Phosphorus can easily bind to soil particles, a state in which plants don’t usually access it. The nutrient generally must be in water in order for the plants to use it. Moreover, as farmers spread more fertilizer, new quantities of phosphorus are made available to crops. But as land erodes or heavy rains hit fields, some of that older phosphorus will make its way into streams, rivers, lakes and ultimately groundwater. In coming decades, greater quantities of legacy phosphorus could get flushed into water sources due to climate change, which is projected to increase heavy precipitation events in the Midwest.