Sources of nutrients fuelling post-flood phytoplankton biomass in a subtropical bay.

Extreme rainfall from an ex-tropical cyclone caused a major flood event in the Logan River system in southeast Queensland, Australia. This resulted in a significant flood plume, containing nutrients and sediment, being discharged into the adjacent estuary/Bay system. The spatial extent of higher phytoplankton biomass (Chl a) matched the distribution of higher nutrient and sediment concentrations post-flood, suggesting nutrients fuelled phytoplankton production. Particulate nitrogen (PN) constituted over 50 % of total nitrogen in floodwaters, with lower proportions of dissolved inorganic nitrogen (DIN) and phosphate (PO4-P). Phytoplankton utilised DIN rapidly but may have maintained growth due to the release of ammonia from suspended sediments and microbial mineralisation of particulate organic nitrogen. Ammonia release from intertidal sediments contributed minimally (0.85 %) to daily phytoplankton nitrogen demands. Our study highlights the need to understand the fate of particulate nitrogen in coastal systems and its role in stimulating phytoplankton growth.

Novel insight into ammonium, phosphate, and iron(II) dynamics in the sediment porewater of a constructed wetland under artificial aeration through the diffusive equilibrium in thin films technique.

The analysis of porewater concentrations in constructed wetland sediments could help to understand biogeochemical processes, the sources and sinks of nutrients, and their effect on overlying water quality. In this study, we measured high-resolution porewater concentration profiles of ammonium (NH4+-N), nitrate (NO3N), phosphate (PO43--P), and ferrous iron (Fe(II)) in-situ in the Laratinga constructed wetland in Mount Barker (South Australia) using diffusive equilibration in thin films (DET) techniques. Measurements were taken under light and dark conditions, and non-aerated and aerated conditions to determine the effect on sediment porewater nutrient concentrations. Baseline surface water nutrient concentrations (NH4+-N > 36 mg L-1, PO43--P > 0.43 mg L-1) greatly exceeded water quality guideline criteria. Aeration of the water column alleviated night-time hypoxic conditions (i.e. dissolved oxygen increased from a minimum of 0.7 mg L-1 to a minimum of 4 mg L-1), and increased the redox potential in the sediment. Significant differences were present for NH4+-N, PO43--P, and Fe(II) concentrations with depth in the sediment. Ammonium concentrations in the sediment reduced under aerated conditions, presumably due to enhanced nitrification. However it was observed that PO43--P and Fe(II) concentrations increased significantly with aeration, especially under dark conditions, and were strongly correlated (R2>0.8). This was not what was hypothesised and points to complex interactions between Fe and P in the sediment. Nitrate concentrations in the sediment were below the detection limit (<0.9 mg L-1) which suggests limited nitrification-denitrification is occurring. Overall the results suggest that DET techniques are useful tools for quantifying porewater concentrations of nutrients in constructed wetlands under various environmental conditions.

Metallic mangroves: Sediments and in situ diffusive gradients in thin films (DGTs) reveal Avicennia marina (Forssk.) Vierh. lives with high contamination near a lead­zinc smelter in South Australia.

From 1889, aerial emissions and effluent from a coastal lead­zinc smelter at Port Pirie, South Australia, have led to the accumulation of lead (Pb), zinc (Zn), arsenic (As), cadmium (Cd) and copper (Cu) in the surrounding marine environment. Despite this, extensive stands of grey mangrove (Avicennia marina) inhabit coastal areas at Port Pirie, right up to the smelter's boundary. To understand the contamination level the mangroves are living in there, elemental concentrations were measured in mangrove sediments, leaves, pneumatophores and fruits at sites 0.30-43.0 km from the smelter. Plant health was assessed via leaf chlorophyll content at four sites with contrasting contamination, as well as in situ labile elemental concentration using diffusive gradients in thin films (DGT). Sites < 1.7 km of the smelter exceeded Australian and New Zealand Environment and Conservation Council (ANZECC) & Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) (2000) sediment quality guideline values for As (78.3-191 mg/kg), Cd (5.17-151 mg/kg), Cu (80.7-788 mg/kg), Pb (2,544-14,488 mg/kg) and Zn (281-62,097 mg/kg), while sites further away showed less enrichment above background. Similarly, elevated elemental concentrations in leaves and pneumatophores occurred closer to the smelter (up to 319 mg/kg Pb; 1,033 mg/kg Zn), while fruits had little contamination of non-essential elements (≤ 5.23 mg/kg). Relationship between sediment and leaf elemental concentration was isometric for Pb and anisometric for others. Labile As, Cd, Cu, Pb and Zn exceeded the 95% and 80% level of species protection in marine water by ANZECC & ARMCANZ (2000) near the smelter, but chlorophyll content did not vary significantly among sites (p > 0.05). These results reveal that A. marina tolerate high elemental contamination at Port Pirie, contributing to lesser but still high contamination in plants, warranting further investigation into non-lethal impacts on mangroves or additional biota inhabiting this ecosystem.

Artificial aeration of an overloaded constructed wetland improves hypoxia but does not ameliorate high nitrogen loads.

High organic loadings to constructed wetlands can result in water quality issues such as low dissolved oxygen and high ammonium concentrations, with artificial aeration a potential mitigation option. This study compared baseline (no aeration - NA), continuous aeration (CA), and intermittent aeration (IA) conditions to improve water quality in a tertiary treatment free water surface constructed wetland (FWS CW) with night time hypoxia/anoxia, and high nutrient concentrations. The response variables included dissolved oxygen (DO), total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), total phosphorus (TP), phosphate (PO43--P), and dissolved organic carbon (DOC). In situ aeration and monitoring was performed from April to June 2021 in a large, field-scale FWS CW, the Laratinga wetlands Mount Barker, South Australia. The results demonstrated that DO increased by an average 2.11 mg L-1 from NA to CA during the night and 1.26 mg L-1 and 1.84 mg L-1 from NA to IA during the night and day respectively when averaging over the basins. The C/N ratio was very low and there was no significant influence of DO on DOC concentrations. There was no significant difference in TN concentrations with the application of aeration aside from a decrease in the channel at night from NA to IA, and an increase in NH4+-N resulted under IA compared with NA in Basin 1 and 2 during the day. This implies that the N loadings exceeded the wetland's ability to complete nutrient conversions at a rate that aligns with input rate. The concentrations of NO3--N increased at night under CA and IA treatments suggesting that some nitrification was promoted, or there was inhibition of dissimilatory nitrate reduction to ammonium. The concentrations of TP and PO43--P significantly increased with the aeration compared with no aeration, however there was no difference between the aeration treatments. This suggested that increased sediment resuspension during aeration increased P in the water. There was no change in DOC with the application of aeration. Overall, the DO increased with aeration application and may be able to better support the wetland ecology; however, the Laratinga wetland is overloaded and the capacity of the wetland to effectively transform and remove nutrients is inhibited, even with the application of artificial aeration.

On-Demand Storage of Photonic Qubits at Telecom Wavelengths.

Quantum memories at telecom wavelengths are crucial for the construction of large-scale quantum networks based on existing fiber networks. On-demand storage of telecom photonic qubits is an essential request for such networking applications but yet to be demonstrated. Here we demonstrate the storage and on-demand retrieval of telecom photonic qubits using a laser-written waveguide fabricated in an ^{167}Er^{3+}:Y_{2}SiO_{5} crystal. Both ends of the waveguide memory are directly connected with fiber arrays with a fiber-to-fiber efficiency of 51%. Storage fidelity of 98.3(1)% can be obtained for time-bin qubits encoded with single-photon-level coherent pulses, which is far beyond the maximal fidelity that can be achieved with a classical measure and prepared strategy. This device features high reliability and easy scalability, and it can be directly integrated into fiber networks, which could play an essential role in fiber-based quantum networks.

Restoration of benthic macrofauna promotes biogeochemical remediation of hostile sediments; An in situ transplantation experiment in a eutrophic estuarine-hypersaline lagoon system.

Estuarine ecosystems have very high ecological and economic value, and also act as a buffer for coastal oceans by processing nutrient inputs from terrestrial sources. However, ongoing pressures from increased urbanisation and agriculture, overlaid by climate change, has reduced inflows and increased nutrient loads that challenge the health and buffering capacity of these ecosystems. This study aimed to investigate whether restoring the bioturbating activity of Simplisetia aequisetis (Polychaeta: Nereididae) and other macrofauna could improve biogeochemical conditions in 'hostile' (i.e. hypersaline, sulfide-rich) sediments. To achieve this aim, we conducted an in situ experiment in the Coorong estuarine-lagoon ecosystem, translocating hostile hypersaline sediments, devoid of bioturbating macrofauna, to a 'healthy' (lower salinity) location where macrobenthic fauna naturally occur, and manipulating the S. aequisetis density in the sediments. Porewater, solid-phase, and diffusive equilibrium and diffusive gradient in thin-films (DET/DGT) measurements showed that bioturbation by macrobenthic fauna significantly influenced sediment biogeochemistry and remediated hostile conditions in sediment within a short time (four weeks) irrespective of S. aequisetis density. Bioturbation promoted sediment oxygenation, while salinity and the concentrations of total organic carbon and porewater sulfide, ammonium, and phosphate all decreased over time at all sediment depths. This research highlights the importance of macrobenthic communities and their functional traits for improving sediment conditions, promoting resilience to eutrophication, providing a nature-based remediation option, and in general ensuring healthy functioning of estuarine ecosystems.

Tandem Probe Analysis Mode for Synchrotron XFM: Doubling Throughput Capacity.

Synchrotron-based X-ray fluorescence microscopy (XFM) analysis is a powerful technique that can be used to visualize elemental distributions across a broad range of sample types. Compared to conventional mapping techniques such as laser ablation inductively coupled plasma mass spectrometry or benchtop XFM, synchrotron-based XFM provides faster and more sensitive analyses. However, access to synchrotron XFM beamlines is highly competitive, and as a result, these beamlines are often oversubscribed. Therefore, XFM experiments that require many large samples to be scanned can penalize beamline throughput. Our study was largely driven by the need to scan large gels (170 cm2) using XFM without decreasing beamline throughput. We describe a novel approach for acquiring two sets of XFM data using two fluorescence detectors in tandem; essentially performing two separate experiments simultaneously. We measured the effects of tandem scanning on beam quality by analyzing a range of contrasting samples downstream while simultaneously scanning different gel materials upstream. The upstream gels were thin (<200 µm) diffusive gradients in thin-film (DGT) binding gels. DGTs are passive samplers that are deployed in water, soil, and sediment to measure the concentration and distribution of potentially bioavailable nutrients and contaminants. When deployed on soil, DGTs are typically small (2.5 cm2), so we developed large DGTs (170 cm2), which can be used to provide extensive maps to visualize the diffusion of fertilizers in soil. Of the DGT gel materials tested (bis-acrylamide, polyacrylamide, and polyurethane), polyurethane gels were most suitable for XFM analysis, having favorable handling, drying, and analytical properties. This gel type enabled quantitative (>99%) transmittance with minimal (<3%) flux variation during raster scanning, whereas the other gels had a substantial effect on the beam focus. For the first time, we have (1) used XFM for mapping analytes in large DGTs and (2) developed a tandem probe analysis mode for synchrotron-based XFM, effectively doubling throughput. The novel tandem probe analysis mode described here is of broad applicability across many XFM beamlines as it could be used for future experiments where any uniform, highly transmissive sample could be analyzed upstream in the "background" of downstream samples.

Long-term water quality response to increased hydraulic loadings in a field-scale free water surface constructed wetland treating domestic effluent.

There is limited understanding of how constructed wetland (CW) water quality may change over time in response to increased wastewater nutrient and hydraulic loadings. We evaluated long-term water quality trends and drivers for a full-scale (8.19 ha) free water surface CW that was developed in 2001 for the treatment of increasing amounts of pre-treated domestic wastewater from the township of Mount Barker, South Australia. Water quality parameter concentrations and loads, hydraulic loadings rates, trend direction assessments (TDAs), and water quality parameter removal efficiencies were analysed over the study period. The wetland received an annual average loading rate of 947, 19644, 31039, 18140, 2985, and 807 kg year-1 for BOD5, TN, NH4-N, TKN-N, NOx-N, and TP respectively and removed on average 8%, 72%, 73%, 78%, 12% and -246% of these loadings respectively. The average influent concentrations for the study period were 2.6, 42.3, 40.6, 35.9, 9.0, and 1.9 mg L-1 for BOD5, TN, NH4-N, TKN-N, NOx-N, and TP respectively. Average concentration removal rates over the study period were 50%, 39%, 40%, 15%, -216% and -600.5% for TN, NH4-N, TKN-N, NOx-N, BOD5 and TP respectively, suggesting that nitrogen was only partly assimilated by the wetland and it was a source of organic material and phosphorus. Using seasonally and inflow rate adjusted data, TDAs predicted virtually certain increases in TN, NH4-N, and TKN-N influent concentrations over time, a decline in NOx-N, no trend in BOD5, and a possible decreasing trend in TP. The inflow explained variance accounted for approximately 50% of the variation in TN, NH4-N and TKN-N effluent concentrations. Annual removal efficiencies of N declined with increasing hydraulic loads, and hydraulic loading rates varied with management practices. Seasonal analysis showed that N removal was greater during summer and lower in winter. Due to local population growth and various management practices, hydraulic loading is variable and has often exceeded design targets. Our findings indicate the long-term performance of CWs need to be closely monitored, as water quality can deteriorate due to increased hydraulic loadings.

Stormwater monitoring using on-line UV-Vis spectroscopy.

Stormwater runoff contains a myriad of pollutants, including faecal microbes, and can pose a threat to urban water supplies, impacting both economic development and public health. Therefore, it is a necessity to implement a real-time hazard detection system that can collect a substantial amount of data, assisting water authorities to develop preventive strategies to ensure the control of hazards entering drinking water sources. An on-line UV-Vis spectrophotometer was applied in the field to collect real-time continuous data for various water quality parameters (nitrate, DOC, turbidity and total suspended solids) during three storm events in Mannum, Adelaide, Australia. This study demonstrated that the trends for on-line and comparative laboratory-analysed samples were complimentary through the events. Nitrate and DOC showed a negative correlation with water level, while turbidity and total suspended solids indicated a positive correlation with water level during the high rainfall intensity. The correlations among nitrate, DOC, turbidity, total suspended solids and water level are the opposite during low rainfall intensity. Nitrate, one of the main pollutants in stormwater, was investigated and used as a surrogate parameter for microbial detection. However, the microbiological data (Escherichia coli) from captured storm events showed poor correlations to nitrate and other typical on-line parameters in this study. This is possibly explained by the nature of the stormwater catchment outside of rain events, where the sources of bacteria and nutrients may be physically separated until mixed during surface runoff as a result of rainfall. In addition, the poor correlations among the microbiological data and on-line parameters could be due to the different sources of bacteria and nutrients that were transported to the stormwater drain where sampling and measurement were conducted.

Innovative method of utilising hydrogen peroxide for source water management of cyanobacteria.

The treatment and control of cyanobacterial blooms using copper-based algaecides in water reservoirs have historically been used; however, due to the adverse impact of copper on the environment, water authorities have been researching and studying new and innovative ways to control cyanobacterial blooms. Hydrogen peroxide has been investigated as an environmentally friendly alternative, and this research aims to determine the impact of water quality on its effectiveness based on the decay characteristics in different water samples. Natural water samples from South Australian reservoirs and river were used to evaluate hydrogen peroxide decomposition and provide a better strategy for water operators in using it as an algaecide. Our experiments show the dependency of hydrogen peroxide decomposition not only on water quality but also on the initial hydrogen peroxide dose. A higher initial hydrogen peroxide dose can trigger the increase of pH, leading to increased consumption of hydrogen peroxide. In addition, the hydrogen peroxide decomposition is significantly accelerated with the rise of copper concentration in water samples. Moreover, it is found that UV light can also affect the decomposition rate of hydrogen peroxide. The hydrogen peroxide decay is more significant under UV light for the samples with lower hydrogen peroxide concentrations. Our study also shows the impact of dissolved organic carbon (DOC) on hydrogen peroxide decomposition is not substantial. The study also presents a modelling method to optimise hydrogen peroxide application based on water quality characteristics. Our findings can provide knowledge for the water industry to produce a suitable model which can be used to optimise the application of hydrogen peroxide for the control of cyanobacteria.

In Situ DGT Sensing of Bioavailable Metal Fluxes to Improve Toxicity Predictions for Sediments.

An increased risk of adverse biological effects of metals in sediments may be accompanied by high labile metal fluxes as measured by the diffusive gradients in thin films (DGT) technique. To improve the usefulness of the DGT technique for sediment quality risk assessments, we used the simpler and more cost-effective piston DGTs rather than planar DGT probes to measure bioavailable metal fluxes in naturally contaminated sediments with widely varying composition (properties, metals and concentrations) and assessed their prediction of toxicity to amphipod reproduction in a flow-through microcosm. DGT pistons were deployed in sediments under different conditions, both in the field (in situ) and in the laboratory in sediment cores (lab-equilibrated) and in homogenized sediments (lab-homogenized). We demonstrated that the metal flux toxic units, DGTTU, measured in situ best predicted the magnitude of toxicity to amphipod reproduction. For sediments that had been highly disturbed before testing, DGTTU were less predictive for observed toxicity, but the copper flux alone (DGTTU-Cu) was effective, indicating copper was the primary cause of toxicity in these highly perturbed sediments. Overall, our study highlighted that the adverse effects induced by excessive bioavailable metals in contaminated sediments can be consistently sensed by the DGT pistons.

Evaluation of the Chelex-DGT technique for the measurement of rare earth elements in the porewater of estuarine and arine sediments.

This study describes the validation of a diffusive gradients in thin film (DGT) technique for determining lanthanide rare earth elements (REEs) and in situ measurements of REEs in sediment pore waters. Laboratory experiments demonstrated that Chelex-100 binding layers had uptake efficiencies ranging from 78.0% to 92.3% for all REEs. An eluent of 1 mol L-1 HNO3 was optimal with elution efficiencies >80% for all REEs. Mass versus time experiments confirmed that DGT uptake was linear for all REEs at pH 8.1, 6.6 and 3.9 over a period of 3-4 days. Diffusion coefficients (D) for all REEs were derived from these experiments using the slopes of the linear regressions. D values varied with pH but were generally similar to values reported previously. The Chelex-100 DGT technique from this study is highly sensitive for the measurement of REE concentrations with detection limits ranging from 1.8 to 45 ng L-1 based on 72 h deployments allowing measurements of natural trace REE levels. Chelex-100 DGT devices were deployed in estuarine and marine sediments over a period of 72 h and most REE porewater concentrations (50-10,410 ng L-1) were successfully measured. Individual depth profiles of REEs showed a complex response, with many peaks and troughs suggesting a high degree of sediment heterogeneity. Depth-averaged REE concentrations showed a typical zig-zag distribution, although patterns varied between sediment types, after the REEs were normalised using the Queensland Mud Composite shale reference. The Chelex-100 DGT technique therefore shows promise for REE measurements in sediments.

Oxidative Dissolution of Sulfide Minerals in Single and Mixed Sulfide Systems under Simulated Acid and Metalliferous Drainage Conditions.

Chalcopyrite, galena, and sphalerite commonly coexist with pyrite in sulfidic waste rocks. The aim of this work was to investigate their impact, potentially by galvanic interaction, on pyrite oxidation and acid generation rates under simulated acid and metalliferous drainage conditions. Kinetic leach column experiments using single-minerals and pyrite with one or two of the other sulfide minerals were carried out at realistic sulfide contents (total sulfide <5.2 wt % for mixed sulfide experiments), mimicking sulfidic waste rock conditions. Chalcopyrite was found to be most effective in limiting pyrite oxidation and acid generation with 77-95% reduction in pyrite oxidation over 72 weeks, delaying decrease in leachate pH. Sphalerite had the least impact with reduction of pyrite dissolution by 26% over 72 weeks, likely because of the large band gap and poor conductivity of sphalerite. Galena had a smaller impact than chalcopyrite on pyrite oxidation, despite their similar band gaps, possibly because of the greater extent of oxidation and the significantly reduced surface areas of galena (area reductions of >47% for galena vs <1.5% for chalcopyrite) over 72 weeks. The results are directly relevant to mine waste storage and confirm that the galvanic interaction plays a role in controlling acid generation in multisulfide waste even at low sulfide contents (several wt %) with small probabilities (≤0.23%) of direct contact between sulfide minerals in mixed sulfide experiments.

Development and evaluation of a new colorimetric DGT technique for the 2D visualisation of labile phosphate in soils.

A new colorimetric technique for the measurement of labile phosphate in soils using the diffusive gradients in thin films (DGT) technique was developed in this study. This technique can determine the mass of phosphate accumulated on the precipitated Zr-oxide based binding gel by forming the blue colour following the standard molybdate-ascorbic acid method. The optimal reaction temperature and coloration time were 20 °C (room temperature) and 26 min. After determining a well-fitted calibration equation, the technique was able to measure phosphate concentration up to 2.5 mg/L for 24 h deployment with a detection limit of 10.1 µg/L. Two-dimensional quantitative visualisation of phosphate diffusion in three phosphorus (P) fertilised soils were obtained using the colorimetric technique. The results from the colorimetric DGT technique were compared to the elution DGT technique and Colwell P extraction. The DGT techniques (colorimetric and elution) and Colwell P measurements demonstrated similar patterns of phosphate diffusion in soil. Both DGT techniques showed similar phosphate concentration along the concentric rings around the fertiliser application. A new, convenient, and fast DGT colorimetric technique was developed, and successfully used to measure the distribution of potentially available phosphate in soils. The new technique is less laborious than current techniques as it does not require any pre-treatment of the binding gel layers or heating during scanning, thus providing faster results. Therefore, the technique may be more suitable for in-field applications and can be used to investigate the in situ diffusion of potentially available phosphate from fertilisers, and relate this to the plant uptake of P.

Association of serum osteocalcin levels with glucose metabolism in trauma patients.

Osteocalcin (OC) is an endocrine hormone that regulates glucose metabolism.The aim of this study was to investigate the relationship between serum OC levels and glucose metabolism after trauma.This was a retrospective study of trauma patients admitted to the Department of Emergency Medicine between October 2017 and April 2019. Age, height, weight, injury severity score, and previous medical history were recorded. Serum N-terminal mid-fragment of OC (N-MID OC), hemoglobin Alc (HbA1c), fasting plasma glucose (FPG), fasting insulin (FINS), C-peptide, and other biochemical indicators were measured. Differences between the HbA1c-L (HbA1c <6.5%) and HbA1c-H (HbA1c ≥6.5%) groups were compared. The association of N-MID OC with indicators of glucose metabolism was analyzed.Out of 394 trauma patients, leukocyte and FPG levels in the HbA1c-H group (n = 93) were higher (P < .05), while N-MID OC levels were lower (P = .011) than the HbA1c-L group (n = 301). N-MID OC was negatively correlated with HbA1c in the total population (r = -0.273, P < .001) as well as in the HbA1c-L (r = -0.289, P < .001) and HbA1c-H (r = -0.390, P < 0.001) groups, and was positively correlated with C-peptide in the HbA1c-H group (r = 0.395, P < .001). The different quartiles in the HbA1c-L showed that N-MID OC declined with increasing HbA1c, which was higher than N-MID OC levels in the HbA1c-H group. Multiple linear regression analysis revealed that serum HbA1c was independently associated with serum OC levels after trauma (ß=-1.608, P < .001).This study strongly suggests the importance of serum OC on glucose metabolism in trauma patients. HbA1c is independently associated with serum OC levels.

In situ, high-resolution measurement of labile phosphate in sediment porewater using the DET technique coupled with optimized imaging densitometry.

Obtaining two-dimensional distributions of reactive phosphorus in sediment porewater is very important for understanding fine-scale phosphorus mobilization and sequestration processes in sediments. In this study, the diffusive equilibrium in thin films (DET) measurement based on computer imaging densitometry (CID) was studied in detail with optimal conditions described. This study focuses on evaluating the two-dimensional colorimetric DET method coupled with CID (DET-CID method) for porewater labile phosphate measurements. The result shows that the red channel filter is the optimum channel for sensitivity to process the image. Additionally, staining time and temperature have great influence on the method, and 20 min staining time and ≥25 °C staining temperature were recommended. The minimum detection limit of labile phosphate of this method was 0.300 mg P/L, and the maximum detection limit could reach 50.00 mg P/L. The DET-CID technique can be used to measure labile phosphate in a wide range of acidic and alkaline water bodies (pH = 2-10 and water hardness from 0 to 2000 mg/L as CaCO3). The linear regression analysis shows that this technique presents very similar results compared with other two existing methods (R2 = 0.999). Our results would give insights into the precisely measurements of labile phosphate in field applications.

Utilization of drinking water treatment sludge in concrete paving blocks: Microstructural analysis, durability and leaching properties.

The management of abundant drinking water treatment sludge (DWTS) in landfill remains an important issue. The reuse of DWTS as construction material could contribute to the development of greener concrete product and to mitigating the detrimental environment effect from excessive production of DWTS. This paper investigates the potential of using DWTS as sand replacement in Concrete Paving Blocks (CPB). Five CPB mixtures were designed and the replacement ratios of sand by DWTS were 0%, 5%, 10%, 15%, and 20%, by weight. Properties of CPB such as compressive strength, water absorption, abrasion resistance, sulfate attack and metal leachability were determined. The results indicated that above 10% of DWTS, the replacement was detrimental to such properties of the CPB. Microstructure analysis proved the addition of DWTS could result in ettringite formation and the interfacial transition zone (ITZ) between the cement matrix and DWTS was more porous than that of sand. In addition, the metal leachability test of CPB demonstrated that the addition of high-copper DWTS into CPB was safe.

Effects of a nitrification inhibitor on nitrogen species in the soil and the yield and phosphorus uptake of maize.

Phosphorus (P) resource availability is declining and the efficiency of applied nutrients in agricultural soils is becoming increasingly important. This is especially true for P fertilizers from recycled materials, which often have low plant availability. Specific co-fertilization with ammonium can enhance P plant availability in soils amended with these P fertilizers, and thus the yield of plants. To investigate this effect, we performed a pot experiment with maize in slightly acidic soil (pH 6.9) with one water-soluble (triple superphosphate [TSP]) and two water-insoluble (sewage sludge-based and hyperphosphate [Hyp]) P fertilizers and an ammonium sulfate nitrate with or without a nitrification inhibitor (NI). The dry matter yield of maize was significantly increased by the NI with the Hyp (from 14.7 to 21.5 g/pot) and TSP (from 40.0 to 45.4 g/pot) treatments. Furthermore, P uptake was slightly increased in all three P treatments with the NI, but not significantly. Olsen-P extraction and P K-edge micro-X-ray absorption near-edge structure (XANES) spectroscopy showed that apatite-P of the water-insoluble P fertilizers mobilized during the plant growth period. In addition, novel nitrogen (N) K-edge micro-XANES spectroscopy and the Mogilevkina method showed that the application of an NI increased the fixation of ammonium in detectable hot spots in the soil. Thus, the delay in the nitrification process by the NI and the possible slow-release of temporarily fixed ammonium in the soil resulted in a high amount of plant available ammonium in the soil solution. This development probably decreases the rhizosphere pH due to release of H+ by plants during ammonium uptake, which mobilizes phosphorus in the amended soil and increases the dry matter yield of maize. This is especially important for water-insoluble apatite-based P fertilizers (conventional and recycled), which tend to have poor plant availability.

A new colorimetric DET technique for determining mm-resolution sulfide porewater distributions and allowing improved interpretation of iron(II) co-distributions.

Measurement of sulfide in pore waters is critical for understanding biogeochemical processes, especially within coastal sediments. Here we report the development of a new colorimetric DET (diffusive equilibration in thin films) technique for determining mm-resolution, two-dimensional sulfide distributions in sediment pore waters. This colorimetric sulfide DET method was based on the standard spectrophotometric methylene blue assay, but modified to allow quantitation of sulfide by computer imaging densitometry. The method detection and effective upper measurement limits of the optimised technique were 3.7 and 1000 µmol L-1, respectively. The optimised sulfide DET method was combined with the colorimetric iron(II) DET method to obtain co-distributions in coastal seagrass (Zostera muelleri) colonised sediment under light and dark conditions. In the dark, seagrass sediments were more reduced than in the light, with large areas being dominated by high porewater sulfide concentrations. These co-distributions were compared with those obtained using the previously described DET-DGT (diffusive gradients in thin films) method for measuring iron(II) and sulfide co-distributions. There was less overlap of iron(II) and sulfide distributions using the sulfide DET as the two DET methods are influenced most by the later hours of deployment, whereas the sulfide-DGT measurement integrates concentrations over the whole deployment period. Overlap was most apparent in very dynamic sediment zones, such as burrow wall sediments.

Comparison of DET, DGT and conventional porewater extractions for determining nutrient profiles and cycling in stream sediments.

Determining inorganic nutrient profiles to support understanding of nitrogen transformations in stream sediments is challenging, due to nitrification and denitrification being confined to particular conditions in potentially heterogeneous sediment influenced by benthic microalgae, rooted aquatic plants and/or diel light cycles. The diffusive gradients in thin films (DGT) and diffusive equilibration in thin films (DET) techniques allow in situ determination of porewater concentration profiles, and distributions for some solutes. In this study, DGT, DET and conventional porewater extraction (sectioning and centrifugation) methods were compared for ammonium and nitrate in stream sediments under light and dark conditions. Two-dimensional distributions of Fe(ii) and PO4-P were also provided to indicate the degree of spatial and temporal heterogeneity in sediment porewater, which can explain the sources and sinks of ammonium at various depths in the sediments. Although the conventional porewater extraction method consistently measured higher NH4-N concentrations than the DGT and DET techniques, the study showed that the DET measurements were the most reliable indicator of porewater NH4-N concentrations, with the DGT data being usefully supplementary. However, a large proportion of the NO3-N concentrations measured by DGT and DET were close to or below the method detection limits. Therefore, further development of these techniques is required to reduce the blanks and detection limits to allow natural low sediment porewater NO3-N concentrations to be accurately monitored using DGT and DET. The study indicated that benthic microalgae had direct and indirect influences on porewater nutrient distributions over light-dark cycles. Overall, DGT and DET techniques can be useful for monitoring porewater nutrient concentrations and profiles and for determining how biological processes drive changes in sediment nutrient concentrations and distributions.