Urea as a nitrogen source for the phytoplankton in the Oslofjord

Ambient concentrations of urea in the inner Oslofjord, Norway, showed a pronounced yearly cycle in 1980, with values in the range 0.1 to 10.0 μg-at N l^-1; this cycle resemble that of ammonia although urea concentrations were usually lower. The uptake of urea by phytoplankton was investigated using ¹⁵N. Urea was usually a less important N source than NH ₄ ⁺ , and accounted for 0 to 53% (mean 19%) of summed NH ₄ ⁺ +NO ₃ ^- + urea uptake rates from April to October. Absolute as well as relative (specific) uptake rates of urea were higher in the summer (June–August) than at other times. Uptake of urea was inhibited by NH ₄ ⁺ concentrations higher than 1 to 2 μg-at N l^-1. The summed NH ₄ ⁺ +NO ₃ ^- + urea uptake rate was exponentially related to temperature.     

Effect of nitrogen source on short-term light and dark CO2 uptake by a marine diatom

Based on a series of short-term incubations involving the marine diatom Chaetoceros simplex (Bbsm), precultured in NH ₄ ⁺ -, NO ₃ ^- -and urea-limited continuous cultures at several dilution rates, we found that both the short-term specific rate of ¹⁴CO₂ uptake and the amount of CO₂ fixed after 8- and 16-min incubations were unaffected by enrichment with NH ₄ ⁺ , urea, or NO ₃ ^- when NH ₄ ⁺ or urea were the preconditioning forms of N, but were slightly suppressed when the cells were first grown on NO ₃ ^- . Similar enrichments in the dark, however, led to significant CO₂ uptake under all conditions of NH ₄ ⁺ enrichment and to similarly enhanced CO₂ uptake, but only at high growth rates, when urea was the source of enrichment nitrogen. Our light results are contrary to some contemporary findings, but there does seem to be agreement that photosynthetic rates of rapidly growing phytoplankton will not be affected by exposure to pulses of nitrogen. Enhanced dark uptake, in contrast, appears to be characteristic of phytoplankton under all degrees of N limitation, and, as such, may be useful as an “all or nothing” index of the nitrogen status of natural waters. There is some indication that the index may be useful in determining both the form of and the degree of N limitation as well.     

Nitrate uptake in marine phytoplankton: Energy sources and the interaction with carbon fixation

Field studies of whole natural phytoplankton communities from Knight Inlet, B. C., Canada and laboratory cultures of the diatom Skeletonema costatum indicate inorganic carbon fixation may be temporarily suppressed following 10 to 15% enrichment with NO ₃ ^- or NH ₄ ⁺ . (This effect is suggested to be due to competition between inorganic carbon and nitrogen for adenosine triphosphate (ATP), and is reduced when chlorophyll a is increased intracellularly after 6 to 8 h.) Results imply that the source of ATP for nitrate uptake is primarily from Photosystem I (cyclic photophosphorylation) in the presence of light. It would appear that a transient nutrient-adaptive response occurs upon addition of extracellular nitrogen.     

Enhanced biohydrogen generation from organic wastewater containing NH 4 + by phototrophic bacteria Rhodobacter sphaeroides AR-3

NH ₄ ⁺ is typically an inhibitor to hydrogen production from organic wastewater by photo-bacteria. In this experiment, biohydrogen generation with wild-type anoxygenic phototrophic bacterium Rhodobacter sphaeroideswas found to be sensitive to NH ₄ ⁺ due to the significant inhibition of NH ₄ ⁺ to its nitrogenase. In order to avoid the inhibition of NH ₄ ⁺ to biohydrogen generation by R. sphaeroides, a glutamine auxotrophic mutant R. sphaeroides AR-3 was obtained by mutagenizing with ethyl methane sulfonate. The AR-3 mutant could generate biohydrogen efficiently in the hydrogen production medium with a higher NH ₄ ⁺ concentration, because the inhibition of NH ₄ ⁺ to nitrogenase of AR-3 was released. Under suitable conditions, AR-3 effectively produced biohydrogen from tofu wastewater, which normally contains 50–60 mg/L NH ₄ ⁺ , with an average generation rate of 14.2 mL/L·h. This generation rate was increased by more than 100% compared with that from wild-type R. sphaeroides.     

Ammonium regeneration and carbon utilization by marine bacteria grown on mixed substrates

We examined the impact of exposing natural populations of marine bacteria (from seawater collected near Woods Hole, Massachusetts, USA) to multiple nitrogen and carbon sources in a series of batch growth experiments conducted from 1989 through 1990. The substrate C:N ratio (C:N_s) was varied from 1.5:1 to 10:1 either with equal amounts of NH ₄ ⁺ and different amino acids or an amino acid mixture, all supplemented with glucose to maintain the C:N_s ratio equal to that of the respective amino acid, or with combinations of glucose and NH ₄ ⁺ alone. A common feature of the experiments involving amino acids was the concurrent uptake of NH ₄ ⁺ and amino acids that persisted as long as a readily assimilable carbon source (glucose in our case) was taken up. There was no net regeneration of NH ₄ ⁺ , even though catabolism of amino acids occurred. Regeneration of NH ₄ ⁺ was evident only after glucose was completely utilized, which usually occurred at the end of exponential growth. The contribution of¹⁵NH ₄ ⁺ to total nitrogen uptake by the end of exponential growth varied from ~60 to 80% when individual amino acids were present and down to ~24% when the amino acid mixture was added. These estimates are conservative because we did not account for possible isotope dilution effects resulting from amino acid catabolism. When NH ₄ ⁺ and glucose were the sole nitrogen and carbon sources, there was a stoichiometric balance between glucose and NH ₄ ⁺ uptake over a wide range of C:N_s ratios, leading to a constant bacterial biomass C:N ratio (C:N_B) of ~4.5:1. As a result NH ₄ ⁺ usage varied from 50% when the C:N_s ratio was 3.6:1, to 100% when the C:N_s ratio was 10:1. Gross growth efficiency varied from ~60% when NH ₄ ⁺ plus glucose were added alone or with the amino acid mixture, to 47% when the individual amino acids were used in place of the mixture. It is thus evident that actively growing bacteria will act as sinks for nitrogen when a carbon source that can be assimilated easily is available to balance NH ₄ ⁺ uptake, even when amino acids are available and are being co-metabolized.     

Estimation of coral growth-rates from laboratory 45Ca-incorporation rates

Laboratory ⁴⁵Ca-incorporation rates in hermatypic coral skeletons have previously been used successfully as an index of physiological function. This laboratory method would become more meanigful if it also provided an absolute measure of coral growth rates. In two coral species, Porites compressa and Pocillopora damicornis, ⁴⁵Ca incorporation rates were obtained from short (0.5 h) laboratory incubations using apical (determined as fast growing) portions of freshly collected coral branches. ⁴⁵Ca exchange across the coenosarc was not significant and not corrected for, whereas diurnal fluctuation in ⁴⁵Ca in Pocillopora damicornis was significant and a necessary correction. A calculated surface area is used to express calcification rate. Typical growth rates calculated from the ⁴⁵Ca-incorporation rates were 20 and 6 mm/year for Porites compressa and Pocillopora damicornis, respectively. These rates are considerably higher than those previously obtained in the laboratory, and compare favorably with field growth rates — 24 and 14 mm/year, respectively.     

Stabilitätsverhalten von ausgewählten anorganischen Spurenstoffen in Niederschlagsproben

The stability of H⁺, NH ₄ ⁺ , and PO ₄ ^3? ions in rainwater samples was in vestigated under different conditions cf storage and transport. Microbiological and physicochemical processes account for changes. Suppression of microbiological activities in deposition networks using conventional analyses may be achieved by adding AgCl-powder and by cooling to +4 °C.     

Seasonal microbial community shift in a saline sewage treatment plant

Activated sludge was monthly sampled from a saline sewage treatment plant of Hong Kong (China) during June 2007 to May 2008 to analyze the microbial community shift along with environmental variations using denaturing gradient gel electrophoresis of polymerase chain reaction amplified 16S rDNA fragments. Environmental changes resulted into a seasonal microbial community shift characterized by alterations in species number and abundance in the sewage treatment plant. Correspondence analysis and cluster analysis on community structure profile showed that the 12 monthly samples fell into four groups, which is in accordance with season changing in Hong Kong. Canonical correspondence analysis revealed that PO ₄ ^3t- -P and NH ₄ ⁺ -N posed more significant effects on community structure than total phosphorus and total nitrogen, respectively. Compared with sludge retention time, influent total phosphorus had an inverse effect on the community structure shift, and chemical oxygen demand and NH ₄ ⁺ -N showed a similar effects. Results of this study may contribute to the development of new knowledge involving the microbial community shift in sewage treatment plants.     

Particle size distributions, PM2.5 concentrations and water-soluble inorganic ions in different public indoor environments: a case study in Jinan, China

In this study, we collected particles with aerodynamic diameter ?2.5 μm (PM_2.5) from three different public indoor places (a supermarket, a commercial office, and a university dining hall) in Jinan, a medium-sized city located in northern China. Water-soluble inorganic ions of PM_2.5 and particle size distributions were also measured. Both indoor and outdoor PM_2.5 levels (102.3–143.8 μg·m^?3 and 160.2–301.3 μg·m^?3, respectively) were substantially higher than the value recommended by the World Health Organization (25 μg·m^?3), and outdoor sources were found to be the major contributors to indoor pollutants. Diurnal particle number size distributions were different, while the maximum volume concentrations all appeared to be approximately 300 nm in the three indoor locations. Concentrations of indoor and outdoor PM_2.5 were shown to exhibit the same variation trends for the supermarket and dining hall. For the office, PM_2.5 concentrations during nighttime were observed to decrease sharply. Among others, SO ₄ ^2? , NH ₄ ⁺ and NO ₃ ^? were found to be the dominant water-soluble ions of both indoor and outdoor particles. Concentrations of NO ₃ ^? in the supermarket and office during the daytime were observed to decrease sharply, which might be attributed to the fact that the indoor temperature was much higher than the outdoor temperature. In addition, domestic activities such as cleaning, water usage, cooking, and smoking also played roles in degraded indoor air quality. However, the results obtained here might be negatively impacted by the small number of samples and short sampling durations.     

Interlinked seasonal variation in biogenic nutrient fluxes and pore-water nutrient concentrations in intertidal sediments

The seasonal variation in biogenic fluxes of NH₄ ⁺, PO₄ ^3? and SiO₂ calculated from the nutrient excretion rates of dominant bivalves (Ruditapes philippinarum and Arcuatula [=Musculista] senhousia), and pore-water nutrient (NH₄ ⁺, PO₄ ^3?, SiO₂ and NO₃ ^? + NO₂ ^?), sedimentary acid-volatile sulfide (AVS) and benthic chlorophyll-a (Chl-a) concentrations was assessed on an intertidal sandflat in the Seto Inland Sea (Japan) from summer 1994 to autumn 1995. In spite of the large variability between sampling dates and stations, significant correlations between biogenic nutrient fluxes and pore-water nutrient concentrations were found, suggesting a seasonal linkage between bivalve-mediated biological processes and chemical features of sediments. This linkage was stronger in surface (0–0.5 cm) than subsurface (0.5–2 cm) sediments, consistent with the autoecological characteristics of R. philippinarum and A. senhousia inhabiting the uppermost sediment layer. Significant temporal variation in pore-water NO₃ ^? + NO₂ ^?, sedimentary AVS and benthic Chl-a concentrations was also found, which was related to both occasional extreme events (e.g., dystrophy) and alternating periods of production and decomposition. This study may serve twofold in (1) contributing to unravel the ecological structure and functioning of natural tidal flats, and the scale of seasonal variability in biotic and sedimentary parameters and (2) providing useful information for assessing the effectiveness of the physico-chemical and biological structure of artificial tidal flats which are growing in number and extension worldwide.     

Metabolism of two dominant epibenthic echinoderms measured at bathyal depths in the Santa Catalina Basin

Metabolism of two abundant echinoderm species constituting 99.6% of the epibenthic megafauna in the Santa Catalina Basin, off southern California, USA was measured at 1 300 m during the 1979 “Bathyal Expedition”. Specimens of the ophiuroid Ophiophthalmus normani and the holothurian Scotoplanes globosa, collected by the submersible “Alvin”, were individually placed in respirometers, and measured in situ for O₂ consumption and ammonium excretion rates. For O. normani, weight-specific O₂ consumption rates decreased with increasing weight and were of comparable magnitude to rates of deep-sea and shallow-water ophiuroids; excretion rates were highly variable. Population O₂ consumption and excretion rates for O. normani (estimated from size-frequency distribution, abundance, and rate regression equations) were 1 129.28 μl O₂ m^-2 h^-1 and 27.30 nmol NH ₄ ⁺ m^-2 h^-1. Weight-specific O₂ consumption and ammonium excretion rates of S. globosa decreased with increasing weight and were of comparable magnitude to rases of shallow-water holothurians. Population O₂ constimption and excretion rates of S. globosa were 1.38 μl O₂ m^-2 h^-1 and 4.86 nmol NH ₄ ⁺ m^-2 h^-1. Combined population O₂ consumption rates for O. normani and S. globosa are of comparable magnitude to that of the sediment community and plankton in the benthic boundary layer (sediment and overlying 50 m water column) of the Santa Catalina Basin.     

Experimental ecology of the temperate scleractinian coral Astrangia danae I. Partition of respiration,photosynthesis and calcification between host and symbionts

Calcification, photosynthesis and respiration of the scleractinian coral Astrangia danae were calculated from the changes in total alkalinity, pH, calculated total CO₂, and oxygen concentration produced by colonies incubated in glass jars. A correction for changes in ammonia, nitrate and nitrite was taken into account and the method evaluated. The fluxes of oxygen and CO₂ were highly correlated (r=0.99). The statistical error of alkalinity determinations was less than 10% of the changes observed in the slowest calcifying samples. Metabolism of polyparium alone was estimated by difference after removal of tissue and reincubation of bare corallum. Zooxanthellae concentration in the polyps was obtained from cell counts made on homogenates of polyp tissue. The calculated photosynthetic rate of the zooxanthellae in vivo was 25 mol O₂ (10⁸ cell)^-1 h^-1 at a light intensity of 120 Ein m^-2 s^-1. In corals having 0.5x10⁹ zooxanthellae/dm² of colony area up to 8% of the total photosynthesis was attributed to the corallum microcosm. Polyp respiration, photosynthesis, and CaCO₃ uptake rates were all much higher than rates previously reported from A. danae, apparently because in these experiments the organisms were better fed. This increased photosynthesis in turn enhanced calcification still further. The symbiosis therefore appears to provide a growth advantage even to fed corals, under the conditions of these experiments.     

Studies on reef corals. III. Fine structural changes of calicoblast cells in Pocillopora damicornis during settling and calcification

The site of reef-coral calcification has been studied in the branching coral Pocillopora damicornis Lamarck. Electron microscopy and X-ray microprobe analysis were performed on the calicoblast epidermis of newly settled larval stages and of adult coral. During settling, the heterogeneous columnar cell composition of the planktonic larva epidermis is replaced by a simple epithelium consisting of a single cell type, the calicoblast cell. Metamorphosis appears tightly linked to settling, with cell changes occurring within hours after attachment, and is marked by the appearance of a new secretory cell. The calicoblast cell of the adult coral is extremely flattened, and interdigitates extensively with adjacent calicoblast cells. This cell possesses a featureless plasma membrane lacking microvilli or flagella. It characteristically contains large membrane-bound vesicles with homogeneously fine granular contents. Preliminary microprobe analysis indicated a higher calcium content in these vesicles than in surrounding tissue; however, not in concentrations suggesting calcium-carbonate precipitation. They may represent sites of organic matrix synthesis. The calicoblast epidermis is separated from the underlying coral skeleton by a narrow gap. This gap appeared devoid of substructure, either organic or inorganic. The coral soft tissues are attached to the skeleton by mesogleal attachment processes, the desmoidal processes. These consist of a complex fibrous network originating in the mesoglea, and inserting onto the skeleton via specialized attachment regions consisting of electron-opaque membranous plaques. Skeletogenesis in reef-corals probably occurs extra-cellularly, external to the calicoblast epidermis, by simple overgrowth of the skeleton.     

Kinetics of the oxidation of endocrine disruptor nonylphenol by ferrate(VI)

The kinetics of the oxidation of endocrine disruptor nonylphenol (NP) by potassium ferrate(VI) (K₂FeO₄) in water as a function of pH 8.0–10.9 at 25°C is presented. The observed second-order rate constants, k _obs, decrease with an increase in pH 269–32 M^?1 s^?1. The speciation of Fe(VI) (HFeO ₄ ^? and FeO ₄ ^2? ) and NP (NP–OH and NP–O^?) species was used to explain the pH dependence of the k _obs values. At a dose of 10 mg L^?1 (50 μM) K₂FeO₄, the half-life for the removal of NP by Fe(VI), under water treatment conditions, is less than 1 min.     

Effects of nitrogen and phosphorus enrichement on in vivo symbiotic zooxanthellae of Pocillopora damicornis

The reef coral Pocillopora damicornis (Linnaeus) was grown for 8 wk in four nutrient treatments: control, consisting of ambient, unfiltered Kaneohe Bay seawater [dissolved inorganic nitrogen (DIN, 1.0 M) and dissolved inorganic phosphate (DIP, 0.3 M)]; nitrogen enrichment (15 M DIN as ammonium); phosphorus enrichment (1.2 M DIP as inorganic phosphate); and 15 M DIN+1.2 M DIP. Analyses of zooxanthellae for C, N, P and chlorophyll a after the 8 wk experiment indicated that DIN enrichment increased the cellular chlorophyll a and excess nitrogen fraction of the algae, but did not affect C cell^-1. DIP enrichment decreased both C and P cell^-1, but the decrease was proportionally less for C cell^-1. the response of cellular P to both DIN and DIP enrichment appeared to be in the same direction and could not be explained as a primary effect of external nutrient enrichment. The observed response of cellular P might be a consequence of in situ CO₂ limitation. DIN enrichment could increase the CO₂ (aq) demand by increasing the net production per unit area. DIP enrichment could slow down calcification, thus decreasing the availability of CO₂ (aq) in the coral tissue.Hawaii Institute of Marine Biology Contribution No. 920     

Metabolic adaptation of the intertidal worm Sipunculus nudus to functional and environmental hypoxia

The scope of anaerobic metabolism of Sipunculus nudus L. was assessed from the maximal activities of some enzymes of the intermediary metabolism and from the concentration of some metabolites accumulated during enhanced muscular activity and during prolonged experimental hypoxia.

1. Maximal enzyme activities demonstrate that the scope of anaerobic glycolysis, as indicated by maximal activities of glycogen phosphorylase (0.84 U g^-1 fresh wt), far exceeds the aerobic capacity, which is assumed not to surpass the activity of succinate dehydrogenase (0.09 U g^-1 fresh wt). Three pyruvate reductase activities (alanopine-, strombine- and octopine dehydrogenase) can possibly terminate anaerobic glycolysis.
2. During muscular activity, energy is provided by the degradation of phospho-L-arginine and by anaerobic glycolysis. Octopine is the major endproduct during functional anaerobiosis while the formation of strombine is less pronounced.
3. During exposure to a nitrogen atmosphere, several anaerobic endproducts are found to accumulate. Anaerobic glycolysis is terminated by strombine synthesis. This opine accumulates in concentrations much higher than octopine. In addition the concentrations of succinate, propionate and acetate are found to increase in tissues, and/or in the coelomic fluid and the incubation water.
4. The relative contribution of energy by the different anaerobic metabolic pathways are estimated during functional and environmental hypoxia.

     

Photochemical reaction of peroxynitrite and carbon dioxide could account for up to 15 % of carbonate radicals generation in surface waters

The carbonate radical (CO ₃ ^?· ) is a photoinduced transient species occurring in surface waters. The carbonate radical can transform both natural compounds and xenobiotics. For instance, it can react with electron-rich substrates such as anilines, phenols and organic sulfur compounds. Here we used the APEX software to assess photochemical reactions, including the formation rates of transient species, based on water chemistry and depth, under summertime irradiation conditions. We found that the reaction between peroxynitrite and carbon dioxide is a potentially significant source of CO ₃ ^?· in sunlit surface waters, and could account for up to 10–15 % of the total CO ₃ ^?· formation. The peroxynitrite pathway to CO ₃ ^?· would be most significant at pH 7–8 and would be enhanced in waters with elevated nitrate and low alkalinity. Therefore, the proposed process could add to the known photochemical sources of CO ₃ ^?· in surface-water environments.     

Neoplasia,regeneration and growth in the reef-building coral Acropora palmata

Abnormal processes of calcification, such as regenerating lesions and neoplasia, situated near the tips(<25 cm) of colonies of Acropora palmata (Lamarck) suppressed normal linear growth. Branches having neoplasia at a larger distance from the tip do not grow significantly differently from controls. This indicates a functional minimal area in terms of energy supply. Neoplasia are pure aragonite and have the same coenosteal structure as regenerative skeletal material. Regeneration of tissue as well as tissue+skeleton lesions involves the simultaneous formation of tissue and regenerative skeleton, trapping foreign material under the regenerated surface. Recovery of a damaged surface slows down with time and this may, in other coral species, result in permanent lesions. A. palmata recovered from all lesions (n=32) within 80 d and appears to be a superior regenerator among Caribbean corals. This is consistent with other life-history characteristics of this highly specialized coral species.     

Calcium exchange and the measurement of calcification rates in the calcareous coralline red alga Amphiroa foliacea

⁴⁵Ca washout data of living thalli of Amphiroa foliacea Lamouroux in the light and dark show that there are three kinetically distinct Ca²⁺-exchanging compartments with approximate half-times (t 1/2) of 300, 20 and 3 min. The two slower compartments appear to be exchange from organic Ca²⁺-binding components of the cell wall, while the fast compartment probably represents exchange on the CaCO₃ crystal surface. Killed and decalcified thalli have a fourth compartment, with a t 1/2 of 20 to 35 min (other compartment half-times are 300, 40, 3 min), which has been identified as the greatly increased intercellular space produced during drying and decalcification. The ⁴⁵Ca and ¹⁴C uptake data show that a large proportion of the label initially taken up is into compartments other than the CaCO₃. As a result of this uptake, binding, and exchange of radioisotope, significant errors occur during the measurement of calcification rates, unless a kinetic analysis is carried out. Using such a technique, CaCO₃ calcification rates of A. folicea were measured with ⁴⁵Ca or ¹⁴C as tracers. Light stimulates calcification by up to 2.6 times, depending upon the age of the plant. Young segments have a markedly higher rate of calcification and photosythesis than do the older segments.     

Urea formation from carbon dioxide and ammonia at atmospheric pressure

Urea synthesis, currently the largest use of carbon dioxide in organic synthesis, is conventionally operated at high pressure and high temperature. Here, we report for the first time that urea forms at atmosphere and ambient temperatures by negative corona discharge in gas phase. The conversion of CO₂ and yields of a solid mixture of urea and ammonium carbamate, which was identified by the ¹³C NMR spectrum, rise with reducing temperatures and increasing molar ratios of NH₃/CO₂ and discharge frequencies. The conversion of carbon dioxide was found to be 82.16?% at 20?°C and 1?atm with a molar flow ratio of n(NH₃)/n(CO₂) of 2.5. High pressure and high temperature as energy inputs are not necessary.