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Statistical extrapolation of nutrient concentrations in the Baltic Sea
Author(s) -
Nordgaard Anders,
Hjorth Urban
Publication year - 1993
Publication title -
environmetrics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.68
H-Index - 58
eISSN - 1099-095X
pISSN - 1180-4009
DOI - 10.1002/env.3170040305
Subject(s) - extrapolation , statistics , data set , nutrient , mathematics , baltic sea , environmental science , soil science , chemistry , geology , organic chemistry , oceanography
In this paper we present some methods for extrapolating nutrient concentrations in the water mass of the Baltic Sea. One purpose is to find the total amounts of nutrients in different basins. Data are modelled as observations from a stochastic process having room coordinates as its parameters. The extrapolation is treated as a statistical prediction procedure divided into two steps. The first step estimates the mean of the concentration at the point to which the extrapolation is made. The second step adds to the estimated mean a linear combination of residuals between estimated means and actual response values in surrounding data points. The coefficients in the linear combination and the number of surrounding points included are decided according to an estimated correlation model. The two steps both include heavy computer calculations consisting of model selection procedures and non‐linear programming algorithms. Three reasonable methods may be deduced from the two steps depending on how we estimate the mean and how correlated the residuals from the estimated means seem to be. The choice of method is based on validation towards the current data set. The extrapolated concentrations have also been integrated over the water volumes to obtain estimates of total amounts of the nutrients. Estimates from the three methods above have been compared.