Evaluation of phosphorus distribution and bioavailability in sediments of a subtropical wetland reserve in southeast China

The phosphorus (P) fractions and bioavailable P in the sediments from the Quanzhou Bay Estuarine Wetland Nature Reserve were investigated using chemical extraction methods for the first time to study the distribution and bioavailability of P in the reserve sediments. A hypothesis was presented suggesting that the bioavailable P in the sediments could be evaluated using the P fractions. The total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP), non-apatite phosphorus (NAIP), and apatite phosphorus (AP) contents in the sediments were in the ranges of 303.87–761.59 mg kg⁻¹, 201.22–577.66 mg kg⁻¹, 75.83–179.16 mg kg⁻¹, 28.86–277.90 mg kg⁻¹, and 127.36–289.94 mg kg⁻¹, respectively. The water soluble phosphorus (WSP), readily desorbable phosphorus (RDP), algal available phosphorus (AAP), and NaHCO₃ extractable phosphorus (Olsen-P) contents in the sediments were in the ranges of 0.58–357.17 mg kg⁻¹, 80.77–586.75 mg kg⁻¹, 1.09–24.12 mg kg⁻¹, and 54.96–676.82 mg kg⁻¹, respectively. The correlation analysis results showed that the NAIP was the major component of the bioavailable P and that the impact of the AP on the bioavailable phosphorus may be minimal. Due to the low TP content in the sediments of the Quanzhou Bay Estuarine Wetland Nature Reserve, the potential pollution risks of P in the sediments may not be very high. The results also show that the bioavailable P concentrations in the sediments of the Quanzhou Bay Estuarine Wetland Nature Reserve could not be evaluated by measuring the P fractions and that the hypothesis was untenable.     

Immobilization of the hyperthermophilic hydrogenase from Aquifex aeolicus bacterium onto gold and carbon nanotube electrodes for efficient H2 oxidation

The electrochemistry of membrane-bound [NiFe] hydrogenase I ([NiFe]-hase I) from the hyperthermophilic bacterium Aquifex aeolicus was investigated at gold and graphite electrodes. Direct and mediated H₂ oxidation were proved to be efficient in a temperature range of 25–70 °C, describing a potential window for H₂ oxidation similar to that of O₂-tolerant hydrogenases. Search for enhancement of current densities and enzyme stability was achieved by the use of carbon nanotube coatings. We report high catalytic currents for H₂ oxidation up to 1 mA cm⁻², 10 times higher than at the bare electrode. Interestingly, high stability of the direct catalytic process was observed when encapsulating A. aeolicus [NiFe]-hase I into a carboxylic functionalized single walled carbon nanotube network. This suggests a peculiar interaction between the enzyme and the electrode material. The parameters that governed the orientation of the enzyme before electron transfer were thus investigated using self-assembled-monolayer gold electrodes. No control of the orientation by the charge or the hydrophobicity of the interface was demonstrated. This behavior was explained on the basis of a structural comparison between A. aeolicus [NiFe]-hase I and Desulfovibrio fructosovorans [NiFe] hydrogenase, which revealed the absence of acidic residues and an additional loop in the environment of the [4Fe–4S] distal cluster in A. aeolicus [NiFe]-hase I. Finally, the effect of inhibitors on the direct oxidation of H₂ by A. aeolicus [NiFe]-hase I encapsulated in a single walled carbon nanotube network was investigated. No inhibition by CO and tolerance toward O₂ were observed. Discussion of the reasons for such tolerance was undertaken on the basis of structural comparison with hydrogenases from aerobic bacteria.     

Response in root morphology and nutrient contents of Myriophyllum spicatum to sediment type

Sediment may play an important role during the submerged macrophyte decline in the eutrophication progress. In order to investigate the response in root morphology and nutrient contents of submerged macrophytes Myriophyllum spicatum to sediment, five sediment types were treated and used (five types of sediment were used in the experiment: treatment 1 was nature sediment + sand, a 50:50 (v/v) mixture, treatment 2 was the studied sediment only, treatment 3 was sediment + nitrogen (N, NH₄Cl 400 mg kg^?1), treatment 4 was sediment + phosphorus (P, NaH₂PO₄ 300 mg kg^?1); treatment 5 was sediment + phosphorus (P, NaH₂PO₄ 600 mg kg^?1)). The results show that the root N content was only significantly affected by adding N in sediments and P was elevated by adding N and P. The root mass and its percentage increased at first, the peak values were reached at 35 d, and then decreased. The root growth was restrained by adding sand and N in sediments, root senescence process was delayed at the later experimental time by adding P in sediments. The increase of root volume showed a similar trend to that of root growth, except for plant with P addition where root volume remained high after 35 d. The root volume decreased while the main root number increased significantly by adding sand in sediments. The mean root length and main root diameter were reduced by adding P in sediments. The compatible sediment nutrient condition is necessary to restore submerged macrophytes in a degraded shallow lake ecosystem, and the effect of sediment on the root morphology and nutrient content is one of the important aspects restricting the restoration of submerged macrophytes.     

Massive uprooting of Littorella uniflora (L.) Asch. during a storm event and its relation to sediment and plant characteristics

During spring storms massive uprooting of Littorella uniflora occurred in a shallow Dutch softwater lake. The aim of this study was to test whether changes in plant morphology and sediment characteristics could explain the observed phenomenon. Uprooting was expected to occur in plants having a high shoot biomass and low root to shoot ratio (R:S), growing on sediments with a high organic matter content. Normally, uprooting of the relative buoyant L. uniflora is prevented by an extensive root system, expressed as a high R:S. This was studied by sampling floating and still rooted L. uniflora plants, as well as sediment and sediment pore water, along a gradient of increasing sediment organic matter content. Increasing organic matter content was related to increasing L. uniflora shoot biomass and consequently decreasing R:S. Furthermore, the results indicated that uprooting indeed occurred in plants growing on very organic sediments and was related to a low R:S. The increased shoot biomass on more organic sediments could be related to increased sediment pore water total inorganic carbon (TIC; mainly CO₂) availability. Additionally, increased phosphorus availability could also have played a role. The disappearance of L. uniflora might lead to higher nutrient availability in the sediments. It is suggested that this could eventually promote the expansion of faster‐growing macrophytes.     

Impact of microphytobenthos and macroinfauna on temporal variation of benthic metabolism in shallow coastal sediments

The impact of microphytobenthos and different abundances of macrofauna (Nereis diversicolor) on temporal variation of benthic metabolism was investigated in laboratory microcosms. Measurements primarily included diurnal fluxes of O₂ and CO₂ as well as sediment profiles of Chlorophyll a and extracellular polymeric substances (EPS). Net and gross primary production (2-5 and 4-7 mmol CO₂ m^{− 2} h^{− 1}, respectively) were relatively stable in both defaunated and faunated sediment throughout a 12 h light period. The CO₂ release from sediments immediately after onset of darkness ranged from 1.5 to 3.5 mmol CO₂ m^{− 2} h^{− 1} followed by a consistent decrease during the next 12 h in the dark. The decrease was more conspicuous in faunated (about 50%) than defaunated (9%) sediment. Total carbon oxidation was in both cases fuelled primarily by microphytobenthic biomass, while EPS only contributed by 1-4%. Diurnal measurements of Nereis diversicolor ventilation activity showed a significant decrease in the dark that corresponds well to the observed decrease in total metabolic activity. It is concluded that changes in solute exchange associated with animals and burrows (e.g. microbial respiration) is a major controlling factor for total sediment metabolism. In general, the faunal impact was evident as about 50% enhanced CO₂ release in the dark, while net primary production was reduced by 30-50%. The turnover time of produced organic carbon is therefore considerably shorter in the presence than absence of macrofauna. Thus, the daily average exchange of CO₂ was almost balanced in bioturbated sediment with a 43% share of carbon oxidation mediated by direct faunal respiration. Defaunated sediment was net autotrophic with daily primary production exceeding microbial carbon oxidation by 40%. The present study clearly demonstrates that knowledge on interactions between microphytobenthos and macrofauna is essential for understanding carbon dynamics in shallow sediments.     

Iron oxidation stimulates organic matter decomposition in humid tropical forest soils

Humid tropical forests have the fastest rates of organic matter decomposition globally, which often coincide with fluctuating oxygen (O₂) availability in surface soils. Microbial iron (Fe) reduction generates reduced iron [Fe(II)] under anaerobic conditions, which oxidizes to Fe(III) under subsequent aerobic conditions. We demonstrate that Fe (II) oxidation stimulates organic matter decomposition via two mechanisms: (i) organic matter oxidation, likely driven by reactive oxygen species; and (ii) increased dissolved organic carbon (DOC) availability, likely driven by acidification. Phenol oxidative activity increased linearly with Fe(II) concentrations (P < 0.0001, pseudo R² = 0.79) in soils sampled within and among five tropical forest sites. A similar pattern occurred in the absence of soil, suggesting an abiotic driver of this reaction. No phenol oxidative activity occurred in soils under anaerobic conditions, implying the importance of oxidants such as O₂ or hydrogen peroxide (H₂O₂) in addition to Fe(II). Reactions between Fe(II) and H₂O₂ generate hydroxyl radical, a strong nonselective oxidant of organic compounds. We found increasing consumption of H₂O₂ as soil Fe(II) concentrations increased, suggesting that reactive oxygen species produced by Fe(II) oxidation explained variation in phenol oxidative activity among samples. Amending soils with Fe(II) at field concentrations stimulated short‐term C mineralization by up to 270%, likely via a second mechanism. Oxidation of Fe(II) drove a decrease in pH and a monotonic increase in DOC; a decline of two pH units doubled DOC, likely stimulating microbial respiration. We obtained similar results by manipulating soil acidity independently of Fe(II), implying that Fe(II) oxidation affected C substrate availability via pH fluctuations, in addition to producing reactive oxygen species. Iron oxidation coupled to organic matter decomposition contributes to rapid rates of C cycling across humid tropical forests in spite of periodic O₂ limitation, and may help explain the rapid turnover of complex C molecules in these soils.     

Inorganic Carbon of Sediments in the Yangtze River Estuary and Jiaozhou Bay

JGOFS results showed that the ocean is a major sink for the increasing atmospheric carbon dioxide resulting from human activity. However, the role of the coastal seas in the global carbon cycling is poorly understood. In the present work, the inorganic carbon (IC) in the Yangtze River Estuary and Jiaozhou Bay are studied as examples of offshore sediments. Sequential extraction was used to divide inorganic carbon in the sediments into five forms, NaCl form, NH₃ H₂O form, NaOH form, NH₂OH HCl form and HCl form. Studied of their content and influencing factors were also showed that NaCl form < NH₃ H₂O form<NaOH form < NH₂OH HCl form<HCl form, and that their influencing factors of pH, Eh, Es, water content, organic carbon, organic nitrogen, inorganic nitrogen, organic phosphorus and inorganic phosphorus on inorganic carbon can be divided into two groups, and that every factor has different influence on different form or on the same form in different environment. Different IC form may transform into each other in the early diagenetic process of sediment, but NaCl form, NH₃ H₂O form, NaOH form and NH₂OH HCl form may convert to HCl form ultimately. So every IC form has different contribution to carbon cycling. This study showed that the contribution of various form of IC to the carbon cycle is in the order of NaOH form>NH₂OH HCl form>NH₃ H₂O form>NaCl form>HCl form, and that the contribution of HCl form contributes little to carbon cycling, HCl form may be one of end-result of atmospheric CO₂. So Yangtze River estuary sediment may absorb at least about 40.96×10¹¹ g atmospheric CO₂ every year, which indicated that offshore sediment play an important role in absorbing atmospheric CO₂.     

Contribution of Methanotrophic and Nitrifying Bacteria to CH4 and NH4+ Oxidation in the Rhizosphere of Rice Plants as Determined by New Methods of Discrimination

Methanotrophic and nitrifying bacteria are both able to oxidize CH₄ as well as NH₄⁺. To date it is not possible to estimate the relative contribution of methanotrophs to nitrification and that of nitrifiers to CH₄ oxidation and thus to assess their roles in N and C cycling in soils and sediments. This study presents new options for discrimination between the activities of methanotrophs and nitrifiers, based on the competitive inhibitor CH₃F and on recovery after inhibition with C₂H₂. By using rice plant soil as a model system, it was possible to selectively inactivate methanotrophs in soil slurries at a CH₄/CH₃F/NH₄⁺ molar ratio of 0.1:1:18. This ratio of CH₃F to NH₄⁺ did not affect ammonia oxidation, but methane oxidation was inhibited completely. By using the same model system, it could be shown that after 24 h of exposure to C₂H₂ (1,000 parts per million volume), methanotrophs recovered within 24 h while nitrifiers stayed inactive for at least 3 days. This gave an “assay window” of 48 h when only methanotrophs were active. Applying both assays to model microcosms planted with rice plants demonstrated a major contribution of methanotrophs to nitrification in the rhizosphere, while the contribution of nitrifiers to CH₄ oxidation was insignificant.     

Potential rates of nitrification and denitrification in an oligotrophic freshwater sediment system

Potential rates of nitrification and denitrification were measured in an oligotrophic sediment system. Nitrification potential was estimated using the CO oxidation technique, and potential denitrification was measured by the acetylene blockage technique. The sediments demonstrated both nitrifying and denitrifying activity. E_h, O₂, and organic C profiles showed two distinct types of sediment. One type was low in organic C, had high O₂ and E_h, and had rates of denitrification 1,000 times lower than the other which had high organic C, low O₂, and low E_h. Potential nitrification and denitrification rates were negatively correlated with E_h. This suggests that environmental heterogeneity in denitrifier and nitrifier populations in oligotrophic sediment systems may be assessed using E_h before sampling protocols for nitrification or denitrification rates are established. There was no correlation between denitrification and nitrification rates or between either of these processes and NH₄ ⁺ or NO₃ ^– concentrations. The maximum rate of denitrification was 0.969 nmole N cm^–3 hour^–1, and the maximum rate of nitrification was 23.6 nmole cm^–3 hour^–1, suggesting nitrification does not limit denitrification in these oligotrophic sediments. Some sediment cores had mean concentrations of 6.0 mg O₂/liter and still showed both nitrification and denitrification activity.     

Characterization of phosphorus fractions in the sediments of a tropical intertidal mangrove ecosystem

Solid phases of phosphorus fractions in the surface and core sediments were studied to understand the biogeochemical cycling and bioavailability of phosphorus in the Pichavaram intertidal mangrove sediments of India. Total P in surface and core sediments ranged between 451–552 and 459–736 μg g⁻¹ respectively and Fe bound P was the dominant fraction. Low levels of Fe bound P in the mangrove zone than the two estuarine zones may be because of high salinity inhibition of phosphate adsorption onto the Fe-oxides/hydroxides. Post-depositional reorganization of P was observed in surface sediments, converting organic P and Fe bound P into the authigenic P. High levels of organic P in the mangrove zone is primarily due to intensive cycling and degradation of organic matter and adsorption of phosphate on the organic molecules. The burial rates and regeneration efficiency of P in the intertidal mangrove ecosystem ranged from 5.41 to 7.27 μmol P cm⁻² year⁻¹ and 0.122 to 0.233 μmol P cm⁻² year⁻¹, respectively. High burial efficiency (≈99%) of P proves the earlier observation of limiting nature of P for the biological productivity. Further, bioavailable P (exchangeable P + Fe bound P + organic P) constituted a considerable proportion of sedimentary P pool of which an average accounted for 55 and 50% in surface and core sediments respectively. The results indicate that significant amount of P is locked in sediments in the form of authigenic P and detrital P which makes P as a limiting nutrient for the biological productivity.     

Phosphorus retention capacity of agricultural headwater ditch sediments under alkaline condition in purple soils area,China

Phosphorus (P) retention by headwater ditch sediments adsorption plays a pivotal ecological role in P buffering in freshwater ecosystems. Previous studies focused on headwater ditch sediment adsorption and its P retention capacity in acid conditions, but little information is available for headwater ditches under alkaline condition. In this study, adsorption behavior of phosphorus was investigated in headwater ditch sediments under alkaline condition using a batch equilibrium technique, thus determining phosphorus retention capacity of headwater ditch sediments collected at 11 sites at base-flow on 2 March 2006 in purple soils area of China. Results showed that headwater ditch sediments had elevated phosphorus sorption maximum (S_max) values (122.72–293.23 mg P kg^?1) and P binding energy (K) values (1.64–8.65 L mg^?1), while they had low equilibrium phosphorus concentration (EPC₀) (0.001–0.108 mg L^?1) and degree of phosphorus saturation (DSP) (1.93–10.19%). Analysis of EPC₀ and soluble P concentration indicated that sediments acted as a sink for P across all headwater ditches. Therefore, there were high intrinsic P retention capacities of headwater ditch sediments. Positive correlations of both K and S_max with oxalate-extractable Fe (r of 0.93 and 0.81, p < 0.05) and total carbon (TC) (r of 0.89 and 0.74, p < 0.05) were found, thus suggesting that organic matter and amorphous or poorly crystalline Fe would play dominant roles in P adsorption in the headwater ditch sediments under alkaline condition. Since neither S_max nor K were correlated with CCE (CaCO₃) (r of 0.15 and ?0.06, p > 0.05), the high-energy sorptive surfaces of Fe oxides were more important than CaCO₃ in P sorption of sediment under alkaline condition. At the same time, these poor correlations between CCE and K and S_max imply a non-linear relationship between P retention and the content of carbonate. The negative correlations of both K and S_max with pH (r of–0.73, and–0.58, p < 0.05) revealed that an increase in pH would not improve sediment retention capacity under alkaline conditions.     

Oxidative stress caused by pyocyanin impairs CFTR Cl− transport in human bronchial epithelial cells

Pyocyanin (N-methyl-1-hydroxyphenazine), a redox-active virulence factor produced by the human pathogen Pseudomonas aeruginosa, is known to compromise mucociliary clearance. Exposure of human bronchial epithelial cells to pyocyanin increased the rate of cellular release of H₂O₂ threefold above the endogenous H₂O₂ production. Real-time measurements of the redox potential of the cytosolic compartment using the redox sensor roGFP1 showed that pyocyanin (100 μM) oxidized the cytosol from a resting value of − 318 ± 5 mV by 48.0 ± 4.6 mV within 2 h; a comparable oxidation was induced by 100 μM H₂O₂. Whereas resting Cl⁻ secretion was slightly activated by pyocyanin (to 10% of maximal currents), forskolin-stimulated Cl⁻ secretion was inhibited by 86%. The decline was linearly related to the cytosolic redox potential (1.8% inhibition/mV oxidation). Cystic fibrosis bronchial epithelial cells homozygous for ΔF508 CFTR failed to secrete Cl⁻ in response to pyocyanin or H₂O₂, indicating that these oxidants specifically target the CFTR and not other Cl⁻ conductances. Treatment with pyocyanin also decreased total cellular glutathione levels to 62% and cellular ATP levels to 46% after 24 h. We conclude that pyocyanin is a key factor that redox cycles in the cytosol, generates H₂O₂, depletes glutathione and ATP, and impairs CFTR function in Pseudomonas-infected lungs.     

Enhanced sulfate reduction and trichloroethylene (TCE) biodegradation in a UASB reactor operated with a sludge developed from hydrothermal vents sediments: Process and microbial ecology

Most Trichloroethylene (TCE) biodegradation reports refer to methanogenic conditions, however, in this work, enhanced sulfidogenesis and TCE biodegradation were achieved in an upflow anaerobic sludge blanket (UASB) reactor in which a completely sulfidogenic sludge, from hydrothermal vents sediments, was developed. The work was divided in three stages, (i) sludge development and sulfate reducing activity (SRA) evaluation, (ii) TCE biodegradation and (iii) SRA evaluation after TCE biodegradation. For (i) SR was 98 ± 0.1%, 84% as sulfide (H₂S, 1200 ± 28 mg/L), sulfate reducing activity (SRA) was 188 ± 50 mg COD H₂S/g VSS*d. For (ii) The reactor reached 74% of TCE removal, concentrations of vinyl chloride of 16 ± 0.3 μM (5% of the TCE added) and ethene 202 ± 81 μM (67% of the TCE added), SRA of 161 ± 7 mg COD H₂S/g VSS*d, 68% of sulfide (H₂S) production and 93% of COD removal. For (iii) SRA was of 248 ± 22 mg COD H₂S/g VSS*d demonstrating no adverse effects due to TCE.Among the genera of the microorganisms identified in the sludge during TCE biodegradation were: Dehalobacter, Desulfotomaculum, Sulfospirillum, Desulfitobacterium, Desulfovibrio and Clostridium. To the best of our knowledge, this is the first report using a sulfidogenic UASB reactor to biodegrade TCE. The overall conclusions of this work are that the reactor is efficient on both, sulfate and TCE biodegradation and it could be used to decontaminate wastewater containing organic solvents and relatively high concentrations of sulfate.     

Sulphide effects on the physiology of Candidatus Accumulibacter phosphatis type I

Sulphate-rich wastewaters can be generated due to (i) use of saline water as secondary-quality water for sanitation in urban environments (e.g. toilet flushing), (ii) discharge of industrial effluents, (iii) sea and brackish water infiltration into the sewage and (iv) use of chemicals, which contain sulphate, in drinking water production. In the presence of an electron donor and absence of oxygen or nitrate, sulphate can be reduced to sulphide. Sulphide can inhibit microbial processes in biological wastewater treatment systems. The objective of the present study was to assess the effects of sulphide concentration on the anaerobic and aerobic physiology of polyphosphate-accumulating organisms (PAOs). For this purpose, a PAO culture, dominated by Candidatus Accumulibacter phosphatis clade I (PAO I), was enriched in a sequencing batch reactor (SBR) fed with acetate and propionate. To assess the direct inhibition effects and their reversibility, a series of batch activity tests were conducted during and after the exposure of a PAO I culture to different sulphide concentrations. Sulphide affected each physiological process of PAO I in a different manner. At 189 mg TS-S/L, volatile fatty acid uptake was 55% slower and the phosphate release due to anaerobic maintenance increased from 8 to 18 mg PO₄-P/g VSS/h. Up to 8 mg H₂S-S/L, the decrease in aerobic phosphorus uptake rate was reversible (Ic₆₀). At higher concentrations of sulphide, potassium (>16 mg H₂S-S/L) and phosphate (>36 mg H₂S-S/L) were released under aerobic conditions. Ammonia uptake, an indicator of microbial growth, was not observed at any sulphide concentration. This study provides new insights into the potential failure of enhanced biological phosphorus removal sewage plants receiving sulphate- or sulphide-rich wastewaters when sulphide concentrations exceed 8 mg H₂S-S/L, as PAO I could be potentially inhibited.

     

Microsensor Measurements of Sulfate Reduction and Sulfide Oxidation in Compact Microbial Communities of Aerobic Biofilms

The microzonation of O₂ respiration, H₂S oxidation, and SO₄^2- reduction in aerobic trickling-filter biofilms was studied by measuring concentration profiles at high spatial resolution (25 to 100 μm) with microsensors for O₂, S^2-, and pH. Specific reaction rates were calculated from measured concentration profiles by using a simple one-dimensional diffusion reaction model. The importance of electron acceptor and electron donor availability for the microzonation of respiratory processes and their reaction rates was investigated. Oxygen respiration was found in the upper 0.2 to 0.4 mm of the biofilm, whereas sulfate reduction occurred in deeper, anoxic parts of the biofilm. Sulfate reduction accounted for up to 50% of the total mineralization of organic carbon in the biofilms. All H₂S produced from sulfate reduction was reoxidized by O₂ in a narrow reaction zone, and no H₂S escaped to the overlying water. Turnover times of H₂S and O₂ in the reaction zone were only a few seconds owing to rapid bacterial H₂S oxidation. Anaerobic H₂S oxidation with NO₃^- could be induced by addition of nitrate to the medium. Total sulfate reduction rates increased when the availability of SO₄^2- or organic substrate increased as a result of deepening of the sulfate reduction zone or an increase in the sulfate reduction intensity, respectively.     

The effects of drying on sediment nitrogen content in a Mediterranean intermittent stream: a microcosms study

Mediterranean climates predispose aquatic systems to both flood and drought periods, therefore, stream sediments may be exposed to desiccation periods. Changes in oxygen concentrations and sediment water content influence the biotic processes implicated in nitrogen dynamics. The objectives of this study were to identify (1) the changes of inorganic nitrogen in stream sediments during the transition from wet to dry conditions, and (2) the underlying processes in N dynamics and its regulation. Extractable sediment NO₃ ⁻-N and NH₄ ⁺-N, organic matter and extractable organic carbon content were assessed during natural desiccation in microcosms with sediments from an intermittent Mediterranean stream. In agreement with our initial hypothesis, our results showed how the NO₃ ⁻-N content of the sediment was enhanced during the first 10 days of sediment drying, whereas NH₄ ⁺-N was lost by 14 days post-drying. During the first 10 days, sediment desiccation seemed to stimulate the net N-mineralization and net nitrification from sediments. Afterwards, the extractable NO₃ ⁻-N concentration sharply dropped, which may be attributed to lower ammonium-oxidation rates as ammonium and organic matter are depleted, and to an increase in NO₃ ⁻-N consumption by microbial populations. Denitrification was inhibited, with a significant decrease as % water-filled pore space lowered. We hypothesize that the sediment inorganic N content enhanced during sediment desiccation could be released as part of the N pulse observed after sediment rewetting. However, the stream N availability after rewetting dried sediments would differ depending on desiccation period duration.     

Quantification of hydrogen peroxide and glucose using 3-methyl-2-benzothiazolinonehydrazone hydrochloride with 10,11-dihydro-5H-benz(b,f)azepine as chromogenic probe

A sensitive, selective, and rapid enzymatic method is proposed for the quantification of hydrogen peroxide (H₂O₂) using 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH) and 10,11-dihydro-5H-benz(b,f)azepine (DBZ) as chromogenic cosubstrates catalyzed by horseradish peroxidase (HRP) enzyme. MBTH traps free radical released during oxidation of H₂O₂ by HRP and gets oxidized to electrophilic cation, which couples with DBZ to give an intense blue-colored product with maximum absorbance at 620 nm. The linear response for H₂O₂ is found between 5 × 10⁻⁶ and 45 × 10⁻⁶ mol L⁻¹ at pH 4.0 and a temperature of 25 °C. Catalytic efficiency and catalytic power of the commercial peroxidase were found to be 0.415 × 10⁶ M⁻¹ min⁻¹ and 9.81 × 10⁻⁴ min⁻¹, respectively. The catalytic constant (k_cat) and specificity constant (k_cat/K_m) at saturated concentration of the cosubstrates were 163.2 min⁻¹ and 4.156 × 10⁶ L mol⁻¹ min⁻¹, respectively. This method can be incorporated into biochemical analysis where H₂O₂ undergoes catalytic oxidation by oxidase. Its applicability in the biological samples was tested for glucose quantification in human serum.     

Phosphorus speciation in Myall Lake sediment, NSW, Australia

The amount of phosphorus and its fractions in the sediment of Lake Myall, NSW, Australia, was assessed using a sequential extraction technique. Five sedimentary phosphorus reservoirs were measured, namely loosely sorbed phosphorus (NH₄Cl–P), iron associated phosphorus (BD–P), calcium bound phosphorus (HCl–P), metal oxide bound phosphorus (NaOH–P) and residual phosphorus (organic and refractory P, Res-P). Samples were taken from the deep and shallow sites of the lake. During the analysis, the average concentrations of each fraction of phosphorus was calculated. The results depicted that the total phosphorus (TP) content and chemically extractable phosphorus in both fine and coarse sediment fractions from the deep sites of the lake were significantly higher than those of the shallow sites, except for HCl–P extracted from the fine sediment fraction. Sediment TP was also strongly and positively correlated to sediment Fe. The phosphorus in the sediment mainly consisted of BD–P and Res-P, while NH₄Cl–P and HCl–P only contributed a minor part. The rank order of the different phosphorus extracts was similar for the two sites, namely Residual-P > BD–P > NaOH–P > HCl–P > NH₄Cl–P.     

Porewater Stoichiometry of Terminal Metabolic Products, Sulfate, and Dissolved Organic Carbon and Nitrogen in Estuarine Intertidal Creek-bank Sediments

Porewater equilibration samplers were used to obtain porewater inventories of inorganic nutrients (NH₄⁺, NO_x, PO₄³⁻), dissolved organic carbon (DOC) and nitrogen (DON), sulfate (SO₄²⁻), dissolved inorganic carbon (DIC), hydrogen sulfide (H₂S), chloride (Cl⁻), methane (CH₄) and reduced iron (Fe²⁺) in intertidal creek-bank sediments at eight sites in three estuarine systems over a range of salinities and seasons. Sulfate reduction (SR) rates and sediment particulate organic carbon (POC) and nitrogen (PON) were also determined at several of the sites. Four sites in the Okatee River estuary in South Carolina, two sites on Sapelo Island, Georgia and one site in White Oak Creek, Georgia appeared to be relatively pristine. The eighth site in Umbrella Creek, Georgia was directly adjacent to a small residential development employing septic systems to handle household waste. The large data set (>700 porewater profiles) offers an opportunity to assess system-scale patterns of porewater biogeochemical dynamics with an emphasis on DOC and DON distributions. SO₄²⁻ depletion (SO₄²⁻)_Dep was used as a proxy for SR, and (SO₄²⁻)_Dep patterns agreed with measured (³⁵S) patterns of SR. There were significant system-scale correlations between the inorganic products of terminal metabolism (DIC, NH₄⁺ and PO₄³⁻) and (SO₄²⁻)_Dep, and SR appeared to be the dominant terminal carbon oxidation pathway in these sediments. Porewater inventories of DIC and (SO₄²⁻)_Dep indicate a 2:1 stoichiometry across sites, and the C:N ratio of the organic matter undergoing mineralization was between 7.5 and 10. The data suggest that septic-derived dissolved organic matter with a C:N ratio below 6 fueled microbial metabolism and SR at a site with development in the upland. Seasonality was observed in the porewater inventories, but temperature alone did not adequately describe the patterns of (SO₄²⁻)_Dep, terminal metabolic products (DIC, NH₄⁺, PO₄³⁻), DOC and DON, and SR observed in this study. It appears that production and consumption of labile DOC are tightly coupled in these sediments, and that bulk DOC is likely a recalcitrant pool. Preferential hydrolysis of PON relative to POC when overall organic matter mineralization rates were high appears to drive the observed patterns in POC:PON, DOC:DON and DIC:DIN ratios. These data, along with the weak seasonal patterns of SR and organic and inorganic porewater inventories, suggest that the rate of hydrolysis limits organic matter mineralization in these intertidal creek-bank sediments.     

Difference characteristics of phosphorus in Chara and two submerged angiosperm species: implications for phosphorus nutrient cycling in an aquatic ecosystem

Phosphorus speciation in three submerged macrophytes species, Chara fibrosa Agardh ex Bruzelius, Najas marina Linnaeus and Vallisneria gigantea Graebner, and the implications for phosphorus nutrient cycling in an aquatic ecosystem were studied, using sequential phosphorus fractionations. The results showed that C.␣fibrosa had a far higher residual ash and calcium content compared with the two angiosperm species, but lower total phosphorus content. Two different fractionation methods for phosphorus showed that the bioavailable water-soluble phosphorus (H₂O-P) and ammonium chloride extractable phosphorus (NH₄Cl-P) of the extractions used represented the major part of total plant phosphorus in the two angiosperm species, while organic phosphorus (NaOH-P) represented a relatively large fraction in C. fibrosa. In this species, about 12–15% of total plant phosphorus was calcium-bound phosphorus (HCl-P), occurring as co-precipitation with calcite encrustation, but this fraction was negligible in the two angiosperm species, i.e. less than 1%. The redox-insensitive forms of HCl-P are considered less bioavailable and not affected by anoxic conditions of bottom sediment, thus have potential as a phosphorus nutrient sink in aquatic ecosystems.