| To better manage legacy phosphorus (P) in the Lake Okeechobee Watershed, reliable techniques to predict P storage and release from its uplands, ditches, streams and wetlands must be developed. Soil test P (STP) procedures such as Mehlich 1-P fail to precisely indicate whether a given soil is capable of retaining additional P (P “sink”) as opposed to functioning as a P source that would pose an environmental risk. The P saturation ratio (PSR) is the molar ratio of sorbed P (P held by the soil) to the sum of likely sorption components (Fe and Al) in the soil. When related to some measure of releasable P in the soil (i.e. water soluble P), PSR can be used as an indicator of the “change point” at which a soil becomes a P source to the environment.
This project intended to determine the threshold PSR (or change point) for wetland soils and sediments, ditches and streams using techniques developed for upland soils. In this approach, water soluble P (WSP) is regressed against PSR for soils with a wide range of P, Fe, and Al concentrations, and the change point determined statistically using a non-linear equation. As part of the exploratory process of obtaining a threshold PSR value, compiled archived data were used to evaluate the feasibility of using some of the data for change point determinations, with the objective of using soils with a good range of P, Fe, and Al values which may not easily be obtained if fresh soils were used. |
