Spatial modelling and prediction on river networks: up model, down model or hybrid?

Preservation of rivers and water resources is crucial in most environmental policies and many carts are made to assess water quality Environmental monitoring of large river networks are based on measurement stations Compared to the total length of river networks, their number is often limited and there is a need to extend environmental variables that are measured locally to the whole river network The objective of this paper is to propose several relevant geostatistical models for river modelling These models use river distance and are based on two contrasting assumptions about dependency along a river network Inference using maximum likelihood, model selection criterion and prediction by kriging are then developed We illustrate our approach on two variables that differ by their distributional and spatial characteristics summer water temperature and nitrate concentration The data come from 141 to 187 monitoring stations in a network on a large river located in the Northeast of Fiance that is more than 5001) km long and includes Meuse and Moselle basins. We first evaluated different spatial models and then gave prediction maps and error variance maps for the whole stream network Copyright (C) 2009 John Wiley & Sons. Ltd