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Determination of ammonia nitrogen in natural waters: Recent advances and applications

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Abstract

Ammonia nitrogen, consisting of un-ionized ammonia and ammonium, is a key parameter for studying the nitrogen cycle and indicating water quality. The measurement of these parameter concentrations is vital for the adequate monitoring of aquatic environments. Here, we review studies that focus on analytical methods for determining ammonia nitrogen in natural waters that were published between 2014 to mid-2019. These methods include spectrophotometric, fluorometric and electrochemical methods, and the features of these different analytical methods are reviewed. In addition, the outlook for future development is discussed.

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... Amoni có thể đi vào môi trường nước thông qua con đường tự nhiên do phân hủy kị khí các vật chất hữu cơ bởi vi sinh vật và do ảnh hưởng từ các hoạt động của con người như nước thải công -nông nghiệp, đô thị, nước rỉ rác… [1]. Trong môi trường nước, amoni có thể chuyển đổi thành các dạng nitơ khác thông qua các quá trình sinh -hóa học khác nhau [2,3]. Nồng độ amoni trong nước tự nhiên có thể biến đổi trong khoảng rộng, từ vài đến hàng trăm mmol/l. ...
... Lượng amoni dư thừa đưa vào nước mặt có thể kích thích quá trình sản sinh nhanh chóng của quần thể sinhthực vật phù du, làm cạn kiệt oxy trong nước và gây ra hiện tượng phú dưỡng và có thể trở thành mối đe dọa đối với hệ sinh thái dưới nước [1]. Đối với nguồn nước dùng cho sinh hoạt thì sự có mặt với nồng độ cao của amoni có thể làm giảm hiệu quả xử lý nước do giảm hiệu quả khử trùng bằng clo và tăng mức tiêu thụ clo, dễ dẫn đến hình thành nitrit và thay đổi về mùi vị [2,6,7]. ...
... Previous reports on quantitative estimation of ammonium ion made use of Nessler's reagent coupled with spectrophotometry techniques [10][11][12]. Another technique for the estimation of ammonium ions is ionselective electrode based potentiometric measurement [13][14][15]. ...
... The solvent extraction technique developed for detection of ammonium ion in aqueous samples is affected by interferents from various cations already present in water [16]. The estimation of ammonium ion in rainwater samples has also been carried out by using a flow-injection chemiluminescence analysis technique [11,13,17,18]. A fluorometric technique coupled with ion chromatography to resolve the interferences by expanding the retention time has also been reported for assessment of ammonium ion [19]. ...
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The fraudulent practice of adding ammonium salts to milk in order to enhance the nitrogen content has serious health implications including renal failure. Ammonium ion detection has been targeted through the conventional analytical methods however, lack of portability and complex operation limits their use for field applications. In this scenario, paper-based test strips and electrochemical sensors can provide strategies for point-of-test applications. Here, an ion-selective paper-based chromogenic strip and an electrochemical sensor has been developed for detection and quantification of ammonium ions. The developed paper-based chromogenic strip showed detection limit of 0.008 % (w/v) for ammonium ions, whereas, electrochemical sensor showed an LOD of 0.0062 ± 0.0023 % (w/v) with a sensitivity of 1.6 × 10 − 5 A.% − 1 .mm − 2. The developed paper-based chromogenic strip and electrochemical sensor can be employed by regulatory bodies and dairy industries to ensure the safety and quality of milk.
... The biomass of immobilized cells was determined via colony plate counting. NH 4 + -N was determined according to Nessler's reagent spectrophotometric method [27], NO 2 − -N was determined using the N-(1-naphthyl)ethylenediamine spectrophotometric method [28], NO 3 − -N was determined using the ultraviolet spectrophotometric method [29], and NH 4 + -N, NO 2 − -N, and NO 3 − -N parameters were measured using a UV-visible spectrophotometer (Shanghai Onra Instruments Ltd., EU-2200, Shanghai, China). An analysis of TN and COD was performed using a multiparameter water quality meter (Lianhua Yongxing Technology Co., Ltd., 5B-3B, Beijing, China). ...
... N was determined according to Nessler's reagent spectrophotometric method [27], NO2 --N was determined using the N-(1-naphthyl)ethylenediamine spectrophotometric method [28], NO3 --N was determined using the ultraviolet spectrophotometric method [29], and NH4 + -N, NO2 --N, and NO3 --N parameters were measured using a UV-visible spectrophotometer (Shanghai Onra Instruments Ltd., EU-2200, China). An analysis of TN and COD was performed using a multiparameter water quality meter (Lianhua Yongxing Technology Co., Ltd., 5B-3B, China). ...
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In this study, modified granular activated carbon (GAC) and immobilized cells were used to improve the biological efficiency of high-ammonia-nitrogen wastewater treatment using microorganisms. The results showed that using sodium-hydroxide-modified activated carbon (NaOH-GAC) greatly increased the immobilized numbers of the ammonia-oxidizing bacteria Alcaligenes sp. TD-94 and Paracoccus sp. TD-10. Using NaOH-GAC increased the number of immobilized cells by 63.27% over GAC. Compared with free cells, those immobilized on modified activated carbon were more effective in the removal of high ammonia nitrogen levels from wastewater. In wastewater with an ammonia nitrogen concentration of 100 mg·L−1, the ammonia nitrogen removal efficiencies of NaOH-GAC-immobilized cells and free cells within 24 h were 100% and 4.17%, respectively. After 45 cycles, NaOH-GAC-immobilized cells maintained an ammonia nitrogen removal efficiency of 79.24%. After 70 days of storage at 4 °C, the ammonia nitrogen removal efficiency was still as high as 100%. The removal efficiencies of ammonia nitrogen (NH4+-N), total nitrogen (TN), and chemical oxygen demand (COD) in high-ammonia-nitrogen wastewater from petrochemical enterprises reached 99.27%, 88.39%, and 69.85%, with removal rates of 75.21, 69.43, and 1117.40 mg·L−1·d−1, respectively. The findings demonstrated that NaOH-GAC improved the capacity of the biological treatment to remove ammonia nitrogen from wastewater and provide a practical option for the remediation of environmental pollution.
... The most important problems of the ion chromatography method include the lack of selectivity in identifying ammonia, damage to the column, and the high cost of detection 26 . Spectrophotometric methods for ammonia determination are known as routine and common technique due to their wide application range and relative feasibility 27 . Several spectrophotometric methods have been used to detect dissolved ammonia in aqueous samples 21 . ...
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The need to identify ammonia is necessary because of its harmful effects on the environment and humans. In this study, a colorimetric method was also developed for the detection of ammonia using silver nanoparticles (AgNPs) synthesized with the green approach. Biosynthesis of AgNPs was performed by silver nitrate as a silver precursor and Smyrnium cordifolium extract as a reducing and stabilizing agent. Plant extract was studied by FTIR and LC/Mass techniques. The optimization of the effective parameters was carried out with central composite design according to silver nitrate concentration, plant extract volume, pH, and temperature. Biosynthetic nano-silver was characterized with XRD, EDS/EDX, FE-SEM, FTIR, TGA, and DLS methods. The AgNPs was validated for ammonia colorimetric detection. Biosynthesis of AgNPs were increased in 20 mM AgNO3, 5 ml Smyrnium cordifolium extract, pH 10, and the temperature of 70 °C. Crystal form of AgNPs characterized with XRD at 2Ѳ value of 38.34°, 44.19°, 64.74°, and 77.59° and spherical shape highlighted in the range between 77.8 and 93 nm. Plant extract consisted of polyphenol (phenolic acid, flavonoid, and terpenoid), fatty acid, amino acid, sugar, purine, and organic acid. AgNPs were used for colorimetric detection of ammonia by shifting the λmax from 580 to 490 nm. A method for ammonia detection was set up, with linear range of 0.5–200 ppm, detection limit of 0.028 ppm and recovery level of 96.3 ± 6.5%. In conclusion, a new biosynthetic method by specified local plant was developed to propose a simple and sensitive colorimetric method for soluble ammonia detection.
... According to the literature, NH 4 + is the predominant form when the water solution pH is below 8.75, whereas NH 3 is the predominant form when the pH is above 9.75 [47]. This behavior of PC-NZK-S adsorbent in the adsorption of NH 4 + in this study is in full agreement with the results obtained from Jahani's study (2023) [46] which studied NH 4 + adsorption on modified natural clinoptilolite zeolite with optimum pH of 8.5. ...
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In this study, porous ceramics, based on available and cost-effective raw materials natural zeolite and kaolin clay, were synthesized and examined as an adsorbent for removing ammonium (NH4+) ions from aqueous solutions. The synthesis was carried out using the foaming method with the addition of sodium dodecyl sulfate as the foaming agent, polyvinyl alcohol as an organic binder, and hydrogen peroxide as the blowing agent. The obtained green and sintered samples were characterized by thermogravimetric analysis, scanning electron microscopy, X-Ray diffraction, and Fourier transform infrared spectroscopy. After sintering, the porosity was 79.49%. The NH4+ adsorption kinetics and isotherms fit the pseudo-second-order and Langmuir models, confirming chemisorption. The maximum adsorption capacity obtained using the Langmuir model was approximately 7.66 mg g-1. The thermodynamic parameters showed that adsorption is a spontaneous and exothermic process. Based on the obtained results, it was demonstrated that the synthesis of porous ceramics based on natural zeolite and kaolin clay is a practical way to increase the adsorption performance of natural zeolite for NH4+ removal from water solutions.
... Kepekatan ammonia-nitrogen tertinggi adalah di stesen S2. Ammonia-nitrogen yang tinggi dalam air adalah daripada pelepasan antropogen seperti pelepasan efluen bandar dan pertanian (Lin et al. 2019). ...
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Sungai Melaka, which serves as a primary source of income for communities in the state of Melaka, has been contaminated by microplastics. This study investigated the abundance and characteristics of microplastics found in water samples from 9 sampling stations along Sungai Melaka. Water quality and the relationship between microplastics and the physicochemical properties of water quality were also analysed in this study. The average abundance of microplastics in Sungai Melaka is 569 particles L-1. Black-coloured microplastics and fragment shapes are the dominant characteristics of microplastics. Polyamide (PA) and polyethylene terephthalate (PET) are the most common polymer types found in all water samples. Total suspended solids (TSS) were identified as a parameter that influences microplastic fibres in Sungai Melaka. Overall, these results provide current information on microplastic pollution in Sungai Melaka and offer important data for further research on microplastics in freshwater ecosystems.
... Ammonia-nitrogen, being the most reduced form of N in water, demands minimal energy during transport and assimilation, making it the favored N source for most plankton with high bioavailability [35,36]. Furthermore, previous research indicates that aside from being utilized by phytoplankton, the process of ammonia-nitrogen absorption in water involves its assimilation and absorption by heterotrophic bacteria as well as nitrification by nitrifying bacteria [37]. ...
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Urban lakes commonly suffer from nutrient over-enrichment, resulting in water quality deterioration and eutrophication. Constructed wetlands are widely employed for ecological restoration in such lakes but their efficacy in water purification noticeably fluctuates with the seasons. This study takes the constructed wetland of Jinshan Lake as an example. By analyzing the water quality parameters at three depths during both summer and winter, this study explores the influence of the constructed wetland on the water quality of each layer during different seasons and elucidates the potential mechanisms underlying these seasonal effects. The results indicate that the constructed wetland significantly enhances total nitrogen (TN) concentration during summer and exhibits the capacity for nitrate–nitrogen removal in winter. However, its efficacy in removing total phosphorus (TP) is limited, and may even serve as a potential phosphorus (P) source for the lake during winter. Water quality test results of different samples indicated they belong to Class III or IV. Restrictive factors varied across seasons: nitrate–nitrogen and BOD5 jointly affected water quality in winter, whereas TP predominantly constrained water quality in summer. These results could provide a reference for water quality monitoring and management strategies of constructed wetlands in different seasons in Jiangsu Province.
... Rights reserved. nitrate-nitrogen-ultraviolet spectrophotometry (Han et al. 2024) Ammonia nitrogen (NH 4 + -N) ammonia nitrogen-Nessler's reagent spectrophotometry (Lin et al. 2019) Total nitrogen (TN) total nitrogen-alkaline potassium persulfate digestion UV spectrophotometric method (Studt et al. 2020) Total phosphorus (TP) total phosphorus-ammonium molybdate spectrophotometric method (Worsfold et al. 2016) Chemical oxygen demand (COD) chemical oxygen demand-fast digestion-spectrophotometric method (Ma 2017) turbidity portable multi-parameter water quality testing Instrument (Xiong and Wang 2018) Content courtesy of Springer Nature, terms of use apply. Rights reserved. ...
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Algal oligosaccharides (AOS) have been shown to effectively promote plant growth. While there have been many studies on the use of AOS in promoting crop growth, few have investigated their potential in improving ecological floating bed wastewater treatment. Therefore, this paper aims to explore the effects and mechanisms of AOS in enhancing ecological floating bed wastewater treatment. Water spinach was cultivated in aquaculture wastewater treated with varying concentrations of AOS (0.025, 0.05, 0.1, and 0.2 mg/L), with an ecological floating bed without AOS serving as the control group. Results shows the addition of AOS can significantly enhancing ecological floating bed plant and microbial accumulation, resulting in profound improvement in ecological floating bed wastewater treatment efficiency. This is evident in the increased plant height, stem diameter, main root length, number of roots, leaf area, above water-surface fresh weight, below water-surface fresh weight, above water-surface dry weight, below water-surface dry weight, chlorophyll a, chlorophyll b, and chlorophyll content. The combination of 0.05 mg/L AOS with the ecological floating bed exhibits the most favorable results, with percentage increases in various indicators were 44.0%, 52.9%, 29.9%, 62.0%, 28.0%, 141.6%, 84.0%, 97.7%, 220.0%, 24.6%, 34.2%, 26.9% compared to the control group. The addition of AOS to the water spinach ecological floating bed system significantly enhances the removal efficiency of water turbidity, chemical oxygen demand (COD), ammonia nitrogen (NH4⁺-N), nitrate nitrogen (NO3⁻-N), total nitrogen (TN), and total phosphorus (TP) water quality indicators. This experiment also investigated the differences in microbial community structure between the control group and the group with the optimal concentration of AOS to study the mechanism of action of AOS. The combination of 0.05 mg/L AOS with the ecological floating bed demonstrates the optimal removal efficiency. This study offers crucial technical insights for further optimizing ecological floating bed technology and improving water purification efficiency.
... The organic matter content is quantified via the external heating-potassium dichromate volumetric method [44]. Ammonium nitrogen is determined using the KCl extraction-indophenol blue colorimetric method followed by spectrophotometry [45]. Nitrate nitrogen is determined using the KCl extraction-colorimetric method. ...
Article
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The combination of no-till farming and green manure is key to nourishing the soil and increasing crop yields. However, it remains unclear how to enhance the efficiency of green manure under no-till conditions. We conducted a two-factor field trial of silage maize rotated with hairy vetch to test the effects of tillage methods and returning. Factor 1 is the type of tillage, which is divided into conventional ploughing and no-tillage; factor 2 is the different ways of returning hairy vetch as green manure, which were also compared: no return (NM), stubble return (H), mulching (HM), turnover (HR, for CT only), and live coverage (LM, for NT only). Our findings indicate that different methods of returning hairy vetch to the field will improve maize yield and quality. The best results were obtained in CT and NT in HM and LM, respectively. Specifically, HM resulted in the highest dry matter quality and yield, with improvements of 35.4% and 31.9% over NM under CT, respectively. It also demonstrated the best economic and net energy performance. However, other treatments had no significant effect on the beneficial utilization and return of nutrients. The LM improved yields under NT by boosting soil enzyme activity, promoting nitrogen transformation and accumulation, and increasing nitrogen use efficiency for better kernel development. Overall, NTLM is best at utilizing and distributing soil nutrients and increasing silage maize yield. This finding supports the eco-efficient cultivation approach in silage maize production in the region.
... Therefore, monitoring ammonium ion levels in water is important to mitigate the impact on the environment and human health. Various detection tools have been developed for the analysis of ammonia nitrogen in water, including FTIR spectroscopy [3], spectrophotometric methods [1,4], colorimetric pH detection [5,6], ion-selective electrodes [7,8], and other optical methods [9][10][11][12]. The most common sensors are based on a sensitive ion-selective membrane, modified with functional groups, that responds to the presence of NH 4 + in water [8,[13][14][15][16]. ...
Article
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Monitoring of ammonium ion levels in water is essential due to its significant impact on environmental and human health. This work aims to fabricate and characterize sensitive, real-time, low-cost, and portable amperometric sensors for low NH4+ concentrations in water. Two strategies were conducted by cyclic voltammetry (CV): electrodeposition of Au nanoparticles on a commercial polyaniline/C electrode (Au/PANI/C), and CV of electropolymerized polyaniline on a commercial carbon electrode (Au/PANIep/C). Au NPs increase the electrical conductivity of PANI and its ability to transfer charges during electrochemical reactions. The electrode performances were tested in a concentration range from 0.35 µM to 7 µM in NH4+ solution. The results show that the Au/PANI/C electrode performs well for high NH4+ concentrations (0.34 µM LoD) and worsens for low NH4+ concentrations (0.01 µM LoD). A reverse performance occurs for the electrode Au/PANIep/C, with a 0.03 µM LoD at low NH4+ concentration and 0.07 µM LoD at high NH4+ concentration. The electrodes exhibit a good reproducibility, with a maximum RSD of 3.68% for Au/PANI/C and 5.94% for Au/PANIep/C. In addition, the results of the repeatability tests show that the electrochemical reaction of sensing is fully reversible, leaving the electrode ready for a new detection event.
... Although the above methods had excellent selectivity and sensitivity, they also had disadvantages such as cumbersome operation and long time, so that they are not suitable for the rapid and real-time monitoring of ammonia nitrogen [9]. Therefore, electrochemical methods with simple operation, fast detection and high sensitivity have gradually attracted the attention of researchers [10]. At present, researchers are constantly working to improve the sensitivity, selectivity and stability of electrochemical detection methods for ammonia nitrogen in order to better meet the needs of practical applications [11]. ...
Article
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Pt-based electrochemical ammonia-nitrogen sensors played a significance role in real-time monitoring the ammonia-nitrogen concentration. The alloying of Pt and transition metals was one of the effective ways to increase the detectability of the sensitive electrode. In this paper, a self-supported electrochemical electrode for the detection of ammonia nitrogen was obtained by the electrodeposition of PtNi alloy nanoleaves on a carbon cloth (PtNi-CC). Experimental results showed that the PtNi-CC electrode exhibited enhanced detection performance with a wide linear range from 0.5 to 500 µM, high sensitivity (7.83 µA µM−1 cm−2 from 0.5 to 150 μM and 0.945 µA µM−1 cm−2 from 150 to 500 μM) and lower detection limit (24 nM). The synergistic effect between Pt and Ni and the smaller lattice spacing of the PtNi alloy were the main reasons for the excellent performance of the electrode. This work showed the great potential of Pt-based alloy electrodes for the detection of ammonia-nitrogen.
... The concentrations of total nitrogen (%), ammonium nitrogen (mg/kg), and nitrate nitrogen (mg/kg) were measured using the Kjeldahl technique (Hu et al., 2022;Lin et al., 2019;Oxukbayeva et al., 2023). ...
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Recultivation of technologically disturbed land is an important objective of environmental protection. The study aimed to examine the impact of the coal mining process on the agrochemical and biochemical parameters of soil. Agrochemical and biochemical analysis of soil samples was conducted before and after the mining reclamation stage. The baseline indicators of coal mines indicated that all studied territories needed a full cycle of technologically disturbed land recultivation measures. Before the initial stage of recultivation, the content of carbonate-ion, bicarbonate-ion, copper, lead, zinc, cadmium, and petroleum products in soil samples from the coal mine met the norms and requirements of authorizing documents, and part of the samples from the territory of the Sample 2 coal mine were marked by increased pH and reduced humus content. All samples exceeded the background values of mobile forms of zinc, manganese, copper, lead, nickel, chromium, and cobalt. To effectively improve soil fertility, it is recommended to use biochar, compost, and/or peat and apply organic and inorganic fertilizers. The next stage of research will involve the biological reclamation of technogenically disturbed areas of the coal mines with cultivated and wild plants.
... By monitoring ammonia nitrogen levels, pollution in river water can be promptly detected, enabling appropriate measures to be taken to prevent water eutrophication and other environmental problems. Furthermore, monitoring ammonia nitrogen levels provides scientific evidence for environmental management and protection, serving as a basis for formulating environmental protection policies and supporting sustainable water resource utilization [7][8][9]. ...
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In line with rapid economic development and accelerated urbanization, the increasing discharge of wastewater and agricultural fertilizer usage has led to a gradual rise in ammonia nitrogen levels in rivers. High concentrations of ammonia nitrogen pose a significant challenge, causing eutrophication and adversely affecting the aquatic ecosystems and sustainable utilization of water resources. Traditional ammonia nitrogen detection methods suffer from limitations such as cumbersome sample handling and analysis, low sensitivity, and lack of real-time and dynamic feedback. In contrast, automated monitoring and ammonia nitrogen prediction technologies offer more efficient methods and accurate solutions. However, existing approaches still have some shortcomings, including sample processing complexity, interference issues, and the absence of real-time and dynamic information feedback. Consequently, deep learning techniques have emerged as promising methods to address these challenges. In this paper, we propose the application of a neural network model based on Long Short-Term Memory (LSTM) to analyze and model ammonia nitrogen monitoring data, enabling high-precision prediction of ammonia nitrogen indicators. Moreover, through correlation analysis between water quality parameters and ammonia nitrogen indicators, we identify a set of key feature indicators to enhance prediction efficiency and reduce costs. Experimental validation demonstrates the potential of our proposed approach to improve the accuracy, timeliness, and precision of ammonia nitrogen monitoring and prediction, which could provide support for environmental management and water resource governance.
... What is more, NH4-N, NO2-N, and NO3-N pose different risks to marine organisms: NH4-N can lead to asphyxia, acidosis, and decreased blood oxygen in fish [32][33][34]; NO2-N can lead to serious electrolyte imbalances in aquatic animals [35,36]; while the toxicity of NO3-N to aquatic organisms is extremely low and almost negligible [12]. When the dissolved oxygen (DO) content in seawater is normal, nitrification will occur, and NH4-N will be converted into NO2-N and then into NO3-N, and the water quality of the seawater will gradually improve. ...
Article
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Ammonia nitrogen (NH4-N), nitrite nitrogen (NO2-N), and nitrate nitrogen (NO3-N) are important nutrients for maintaining the ecological balance of seawater archipelagos. Obtaining the concentrations of the three nitrogenous compounds simultaneously can allow us to comprehensively analyze nitrogen cycling in archipelago waters, which is beneficial to the ecological protection of both agriculture and fisheries. The existing studies have usually considered a single nitrogen compound or dissolved inorganic nitrogen (DIN), which can only identify the water quality but cannot comprehensively judge the water purification situation or the toxicity of the nitrogen compounds in the water. In the process of constructing an inversion model, only the specific bands of remote sensing imageries used in training/learning are directly related to the actual measured values, ignoring the fact that the specific bands contain information on water quality parameters is different that would affect the fitting accuracy. Furthermore, the existing empirical models and machine learning models have not yet been applied to high-resolution inversion in archipelago waters with active fishing activities. In view of this, we constructed a multiple weighted regression model considering spatial characteristics (S-WSVR) to simultaneously retrieve the distribution of NH4-N, NO2-N, and NO3-N in archipelagic waters. By using the S-WSVR model and considering the complexity of the spatial distribution of the three nitrogen compounds in the mesoscale archipelagic waters, longitude and latitude were added to the experimental dataset as spatial features to fit the nonlinear spatial relationships. Meanwhile, a multivariate weighting module based on the Mahalanobis distance was integrated to calculate the contribution of the characteristic bands and improve the inversion accuracy. The S-WSVR model was applied in the water of Changshan Islands, China, with a retrieval resolution of 30 m, and the r-values of the three nitrogen compounds achieved 0.9063, 0.8900, and 0.9755, respectively. Notably, the sum of the three nitrogen compounds has an r-value of 0.9028 when compared with the measured DIN. In addition, we obtained the Landsat 8 characteristic bands for the three nitrogen compounds and plotted the spatial distributions of the nitrogen compounds in spring and autumn from 2013 to 2022. By analyzing the spatio-temporal variations, it was apparent that the three nitrogen compounds are controlled by human activities and river inputs, and the anoxic discharge of the Yalu River has a strong influence on NO2-N content. Therefore, the accurate estimation in this study can provide scientific support for the protection of sensitive archipelago ecosystems.
... Las altas concentraciones de amonio pueden tener grandes consecuencias ecológicas por la disminución de oxígeno disuelto en el agua causada por el proceso de oxidación, además, de indicar alteraciones en el ciclo normal de nitrógeno por contaminación antropogénica (Roldán y Ramírez, 2008;Lin et al., 2019). Los valores de NH 4+ en la Reserva Ecológica El Renacer de la Laguna oscilan de 0,57 a 1, 02 mg/L en invierno y de 0,03 a 0,06 mg/L en verano, presentando niveles de NH 4+ por debajo del límite de detección en primavera y otoño. ...
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Publicación que compila trabajos completos presentados en las VII Jornadas Interdisciplinarias "Ciclo del Agua en Agroecosistemas". Centro de Estudios Transdisciplinarios del Agua. Facultad de Ciencias Veterinarias, Universidad de Buenos Aires. Argentina.
... The concentration of NH 4 + was determined using indothymol blue method (ITB) (Zamora-Garcia et al. 2021). This method is based on the Berthelot reaction, and it is the most widely used colorimetric method for the determination of ammonia in wastewater (Lin et al. 2019). It is based on the development of the indothymol blue color formed between ammonia and thymol. ...
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Cationic ligand exchange is one of the most predominant mechanisms for the removal of ammonia from wastewater through complex formation. The complexation technique occurs between the metal ions loaded on the surface of Amberlite IR-120 and ammonia which is present in the medium. Cu(II)-loaded Amberlite IR-120 (R-Cu²⁺) was prepared and described using FT-IR, TGA, SEM, and EDX techniques. The prepared R-Cu²⁺ was applied for the elimination of ammonia from an aqueous solution. Different cations such as Co²⁺ and Ni²⁺ were loaded onto Amberlite IR-120 to study the impact of counter cation on the removal efficiency of ammonia. The ammonia removal percentage followed the order; R-Cu²⁺ > R-Ni²⁺ > R-Co²⁺. The effects of contact time, pH, initial concentration, temperature, and coexisting ions on the removal of ammonia from wastewater by R-Cu²⁺ were investigated. The equilibrium adsorbed amount of ammonia was found to be 200 mg/g at pH = 8.6 and 303 K within 60 min using 0.1 g R-Cu²⁺ and an initial concentration of ammonia of 1060 mg/L. The removal of ammonia using R-Cu²⁺ obeyed the non-linear plot of both Freundlich and Langmuir isotherms. According to the thermodynamic parameters, the adsorption of ammonia onto R-Cu²⁺ was an endothermic and spontaneous process. The time-adsorption data followed the pseudo-second-order and intraparticle diffusion models. Moreover, the resulting product (R-Cu(II)-amine composite) from the adsorption process exhibited high catalytic activity and could be low-cost material for the elimination of dyes such as aniline blue (AB), methyl green (MG), and methyl violet 2B (MV2B) from wastewater. Graphical Abstract
... Ammonia is present in one of two species depending on the pH, unionized (ammonia, NH 3 ) and cationic ammonia (ammonium, NH 4 + ). At pH < 8.75, ammonium is the predominant species, whereas ammonia predominates when the water pH is above 9.75 [1]. It is thought that un-ionized ammonia is the reason behind ammonia toxicity; un-ionized ammonia has adverse effects on fish growth, organ weight, hematocrit, and gill conditions [2]. ...
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Ammonia is a serious contaminant of aquaculture water due to its continuous release into the water environment during the biological processes of aquatic animals. Ammonia accumulation in water has negative environmental impacts, including eutrophication and the death of aquatic organisms. Therefore, sensitive and accurate determination of ammonia is an urgent need, especially in pisciculture systems. Here, we report the fabrication of a novel magnetic-hyperbranched nanomaterial-based ammonia-sensing probe for the fast and sensitive determination of ammonia in water. The proposed probe is composed of poly(amidoamine) (PAMAM)-coated superparamagnetic iron oxide nanoparticles (SPIONs) decorated with silver nano-particles. Changing the ammonia concentration is associated with a corresponding change in the surface plasmon resonance property of silver nanoparticles. The proposed nanosystem was characterized with FTIR spectroscopy, SEM imaging, energy-dispersive X-ray (EDX) analysis, TEM imaging, X-ray diffractometry (XRD), and vibrating sample magnetometry (VSM). The TEM images showed a homogenous and uniform distribution of the nanoparticles with an average nanoparticle size of 200 nm, while the surface silver nanoparticles have an average particle size of 10-50 nm. The proposed optical ammonia sensor was successfully used to determine the concentration of ammonia in water samples by measuring the change in the solution absorbance at 428 nm. The obtained results revealed high recovery values (96.3-104.7%) and very low detection (LOD = 5.69 mg/L) and quantification (LOQ = 18.96 mg/L) limits. The standard plot is linear in the concentration range of 10-50 mg/L with an r 2 value of 0.9980. Sandell's sensitivity of the most promising sensor (NP-III) among the investigated systems was found to be 0.15 µg/cm 2 , which indicates high sensitivity.
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The phenomenon of acidic failure frequently occurs in the anaerobic digestion (AD) of sole corn stover (CS), which also lacks a systematic understanding of domestication and recovery strategies. Therefore, this study focused on methane production efficiency and dominant microbial responses throughout the domestication, start-up, acidification, and recovery stages. During the 230 days of domestication, AD of sole CS achieved stable methane production rates (74.60-92.74 mL/g TS) and methane percentages (41.18-48.44%). The recovery of methane production could be achieved by diluting and adding NaHCO3. CS with a smaller particle size (2 mm) exhibited slower recovery but had a better recovery effect compared to 5 and 8 mm. Before and after the acidification stage, the dominant bacterial genera changed from Pseudomonas, Caproiciproducens and Proteiniphilum to Pseudomonas; the dominant archaeal genera changed from Methanosaeta and Methanobacterium to Bathyarchaeia. The above results provide feasible strategies for the recovery of AD applications of CS.
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The factors of water quality in the intensive marine stichopus japonicus aquaculture process are changing with seasons, so water temperature, salinity, pH value and nitrite were selected as auxiliary variables to measure the concentration of ammonia nitrogen. FCM (Fuzzy C-means) algorithm was adopted to classify them. Based on the EM (Expectation Maximization) algorithm, fuzzy sub-models of ammonia nitrogen concentration were constructed around each operating point, and finally the fuzzy sub-models were combined according to the posterior distribution of the characteristics of the sampling data. Based on the data collected at Xinyulong Marine Biological Seed Technology Co., Ltd, in Dalian China, the ammonia nitrogen concentration prediction model was tested and verified.
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The aim of the present study was to evaluate the spatio-temporal variability of various physical and chemical parameters of water quality and to determine the trophic state of Lake Ardibo. Water samples were collected from October 2020 to September 2021 at three sampling stations in four different seasons. A total of 14 physico-chemical parameters, such as water temperature, pH, dissolved oxygen (DO), electrical conductivity, turbidity, alkalinity, Secchi-depth, nitrate, ammonia, silicon dioxide, soluble reactive phosphorus, total phosphorus, chloride, and fluoride were measured using standard methods. The results demonstrated that seasonal variation existed throughout the study period. Except for turbidity, the water quality of the lake varied significantly within the four seasons (ANOVA, p < 0.05). DO levels decreased significantly during the dry season following water mixing events. Chlorophyll-a measurements exhibit significant seasonal differences ranging from 0.58 μg L−1 in the main-rainy season to 8.44 μg L−1 in the post-rainy period, indicating a moderate algal biomass production. The overall category of Lake Ardibo was found to be under a mesotrophic state with medium biological productivity. A holistic lake basin approach management is suggested to maintain water quality and ecological processes and to improve the lake ecosystem services.
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The excessive enrichment of nitrate in the environment can be converted into ammonia (NH3) through electrochemical processes, offering significant implications for modern agriculture and the potential to reduce the burden of the Haber–Bosch (HB) process while achieving environmentally friendly NH3 production. Emerging research on electrocatalytic nitrate reduction (eNitRR) to NH3 has gained considerable momentum in recent years for efficient NH3 synthesis. However, existing reviews on nitrate reduction have primarily focused on limited aspects, often lacking a comprehensive summary of catalysts, reaction systems, reaction mechanisms, and detection methods employed in nitrate reduction. This review aims to provide a timely and comprehensive analysis of the eNitRR field by integrating existing research progress and identifying current challenges. This review offers a comprehensive overview of the research progress achieved using various materials in electrochemical nitrate reduction, elucidates the underlying theoretical mechanism behind eNitRR, and discusses effective strategies based on numerous case studies to enhance the electrochemical reduction from NO3˗ to NH3. Finally, this review discusses challenges and development prospects in the eNitRR field with an aim to guide design and development of large‐scale sustainable nitrate reduction electrocatalysts.
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The precise and rapid detection of ammonia nitrogen is of paramount importance in safeguarding water environments. In this study, we introduce a novel approach for electrochemical ammonia sensing using nanocubic copper electrodes, fabricated through a straightforward electrodeposition technique. A comprehensive characterization of the copper electrode sheds light on the pivotal role of deposition in shaping the morphology of copper particles, subsequently impacting the ammonia sensing capabilities. Through an in-depth investigation of the electrochemical behavior of nanocubic copper electrodes, we unveil how ammonia enhances electron transfer during copper oxidation by forming robust coordination with Cu(II) and simultaneously disrupting the oxide layer on the copper surface. This synergistic effect process has been effectively harnessed for the rapid electrochemical quantification of ammonia nitrogen. Linear scan voltammetry results reveal a direct relationship between peak currents and ammonia nitrogen concentrations spanning the broad range of 0.1–100 ppm. Notably, the nanocubic copper electrode exhibits a low detection limit, exceptional resistance to interference and impressive repeatability. Moreover, our practical testing in real water samples show the nanocubic copper electrode’s superior performance over the spectrometric method in determining ammonia nitrogen concentrations. These findings underscore the potential of the nanocubic copper electrode for high-performance ammonia sensing applications. Fullsize Image
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Oceanic water columns, their overall health, and the ongoing biogeochemical processes in these oceanic masses are integral in regulating several global phenomena and providing ecosystem services to humankind. Ever since the potential of oceanic water bodies and the significance of all the biotic life forms in this hydrosphere have been realized by the global scientific community, measuring and monitoring these water masses have become imperative.
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Aquaculture is the practice of cultivating and farming aquatic organisms under controlled conditions. High pH conditions, more toxic ammonia is present which can be harmful to aquatic organisms, particularly fish. The presence of ammonia in water can have implications for dissolved oxygen (DO) levels. The purpose of this study was to develop Internet of things (IoT) for measurement pH, DO and ammonia-nitrogen using Blynk platform. Additionally, the study aimed to determine physicochemical parameters trend in aquaponic system using IoT application. The reading of pH and DO from IoT sensor were collected from Blynk platform every ten seconds and ammonia nitrogen was observed twice a month. The presence of ammonia nitrogen in aquaponic system was determined using Nitrogen-ammonia reagent set, TNT, AmVer (Salicylate), High range. The data from this study were statistically analysed using Microsoft Excel 2019 to perform one-way ANOVA. Through this study, it could be concluded that internet accessibility is statistically significant to intention to use internet of things (IoT) application and the use of IoT sensors in aquaponic systems has yielded advantages
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Biofilm-based biological nitrification is widely used for ammonia removal, while hasn't been explored for ammonia analysis. The stumbling block is the coexist of nitrifying and heterotrophic microbes in real environment resulting in non-specific sensing. Herein, an exclusive ammonia sensing nitrifying biofilm was screened from natural bioresource, and a bioreaction-detection system for the on-line analysis of environmental ammonia based on biological nitrification was reported. The nitrifying microbes were aggregated into a nitrifying biofilm through a result-oriented bioresource enrichment strategy. The predominant nitrifying population and progressive surface reaction in the plug flow bioreactor led to the exclusive and exhaustive ammonia biodegradation for the establishment of a novel analytical method. The on-line ammonia monitoring prototype achieved complete biodegradation for determining ammonium nitrogen within 5 min and showed exceptional reliability in long-term real sample measurements without frequent calibration. This work offers a low-threshold natural screening paradigm for developing sustainable bioresource-based analytical technologies.
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A novel, inexpensive, and sensitive microanalytical system for the determination of total ammonia-nitrogen (ammonia-N) in water was developed. The system was designed to detect ammonia using an in-line purging system coupled with a newly designed gas converging flow cell incorporating in-line paper-based colorimetric detection. The gas converging flow cell served as a gas chamber, a paper-based device holder, and a color detection cell. The paper-based device was impregnated with butterfly pea extract (a natural acid-base indicator), the color of which changed on the basis of the generated ammonia gas. Analytical parameters such as concentration of natural indicator and purging time were studied and optimized. The color image could be captured by an integrated endoscope camera or smartphone and analyzed by ImageJ software in RGB mode. Under optimal conditions, two linear dynamic ranges were observed. By using 1:2 (v/v) diluted 2% (w/v) butterfly pea extract in Milli-Q water, a low linear concentration range of 0.05–0.9 mg L−1 with a limit of detection (LOD) of 0.02 mg L−1 and limit of quantification (LOQ) of 0.05 mg L−1 was achieved. By using a non-diluted 2% (w/v) butterfly pea extract, a high linear concentration range of 0.5–4 mg L−1 with an LOD of 0.1 mg L−1 and LOQ of 0.3 mg L−1 was obtained. Finally, the optimized method was leveraged to determine ammonia-N in various water samples from shrimp farming.
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Increased ocean temperature due to global warming affects the health and immunity of fish. In this study, juvenile Paralichthys olivaceus were exposed to high temperature after pre-heat (Acute: Acute heat shock at 32 °C, AH-S: Acquired heat shock at 28 °C & short recovery (2h) and heat shock at 32 °C, AH-L: acquired heat shock at 28 °C and long recovery (2 days), AH-LS: acquired heat shock at 28 °C & long (2 days) + short (2h) recovery). Heat shock after pre-heat significantly upregulated various immune-related genes, including interleukin 8 (IL-8), c-type lysozyme (c-lys), immunoglobulin M (IgM), Toll-like receptor 3 (tlr3), major histocompatibility complex IIα (mhcIIα) and cluster of differentiation 8α (cd8α) in the liver and brain of P. olivaceus. This study showed pre-exposure to high temperatures below the critical temperature can activate fish immunity and increase tolerance to high temperatures.
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Potential stability and reproducibility of solid-contact ion-selective electrodes (SC-ISEs) are key to ensure reliable accuracy of actual water sample monitoring. However, undesirable water layer formed at interface of SCs and ion-selective membranes inevitably changes the interfacial potential. Here a superhydrophobic polyaniline (PANI) SC is presented to improve potential response of NH4⁺-ISE. Electrodeposition methods are used to control PANI growth and perfluorooctanoic acid co-doping, forming PANI SCs with different wettabilities. Though constructed SC-NH4⁺-ISEs show detection linear ranges from 10⁻⁵ to 10⁻¹ M, superhydrophobic SC-ISE has a slope (58.07 mV/dec) closest to the ideal Nernstian slope. Importantly, superhydrophobic SC greatly inhibits water layer formation and enables SC-NH4⁺-ISE to have a very stable potential response. Potential drift is only 13.6 ± 3.2 µV/h for 12 h continuous measurement and standard deviation of the standard potential is 0.96 mV (n = 3), which are 55.7 and 5.4 times lower than those of unmodified SC-ISE, respectively. Moreover, superhydrophobic SC-ISE exhibits excellent potential stability against external interferences and even during actual wastewater monitoring. Once water layer is formed in unmodified SC-ISE, inaccuracy of measured NH4⁺ concentrations in actual wastewater reaches ca. 37%. This study demonstrates that superhydrophobic SC can efficiently improve potential response of SC-ISEs.
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Wastewater is any water source that a human has used for domestic, agricultural, commercial, or industrial activity. Wastewater needs to be treated before being discharged into the environment to reduce contamination of water bodies. The wastewater treatment must follow the Environmental Quality (Sewage) Regulations, 2009. Rivers in Malaysia continue to suffer wastewater pollution from the inefficiency of treatment. Wastewater has been recognized as the significant cause of these issues. Many physical, chemical, and biological techniques have evolved for sewage treatment. It has been observed that biological procedures are advantageous, and one of these procedures that can be considered is phytoremediation. Thus, this study investigated the effectiveness of water hyacinths in treating wastewater, such as the effluent from the wastewater treatment plant, river, and pond in Pusat Asasi, UiTM Dengkil, Selangor, by phytoremediation. Different parameters of pH, suspended solids, phosphorus, ammonia-nitrogen, nitrite-nitrogen, nitrate-nitrogen, chemical oxygen demand and biological oxygen demand have been assessed. The research has been conducted with experimental works of 14 days. The laboratory works showed a significant reduction in most parameters after two weeks of phytoremediation.
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Dynamically distributed at trace levels in the open ocean, ammonium is one of the most important and reactive nitrogen compounds in the marine environment. Obtaining reliable measurements of ammonium concentrations is thus a prerequisite to fully understand its role in marine biogeochemical processes, but remains challenging. Among others, quantification and identification of different sources of blanks is an outstanding issue, due partly to the fact that ammonium‐free water is very difficult to prepare and/or preserve. Building on a recently developed method using solid phase extraction combined with fluorescence detection (SPE‐Flu), we examined the kinetics of the ortho‐phthaldialdehyde‐sulfite‐ammonium reaction and introduce a new approach to quantifying reagent blanks via a “reagents addition” method. The reagent blank of the method, equivalent to 6.7 ± 1.5 nmol L−1 of ammonium under our experimental settings, accounted for up to 27% of the ammonium background in seawater samples collected from the oligotrophic ocean. We also showed that the SPE‐Flu method is highly specific, with negligible interference from three types of amines and 15 types of amino acids at nanomolar concentrations, which are typical of open ocean regimes. The determination of the reagent blank allowed for optimized data reduction, which was applied to a study in the oligotrophic South China Sea. Water column profiles showed a very well‐defined structure and smooth distribution of ammonium concentrations, consistent with the distribution of other parameters. We thus contend that our proposed approach provides a way to further optimize the quantification of ammonium concentrations in natural seawater via the SPE‐Flu method.
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A continuous flow method for the determination of ammonium concentration in seawater from a nanomolar to a micromolar level is described. To prevent spurious peaks derived from salinity difference, a gas-permeable hydrophobic membrane filter was used to separate the manifold into an outgassing section and an indophenol blue reaction section. The indophenol blue reaction section was adopted for colorimetric analysis and is equipped with a 1-m path length liquid capillary cell and a fiber-optic spectrometer, which is able to record the absorbance at multiple wavelengths. The minimum detection limit at wavelength 630 nm is 5.5 ± 1.8 nM, and the calibration curves are linear to at least 2,000 nM. In addition, the minimum detection limit at wavelength 530 nm was 13 ± 5.3 nM, and linear calibration curves were observed until at least 10,000 nM. The slopes of the calibration curves were similar for standards prepared using filtered seawater and ultrapure water. The ammonium concentration of the ultrapure water was similar to those of ion-exchanged water and unfiltered low-nutrient seawater, but was significantly lower than those of filtered seawater and solutions that contained sodium hydroxide. Therefore, ultrapure water is optimal for both blank and standard preparations because of its stable quality and availability. Given its large concentration range and the use of readily available blanks, this method is suitable for the determination of ammonium concentration and helps our understanding of ammonium dynamics in the ocean.
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A novel home-made portable fluorescence detector that is simple, smaller, and transportable for shipboard analysis of ammonium in estuarine and coastal waters was developed and applied in a flow system for ammonium analysis based on the reaction of ammonium, OPA and sulfite in this study. The detector incorporates a UV-LED, two band pass filters, a photomultiplier tube (PMT), a modified flow cell and an electronic circuit with a constant voltage supply and a constant current supply. The modified flow cell of the detector used in this study could avoid the interference of air bubbles on the fluorescence signal. A 100 nmol•L-1 ammonium standard solution was continuously measured for 90 min. RSD of 0.8% (n = 38) was obtained, indicating a good stability of the detector. Compared with a commercial PMT-FL fluorescence detector, the home-made one was smaller, lighter and with better sensitivity (approximately 11.4% higher). The effect parameters of the flow system were optimized. Under the optimal conditions, the detection limit of 2.1 nmol•L-1 within the working range of 0-300 nmol•L-1 was obtained. With the underway sampling system, the home-made portable fluorescence detector was applied in Jiulongjiang Estuary and the distribution of ammonium in surface seawater was obtained.
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To more efficiently process the large sample numbers for quantitative determination of ammonium (NH4+) and phosphate (orthophosphate, PO43-) generated during comprehensive growth experiments with the marine Roseobacter group member Phaeobacter inhibens DSM 17395, specific colorimetric assays employing a microplate reader (MPR) were established. The NH4+ assay is based on the reaction of NH4+ with hypochlorite and salicylate, yielding a limit of detection of 14 µM, a limit of quantitation of 36 µM, and a linear range for quantitative determination up to 200 µM. The PO43-assay is based on the complex formation of PO43- with ammonium molybdate in the presence of ascorbate and zinc acetate, yielding a limit of detection of 13 µM, a limit of quantitation of 50 µM, and a linear range for quantitative determination up to 1 mM. Both MPR-based assays allowed for fast (significantly lower than 1 h) analysis of 21 samples plus standards for calibration (all measured in triplicates) and showed only low variation across a large collection of biological samples.
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Seasonal and die1 changes in nutrient concentrations and nitrogen assimilation rates were used to assess the effects of NH,+ on NO,- assimilation. Surface-water NO,- concentrations ranged from 6 to 17 ah4 while NH.,+ concentrations ranged from 0 to 0.4 PM. Total N assimilation ranged from 84 to 732 nM d-r but showed no seasonal trend. NH,' and urea concentrations were < 1% of total dissolved inorganic N, but use of this "regenerated" N still accounted for 44-89*/s of total N assimilation. Rates of NO,- assimilation were negatively correlated with ambient NH,+ concen- trations, and concentrations of NH., + between 0.1 and 0.3 PM caused complete inhibition of NOs- assimilation, NO,- was more important as a source of N in spring than in summer. We attribute this pattern to a summer increase in turnover rates for NH;'. Turnover times for the dissolved NH,+ pool were half as long in August as in May. Grazing and recycling in the euphotic zone apparently both play significant roles in preventing depletion of NO,- in the oceanic subarctic Pacific.
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Our understanding of the players and pathways of the global nitrogen cycle has advanced substantially over recent years with discoveries of several new groups of organisms and new types of metabolism. This review focuses on recently discovered processes that add new functionality to the nitrogen cycle and on the organisms that perform these functions. The processes include denitrification and other dissimilatory nitrogen transformations in eukaryotes, anaerobic ammonium oxidation, and anaerobic methane oxidation with nitrite. Of these, anaerobic ammonium oxidation coupled to nitrite reduction by anammox bacteria has been well documented in natural environments and constitutes an important sink for fixed nitrogen. Benthic foraminifera also contribute substantially to denitrification in some sediments, in what potentially represents an ancestral eukaryotic metabolism. The ecophysiology of the novel organisms and their interactions with classical types of nitrogen metabolism are important for understanding t...
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RELIABLE measurement of trace species in natural waters is essential for studies of pollution or trace-element cycling, but is difficult, partly because the distribution of chemical species often changes during sampling and storage1. In situ measurements can overcome these problems, but the few measurements made previously have involved complicated systems that cannot be used routinely1,2. Here we describe a simple technique for measuring trace-metal concentrations in situ in water. The technique incorporates an ion-exchange resin separated from the solution by an ion-permeable gel membrane. Mass transport through the gel is diffusion-controlled and thus well defined, making it possible to obtain quantitative data on concentration and speciation over relatively short time periods (from one hour to several weeks). We present measurements of zinc concentrations in sea water using this technique which agree well with electrochemical measurements. In principle, our technique should be applicable to any inorganic or organic diffusing species.
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Replies to the questionnaire on the determination of ammonia, sent to participants in the Fifth ICES Intercomparison Exercise for nutrients in seawater, are evaluated. The conclusions provide some useful recommendations for analysts.Berthelot's reaction (formation of indophenol-blue) is the basis of the colorimetry used by the great majority of participants, and their individual methods are examined in detail. Application of the indophenol-blue method to seawater poses some specific problems, for example, precipitation, and variation of the pH of the matrix as a function of salinity. Basic principles are discussed and participants' procedures are compared with those most commonly used in the literature. Large disparities in reaction and operating conditions are evident between these many versions of what is nominally the same method. Various points of the reaction mechanism are examined in order to determine optimal ranges for reagent concentrations.Procedures for calibration, measuring the blank, and defining the concentration-zero are also evaluated, as the intercomparison results indicate that systematic (particularly relative) errors are widespread. The use of low-nutrient seawater as a calibration matrix is strongly recommended if errors such as those incurred by the use of demineralised water or artificial seawater are to be avoided.Sources of contamination are discussed, the majority of participants being aware that ambient laboratory air can be a major problem.In general, users of automated methods produce better results than users of manual methods, but this may simply reflect a tendency for the former to be the more experienced analysts. Although it was not possible consistently to relate performance in the intercomparison with methodology, it would appear that many procedures deviate from optimal operating conditions, while some are unnecessarily complicated and might benefit from simplification. Analysts are invited to re-examine their ammonia methods, with particular attention to suitability of reagents and reaction conditions, use of adequate blank and calibration procedures and matrices, correction for refraction effects and identification of local contamination sources.
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Available data on the pH and temperature dependence of ammonia toxicity to aquatic organisms were examined and their agreement with various models was evaluated. A model which considers alteration of the relative concentration of un-ionized ammonia at the gill surface failed to adequately describe either pH or temperature dependence. A model that assumes that un-ionized ammonia and ammonium ion are jointly toxic was strongly supported by the data on pH dependence, but could not explain observed temperature dependence. Temperature dependence can be described empirically by a simple log-linear model. The effects of pH and temperature were generally found to be qualitatively and quantitatively similar among fish species.
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