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1.
Short-term variations in the abundance and cell volume of bacterioplankton in an artificial tropical lake 总被引:1,自引:0,他引:1
Jugnia Louis B. Tadonléké Rémy D. Sime-Ngando Télesphore Foto Samuel M. Kemka N. 《Hydrobiologia》1998,385(1-3):113-119
Circadian and spatial fluctuations in bacterioplankton abundance and cell volume were examined, for the first time, in the
Municipal Lake located in the down town area of Yaoundé (Capital of Cameroon, Central Africa, ca 3° 52′ N, 11° 31′ E). Bacterial
cell volumes (range, 0.05 to 0.2 μm3) were consistent with those reported for other aquatic systems while bacterial densities
(0.8 to 2 × 108 cells ml-1) were among the highest values reported in pelagic systems. These variables and chlorophyll a and
dissolved oxygen concentrations within a single depth-zone varied from 13 to 61%, while water temperature fluctuated only
from 2 to 6%. Spatial fluctuations of physical-chemical and biological variables were generally higher during the day-time
than during the night-time. A significant diel variation was provided for bacterial cell volume in the surface waters where
synchronized cell division was occurring during the night. The measured bacterial abundances in this study were 4 to 17 fold
higher than values known from other lakes of similar trophic status, and both cell abundance and volume were not correlated
with chlorophyll. We conclude that this was due to the dependence of bacterial populations to different sources of allochthonous
substrates, including untreated sewage from the major influents of the lake, resuspension of benthic material, and substrate
releasing from macrophytes which are prevalent in the littoral zone of the lake.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
2.
Autolytic degradation of yeast RNA occurs in many foods and beverages and can impact on the sensory quality of the product,
but the resulting complex mixture of nucleotides, nucleosides and nucleobases has not been properly characterised. In this
study, yeast autolysis was induced by incubating cell suspensions of Saccharomyces cerevisiae at 30–60 °C (pH 7.0), and at pH 4.0–7.0 (40 °C) for 10–14 days, and the RNA degradation products formed during the process
were determined by reversed-phase HPLC. Up to 95% of cell RNA was degraded, with consequent leakage into the extracellular
environment of mainly 3′-, 5′- and 2′-ribonucleotides, and lesser amounts of polynucleotides, ribonucleosides and nucleobases.
The rate of RNA degradation and the composition of the breakdown products varied with temperature and pH. RNA degradation
was fastest at 50 °C (pH 7.0). Autolysis at lower temperatures (30 °C and 40 °C) and at pH 5.0 and 6.0 favoured the formation
of 3′-nucleotides, whereas autolysis at 40 °C and 50 °C (pH 7.0) favoured 5′- and 2′-nucleotides. The best conditions for
the formation of the two flavour-enhancing nucleotides, 5′-AMP and 5′-GMP, were 50 °C (pH 7.0) and pH 4.0 (40 °C), respectively. 相似文献
3.
J. E. Tomilova V. V. Kuznetsov M. A. Abdurashitov N. A. Netesova S. Kh. Degtyarev 《Molecular Biology》2010,44(4):606-615
The M1.Bst19I DNA-methyltransferase gene from restriction-modification system Bst19I (recognition sequence 5′-GCATC-3′) in
Bacillus stearothermophilus 19 has been cloned in the expressing vector pJW that carries a tandem of thermo inducible promoters P
R
/P
L
from phage λ. Highly purified enzyme has been isolated by chromatography on various resins from Escherichia coli cells where it is accumulated in a soluble form. The study of M1.Bst19I properties has revealed that the enzyme has a temperature
optimum at 50°C and demonstrates maximal activity at pH 8.0. M1.Bst19I modifies adenine in sequence 5′-GCATC-3′. Kinetic parameters
of M1.Bst19I DNA methylation reaction have been determined as follows: Km for λ DNA is 0.68 ± 0.07 μM, Km for S-adenosyl-L-methionine is 2.02 ± 0.31 μM. Catalytical constant (k
cat) is 1.8 ± 0.05 min−1. Comparative analysis of Target Recognition Domain amino acid sequences for M1.Bst19I and other α-N6-DNA-methyltransferases
has allowed us to suggest the presence of two types of the enzymes containing ATG or ATC triplets in the recognition sequence. 相似文献
4.
Tarasova MV Kuznetsov VV Netesova NA Gonchar DA Degtyarev SKh 《Biochemistry. Biokhimii?a》2010,75(12):1484-1490
A restriction-modification system from Bacillus psychrodurans AC (recognition sequence 5′-CCGC-3′) comprises two DNA methyltransferases: M1.BspACI and M2.BspACI. The bspACIM1 gene was cloned in the pJW2 vector and expressed in Escherichia coli cells. High-purity M1.BspACI preparation has been obtained by chromatography on different carriers. M1.BspACI has a temperature
optimum of 30°C and demonstrates maximum activity at pH 8.0. M1.BspACI modifies the first cytosine in the recognition sequence
5′-CCGC-3′. The kinetic parameters of M1.BspACI DNA methylation are as follows: K
m for phage λ DNA is 0.053 μM and K
m for S-adenosyl-L-methionine is 5.1 μM. The catalytic constant (k
cat) is 0.095 min−1. 相似文献
5.
Summary Several metabolic compounds have been found to be competitive inhibitors of the anomerase activity of phosphoglucose isomerase
(EC 5.3.1.9).Ki values for erythrose 4-phosphate, 6-phosphogluconate, and fructose 1,6-bisphosphate for the anomerase reaction are 0.32 μM,
21 μM, and 84 μM respectively at 0° and pH 8.2. A significant difference between the fructose, 1,6-bisphosphate inhibition
constants for both activities was found (ki(isomerase)=800 μM and Ki(anomerase)=84 μM). Also the Km values for both activities were found to be significantly different (Km(isomerase)=140 μM and Km(anomerase)=3.6 μM).
Attempts to independently alter the anomerase to isomerase activity ratio through protein modification yielded mixed results.
While several modifying reagents destroyed the catalytic activities at identical rates, inactivation by iodoacetamide or pyridoxal
5′ phosphate sensitized photo-oxidation displayed differential initial effects on the two activities with the anomerase activity
being the less affected. These data support the theory that an imidazole residue is catalytically important for isomerization,
but less so for anomerization. 相似文献
6.
The critical micellar concentration (CMC) of stearoylcarnitine was determined at different pH values at room temperature by fluorescence spectroscopy, monitoring the spectral changes of 8-anilinonaphthalene-1-sulfonate (ANS). The CMC was found to vary with pH, increasing from about 10 μM at pH 3.0 to ca. 25 μM at pH 7.0, but decreasing slightly with further increase in pH to approximately 19 μM at pH 10.0. Differential scanning calorimetry (DSC) shows that stearoylcarnitine dispersed in water at low concentration undergoes a broad thermotropic phase transition at 44.5°C, with a transition enthalpy of 15.0 kcal/mol. The transition temperature (T
t) shifts to ca. 50.5°C in the presence of 1 mM EDTA or when the concentration is increased significantly. The turbidity of aqueous dispersions of stearoylcarnitine was found to be considerably high at low temperatures, which decreases quite abruptly over a short temperature range, indicating that a transition occurs from a phase of large aggregates to one of much smaller aggregates, most likely micelles. The phase transition temperature was determined as 29.1°C at pH 3.0, which increased with increasing pH up to a value of 55.3°C at pH 8.6 and remains nearly constant thereafter up to pH 11.2. The pH dependence of CMC and T
t suggest that the pK
a of the carboxyl group of long chain acylcarnitines shifts to higher temperatures upon aggregation (micelles or bilayer membranes). 相似文献
7.
U. H. Brockmann 《Aquatic Ecology》1994,28(3-4):371-381
In the low salinity region of the Elbe estuary in March–April 1992 the turbidity zone was characterized by high loads of suspended
matter, 7% of which was organic material (750 μM C) at the surface. Particulate nitrogen, phosphorus and carbohydrates concentrations
reached 55 μM N, 10 μM P and more than 15 μM glc. eq., corresponding to 13% of total C, at the surface and increasing threefold
near the bottom.
In spite of the peaking of particulate organic material levels in the maximum turbidity zone, there were only consistent qualitative
changes in total particulate C, N, P, and carbohydrates along the Elbe estuary. Downstream, both the percentage of particulate
organic material and the turbidity: organic material ratio decreased, indicating decomposition in the upper estuary and dilution
with inorganic suspended matter from the lower estuary.
Diatoms, the dominant phytoplankton group, decreased from the upper reaches towards the turbidity zone by 0.3 (surface) and
1.5 mg C l−1 (bottom). This corresponded to 12 and 60% of the decrease in total particulate carbon. Estimated local input of organic carbon
by primary production (21 μg Cl−1d−1) was almost compensated by calculated minimum grazing (14 μg C l−1d−1). Considering net primary production and grazing, the dissimilation by zooplankton (5 μg C l−1d−1) and heterotrophic bacterial decomposition (48 μg C l−1d−1), when summed over the estimated flushing time (12 days) represented a loss of suspended organic matter of 0.6 mg Cl−1. Since this was only 20% of the observed decrease in particulate carbon, significant dilution processes must be assumed.
Dissolved organic nitrogen decreased from 35 to 10 μM N and dissolvd organic phosphorus from 0.6 to 0.1 μM P towards the sea,
mainly due to dilution. The distribution of phosphate, with highest loads in the turbidity maximum of 2.4 μM, suggested an
interaction with the accumulated load of particulate material. 相似文献
8.
Fish kills of milkfish Chanos chanos and tilapia Oreochromis spp. now occur frequently in brackish, marine, and freshwater
farms (ponds, pens, and cages) in the Philippines. Aquafarms with high organic load, limited water exchange and circulation,
no aeration, and high stocking and feeding rates can become oxygen-depleted and allow sulfide from the sediments to appear
in the water column and poison free-swimming fish. The sulfide tolerance of 2–5 g milkfish and 5–8 g O. mossambicus was determined
in 25-liter aquaria with flow-through sea water (100 ml min-1) at 26–30 °C and sulfide stock solutions pumped in at 1ml min-1.
Total sulfide concentrations in the aquaria were measured by the methylene blue method and used in the regression against
the probits of % survival. Four experiments showed that the two species have similar sulfide tolerance. In sea water of pH
8–8.5, about 163 ± 68 μM or 5.2 ± 2.2 mg l-1 total sulfide (mean ± 2 se) or 10 μM or 313 μg l-1 H2S was lethal to 50% of the
fish in 4–8 h, and 61 ± 3 μM total sulfide or 4 μM H2S in 24–96 h (to convert all sulfide concentrations: 1 μM = 32 μg l-1).
Earthen pond bottoms had 0–382 μM total dissolved sulfide (mean ± sd = 54 ± 79 μM, n = 76); a tenth of the samples had >200
μM. The water column may have such sulfide levels under hypoxic or anoxic conditions. To simulate some of the conditions during
fish kills, 5–12 g milkfish were exposed to an abrupt increase in sulfide, alone or in combination with progressive respiratory
hypoxia and decreasing pH. The tests were done in the same flow-through set-up but with sulfide pumped in at 25 ml min-1.
The lethal concentration for 50% of the fish was 197 μM total sulfide or 12 μM H2S at 2 h, but 28–53 μM sulfide allowed fish
to survive 6–10 h. Milkfish in aquaria with no aeration nor flow-through sea water died of respiratory hypoxia in 5–8 h when
oxygen dropped from 6 to 1 mg l-1. Under respiratory hypoxia with 30–115 μM sulfide, the fish died in 2.5–4 h. Tests with
low pH were done by pumping a weak sulfuric acid solution at 25 ml min-1 into aquaria with flow-through sea water such that
the pH dropped from 8 to 4 in 5 h. Under these conditions, milkfish died in 7–9 h when the pH was 3.5. When 30–93 μM sulfide
was pumped in with the acid, the fish died in 2–6 h when the pH was still 4.5–6.3. Thus, sulfide, hypoxia, and low pH are
each toxic to milkfish at particular levels and aggravate each other's toxicity. Aquafarms must be well oxygenated to prevent
sulfide toxicity and fish kills.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Bacteroids formed by Mesorhizobium ciceri CC 1192 in symbiosis with chickpea plants (Cicer arietinum L.) contained a single form of citrate synthase [citrate oxaloacetate-lyase (CoA-acetylating) enzyme; EC 4.1.3.7], which
had the same electrophoretic mobility as the enzyme from the free-living cells. The citrate synthase from CC 1192 bacteroids
had a native molecular mass of 228 ± 32 kDa and was activated by KCl, which also enhanced stability. Double reciprocal plots
of initial velocity against acetyl-CoA concentration were linear, whereas the corresponding plots with oxaloacetate were nonlinear.
The K
m value for acetyl-CoA was 174 μM in the absence of added KCl, and 88 μM when the concentration of KCl in reaction mixtures
was 100 mM. The concentrations of oxaloacetate for 50% of maximal activity were 27 μM without added KCl and 14 μM in the presence
of 100 mM KCl. Activity of citrate synthase was inhibited 50% by 80 μM NADH and more than 90% by 200 μM NADH. Inhibition by
NADH was linear competitive with respect to acetyl-CoA (K
is = 23.1 ± 3 μM) and linear noncompetitive with respect to oxaloacetate (K
is = 56 ± 3.8 μM and K
ii = 115 ± 15.4 μM). NADH inhibition was relieved by NAD+ and by micromolar concentrations of 5′-AMP. In the presence of 50 or 100 mM KCl, inhibition by NADH was apparent only when
the proportion of NADH in the nicotinamide adenine dinucleotide pool was greater than 0.6. In the microaerobic environment
of bacteroids, NADH may be at concentrations that are inhibitory for citrate synthase. However, this inhibition is likely
to be relieved by NAD+ and 5′-AMP, allowing carbon to enter the tricarboxylic acid cycle.
Received: 14 July 1999 / Accepted: 20 September 1999 相似文献
10.
During January 1989, phytoplankton biomass and species composition were studied in a north / south transect at the Weddell / Scotia
Confluence (47°W), between 57° and 61°30′S. Results showed a diatom bloom in the Scotia Sea (chlorophyll a 1.9 μg l−1, particulate organic carbon 239 μg l−1), dominated by Fragilariopsis cylindrus, Dactyliosolen antarcticus and Chaetoceros dichaeta. Low chlorophyll a / phaeopigments ratios (about 1.4) and silicate concentrations (15 μmol l−1) suggested that this was an advanced bloom phase, probably linked to high grazing pressure. Minimum chlorophyll a values of 0.1–0.2 μg l−1 and particulate organic carbon 46 μg l−1 were found at the Weddell / Scotia Front and in a subsurface layer of the Weddell Sea Water. In the southern part of the
transect (61°30′S), in the Weddell Sea, a second surface maximum was found (chlorophyll a 0.9 μg l−1, particulate organic carbon 120 μg l−1), but with a different species composition, with Cryptomonas sp. dominant. Our results show a succession within the diatom community in the Weddell / Scotia Confluence Waters when comparing
the three EPOS legs. In the Weddell Sea from spring to summer, nanoflagellates, with only a minor contribution from diatoms,
persist over a long period with little change in the community structure. We suggest that the frontal system, together with
the receding ice edge and the grazing pressure of either krill or protozooplankton, are mainly responsible for the phytoplankton
distribution patterns found.
Received: 3 July 1996 / Accepted: 3 November 1996 相似文献
11.
Aluminum in lake water and in the organs of the fish Tribolodon hakonensis was investigated in Lake Usoriko (pH 3.6), Lake Inawashiroko (pH 5.0), and the Tenryu River (pH 7.7). The concentration of
total soluble aluminum in the water was 0.51 mg l−1 in Usoriko, 0.05 mg l−1 in Inawashiroko, and less than 0.01 mg l−1 in the Tenryu. The chemical forms of soluble aluminum in the acid water were characterized as Al3+, AlL2+, and AlL≦1+. More than 90% of soluble aluminum in the water of Usoriko was Al3+, whereas AlL2+ was dominant in the water of Inawashiroko. The aluminum concentration in the organs of T. hakonensis in Usoriko was 42 μg g−1 wet weight in gills, 4.2 μg g−1 in muscle, 6.9 μg g−1 in bone, 12.7 μg g−1 in liver, 6.0 μg g−1 in kidney, and 6.0 μg g−1 in intestine, indicating accumulation of aluminum in the gills. The aluminum concentration in the organs of T. hakonensis living in Inawashiroko was approximately the same, in spite of the difference in water chemistry of the two acid lakes, especially
for pH and aluminum. This suggests that aluminum accumulation might be controlled in the fish living in the acid lakes. In
contrast, the aluminum concentration in the gills of T. hakonensis from the Tenryu was 2 μg g−1.
Received: May 20, 1999 / Accepted: December 10, 1999 相似文献
12.
The total iron (TFe) concentrations in five rivers to a Galician Ria (averages 1.0–4.5 μM) was within the pristine range,
but in rainwater it was higher (17 μM). TFe values of small sewage treatment plants (STP) ranged between 3 and 4 μM, whereas
in the largest was 11 μM. Particulate iron in rivers was five times more abundant than dissolved iron, except in the Lagares
where it was 20 times higher, but in the STDs the dissolved/particulate coefficients varied from 0.1 to 1.1 and in the rainwater
it was lower than 0.4. Equations of water flow versus iron flux were obtained to quantify the iron contribution from the freshwater
sources to the Vigo Ria. It receives annually 490 tons of iron (6% in dissolved form) and 90% of this comes from industries
focused on metal processes. The contaminated Lagares River accounts for the main input of TFe (327 t a−1), followed by rainwater (78 t a−1), the Oitavén River (28 t a−1) and Vigo STP (33 t a−1). Anthropogenic activities have increased the amount of iron flowing into the Ria by roughly ten times and this could upset
the biogeochemical cycle in similar coastal systems. 相似文献
13.
Hilde Eggermont James M. Russell Georg Schettler Kay Van Damme Ilse Bessems Dirk Verschuren 《Hydrobiologia》2007,592(1):151-173
This study describes the physical and chemical properties of 17 Afroalpine lakes (>2 m deep) and 11 pools (<2 m deep) in the
Rwenzori mountains, Uganda-DR Congo, with the aim to establish the baseline conditions against which to evaluate future environmental
and biological changes in these unique tropical ecosystems, and to provide the foundation for lake-based paleoenvironmental
studies. Most Rwenzori lakes are located above 3,500 m elevation, and dilute (5–52 μS/cm specific conductance at 25°C) open
systems with surface in- and outflow. Multivariate ordination and pairwise correlations between environmental variables mainly
differentiate between (1) lakes located near or above 4,000 m (3,890–4,487 m), with at least some direct input of glacial
meltwater and surrounded by rocky catchments or alpine vegetation; and (2) lakes located mostly below 4,000 m (2,990–4,054
m), remote from glaciers and surrounded by Ericaceous vegetation and/or bogs. The former group are mildly acidic to neutral
clear-water lakes (surface pH: 5.80–7.82; Secchi depth: 120–280 cm) with often above-average dissolved ion concentrations
(18–52 μS/cm). These lakes are (ultra-) oligotrophic to mesotrophic (TP: 3.1–12.4 μg/l; Chl-a: 0.3–10.9 μg/l) and phosphorus-limited (mass TN/TP: 22.9–81.4). The latter group are mildly to strongly acidic (pH: 4.30–6.69)
waters stained by dissolved organic carbon (DOC: 6.8–13.6 mg/l) and more modest transparency (Secchi-disk depth: 60–132 cm).
Ratios of particulate carbon, particulate nitrogen and chlorophyll a in these lakes indicate that organic matter in suspension is primarily derived from the lakes’ catchments rather than aquatic
primary productivity. Since key features in the Rwenzori lakes’ abiotic environment are strongly tied to temperature and catchment
hydrology, these Afroalpine lake ecosystems can be expected to respond sensitively to climate change and glacier melting.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
14.
Methylosinus trichosporium OB3b is a methanotrophic bacterium containing particulate methane monooxygenase (MMO), which catalyzes the hydroxylation
of methane to methanol. The methanol is further oxidized to formaldehyde by methanol dehydrogenase (MDH). We developed a novel
compulsory circulation diffusion system for cell cultivation. A methane/air mixture (1:1, v/v) was prepared in a tightly sealed
gas reservoir and pumped into a nitrate mineral salt culture medium under optimal conditions (5 μM CuSO4, pH 7.0, 30°C). Cells were harvested, washed, and resuspended (0.6 mg dry cells/mL) in a 500 mL flask in 100 mL of 10 mM
phosphate buffer (pH 7.0) containing 100 mM NaCl and 1 mM EDTA as MDH inhibitors, and 20 mM sodium formate. A single 12 h
batch reaction at 25°C yielded a final concentration of 13.2 mM methanol. The use of a repeated batch mode, in which the accumulated
methanol was removed after each of three 8 h cycles over a 24 h period, showed a productivity of 2.17 μmol methanol/h/mg dry
cell wt. Finally, a lab-scale reaction performed using a 3 L cylindrical reactor with a working volume of 1 L produced 13.7
mM methanol after 16 h. Our results identify a simple process for improving the productivity of biologically derived methanol
and, therefore the utility of methane as an energy source. 相似文献
15.
Thioredoxin reductase (TrxR, EC 1.6.4.5) of Deinococcus radiophilus was purified by steps of sonication, ammonium sulfate fractionation, 2′5′ ADP Sepharose 4B affinity chromatography, and Sephadex
G-100 gel filtration. The purified TrxR, which was active with both NADPH and NADH, gave a 368 U/mg protein of specific activity
with 478-fold purification and 18% recovery from the cell-free extract. An isoelectric point of the purified enzymes was ca.
4.5. The molecular weights of the purified TrxR estimated by PAGE and gel filtration were about 63.1 and 72.2 kDa, respectively.
The molecular mass of a TrxR subunit is 37 kDa. This suggests that TrxR definitely belongs to low molecular weight TrxR (L-TrxR).
The Km and Vmax of TrxR for NADPH are 12.5 μM and 25 μM/min, whereas those for NADH are 30.2 μM and 192 μM/min. The Km and
Vmax for 5, 5′-dithio-bis-2-nitrobenzoic acid (DTNB, a substituted substrate for thioredoxin) are 463 μM and 756 μM/min, respectively.
The presence of FAD in TrxR was confirmed with the absorbance peaks at 385 and 460 nm. The purified TrxR was quite stable
from pH 3 to 9, and was thermo-stable up to 70°C. TrxR activity was drastically reduced (ca. 70%) by Cu2+, Zn2+, Hg2+, and Cd2+, but moderately reduced (ca. 50%) by Ag+. A significant inhibition of TrxR by N-ethylmaleimide suggests an occurrence of cysteine at its active sites. Amino acid
sequences at the N-terminus of purified TrxR are H2N-Ser-Glu-Gln-Ala-Gln-Met-Tyr-Asp-Val-Ile-Ile-Val-Gly-Gly-Gly-Pro-Ala-Gly-Leu-Thr-Ala-COOH. These sequences show high similarity
with TrxRs reported in Archaea, such as Methanosarcina mazei, Archaeoglobus fulgidus etc. 相似文献
16.
L. Charpy M. Rodier A. Couté C. Perrette-Gallet C. Bley-Loëz 《Coral reefs (Online)》2010,29(3):771-783
Closure of the Clipperton Island atoll (10°17′ N 109°13′ W), now a meromictic lake, is estimated to have occurred between
1839 and 1849. It was still closed in 2005. Brackish waters in the upper layer (0–10 m) were oxygenated, while saline waters
in the deep layer (>20 m) were anoxic. Allowing for the methodological difficulties of earlier measurements, the physical
characteristics of the lagoon did not seem to have changed significantly since the last expedition (1980). The intermediate
layer between brackish and saline waters was characterized by a strong density gradient and a temperature inversion of up
to 1.6°C. Microbial activity, water exchange between the deep layer and surrounding oceanic waters and the geothermal flux
hypothesis are discussed. The low DIN and SRP concentrations observed in the upper layer, despite high nutrient input by seabird
droppings, reflect the high nutrient uptake by primary producers as attested by the elevated overall gross primary production
(6.6 g C m−2 day−1), and high suspended photosynthetic biomass (2.23 ± 0.23 μg Chl a l−1) and production (263 ± 27 μg C l−1 day−1). Phytoplankton composition changed in 67 years with the advent of new taxa and the disappearance of previously recorded
species. The freshwater phytoplanktonic community comprised 43 taxa: 37 newly identified during the expedition and 6 previously
noted; 16 species previously found were not seen in 2005. The closure of the lagoon, combined with the positive precipitation–evaporation
budget characteristic of the region, has induced drastic changes in lagoon functioning compared with other closed atolls. 相似文献
17.
The agarophyte red alga Gracilaria verrucosa occurs widely in Chilika Lake, one of the RAMSAR wetland sites in India. The lake is situated in the extreme southeast corner
of Orissa between latitudes 19°28′ and 19°54′ N and longitudes 85°06′ and 85°35′ E. The natural biomass production is not
sufficient for the agar industry, and the only alternative is to maximize the production of the seaweed through mass cultivation
by seaweed farming. To elucidate important aspects of the growth and development of G. verrucosa, experimental field cultivation was undertaken at Langaleswar and Samal sites of Chilika Lake using ropes and raft methods
during March to August, 2009. After 30 days of cultivation a maximum 15- and 13.8-fold increase in biomass in raft culture
and rope culture, respectively, was observed at Langaleswar and an 11.6- and 11.0-fold increase in biomass at Samal. Environmental
parameters such as temperature, salinity, pH, transparency, DO, conductivity, nitrate, and phosphate were monitored at both
stations, and the influence of environmental parameters is discussed. 相似文献
18.
This study considers the cycling of nitrogen in the waters of the North Sea, particularly focussing on organic nitrogen. Dissolved
inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and particulate organic nitrogen (PON) were measured in the North
Sea over a one-year period (autumn 2004–summer 2005). The surface water concentrations of nitrate, ammonium, DON and PON during
the present study ranged from <0.1–7.2 μM, <0.1–2.0 μM, 1.9–11.2 μM and 0.3–5.6 μM, respectively, with DON the dominant fraction
of total nitrogen at all times. These nutrients concentrations were significantly lower compared to previous studies in the
southern North Sea. The seasonal variations showed high mean surface concentrations of nitrate (4.7 ± 0.6 μM) and DON (8.9 ± 0.9 μM),
low ammonium (<0.1 μM) and PON (0.8 ± 0.1 μM) in winter, shifting to low nitrate (0.3 ± 0.3 μM) and DON (4.2 ± 1.2 μM) in
summer, with high ammonium (0.8 ± 0.4 μM) in autumn and PON (2.5 ± 1.2 μM) in spring. Highest mean surface DON concentration
was measured in winter and may be due to resuspension of the organic matter from the bottom sediments. For autumn and spring,
phytoplankton DON release was likely to be the most significant source of DON as shown by high concentrations of low molecular
weight (LMW) DON and its positive correlation to chlorophyll a. Low total and LMW DON concentrations during summer were likely to be due to the uptake of the LMW DON fraction by phytoplankton
and bacteria and the stratification of the water column. DON is therefore shown to be a potentially important source of nitrogen
in shelf seas especially after the spring bloom has depleted nitrate to limiting concentrations.
Handling editor: L. Naselli-Flores 相似文献
19.
For the cyclooxygenase reaction of prostaglandin-H-synthase isolated from ram vesicular glands, dependences of the initial
reaction rate, the maximal yield of the product, and the rate constant of enzyme inactivation in the course of reac- tion
on oxygen concentration were studied in the absence and in the presence of electron donor in the reaction medium. It is shown
that in the absence of electron donor the cyclooxygenase reaction is strictly governed by Michaelis-Menten kinet- ics over
a wide range of oxygen concentrations (5–800 μM). In the presence of electron donor in the reaction medium it was found that
cyclooxygenase reaction is inhibited by an excess of dissolved oxygen: the maximal values of the initial reaction rate and
yield of the product are attained at oxygen concentration 50 μM, and its increase to 500 μM causes twofold decrease in the
initial rate and maximal yield. The rate constant of enzyme inactivation in the course of reaction increases on increase in
oxygen concentration both in the presence and in the absence of electron donor. 相似文献
20.
Concentration and transport of dissolved and suspended substances in the Orinoco River 总被引:11,自引:4,他引:7
The Orinoco River, which is hydrologically unregulated and has a minimally disturbed watershed, was sampled quantitatively
over a four-year interval. In conjunction with the sampling, a method was developed for quantifying statistical uncertainty
in the estimates of annual transport. The discharge-weighted mean concentration of total suspended solids in the Orinoco River
is 80 mg/l, which corresponds to total annual transport of 90 × 106 t/y, or, expressed per unit of watershed area, 960 kg/ha/y, of which 96% is inorganic. The mean for dissolved solids is 34
mg/l, of which 25 mg/l is inorganic. The total transport of inorganic material, with a small allowance for bedload, is 128
× 106 t/y, which corresponds to an erosion rate of 4 cm/1000 y. Concentrations of dissolved and suspended constituents derived
from rock weathering are very low because of dilution from high runoff (1190 mm/y), coverage of the southern part of the drainage
by shield rock, and minimal watershed disturbance. Seasonal patterns in dissolved and suspended constituents are repeated
with a high degree of consistency from one year to the next.
For most variables, relationships between transport and discharge are described adequately by a power function. There are
three categories of response to changing discharge: purging (exponent > 1: soluble organic fractions and all particulate fractions),
dilution (exponent 0–1: major ionic solids and silicon), and conservation (exponent < 0: nitrate, interannual). Variability
across seasons and across years is highest for the particulate constituents, but within this group variability is lower for
the organic than for the inorganic components. Major ions that originate primarily from the atmosphere have a higher seasonal
variability than major ions that originate primarily from weathering. Potassium and soluble silicon have the lowest variabilities.
Variability is much lower across years than across seasons for most constituents.
Because of high runoff per unit area, the Orinoco drainage has a high specific transport of organic carbon (72 kg/ha/y, 6.8
× 106 t/y, 1.6% of global river transport), even though the concentrations of organic carbon in the river are not exceptionally
high (mean, 4.4 mg/l dissolved, 1.4 mg/l particulate). Concentrations of ammonium (35 μg/l as N) and of nitrate (80 μg/l as
N) are high given the undisturbed nature of the watershed and the high amount of runoff. The high transport rate for total
nitrogen (5.7 kg/ha/y, 0.54 × 106 t/y, l.5% of global river transport) can be sustained only by high rates of nitrogen fixation within the watershed. Concentrations
of soluble phosphorus are within the range expected for undisturbed river systems (20 μg/l), but concentrations of particulate
phosphorus are low because the amounts of particulate matter are small and the phosphorus per unit weight of suspended matter
is low. Phosphorus transport (0.75 kg/ha/y) can be accounted for easily by weathering of the parent material, even within
the Guayana Shield, where weathering rates are lowest. Biological modification of nutrient and carbon fractions during transit
along the main stem are minimal. 相似文献