Spatial estimation of nutrient distributions in the Gulf of Riga sediments using Cokriging

Basinwide mass budgets and models are important tools in coastal zone analysis. Sediments play an important role, as storage, in the nutrient dynamics of these relatively shallow regions. Due to economic and practical reasons, sediment sampling is often made rather sparsely and irregularly. Most interpolation methods are therefore not suitable, as they demand a great deal of data sampled on a regular grid. Cokriging is a method that, at least in some part, overcomes these drawbacks. From a monitoring point of view it is a favourable method, as it incorporates information from additional variables, that may be more economical and more frequently sampled. Estimates of spatial distribution and total amounts were carried out for organic carbon, nitrogen and phosphorus in the Gulf of Riga surficial sediments. Loss on ignition was included as a covariable. Using known deposition rates on the accumulation bottoms, the mean sink values of these substances were estimated and compared with previous model results. For this study, the resulting total amounts were 1 100 000, 129 000 and 14 000 tons for carbon, nitrogen and phosphorus, respectively. This leads to an annual accumulation of 5 g C m^-2.