Effects of redox on the phosphorus removal ability of iron-rich phosphorus sorption materials.

Iron-rich phosphorus (P) sorption materials (PSMs) are often used in P removal structures, a best management practice able to sequester dissolved P from surface runoff, subsurface drainage, and wastewater. The use of bottom-upward flow in these structures is of great interest, but it creates an intrinsic complication: the presence of stagnant water between flow events may cause structures to develop anoxic conditions. It is unknown whether the redox sensitivity of iron (Fe), the predominant element in Fe-rich PSMs, will affect P binding under anoxic conditions. Understanding the potential impact of intermittent anoxic conditions on the solubility of previously adsorbed P is imperative for determining the feasibility of the bottom-up flow design. The objective of this research was to investigate the (1) development of anoxic conditions in the presence of Fe-rich PSM and tile drainage, (2) Fe-bound P mobilization and solubility, and (3) changes in P sorption capacity of Fe-rich PSMs after oxic conditions are restored. Three Fe-rich PSMs were tested in batch incubation studies: acid mine drainage residual, Fe-coated alumina, and steel metal shavings. Non-treated and P-treated PSM samples were incubated in biogeochemical reactors for as long as necessary to reach Eh = -200 mV. After incubation, dissolved P concentrations in P-treated samples and non-treated samples were similarly low, indicating stability of P retention of PSMs under anoxic conditions. The P removal ability of non-treated PSMs before and after undergoing incubation was not significantly altered, as determined in flow-through experiments. Potentially harmful trace metals were not detected in the incubated solutions. Our research shows that the development of anoxic conditions does not significantly impact PSMs Fe-bound P dissolution, and the P removal ability of PSMs persists after oxic conditions are reestablished.

New phosphorus losses via tile drainage depend on fertilizer form, placement, and timing.

Agricultural phosphorus (P) losses are harmful to water quality, but knowledge gaps about the importance of fertilizer management practices on new (recently applied) sources of P may limit P loss mitigation efforts. Weighted regression models applied to subsurface tile drainage water quality data enabled estimating the new P losses associated with 155 P applications in Ohio and Indiana, USA. Daily discharge and dissolved reactive P (DRP) and total P (TP) loads were used to detect increases in P loss following each application which was considered new P. The magnitude of new P losses was small relative to fertilizer application rates, averaging 79.3 g DRP ha-1 and 96.1 g TP ha-1 , or <3% of P applied. The eight largest new P losses surpassed 330 g DRP ha-1 or 575 g TP ha-1 . New P loss mitigation strategies should focus on broadcast liquid manure applications; on average, manure applications caused greater new P losses than inorganic fertilizers, and surface broadcast applications were associated with greater new P losses than injected or incorporated applications. Late fall applications risked having large new P losses applications. On an annual basis, new P contributed an average of 14% of DRP and 5% of TP losses from tile drains, which is much less than previous studies that included surface runoff, suggesting that tile drainage is relatively buffered with regard to new P losses. Therefore old (preexisting soil P) P sources dominated tile drain P losses, and P loss reduction efforts will need to address this source.

Phosphate removal by low-cost industrial byproduct iron shavings: Efficacy and longevity.

Iron shavings (IS) are low-cost industrial byproducts that show great potential in removing phosphorus (P) from contaminated water. This work investigates the effectiveness of IS for P (PO4-P) removal and emphasizes its pretreatment and longevity. A 4-d pretreatment of IS with 2.5 % NaCl resulted in a significant increase in P adsorption capacity, from approximately 1.0 to 2.5 mg/g. In column tests, the P removal efficiency remained above 60 % over 60 d, with a capacity of 4.1 mg P/g. Longevity tests involved seven adsorption-regeneration cycles, with an effective IS regeneration by 1 N NaOH and neutralization by HCl solution (pH=2), and the P adsorption capacity only slightly decreased from 2.14 to 1.75 mg P/g. To significantly improve the IS regeneration operation, we employed induction heating and compared an intermittent 10-s induction heating with an isothermal hot NaOH (85 ℃) treatment in 10-min desorption tests (95.3 % versus 56.6 % regeneration). We further found that IH completely regenerated IS in 5 min with 100 s of IH application, but 30 min were needed for hot NaOH (85 ℃) treatment. SEM/EDX, XRD, and XPS tests were conducted to track the changes in the morphology, crystallinity, and surface oxidation products of IS in the cycle tests. Notably, IS surface changed from coarse to smooth with fewer reactive sites and a higher conversion of amorphous Fe oxides to more crystalline Fe3O4, resulting in lower reactivity and fewer exposed Fe0 sites over multiple cycles. All of these mechanisms contributed to the deterioration in P removal capacity. Overall, this study provides a solid foundation for applying low-cost IS in effectively removing P from agricultural runoff.

Techno-Economic Analysis of Phosphorus Removal Structures.

Excess phosphorus (P) is a major pollutant in aquatic systems. Phosphorus removal structures, landscape-scale filters designed to capture dissolved P from runoff, drainage, and wastewater offer promise in curbing P pollution. While the environmental benefits of various P removal structures are well documented, the cost-effectiveness of each structure's ability to sequester P is lacking. In this study, we compare the cost-effectiveness of P removal of the most prominent P removal structures. Specifically, we calculate the average cost per kilogram (kg) of P removed by eight different P removal structures across a range of parameter assumptions. Absent constraints, we found that (1) larger structures that use (2) regionally available phosphorus sorption materials that are (3) byproducts of industrial production (e.g., metal shavings and steel slag) rather than manufactured are more cost-effective. The average cost of P removal for most structures varies from $100 to 1300 per kg in our baseline estimations, which is comparable to the average cost for wastewater treatment. This work provides further information to guide the optimal implementation of P removal structures for conservationists.

Consequences of 33 Years of Plastic Film Mulching and Nitrogen Fertilization on Maize Growth and Soil Quality.

Plastic film mulching and urea nitrogen fertilization are widely used in agricultural ecosystems, but both their long-term use may leave a negative legacy on crop growth, due to deleterious effects of plastic and microplastic accumulation and acidification in soil, respectively. Here, we stopped covering soil with a plastic film in an experimental site that was previously covered for 33 years and compared soil properties and subsequent maize growth and yield between plots that were previously and never covered with the plastic film. Soil moisture was about 5-16% higher at the previously mulched plot than at the never-mulched plot, but NO3- content was lower for the former when with fertilization. Maize growth and yield were generally similar between previously and never-mulched plots. Maize had an earlier dough stage (6-10 days) in previously mulched compared to never-mulched plots. Although plastic film mulching did add substantial amounts of film residues and microplastic accumulation into soils, it did not leave a net negative legacy (given the positive effects of the mulching practice in the first place) for soil quality and subsequent maize growth and yield, at least as an initial effect in our experiment. Long-term urea fertilization resulted in a pH decrease of about 1 unit, which bring a temporary maize P deficiency occurring in early stages of growth. Our data add long-term information on this important form of plastic pollution in agricultural systems.

Uncertainty in phosphorus fluxes and budgets across the US long-term agroecosystem research network.

Phosphorus (P) budgets can be useful tools for understanding nutrient cycling and quantifying the effectiveness of nutrient management planning and policies; however, uncertainties in agricultural nutrient budgets are not often quantitatively assessed. The objective of this study was to evaluate uncertainty in P fluxes (fertilizer/manure application, atmospheric deposition, irrigation, crop removal, surface runoff, and leachate) and the propagation of these uncertainties to annual P budgets. Data from 56 cropping systems in the P-FLUX database, which spans diverse rotations and landscapes across the United States and Canada, were evaluated. Results showed that across cropping systems, average annual P budget was 22.4 kg P ha-1 (range = -32.7 to 340.6 kg P ha-1 ), with an average uncertainty of 13.1 kg P ha-1 (range = 1.0-87.1 kg P ha-1 ). Fertilizer/manure application and crop removal were the largest P fluxes across cropping systems and, as a result, accounted for the largest fraction of uncertainty in annual budgets (61% and 37%, respectively). Remaining fluxes individually accounted for <2% of the budget uncertainty. Uncertainties were large enough that determining whether P was increasing, decreasing, or not changing was inconclusive in 39% of the budgets evaluated. Findings indicate that more careful and/or direct measurements of inputs, outputs, and stocks are needed. Recommendations for minimizing uncertainty in P budgets based on the results of the study were developed. Quantifying, communicating, and constraining uncertainty in budgets among production systems and multiple geographies is critical for engaging stakeholders, developing local and national strategies for P reduction, and informing policy.

Estimating the variability of steel slag properties and their influence in phosphorus removal ability.

Steel slag has been proven to be an effective phosphorus (P) removal media, and a potential aid to mitigate point and nonpoint P pollution in freshwater systems. However, the behavior of steel slag as a P sorption material (PSM) is often oversimplified through the generalization of its chemical and physical properties, preventing proper design of P removal structures. In this work, we tested eighteen steel slag samples from different batches, production processes, and steel-making plants, for the purpose of relating slag origin and chemical and physical properties to P removal ability, under two different flow regimes. Slag samples were also coated with aluminum (Al) and tested for P removal. Characterization included elemental composition, particle density, buffer capacity, and P removal ability. There was great variability in the evaluated properties across slag sources and origin, compelling the individual characterization of steel slag samples, since their intrinsic characteristics were key variables in determining their potential P removal capacity. Specifically, electrical conductivity (EC), bulk density, particle density and magnesium (Mg) content could explain around 70% of the variability of P removal by uncoated steel slags. Increasing residence time (RT) always increased P removal for uncoated slags. Steel slags showed a high variability in their P removal ability, but such variability was considerably decreased by coating the slags with Al. Additionally, the Al-coating process significantly improved P removal performance under more rapid flows (lower RT).

Development of a rapid field testing method for metals in horizontal directional drilling residuals with XRF sensor.

Portable X-ray fluorescence (pXRF) spectrometer allows fast in-situ elemental determination without wet digestion for soils or geological materials, but the use of XRF on wet materials is not well documented. Our objective was to develop a rapid field method using pXRF to measure metals in the residues from horizontal directional drilling (HDD) operations so that proper disposal decisions can be made in-situ. To establish the procedure, we spiked soil samples with 4 concentrations of Cr, Ni, Cu, Zn, As, Cd, and Pb up to 1000 mg kg-1, and then the metal concentrations were determined by wet chemical method after drying and acid digestion (standard method), and by pXRF, also at laboratory conditions, after drying and at two different moisture conditions. The measurements by pXRF and standard method after drying and after removal of excess water (AREW) were highly correlated with slopes ranging from 0.83 ± 0.01 to 1.08 ± 0.01 (P < 0.001) for all metals. The relationship was better AREW than the saturated paste without removal of excess water and the moisture content affected only the accuracy of As, Cd, and Pb. The procedure established was successfully used for HDD residues collected from 26 states of US with moisture content ranging from 14 to 83% AREW. The pXRF was proven to be a reliable tool for fast detection of common metals in dried soils and HDD residues, and samples containing < 30% moisture content without needing to correct for moisture. If the moisture is > 30%, excess water in samples need to be removed with a commercially available filter press to achieve high accuracy. The developed procedures reduce time of metal detection from days to about an hour which allows drilling operators to make quick decisions on soil or HDD disposal.

Less Agricultural Phosphorus Applied in 2019 Led to Less Dissolved Phosphorus Transported to Lake Erie.

Extreme precipitation events affect water quantity and quality in various regions of the world. Heavy precipitation in 2019 resulted in a record high area of unplanted agricultural fields in the U.S. and especially in the Maumee River Watershed (MRW). March-July phosphorus (P) loads from the MRW drive harmful algal bloom (HAB) severity in Lake Erie; hence changes in management that influence P export can ultimately affect HAB severity. In this study, we found that the 2019 dissolved reactive P (DRP) load from March-July was 29% lower than predicted, while the particulate P (PP) load was similar to the predicted value. Furthermore, the reduced DRP load resulted in a less severe HAB than predicted based on discharge volume. The 29% reduction in DRP loss in the MRW occurred with a 62% reduction in applied P, emphasizing the strong influence of recently applied P and subsequent incidental P losses on watershed P loading. Other possible contributing factors to this reduced load include lower precipitation intensity, altered tillage practices, and effects of fallow soils, but more data is needed to assess their importance. We recommend conservation practices focusing on P application techniques and timing and improving resiliency against extreme precipitation events.

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.

Investigation of Atrazine Sorption to Biochar With Titration Calorimetry and Flow-Through Analysis: Implications for Design of Pollution-Control Structures.

Atrazine is one of the most common broad-leaf herbicides used in the world. However, due to extensive use for many years, atrazine often appears in surface and groundwater. Atrazine transport is inhibited by degradation or sorption to soil components, especially organic matter. Biochar is a charcoal-like material produced from pyrolysis of biomass. Due to the amount and type of functional groups found on biochar, this product has shown potential for sorption of atrazine from solution. There is an interest in developing best management practices utilizing biochar to filter atrazine from non-point drainage with pollution-control structures such as blind inlets. The objective of this study was to explore the kinetics and thermodynamics of atrazine sorption to biochar using two different approaches: flow-through sorption cells and isothermal titration calorimetry (ITC). Twenty-five milligrams of an oak (Quercus spp.)-derived biochar was suspended in water and titrated 25 times (0.01 mL per titration) with atrazine at three different concentrations, and by a single titration (0.25 mL), with heat of reaction directly measured with ITC. A benchtop atrazine sorption study that simulated the titration experiment was also conducted. A continuous flow-through system was used to quantify the impact of contact time on atrazine sorption to biochar. Atrazine sorption to biochar displayed both exothermic and endothermic signals within each titration, although the net reaction was exothermic and proportional to the degree of sorption. Net enthalpy was -4,231 ± 130 kJ mole-1 atrazine sorbed. The existence of both exotherms and endotherms within a single titration, plus observation of an initial fast reaction phase from 0 to 300 s followed by a slower phase, suggested multiple sorption mechanisms to biochar. Results of flow-through tests supported kinetics observations, with the 300 s contact time removing much more atrazine compared to 45 s, while 600 s improved little compared to 300 s. Based on flow-through results, annual atrazine removal goal of 50%, and typical Midwestern U.S. tile drainage conditions, a pollution-control structure implementing this biochar sample would require 32 and 4 Mg for a design utilizing a contact time of 45 and 300 s, respectively. Future work is necessary for estimating degradation of atrazine sorbed to biochar.

Denitrifying woodchip bioreactor and phosphorus filter pairing to minimize pollution swapping.

Pairing denitrifying woodchip bioreactors and phosphorus-sorbing filters provides a unique, engineered approach for dual nutrient removal from waters impaired with both nitrogen (N) and phosphorus (P). This column study aimed to test placement of two P-filter media (acid mine drainage treatment residuals and steel slag) relative to a denitrifying system to maximize N and P removal and minimize pollution swapping under varying flow conditions (i.e., woodchip column hydraulic retention times (HRTs) of 7.2, 18, and 51 h; P-filter HRTs of 7.6-59 min). Woodchip denitrification columns were placed either upstream or downstream of P-filters filled with either medium. The configuration with woodchip denitrifying systems placed upstream of the P-filters generally provided optimized dissolved P removal efficiencies and removal rates. The P-filters placed upstream of the woodchip columns exhibited better P removal than downstream-placed P-filters only under overly long (i.e., N-limited) retention times when highly reduced effluent exited the woodchip bioreactors. The paired configurations using mine drainage residuals provided significantly greater P removal than the steel slag P-filters (e.g., 25-133 versus 8.8-48 g P removed m-3 filter media d-1, respectively), but there were no significant differences in N removal between treatments (removal rates: 8.0-18 g N removed m-3 woodchips d-1; N removal efficiencies: 18-95% across all HRTs). The range of HRTs tested here resulted in various undesirable pollution swapping by-products from the denitrifying bioreactors: nitrite production when nitrate removal was not complete and sulfate reduction, chemical oxygen demand production and decreased pH during overly long retention times. The downstream P-filter placement provided a polishing step for removal of chemical oxygen demand and nitrite.

Streambanks: A net source of sediment and phosphorus to streams and rivers.

Sediment and phosphorus (P) are two primary pollutants of surface waters. Many studies have investigated loadings from upland sources or even streambed sediment, but in many cases, limited to no data exist to determine sediment and P loading from streambanks on a watershed scale. The objectives of this paper are to review the current knowledge base on streambank erosion and failure mechanisms, streambank P concentrations, and streambanks as P loading sources and then also to identify future research needs on this topic. In many watersheds, long-term loading of soil and associated P to stream systems has created a source of eroded soil and P that may interact with streambank sediment and be deposited in floodplains downstream. In many cases streambanks were formed from previously eroded and deposited alluvial material and so the resulting soils possess unique physical and chemical properties from adjacent upland soils. Streambank sediment and P loading rates depend explicitly on the rate of streambank migration and the concentration of P stored within bank materials. From the survey of literature, previous studies report streambank total P concentrations that consistently exceeded 250 mg kg(-1) soil. Only a few studies also reported water soluble or extractable P concentrations. More research should be devoted to understanding the dynamic processes between different P pools (total P versus bioavailable P), and sorption or desorption processes under varying hydraulic and stream chemistry conditions. Furthermore, the literature reported that streambank erosion and failure and gully erosion were reported to account for 7-92% of the suspended sediment load within a channel and 6-93% of total P. However, significant uncertainty can occur in such estimates due to reach-scale variability in streambank migration rates and future estimates should consider the use of uncertainty analysis approaches. Research is also needed on the transport rates of dissolved and sediment-bound P through the entire stream system of a watershed to identify critical upland and/or near-stream conservation practices. Extensive monitoring of the impact of restoration/rehabilitation efforts on reducing sediment and P loading are limited. From an application standpoint, streambank P contributions to streams should be more explicitly accounted for in developing total maximum daily loads in watersheds.

Evaluation of a universal flow-through model for predicting and designing phosphorus removal structures.

Phosphorus (P) removal structures have been shown to decrease dissolved P loss from agricultural and urban areas which may reduce the threat of eutrophication. In order to design or quantify performance of these structures, the relationship between discrete and cumulative removal with cumulative P loading must be determined, either by individual flow-through experiments or model prediction. A model was previously developed for predicting P removal with P sorption materials (PSMs) under flow-through conditions, as a function of inflow P concentration, retention time (RT), and PSM characteristics. The objective of this study was to compare model results to measured P removal data from several PSM under a range of conditions (P concentrations and RT) and scales ranging from laboratory to field. Materials tested included acid mine drainage residuals (AMDRs), treated and non-treated electric arc furnace (EAF) steel slag at different size fractions, and flue gas desulfurization (FGD) gypsum. Equations for P removal curves and cumulative P removed were not significantly different between predicted and actual values for any of the 23 scenarios examined. However, the model did tend to slightly over-predict cumulative P removal for calcium-based PSMs. The ability of the model to predict P removal for various materials, RTs, and P concentrations in both controlled settings and field structures validate its use in design and quantification of these structures. This ability to predict P removal without constant monitoring is vital to widespread adoption of P removal structures, especially for meeting discharge regulations and nutrient trading programs.

Phosphate sorption by three potential filter materials as assessed by isothermal titration calorimetry.

Phosphorus eutrophication of lakes and streams, coming from drained farmlands, is a serious problem in areas with intensive agriculture. Installation of phosphate (P) sorbing filters at drain outlets may be a solution. The aim of this study was to improve the understanding of reactions involved in P sorption by three commercial P sorbing materials, i.e. Ca/Mg oxide-based Filtralite-P, Fe oxide-based CFH-12 and Limestone in two particle sizes (2-1 mm and 1-0.5 mm), by means of isothermal titration calorimetry (ITC), sorption isotherms, sequential extractions and SEM-EDS. The results indicate that P retention by CFH is due to surface complexation by rapid formation of strong Fe-P bonds. In contrast, retention of P by Filtralite-P and Limestone strongly depends on pH and time and is interpreted due to formation of calcium phosphate precipitate(s). Consequently, CFH can unambiguously be recommended as P retention filter material in drain outlets, whereas the use of Filtralite-P and Limestone has certain (serious) limitations. Thus, Filtralite-P has high capacity to retain P but only at alkaline pH (pH ≥ 10) and P retention by Limestone requires long-time contact and a high ratio between sorbent and sorbate.

Forage and tree seedling growth in a soil with an encased swine sludge layer.

The closure of swine farms requires decommissioning of lagoons that contain large amounts of swine solids (sludge). Sludge is typically transported and land applied to soils. However, in some cases this process could be economically prohibitive and/or unpractical. An alternative idea is to encase sludge with lagoon soil berms after removing overlying effluent, followed by establishment of forages or short-rotation woody crops on the encased sludge. The objective of this study was to investigate growth potential for several forages and tree species into a pure layer of swine sludge. Alfalfa (Meticago sativa), bermudagrass (Cynodon dactylon), switchgrass (Panicum virgatum), green ash (Fraxinus pennsylvanica), black locust (Robinia pseudoacacia), and sycamore (Platanus occidentalis) were established in 40 cm deep pots consisting of a lagoon berm soil overlaying a sludge layer for 12 w followed by analysis of aboveground and belowground biomass production. "New" and "old" sludge was collected from an active 10 year old lagoon and decommissioned 50 year old lagoon, respectively. A control (soil only) was used. Encased sludge treatments increased forage biomass production. Sycamore and green ash were sensitive to new sludge but not old sludge as these species had less biomass production in new sludge than control and showed tissue trace nutrient deficiencies. While both sludge materials contained adequate nutrients, the new sludge had a salt concentration 1.8 times higher than old sludge as indicated by electrical conductivity (12.4 mS). Thus, the forage crops and black locust were able to thrive in new sludge due to their salt tolerance.

Phosphorus removal with by-products in a flow-through setting.

Phosphorus (P) losses to surface waters can result in eutrophication. Some industrial by-products have a strong affinity for dissolved P and may be useful in reducing nonpoint P pollution with landscape-scale runoff filters. Although appreciable research has been conducted on characterizing P sorption by industrial by-products via batch isotherms, less data are available on P sorption by these materials in a flow-through context integral to a landscape P filter. The objectives of this study were to evaluate several industrial by-products for P sorption in a flow-through setting, to determine material chemical properties that have the greatest impact on P sorption in a flow-through setting, and to explore how retention time (RT) and P concentration affect P removal. Twelve materials were characterized for chemical properties that typically influence P removal and subjected to flow-through P sorption experiments in which five different RTs and P concentrations were tested. The impact of RT and P concentrations on P removal varied based on material chemical properties, mainly as a function of oxalate-extractable aluminum (Al), iron (Fe), and water-soluble (WS) calcium (Ca). Statistical analysis showed that materials elevated in oxalate-extractable Al and Fe and WS Ca and that were highly buffered above pH 6 were able to remove the most P under flow-through conditions. Langmuir sorption maximum values from batch isotherms were poorly correlated with and overestimated P removal found under flow-through conditions. Within the conditions tested in this study, increases in RT and inflow P concentrations increased P removal among materials most likely to remove P via precipitation, whereas RT had little effect on materials likely to remove P via ligand exchange.

Trapping phosphorus in runoff with a phosphorus removal structure.

Reduction of phosphorus (P) inputs to surface waters may decrease eutrophication. Some researchers have proposed filtering dissolved P in runoff with P-sorptive byproducts in structures placed in hydrologically active areas with high soil P concentrations. The objectives of this study were to construct and monitor a P removal structure in a suburban watershed and test the ability of empirically developed flow-through equations to predict structure performance. Steel slag was used as the P sorption material in the P removal structure. Water samples were collected before and after the structure using automatic samples and analyzed for total dissolved P. During the first 5 mo of structure operation, 25% of all dissolved P was removed from rainfall and irrigation events. Phosphorus was removed more efficiently during low flow rate irrigation events with a high retention time than during high flow rate rainfall events with a low retention time. The six largest flow events occurred during storm flow and accounted for 75% of the P entering the structure and 54% of the P removed by the structure. Flow-through equations developed for predicting structure performance produced reasonable estimates of structure "lifetime" (16.8 mo). However, the equations overpredicted cumulative P removal. This was likely due to differences in pH, total Ca and Fe, and alkalinity between the slag used in the structure and the slag used for model development. This suggests the need for an overall model that can predict structure performance based on individual material properties.

Alternative poultry litter storage for improved transportation and use as a soil amendment.

Transportation of poultry litter out of nutrient limited watersheds such as the Illinois River basin (eastern Oklahoma) is a logical solution for minimizing phosphorus (P) losses from soils to surface waters. Transportation costs are basedon mass of load and distance transported. This study investigated an alternative litter storage technique designed to promote carbon (C) degradation, thereby concentrating nutrients for the purpose of decreasing transportation costs through decreased mass. Poultry litter was stored in 0.90-Mg conical piles under semipermeable tarps and adjusted to 40% moisture content, tested with and without addition of alum (aluminum sulfate). additional study was conducted using 3.6-Mg piles under the same conditions, except tested with and without use of aeration pipes. Samples were analyzed before and after (8 wk) storage. Litter mass degradation (i.e., loss in mass due to organic matter decomposition) was estimated on the basis of changes in litter total P contents. Additional characterization included pH, total nutrients, moisture content, total C, and degree of humification. Litter storage significantly decreased litter mass (16 to 27%), concentrated nutrients such as P and potassium (K) and increased proportion of fulvic and humic acids. The addition of aeration pipes increased mass degradationrelative to piles without aeration pipes. Nitrogen volatilization losses were minimized with alum additions. Increases in P and K concentrations resulted in greater monetary value per unit mass compared with fresh litter. Such increases translate to increased litter shipping distance and cost savings of $17.2 million over 25 yr for litter movement out of eastern Oklahoma.