Low PO4 Research Articles

Quantitative Insights into Phosphate-Enhanced Lead Immobilization on Goethite.

Despite extensive study, geochemical modeling often fails to accurately predict lead (Pb) immobilization in environmental samples. This study employs the Charge Distribution MUlti-SIte Complexation (CD-MUSIC) model, X-ray absorption fine structure (XAFS), and density functional theory (DFT) to investigate mechanisms of phosphate (PO4) induced Pb immobilization on metal (hydr)oxides. The results reveal that PO4 mainly enhances bidentate-adsorbed Pb on goethite via electrostatic synergy at low PO4 concentrations. At relatively low pH (below 5.5) and elevated PO4 concentrations, the formation of the monodentate-O-sharing Pb-PO4 ternary structure on goethite becomes important. Precipitation of hydropyromorphite (Pb5(PO4)3OH) occurs at high pH and high concentrations of Pb and PO4, with an optimized log Ksp value of -82.02. The adjustment of log Ksp compared to that in the bulk solution allows for quantification of the overall Pb-PO4 precipitation enhanced by goethite. The CD-MUSIC model parameters for both the bidentate Pb complex and the monodentate-O-sharing Pb-PO4 ternary complex were optimized. The modeling results and parameters are further validated and specified with XAFS analysis and DFT calculations. This study provides quantitative molecular-level insights into the contributions of electrostatic enhancement, ternary complexation, and precipitation to phosphate-induced Pb immobilization on oxides, which will be helpful in resolving controversies regarding Pb distribution in environmental samples.

Increasing tidal inundation corresponds to rising porewater nutrient concentrations in a southeastern U.S. salt marsh.

Salt marshes are ecologically and economically important features of coastal environments that are vulnerable to sea level rise, the rate of which has accelerated in recent decades along the southeastern US Atlantic coast. Increased flooding frequency and duration across the marsh platform is predicted to impact vegetation community structure and overall marsh persistence, but the effect of changing inundation patterns on biogeochemical processes in marsh sediments remains largely unexplored. As part of a long-term monitoring effort to assess how marshes are responding to sea level rise in North Inlet estuary (South Carolina, USA), we collected data on porewater nutrient concentrations from a series of permanent monitoring plots across multiple transects spanning the marsh elevation gradient during the growing season from 2009 to 2019. Additionally, we calculated time inundated for each plot using local water level data and high-resolution elevation measurements to assess the change in time flooded at each plot. Our results indicate that both NH4 and PO4 nutrient concentrations have increased in most permanent plots over the 11-year study period and that nutrient concentrations are higher with increasing proximity to the creek. Spatial patterns in nutrient increases through time are coincident with considerable increases in tidal inundation observed over the marsh platform. Across plots located in the low marsh, porewater NH4 and PO4 concentrations have risen at average rates of 8.96 μM/year and 0.86 μM/year, respectively, and have reached rates as high as 27.25 μM/year and 3.13 μM/year. We suggest that increased inundation time due to rising sea level has altered biogeochemical conditions influencing nutrient availability in marsh porewater, resulting in increases that likely have relevance for larger scale nutrient cycles as well as marsh ecosystem stability and function.

A new sampling method with zirconium‐loaded resin for phosphate oxygen isotope analysis in oligotrophic freshwater systems

The phosphate oxygen isotope ratio ( ) is a useful technique to trace the sources and biogeochemical cycles of phosphorus (P) in aquatic ecosystems. However, has not been widely used in oligotrophic freshwater systems due to technical and methodological difficulties in collecting sufficient phosphate (PO4 ) for the analysis, which sometimes requires hundreds of liters of the water sample. In this study, a new approach (PaS-Zir) was developed for the analysis in oligotrophic freshwater systems using zirconium (Zr)-loaded (ZrIRC) resin, which has a high affinity for PO4 . ZrClO2 was added to Amberlite IRC748 to obtain the ZrIRC resin. The adsorption/desorption experiment using KH2 PO4 with a known value of was conducted to determine the adsorption/desorption properties of the resin and the likelihood of isotopic fractionation. By installing mesh bags filled with the resin, the PaS-Zir approach was used in two rivers with low PO4 concentrations (0.2 and 5.3μmol/L). A conventional sampling method was also performed in the study river with a higher PO4 concentration to validate the efficacy of the PaS-Zir method. The adsorption/desorption experiment demonstrated that the ZrIRC resin possessed a sufficient adsorption capacity (153 μmol/resin-mL) and exhibited little isotopic fractionation during the adsorption/desorption processes. Using the PaS-Zir method, we were able to collect sufficient PO4 samples for the analysis from the rivers within at least 4 days of mesh bag installation. The values (14.2‰ ±0.2‰) obtained using the PaS-Zir method were comparable to those obtained using the conventional method (14.0‰ ±0.03‰). We proved that the PaS-Zir method is applicable to oligotrophic freshwater systems and is generally more efficient than the conventional method. In addition, our method is useful for improving the understanding of the P dynamics of oligotrophic ecosystems because of the extremely low concentration of PO4 commonly found in them, which are often prone to P pollution.

Kleen enema Hypophosphatemia correction in hemodialysis patients.

Dialysis fluid (Dialysate) is a solution consisting of inorganic ions and glucose. Its constitution is almost physiologic. Dialysate is prepared by mixing two concentrates (either liquid or powder form). Two concentrates are labeled as acidic bath (Bath A) and basic bath (Bath B). Bath A contains sodium, chloride and glucose at physiologic concentration. While Bath B is bicarbonate solution contains bicarbonate slightly greater than physiologic concentration to treat metabolic acidosis.
 Just as therapeutic drugs, Dialysis fluid constituents can be adjusted as per individual patient's needs. Potassium and calcium baths are available to alter concentration of these ions. Phosphorous is normally not present in dialysate. Though hyperphosphatemia is one of the major clinical problem in renal failure, low serum phosphorous (PO4) is frequently encountered clinical entity. In chronic dialysis patient low PO4 is encountered as component of adynamic bone disease. Likewise, phosphorus dis balance is frequent electrolyte imbalance in critically ill patients with renal injury. Dialysis with low PO4 is always a challenge for nephrologist and intensivist.
 Case reports are available on treatment of symptomatic hypophsotemia using convention hemodialysis with poshphorous enriched dialysate fluid.

Speciation and pH- and particle size-dependent solubility of phosphorus in tropical sandy soils

Growing demands for crops have expanded agricultural production to sandy soils with low available phosphorus (P) content and high P mobility. Knowledge of P speciation and solubility in such soils is poorly understood. Here we investigated: i) the P speciation in the clay size fraction of sandy soils, ii) the pH-dependent solubility of soil orthophosphate (PO4–P), and iii) the particle size-dependent solubility of the soil P. The studied loamy sand soils were low in organic matter (2.6–7.9 g kg−1) and deficient in available P (1.5–8.5 mg kg−1), and kaolinite (21%) was the only clay mineral identified using X-ray diffraction technique in the clay-sized particles. The P K-edge X-ray absorption near edge structure analysis revealed that P associated with Al phases, 45% adsorbed to gibbsite and 35% in variscite (AlPO₄·2H₂O), dominated the P speciation in the clay-sized particles. The very low PO4–P solubilities in the investigated bulk soils exhibited a pronounced positive pH-dependent pattern that was consistent with the pH-dependent solubility of Al3+ and Fe3+. Geochemical modeling suggested that the maximum PO4–P solubilities were linked to the solubility of variscite and strengite (FePO₄·2H₂O), indicating that PO4–P solubilities were controlled by the solubility of Al3+ and Fe3+ as restricted by the pH-dependent solubility of Al phases and Fe (hydr)oxides. The analysis of particle size fractions revealed that the largest size fraction (1000–2000 µm), containing visible plant debris and contributing the least to total soil mass (<0.126%), contained most of the total soil P stocks (50–60%). The small size factions (<250 µm) were the key to available PO4–P. Our data highlighted the pivotal role of Al/Fe (hydr)oxides and kaolinite in controlling the pH-dependent solubility of PO4–P in these tropical sandy soils having very limited contents of total and available P and a high risk of P loss.

Hypocalcemia in Setting of Malignancy of Unknown Origin: A Case Report

Background: Hypercalcemia is a common finding well-recognized in up to 30% of cases of malignancy, associated with poor prognosis and advanced disease state. Hypocalcemia, while uncommon, can also be found in cases of malignancy facilitated by its own unique mechanism and etiologies. We present a case of severe hypocalcemia in the setting of malignancy of unknown origin. Clinical Case: 72-year-old female with a history of metastatic carcinoma of unknown origin, followed actively by Oncology, presented acutely with shortness of breath, chest pain, stiff hands and clenched fist. Patient had reported a 20 lbs weight loss over three months with a “knot” in the epigastric area affecting appetite and interfering with eating. Prior CT showed diffuse adenopathy with diffuse permeative bone destruction highly suspicious for malignancy. Follow up PET-CT showed mixed lytic lesion and sclerotic changes throughout the entire skeleton from the skull to mid thighs compatible with osseous metastatic. Initial tests show severe hypocalcemia with appropriately PTH elevation and normal vitamin D25 (calcium 5.5 mg/dL, albumin 3.9 g/dL, phosphorus (PO4) 2.3 mg/dL, magnesium (Mg) 1.5 mg/dL, PTH 243 pg/mL, vitamin D25 31.44 ng/mL). Further workup shows normal creatinine levels (0.88 mmol/L) and elevated alkaline phosphatase (1140 IU/L). Physical exam revealed bilaterally clenched fist and positive Chvostek sign. After two doses of 2 grams calcium gluconate, calcium had improved up to 7.2 mg/dL (corrected 7.76 mg/dL, albumin 3.3 g/dL) with plans to replete Mg and PO4. Patient was started on Calcium-Vitamin-D 500-200 mg-units (Oscal) two tabs trice daily. However, calcium continues to drop the next day with levels at 5.7 mg/dL (corrected 6.42 mg/dL, albumin 3.1 g/dL). A calcium infusion of 10 grams was then given over 16 hours. Calcitriol 0.25 mg twice daily was started. 24-hour urine study showed low calcium excretion (<0.8 mg/dL), normal Mg excretion (6.5 mg/dL) with an adequate creatinine collected (0.6 grams) showing no deficiencies in kidney resorption. Prior to discharge, patient’s calcium had stabilized (corrected 8.2 mg/dL, albumin 3.4 g/dL) and her associated symptoms had resolved. She was discharged on Oscal 2 tabs 4 times daily and Calcitriol 1 mcg twice daily. Conclusion: Given these biochemical results and imaging evidence of bone metastases, this case highlights the uncommon findings of hypocalcemia in the setting of malignancy. With the combination of low 24-hour urine calcium, elevated PTH, normal vitamin D25, low PO4, normal kidney function and increased alkaline phosphatase, these findings most likely indicate hypocalcemia secondary to osteoblastic bone metastasis, resulting from deposition of calcium in osteoblastic lesions.

Does differential phosphorus processing by plankton influence the ecological state of shallow lakes?

Shallow lakes have a tendency to settle into turbid or clear-water states, the latter having lower concentrations of total phosphorus (TP). However, how P-cycling is affected by and perhaps contributes to maintaining the different states is not well understood, in part because quantifying the processes involved by traditional methods is difficult. To elucidate these processes, we conducted experiments using 32P-PO4 as a tracer on samples collected from the unrestored, unvegetated sections of Huizhou West Lake where turbid water prevails as well as the restored, clear-water, macrophyte-rich waters of the lake. We measured PO4 uptake rates, 32P-PO4 accumulation by various plankton size-fractions (picoplankton (0.2–2 μm), nanoplankton (2–20 μm) and microplankton (>20 μm)) as well as release rates of 32P-PO4 by labelled plankton. Our results revealed slow PO4 uptake in the turbid state due to low PO4 concentration, slow recycling of the high particulate P, and high levels of particulate 32P which may allow for continuous high growth and biomass of phytoplankton. In contrast, in the clear water state, the uptake of PO4 was rapid due to a higher PO4 concentration, the recycling rates of particulate 32P were high and the levels of particulate 32P were low, potentially constraining the phytoplankton growth. A greater proportion of particulate 32P was in the microplankton fraction in clear waters, suggesting that grazing by microplankton may play an important role in the rapid P recycling in clear-waters. Our results provide some evidence for a reinforcement of the turbid conditions (low recycling rate) when the lake is in a turbid state and vice versa when in the clear water state. The results add new knowledge to the understanding of P cycling in shallow lakes and illustrate the utility of using P-kinetics in contrasting states in plankton communities.

THE IMPACT OF SEAWEED FARMING ON THE PHYTOPLANKTON COMMUNITY STRUCTURE

This study was aimed to analyze the impact of seaweed farming on changes in the structure of phytoplankton communities on various ecosystems and their relationship with environmental factors. The study was conducted in May-October 2017 in the waters of Karampuang Island, Mamuju Regency. Plankton samples were collectedfromthreecultivationareas, namely areas with sandy bottom (control), seagrass beds, and coral reefs. In each area, three media were placed with a longline system, size 40 x 30 m2 (as replication). Sampling was carried out at the beginning before initiation of the cultivation and every two weeks after cultivation was started for 42 days. Phytoplankton sampling and measurement of environmental factors were carried out at fivesamplingpoints representing the cultivation areas. In sandy areas, sampling was also applied in areas outside the cultivation at a distance of 25m and 50m. Variance analysis was used to analyze differences in the species number and abundance of phytoplankton. Ecological indices was used to test phytoplankton biodiversity. PCA was used to analyze its relationship with environmental factors. Differences in the species number and abundance of phytoplankton between farming areas according to temporal scale were found. The high number and speciesabundance of phytoplankton were found in seagrass areas and significantly different from coral reefs and sandy area. Seaweed farming at the beginning of the farming period showed a positive impact by increasing the number of species and abundance of phytoplankton, but then decreased after entering Week 4-Week 6, along with the occurrence of ice-ice disease on the seaweed. Diversity index value was classified as medium with high equality without the dominance of particular species. The high number of species and abundance of phytoplankton occured at second weeks in all cultivation areas which are characterized by abundance of zooplankton with environmental characteristics, i.e. high DO and low PO4, NO3, andDOM.

Influence of Soil Phosphate on the Accumulation and Toxicity of Arsenic and Antimony in Choy Sum Cultivated in Individually and Co-contaminated Soils.

Fertilizers containing phosphate (PO43- ) are commonly used within the agricultural industry and are known to increase the bioavailability and mobility of metalloids like arsenic (As). This may increase plant uptake of As and hence pose a risk to human health. Arsenic and antimony (Sb) often co-occur in contaminated soils; however, little is known about the interactions between As and Sb with PO43- on their bioavailability, accumulation, and toxicity in plants. The present study investigated individual and combined As and Sb-contaminated soils across 2 soil PO43- concentrations using a commonly consumed leafy vegetable, choy sum (Brassica chinensis var. parachinensis). Increased soil PO43- had no clear influence on the bioavailability of As or Sb (derived from a sequential extraction procedure). At high PO43- concentration, B. chinensis accumulated higher amounts of As in the shoots and roots in both individual and co-contaminated soil, whereas Sb accumulation increased only when Sb was the only contaminant. When As was the only contaminant, the translocation of As from roots to shoots decreased as soil PO43- increased. Increased soil PO43- had no influence on Sb translocation from root to shoot. Although As was toxic (impaired growth) at low PO43- soil concentration, no toxicity was observed in the high-PO43- soil. No toxicity was observed for Sb in either low- or high-PO43- soils. Increased soil PO43- concentration ameliorated or masked As toxicity to plant growth and led to higher As concentration in the plant's edible parts. The addition of high soil PO43- concentrations ameliorated or masked As toxicity to plant growth in both individually and As + Sb co-contaminated soil; however, the plant's edible parts accumulated higher As and Sb concentrations. Environ Toxicol Chem 2020;39:1233-1243. © 2020 SETAC.

Using Ca[sbnd]Fe layered double hydroxide transformation to optimise phosphate removal from waste waters

Single phase CaFe layered double hydroxide (LDH) minerals containing Cl− species in the interlayer was synthesized by coprecipitation with a CaII: FeIII ratio of 2: 1. In both phosphate (PO4) free water and at low aqueous PO4 concentration, the LDH was fully transformed into a mixture of a “ferrihydrite-like” material, calcite and soluble calcium species. Mössbauer spectroscopy and transmission electron microscopy showed that phosphate was removed by the “ferrihydrite like” phase that contained a significant quantity of Ca. At high phosphate concentration the Ca species released from the LDH precipitated to form hydroxyapatite leading to a maximal removal capacity of ~ 130 mg P-PO4 g−1. The CaFe LDH was deposited onto a pozzolana volcanic rock in order to perform a column experiment under hydrodynamic conditions for 70 days. A high removal capacity was observed, a qB of ~ 4 mg P-PO4 g−1 was measured at the breakthrough of the column, however the pH in the outflow was measured to be higher than 11. Such an increase was due to the very high solubility of the CaFe LDH.

Phosphate limitation alleviates the inhibitory effect of manganese on itaconic acid production by Aspergillus terreus

Abstract Lignocellulosic biomass has the potential to serve as a low-cost source of sugars for production of itaconic acid (IA, a building block platform chemical) by fermentation with Aspergillus terreus. However, the IA production from biomass hydrolysate was severely inhibited. Mn2+ was found to inhibit the IA production strongly. The effect of Mn2+ on each medium component (KH2PO4, NH4NO3, MgSO4·7H2O, CaCl2·2H2O, FeCl3·6H2O, ZnSO4·7H2O, and CuSO4·7H2O) was evaluated for sugar utilization and IA production by A. terreus NRRL 1972. Both K+ and PO4−3 were necessary for IA production. Low PO4−3 in the medium greatly alleviated the inhibitory effect of Mn2+ on IA production. However, high PO4−3 (K+) was detrimental for IA production in the presence of Mn2+. The inhibitory effect of Mn2+ on IA production was partly eliminated by increasing the CuSO4·7H2O level in the medium. This is the first report on the effect of phosphate limitation to alleviate the inhibition of IA production by Mn2+ and on the relationship of Mn2+ on the medium components for utilization of sugar and production of IA.

Effects of stream velocity and phosphorus concentrations on alkaline phosphatase activity and carbon:phosphorus ratios in periphyton

We studied several streams spanning a steep dissolved phosphorus (PO4–P) gradient to test the hypothesis that faster stream velocity would reduce alkaline phosphatase activity (APA) and carbon:phosphorus (C:P) of benthic periphyton because higher velocities should increase the supply rate of dissolved phosphorus at the community–water interface. We tested the hypothesis that the differences in APA and C:P between fast and slow velocity locations within a stream reach would decline as stream PO4–P concentrations increased, and, therefore, velocity effects should be the greatest at low levels of PO4–P. APA declined in response to both the increased water velocity and PO4–P, but the effect of velocity on APA was negligible at the highest levels of PO4–P. Further, we found a strong, negative relationship between periphyton C:P and PO4–P levels as hypothesized, but did not detect significant relationship between C:P and velocity after accounting for the effects of PO4–P. The lack of an effect of velocity on C:P is probably due to the higher levels of APA in low-velocity, low PO4–P reaches, as the higher APA rates reflect an alternative pathway for acquiring sufficient PO4–P to sustain periphytic growth and metabolism. These results have important implications for stream ecosystem function because of the increasing frequency of extreme weather events associated with the climate change, particularly droughts that reduce or eliminate perennial stream flow, and further illustrate the important effects of stream flow on biogeochemical processes.

A tale of two gyres: Contrasting distributions of dissolved cobalt and iron in the Atlantic Ocean during an Atlantic Meridional Transect (AMT-19)

Cobalt (Co) and iron (Fe) are essential for phytoplankton nutrition, and as such constitute a vital link in the marine biological carbon pump. Atmospheric deposition is an important, and in some places the dominant, source of trace elements (TEs) to the global ocean. Dissolved cobalt (dCo) and iron (dFe) were determined along an Atlantic Meridional Transect (AMT-19; Oct/Nov 2009) between 50°N and 40°S in the upper 150m in order to investigate the behaviour and distribution of these two essential, bioactive TEs. During AMT-19, large differences in the distributions of dCo and dFe were observed. In the North Atlantic gyre provinces, extremely low mixed layer dCo concentrations (23±9pM) were observed, which contrasts with the relatively high mixed layer dFe concentrations (up to 1.0nM) coincident with the band of highest atmospheric deposition (∼5–30°N). In the South Atlantic gyre, the opposite trend was observed, with relatively high dCo (55±18pM) observed throughout the water column, but low dFe concentrations (0.29±0.08nM). Given that annual dust supply is an order of magnitude greater in the North than the South Atlantic, the dCo distribution was somewhat unexpected. However, the distribution of dCo shows similarities with the distribution of phosphate (PO43−) in the euphotic zone of the Atlantic Ocean, where the North Atlantic gyre is characterised by chronically low PO4, and higher concentrations are observed in the South Atlantic gyre (Mather et al., 2008), suggesting the potential for a similar biological control of dCo distributions. Inverse correlations between dCo and Prochlorococcus abundance in the North Atlantic gyre provinces, combined with extremely low dCo where nitrogen fixation rates were highest (∼20–28°N), suggests the dominance of biological controls on dCo distributions. The contrasting dCo and dFe distributions in the North and South Atlantic gyres provides insights into the differences between the dominant controls on the distribution of these two bioactive trace metals in the central Atlantic Ocean.

Genomic potential for arsenic efflux and methylation varies among global Prochlorococcus populations.

The globally significant picocyanobacterium Prochlorococcus is the main primary producer in oligotrophic subtropical gyres. When phosphate concentrations are very low in the marine environment, the mol:mol availability of phosphate relative to the chemically similar arsenate molecule is reduced, potentially resulting in increased cellular arsenic exposure. To mediate accidental arsenate uptake, some Prochlorococcus isolates contain genes encoding a full or partial efflux detoxification pathway, consisting of an arsenate reductase (arsC), an arsenite-specific efflux pump (acr3) and an arsenic-related repressive regulator (arsR). This efflux pathway was the only previously known arsenic detox pathway in Prochlorococcus. We have identified an additional putative arsenic mediation strategy in Prochlorococcus driven by the enzyme arsenite S-adenosylmethionine methyltransferase (ArsM) which can convert inorganic arsenic into more innocuous organic forms and appears to be a more widespread mode of detoxification. We used a phylogenetically informed approach to identify Prochlorococcus linked arsenic genes from both pathways in the Global Ocean Sampling survey. The putative arsenic methylation pathway is nearly ubiquitously present in global Prochlorococcus populations. In contrast, the complete efflux pathway is only maintained in populations which experience extremely low PO4:AsO4, such as regions in the tropical and subtropical Atlantic. Thus, environmental exposure to arsenic appears to select for maintenance of the efflux detoxification pathway in Prochlorococcus. The differential distribution of these two pathways has implications for global arsenic cycling, as their associated end products, arsenite or organoarsenicals, have differing biochemical activities and residence times.

Survival mechanisms of phytoplankton in conditions of stratification‐induced deprivation of orthophosphate: Northern Adriatic case study

Phytoplankton abundance in the northern Adriatic during the summer 2008 indicated that the system was highly productive, in spite of low orthophosphate (PO4) concentrations. Mechanisms by which phytoplankton adapted to PO4 deprivation during the summer stratification were studied. In upper, more productive waters, phytoplankton induced high alkaline phosphatase activity (APA) to obtain phosphorus (P) from the dissolved organic pool, and the P turnover time mediated by phytoplankton APA was very short (2 min to 1.5 h). High‐affinity enzymatic activity combined with high hydrolysis rates enabled metabolic flexibility to the phytoplankton in this heterogeneous and fluctuating environment. Another possible mechanism of adaptation to the PO4 deficit during the summer was a shift toward smaller cells. The smaller nanophytoplankton, supported by higher surface : volume ratios, were presumably able to produce more alkaline phosphatase, an exoenzyme bound to the cell surface. Progressive decrease of large cells and increase of smaller cells in the phytoplankton community during summer supported this hypothesis. In upper waters with low PO4 concentrations, phytoplankton reduced their P demand by a preferential synthesis of non‐phospholipids. In bottom waters, phytoplankton abundance was markedly lower than in upper waters and growth was probably light limited. In these deeper waters with higher PO4 concentrations, phytoplankton cells did not use APA to obtain P and were able to synthesize more phospholipids. In deeper waters, growth of bigger cells was favored.

Development of an attached growth reactor for NH4–N removal at a drinking water supply system in Kathmandu Valley, Nepal

Higher concentrations of ammonium (NH4–N) and iron (Fe) than a standard for drinking are typical characteristics of groundwater in the study area. To remove NH4–N and Fe, the drinking water supply system in this study consists of a series of treatment units (i.e., aeration and sedimentation, filtration, and chlorination); however, NH4−N in treated water is higher than a standard for drinking (i.e., <1.5 mg NH4–N/L). The objective of this study, therefore, is to develop an attached growth system containing a fiber carrier for reducing NH4–N concentration within a safe level in the treated water. To avoid the need of air supply for nitrification, groundwater was continuously dripped through the reactor. It made the system simple operation and energy efficient. Effects of reactor design (reactor length and carrier area) were studied to achieve a high NH4−N removal efficiency. In accordance with raw groundwater characteristics in the area, effects of low inorganic carbon (IC) and phosphate (PO4–P) and high Fe on the removal efficiency were also investigated. The results showed a significant increase in NH4–N removal efficiency with reactor length and carrier area. A low IC and PO4–P had no effect on NH4–N removal, whereas a high Fe decreased the efficiency significantly. The first 550 days operation of a pilot−scale reactor installed in the drinking water supply system showed a gradual increase in the efficiency, reaching to 95−100%, and stability in the performance even with increased flow rate from 210 to 860 L/day. The high efficiency of the present work was indicated because only less than 1 mg of NH4−N/L was left over in the treated water.

Pyromorphite formation from montmorillonite adsorbed lead

Pyromorphite formation from montmorillonite adsorbed lead The reaction of Pb-adsorbed montmorillonite with aqueous solutions of PO4 and Cl ions results in the decrease in phosphate concentration associated with the formation of a new phase - pyromorphite Pb5(PO4)3Cl. Pyromorphite crystals range in size from hundreds of nm to several tens of μm, depending on the PO4, K, and Ca concentrations in the reacting system. A strong ion-exchange effect of K+ and Ca2+ cations on desorption of Pb2+ from Pb-adsorbed montmorillonite was observed. Also, a high concentration of cations leads to a rapid desorption of Pb and the formation of fine pyromorphite crystals. In contrast, low PO4, K and Ca concentrations result in the formation of relatively large euhedral crystals. Final Pb concentrations are much lower in experimental sets than in control experiments with no phosphate present.

Spatial patterns of P fractions and chemical properties in soils of two native shrub communities in Senegal

Two shrub species (Piliostigma reticulatum (D.C.) Hochst (Caesalpinioideae) and Guiera senegalensis J.F. Gmel (Combretaceae) are commonly found in farmers’ fields at varying densities in semi-arid Senegal and throughout the Sahel where soils have chronically low phosphorus (P) availability. It seems plausible that shrub litter and the rhizospheres could influence P fractions and other chemical soil properties that affect crop productivity. Thus, a study was done at two sites, on the distribution of inorganic and organic soil P pools, organic C levels, and pH in soil beneath and outside the canopies of P. reticulatum and G. senegalensis (0-30 cm depth). Both sites had low total P ranging from 64 mg P kg−1 to 135 mg P kg-1, and low extractable PO4 (resin Pi) (1–6 mg P kg−1) with P fractions dominated by NaOH-P. Organic P (Po) made up about 50% of total P, and most of the organic P (>60%) was found in the NaOH-P fractions. The labile P, particularly bicarb-Po was higher in soil beneath shrub canopies (8.4 mg P kg −1), than outside the canopy (6.2 mg P kg −1). Similarly, C, N and P to a lesser extent, were more concentrated beneath shrub canopies. P. reticulatum soil was dominated by the NaOH-Po fraction, whereas G. senegalensis had higher bicarb-Po at one of the study sites. An index of biologically available organic P (Bicarb-Po) / (Bicarb-Po + Bicar-Pi + Resin Pi) was > 60% and indicates that biological processes represent an important part of P cycling in these shrub ecosystems. The differential ability of shrubs in modifying soil chemical properties under their canopies has major implications for biogeochemical cycling of nutrients and C in sandy soils of semi arid Sahelian ecosystems.

Phosphate supply and arsenate toxicity in ectomycorrhizal fungi

Three species of ectomycorrhizal fungi (Hebeloma crustuliniforme, Suillus variegatus and Cenococcum geophilum) were grown in axenic culture amended with range of AsO4(3-) concentration under three different PO4(3-) regimes. The fungi exhibited different growth responses to AsO4(3-) that varied with PO4(3-) concentration. Suillus variegatus showed the greatest sensitivity to AsO4(3-), with growth almost completely inhibited in the presence of AsO4(3-) under the lower two PO4(3-) treatments. Under the highest PO4(3-) treatment however, growth was enhanced and S. variegatus was able to persist at AsO4(3-) concentrations of up to 4 mM. Hebeloma crustuliniforme also showed high sensitivity to AsO4(3-) especially at low PO4(3-) concentration. The two higher PO4(3-) treatments had an ameliorating effect on AsO4(3-) toxicity in H. crustuliniforme. This demonstrates the ability of PO4(3-) to alleviate AsO4(3-) toxicity. The response from S. variegatus and H. crustuliniforme, both basidiomycetes, was in contrast to the ascomycete C. geophilum. This fungus demonstrated tolerance to AsO4(3-) when grown in culture solution and PO4(3-) did not have an ameliorating effect on AsO4(3-) toxicity in C. geophilum.

Phytoplankton index of biotic integrity for Chesapeake Bay and its tidal tributaries

A Phytoplankton Index of Biotic Integrity (P-IBI) was developed from data collected during 18 yr 91985–2002) of the Chesapeake Bay Water Quality Monitoring Program. Dissolved inorganic nitrogen (DIN), orthophosphate (PO4), and Secchi depth were used to characterize phytoplankton habitat conditions. Low DIN and PO4 concentrations and high Secchi depths characterized least-impaire conditions. Thirty-eight phytoplankton metrics were tested for their ability to discriminate between impaired and least-impaired habitat conditions. Twelve discriminatory metrics were chosen, and different combinations of these twelve metrics were scored and used to create phytoplankton community indexes for spring and summer in the four salinity regimes in Chesapeake Bay. The scoring criteria for each metric were based on the distribution of the metric’s values in least-impaired conditions relative to the distribution in impaired conditions. An independent data set and jackknife validation procedure were used to examine P-IBI performance. The P-IBI correctly classified 70.0–84.4% of the impaired and least-impaired samples, grouped by season and salinity, in the calibration data set. The P-IBI is a management tool to assess phytoplankton community status relative to estuarine nutrient and light conditions.