Phosphorus release from alkaline soils to floodwater under simulated spring snowmelt conditions

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Elevated phosphorus concentrations in freshwater lakes may trigger excessive growth of toxic blue-green algae, a major environmental problem affecting the Great Lakes, Lake Winnipeg and many other lakes across North America. Toxic algal blooms can lead to death of fish, other animals and also may threaten human health. In agriculture-dominated landscapes, runoff from crop fields may contribute significant amounts of phosphorus to lake water. Due to the relatively flat landscape, along with slowly permeable heavy clay soils, most agricultural soils in the prairies are poorly drained. These lands often get flooded for a period ranging from a few days to several weeks during spring snowmelt. Prolonged flooding deprives the soil of oxygen, which results in anaerobic soil conditions. The anaerobic processes in soils tend to enhance the release of phosphorus from soil to floodwater. This effect is well documented for iron-rich acidic soils; however, information for alkaline and calcareous soils, which are typical of Northern Great Plains is limited. Our previous studies using alkaline soils showed a significant increase in phosphorus concentration in floodwater under simulated summer rainfall flooding in majority of soils. The magnitude of increase can be up to about 15-fold depending on the soil. In the Canadian prairies, spring snowmelt runoff is the dominant mode of phosphorus losses from soils, which occurs under cold temperatures with frequent freeze-thaw events. While enhanced phosphorus availability in soil has been well documented for flooding at room temperatures and summer rainfall flooding, there is little available information on phosphorus release from soils during spring snowmelt flooding. The proposed research will address these knowledge gaps. Focusing on calcareous and non-calcareous alkaline soils, we will generate new information on the release and mobilization of phosphorus by simulating spring snowmelt conditions, with cold temperatures and freeze-thaw events. Through a comprehensive multi-year program of laboratory incubation and field microcosm experiments, we will systematically investigate how anaerobic conditions changes phosphorus composition in flooded soils, and the influence of temperature variations and freeze-thaw events on these changes. We will then examine how soil phosphorus composition changes relate to the release and mobilization of phosphorus from soil to surface floodwater at different times of flooding. Based on the information, we will develop a model to identify soils that have the potential to release large quantities of phosphorus to floodwater under spring snowmelt flooding. The information generated and the predictive model will be valuable in developing nutrient and water management guidelines, which can be used to minimize phosphorus losses from the agricultural soils in a region into waterways.**