Vegetative filter strips to reduce surface runoff phosphorus transport from mining sand tailings in the Upper Peace River basin of central Florida

Runoff non-point source pollution from phosphate mining areas is a potential risk to ecosystems in many parts of the world. Mining sand tailings that still contain apatite (phosphate rock) shape the landscapes in reclaimed lands at the upper Peace River basin of Central Florida. The objectives of this research were to assess the surface runoff pollution loads from the mining sand tailings in Central Florida and to evaluate and model the efficiency of vegetative filter strips to control phosphorus (P) from these areas. Field experimental data were collected from two sites with different slopes, source-to-filter ratios, and soil properties representative of the surrounding area. The numerical model VFSMOD-W was used to predict overland flow and sediment trapping within the filter and was linked to a simplified P transport algorithm based on experimental data to predict TP, PP, and DP fractions in the filter outflow. An advanced global inverse optimization technique is used for the model calibration process, and consideration to the uncertainty of the measured data is given.; Phosphorus in soils of the area was in the form of apatite, as indicated by x-ray diffraction (XRD). TP concentrations were about 17.0-25.7 g/kg and Ca- and Mg-bound P accounted for about 95% of TP. DP concentrations were about 0.4-3.0 mg/L in surface runoff collected from the experimental sites. Release of P from the soils was primarily from apatite dissolution rather than desorption from metal oxides that is more typical of soils of the region. Runoff volume, sediment, TP, and DP were reduced by at least 62%, 97%, 96%, and 66%, respectively, within the vegetative filters. The VFSMOD-W can predict hydrology transport well (Nash and Sutcliffe efficiency (Ceff), 0.60 < Ceff < 0.99) for all but small events (peak runoff flow rate in the VFS < 0.4 L/s) due likely to large measurement uncertainty in the small events. The good predictions in runoff and sediment outflow from the filter result in good predictions of PP transport since apatite is a main component of sediment. A good prediction of DP filter outflow was found when considering rainfall impact on DP dissolved from apatite in surface soil. The inclusion of the uncertainty of measured data in the goodness-of-fit indicators provides us more realistic information to evaluate model performance and data sets. VFSMOD-W successfully predicts runoff, sediment, and P transport from phosphate mining sand tailings, which provides management agencies with a design tool for controlling runoff and P transport.