A semiparametric method for estimating the scale of fluctuation

Meek, D. W.

doi:10.1016/s0098-3004(01)00029-2

Cited by 13 publications

(11 citation statements)

References 14 publications

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“…Meek (2001) presents a semiparametric, iterative method of estimating θ using SAS macros (SAS Institute, Cary, NC), which was applied to data from the 210‐tile, 230‐tile, and 330‐stream sites. Briefly, ρ( m ) and θ were determined on the weekly data, for both Q and L , and for regression residuals from fitting of Eq.…”

Section: Methodsmentioning

confidence: 99%

Evaluation of Nitrate Nitrogen Fluxes from a Tile‐Drained Watershed in Central Iowa

et al. 2003

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Nitrate N fluxes from tile‐drained watersheds have been implicated in water quality studies of the Mississippi River basin, but actual NO3–N loads from small watersheds during long periods are poorly documented. We evaluated discharge and NO3–N fluxes passing the outlet of an Iowa watershed (5134 ha) and two of its tile‐drained subbasins (493 and 863 ha) from mid‐1992 through 2000. The cumulative NO3–N load from the catchment was 168 kg ha−1, and 176 and 229 kg ha−1 from the subbasins. The outlet had greater total discharge (1831 mm) and smaller flow‐weighted mean NO3–N concentration (9.2 mg L−1) than the subbasins, while the larger subbasin had greater discharge (1712 vs. 1559 mm) and mean NO3–N concentration (13.4 vs. 11.3 mg L−1) than the smaller subbasin. Concentrations exceeding 10 mg L−1 were common, but least frequent at the outlet. Nitrate N was generally not diluted by large flows, except during 1993 flooding. The outlet showed smaller NO3–N concentrations at low flows. Relationships between discharge and NO3–N flux showed log–log slopes near 1.0 for the subbasins, and 1.2 for the outlet, considering autocorrelation and measurement‐error effects. We estimated denitrification of subbasin NO3–N fluxes in a hypothetical wetland using published data. Assuming that temperature and NO3–N supply could limit denitrification, then about 20% of the NO3–N would have been denitrified by a wetland constructed to meet USDA‐approved criteria. The low efficiency results from the seasonal timing and NO3–N content of large flows. Therefore, agricultural and wetland best management practices (BMPs) are needed to achieve water quality goals in tile‐drained watersheds.

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Section: Methodsmentioning

confidence: 99%

Evaluation of Nitrate Nitrogen Fluxes from a Tile‐Drained Watershed in Central Iowa

et al. 2003

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“…::;12.0 (Meek, 2001 Shapiro and Botha's (1991) fig. 2 fit is considered valid then by constructing the related correlogram, interpolating, then numerically integrating p(h) for the plot, one finds that Co : : : ; 0, Co + C s :::; 11.6, and e : : : ; 48.…”

Section: Evaluation Criteriamentioning

confidence: 99%

“…1, exhibits a two-level nested structure with the second level starting at about h = 81 with h in meters; thus it could be argued one could use the values of y(h) for h ::; 80. Several published works (e.g., Clark, 1979;Shapiro and Botha, 1991;and Meek, 2001), however, have considered only the inner series for h ::; 75, hence, this exercise does also. Values ranged from y(1) = 0.42 to y(66) = 14.17 with "(=8.16 and the following quartiles: Y25 = 5.98, Y50 = 9.34, and Y75 = 10.69.…”

Section: Empirical Semivariogram Selectionmentioning

confidence: 99%

“…Moreover they generally require mathematical programming software and experience. While ad hoc semiparametric methods are another possible alternative (see e.g., Meek, 2001), simple parametric models have their appeal and place. Using widely available nonlinear regression programs, other simple parametric models or simplified forms of nonparametric models with all the parameters explicit can be considered and evaluated.…”

Section: Regression Modeling Proceduresmentioning

confidence: 99%

“…Similarly for the far end, the mean of say the last 5% or more of the series is used (notice the parameter is essentially the sill for the last segment for a splined-line segments model). My semiparametic alternative utilizes these ideas to avoid trying to model the rise section altogether (Meek, 2001).…”

Section: Modeling Evaluationmentioning

confidence: 99%

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Another Look at Clark's Adit-Silver Series

Meek¹

2001

Conference on Applied Statistics in Agriculture

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The empirical semivariogram for Clark's adit-silver series has been the subject of several publications. Its use in the literature along with some other discussed considerations makes this series a suitable selection for a classroom or workshop semivariogram modeling exercise. My emphasis in this exercise is on estimating the scale of fluctuation (8). Alternative unbounded, bounded asymptotic, and bounded transitional models are developed via weighted least-squares estimation for both regular and integral semivariogram parameterizations (ISV). Results are compared with Clark's recommendation along with some other traditional models, nonparametric models, and ad hoc numerical methods. When a given model fits well using the regular method, generally the ISV does also. When a given model fits poorly using the regular method, however, generally the ISV form fits much worse, or gives unrealistic parameter estimates, or diverges. While an unbounded rational polynomial exponential performs well and presents some interesting existence considerations, for practical purposes the series can be considered bounded and a hyperbolic tangent is selected as the best performing simple parameterization. The ISV for the hyperbolic tangent gives parameter and 8 estimates closest to ad hoc independent values for them. In the spirit of non parametric models, however, splined-line segments can perform extremely well if parameter parsimony and parameter interpretation are not deemed important considerations by a given modeler.

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