Accuracy in material budget estimates with regard to temporal and spatial resolution of monitored factors

Abstract

The flushing of a continuously supplied conservative tracer in a multibasin estuary was studied using a hydrodynamical distribution model, vertically subdivided into two layers for mixing parameterization. The model has a sufficient number of grid cells to permit a spatial resolution of the tracer plume. The water exchange between different modelled basins was provided by previous simulation results from a circulation model with a temporal resolution of 1 h. The tracer turnover has been statistically analysed with regard to the content of the inner basin estimated from profile sampling and the transport across its adjacent sounds, respectively. Both of these methods of assessing the turnover of material have been employed in the ongoing biological field program in the actual estuary. The primary goal of the present paper has been to evaluate the trade-off between sampling resolution (in time and space) vs. the relative deviation of the estimates from the values corresponding to the highest resolution. It is concluded that the accuracy of these two different kinds of estimates will be determined by both a systematic and a nonsystematic deviation. The systematic deviation for content estimates seems possible to compensate for, since it is mainly determined by the position of the samples in the vertical and horizontal gradients. For transport estimates the systematic error is zero only when corresponding flow and concentration data are sampled simultaneously. At different sampling frequencies the expected accuracy is not likely to be improved by using more sophisticated methods than linear interpolation for missing data.