoundments.
Static evaluations do not provide an adequate approach to such problems. A new evaluation frame is proposed. Nominal system
behavior over time is characterized by a stochastic envelope around a nominal trajectory. We show that both the state variance
and the sampling variance can change over time. In this context, environmental regulations can be framed as constraints, targets,
or conformance to ideal trajectories. Statistical tests for determining noncompliance are explored relative to process variance,
sample error, and sample size. Criteria are elucidated for choosing properties to monitor, sample size, and sampling interval. |
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Keywords: | Stochastic models Monitoring Statistical tests Experimental design |
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