Mmol NH Research Articles

Total And Immobilized Enzymatic Activity Of Organic Materials Before And After Composting

The evaluation of residual organic materials as a source of enzymatic activities immobilized in the humus matrix is a little explored research area, particularly in the case of organic materials derived from municipal wastes. Enzymes catalyze most soil reactions essential for soil functionality. The advantage of humus enzyme-complexes (immobilized enzymes) with regards to free enzymes is that the former are protected in the humic colloid, being more resistant to denaturing agents and other adverse soil conditions. This explains the interest in use of organic wastes (which are produced in an increasingly amount and consequently are economical) as a source of immobilized enzymes, which could be concentrated and used to improve the quality of degraded or contaminated soils. The goal of this study was (i) to assess the potential of sewage sludge (SS) and the organic fraction of municipal solid waste (MSW), as well as their respective composts (CSS and CMSW) as sources of enzymes, (ii) to determine the proportion of such enzymes which are immobilized in the humic matrix of these organic materials, and (iii) to determine the effect of the composting process on the total and the immobilized enzymatic activities of the organic materials. Dehydrogenase (DHA), urease, protease-BAA, alkaline phosphatase (ALP), β-glucosidase (GLA) and o-diphenol oxidase (DPO) activities were determined both in the organic materials and in their humic extracts (except DHA). Sewage sludge had the highest total values of urease, protease-BAA, ALP and DHA activity (12.7 μol NH4+-N g−1 h−1, 40.6 μmol NH4+-N g−1 h−1, 75.7 μmol PNP g−1 h−1 and 0.3 μmol INTF g−1 h−1, respectively), which decreased with composting, but MSW had the highest total value of DPO activity. For both organic materials, a low percentage of total enzymatic activities were linked to humus (0.6-22%), except in the case of DPO activity. The SS and MSW composting process had a positive effect on the urease, protease-BAA, DPO and ALP immobilization in the humic matrix, as reflected by the higher immobilized activity/total activity ratios in the compost than in the fresh materials.

Photochemical production of ammonium and transformation of dissolved organic matter in the Baltic Sea

The release of ammonium from the photochemical degradation of dissolved organic matter (DOM) has been proposed by earlier studies as a potentially important remineralisation pathway for refractory organic nitrogen. In this study the photochemical production of ammonium from Baltic Sea DOM was assessed in the laboratory. Filtered samples from the Bothnian Bay, the Gulf of Finland and the Arkona Sea were exposed to UVA light at environmentally relevant levels, and the developments in ammonium concentrations, light absorption, fluorescence and molecular size distribution were followed. The exposures resulted in a decrease in DOM absorption and loss of the larger sized fraction of DOM. Analysis of the fluorescence properties of DOM using parallel factor analysis (PARAFAC) identified 6 independent components. Five components decreased in intensity as a result of the UVA exposures. One component was produced as a result of the exposures and represents labile photoproducts derived from terrestrial DOM. The characteristics of DOM in samples from the Bothnian Bay and Gulf of Finland were similar and dominated by terrestrially derived material. The DOM from the Arkona Sea was more autochthonous in character. Photoammonification differed depending on the composition of DOM. Calculated photoammonification rates in surface waters varied between 121 and 382 μmol NH 4 + L − 1 d − 1 . Estimated areal daily production rates ranged between 37 and 237 μmol NH 4 + m − 2 d − 1 , which are comparable to atmospheric deposition rates and suggest that photochemical remineralisation of organic nitrogen may be a significant source of bioavailable nitrogen to surface waters during summer months with high irradiance and low inorganic nitrogen concentrations.

Stable isotopic detection of ammonium and nitrate assimilation by phytoplankton in the Waquoit Bay estuarine system

We measured concentration and δ15N of chlorophyll a (Chl a), NO3‐, and NH4+ along a salinity gradient in Childs River, Massachusetts, in winter, spring, and summer. We used the δ15N of Chl a as a proxy for the phytoplankton δ15N to minimize potential ambiguities from other material in seston. NO3‐ concentration ranged from 0 to 50 µmol L21 and NH4+ from 0 to 8 µmol L‐1; both forms decreased with increasing salinity. NO3‐ concentration was generally higher than NH4+. Chl a concentrations ranged between 1 and 15 mg m‐3 in winterspring and had a summer midestuarine peak of 95 mg m‐3. The δ15N of NO3‐ and NH4+ ranged from ‐10‰ to +7‰ and ‐3‰ to +13‰, respectively, and decreased approximately linearly with increasing salinity. The δ15N of NO3‐ reflected the predominance of groundwater as the source of NO3‐ to the estuary, whereas the δ15N of NH4+ indicated that regeneration was the main NH4+ source. Throughout the estuary, NO3‐ was isotopically lighter than NH4+. Phytoplankton δ15N increased from winter to summer and was relatively invariant with salinity, in contrast to the δ15N of dissolved inorganic nitrogen. A comparison of the δ15N of phytoplankton, NO3‐, and NH4+ indicated that phytoplankton in Childs River derived 53% to 97% of their N from NH4+. Phytoplankton acquired their stable nitrogen isotopic ratio upstream, then maintained that ratio during downstream transport. The fractionation factor for phytoplankton NH4+ uptake was +4.0‰ ± 0.6‰, which was in the lower range of other estimates, indicating that phytoplankton might have been N limited.

Respiration, calcification, and excretion of the invasive slipper limpet, Crepidula fornicata L.: Implications for carbon, carbonate, and nitrogen fluxes in affected areas

We measured in situ respiration, calcification, and excretion of the slipper limpet, Crepidula fornicata L., and considered both seasonal variations and individual size, to estimate the effects of this exotic species on annual budgets of carbon, carbonate, and nitrogen in the Bay of Brest (France). Respiration, calcification, and excretion rates changed significantly with size and season. Oxygen consumption varied from 6 to 63 µmol O2 g-1 ash-free dry weight (AF dry wt) h-1, which corresponded to a carbon dioxide release that ranged from 2 to 44 µmol CO2 g-1 AF dry wt h-1. Maximum respiration rates were observed in summer, and minimum rates were observed in winter. CaCO3 production ranged from 24 to 44 µmol CaCO3 g-1 AF dry wt h21 from winter to summer, respectively. Ammonium release varied from 0.7 to 3.1 µmol NH4+ g-1 AF dry wt h-1, with the highest excretion rate in spring. Total carbon release by C. fornicata in highly colonized zones in the Bay of Brest averaged 290 g C m-2 yr-1, carbonate production was ~515 g CaCO3 m-2 yr-1, and nitrogen production by ammonium excretion was ~25 g N m-2 yr-1. C. fornicata respiration and excretion account for 55% and 85% of the benthic community respiration and excretion, respectively. These results illustrate the importance of this invasive species to carbon and nitrogen cycles, including biogenic carbonate production, in coastal ecosystems.

A Strain of Pseudomonas sp. Isolated from Piggery Wastewater Treatment Systems with Heterotrophic Nitrification Capability in Taiwan

A high concentration of NH(4) (+) in piggery wastewater is major problem in Taiwan. Therefore, in our study, we isolated native heterotrophic nitrifiers for piggery wastewater treatment. Heterotrophic nitrifier AS-1 was isolated and characterized from the activated sludge of a piggery wastewater system. Sets of triplicate crimp-sealed serum bottles were used to demonstrate the heterotrophic nitrifying capability of strain AS-1 in an incubator at 30 degrees C. All serum bottles contained 80 mL medium, and the remainder of the bottle headspace was filled with pure oxygen. The experimental results showed that 2.5 +/- 0.2 mmol L(-1) NH(4) (+) was removed by 58 hours, and, eventually, 1.5 +/- 0.5 mmol L(-1) N(2) and 0.2 +/- 0.0 mmol L(-1) N(2)O were produced. The removal rate of NH(4) (+) by the strain AS-1 was 1.75 mmol NH(4) (+) g cell(-1) h(-1). This strain was then identified as Pseudomonas alcaligenes (97% identity) by sequencing its 16S rDNA and comparing it with other microorganisms. Thus, strain AS-1 displays high promise for future application for in situ NH(4) (+) removal from piggery wastewater.

Benthic decomposition of Ulva lactuca: A controlled laboratory experiment

The degradation of an Ulva lactuca mat (0.2 kg dw m −2) was studied in a controlled flow-through mesocosm for 31 d. Sediment chambers without U. lactuca served as controls. Fluxes of ∑CO 2, O 2, inorganic nitrogen, and urea were determined during the incubation period in addition to sulfate reduction rates, POC and PON content, enumeration of specific bacterial populations and evaluation of the physiological state of the added U. lactuca thalli. After U. lactuca addition to the chambers, there was an immediate increase in the efflux of ∑CO 2 from 11 to 27 mmol-C m −2 d −1 and a concomitant increase in O 2 uptake from 11 to 23 mmol m −2 d −1. These effluxes remained elevated throughout the incubation period. In contrast, the NH 4 + efflux increased from 0.1 to 1.8 mmol NH 4 + m −2 d −1 during the first 3 d of incubation, followed by 6 d with a constant efflux rate, after which time it decreased gradually to 0.3 mmol NH 4 + m −2 d −1 by the end of the experiment. In total, NH 4 +accounted for 83% of the total nitrogen efflux after addition of U. lactuca. During the 31 d incubation period there was a continuous colonization of the thalli by bacteria. Sulfate reducers associated with the thalli accounted for 3% of the carbon oxidation on day 31. The molar C:N ratio in mineralization products (the ratio between the efflux of ∑CO 2 and NH 4 + + NO 2 − + NO 3 −) increased from 15 mol mol −1 at day 11 after U. lactuca addition to >80 mol mol −1 by the end of the incubation. Since the C:N ratio in the mineralization products was much higher than the original thallus material (8.9 mol mol −1) it is probable that a preferential incorporation of NH 4 + into the increasing bacterial biomass occurred. The nitrogen for bacterial growth was most likely obtained from degradation of U. lactuca thalli as there was no stimulation of urea-N turnover in the sediment during incubation. The net increase in bacteria cell number in the 18-mm thick thallus layer was estimated to be 7.6 × 10 9 to 2.4 × 10 10 bacterial cells cm −3. In contrast, the bacterial cell number remained constant in the −Ulva incubations.

Impacts of mussel (Mytilus galloprovincialis) farming on oxygen consumption and nutrient recycling in a eutrophic coastal lagoon

Fluxes of oxygen, nitrogen and phosphorus were determined in two areas of the Sacca di Goro lagoon, at a site influenced by the farming of the mussel Mytilus galloprovincialis and a control site. Mussel farming induced intense biodeposition of organic matter to the underlying sediments, which stimulated sediment oxygen demand, and inorganic nitrogen and phosphorus regeneration rates compared to the nearby control station. Overall benthic fluxes (–11.4 ± 6.5 mmol O2 m−2 h−1; 1.59 ± 0.47 mmol NH4+ m−2 h−1 and 94 ± 42 μmol PO43− m−2 h−1) at the mussel farm are amongst the highest ever recorded for an aquaculture impacted area and question the belief that farming of filter-feeding bivalves has inherently lower impacts than finfish farming. In situ incubations of intact mussel ropes demonstrated that the mussel rope community was an enormous sink for oxygen and particulate organic matter, and an equally large source of dissolved inorganic nitrogen and phosphate to the water column. Overall, a one meter square area of␣mussel farm (mussel ropes and underlying sediment) was estimated to have an oxygen demand of 46.8 mmol m2 h−1 and to regenerate inorganic nitrogen and phosphorus at rates of 8.5 and 0.3 mmol m2 h−1, with the mussel ropes accounting for between 70 and more than 90% of the overall oxygen and nutrient fluxes. Even taking into account that within the farmed area of the Sacca di Goro lagoon, there are 15–20 m−2 of open water for each one covered with mussel ropes, the mussel ropes would account for a large and often dominant part of overall oxygen and nutrient fluxes. These results demonstrate that it is essential to take into account the activity of the cultivated organisms and their epiphytic community when assessing the impacts of shellfish farming. Overall, whilst grazing by the mussel rope community could act as a top-down control on the phytoplankton, most of the ingested organic matter is rapidly recycled to the water column as inorganic nutrients, which would be expected to stimulate phytoplankton growth. Consequently, the net effect of the mussel farming on phytoplankton dynamics, may be to increase phytoplankton turnover and overall production, rather than to limit phytoplankton biomass.

Seasonal variation in metabolism of cultured Pacific oyster, Crassostrea gigas, in Sanggou Bay, China

Rates of respiration and excretion of the Pacific oyster, Crassostrea gigas, were measured seasonally from June 2002 to July 2003 under ambient conditions of food, water temperature, pH, and salinity in Sanggou Bay, an important mariculture coast in north China. The aim of this study is to obtain fundamental data for further establishing an energy budget model and assessing the carrying capacity for cultivation of C. gigas in north China. Oysters were collected monthly or bimonthly from the integrated culture areas of bivalve and kelp in the bay. Oxygen consumption and ammonium and phosphorus excretion rates were measured, and ratios of O/N and N/P were calculated. One-way ANOVA was applied to determine differences among these parameters that act as a function of seasonal variation. All the physiological parameters yielded highly significant variations with season ( P < 0.01). The rate of respiration varied seasonally, with the highest oxygen consumption rate in July and the lowest rate in January, ranging from 0.07 to 2.13 mg O 2 h − 1 g − 1dry tissue weight (DW). Maximum and minimum ammonium excretion rates were recorded in August and January, respectively, ranging from 0.51 to 5.40 μmol NH 4–N h − 1g − 1 DW. Rates of phosphorus excretion varied from 0.11 (in January) to 0.64 (in July) μmol PO 4–P h − 1g − 1 DW. The O/N and N/P ratios changed from 9.2 (in January) to 59.8 (in July) and from 4.6 (in January) to 10.9 (in August), respectively. For each season, the allometric relationship between the physiological response (e.g., rate of oxygen consumption, ammonium and phosphorus excretion) and DW of the animal was estimated using the formula: Y = a × DW b .

Response of the microbial food web to manipulation of nutrients and grazers in the oligotrophic Gulf of Aqaba and northern Red Sea

The control mechanisms within the pelagic microbial food web of the oligotrophic Gulf of Aqaba and the northern Red Sea were investigated in the spring of 1999. Nutrient conditions and potential grazer impact were manipulated in a series of dilution experiments. Ambient nutrient concentrations and autotrophic biomass were very low (0.23–1.21 µmol NO3 l−1, 0.06–0.98 µmol NH4 l−1, 1.08–1.17 µmol Si l−1, 0.08–0.12 µmol P l−1, 0.15–0.36 µg chlorophyll a l−1). The planktonic community was characterized by low abundances [3.0–5.5×105 heterotrophic bacteria ml−1, 0.58–7.2×103 ultraphytoplankton 8 µm l−1, 0.93–5.4×102 microzooplankton l−1] and dominated by small forms (0.2–8 µm). Dinoflagellates and oligotrichous ciliates were the most common groups in initial samples among the phytoplankton >8 µm and microzooplankton, respectively. Results show that bottom-up and top-down control mechanisms operated simultaneously. Small organisms were vulnerable to grazing, with maximum grazing rates of 1.1 day−1 on heterotrophic bacteria and 1.3 day−1 on ultraphytoplankton. In contrast, algae >8 µm showed stronger signs of nutrient limitation, especially when the final assemblages were dominated by diatoms. Synechococcus sp. were not grazed and only showed moderate to no response to nutrient additions. The high spatial and temporal variation of our results indicates that the composition of the planktonic community determines the prevailing control mechanisms. It further implies that, at this transitional time of the year (onset of summer stratification), the populations fluctuate about an equilibrium between growth and grazing.

Enrichment of Anammox from Activated Sludge and Its Application in the CANON Process

A microbial culture capable of actively oxidizing ammonium to dinitrogen gas in the absence of oxygen, using nitrite as the electron acceptor, was enriched from local activated sludge (Western Australia) in <14 weeks. The maximum anaerobic ammonium oxidation (i.e., anammox) activity achieved by the anaerobic culture was 0.26 mmol NH (4) (+) (g biomass)(-1) h(-1) (0.58 kg total-N m(-3) day(-1)). Qualitative FISH analysis (fluorescence in situ hybridization) confirmed the phylogenetic position of the enriched microorganism as belonging to the order Planctomycetales, in which all currently identified anammox strains fall. Preliminary FISH analysis suggests the anammox strain belongs to the same phylogenetic group as the Candidatus 'Brocadia anammoxidans' strain discovered in the Netherlands. However, there are quite a few differences in the target sites for the more specific probes of these organisms and it is therefore likely to represent a new species of anammox bacteria. A small amount of aerobic ammonium-oxidizing biomass was inoculated into the anammox reactor (10% v/v) to initiate completely autotrophic nitrogen removal over nitrite (the CANON process) in chemostat culture. The culture was always under oxygen limitation and no organic carbon was added. The CANON reactor was operated as an intermittently aerated system with 20 min aerobiosis and 30 min anaerobiosis, during which aerobic and anaerobic ammonium oxidation were performed in sequential fashion, respectively. Anammox was not inhibited by repeated intermittent exposure to oxygen, allowing sustained, completely autotrophic ammonium removal (0.08 kg N m(-3) day(-1)) for an extended period of time.

Synthesis, characterization and comparison of catalytic properties of NiMo- and NiW/Ti-MCM-41 catalysts for HDS of thiophene and HVGO

Hydrotreating of heavy oil fractions is usually carried out in fixed bed reactors using alumina-supported Ni-Mo and Co-Mo catalysts. The catalytic properties of hybrid Al- and Ti-MCM-41 materials were compared for HDS of thiophene and heavy vacuum gas oil (HVGO) derived from Maya crude. Upon addition of 20 wt.% TiO 2, the hexagonal symmetry of the pore arrays was unchanged, but the surface area increased from about 1040 up to 1138 m 2/g. In parallel, NH 3-thermal programmed desorption (TPD) studies showed an increase of surface acidity with TiO 2 content, i.e., from 38 μmol NH 3/g for initial MCM-41 to about 62 μmol NH 3/g for 80% Ti-substituted Si-MCM-41. Also, Ni-Mo and Ni-W metal loadings increased the total surface acidity, from about 44 μmol NH 3/g for NiMo/MCM-41 to about 148 μmol NH 3/g for NiMo/MCM-41. Also, the hydrothermal stability of the Ti-MCM-41 materials increased from about 500 °C up to 600 °C under 100% water vapor. Finally, sulfided forms of Ti-MCM-41-supported Ni-Mo and Ni-W catalysts were tested for HDS of heavy vacuum gas oil and thiophene at 350 °C, the NiMo/Ti-MCM-41 and NiW/Ti-MCM-41 catalysts with 50% Ti showing the highest activity, which was comparable to reference catalysts.

Preparation of TiO2–ZrO2 mixed oxides with controlled acid–basic properties

Abstract Titania–zirconia mixed oxides with various ZrO 2 content in TiO 2 (10, 50 and 90 wt.%) were prepared by the sol–gel method. High specific surface areas (77–244 m 2 /g) were obtained. Acidity determined by NH 3 -TPD and FTIR-pyridine adsorption showed that in mixed oxides the number of acid sites is dramatically increased; it varies from 173 μmol NH 3 /g for TiO 2 to 1226–1456 μmol NH 3 /g for the mixed oxides. FTIR-pyridine adsorption showed the presence of Lewis sites in the catalysts. Basic sites were identified by FTIR-CO 2 adsorption, suggesting the formation of mixed oxides with acid–basic properties. XRD spectra identified anatase in the TiO 2 rich region, amorphous material in the mixed oxide 50–50 TiO 2 –ZrO 2 and tetragonal and monoclinic crystalline phases in the ZrO 2 rich region. Activity in the isopropanol decomposition showed a good correlation between the acid–basic properties and the selectivity to propene, acetone and isopropyl ether. The latter was found as a product which mainly depends of the acid sites density.

Physiological responses and scope for growth of &lt;i&gt;Ruditapes decussatus&lt;/i&gt; from Ria Formosa, southern Portugal, exposed to increased ambient ammonia

In this study we investigate the effects of exposure to increased ambient ammonia-N concentrations as a cause of decreased scope for growth and mortality of R.decussatus during the summer months in Ria Formosa, southern Portugal. The physiological measurements were performed at 20 oC and average total ammonia-N concentrations (TA-N) were 9, 48, 85, 134 and 260 µmol l -1 (corresponding to 0.2, 1.1, 2.0, 3.2 and 6.2 µmol l -1 NH 3 ). No mortality was observed. Our results show that during short term exposure to TA-N concentrations >48 µmol l -1 (1.1 µmol NH 3 ), R.decussautus survives at the expense of energy reserves. No energy is available for growth and reproduction. Though it is uncertain how intermittent exposures during tidal cycles will affect the long-term survival of R.decussatus in the Ria Formosa, high ammonia concentrations together with unfavourable physical and chemical summer gradients in the sediment can clearly contribute to the high mortality that has been registered in recent years (Ferreira et al. 1989). The sensitivity of the physiological energetics approach and the need to assess tolerance of infaunal bivalves addressing endpoints that can provide insight into the condition for growth and reproduction of the population is stressed.

Effect of ammonium chloride on the growth and metabolism of bovine ovarian granulosa cells and the development of ovine oocytes matured in the presence of bovine granulosa cells previously exposed to ammonium chloride

Three experiments determined first, the effect of increasing ammonium chloride (NH 4Cl) concentrations on the growth and metabolism of bovine granulosa cells isolated from small and medium-sized bovine ovarian follicles; secondly, whether the changes in granulosa cell growth and metabolism induced by NH 4Cl were reversible; and thirdly, whether granulosa cells, previously conditioned with NH 4Cl, were able to support maturation of oocytes in vitro. In Experiment 1, using a 2 ( follicle size class )×5 ( NH 4 Cl concentration ) factorial design, granulosa cells from small or medium-sized ovarian follicles were incubated for 96 h with 0, 0.2, 0.4, 0.8 or 1.6 μmol NH 4Cl/ml. Experiment 2 used a split plot factorial design where granulosa cells were incubated for 96 h in the presence or absence of 1 μmol/ml NH 4Cl and then incubated in the absence or presence of 1 μmol/ml NH 4Cl for a further 48 h. Finally in Experiment 3, ovine oocytes were matured on layers of bovine granulosa cells which had not been conditioned with NH 4Cl or conditioned with 0.5 or 1.0 μmol/ml NH 4Cl and development of embryos to the blastocyst stage followed and blastocyst quality assessed. In Experiment 1, incubation of granulosa cells in increasing concentrations of NH 4Cl reduced cell growth, increased cell protein concentrations and increased the amounts of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) oxidised and oestradiol and progesterone produced per 10 5 cells. Cells from medium-sized follicles were more sensitive to NH 4Cl concentration and oxidised more MTT and produced less progesterone at high NH 4Cl concentrations than cells from small-sized follicles. When, in Experiment 2, NH 4Cl was removed from cell culture after 96 h incubation, cells previously exposed to NH 4Cl grew at a slower rate during the subsequent 48 h, contained more cellular protein, oxidised more MTT and produced more oestradiol and progesterone than cells not previously exposed to NH 4Cl. Maturation of ovine oocytes in coculture with bovine granulosa cells not exposed to NH 4Cl (Experiment 3) increased egg cleavage rate and the proportion of cleaved eggs which developed to the blastocyst stage. Conditioning of granulosa cells with NH 4Cl supported egg cleavage and development to the blastocyst stage at rates similar to those observed in the absence of granulosa cells. In conclusion, these experiments showed that the in vitro growth and metabolism of granulosa cells were altered by concentrations of NH 4Cl similar to ammonium ion concentrations measured in follicular fluid and that these effects were not immediately reversible. Furthermore, the ability of granulosa cells conditioned with NH 4Cl to support in vitro maturation of oocytes was impaired.

Nature of ammonium ion adsorption by sepiolite: analysis of equilibrium data with several isotherms

Adsorption isotherms for an ammonium ion–sepiolite system have been established for initial ammonium ion solution concentrations in the range of 8.32–388.06 mmol NH 4 +/L (150–7000 ppm). The change of the “g sepiolite/mL solution” ratios from 1/10 to 1/70 caused an increase in the adsorption from 1.82 to 3.70 mmol NH 4 +/g for the average particle size of 2.8 mm. The equilibrium data were fitted to “general-purpose isotherms” and “first-order adsorption model”, and the adjustable parameters of the isotherms were estimated by nonlinear least-squares analysis. Langmuir and Freundlich models were found insufficient to explain the adsorption equilibrium, while Langmuir–Freundlich and Tooth isotherms explained the data well. Goodness of fit increased with the increased sepiolite quantity in the treated suspension.

Seasonal variations in the physiological condition of the benthic amphipods Monoporeia affinis and Pontoporeia femorata in the Gulf of Riga (Baltic Sea)

Seasonal variations in the physiological condition of two benthic deposit-feeding amphipods were studied in two environmentally differing areas in the Gulf of Riga (Baltic Sea) with the purpose of estimating their role in benthic mineralisation. At the shallower (26 m) nearshore station, Monoporeia affinis exhibited low ammonia excretion rate (VNH 4 + ) throughout the year. After intensive accumulation of lipids in spring, the lipid reserves of the individuals became rapidly depleted during autumn. Gravid females in winter-early spring showed exceedingly low lipid and triacylglycerol (TAG) levels compared to studies carried out in open-sea areas. Pontoporeia femorata studied at the deeper (43 m) offshore station exhibited a higher VNH 4 + at all times with no significant seasonal variation. Lipid and TAG accumulated continuously until November, reaching higher levels than recorded previously for this species. Experiments showed that the temperature coefficient Q10 determined for VNH 4 + is likely to depend on the recent feeding history of the amphipods. Mineralisation of nitrogen and carbon by the amphipod populations at the study sites was estimated to be 1.7-3.0 g C and 11.3-13.5 mmol NH 4 + m–2 yr–1. Conclusively, both biotic and abiotic factors affect the condition of the amphipods, while the species also have genuine differences in their metabolic characteristics.

The Smallest Vertebrate, Teleost Fish, Can Utilize Synthetic Dipeptide-Based Diets

In vitro studies of brush-border intestinal transport of dipeptides and cytoplasmic hydrolysis in fish suggest that these processes could be key mechanisms in the absorption and utilization of nutrients for growth. However, in vivo experimentation to study the nutritional importance of these processes was needed. We compared three dietary formulations based on free, peptide and protein sources of amino acids. Our results were the first to show that a synthetic dipeptide (PP)-based diet could support growth in the early stages of ontogenesis of a teleost fish, rainbow trout (Oncorhynchus mykiss), whereas a free amino acid (FAA)-based diet failed. We found that fish fed an FAA-based diet had an increased rate of ammonia excretion [1.78 +/- 0.19 mmol NH(3)-N/(kg body wt.h)], compared with fish fed a PP-based diet [1.25 +/- 0.07 mmol NH(3)-N/(kg body wt.h)], suggesting that deamination is involved in the metabolism of dietary FAA. Teleost fish are known to obtain a high proportion of total energy from protein, compared with higher vertebrates. However, we found that feeding trout alevins a PP-based diet increased postprandial oxygen consumption for 2 to 24 h, whereas other treatments decreased 24-h postprandial metabolism. This may indicate that peptide metabolism is less efficient than protein metabolism. Juvenile rainbow trout differed from alevins in their response to FAA- and PP-based diets. These observations strongly suggest that intestinal dietary peptide transport and hydrolysis could support protein synthesis and growth in vertebrates that respond poorly to FAA-based diets. We conclude that nutrient administration may be improved by manipulating dietary peptide composition and peptide/protein ratios, leading to better utilization of synthetic peptides, with nutritional and therapeutic implications for all vertebrates.

Nutrient uptake by coral-reef microatolls

We measured rates of ammonium and phosphate uptake into 12 microatolls at One Tree reef lagoon, Australia, on 14 occasions over a range of seasonal and meteorological conditions from 1993 to 1995. Nine of the microatolls were spiked with ammonia and/or phosphate every low tide (2.5–4 h) during low- (15-month) and high- (13-month) loading periods. The remaining three microatolls that were not spiked with nutrient served as reference conditions. Ammonium concentrations were elevated from an average background of 0.7 to 11 µM NH4 during the low-loading period and 36 µM NH4 during the high-loading period, resulting in a loading to the benthos of 3.5 and 18 mmol NH4 m–2 low tide–1. Phosphate concentrations were elevated from an average background of 0.2 to 2.3 and 5.1 µM PO4 during low- and high-loading periods, respectively, resulting in a loading of 0.66 and 3.9 mmol PO4 m–2 low tide–1. Ammonium and phosphate concentrations decreased significantly over low-tides, and uptake rates were proportional to concentrations (first-order). The average uptake-rate constant, S (m s–1), for ammonium and phosphate did not differ between the two loading periods but was highly variable. Averaged over both loading periods, S for ammonium was 129±74×10–6 m s–1 and S for phosphate was 67±39×10–6 m s–1. At background nutrient concentrations, estimated nutrient-uptake rates were 7.8 mmol NH4 m–2 day–1 and 1.2 mmol PO4 m–2 day–1. Excretion rates—calculated from the mean difference in uptake rates measured in reference and nutrient-enriched microatolls—were estimated to be 4.3 mmol NH4 m–2 day–1 and 0.9 mmol PO4 m–2 day–1. We reason and suggest that nutrient uptake rates in these microatolls were close to mass-transfer limited rates. We conclude that nutrient uptake into coral reefs can be highly dynamic, varying 10-fold spatially and temporally.

Effect of Fasting for Two Days on the Excretion of Ammonium in Dogs with Chronic Metabolic Acidosis

Background: The source of glutamine for renal ammonium production is ultimately dietary protein in the fed state and body proteins in fasting. Objective: Our objective was to determine if less NH⁺₄ would be excreted by fasted dogs with chronic metabolic acidosis resulting in conservation of lean body mass. Methods: Acid-loaded fed and fasted dogs were given 10 mmol NH₄Cl/kg for 5 days; the fasted group had food withheld on days 4 and 5. Results: The renal production of NH⁺₄ was not significantly different in both acid-loaded groups, yet the rate of NH⁺₄ excretion was significantly lower in the fasted dogs (8 vs. 21 mmol NH⁺₄/mmol creatinine). The urine pH was significantly higher (6.0 versus 5.5) while titratable acid and the urine flow rate were significantly lower in these fasted dogs. Despite nearly equal urine flow rates and Na⁺ excretion rates after an infusion of saline, the fasted dogs failed to increase the rate of excretion of NH⁺₄ to rates seen in the fed group. Conclusions: The lower rate of excretion of NH⁺₄ in fasted, acidotic dogs appeared to be due to a lower distal H⁺ secretion. This may help preserve lean body mass during fasting.

Influence of pore size distribution on Pt dispersion in Pt-Sn/Al 2O 3 reforming catalyst

Pt-Sn/Al 2O 3 catalysts; Pt (0.35 wt.%), Sn (0.42 wt.%) and chlorine (∼1.0 wt.%) were prepared by incipient wetness impregnation and characterized by nitrogen adsorption–desorption, NH 3 adsorption microcalorimetry and H 2–O 2 titrations. In catalysts with almost similar values of S BET (170–180 m 2 g −1), total acidity (0.32–0.36 mmol NH 3 g −1), a significant variation in Pt dispersion was observed with the difference in meso pore size distribution in 20–100 Å diameter range. As the vol.% in 20–100 Å range is increased from 18 to 63%, the Pt dispersion increased from 57 to 81%. A greater abundance of relatively narrow meso pores (20–100 Å diameter) facilitate the fine dispersion of Pt moieties on the alumina surface. At least, a 30% fraction of the total pore volume should lie in 20–100 Å pores in order to obtain a reasonably good Pt dispersion (∼75%). Although, a further increase of volume in these pores from 30 to 60% improves the Pt dispersion, but decreases the total pore volume presumably due to a sharp decline in larger pores (100–200 Å) which contribute more towards the pore volume.