Variance Reduction for Trend Analysis of Hydrochemical Data in Brackish Waters

摘要

We propose one parametric and one nonparametric method for conducting trend tests on nutrient concentrations in brackish waters taking into account that the temporal variation in both nitrogen and phosphorus records can be strongly influenced by the mixing of sea water and fresh water. Both methods utilise salinity as a covariate in the trend analysis. Data on total phosphorus in the Baltic Sea showed that there was a downward trend, although it was very weak when the natural fluctuations in salinity had been taken into account.