Phosphorus Sequestration Research Articles

Sequestration of phosphorus from wastewater by cement-based or alternative cementitious materials

Cement-based and alternative cementitious materials were tested in the laboratory for their capability of removing phosphate from wastewater. The results demonstrated that both Langmuir and Freundlich adsorption isotherms were suitable for describing the adsorption characteristics of these materials. Among the four types of filter media tested, the cement-based mortar A has the highest value of maximum adsorption (30.96 mg g−1). The P-bonding energy (KL) and adsorption capacity (K) exhibited a positive correlation with the total content of Al2O3 and Fe2O3 in each mortar. The maximum amount of P adsorbed (Qm) and adsorption intensity (1/n) exhibited a positive correlation with the CaO content in each mortar. For three of them, the P-removal rates were in excess of 94 percent for phosphorus concentrations ranging from 20 to 1000 mg L−1. The underlying mechanisms were examined using field emission scanning microscopy (FESEM), coupled with energy-dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (XRD). The results reveal that the removal of phosphate predominantly followed a precipitation mechanism in addition to weak physical interactions between the surface of adsorbent filter media and the metallic salts of phosphate. The use of cement-based or alternative cementitious materials in the form of ground powder shows great promise for developing a cost-effective and environmentally sustainable technology for P-sequestration and for wastewater treatment.

Batch investigations on P immobilization from wastewaters and sediment using natural calcium rich sepiolite as a reactive material

Phosphorus from wastewaters and sediment flux to surface water represents a major source of lake eutrophication. Active filtration and in situ capping (which refers to placement of a covering or cap over an in-situ deposit of contaminated sediment) are widely used as a means to immobilize phosphorus from wastewaters and sediment, to mitigate lake eutrophication. There is, however, a need to develop more efficient means of immobilizing phosphorus through the development of binding agents. In this study, natural calcium-rich sepiolite (NCSP) was calcined at a range of temperatures, to enhance its phosphorus removal capacity. Batch studies showed that the 900 °C calcinated NCSP (NCSP900) exhibited excellent sorption performance, attaining a phosphorus removal efficiency of 80.0%–99.9% in the range of 0.05 mg/L–800 mg/L phosphorus concentrations with a dosage of 20 g/L. The material displayed rapid sorption rate (maximum amount of 99.9% of phosphate removal with 5 min) and could lower the very high phosphate concentration (200 mg/L) to less than 0.1 mg/L after 4 h adsorption. It was also noted that factors such as pH, competing anions (except HCO3−) and humic acid, had no effect on phosphorus removal capacity. The sediment immobilization experiment indicated that NCSP900 had the capacity to transform reactive phosphorus into inert-phosphorus and significantly reduce the amount of algal-bioavailable phosphorus. The excellent phosphorus binding performance of NCSP900 was mainly due to the improvement of point of zero charge (pHPZC) as well as the transformation of the inert-calcium of NCSP to active free CaO during calcination. Phosphorus speciation indicated that phosphorus was mainly captured by relatively stable calcium-bound phosphorus (Ca-P) precipitation, which can account for 80.1% of the total phosphorus. This study showed that NCSP900 could be used as an efficient binding agent for the sequestration of phosphorus from wastewaters and sediment.

Effect of plant species on water quality at the outlet of a sludge treatment wetland

Sludge treatment wetlands are mainly used to reduce the volume of activated sludge, and the pollutants at the outlet are generally returned to the wastewater treatment plant. However, in cases where sludges are produced far from treatment plants not only must the sludge be treated, but the discharge of pollutants into the surrounding environment must also be limited. The aim of this study was to evaluate the efficiency of different plant species in optimising pollutant removal in a decentralised sludge treatment wetland. In addition, a new system design was assessed, in which the wetland was not completely drained, and a saturated layer was created using an overflow. The experimental setup consisted of 16 mesocosms in total, planted with monocultures of Phragmites australis, Typha angustifolia and Scirpus fluviatilis, and unplanted controls, each in four replicates.The experiment was conducted during the third summer of operation after setup. The system was fed with highly concentrated fish farm sludge at a load of 30 kg of total solids m−2 yr−1. Results showed that such wetlands were highly efficient, with removal rates between 94% and 99% for most pollutants. Planted systems generally outperformed the unplanted control, with a significantly lower mass of pollutants at the outlet of the sludge treatment wetland planted with Phragmites, followed by those with Typha and then Scirpus. The distinct influence of plant species on pollution removal was explained by the sequestration of nitrogen and phosphorus in plant tissues and by the rhizosphere effect, which enhance the biodegradation of organic matter, allowed the nitrification process and created redox conditions favourable to the sorption of phosphorus. Filtration and evapotranspiration rates played a major role in limiting the discharge of pollutants, and the impact was enhanced by the fact that the sludge treatment wetland was not completely drained.

Linking Phosphorus Sequestration to Carbon Humification in Wetland Soils by 31P and 13C NMR Spectroscopy

Phosphorus sequestration in wetland soils is a prerequisite for long-term maintenance of water quality in downstream aquatic systems, but can be compromised if phosphorus is released following changes in nutrient status or hydrological regimen. The association of phosphorus with relatively refractory natural organic matter (e.g., humic substances) might protect soil phosphorus from such changes. Here we used hydrofluoric acid (HF) pretreatment to remove phosphorus associated with metals or anionic sorption sites, allowing us to isolate a pool of phosphorus associated with the soil organic fraction. Solution (31)P and solid state (13)C NMR spectra for wetland soils were acquired before and after hydrofluoric acid pretreatment to assess quantitatively and qualitatively the changes in phosphorus and carbon functional groups. Organic phosphorus was largely unaffected by HF treatment in soils dominated by refractory alkyl and aromatic carbon groups, indicating association of organic phosphorus with stable, humified soil organic matter. Conversely, a considerable decrease in organic phosphorus following HF pretreatment was detected in soils where O-alkyl groups represented the major fraction of the soil carbon. These correlations suggest that HF treatment can be used as a method to distinguish phosphorus fractions that are bound to the inorganic soil components from those fractions that are stabilized by incorporation into soil organic matter.

The Effectiveness and Feasibility of Using Ochre as a Soil Amendment to Sequester Dissolved Reactive Phosphorus in Runoff

Incidental losses of dissolved reactive phosphorus (DRP) to a surface waterbody originate from direct losses during land application of fertilizer, or where a rainfall event occurs immediately thereafter. Another source is the soil. One way of immobilising DRP in runoff before discharge to a surface waterbody, is to amend soil within the edge of field area with a high phosphorus (P) sequestration material. One such amendment is iron ochre, a by-product of acid mine drainage. Batch experiments utilising two grassland soils at two depths (topsoil and sub-soil), six ochre amendment rates (0, 0.15, 1.5, 7.5, 15 and 30 g kg−1 mass per dry weight of soil) and five P concentrations (0, 5, 10, 20 and 40 mg L−1) were carried out. A proportional equation, which incorporated P sources and losses, was developed and used to form a statistical model. Back calculation identified optimal rates of ochre amendment to soil to ameliorate a specific DRP concentration in runoff. Ochre amendment of soils (with no further P inputs) was effective at decreasing DRP concentrations to acceptable levels. A rate of 30 g ochre kg−1 soil was needed to decrease DRP concentrations to acceptable levels for P inputs of ≤10 mg L−1, which represents the vast majority of cases in grassland runoff experiments. However, although very quick and sustained metal release above environmental limits occurred, which makes it unfeasible for use as a soil amendment to control P release to a waterbody, the methodology developed within this paper may be used to test the effectiveness and feasibility of other amendments.

Subsurface transport of orthophosphate in five agricultural watersheds, USA

Concentrations of dissolved orthophosphate (ortho P) in the unsaturated zone, groundwater, tile drains, and groundwater/stream water interfaces were assessed in five agricultural watersheds to determine the potential for subsurface transport. Concentrations of iron oxides were measured in the aquifer material and adsorption of ortho P on oxide surfaces was assessed by geochemical modeling. Attenuation of ortho P in these aquifers was attributed primarily to sorption onto iron oxides, and in one location onto clay minerals. Only one location showed a clear indication of phosphorus transport to a stream from groundwater discharge, although groundwater did contribute to the stream load elsewhere. Subsurface ortho P movement at a site in California resulted in a plume down gradient from orchards, which was attenuated by a 200 m thick riparian zone with natural vegetation. Iron oxides had an effect on phosphorus movement and concentrations at all locations, and groundwater chemistry, especially pH, exerted a major control on the amount of phosphorus adsorbed. Groundwater pH at a site in Maryland was below 5 and that resulted in complete sequestration of phosphorus and no movement toward the stream. Geochemical modeling indicated that as the surfaces approached saturation, groundwater concentrations of ortho P rise rapidly.

Phosphorus sequestration in Fe-rich sediments from two Brazilian tropical reservoirs

Abstract This study investigates the important role of Fe-oxide/hydroxide-rich bottom sediments, from two Brazilian tropical reservoirs, on P sequestration from the overlying waters, which decreases the risk of eutrophication. Data on P fractionation indicates that P adsorption capacity of sediments is predominantly associated with Fe, followed by orthosphosphate adsorbed onto Al hydr(oxides) and onto different forms of apatite (Ca–P). The soluble and loosely bound P-forms are low. To have a better understanding of the role of Fe oxides on the adsorption and sequestration of P in the reservoirs, data obtained by sequential extraction of P have been related to concentrations of total Fe and of various Fe-fractions extracted through an optimized fractionation scheme. These analyses indicated high levels of Fe bound to oxides/hydroxides. These mineral oxides, and the preponderance of pH-dependent charged clay minerals (kaolinite) in the clay fraction, induce the sequestration of the P entering the lakes, mainly in particulate form, by strong retention of PO 4 3 - through surface adsorption and precipitation phenomena. Phosphorus-retention provided by the replacement of OH− groups on the basal plane of the minerals, for P anions, decreases the negative impact of P inputs in these water systems. There is significant correlation between the concentrations of soluble reactive P in the water (SRP) and major chemical components of sediments (SiO2, Fe2O3, Al2O3, K2O, P2O5), which are related to the dominant bedrock geology. The interaction of SRP with bed-sediments and the chemical conditions of the environment (decrease of redox potential with depth and, in the dry period, a low O2 abundance), can explain fluctuations of SRP and TP (total P) in the water column. Due to the dynamic equilibrium in the sediment–water interface, in the dry season, reducing conditions in hypoliminia enhance the reduction of Fe(III) to the more soluble Fe(II) with subsequent release of the strongly retained P. This mechanism increases the soluble P fraction in sediments and the soluble reactive P in the water column, in this period. The straight linkage between geochemical properties of sediments and P concentration in the water column reported in this article suggests that study of the mineralogical and geochemical composition of bottom sediments could help to improve model predictions of P concentrations in surface waters.

Phosphate release from waste stabilisation pond sludge: significance and fate of polyphosphate

Net phosphorus removal from waste stabilisation pond (WSP) systems is governed by the rate of phosphorus incorporation into the sludge layer and the rate of phosphorus release from this sludge back to the overlying wastewater. Luxury uptake of phosphorus by microalgae has been shown to occur under WSP conditions in the laboratory; however, the significance of this mechanism and the fate of polyphosphate contained in the settled solids have not previously been investigated. In this work the analysis of sludge samples from three WSP showed that up to 71% of the total phosphorus in the sludge was in the form of polyphosphate. This indicates that polyphosphate accumulation could potentially be an important mechanism for phosphorus sequestration in WSP and challenges the common view that chemical precipitation is the predominant phosphorus removal mechanism in these systems. The release of phosphate from WSP sludge samples was monitored in the laboratory. The samples from two different pond systems had release rates in the order of 4.3 microgP/gTSS.d. However, the third sample which was collected during an algal bloom had a release rate of 12.4 microgP/gTSS.d. Phosphate release from fresh microalgal sludge grown under laboratory conditions was also studied and was shown to have a release rate of 160 microgP/gTSS.d. Analysis of polyphosphate during the experiments on laboratory grown microalgal sludge showed that polyphosphate was indeed degraded resulting in phosphate release. Interestingly, after the initial release phase phosphorus was assimilated by the biomass and some polyphosphate was reformed. It is likely that this is due to bacterial growth in the sludge.

Facilitated Iron Reduction as a Possible Means of Rejuvenating Phosphorus Removal Performance of Filtration Substrates

In order to mitigate nutrient pollution in surface runoff more sustainably, the finite capacity for phosphorus (P) sequestration in best management practices (BMP) that rely heavily on sorption processes must be addressed. These BMP include sand filters, bioretention cells, and several types of constructed wetland. This study investigated facilitated microbial reduction of iron-based filtration substrates to promote controlled release of P previously sequestered by the BMP, P harvest for recycling, and rejuvenation of the substrate sorption capacity. Total dissolved P was well correlated with total dissolved iron during the reduction process, indicating that microbial iron reduction was capable of releasing previously sequestered P from substrates. Furthermore, results indicated that a sufficient carbon source was necessary but addition of a microbial culture was not necessary to facilitate iron reduction. While a large percentage of the previously sequestered P was removed, the process was much slower than initial sequestration of P by adsorption, and further research is needed to promote a more rapid release of P in order to optimize the rejuvenation process for field application.

Microbial sequestration of phosphorus in anoxic upwelling sediments

Organic phosphorus is removed from the ocean by its conversion to phosphorite. Laboratory incubations suggest that bacteria catalyse phosphorite formation, and that the rate of conversion is greatest under anoxic conditions. Phosphorus is an essential nutrient for life. In the ocean, phosphorus burial regulates marine primary production1,2. Phosphorus is removed from the ocean by sedimentation of organic matter, and the subsequent conversion of organic phosphorus to phosphate minerals such as apatite, and ultimately phosphorite deposits3,4. Bacteria are thought to mediate these processes5, but the mechanism of sequestration has remained unclear. Here, we present results from laboratory incubations in which we labelled organic-rich sediments from the Benguela upwelling system, Namibia, with a 33P-radiotracer, and tracked the fate of the phosphorus. We show that under both anoxic and oxic conditions, large sulphide-oxidizing bacteria accumulate 33P in their cells, and catalyse the nearly instantaneous conversion of phosphate to apatite. Apatite formation was greatest under anoxic conditions. Nutrient analyses of Namibian upwelling waters and sediments suggest that the rate of phosphate-to-apatite conversion beneath anoxic bottom waters exceeds the rate of phosphorus release during organic matter mineralization in the upper sediment layers. We suggest that bacterial apatite formation is a significant phosphorus sink under anoxic bottom-water conditions. Expanding oxygen minimum zones are projected in simulations of future climate change6, potentially increasing sequestration of marine phosphate, and restricting marine productivity.

A record of phosphorus dynamics in oligotrophic lake sediment

Historical phosphorus (P) dynamics were studied using sediment cores from three oligotrophic, acidic lakes in Maine, USA. Long-term oligotrophy of these lakes is consistent with high sediment aluminum (as Al(OH)3) concentrations, as Al inhibits internal P loading, even under reducing conditions. The role of microbially-mediated reactions in controlling redox conditions was evaluated by estimating microbial biomass and relative abundance of specific functional groups. Sediments were fractionated using a sequential chemical extraction technique and all lakes met criteria for P retention based on threshold sediment concentrations of Al, Fe, and P fractions as determined by (Kopacek et al. (2005) Limnol Oceanogr 52: 1147–1155). Sediment NaOH-extractable molybdate-reactive P (rP) and non-reactive P (nrP) represent P associated with non-reducible phases, and organic matter-related P, respectively. Total P (TP) does not decrease with sediment depth, as is typical of eutrophic lake sediments; however, nrP/TP decreases and rP/TP increases for all three lakes, indicating nrP mineralization without any significant upward diffusion and release into the hypolimnion; i.e. diagenesis of P is conservative within the sediment. Two diagenetic models were developed based on nrP and rP concentrations as a function of sediment age. The first model assumes a first-order decay of nrP, the rate coefficient being a function of time, and represents irreversible nrP mineralization, where the produced PO4 is permanently sequestered by the sediment. The second model assumes a first-order reversible transformation between nrP and rP, representing biotic mineralization of organic P followed by incorporation of inorganic P into microbial biomass. Both models reflect preservation of TP with no loss to overlying water. The rate coefficients give us insight into qualities of the sediment that have affected mineralization and sequestration of phosphorus throughout the 210Pb-dateable history of each lake. Similar models could be constructed for other lakes to help reconstruct their trophic histories. Paleolimnological reconstruction of the sediment P record in oligotrophic lakes shows mineralization of nrP to rP, but unlike the case in eutrophic lake sediments, sediment TP is preserved in these sediments.

Vegetative Covers for Sediment Control and Phosphorus Sequestration from Dairy Waste Application Fields

Excessive phosphorus (P) in runoff contributes to eutrophication of fresh water bodies. Studies have shown that manure and effluent from animal feeding operations (AFOs) applied to waste application fields (WAFs) have contributed to excess P in segments of the North Bosque River in north central Texas. There is a growing need for environmentally sound, economically viable, and easily implemented best management practices (BMPs) to control such pollution. Vegetative buffer strips offer a potential solution for reducing runoff P from WAFs by extracting it from soil and reducing sediment P delivery to streams by decreasing runoff and soil erosion. In a field study, ten plots (5 m 5 m) were assigned to five replicated treatments, namely control (bare ground), cool-season grass, warm-season forb, warm-season grass, and warm-season legume, to assess their efficacy for runoff sediment control and P sequestration. Plots were established on a coastal Bermuda grass WAF that received dairy lagoon effluent. Runoff collection systems were installed on the upstream and downstream margins of each plot. Natural rainfall runoff samples were collected and analyzed for total P, dissolve reactive P, and total suspended solids (TSS). Additionally, the total mass of runoff collected from each subplot was estimated. Results show that the warm-season forb and warm-season grass covers were the most effective treatments for reduction of runoff P, primarily due to reduced sediment content in the runoff compared to other treatments.

Effect of Aluminum‐Containing Amendments on Phosphorus Sequestration of Wastewater Treatment Wetland Soil

Little research has been conducted on methods to restore the P removal capacity of older constructed wetlands, as P treatment capacity can decrease with time. We investigated the capacity of alum and three Al‐containing alternatives (alum residual, polyaluminum chloride [PAC], and partially neutralized aluminum sulfate [PNAS]), at three rates (9, 18, and 36 g Al m−2) to reduce P concentrations. Water column pH of the alum treatment was significantly less than all other treatments, averaging 3.65 ± 1.12, while PAC (4.85 ± 0.96) and PNAS (4.21 ± 0.93) treatments had pH values significantly less than the alum residual and controls. Soluble reactive P decreased in the water column of all the treatments (−60.41 to −2.11 mg m−2 d−1). At all dosage rates, alum and PNAS were most effective at binding P, followed by PAC, while the alum residual was least effective. Significantly less P removal occurred in the 9 g Al m−2 alum, PNAS, and PAC treatments than the higher Al dosages. Dosage was inversely related to microbial biomass and activity in the surface soil, suggesting short‐term negative effects of chemical additions. Results suggest that a low‐dosage Al amendment application to wetland soil can, in the short term, prevent release of P from organic soil into the water column as well as remove P from the water column. Long‐term studies are needed, however, to verify P removal efficacy with time and the effects of continued applications on nutrient availability.

Use of Ochre from an Abandoned Metal Mine in the South East of Ireland for Phosphorus Sequestration from Dairy Dirty Water

Ochre found at coal mine drainage sites in the United Kingdom shows a high phosphorus (P) retention capacity with little mobilization of metals. This indicates that ochre has the potential to adsorb P from agricultural wastewaters for possible use as a fertilizer. Little research has focused on the ability of metal mine ochre to sequester P in an environmentally sustainable way. Untreated acid mine drainage from an abandoned copper-sulfur mine in the Avoca-Avonmore catchment in the south east of Ireland results in extensive low-value ochre deposition. In this study, P-amended water (50 mL) was mixed with this ochre (2.5 g) in batch experiments, and a maximum P adsorption capacity, calculated from the Langmuir equation, of between 16 and 21 g P kg(-1) was calculated. However, mobilization of heavy metals from Avoca ochre in distilled, surface, and dirty water batch experiments was observed. This mobilization may inhibit ochre's use in P removal from wastewaters.

Phosphorus sequestration in soil aggregates after long-term tillage and cropping

Cultivated soils in the Everglades are being converted to their historic use as pastures or seasonally flooded prairies as parts of restoration efforts, but long-term cultivation may have altered soil P distribution and availability which may pose eutrophication hazards upon change in land use. The objectives of this study were to determine the distribution of P in soil chemical and physical fractions for contrasting long-term land management practices. The distribution of P in labile, Fe–Al bound, Ca bound, humic–fulvic acid, and residual pools in five aggregate-size fractions were measured for fields under sugarcane ( Saccharum sp.) cropping for 50 years and perennial pasture for 100 years. Both land uses were characterized by a high degree of macroaggregation, as aggregates >0.25 mm contained 76 and 83% of the total soil under cultivation and pasture, respectively. Soils under sugarcane sequestered a total of 77 kg ha −1 more P than pasture at 0–15 cm. The distribution of P in chemical fractions significantly varied between land uses as cultivation increased P sequestration in Ca-bound fractions more for sugarcane (244 kg P ha −1) than pasture (65 kg P ha −1). Pasture sequestered more P in organic pools, as storage in humic–fulvic acid and residual fractions were 26 and 25%, respectively, higher than sugarcane. Labile P was 100% higher for pasture than sugarcane, but Fe–Al bound P storage did not differ between land uses. Aggregation increased P sequestration in humic–fulvic acid and residual fractions, and P storage in organic pools increased with increasing aggregate size. In contrast, cultivation decreased aggregation and increased P accumulation in inorganic fractions. Long-term cultivation altered the distribution of soil P from organic to inorganic pools. The P stored in inorganic pools is stable under current land use, but may be unstable and pose eutrophication hazards upon onset of future land use change to the seasonally flooded prairie ecosystem.

Marine Polyphosphate: A Key Player in Geologic Phosphorus Sequestration

The in situ or authigenic formation of calcium phosphate minerals in marine sediments is a major sink for the vital nutrient phosphorus. However, because typical sediment chemistry is not kinetically conducive to the precipitation of these minerals, the mechanism behind their formation has remained a fundamental mystery. Here, we present evidence from high-sensitivity x-ray and electrodialysis techniques to describe a mechanism by which abundant diatom-derived polyphosphates play a critical role in the formation of calcium phosphate minerals in marine sediments. This mechanism can explain the puzzlingly dispersed distribution of calcium phosphate minerals observed in marine sediments worldwide.

NMR and mass spectrometry of phosphorus in wetlands

SummaryThere is at present little information on the long‐term stability of phosphorus sequestered in wetlands. Phosphorus sequestered during high loading periods may be relatively unstable and easily remobilized following changes in nutrient status or hydrological regime, but the chemical forms of sequestered phosphorus that do remobilize are largely unknown at this time. A lack of suitable analytical techniques has contributed to this dearth of knowledge regarding the stability of soil organic phosphorus. We analysed phosphorus in soils from the ‘head’ of Rescue Strand tree island and an adjacent marsh in the Florida Everglades by 31P nuclear magnetic resonance (NMR) spectroscopy and high‐resolution mass spectrometry. Tree islands are important areas of biodiversity within the Everglades and offer a unique opportunity to study phosphorus sequestration because they are exposed to large phosphorus loads and appear to be natural nutrient sinks. The 31P NMR profiling of extracts from surface and sediment samples in the tree island indicates that phosphorus input to Rescue Strand tree island soils is mostly in the form of inorganic ortho‐phosphate and is either refractory when deposited or rapidly recycled by the native vegetation into a stable phosphorus pool largely resistant to re‐utilization by plants or microbes. Mass spectrometry revealed the presence of inositol hexakisphosphate, a common organic monophosphate ester not previously observed in Everglades’ soils.

Dairy Effluent Phosphorus Sequestration of Soils in Erath County, Texas

The upper north Bosque River in Erath County is an impaired watershed, one of the causes being high concentrations of dairy effluent runoff. Dairies are seeking economical solutions for managing large volumes of manure in an environmentally friendly manner. This study identifies soil properties that contribute to P sequestration and specific soils in Erath County that effectively sequester P, thereby reducing P runoff. Chemical soil properties and clay percentages were analyzed and three tests were conducted to determine soil P sequestration potential: an ex situ lysimeter study, a P sorption capacity study, and an in situ lysimeter study. Clay, calcium carbonate equivalents, and soil reaction were properties with the greatest influence on P sequestration. Calcareous clay loam soils were identified as most effective in Erath County for manure effluent application because of the formation of calcium-phosphate bonds.

Plant senescence: A mechanism for nutrient release in temperate agricultural wetlands

The beneficial uptake of nutrients by wetland plants is countered to some extent by nutrient release back into the aquatic environment due to vegetative die-back. This current study examined whether Leersia oryzoides, a common wetland plant, exhibits luxury uptake of nutrients from simulated farm runoff. The study also tested whether with subsequent decomposition, these nutrients are released back into the water column. When exposed to elevated (>2 mg/L N and P) runoff, L. oryzoides assimilated significantly higher concentrations of nitrogen ( p < 0.001) and phosphorus ( p < 0.001) in above-ground biomass as compared to non-enriched treatments (<0.05 mg/L N and P). Subsequently, senescence of enriched above-ground biomass yielded significantly higher concentrations of phosphorus (2.19 ± 0.84 mg P/L). Using L. oryzoides as our model, this study demonstrates nitrogen and phosphorus sequestration during the growing season and release of phosphorus in the winter.

Phosphorus Sequestration by Chemical Amendments to Reduce Leaching from Wastewater Applications

Phosphorus-immobilizing amendments can be useful in minimizing P leaching from high P soils that may be irrigated with wastewater. This study tested the P-binding ability of various amendment materials in a laboratory incubation experiment and then tested the best amendment in a field setup using drainage lysimeters. The laboratory experiment involved incubating 100-g samples of soil (72 mg kg(-1) water-extractable phosphorus, WEP) with various amendments at different rates for 63 d at field moisture capacity and 25 degrees C. The amendments tested were alum [Al2SO4)3.14H2O], ferric chloride (FeCl3), calcium carbonate (CaCO3), water treatment residual (WTR), and sugarbeet lime (SBL). Ferric chloride and alum at rates of 1.5 and 3.9 g kg(-1), respectively, were the most effective amendments that decreased WEP to 20 mg kg(-1), below which leaching has previously been shown to be low. Alum (1.3 kg m(-2)), which is less sensitive to redox conditions, was subsequently tested under field conditions, where it reduced WEP concentration in the 0- to 0.15-m layer from 119 mg kg(-1) on Day 0 to 36.1 mg kg(-1) (85% decrease) on Day 41. Lysimeter breakthrough tests using tertiary-treated potato-processing wastewater (mean total phosphorus [TP] = 3.4 mg L(-1)) showed that alum application reduced leachate TP and soluble reactive phosphorus (SRP) concentrations by 27 and 25%, respectively. These results indicate that alum application may be an effective strategy to immobilize P in high P coarse-textured soils. The relatively smaller decreases in TP and SRP in the leachate compared to WEP suggest some of the P may be coming from depths below 0.2 m. Thus, to achieve higher P sequestration, deeper incorporation of the alum may be necessary.