Are Floodplain Soils a Potential Phosphorus Source When Inundated That Can Be Effectively Managed?

Abstract

The growing concern over phosphorus (P) and water quality has led to questions as to where the loads originate and how to control landscape inputs from the watershed. We collected soil cores from two locations in the Illinois River watershed to examine the relationship between stored soil P and the amount of soluble reactive P (SRP) released into the water when soils are flooded. After inundation, P flux calculations for durations of ∼24 h ranged from less than 0.1 to 9.3 mg SRP m h. Soil test P (STP), measured as water-extractable P and Mehlich-III P, correlated with SRP flux, where higher STP resulted in increased P flux to the overlying water. Floodplain soils have the potential to be a P source, potentially releasing more than 1600 mg m yr (>16 kg ha yr) depending on length and frequency of inundation and on STP content. Applying water treatment residuals (WTRs) significantly reduced P flux from the cores. Hence, WTR application to critical source areas provides a mitigation strategy to manage floodplain soils and potential SRP release.