Sampling design for total and filterable reactive phosphorus monitoring in a lowland stream: considerations of spatial variability, measurement uncertainty and statistical power.

An analysis for spatial variation of phosphorus (P) concentrations in the dissolved and particulate compartments of Latrobe River water in Victoria, Australia is described. Water sampling was based on a nested hierarchical design and variation was measured at different spatial scales. Total variance of the dissolved and particulate P compartments was partitioned using analysis of variance (ANOVA) to determine the spatial scale that requires most sampling effort. Statistical power analysis was used to determine the optimum sample size for the spatial scale. An uncertainty budget was estimated from sampling and analytical uncertainty. Ten and twelve samples, at the smallest spatial scale, required the greatest sampling effort, and led to the greatest required statistical power for the determination of dissolved and particulate P, respectively, in the Latrobe River catchment. The results emphasize the need for aquatic chemists to be aware of the ramifications of different types of uncertainty and variance in environmental studies.