Using wetland nutrient modelling to estimate River Murray and floodplain wetland water exchange

Abstract: River water quality is substantially influenced by adjacent wetlands. The water exchange estimate is a step in the process of developing a model capable of simulating management strategies for wetlands of the Lower River Murray and their effect on nutrient load in the river. An expanded wetland process model was used to find the water exchange between wetlands, where there is a lack of channel morphology data and no measured wetland water turnover. This paper describes the development of the wetland ecosystem model WETMOD to include spatial driving variables of the floodplain landscape. The added spatial driving variables for WETMOD are used to account for local variations and inflow into a wetland, particularly to reflect bi-directional water and nutrient exchange between the River Murray and the wetlands. The spatial driving variables are derived from a database containing site-specific flow and nutrient data from the river and wetlands. In order to simulate the water exchange between individual wetlands and the River Murray an ad hoc flux estimation technique was developed. This was based on a combination of the river flow volume and the wetland specific budget of phosphorus (PO4-P) simulated by WETMOD. We demonstrate that it is possible to obtain the turnover volume of water in a wetland using nutrient modelling output.