John D. Spurrier

In situ metabolism of an oyster reef

Abstract The in situ metabolism of an oyster reef in North Inlet, South Carolina, was observed for 1 yr using a portable plastic tunnel technique. The fluxes of oxygen, Chl a and ammonium to and from the reef were determined every 10.2 days (33 tidal cycles) for 1 yr and the technique of regression estimation was used to compute annual estimates. The oyster reef took up 6.5 kg·m −2 of oxygen and 23.7 g·m −2 of Chl a over the year. Ammonium release was 124.8 g·m −2 for the same period. The O:N ratio of the fluxes on the reef was ≈ 30:1, indicating carbohydrate and lipid catabolism. Because of the high rates of Chl a and oxygen uptake and ammonium release observed with the in sity tunnel technique, oyster reefs should be considered even more important components in estuarine processes than previously thought.

On the null distribution of the Kruskal–Wallis statistic

This article extends existing tables of null probability points for the Kruskal–Wallis statistic and compares various methods for approximating these probability points. Van de Wiels technique of partitioning the combined ranking into the upper and lower ranks is combined with Iman, Quade, and Alexanders recursive formula to find the joint distribution of the rank totals for each sample. The Kruskal–Wallis statistics distribution is then accumulated. It is shown that the well-known chi-square approximation of Kruskal–Wallis probability points is overly conservative. Four other methods are shown to provide better approximations than the chi-square approximation.

Exact Confidence Bounds for all Contrasts of Three or More Regression Lines

Abstract It is desired to compare κ ≥ 3 treatments. Under the assumption of iid normal errors, it is well known that the Scheffe method produces exact simultaneous confidence bounds for all contrasts of the treatment means. Furthermore, it is known that the Scheffe method is conservative when one desires confidence bounds for a specific subset of contrasts of means. Exact methods, such as those due to Tukey and Dunnett, yield tighter bounds than the Scheffe method for specific subsets of contrasts of means. In this article, multiple comparisons of the κ treatments are done not in terms of their means, but rather in terms of a parametric function. The parametric function of interest is the simple linear regression model, E(Y|x). It is desired to find simultaneous confidence bounds for all contrasts of the κ simple linear regression models. Although the Scheffe method can be used to find such bounds, this is extremely conservative. The union-intersection method is used to develop simultaneous confidence bou...

An overview of tests for exponentiality

Developments since 1960 in goodness-of-fit tests for the one and two parameter exponential models using both complete and censored samples are reviewed. Special attention is given to both the omnibus or general alternative and to specialized alter-natives such as the class of distributions with increasing failure rates. The use of transformations in developing tests is also discussed.

Comparison of two regression lines over a finite interval.

The likelihood ratio test is presented for testing the equality of two regression lines versus the ordered alternative that Line 1 lies above Line 2 on a prescribed finite interval of values of the independent variable. Homoscedastic normal errors are assumed. An application is discussed and data from it are used to illustrate the methodology. A table of exact critical values is presented for alpha = .01, .05 and .10 for various degrees of freedom. Power comparisons are made with competing tests.

Successive comparisons between ordered treatments

Abstract A method is proposed for one- and two-sided comparison of means of adjacent ordered treatments with the one-way layout or randomized complete block model while maintaining a designated overall Type I error rate. For the case of equal sample sizes and r ⩽ 6 treatments, tables of exact critical values are presented and the improvement over existing conservative methods is investigated. Approximate techniques are proposed for r ⩾ 7.

The flume design — a methodology for evaluating material fluxes between a vegetated salt marsh and the adjacent tidal creek☆

An experimental flume is described which can be used as a tool to assess whether a vegetated marsh surface is a source or sink for nutrients via tidal inundation. An initial calibration study (two tidal cycles) was conducted to determine the optimum sampling design and aid in model development for flux calculations. A statistical analysis of the data showed a negligible concentration difference as a function of water depth for most of the constituents analyzed. This coupled with the low tidal velocities over the marsh surface (<1.5cm/s) suggested that a volumetric model was adequate for calculations of instantaneous discharge and nutrient flux through any station perpendicular to tidal flow. The resultant instantaneous mass flux calculations showed that water discharge was one of the dominant factors controlling the movement of material. A sine-cosine statistical model utilizing the main tidal periodicities was designed to: (1) model the instantaneous fluxes, (2) calculate the average net flux of suspended and dissolved materials, and (3) test the hypothesis that the average net flux equals zero versus a two-sided alternative using a standard regression t-test.

Estimating the net flux of nutrients between a salt marsh and a tidal creek

Statistical aspects of estimating net fluxes of nutrients between a salt marsh and a tidal creek on a tidal cycle basis and an annual basis are explored. For individual tidal cycles, the instantaneous flux of a nutrient is written in a constrained linear model as a function of time. The model is rewritten as an unconstrained model, and net flux is shown to be a linear combination of the parameters of the model. Standard linear models techniques can be used to make inferences about net fluxes on a tidal cycle basis. Considering a year as a finite population of tidal cycles, annual net flux can be estimated using a regression estimator. In the case of the flux of dissolved nitrite plus nitrate, the marsh was found to be a statistically significant sink for nitrogen (in this form) from adjacent tidal creeks.

Nitrogen exchange between a southeastern USA salt marsh ecosystem and the coastal ocean

The salt marsh ecosystem at North Inlet, South Carolina, USA consistently exported dissolved inorganic nitrogen via tidal exchange with the coastal Atlantic Ocean. Concentrations centrations of NH4+and NO3-+NO2-displayed distinct tidal patterns with rising values during ebb flow. These patterns suggest the importance of biogeochemical processes in the flux of material from the salt marsh. NH4+export peaked during the summer (15 to 20 mg m-2 tide-1) during a net balance of tidal water exchange. Remineralization of NH4+within the salt marsh system appears to be contributing to the estimated annual net export of bout 4.7 g NH4+-N m-2 yr-1. NO3-+NO2-exports were higher in the fall and winter of 1979 (2 to 4 mg N m-2 tide-1). The winter export coincided with a considerable net export of water with no distinctive concentration patterns, suggesting a simple advective export. However, the fall peak of NO3-+NO2-export occurred during a period of net water balance in tidal exchange and an insignificant freshwater input from the western, forested boundary. During the summer and fall, tidal concentration patterns were particularly apparent, suggesting that nitrification within the salt marsh system was contributing to the estimated annual net export of ca 0.6 g NO3-+NO2--N m-2 yr-1.

Exact Simultaneous Confidence Intervals for Pairwise Comparisons of Three Normal Means

Abstract The problem of simultaneously estimating the pairwise differences of means of three independent normal populations with equal variances is considered. A computational method involving a bivariate t density is used to form confidence intervals with simultaneous coverage probability equal to 1 — a. For equal sample sizes, the method is the Tukey studentized range procedure. With unequal sample sizes, the method is superior to the various generalized Tukey methods. A table of probability points is presented for small sample sizes. A large-sample approximation based on the bivariate normal and studentized range distributions is given.