Spatial modeling on the nutrient retention of an estuary wetland

There is a great potential to use the estuary wetland as a final filter for nutrient enriched river water, and reduce the possibility of coastal water eutrophication. Based upon field data, spatial models were designed on a stepwise basis to simulate the nutrient reduction function of the wetland in the Liaohe Delta. The model contained two major subsystems: the canal system and the reed field. In the preliminary model, a non-linear regression model was established for the nutrient reduction in the canal system, while a percentage-based reduction model was used for the reed fields. It was first tested in one of the irrigation areas and finally extrapolated into the whole study area. Validation against field data indicated that the preliminary model was robust enough to simulate the nutrient removal process in the system. But the process model used for the reed field was much too simple compared to the model for the canal system. A more sophisticated linear regression model based on Maunder and Mauring's work was finally adopted for the reed system. According to the simulation results, more than 3200 tonnes of total nitrogen (TN) and 77 tonnes of soluble reactive phosphorous (SRP) could be removed by the reed-canal system during the irrigation period in 1998, which was only one tenth of its total reduction capacity.