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1.
Electrocatalytic nitrite (NO 2−) reduction reaction (NO 2−RR) for ammonia (NH 3) synthesis is a promising alternative for NO 2− resource utilization. Herein, a dual-site copper-cobalt oxide catalyst is reported for the efficient electrocatalytic reduction of NO 2− to NH 3, exhibiting NH 3 Faradaic efficiency that remained above 95% (0.1 m NaNO 2) over a wide potential window (−0.1 to −0.6 V vs reversible hydrogen electrode, vs RHE). More importantly, the high NH 3 Faradaic efficiency maintains an over 85% (−0.1 to −0.3 V vs RHE) at a low concentration of NaNO 2 (0.01 m ). Theoretical calculations demonstrate that CuO serves the *NO 2 to *NO and is subsequently converted to NH 3 on Co 3O 4. Coupled anodic ethylene glycol (EG) oxidation reaction endows low cell voltage (ΔU = 480 mV, 10 mA cm −2) and energy consumption saving (>23%) in a two-electrode system. This work provides a reference for a co-upcycling electrolyzer for NO 2− and EG. 相似文献
2.
A comparative study to produce the correct influent for Anammox process from anaerobic sludge reject water (700–800 mg NH 4+-N L −1) was considered here. The influent for the Anammox process must be composed of NH 4+-N and NO 2−-N in a ratio 1:1 and therefore only a partial nitrification of ammonium to nitrite is required. The modifications of parameters (temperature, ammonium concentration, pH and solid retention time) allows to achieve this partial nitrification with a final effluent only composed by NH 4+-N and NO 2−-N at the right stoichiometric ratio. The equal ratio of HCO 3−/NH 4+ in reject water results in a natural pH decrease when approximately 50% of NH 4+ is oxidised. A Sequencing batch reactor (SBR) and a chemostat type of reactor (single-reactor high activity ammonia removal over nitrite (SHARON) process) were studied to obtain the required Anammox influent. At steady state conditions, both systems had a specific conversion rate around 40 mg NH 4+-N g −1 volatile suspended solids (VSS) h −1, but in terms of absolute nitrogen removal the SBR conversion was 1.1 kg N day −1 m −3, whereas in the SHARON chemostat was 0.35 kg N day −1 m −3 due to the different hydraulic retention time (HRT) used. Both systems are compared from operational (including starvation experiments) and kinetic point of view and their advantages/disadvantages are discussed. 相似文献
3.
The effects of NH 4+ or NO 3− on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 μM the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g −1 d −1), whereas the growth rate of Glyceria was 16% higher in NH 4+-N cultures than in NO 3−-N cultures (mean = 66.7 and 57.4 mg g −1 d −1 of NH 4+ and NO 3− treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH 4+ cultures than in NO 3− cultures, 123.5 and 129.7%, respectively.Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH 4+ treated plants by 16%. The tissue NH 4+ concentration (mean = 1.6 μmol g fresh wt −1) was not affected by N treatment, whereas NO 3− contents were higher in NO 3− (mean = 1.5 μmol g fresh wt −1) than in NH 4+ (mean = 0.4 μmol g fresh wt −1) treated plants. In Phragmites, NH 4+ (mean = 1.6 μmol g fresh wt −1) and NO 3− (mean = 0.2 μmol g fresh wt −1) contents were not affected by the N regime. Species did not differ in NH 4+ (mean = 56.5 μmol g −1 root dry wt h −1) and NO 3− (mean = 34.5 μmol g −1 root dry wt h −1) maximum uptake rates ( Vmax), and Vmax for NH 4+ uptake was not affected by N treatment. The uptake rate of NO 3− was low in NH 4+ treated plants, and an induction phase for NO 3− was observed in NH 4+ treated Phragmites but not in Glyceria. Phragmites had low Km (mean = 4.5 μM) and high affinity (10.3 l g −1 root dry wt h −1) for both ions compared to Glyceria ( Km = 6.3 μM, affinity = 8.0 l g −1 root dry wt h −1). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH 4+-N source may participates in the observed success of Glyceria at NH 4+ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites. 相似文献
4.
While increased nutrient concentrations and eutrophication are recognized to be among the causative factors contributing to algal blooms, including harmful algal blooms (HABs), relationships between nutrient fluxes and specific blooms are often not well defined or understood. In an attempt to better decipher these relationships, we employed in situ nutrient monitors to collect time-series data to document variability ranging from hourly to monthly, including rain events and the resulting response of phytoplankton biomass. Multiple deployments are reported here, all conducted in tributaries of Chesapeake Bay. The suite of nutrients that were monitored varied with deployment; examples given here include nitrate + nitrite (NO 3− + NO 2−), ammonium (NH 4+), phosphate (PO 43−), and urea. Common features in the data included highly varying concentrations on time -scales of a few hours related to tidal oscillations, and longer-term responses on the scale of days related to rainfall events. Increases following rainfall events for all nutrients generally tended to be many fold, up to an order of magnitude, higher than pre-rainfall concentrations. However, the time scale of response to rainfall for individual nutrients varied. Ephemeral increases in PO 43− and urea typically were contemporaneous with rain events, and were also followed by longer-term sustained increases relative to pre-rainfall levels. Increases in NO 3− + NO 2− and NH 4+ lagged rainfall events by a period of several days and generally lasted for several days. These dynamics generally would be missed by traditional manual sampling. Algal responses tended to follow the increases in nitrogen, underscoring nitrogen limitation in these systems even when ambient concentrations were not depleted. 相似文献
5.
The nitrogen (N) uptake kinetic parameters for Microcystis field assemblages collected from the San Francisco Bay Delta (Delta) in 2012 and non-toxic and toxic laboratory culture strains of M. aeruginosa were assessed. The 15N tracer technique was used to investigate uptake of ammonium (NH 4+), nitrate (NO 3−), urea and glutamic acid over short-term incubations (0.5–1 h), and to study inhibition of NO 3−, NH 4+ and urea uptake by NH 4+, NO 3− and NH 4+, respectively. This study demonstrates that Delta Microcystis can utilize different forms of inorganic and organic N, with the greatest capacity for NH 4+ uptake and the least for glutamic acid uptake, although N uptake did not always follow the classic Michaelis–Menten hyperbolic relationship at substrate concentrations up to 67 μmol N L −1. Current ambient N concentrations in the Delta may be at sub-saturating levels for N uptake, indicating that if N loading (especially NH 4+) were to increase, Delta Microcystis assemblages have the potential for increased N uptake rates. Delta Microcystis had the highest specific affinity, α, for NH 4+ and the lowest for NO 3−. In culture, N uptake by non-toxic and toxic M. aeruginosa strains was much higher than from the field, but followed similar N utilization trends to those in the field. Neither strain showed severe inhibition of NO 3− uptake by NH 4+ or inhibition of NH 4+ uptake on NO 3−, but both strains showed some inhibition of urea uptake by NH 4+. 相似文献
7.
The nitrogen uptake and growth capabilities of the potentially harmful, raphidophycean flagellate Heterosigma akashiwo (Hada) Sournia were examined in unialgal batch cultures (strain CCMP 1912). Growth rates as a function of three nitrogen substrates (ammonium, nitrate and urea) were determined at saturating and sub-saturating photosynthetic photon flux densities (PPFDs). At saturating PPFD (110 μE m −2 s −1), the growth rate of H. akashiwo was slightly greater for cells grown on NH 4+ (0.89 d −1) compared to cells grown on NO 3− or urea, which had identical growth rates (0.82 d −1). At sub-saturating PPFD (40 μE m −2 s −1), both urea- and NH 4+-grown cells grew faster than NO 3−-grown cells (0.61, 0.57 and 0.46 d −1, respectively). The N uptake kinetic parameters were investigated using exponentially growing batch cultures of H. akashiwo and the 15N-tracer technique. Maximum specific uptake rates ( Vmax) for unialgal cultures grown at 15 °C and saturating PPFD (110 μE m −2 s −1) were 28.0, 18.0 and 2.89 × 10 −3 h −1 for NH 4+, NO 3− and urea, respectively. The traditional measure of nutrient affinity—the half saturation constants ( Ks) were similar for NH 4+ and NO 3− (1.44 and 1.47 μg-at N L −1), but substantially lower for urea (0.42 μg-at N L −1). Whereas the α parameter ( α = Vmax/ Ks), which is considered a more robust indicator for substrate affinity when substrate concentrations are low (< Ks), were 19.4, 12.2 and 6.88 × 10 −3 h −1/(μg-at N L −1) for NH 4+, NO 3− and urea, respectively. These laboratory results demonstrate that at both saturating and sub-saturating N concentrations, N uptake preference follows the order: NH 4+ > NO 3− > urea, and suggests that natural blooms of H. akashiwo may be initiated or maintained by any of the three nitrogen substrates examined. 相似文献
8.
Temporal and spatial variability in the kinetic parameters of uptake of nitrate (NO 3−), ammonium (NH 4+), urea, and glycine was measured during dinoflagellate blooms in Changjiang River estuary and East China Sea coast, 2005. Karenia mikimotoi was the dominant species in the early stage of the blooms and was succeeded by Prorocentrum donghaiense. The uptake of nitrogen (N) was determined using 15N tracer techniques. The results of comparison kinetic parameters with ambient nutrients confirmed that different N forms were preferentially taken up during different stages of the bloom. NO 3− ( Vmax 0.044 h −1; Ks 60.8 μM-N) was an important N source before it was depleted. NH 4+ ( Vmax 0.049 h −1; Ks 2.15 μM-N) was generally the preferred N. Between the 2 organic N sources, urea was more preferred when K. mikimotoi dominated the bloom ( Vmax 0.020 h −1; Ks 1.35 μM-N) and glycine, considered as a dominant amino acid, was more preferred when P. donghaiense dominated the bloom ( Vmax 0.025 h −1; Ks 1.76 μM-N). The change of N uptake preference by the bloom-forming algae was also related to the variation in ambient N concentrations. 相似文献
9.
The effect of NH 4+/NO 3− availability on nitrate reductase (NR) activity in Phragmites australis and Glyceria maxima was studied in sand and water cultures with the goal to characterise the relationship between NR activity and NO 3− availability in the rhizosphere and to describe the extent to which NH 4+ suppresses the utilization of NO 3− in wetland plants.The NR activity data showed that both wetland helophytes are able to utilize NO 3−. This finding was further supported by sufficient growth observed under the strict NO 3− nutrition. The distribution of NR activity within plant tissues differed between species. Phragmites was proved to be preferential leaf NO 3− reducer with high NR activity in leaves (NR max > 6.5 μmol NO 2− g dry wt −1 h −1) under all N treatments, and therefore Phragmites seems to be good indicator of NO 3− availability in flooded sediment. In the case of Glyceria the contribution of roots to plant NO 3− reduction was higher, especially in sand culture. Glyceria also tended to accumulate NO 3− in non-reduced form, showing generally lower leaf NR activity levels. Thus, the NR activity does not necessarily correspond with plant ability to take up NO 3− and grow under NO 3−-N source. Moreover, the species differed significantly in the content of compounds interfering with NR activity estimation. Glyceria, but not Phragmites, contained cyanogenic glycosides releasing cyanide, the potent NR inhibitor. It clearly shows that the use of NR activity as a marker of NO 3− utilization in individual plant species is impossible without the precise method optimisation. 相似文献
10.
Environmental factors that shape dynamics of benthic toxic blooms are largely unknown. In particular, for the toxic dinoflagellate Ostreopsis cf. ovata, the importance of the availability of nutrients and the contribution of the inorganic and organic pools to growth need to be quantified in marine coastal environments. The present study aimed at characterizing N-uptake of dissolved inorganic and organic sources by O. cf . ovata cells, using the 15N-labelling technique. Experiments were conducted taking into account potential interactions between nutrient uptake systems as well as variations with the diel cycle. Uptake abilities of O. cf. ovata were parameterized for ammonium (NH 4+), nitrate (NO 3−) and N-urea, from the estimation of kinetic and inhibition parameters. In the range of 0 to 10 μmol N L −1, kinetic curves showed a clear preference pattern following the ranking NH 4+ > NO 3− > N-urea, where the preferential uptake of NH 4+ relative to NO 3− was accentuated by an inhibitory effect of NH 4+ concentration on NO 3− uptake capabilities. Conversely, under high nutrient concentrations, the preference for NH 4+ relative to NO 3− was largely reduced, probably because of the existence of a low-affinity high capacity inducible NO 3− uptake system. Ability to take up nutrients in darkness could not be defined as a competitive advantage for O. cf. ovata. Species competitiveness can also be defined from nutrient uptake kinetic parameters. A strong affinity for NH 4+ was observed for O. cf. ovata cells that may partly explain the success of this toxic species during the summer season in the Bay of Villefranche-sur-mer (France). 相似文献
11.
The present work deals with optimization of adventitious shoot culture of Bacopa monnieri for the production of biomass and bacoside A and has investigated the effects of macro elements (NH 4NO 3, KNO 3, CaCl 2, MgSO 4 and KH 2PO 4) and nitrogen source [NH 4
+/NO 3
−] of Murashige and Skoog (Physiol Plant 15:473–497, 1962) medium (MS) on accumulation of biomass and bacoside A content. Optimum number of adventitious shoots (99.33 shoots explant −1), fresh weight (1.841 g) and dry weight (0.150 g) were obtained in the medium with 2.0× strength of NH 4NO 3. The highest production of bacoside A content was also recorded in the medium of 2.0× NH 4NO 3, which produced 17.935 mg g −1 DW. The number of adventitious shoot biomass and bacoside A content were optimum when the NO 3
− concentration was higher than that of NH 4
+. Maximum number of shoots (70.00 shoots explant −1), biomass (fresh weight 1.137 g and dry weight 0.080 g) and also bacoside A content (27.106 mg g −1 DW) were obtained at NH 4
+/NO 3
− ratio of 14.38/37.60 mM. Overall, MS medium supplemented with 2.0× NH 4NO 3 is recommended for most efficient bacoside A production. 相似文献
12.
Nitrogen (N) limits plant productivity and its uptake and assimilation may be regulated by N source, N availability, and nitrate
reductase activity (NRA). Knowledge of how these factors interact to affect N uptake and assimilation processes in woody angiosperms
is limited. We fertilized 1-year-old, half-sib black walnut ( Juglans nigra L.) seedlings with ammonium (NH 4
+) [as (NH 4) 2SO 4], nitrate (NO 3
−) (as NaNO 3), or a mixed N source (NH 4NO 3) at 0, 800, or 1,600 mg N plant −1 season −1. Two months following final fertilization, growth, in vivo NRA, plant N status, and xylem exudate N composition were assessed.
Specific leaf NRA was higher in NO 3
−-fed and NH 4NO 3-fed plants compared to observed responses in NH 4
+-fed seedlings. Regardless of N source, N addition increased the proportion of amino acids (AA) in xylem exudate, inferring
greater NRA in roots, which suggests higher energy cost to plants. Root total NRA was 37% higher in NO 3
−-fed than in NH 4
+-fed plants. Exogenous NO 3
− was assimilated in roots or stored, so no difference was observed in NO 3
− levels transported in xylem. Black walnut seedling growth and physiology were generally favored by the mixed N source over
NO 3
− or NH 4
+ alone, suggesting NH 4NO 3 is required to maximize productivity in black walnut. Our findings indicate that black walnut seedling responses to N source
and level contrast markedly with results noted for woody gymnosperms or herbaceous angiosperms. 相似文献
13.
In a study of the control of metabolite formation, prodigiosin production by Serratia marcescens was used as a model. Specific production rates of prodigiosin formation were determined using batch culture technique. Sucrose as carbon source and NH 4NO 3 as nitrogen source resulted in a specific production rate of 0.476 mg prodigiosin (g cell dry weight) −1 h −1. Prodigiosin formation and productivity was inversely correlated to growth rate when the bacterium was grown under carbon limitation on a defined medium in a chemostat culture. The maximum specific growth rate ( μmax) was 0.54 h −1 and prodigiosin was formed in amounts over 1 mg l −1 up to a growth rate (μ) of 0.3 h −1 at steady state conditions. At a dilution rate of 0.1 h −1 growth at steady state with carbon and phosphate limitation supported prodigiosin formation giving a similar specific yield [1.17 mg prodigiosin (g cell dry weight) −1 and 0.94 mg g −1, respectively], however, cells grown with nitrogen limitation [(NH 4) 2SO 4] did not form prodigiosin. Productivity in batch culture was 1.33 mg l −1 h −1 as compared to 0.57 mg l −1 h −1 in the chemostat. 相似文献
14.
The co-culture system of denitrifying anaerobic methane oxidation (DAMO) and anaerobic ammonium oxidation (Anammox) has a potential application in wastewater treatment plant. This study explored the effects of permutation and combination of nitrate, nitrite, and ammonium on the culture enrichment from freshwater sediments. The co-existence of NO3
−, NO2
−, and NH4
+ shortened the enrichment time from 75 to 30 days and achieved a total nitrogen removal rate of 106.5 mg/L/day on day 132. Even though ammonium addition led to Anammox bacteria increase and a higher nitrogen removal rate, DAMO bacteria still dominated in different reactors with the highest proportion of 64.7% and the maximum abundance was 3.07 ± 0.25 × 108 copies/L (increased by five orders of magnitude) in the nitrite reactor. DAMO bacteria showed greater diversity in the nitrate reactor, and one was similar to M. oxyfera; DAMO bacteria in the nitrite reactor were relatively unified and similar to M. sinica. Interestingly, no DAMO archaea were found in the nitrate reactor. This study will improve the understanding of the impact of nitrogen source on DAMO and Anammox co-culture enrichment. 相似文献
15.
The effects of inorganic nitrogen (N) source (NH 4+, NO 3− or both) on growth, biomass allocation, photosynthesis, N uptake rate, nitrate reductase activity and mineral composition of Canna indica were studied in hydroponic culture. The relative growth rates (0.05-0.06 g g −1 d −1), biomass allocation and plant morphology of C. indica were indifferent to N nutrition. However, NH 4+ fed plants had higher concentrations of N in the tissues, lower concentrations of mineral cations and higher contents of chlorophylls in the leaves compared to NO 3− fed plants suggesting a slight advantage of NH 4+ nutrition. The NO 3− fed plants had lower light-saturated rates of photosynthesis (22.5 μmol m −2 s −1) than NH 4+ and NH 4+/NO 3− fed plants (24.4-25.6 μmol m −2 s −1) when expressed per unit leaf area, but similar rates when expressed on a chlorophyll basis. Maximum uptake rates ( Vmax) of NO 3− did not differ between treatments (24-35 μmol N g −1 root DW h −1), but Vmax for NH 4+ was highest in NH 4+ fed plants (81 μmol N g −1 root DW h −1), intermediate in the NH 4NO 3 fed plants (52 μmol N g −1 root DW h −1), and lowest in the NO 3− fed plants (28 μmol N g −1 root DW h −1). Nitrate reductase activity (NRA) was highest in leaves and was induced by NO 3− in the culture solutions corresponding to the pattern seen in fast growing terrestrial species. Plants fed with only NO 3− had high NRA (22 and 8 μmol NO 2− g −1 DW h −1 in leaves and roots, respectively) whereas NRA in NH 4+ fed plants was close to zero. Plants supplied with both forms of N had intermediate NRA suggesting that C. indica takes up and assimilate NO 3− in the presence of NH 4+. Our results show that C. indica is relatively indifferent to inorganic N source, which together with its high growth rate contributes to explain the occurrence of this species in flooded wetland soils as well as on terrestrial soils. Furthermore, it is concluded that C. indica is suitable for use in different types of constructed wetlands. 相似文献
16.
Excess inorganic nitrogen in water poses a severe threat to enviroment. Removal of inorganic nitrogen by heterotrophic nitrifying–aerobic denitrifying microorganism is supposed to be a promising and applicable technology only if the removal rate can be maintained sufficiently high in real wastewater under various conditions, such as high concentration of salt and wide range of different nitrogen concentrations. Here, a new heterotrophic nitrifying–aerobic denitrifying bacterium was isolated and named as Pseudomonas mendocina TJPU04, which removes NH4+-N, NO3−-N and NO2−-N with average rate of 4.69, 5.60, 4.99 mg/L/h, respectively. It also maintains high nitrogen removal efficiency over a wide range of nitrogen concentrations. When concentration of NH4+-N, NO3−-N and NO2−-N was up to 150, 150 and 50 mg/L, 98%, 93%, and 100% removal efficiency could be obtained, respectively, after 30-h incubation under sterile condition. When it was applied under non-sterile condition, the ammonia removal efficiency was slightly lower than that under sterile condition. However, the nitrate and nitrite removal efficiencies under non-sterile condition were significantly higher than those under sterile condition. Strain TJPU04 also showed efficient nitrogen removal performance in the presence of high concentration of salt and nitrogen. In addition, the removal efficiencies of NH4+-N, NO3−-N and TN in real wastewater were 91%, 52%, and 75%, respectively. These results suggest that strain TJPU04 is a promising candidate for efficient removal of inorganic nitrogen in wastewater treatment. 相似文献
17.
This study represents the most comprehensive assessment of kinetic parameters for Karenia brevis to date as it encompasses natural populations sampled during three different bloom years in addition to cultured strains under controlled conditions. Nitrogen (N) uptake kinetics for ammonium (NH 4+), nitrate (NO 3−), urea, an amino acid mixture, individual amino acids (glutamate and alanine), and humic substrates were examined for the toxic red tide dinoflagellate, K. brevis, during short term incubations (0.5–1 h) using 15N tracer techniques. Experiments were conducted using natural populations collected during extensive blooms along the West Florida Shelf in October 2001, 2002, and 2007, and in cultured strains (CCFWC 251 and CCFWC 267) obtained from the Florida Fish and Wildlife Institute culture collection. Kinetic parameters for the maximum uptake velocity ( Vmax), half-saturation concentration ( Ks), and the affinity constant ( α) were determined. The affinity constant is considered a more accurate indicator of substrate affinity at low concentrations. K. brevis took up all organic substrates tested, including N derived from humic substances. Uptake rates of the amino acid mixture and some NO 3− incubations did not saturate even at the highest substrate additions (50–200 μmol N L −1). Based upon the calculated α values, the greatest substrate preference was for NH 4+ followed by NO 3− ≥ urea, humic compounds and amino acids. The ability of K. brevis to utilize a variety of inorganic and organic substrates likely helps it flourish under a wide range of nutrient conditions from bloom initiation in oligotrophic waters offshore to bloom maintenance near shore where ambient nutrient concentrations may be orders of magnitude greater. 相似文献
18.
CO 2 electrochemical reduction (CO 2RR) can mitigate environmental issues while providing valuable products, yet challenging in activity, selectivity, and stability. Here, a CuS-Bi 2S 3 heterojunction precursor is reported that can in situ reconstruct to Cu-doped Bismuth (CDB) electrocatalyst during CO 2RR. The CDB exhibits an industrial-compatible current density of −1.1 A cm −2 and a record-high formate formation rate of 21.0 mmol h −1 cm −2 at −0.86 V versus the reversible hydrogen electrode toward CO 2RR to formate, dramatically outperforming currently reported catalysts. Importantly, the ultrawide potential region of 1050 mV with high formate Faradaic efficiency of over 90% and superior long-term stability for more than 100 h at −400 mA cm −2 can also be realized. Experimental and theoretical studies reveal that the remarkable CO 2RR performance of CDB results from the doping effect of Cu which optimizes adsorption of the *OCHO and boosts the structural stability of metallic bismuth catalyst. This study provides valuable inspiration for the design of element-doping electrocatalysts to enhance catalytic activity and durability. 相似文献
19.
In this study, we investigated the effects of different stocking densities water quality and blood parameters during the transportation of the Siberian sturgeon ( Acipenser baerii). Experiments were carried out in high-density polyethylene tank with three different stocking densities (50, 100 and 150 kg/m 3) for 20 h. Ammonium nitrogen (NH 4-N) and nitrite nitrogen (NO 2-N) were measured in the water samples. The erythrocyte, leucocyte, haematocrit (HCT), haemoglobin (Hb), cortisol, and sodium ion (Na +) were measured in blood samples. Ammonium nitrogen and nitrite nitrogen concentrations in the water have increased in parallel with the stocking density depending on the time. In the highest stocking density, the maximum levels of NH 4-N and NO 2-N at the 16 th h reached 2.64 mg/L and 4.74 mg/L, respectively. Erythrocyte, leucocyte, HCT, and Hb values did not differ significantly between the experimental groups ( p > .05). The results showed that fish could be transported safely for 20 h in 15℃ water temperature at 50 kg/m 3 stocking density; however, stocking density of 100 kg/m 3 and over could threaten fish welfare and health as from 16 th h. 相似文献
20.
The toxic HAB dinoflagellate Karenia brevis (Davis) G. Hansen & Ø. Moestrup (formerly Gymnodinium breve) exhibits a migratory pattern atypical of dinoflagellates: cells concentrate in a narrow (∼0–5 cm) band at the water surface during daylight hours due to phototactic and negative geotactic responses, then disperse downward at night via non-tactic, random swimming. The hypothesis that this daylight surface aggregation behavior significantly influences bacterial and algal productivity and nutrient cycling within blooms was tested during a large, high biomass (chlorophyll a >19 μg L −1) K. brevis bloom in October of 2001 by examining the effects of this surface layer aggregation on inorganic and organic nutrient concentrations, cellular nitrogen uptake, primary and bacterial productivity and the stable isotopic signature ( δ15N, δ13C) of particulate material. During daylight hours, concentrations of K. brevis and chlorophyll a in the 0–5 cm surface layer were enhanced by 131% (±241%) and 32.1% (±86.1%) respectively compared with an integrated water sample collection over a 0–1 m depth. Inorganic (NH 4, NO 3+2, PO 4, SiO 4) and organic (DOP, DON) nutrient concentrations were also elevated within the surface layer as was both bacterial and primary productivity. Uptake of nitrogen (NH 4+, NO 3−, urea, dissolved primary amines, glutamine and alanine) compounds by K. brevis was greatest in the surface layer for all compounds tested, with the greatest enhancement evident in urea uptake rates, from 0.08 × 10 −5 ng N K. brevis cell −1 h −1 to 3.1 × 10 −5 ng N K. brevis cell −1 h −1. These data suggests that this surface aggregation layer is not only an area of concentrated cells within K. brevis blooms, but also an area of increased biological activity and nutrient cycling, especially of nitrogen. Additionally, the classic dinoflagellate migration paradigm of a downward migration for access to elevated NO 3− concentrations during the dark period may not apply to certain dinoflagellates such as K. brevis in oligotrophic nearshore areas with no significant nitricline. For these dinoflagellates, concentration within a narrow surface layer in blooms during daylight hours may enhance nutrient supply through biological cycling and photochemical nutrient regeneration. 相似文献
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