Mechanisms of Phosphorus Removal by Phosphorus Sorbing Materials.

Stormwater filters are a structural best management practice designed to reduce dissolved P losses from runoff. Various industrial byproducts are suitable for use as P sorbing materials (PSMs) for the treatment of drainage water; P sorption by PSMs varies with material physical and chemical properties. Previously, P removal capacity by PSMs was estimated using chemical extractions. We determined the speciation of P when reacted with various PSMs using X-ray absorption near edge structure (XANES) spectroscopy. Twelve PSMs were reacted with P solution in the laboratory under batch or flow-through conditions. In addition, three slag materials were collected from working stormwater filtration structures. Phosphorus K-edge XANES spectra were collected on each reacted PSM and compared with spectra of 22 known P standards using linear combination fitting in Athena. We found evidence of formation of a variety of Ca-, Al-, and/or Fe-phosphate minerals and sorbed phases on the reacted PSMs, with the exact speciation influenced by the chemical properties of the original unreacted PSMs. We grouped PSMs into three general categories based on the dominant P removal mechanism: (i) Fe- and Al-mediated removal [i.e., adsorption of P to Fe- or Al-(hydro-)oxide minerals and/or precipitation of Fe- or Al-phosphate minerals]; (ii) Ca-mediated removal (i.e., precipitation of Ca-phosphate mineral); and (iii) both mechanisms. We recommend the use of Fe/Al sorbing PSMs for use in stormwater filtration structures where stormwater retention time is limited because reaction of P with Fe or Al generally occurs more quickly than Ca-P precipitation.

Nutrient leaching from mixed-species Florida residential landscapes.

Nutrient losses from residential lawns and landscapes can negatively impact water quality. Information about nutrient leaching from established residential landscapes containing a mixture of woody ornamental plants and turfgrass is limited. The objective of our study was to determine the effect of vegetation cover (turfgrass vs. woody ornamental) on nutrient leaching from established landscapes. Nine drainage lysimeters were planted with three vegetation treatments with the following coverage: (i) 60% turfgrass, 40% ornamental; (ii) 75% turfgrass, 25% ornamental; and (iii) 90% turfgrass, 10% ornamental. Daily leachate samples were collected and combined to produce weekly flow-weighted samples for 1 yr. Leachate samples were analyzed for total Kjeldahl N (TKN), nitrate (+ nitrite)-N (NO), ammonium-N (NH-N), and dissolved reactive phosphorus (DRP). The ratio of actual evapotranspiration (ET) to reference evapotranspiration (ET) was similar among treatments. However, drainage from the 90% turfgrass lysimeters was periodically higher than from the 60 and/or 75% turfgrass treatments. In most cases, leachate N and P concentrations and loads followed the same trend as drainage. The addition of shrubs in the 60 and 75% turfgrass treatments reduced leachate when rainfall was low and irrigation was the main water input. We suggest that established woody ornamental plants are more effective at absorbing water and nutrients than turfgrass due, in part, to increased root biomass and deeper rooting of established woody plants, which allows for more efficient uptake of soil water and nutrients. The use of woody plants in residential landscapes can reduce nutrient leaching in urban areas.