Estimation of nitrogen dynamics in a vertical-flow constructed wetland

The vertical-flow constructed wetland (VFCW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewater and stormwater. The aim of this study was to develop a model using the STELLA software for estimating nitrogen (N) dynamics in an artificial VFCW (i.e., a substrate column with six zones) associated with a growing Cyperus alternifolius species under a wetting (wastewater) -to-drying ratio of 1:3. The model was calibrated by our experimental data with a reasonable agreement prior to its applications. Simulations showed that rates of NH₄⁺-N and NO₃⁻-N leaching decreased with increasing zone number (or column depth), although such a decrease was much more profound for NH₄⁺-N. Our simulations further revealed that rate of NH₄⁺-N leaching decreased with time within each zone, whereas rate of NO₃⁻-N leaching increased with time within each zone. Additionally, both the rates of NH₄⁺-N and NO₃⁻-N leaching through zones followed the water flow pattern: breakthrough during wetting period and cessation during drying period. In general, the cumulative amounts of total nitrogen (TN) were in the following order: leaching > denitrification > uptake > settlement. About 54% of the TN from the wastewater flowed out of the VFCW system, 18% of TN lost due to denitrification, 6% of TN was taken up by roots of a single plant (one hill), and the rest of 22% TN from the wastewater was removed from other mechanisms, such as volatilization, adsorption, and deposition. This study suggested that to improve the overall performance of a VFCW for N removal, prevention of N leaching loss was one of the major issues.     

Estimation of long-term variation in nutrient loads from the Hii River by comparing the change in observed and calculated loads in the catchments

To study the long-term change in nutrient loads from the Hii River to Lake Shinji, water samples were taken repeatedly over a year in 1983/1984 and again in 2001/2002. Annual total nitrogen (TN) loads, estimated from observations of water quality and river flow, increased from 860 to 920 t with a corresponding increase in NO₃–N concentration during the cool season. In contrast, total phosphorus (TP) loads decreased from 96 to 62 t. Annual TN and TP loads, calculated using emission factors and annual statistics for the catchments, showed a tendency to decline from 1986 to 2002. No source could be identified which would result in the increase in TN in the catchments, therefore, the increase in observed TN loads was considered to originate in other areas. Atmospheric nitrogen deposition transported from long distances has elevated the sum of NH₄–N and NO₃–N concentration in rainwater in the cool season. Therefore, it was considered that this resulted in the increase in TN loads in the Hii River.     

Integrated stream and wetland restoration: A watershed approach to improved water quality on the landscape

Water quality in Upper Sandy Creek, a headwater stream for the Cape Fear River in the North Carolina Piedmont, is impaired due to high N and P concentrations, sediment load, and coliform bacteria. The creek and floodplain ecosystem had become dysfunctional due to the effects of altered storm water delivery following urban watershed development where the impervious surface reached nearly 30% in some sub-watersheds. At Duke University, an 8-ha Stream and Wetland Assessment Management Park (SWAMP) was created in the lower portion of the watershed to assess the cumulative effect of restoring multiple portions of stream and former adjacent wetlands, with specific goals of quantifying water quality improvements. To accomplish these goals, a three-phase stream/riparian floodplain restoration (600 m), storm water reservoir/wetland complex (1.6 ha) along with a surface flow treatment wetland (0.5 ha) was ecologically designed to increase the stream wetland connection, and restore groundwater wetland hydrology. The multi-phased restoration of Sandy Creek and adjacent wetlands resulted in functioning riparian hydrology, which reduced downstream water pulses, nutrients, coliform bacteria, sediment, and stream erosion. Storm water event nutrient budgets indicated a substantial attenuation of N and P within the SWAMP project. Most notably, (NO₂⁻ + NO₃⁻)-N loads were reduced by 64% and P loads were reduced by 28%. Sediment retention in the stormwater reservoir and riparian wetlands showed accretion rates of 1.8 cm year⁻¹ and 1.1 cm year⁻¹, respectively. Sediment retention totaled nearly 500 MT year⁻¹.     

Nitrogen uptake responses of Gracilaria vermiculophylla (Ohmi) Papenfuss under combined and single addition of nitrate and ammonium

The ammonium (NH₄⁺) and nitrate (NO₃⁻) uptake responses of tetrasporophyte cultures from a Portuguese population of Gracilaria vermiculophylla were studied. Thalli were incubated at 5 nitrogen (N) levels, including single (50 μM of NH₄⁺ or NO₃⁻) and combined addition of each of the N sources. For the combined additions, the experimental conditions attempted to simulate 2 environments with high N availability (450 μM NO₃⁻ + 150 μM NH₄⁺; 250 μM NO₃⁻ + 50 μM NH₄⁺) and the mean N concentrations occurring at the estuarine environment of this population (30 μM NO₃⁻ + 5 μM NH₄⁺). The uptake kinetics of NH₄⁺ and NO₃⁻ were determined during a 4 h time-course experiment with N deprived algae. The experiment was continued up to 48 h, with media exchanges every 4 h. The uptake rates and efficiency of the two N sources were calculated for each time interval. For the first 4 h, G. vermiculophylla exhibited non-saturated uptake for both N sources even for the highest concentrations used. The uptake rates and efficiency calculated for that period (V_0-4 h), respectively, increased and decreased with increasing substrate concentration. NO₃⁻ uptake rates were superior, ranging from 1.06 ± 0.1 to 9.65 ± 1.2 μM g(dw)⁻¹ h⁻¹, with efficiencies of 19% to 53%. NH₄⁺ uptake rates were lower (0.32 ± 0.0 to 5.75 ± 0.08 μM g(dw)⁻¹ h⁻¹) but G. vermiculophylla removed 63% of the initial 150 μM and 100% at all other conditions. Uptake performance of both N sources decreased throughout the duration of the experiment and with N tissue accumulation. Both N sources were taken up during dark periods though with better results for NH₄⁺. Gracilaria vermiculophylla was unable to take up NO₃⁻ at the highest concentration but compensated with a constant 27% NH₄⁺ uptake through light and dark periods. N tissue accumulation was maximal at the highest N concentration (3.9 ± 0.25% dw) and superior under NH₄⁺ (3.57 ± 0.2% dw) vs NO3 (3.06 ± 0.1% dw) enrichment. The successful proliferation of G. vermiculophylla in estuarine environments and its potential utilization as the biofilter component of Integrated Multi-Trophic Aquaculture (IMTA) are discussed.     

Assembly of two low-dimensional coordination polymers from Ag(I) and Cd(II) and 2,3-bis(2-pyridyl)pyrazine

Polydentate nitrogen heterocycle ligand 2,3-bis(2-pyridyl)pyrazine (2,3-dpp) reacted with M(NO₃)_x (M = Ag, x = 1; M = Cd, x = 2) to give two new complexes [Ag(2,3-dpp)(NO₃)]₂ (1) and [Cd(2,3-dpp)(NO₃)₂]_n (2). Both complexes have been characterized by single-crystal X-ray diffraction, elemental analyses, IR and ¹H NMR spectroscopy. Single-crystal X-ray analyses showed that complex 1 crystallized in monoclinic, space group P2₁/n is a dimmer containing penta-coordinated Ag⁺ ion. While compound 2 has 1D chain-like structure with repeat unit Cd(2,3-dpp)(NO₃)₂, in which the Cd(II) presents octa-coordinated N4O4 donor set with two four-membered chelating rings and two five-membered chelating rings around Cd(II) ion. Meanwhile, every neutral chain [Cd(2,3-dpp)(NO₃)₂]_n is mutually connected by face-to-face π?π packing interactions to form a two dimensional layer. Furthermore, antibacterial activities of compound 1 and luminescent property of the compound 2 are also investigated.     

Kinetics of the complexation of nickel(II) with 1,10-phenanthroline and its derivatives in acetonitrile-water mixed solvents

The kinetics of the complexation of Ni(II) with 1,10-phenanthroline(phen), 4,7-dimethyl-1,10-phenanthroline(dmphen), and 5-nitro-1,10-phenanthroline(NO₂phen) in acetonitrile-water mixed solvents of acetonitrile mole fraction x_AN = 0, 0.05, 0.1, 0.2 and 0.3 at 288, 293, 298 and 303 K have been studied by stopped-flow method at ionic strength of 1.0 (NaClO₄) and pH 7.4. The corresponding activation enthalpy, entropy, and free energy were determined from the observed rate constants. The complexation of Ni(II) with the three ligands has comparable observed rate constants; in pure water the observed rate constants are (×10³ dm³ mol⁻¹ s⁻¹) 2.31, 2.57, and 1.38 for phen, dmphen and NO₂phen, respectively. The corresponding activation parameters for the three ligands are, however, considerably different; in pure water the ΔH^‡/ΔS^‡ (kJ mol⁻¹/J K⁻¹ mol⁻¹) are 44.7/−30.2, 19.5/−114.1, and 32.2/−76.9 for phen, dmphen, and NO₂phen, respectively. The effects of solvent composition on the kinetics are also markedly different for the three ligands. The ΔH^‡ and ΔS^‡ showed a minimum at x_AN = 0.1 for phen; for dmphen and NO₂phen, however, maxima at x_AN = 0.2 were observed. Nevertheless, there is an effective enthalpy-entropy compensation for the ΔH^‡/ΔS^‡ of all the three ligands, demonstrating the significant effects of the changes in solvation and solvent structure on the complexation kinetics. As the rate-determining step of Ni(II) complexation is the dissociation of a water molecule from Ni(II), the solvent and ligand dependencies in the Ni(II) complexation kinetics are ascribed to the change in solvation status of the ligands and the altered solvent structures upon changing solvent composition.     

Nitrogen nutrition of Canna indica: Effects of ammonium versus nitrate on growth, biomass allocation, photosynthesis, nitrate reductase activity and N uptake rates

The effects of inorganic nitrogen (N) source (NH₄⁺, NO₃⁻ or both) on growth, biomass allocation, photosynthesis, N uptake rate, nitrate reductase activity and mineral composition of Canna indica were studied in hydroponic culture. The relative growth rates (0.05-0.06 g g⁻¹ d⁻¹), biomass allocation and plant morphology of C. indica were indifferent to N nutrition. However, NH₄⁺ fed plants had higher concentrations of N in the tissues, lower concentrations of mineral cations and higher contents of chlorophylls in the leaves compared to NO₃⁻ fed plants suggesting a slight advantage of NH₄⁺ nutrition. The NO₃⁻ fed plants had lower light-saturated rates of photosynthesis (22.5 μmol m⁻² s⁻¹) than NH₄⁺ and NH₄⁺/NO₃⁻ fed plants (24.4-25.6 μmol m⁻² s⁻¹) when expressed per unit leaf area, but similar rates when expressed on a chlorophyll basis. Maximum uptake rates (V_max) of NO₃⁻ did not differ between treatments (24-35 μmol N g⁻¹ root DW h⁻¹), but V_max for NH₄⁺ was highest in NH₄⁺ fed plants (81 μmol N g⁻¹ root DW h⁻¹), intermediate in the NH₄NO₃ fed plants (52 μmol N g⁻¹ root DW h⁻¹), and lowest in the NO₃⁻ fed plants (28 μmol N g⁻¹ root DW h⁻¹). Nitrate reductase activity (NRA) was highest in leaves and was induced by NO₃⁻ in the culture solutions corresponding to the pattern seen in fast growing terrestrial species. Plants fed with only NO₃⁻ had high NRA (22 and 8 μmol NO₂⁻ g⁻¹ DW h⁻¹ in leaves and roots, respectively) whereas NRA in NH₄⁺ fed plants was close to zero. Plants supplied with both forms of N had intermediate NRA suggesting that C. indica takes up and assimilate NO₃⁻ in the presence of NH₄⁺. Our results show that C. indica is relatively indifferent to inorganic N source, which together with its high growth rate contributes to explain the occurrence of this species in flooded wetland soils as well as on terrestrial soils. Furthermore, it is concluded that C. indica is suitable for use in different types of constructed wetlands.     

Nitrogen nutrition of Salvinia natans: Effects of inorganic nitrogen form on growth,morphology, nitrate reductase activity and uptake kinetics of ammonium and nitrate

In this study we assessed the growth, morphological responses, and N uptake kinetics of Salvinia natans when supplied with nitrogen as NO₃⁻, NH₄⁺, or both at equimolar concentrations (500 μM). Plants supplied with only NO₃⁻ had lower growth rates (0.17 ± 0.01 g g⁻¹ d⁻¹), shorter roots, smaller leaves with less chlorophyll than plants supplied with NH₄⁺ alone or in combination with NO₃⁻ (RGR = 0.28 ± 0.01 g g⁻¹ d⁻¹). Ammonium was the preferred form of N taken up. The maximal rate of NH₄⁺ uptake (V_max) was 6–14 times higher than the maximal uptake rate of NO₃⁻ and the minimum concentration for uptake (C_min) was lower for NH₄⁺ than for NO₃⁻. Plants supplied with NO₃⁻ had elevated nitrate reductase activity (NRA) particularly in the roots showing that NO₃⁻ was primarily reduced in the roots, but NRA levels were generally low (<4 μmol NO₂⁻ g⁻¹ DW h⁻¹). Under natural growth conditions NH₄⁺ is probably the main N source for S. natans, but plants probably also exploit NO₃⁻ when NH₄⁺ concentrations are low. This is suggested based on the observation that the plants maintain high NRA in the roots at relatively high NH₄⁺ levels in the water, even though the uptake capacity for NO₃⁻ is reduced under these conditions.     

Effects of inorganic nitrogen forms on growth, morphology, nitrogen uptake capacity and nutrient allocation of four tropical aquatic macrophytes (Salvinia cucullata, Ipomoea aquatica, Cyperus involucratus and Vetiveria zizanioides)

This study assesses the growth and morphological responses, nitrogen uptake and nutrient allocation in four aquatic macrophytes when supplied with different inorganic nitrogen treatments (1) NH₄⁺, (2) NO₃⁻, or (3) both NH₄⁺ and NO₃⁻. Two free-floating species (Salvinia cucullata Roxb. ex Bory and Ipomoea aquatica Forssk.) and two emergent species (Cyperus involucratus Rottb. and Vetiveria zizanioides (L.) Nash ex Small) were grown with these N treatments at equimolar concentrations (500 μM). Overall, the plants responded well to NH₄⁺. Growth as RGR was highest in S. cucullata (0.12 ± 0.003 d⁻¹) followed by I. aquatica (0.035 ± 0.002 d⁻¹), C. involucratus (0.03 ± 0.002 d⁻¹) and V. zizanioides (0.02 ± 0.003 d⁻¹). The NH₄⁺ uptake rate was significantly higher than the NO₃⁻ uptake rate. The free-floating species had higher nitrogen uptake rates than the emergent species. The N-uptake rate differed between plant species and seemed to be correlated to growth rate. All species had a high NO₃⁻ uptake rate when supplied with only NO₃⁻. It seems that the NO₃⁻ transporters in the plasma membrane of the root cells and nitrate reductase activity were induced by external NO₃⁻. Tissue mineral contents varied with species and tissue, but differences between treatments were generally small. We conclude, that the free-floating S. cucullata and I. aquatica are good candidate species for use in constructed wetland systems to remove N from polluted water. The rooted emergent plants can be used in subsurface flow constructed wetland systems as they grow well on any form of nitrogen and as they can develop a deep and dense root system.     

Nitrogen dynamics in Lake Okeechobee: forms,functions, and changes

Total nitrogen (TN) in Lake Okeechobee, a large, shallow, turbid lake in south Florida, has averaged between 90 and 150 μM on an annual basis since 1983. No TN trends are evident, despite major storm events, droughts, and nutrient management changes in the watershed. To understand the relative stability of TN, this study evaluates nitrogen (N) dynamics at three temporal/spatial levels: (1) annual whole lake N budgets, (2) monthly in-lake water quality measurements in offshore and nearshore areas, and (3) isotope addition experiments lasting 3 days and using ¹⁵N-ammonium (¹⁵NH₄ ⁺) and ¹⁵N-nitrate (¹⁵NO₃ ⁻) at two offshore locations. Budgets indicate that the lake is a net sink for N. TN concentrations were less variable than net N loads, suggesting that in-lake processes moderate these net loads. Monthly NO₃ ⁻ concentrations were higher in the offshore area and higher in winter for both offshore and nearshore areas. Negative relationships between the percentage of samples classified as algal blooms (defined as chlorophyll a > 40 μg l⁻¹) and inorganic N concentrations suggest N-limitation. Continuous-flow experiments over intact sediment cores measured net fluxes (μmol N m⁻² h⁻¹) between 0 and 25 released from sediments for NH₄ ⁺, 0–60 removed by sediments for NO₃ ⁻, and 63–68 transformed by denitrification. Uptake rates in the water column (μmol N m⁻² h⁻¹) determined by isotope dilution experiments and normalized for water depth were 1,090–1,970 for NH₄ ⁺ and 59–119 for NO₃ ⁻. These fluxes are similar to previously reported results. Our work suggests that external N inputs are balanced in Lake Okeechobee by denitrification.     

A family of lanthanide-containing molecular open frameworks with high porosity: [Ln(abdc)(Habdc), nH2O]∞ with Ln = La-Eu and 8 ? n ? 11

Reactions in water between the di-sodium salt of amino terepthalic acid (C₈H₃NO₄Na₂) and a lanthanide chloride lead to a family of 3D-coordination polymers with general chemical formula [Ln(C₈H₃NO₄)(C₈H₄NO₄), O]_∞ where Ln = La-Eu (except Pm) and 8 ? n ? 11. All these compounds are isostructural. High quality single crystals of [Ln(C₈H₃NO₄)(C₈H₄NO₄), nH₂O]_∞ with Ln = La-Sm (except Pm) and 8 ? n ? 11 have been obtained by slow diffusion in agar-agar gels. The crystal structure has been solved for the Nd-containing compound. This compound crystallizes in the cubic system, space group Ia-3 (no. 206) with a = 26.8056(5) Å. The crystal structure can be described as the juxtaposition of large channels with square cross-section.The channels are filled by highly disordered crystallization water molecules. The dehydration of the compounds by freeze-drying is possible and most of the crystallization water molecules can be removed without destruction of the molecular skeleton. The partially dehydrated compounds have general chemical formula [Ln(abdc)(Habdc), 2H₂O]_∞ with Ln = La-Eu except Pm. The porosity of the Nd-containing compound has been estimated by computational methods to 2170 m² g⁻¹. This dehydrated compound reversibly binds water when exposed to wet atmosphere restoring the initial hydrated phase.     

Isolation of Pseudomonas stutzeri in wastewater of catfish fish-ponds in the Mekong Delta and its application for wastewater treatment

The aim of this study was to explore the potential for reducing soluble N load in fishpond wastewater using naturally occurring denitrifying bacteria. Twenty-seven isolates were selected from in wastewater (liquid/solid) of catfish-ponds located along the Tien river, in the Mekong Delta, Vietnam in SW-LB medium (artificial seawater Luria-Britani medium) supplemented with 10 mM NH₄ and NO₃ and twenty-five isolates were identified as Pseudomonas stutzeri based on similarity of PCR-16S rRNA using universal primers and specific primers. Four isolates were effective in lowering soluble N (NH₄, NO₂ and NO₃) levels in fishpond water from 10 mg/L to negligible amounts after four days. Further experiments are underway to determine the fate of N lost from solution and the relative activity of ammonia oxidation, and nitrite and nitrate reduction by P. stutzeri isolates.     

Extended molecular networks based on Zn and Cd imparting N-substituted imidazole

Synthesis of complexes with the formulations [M(CPI)₂Cl₂] (M = Zn, 1; M = Cd, 4) and [M(CPI)₆](X)₂ (M = Zn, X = NO₃⁻, 2; X = ClO₄⁻, 3; M = Cd, X = NO₃⁻, 5; X = ClO₄⁻, 6) have been achieved from the reactions of MCl₂, M(NO₃)₂·xH₂O and M(ClO₄)₂·xH₂O (M = Zn, Cd) with 1-(4-cyanophenyl)-imidazole (CPI). Complexes 1-6 have been characterized by elemental analyses and spectral studies (IR, ¹H, ¹³C NMR, electronic absorption and emission). Molecular structures of 1, 2, 3 and 6 have been determined crystallographically. Weak interaction studies on the complexes revealed presence of various interesting motifs resulting from C-H···N, C-H···Cl and π-π stacking interactions. The complexes under study exhibit strong luminescence at ∼450 nm in DMSO at room temperature.     

Riverine nitrogen export in Swedish catchments dominated by atmospheric inputs

We present the first estimates of net anthropogenic nitrogen input (NANI) in European boreal catchments. In Swedish catchments, nitrogen (N) deposition is a major N input (31–94%). Hence, we used two different N deposition inputs to calculate NANI for 36 major Swedish catchments. The relationship between riverine N export and NANI was strongest when using only oxidized deposition (NO_y) as atmospheric input (r² = 0.70) rather than total deposition (i.e., both oxidized and reduced nitrogen, NO_y + NH_x deposition, r² = 0.62). The y-intercept (NANI = 0) for the NANI calculated with NO_y is significantly different from zero (p = 0.0042*) and indicates a background flux from the catchment of some 100 kg N km^?2 year^?1 in addition to anthropogenic inputs. This agrees with similar results from North American boreal catchments. The slope of the linear regressions was 0.25 for both N deposition inputs (NO_y and NO_y + NH_x), suggesting that on average, 25% of the anthropogenic N inputs is exported by rivers to the Baltic Sea. Agricultural catchments in central and southern Sweden have increased their riverine N export up to tenfold compared to the inferred background flux. Although the relatively unperturbed northernmost catchments receive significant N loads from atmospheric deposition, these catchments do not show significantly elevated riverine N export. The fact that nitrogen export in Swedish catchments appears to be higher in proportion to NANI at higher loads suggests that N retention may be saturating as loading rates increase. In northern and western Sweden the export of nitrogen is largely controlled by the hydraulic load, i.e., the riverine discharge normalized by water surface area, which has units of distance time^?1. Besides hydraulic load the percent total forest cover also affects the nitrogen export primarily in the northern and western catchments.     

P NMR and Raman spectroscopic and voltammetric studies on the formation and conversion processes of Keggin-type molybdotungstophosphate(V) and -arsenate(V) complexes in aqueous-organic solvents

The formation conditions of Keggin-type molybdotungstophosphate(V) (PW_xMo_12 − xO₄₀ ³⁻ (PW_xMo_12 − x), x=0-12) and -arsenate(V) (AsW_xMo_12 − xO₄₀ ³⁻ (AsW_xMo_12 − x)) complexes in aqueous-organic solvents were investigated with ³¹P NMR, Raman spectroscopy, and cyclic voltammetry. The conversion processes of the PMo₁₂ and the PW₁₂ anions into the PW_xMo_12 − x anions were also examined and compared with those of the AsMo₁₂ and AsW₁₂ anions into the AsW_xMo_12 − x anions. The mean vibration frequencies of the PW_xMo_12 − x and AsW_xMo_12 − x (x=1-11) complexes were calculated in IR and Raman spectra from those of the PMo₁₂ and PW₁₂, and AsMo₁₂ and AsW₁₂ complexes, respectively.     

Synthetic, EPR spectroscopic, magnetic and X-ray crystallographic structural studies on copper(II) complexes of the tridentate N2S donor ligand formed from 6-methyl-2-formylpyridine and S-methyldithiocarbazate (Hmpsme)

New copper(II) complexes of general empirical formula, Cu(mpsme)X · xCH₃COCH₃ (mpsme = anionic form of the 6-methyl-2-formylpyridine Schiff base of S-methyldithiocarbazate; X = Cl, N₃, NCS, NO₃; x = 0, 0.5) have been synthesized and characterized by IR, electronic, EPR and susceptibility measurements. Room temperature μ_eff values for the complexes are in the range 1.75-2.1 μ_B typical of uncoupled or weakly coupled Cu(II) centres. The EPR spectra of the [Cu(mpsme)X] (X = Cl, N₃, NO₃, NCS) complexes reveal a tetragonally distorted coordination sphere around the mononuclear Cu(II) centre. We have exploited second derivative EPR spectra in conjunction with Fourier filtering (sine bell and Hamming functions) to extract all of the nitrogen hyperfine coupling matrices. While the X-ray crystallography of [Cu(mpsme)NCS] reveals a linear polymer in which the thiocyanate anion bridges the two copper(II) ions, the EPR spectra in solution are typical of a magnetically isolated monomeric Cu(II) centres indicating dissociation of the polymeric chain in solution. The structures of the free ligand, Hmpsme and the {[Cu(mpsme)NO₃] · 0.5CH₃COCH₃}₂ and [Cu(mpsme)NCS]_n complexes have been determined by X-ray diffraction. The {[Cu(mpsme)NO₃] 0.5CH₃COCH₃}₂ complex is a centrosymmetric dimer in which each copper atom adopts a five-coordinate distorted square-pyramidal geometry with an N₂OS₂ coordination environment, the Schiff base coordinating as a uninegatively charged tridentate ligand chelating through the pyridine and azomethine nitrogen atoms and the thiolate, an oxygen atom of a unidentate nitrato ligand and a bridging sulfur atom from the second ligand completing the coordination sphere. The [Cu(mpsme)(NCS)]_n complex has a novel staircase-like one dimensional polymeric structure in which the NCS⁻ ligands bridge two adjacent copper(II) ions asymmetrically in an end-to-end fashion providing its nitrogen atom to one copper and the sulfur atom to the other.     

Overyielding and the role of complementary use of nitrogen in wetland plant communities

Biodiversity and ecosystem functioning experiments have demonstrated that plant biomass of species grown in mixtures is often greater than plant biomass of monocultures (i.e., mixtures over yield). While we understand that plant species utilize resources differently, how a combination of species increases resource use and productivity is not well known, especially in wetland ecosystems. Here, we used a mesocosm experiment to explore diversity effects on plant biomass production and to examine the role of N partitioning as a mechanism for overyielding in wetland ecosystems. Plant functional groups (FGs) represented the unit of diversity, and we included five levels of diversity (0-4 FGs). To test for N partitioning, we used a stable isotope technique to determine niche breadth and proportion similarity of inorganic N use (NO₃⁻ and NH₄⁺) for individual FGs as well as mixtures containing 3 and 4 FGs. We found that total plant biomass increased in the first season from an average of 290 ± 60 SE g ash-free dry mass (AFDM) m⁻² at the 1 FG level to 490 ± 70 g AFDM m⁻² at the 4 FG level and in the second season from an average of 560 ± 80 g AFDM m⁻² at the 1 FG level to 1000 ± 90 g AFDM m⁻² at the 4 FG level indicating overyielding. Plant species comprising the majority of mesocosm biomass demonstrated preferential uptake of ¹⁵NO₃⁻, while species with relatively less biomass (e.g., Acorus calamus and Carex crinita) preferred ¹⁵NH₄⁺. Concentrations of ¹⁵N in biomass increased with FG richness, but only in the ¹⁵NO₃⁻ treatment. Niche breadth did not vary among levels of FG richness. We observed a greater niche overlap with an increase of FGs, with species taking up greater proportion of ¹⁵NO₃⁻ than ¹⁵NH₄⁺. Our results indicate that plant overyielding in wetland mesocosms is not the result of niche partitioning of N chemical forms, but is associated with greater uptake of NO₃.     

A pilot study on the regeneration of ferrous chelate complex in NOx scrubber solution by a biofilm electrode reactor

A chemical absorption-biological reduction integrated process has been proposed for the removal of nitrogen oxides (NO_x) from flue gases. In this study, we report a new approach using biofilm electrode reactor (BER) to regenerate Fe(II)EDTA via simultaneously reducing Fe(II)EDTA-NO and Fe(III)EDTA in NO_x scrubber solution. Biofilm formed on the surface of the cathode was confirmed by Environmental Scan Electro-Microscope. Experimental results demonstrated that it was effective and feasible to utilize the BER to promote the reduction of Fe(II)EDTA-NO and Fe(III)EDTA simultaneously. The reduction efficiency of Fe(II)EDTA-NO and Fe(III)EDTA was up to 85% and 78%, respectively when the BER was continuously operated with electricity current at 30 mA. The absence of electricity induced an immediate decrease in reduction efficiency, indicating that the bio-regeneration of ferrous chelate complex was electrochemically accelerated. The present approach is considered advantageous for the enhanced bio-reduction in the NO_x scrubber solution.     

Influence of substituents on the structures of hybrid complexes constructed from tetranuclear copper(I) 1,2,4-triazolate clusters and octamolybdates

By changing the substituents on 1,2,4-triazole ring, six novel organic-inorganic hybrid complexes constructed from tetranuclear copper(I) 1,2,4-triazolate clusters and octamolybdates, [{Cu₄(L)_x}Mo₈O₂₆] (L = 3,5-diamino-1,2,4-triazole (datrz) and x = 4 for 1; L = 3-amino-1,2,4-triazole (3atrz) and x = 4 for 2; L = 3,5-dimethyl-1,2,4-triazole (dmtrz) and x = 4 for 3; L = 3,5-dimethyl-4-amino-1,2,4-triazole (dmatrz) and x = 6 for 4; L = 3,5-diethyl-4-amino-1,2,4-triazole (deatrz) and x = 4 for 5; L = 3,5-di(n-propyl)-4-amino-1,2,4-triazole (dpatrz) and x = 3 for 6), were obtained. The tetranuclear Cu(I) cluster in compound 1 acts as charge-compensating unit, which is the first polynuclear metal 1,2,4-triazole structure only with N1, N2 bridging mode. Compounds 2, 4, 5 and 6 are of polymeric 1D chains and 3 is of a 2D layer structure. In 2, three distinct Cu(I)-coordination geometries, distorted tetrahedral, T-shaped and V-shaped linear Cu(I), are observed in the same structure. The first extended hybrid structure constructed by δ-octamolybdates is founded in 4. A novel [Mo₈O₂₆]⁴⁻ anion is found in 5, which contains only three crystallographically independent Mo atoms. In compounds 5 and 6, terminal oxo groups of octamolybdate cluster act as μ₃-oxo bridges to link the copper(I) coordination complexes; such an unusual linking manner is unique in the coordination chemistry of octamolybdates with transition metal fragments. The influences of substituent on the structures of the tetranuclear units are also discussed in details.     

Rates, controls and potential adverse effects of nitrate removal in a denitrification bed

Denitrification beds are a simple approach for removing nitrate (NO₃⁻) from a range of point sources prior to discharge into receiving waters. These beds are large containers filled with woodchips that act as an energy source for microorganisms to convert NO₃⁻ to nitrogen (N) gases (N₂O, N₂) through denitrification. This study investigated the biological mechanism of NO₃⁻ removal, its controlling factors and its adverse effects in a large denitrification bed (176 m × 5 m × 1.5 m) receiving effluent with a high NO₃⁻ concentration (>100 g N m⁻³) from a hydroponic glasshouse (Karaka, Auckland, New Zealand). Samples of woodchips and water were collected from 12 sites along the bed every two months for one year, along with measurements of gas fluxes from the bed surface. Denitrifying enzyme activity (DEA), factors limiting denitrification (availability of carbon, dissolved organic carbon (DOC), dissolved oxygen (DO), temperature, pH, and concentrations of NO₃⁻, nitrite (NO₂⁻) and sulfide (S²⁻)), greenhouse gas (GHG) production - as nitrous oxide (N₂O), methane (CH₄), carbon dioxide (CO₂) - and carbon (C) loss were determined. NO₃⁻-N concentration declined along the bed with total NO₃⁻-N removal rates of 10.1 kg N d⁻¹ for the whole bed or 7.6 g N m⁻³ d⁻¹. NO₃⁻-N removal rates increased with temperature (Q₁₀ = 2.0). In laboratory incubations, denitrification was always limited by C availability rather than by NO₃⁻. DO levels were above 0.5 mg L⁻¹ at the inlet but did not limit NO₃⁻-N removal. pH increased steadily from about 6 to 7 along the length of the bed. Dissolved inorganic carbon (C-CO₂) increased in average about 27.8 mg L⁻¹, whereas DOC decreased slightly by about 0.2 mg L⁻¹ along the length of the bed. The bed surface emitted on average 78.58 μg m⁻² min⁻¹ N₂O-N (reflecting 1% of the removed NO₃⁻-N), 0.238 μg m⁻² min⁻¹ CH₄ and 12.6 mg m⁻² min⁻¹ CO₂. Dissolved N₂O-N increased along the length of the bed and the bed released on average 362 g dissolved N₂O-N per day coupled with N₂O emission at the surface about 4.3% of the removed NO₃⁻-N as N₂O. Mechanisms to reduce the production of this GHG need to be investigated if denitrification beds are commonly used. Dissolved CH₄ concentrations showed no trends along the length of the bed, ranging from 5.28 μg L⁻¹ to 34.24 μg L⁻¹. Sulfate (SO₄²⁻) concentrations declined along the length of the bed on three of six samplings; however, declines in SO₄²⁻ did not appear to be due to SO₄²⁻ reduction because S²⁻ concentrations were generally undetectable. Ammonium (NH₄⁺) (range: <0.0007 mg L⁻¹ to 2.12 mg L⁻¹) and NO₂⁻ concentrations (range: 0.0018 mg L⁻¹ to 0.95 mg L⁻¹) were always very low suggesting that anammox was an unlikely mechanism for NO₃⁻ removal in the bed. C longevity was calculated from surface emission rates of CO₂ and release of dissolved carbon (DC) and suggested that there would be ample C available to support denitrification for up to 39 years.This study showed that denitrification beds can be an efficient tool for reducing high NO₃⁻ concentrations in effluents but did produce some GHGs. Over the course of a year NO₃⁻ removal rates were always limited by C and temperature and not by NO₃⁻ or DO concentration.