MONITORING NUTRIENT TRANSPORT IN LARGE RIVERS

The problem of estimating nutrient transport in large rivers and the u ncertainty of such load estimates was studied both empirically and the oretically. In the empirical part of the study, time series of data fr om the Rhine, Meuse, Vistula and Oder Rivers were examined. The result s of this data analysis justify the use of linear interpolation to est imate concentrations prevailing between sampling occasions. A special study of the spatial variation of concentrations within different cros s-sections of the Vistula river showed that such variation can contrib ute substantially to the uncertainty of load estimates. In general, ho wever, sampling at one point in the cross-section did not result in bi ased load estimates. In the theoretical part of the study, simple ARMA (autoregressive-moving average) models were used to derive generally applicable formulas for the expected mean square error of load estimat es based on serially dependent concentration data. These formulas were then used to estimate the uncertainty of calculated nutrient loads in the Rhine and the Vistula, respectively.