EVALUATING SOIL PHOSPHORUS RETENTION AND RELEASE POTENTIAL ON LANDS RECEIVING PAYMENT FOR ENVIRONMENTAL SERVICES.

Transcription

1 EVALUATING SOIL PHOSPHORUS RETENTION AND RELEASE POTENTIAL ON LANDS RECEIVING PAYMENT FOR ENVIRONMENTAL SERVICES. M. Clark 1, P. Bohlen 2, S. Shukla 3, S. Lynch 4, L. Shabman 5, H. Swain 6 and E. Boughton 7 1 Soil and Water Science Department, University of Florida, Gainesville, FL USA 2 Department of Biology, University of Central Florida, Orlando, FL USA 3 Department of Agricultural and Biological Engineering, University of Florida, Immokalee, FL USA 4 Agricultural - Markets Unit, World Wildlife Fund, Washington, DC USA 5 Resources for the Future, Washington, DC USA 6 Archbold Biological Station, Venus FL USA 7 MacArthur Agro-Ecology Research Center, Lake Placid, FL USA

2 Concern Over Phosphorus Lake Okeechobee was listed in 1998 as being use impaired by nutrients (particularly, phosphorus), dissolved oxygen, ammonia, chlorides, coliforms, and iron. (FDEP) Protective numeric criteria of 40 ppb total phosphorus was established for the pelagic zone of the lake Corresponding TMDL set at 140 metric tons. Most management actions in the watershed need to consider potential effects on phosphorus loads to the lake.

3 Soil Objective within FRESP Original: Develop a tool to evaluate the potential increase in phosphorus release from soils in response to implementation of water management alternative. Identify high risk sites. Subsequent: Identify opportunity sites. Identify phosphorus hot spots within water management area. Guide strategies to mitigate P release if risk is high.

4 Phosphorus Dynamics 101 The majority of phosphorus in the landscape is stored in soils. Phosphorus can bind with other elements in the soil mainly Iron (Fe +3 ) and Aluminum (Al +3 ) and become permanently or temporarily unavailable to plants or leaching. Accumulated phosphorus (legacy phosphorus) can later be released depending on porewater and floodwater phosphorus concentration, solution characteristics (ph, redox), availability of Iron and Aluminum to bind phosphorus and biological uptake and burial in organic sediment.. Numerous soil analysis and metrics can be used to estimate phosphorus availability. A l3+ Al +3 Fe +3 PO 4-3 PO 4-3 PO 4-3 Diffusion flux Convective flux

5 Phosphorus Parameters Evaluated SRP WSP TP M1-TP M3-TP HCl-Tpi HCl-TP M1-PSR M3-PSR HCl-PSR HCl2-PSR EPC M1-SPSC M3-SPSC Soluble Reactive Phosphorus Water Soluble Phosphorus Total Phosphorus Mehlich-1 extractable phosphorus Mehlich-3 extractable phosphorus Total inorganic phosphorus HCl extractable phosphorus Phosphorus Sorption Ratio based on Mehlich-1 extractible phosphorus Phosphorus Sorption Ratio based on Mehlich-3 extractible phosphorus Phosphorus Sorption Ratio based on HCl extractible phosphorus Phosphorus Sorption Ratio based on double HCl extractible phosphorus Equilibrium Phosphorus Concentration Soil Phosphorus Sorption Capacity based on Mehlich-1 extractible phosphorus Soil Phosphorus Sorption Capacity based on Mehlich-3 extractible phosphorus

6 Field Soil Sampling Edge Center Upland Williamson Ranch Syfrette Ranch

7 0.0 ppm 0.1 ppm 0.5 ppm 1.0 ppm 10 ppm Soils Analysis Samples were analyzed at the State Soil Testing Laboratory at the University of Florida (mehlich-1 TP, SPSC), or UF Wetland Biogeochemistry Laboratory (EPC). Determination of Equilibrium Phosphorus Concentration

8 Soil Phosphorus Sorption Capacity SPSC (mg kg -1 ) Sink Sink y = -11.5x R 2 = 0.8 A & E horizon Negative SPSC, n=159 Positive SPSC, n=602 WSP (mg kg -1 ) Bh horizon Source Source When SPSC is positive, soil is a P sink When SPSC is negative, soil is a P source SPSC is additive; it is possible to calculate SPSC to any specified depth or area Able to predict whether a given volume or weight of soil is a P source or sink

9 EPC Results Site Average = Center Average = Edge Average = Upland Average =

10 EPC Results Site Average = Center Average = Edge Average = Upland Average =

11 FRESP Site Average EPC Ranch n EPC

12 EPC, ppm Application of EPC EPC Maximum value What are thresholds of concern? How should they be determine? sample ID

13 Comparison of Soil Parameter with Edge of Field Water Quality

14 Near Field and Far Field Predictors of Water Column Phosphorus Concentration Near Field Effectively measured by soil extractions EPC, WSP etc. Diffusion flux Convective flux additions and deletions during conveyance Plant decomposition, manure, etc. Biological uptake, Dilution, evaporative concentration. Far Field Edge of Field

15 Correlation between Soil Parameters and Edge of Field Phosphorus Concentration all zones Center zone Edge zone Upland zone Ln Ln Ln Ln Parameter Linear Transform Linear Transform Linear Transform Linear Transform SRP WSP TP M1-TP M3-TP HCl-Tpi HCl-TP M1-PSR M3-PSR HCl-PSR HCl2-PSR EPC M1-SPSC M3-SPSC

16 Summary of Soil Metric Selection Equilibrium Phosphorus Concentration (EPC) good predictor of soil<>porewater exchange of phosphorus not a good predictor at catchment scale costly to measure Upland Mehlich-1 Total Phosphorus very good predictor of catchment scale phosphorus discharge concentration may have limited application for spatial hot spot identification does not provide estimate of phosphorus storage or release capacity commonly collected to determine soil phosphorus fertility Mehlich-1 derived Soil Phosphorus Sorption Capacity good predictor of catchment scale phosphorus discharge can identify spatial hot spots can provide an estimate of additional mass of phosphorus that can be stored or released from area

17 discharge phosphorus concentration mg/l Conceptual Guidance for use of Soil Phosphorus Metrics Scales are derived from data collected during FRESP, but should be calibrated for area of application. Left side scale used to evaluate individual sampling location hot spot. Right side scale used to evaluate overall site condition and need for additional intervention. Mitigation threshold derived from correlation between M1-TP and edge of field water column concentration of mg L -1.

18 Questions?