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

淡水湖中磷浓度的升高可能引发有毒蓝绿藻的过度生长，这是影响五大湖、温尼伯湖和北美许多其他湖泊的主要环境问题。有毒的藻华会导致鱼类和其他动物死亡，也可能威胁到人类的健康。在农业为主的景观中，农田的径流可能会向湖水中贡献大量的磷。由于相对平坦的地形，以及渗透性较慢的重粘土，草原上的大多数农业土壤排水性很差。在春季融雪期间，这些土地通常会被淹没几天到几周。长时间的洪水剥夺了土壤的氧气，导致厌氧土壤条件。土壤中的厌氧过程倾向于促进磷从土壤向洪水的释放。这种效应在富含铁的酸性土壤中得到了充分的证明；然而，关于北方大平原典型的碱性和钙质土壤的资料有限。我们之前对碱性土壤的研究表明，在大多数土壤中，在模拟夏季降雨洪水的情况下，洪水中的磷浓度显著增加。根据土壤的不同，增加幅度可达15倍左右。在加拿大大草原，春季融雪径流是土壤磷流失的主要模式，这发生在寒冷的温度下，经常发生冻融事件。虽然在室温下的洪水和夏季降雨洪水中，土壤中磷的有效性得到了充分的证明，但在春季融雪洪水中，土壤中磷的释放却很少。拟议的研究将解决这些知识差距。以钙质和非钙质碱性土壤为研究对象，我们将通过模拟春季融雪条件、低温和冻融事件来获得关于磷释放和动员的新信息。通过多年的实验室培养和现场微观实验，我们将系统地研究厌氧条件如何改变淹水土壤中的磷组成，以及温度变化和冻融事件对这些变化的影响。然后，我们将研究在不同的洪水时期，土壤磷组成的变化与磷从土壤到地表洪水的释放和动员之间的关系。基于这些信息，我们将开发一个模型，以识别在春季融雪洪水下有可能向洪水释放大量磷的土壤。所产生的信息和预测模型将对制定养分和水管理指南有价值，可用于最大限度地减少一个地区农业土壤中磷流入水道的损失

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.**