共查询到20条相似文献,搜索用时 875 毫秒
1.
The spatial and temporal distributions of dissolved inorganic nutrients were investigated between May 1996 and April 1997
in Mida Creek, a mangrove area along the north coast region of Kenya. The nutrient levels of pore water from boreholes/wells
within the surrounding area of the creek were also investigated for comparison. In addition, phytoplankton distribution in
Mida Creek was assessed in three stations within the creek in order to determine the structure and succession stages of the
phytoplankton community and to provide an indication of the status of primary productivity of the creek.
Measurements carried out within the creek revealed that the mean concentration ranges for NH4+ –N, (NO
2− + NO3−)−N, PO43− −P and SiO32− −Si were: 0.002–5.45; 0.12–5.63; 0.10–0.58 and 1.31–81.36 μM, respectively. For the case of boreholes/wells found in the
surrounding area, their respective nutrient levels were found to lie in the ranges 0.4–907.0; 16.7–4897.0; 1.09–22.39 and
83.9–596.0 μM. A total of 295 species of phytoplankton belonging to 78 genera were identified with great temporal variability
in abundance in all the stations sampled. The most dominant algal members in the Creek included Chaetoceros spp., Chroococcus
limneticus and Oscillatoria spp. The diversity values recorded were indicative of mesotrophic conditions. The highest nutrient
concentration levels within the creek were measured during the wet season as compared to dry season and this trend closely
corresponded with that of the phytoplankton productivity. However, no significant variation ( p > 0.05) was found in all cases
with respect to the tidal cycles. On the contrary, diurnal nutrient concentrations especially in areas with high flooding
duration (>12 h) were found to be highest during the dry season as opposed to wet season for all nutrients except for SiO32−. The relatively high nutrient laden groundwater outflow into the creek water, coupled with surface runoff events during wet
season, are the two main factors responsible for the elevated nutrients in the creek waters in the absence of river inflow
into the creek. 相似文献
2.
Raphaël N’doua Etilé Aka Marcel Kouassi Maryse N’guessan Aka Marc Pagano Valentin N’douba N’guessan Joël Kouassi 《Hydrobiologia》2009,624(1):171-189
Zooplankton constitutes a sensitive tool for monitoring environmental changes in coastal lagoons; however, the available information
on zooplankton communities is not sufficient to optimize their rational management. The relationships between zooplankton
distribution and environmental factors were studied in a tropical lagoon to test whether the indicator properties of zooplankton
assemblages could be used to monitor water quality, in a context of expected eutrophication provoked by an increasing anthropogenic
activity. Twenty-one (21) stations were sampled monthly from January to December 2004. The community was composed of 65 taxa
including Copepoda, Rotifera, and Cladocera. Copepoda was the most abundant group (81% of total numbers). The main zooplankton
species were Oithona brevicornis, Acartia clausi, and Brachionus plicatilis. The highest zooplankton abundance (171–175 ind. l−1) was recorded during the long, dry season (February–April) and the lowest (40–45 ind. l−1) during the rainy and the flood periods (June–July). At a spatial level, the lowest abundance was observed in the estuarine
zone. During the dry seasons (December–April and August–September), marine zooplankton taxa were abundant near the channel
of Grand-Lahou, and brackish water taxa dominated in the other sites. Multivariate analyses (Co-inertia) showed that the composition
of zooplanktonic communities and their spatio-temporal variations were mainly controlled by salinity variations closely linked
to the climatic and hydrological context. The role of the trophic state on zooplankton communities could not be clearly evidenced.
Our results and a comparison with previous studies in the neighboring, highly polluted Ebrié Lagoon suggest that the ratio
between Oithona and Acartia abundance could be used as biological indicator for the water quality.
Handling editor: S. I. Dodson 相似文献
3.
Estimates of biomass and primary productivity in a high-altitude maple forest of the west central Himalayas 总被引:4,自引:0,他引:4
S. C. Garkoti 《Ecological Research》2008,23(1):41-49
The paper describes the biomass and productivity of maple (Acer cappadocicum) forest occurring at an altitude of 2,750 m in the west central Himalayas. Total vegetation biomass was 308.3 t ha−1, of which the tree layer contributed the most, followed by herbs and shrubs. The seasonal forest-floor litter mass varied
between 5.4 t ha−1 (in rainy season) and 6.6 t ha−1 (in winter season). The annual litter fall was 6.2 t ha−1, of which leaf litter contributed the largest part (59% of the total litter fall). Net primary productivity of total vegetation
was 19.5 t ha−1 year−1. The production efficiency of leaves (net primary productivity/leaf mass) was markedly higher (2.9 g g−1 foliage mass year−1) than those of the low-altitude forests of the region. 相似文献
4.
The estuarine red alga,Bostrychia radicans, was subjected to osmotic stresses ranging from hypo-osmotic (9.9‰) to hyperosmotic conditions (37.4‰). The growth rate decreased
with increasing salinities and showed a maximum in a mesohaline medium, while the photosynthetic rate and the chlorophyll
a content increased under hyper-osmotic conditions. The rate of respiration remained constant over the salinity range tested.B. radicans revealed typical characteristics of “shade plants” having a low light compensation point at 3–4 μE m−2 s−1 correlated with a low photon flux density of 70–100 μE m−2 s−1 for saturation of photosynthesis. These physiological properties may explain the success ofB. radicans in estuarine habitats. 相似文献
5.
Vinícius Peruzzi de Oliveira Luiz Fernando Jardim Bento Alex Enrich Prast 《Wetlands Ecology and Management》2011,19(5):389-395
Short-term spatial and temporal heterogeneity of oxygen dynamics and net primary production were studied in a tree day diurnal
variation at a tidal tropical salt flat in the estuarine system of Sepetiba/Guaratiba coastal plain, Rio de Janeiro, Brazil.
Oxygen concentrations were measured in situ with high temporal and spatial resolution oxygen microsensors. The results showed
a remarkable heterogeneity of both oxygen penetration depth (from 0.18 to 0.85 cm) and net primary production (from −0.085
to 0.115 μmol O2 cm−2 s−1) at different stations and sampling periods. Fast variations in abiotic factors like salinity and light due to the variable
rainy weather were possibly the drivers of the high heterogeneity. In conclusion, short-term temporal changes could have a
remarkable influence in sediment microalgae primary production. Not considering these changes can lead to wrong conclusions
concerning the role and importance of sediment microalgae on tidal salt flats. 相似文献
6.
Dynamic of Virioplankton Abundance and Its Environmental Control in the Charente Estuary (France) 总被引:2,自引:0,他引:2
The Charente River provides nutrient- and virus-rich freshwater input to the Marennes Oléron Basin, the largest oyster-producing
region in Europe. To evaluate virioplankton distribution in the Charente Estuary and identify which environmental variables
control dynamic of virioplankton abundance, five stations defined by a salinity gradient (0–0.5, 0.6–5, 13–17, 20–24, and
higher than 30 PSU) were surveyed over a year. Viral abundance was related to bacterioplankton abundance and activities, photosynthetic
pigments, nutrient concentration, and physical parameters (temperature and salinity). On a spatial scale, virus displayed
a decreasing pattern seaward with abundance ranging over the sampling period from 1.4 × 107 to 20.8 × 107 viruses mL−1 making virioplankton the most abundant component of planktonic microorganisms in the Charente Estuary. A good correlation
was found between viral and bacterial abundance (rs = 0.85). Furthermore, bacterial abundance was the most important predictor of viral abundance explaining alone between 66%
(winter) and 76% (summer) of viral variability. However, no relation existed between viral abundance and chlorophyll a. Temporal variations in viral distributions were mainly controlled by temperature through the control of bacterial dynamics.
Spatial variations of viral abundance were influenced by hydrodynamic conditions especially during the winter season where
virioplankton distribution was entirely driven by mixing processes. 相似文献
7.
Sharon M. L. Ewe Evelyn E. Gaiser Daniel L. Childers David Iwaniec Victor H. Rivera-Monroy Robert R. Twilley 《Hydrobiologia》2006,569(1):459-474
We present here a 4-year dataset (2001–2004) on the spatial and temporal patterns of aboveground net primary production (ANPP)
by dominant primary producers (sawgrass, periphyton, mangroves, and seagrasses) along two transects in the oligotrophic Florida
Everglades coastal landscape. The 17 sites of the Florida Coastal Everglades Long Term Ecological Research (FCE LTER) program
are located along fresh-estuarine gradients in Shark River Slough (SRS) and Taylor River/C-111/Florida Bay (TS/Ph) basins
that drain the western and southern Everglades, respectively. Within the SRS basin, sawgrass and periphyton ANPP did not differ
significantly among sites but mangrove ANPP was highest at the site nearest the Gulf of Mexico. In the southern Everglades
transect, there was a productivity peak in sawgrass and periphyton at the upper estuarine ecotone within Taylor River but
no trends were observed in the C-111 Basin for either primary producer. Over the 4 years, average sawgrass ANPP in both basins
ranged from 255 to 606 g m−2 year−1. Average periphyton productivity at SRS and TS/Ph was 17–68 g C m−2 year−1 and 342–10371 g C m−2 year−1, respectively. Mangrove productivity ranged from 340 g m−2 year−1 at Taylor River to 2208 g m−2 year−1 at the lower estuarine Shark River site. Average Thalassia testudinum productivity ranged from 91 to 396 g m−2 year−1 and was 4-fold greater at the site nearest the Gulf of Mexico than in eastern Florida Bay. There were no differences in periphyton
productivity at Florida Bay. Interannual comparisons revealed no significant differences within each primary producer at either
SRS or TS/Ph with the exception of sawgrass at SRS and the C−111 Basin. Future research will address difficulties in assessing
and comparing ANPP of different primary producers along gradients as well as the significance of belowground production to
the total productivity of this ecosystem. 相似文献
8.
Checo Colón-Gaud Scot Peterson Matt R. Whiles Susan S. Kilham Karen R. Lips Cathy M. Pringle 《Hydrobiologia》2008,603(1):301-312
Allochthonous inputs of detritus represent an important energy source for streams in forested regions, but dynamics of these
materials are not well studied in neotropical headwater streams. As part of the tropical amphibian declines in streams (TADS)
project, we quantified benthic organic matter standing stocks and organic seston dynamics in four Panamanian headwater streams,
two with (pre-amphibian decline) and two without (post-decline) healthy amphibian assemblages. We also measured direct litterfall
and lateral litter inputs in two of these streams. Continuous litterfall and monthly benthic samples were collected for 1 year,
and seston was collected 1–3 times/month for 1 year at or near baseflow. Direct litterfall was similar between the two streams
examined, ranging from 934–1,137 g DM m−2 y−1. Lateral inputs were lower, ranging from 140–187 g DM m−1 y−1. Dead leaves (57–60%), wood (24–29%), and green leaves (8–9%) contributed most to inputs, and total inputs were generally
higher during the rainy season. Annual habitat-weighted benthic organic matter standing stocks ranged from 101–171 g AFDM
m−2 across the four study reaches, with ∼4 × higher values in pools compared to erosional habitats. Total benthic organic matter
(BOM) values did not change appreciably with season, but coarse particulate organic matter (CPOM, >1 mm) generally decreased
and very fine particulate organic matter (VFPOM, 1.6–250 μm) generally increased during the dry season. Average annual seston
concentrations ranged from 0.2–0.6 mg AFDM l−1 (fine seston, <754 μm >250 μm) and 2.0–4.7 mg AFDM l−1 (very fine, <250 μm >1.6 μm), with very fine particles composing 85–92% of total seston. Quality of fine seston particles
in the two reaches where tadpoles were present was significantly higher (lower C/N) than the two where tadpoles had been severely
reduced (P = 0.0028), suggesting that ongoing amphibian declines in this region are negatively influencing the quality of particles
exported from headwaters. Compared to forested streams in other regions, these systems receive relatively high amounts of
allochthonous litter inputs but have low in-stream storage.
Handling editor: J. Padisak 相似文献
9.
Mesozooplankton community in the Bay of Bengal (India): spatial variability during the summer monsoon 总被引:2,自引:0,他引:2
This study addresses the spatial variability in mesozooplankton biomass and composition in the Central and Western Bay of
Bengal (India) during the summer monsoon season of 2001. Perennially warmer sea surface temperatures (>28°C), stratified top
layer (sea surface salinity, 28–33 psu), high turbidity, and low nutrient concentrations due to weak/null upwelling and light
limitation make the Bay of Bengal a region of low primary productivity. Despite this, mesozooplankton biomass values, i.e.
2.9–104 mg C m−3 in the Central Bay and 1.3–31 mg C m−3 in the Western Bay, observed in the mixed layer (2–51 m) during the summer monsoon were in the same range as reported from
the more productive Arabian Sea. Mesozooplankton biomass was five times and density 18 times greater at stations with signatures
of cold-core eddies, causing a higher spatial heterogeneity in zooplankton distribution. Among the 27 taxonomic groups recorded
during the season, Copepoda was the most abundant group in all samples followed by Chaetognatha. The dominant order of Copepoda,
Calanoida, was represented by 132 species in a total of 163 species recorded. Oncaea venusta was the key copepod species in the Bay. In the Central Bay, the predominant copepod species were carnivorous/omnivorous vis-a-vis
mostly herbivores in the Western Bay. Pleuromamma indica increased to its maximum abundance at 18°N in the Central Bay, coinciding with the lowest dissolved oxygen concentrations.
The Central Bay had higher mesozooplankton biomass, copepod species richness and diversity than in the Western Bay. Although
zooplankton biomass and densities were greater at the eddy stations, correlation between zooplankton and chl a was not statistically significant. It appears that the grazer mesozooplankton rapidly utilize the enhanced phytoplankton
production in cold-core eddies. 相似文献
10.
Darlan de Jesus de Brito Simith Adelson Silva de Souza Cristiana Ramalho Maciel Fernando Araújo Abrunhosa Karen Diele 《Helgoland Marine Research》2012,66(1):77-85
Larvae of many marine decapod crustaceans are released in unpredictable habitats with strong salinity fluctuations during
the breeding season. In an experimental laboratory study, we investigated the influence of seven different salinities (0,
5, 10, 15, 20, 25 and 30) on the survival and development time of fiddler crab zoea larvae, Uca vocator, from northern Brazilian mangroves. The species reproduces during the rainy season when estuarine salinity strongly fluctuates
and often reaches values below 10 and even 5. Salinity significantly affected the survival rate and development period from
hatching to megalopa, while the number of zoeal stages remained constant. In salinities 0 and 5, no larvae reached the second
zoeal stage, but they managed to survive for up to 3 (average of 2.3 days) and 7 days (average of 5.1 days), respectively.
From salinity 10 onwards, the larvae developed to the megalopal stage. However, the survival rate was significantly lower
(5–15%) and development took more time (average of 13.5 days) in salinity 10 than in the remaining salinities (15–30). In
the latter, survival ranged from 80–95% and development took 10–11 days. Given the 100% larval mortality in extremely low
salinities and their increased survival in intermediate and higher salinities, we conclude that U. vocator has a larval ‘export’ strategy with its larvae developing in offshore waters where salinity conditions are more stable and
higher than in mangrove estuaries. Thus, by means of ontogenetic migration, osmotic stress and resulting mortality in estuarine
waters can be avoided. 相似文献
11.
Two variants of open photobioreactors were operated at surface-to-volume ratios up to 170 m−1. The mean values for July and September obtained for photobioreactor PB-1 of 224 m2 culture area (length 28 m, inclination 1.7%, thickness of algal culture layer 6 mm), operated in Třeboň (49∘N), Czech Republic, were: net areal productivity, P
net = 23.5 and 11.1 g dry weight (DW) m−2 d−1; net photosynthetic efficiency (based on PAR – Photosynthetic Active Radiation), η = 6.48 and 5.98%. For photobioreactor PB-2 of 100 m2 culture area (length 100 m, inclination 1.6%, thickness of algal culture layer 8 mm) operated in Southern Greece (Kalamata, 37∘N) the mean values for July and October were: P
net = 32.2 and 18.1 g DW m−2 d−1, η = 5.42 and 6.07%. The growth rate of the alga was practically linear during the fed-batch cultivation regime up to high biomass densities of about 40 g DW L−1, corresponding to an areal density of 240 g DW m−2 in PB-1 and 320 g DW m−2 in PB-2. Night biomass loss (% of the daylight productivity, P
L) caused by respiration of algal cells were: 9–14% in PB-1; 6.6–10.8% in PB-2. About 70% of supplied CO2 was utilized by the algae for photosynthesis. The concentration of dissolved oxygen (DO) increased from about 12 mg L−1 at the beginning to about 35 mg L−1 at the end of the 100 m long path of suspension flow in PB-2 at noon on clear summer days. Dissipation of hydraulic energy and some parameters of turbulence in algal suspension on culture area were estimated quantitatively. 相似文献
12.
Jiří Masojídek Jiří Kopecký Luca Giannelli Giuseppe Torzillo 《Journal of industrial microbiology & biotechnology》2011,38(2):307-317
This work aims to: (1) correlate photochemical activity and productivity, (2) characterize the flow pattern of culture layers
and (3) determine a range of biomass densities for high productivity of the freshwater microalga Chlorella spp., grown outdoors in thin-layer cascade units. Biomass density, irradiance inside culture, pigment content and productivity
were measured in the microalgae cultures. Chlorophyll-fluorescence quenching was monitored in situ (using saturation-pulse
method) to estimate photochemical activities. Photobiochemical activities and growth parameters were studied in cultures of
biomass density between 1 and 47 g L−1. Fluorescence measurements showed that diluted cultures (1–2 g DW L−1) experienced significant photostress due to inhibition of electron transport in the PSII complex. The highest photochemical
activities were achieved in cultures of 6.5–12.5 g DW L−1, which gave a maximum daylight productivity of up to 55 g dry biomass m−2 day−1. A midday depression of maximum PSII photochemical yield (F
v/F
m) of 20–30% compared with morning values in these cultures proved to be compatible with well-performing cultures. Lower or
higher depression of F
v/F
m indicated low-light acclimated or photoinhibited cultures, respectively. A hydrodynamic model of the culture demonstrated
highly turbulent flow allowing rapid light/dark cycles (with frequency of 0.5 s−1) which possibly match the turnover of the photosynthetic apparatus. These results are important from a biotechnological point
of view for optimisation of growth of outdoor microalgae mass cultures under various climatic conditions. 相似文献
13.
Specific growth rates of heterotrophic bacterioplankton have been frequently estimated from in situ bacterial production (BP)
to biomass (BB) ratios, using a series of assumptions that may result in serious discrepancies with values obtained from predator-free
cultures. Here, we used both types of approaches together with a comprehensive assessment of single-cell physiological characteristics
(membrane integrity, nucleic acid content, and active respiration) of coastal bacterioplankton during a complete annual cycle
(February 2007–January 2008) in the southern Bay of Biscay off Xixón, Spain. Both leucine and thymidine incorporation rates
were used in conjunction with empirical tracer to carbon or cells conversion factors (eCFs) to accurately derive BP. Leu and
TdR incorporation rates covaried year-round, as did the corresponding eCFs at 0 and 50 m depth. eCFs peaked in autumn, with
mean annual values close to the theoretical ones (3.4 kg C mol Leu−1 and 2.0 × 1018 cells mol TdR−1). Bacterial abundance (0.2–1.5 × 106 cells L−1) showed a bimodal distribution with maxima in May and October and minima in March. Live (membrane-intact) cells dominated
year-round (79–97%), with high nucleic acid cells (42–88%) and actively respiring bacteria (CTC+, 1–16%) showing distinct
surface maxima in April and July, respectively. BB (557–1,558 mg C m−2) and BP (7–139 mg C m−2 day−1) presented two distinct peaks in spring and autumn, both of similar size due to a strong upwelling event observed in September.
Specific growth rates (0.35–3.8 day−1) were one order of magnitude higher in predator-free incubations than bacterial turnover rates derived from integrated BP:BB
ratios (0.01–0.16 and 0.01–0.09 day−1, for Leu and TdR, respectively) and were not correlated, probably due to a significant contribution of low activity cells
to total standing stocks. The Leu:TdR molar ratio averaged for the water column (6.6–25.5) decreased significantly with higher
integrated BB, indicating that low standing stocks tend to present unbalanced growth. Discrepancies about the true magnitude
of specific growth rates must be solved before fully appreciating the role of bacteria in the ocean carbon cycle. 相似文献
14.
Paul I. Boon 《Microbial ecology》1991,22(1):27-52
Billabongs, lentic waterbodies common to the floodplain of Australian rivers, differ considerably from the lotic riverine
environment in terms of hydrology, physiochemical characteristics, and biological assemblages present. As little is known
regarding the bacterial ecology of billabong habitats, a comparison was made of the bacterial assemblages in the water column
of seven paired river/billabong sites in the Murray-Darling Basin of southeastern Australia. Billabongs supported larger populations
of bacteria (1–157×109 cells liter−1; 11–10,270 μg C liter−1) than did rivers (1–10×109 cells liter−1; 6–143 μg C liter−1). Phospholipid analyses confirmed that billabongs (14–111 μg phospholipid fatty acid liter−1) had larger bacterial populations than rivers (<12 μg liter−1). Bacterial production, measured with3H-leucine, was also greater in billabongs (0.28–3.05 μg C liter−1 hour−1) than rivers (0.05–0.62 μg C liter−1 hour−1). Production calculated from the frequency of dividing cells confirmed this conclusion, and suggested bacterial production
in some billabongs could exceed 100 μg C liter−1 hour−1. An INT-formazan method indicated that usually <25% of bacterial cells were active in either habitat, but this was probably
an underestimate of the bona fide value. Turnover times of glucose were usually shorter in billabongs, and the cell-specific
activity greater for billabong than river assemblages. The factors most likely to be responsible for the differences between
the bacterial assemblages in rivers and billabongs relate to hydrological regime and the availability of organic carbon substrates. 相似文献
15.
Interactions between microbial growth and substrate degradation are important in determining the performance of trickle-bed
bioreactors (TBB), especially when salt is added to reduce biomass formation in order to alleviate media clogging. This study
was aimed at quantifying salinity effects on bacterial growth and substrate degradation, and at acquiring kinetic information
in order to improve the design and operation of TBB. Experiment works began by cultivating a mixed culture in a chemostat
reactor receiving artificial influent containing a mixture of benzene, toluene, and xylene (BTX), followed by using the enrichment
culture to degrade the individual BTX substrates under a particular salinity, which ranged 0–50 g l−1 in batch mode. Then, the measured concentrations of biomass and residual substrate versus time were analyzed with the microbial
kinetics; moreover, the obtained microbial kinetic constants under various salinities were modeled using noncompetitive inhibition
kinetics. For the three substrates the observed bacterial yields appeared to be decreased from 0.51–0.74 to 0.20–0.22 mg mg−1 and the maximum specific rate of substrate utilization,
declined from 0.25–0.42 to 0.07–0.11 h−1, as the salinity increased from 0 to 50 NaCl g l−1. The NaCl acted as noncompetitive inhibitor, where the modeling inhibitions of the coefficients, K
T(S), were 22.7–29.7 g l−1 for substrate degradation and K
T(μ), 13.0–19.0 g l−1, for biomass formation. The calculated ratios for the bacterial maintenance rate, m
S, to
further indicated that the percentage energy spent on maintenance increased from 19–24 to 86–91% as salinity level increased
from 0 to 50 g l−1. These results revealed that the bacterial growth was more inhibited than substrate degradation by the BTX oxidizers under
the tested salinity levels. The findings from this study demonstrate the potential of applying NaCl salt to control excessive
biomass formation in biotrickling filters. 相似文献
16.
Abstract
The investigation of the bacterial community in the Kühw?rter Wasser, a macrophyte-dominated arm of the River Danube backwater
system near Vienna, revealed that variation in microbial densities and biomass could be related to a characteristic sequence
in morphotype composition over the seasons. Maximal bacterial cell numbers and biomass occured in early summer, with values
of up to 9 × 109 cells l−1 and 122 μg C l−1, respectively, caused by a massive increase of vibrio-shaped cells. On the other hand, in early spring, filamentous bacteria
were responsible for a marked increase in bacterial biomass, making up 40% of the total bacterial biomass. Over the year,
rod-shaped cells were the dominating morphotype, while the biomass of cocci was rather negligible. In winter, cell numbers
and biomass showed minimal values with 2.0 × 109 cells l−1 and 28 μg C l−1, respectively, and bacteria were considered to be substrate and temperature limited during this period. Saturation values
of the incorporation of 3H-thymidine into DNA, for the estimation of bacterial secondary production, varied seasonally, ranging from 5 nm to 40 nm. Thus, saturation experiments needed to be conducted on a regular basis. Also, the amount of labeled thymidine in the DNA,
as a percentage of labeled thymidine in the TCA precipitate, varied over the year. Minimum values of 45% were recorded during
the cold season, while maximum values of 75–80% at the beginning of June coincided with high chlorophyll a values and minimal K
m-values derived from saturation experiments. The potential role of the nitrogen-rich nucleoside thymidine as a readily utilizable
substrate for bacteria during labeling experiments, under varying conditions of substrate availability, is discussed. Bacterial
secondary production rates ranged from 0.3 μg C l−1 h−1 in winter to values of 10 μg C l−1 h−1 in August, where phytoplanktonic biomass reached the summer maximum, and bacterial biomass was calculated to be renewed 3
times per day. An estimation of the bacterial carbon demand showed that for the major part of the year, with the exception
of early spring, the bacterioplankton community in the Kühw?rter Wasser was dependent on carbon sources other than phytoplanktonic
primary production.
Received: 22 March 1996; Revised: 1 August 1996 相似文献
17.
The salinity tolerances of four species of small fishes native to the Murray-Darling river system were measured. Slow acclimation
LD50s were 43.7 ± 1.7 g L−1 for Craterocephalus stercusmuscarum Gunther, 38.0 ± 1.1 g L−1 for Hypseleotris klunzingeri (Ogilby), 58.7 ± 0.9 g L−1 for Retropinna semoni (Weber), and 29.8 ± 0.7 g L−1 for Melanotaenia splendida (Castelnau). The salinity tolerance of M. splendida was also measured by direct transfer, providing an estimated LD50 (infinite exposure time) of 20.8 g L−1, ∼ 70% of the slow acclimation value. Results suggest that at least adults of the species studied are under no threat from
present or foreseeable salinities in the Murray River. 相似文献
18.
Tropical upper montane forests usually comprise trees of small stature with a relatively low aboveground productivity. In
contrast to this rule, in the Cordillera de Talamanca (Costa Rica), tall trees (>35 m in height and more than 60 cm in diameter)
are characteristic for the upper montane old-growth oak forests which are growing at an altitude of almost 3,000 m close to
the alpine timberline. For these exceptional forests, productivity data are not yet available. In this study, we analyzed
litterfall and its components (tree leaves, litter of epiphytic vascular and non-vascular plants, mistletoes, twigs and other
canopy debris) in three forest stands belonging to different successional stages and related seasonal changes in litterfall
to micrometeorological variables. The studied stands were early-successional forest (10–15-year-old), mid-successional forest
(40-year-old), and old-growth forest. The stands are dominated by Quercus copeyensis and are located at 2,900-m altitude. Total litterfall was highest in the mid-successional forest (1,720 g m−2 y−1), and reached 1,288 g m−2 y−1 in the old-growth forest and 934 g m−2 y−1 in the early-successional forest. Litter mass was dominated by leaves in all stages (56–84% of total litterfall). In the old-growth
forest, however, twigs and small canopy debris particles (33%), epiphytes (6%), and mistletoes (5%) also contributed substantially
to litter mass. Leaf litterfall showed a clear seasonal pattern with a negative correlation to monthly precipitation and highest
values in the dry season (January–April). However, the strongest correlation existed with minimum air temperature (negative),
probably because temperatures already dropped at the end of the rainy season, when precipitation had not yet declined and
leaf shedding already increased. In contrast, litterfall of epiphyte mass, and twigs and other debris was mostly dependent
on occasional strong winds. We conclude that the upper montane oak forests of the Cordillera de Talamanca are exceptional
with respect to the large tree size and the relatively high productivity as indicated by litterfall. Litter mass was especially
high in the mid-successional and old-growth forests, where the observed annual totals are among the highest recorded for tropical
forests so far. 相似文献
19.
Fine root vertical distribution and temporal dynamics in mature stands of two enset (Enset ventricosum Welw Cheesman) clones 总被引:2,自引:0,他引:2
Quantification of the role of fine roots in the biological cycle of nutrients necessitates understanding root distribution,
estimating root biomass, turnover rate and nutrient concentrations, and the dynamics of these parameters in perennial systems.
Temporal dynamics, vertical distribution, annual production and turnover, and nitrogen use of fine roots (≤2 mm in diameter)
were studied in mature (5-year-old) stands of two enset (Ensete ventricosum) clones using the in-growth bag technique. Live fine root mass generally decreased with increasing depth across all seasons
except the dry period. Except for the dry period, more than 70% of the fine root mass was in the above 0-20 cm depth, and
the fine root mass in the upper 0–10 cm depth was significantly higher than in the lowest depth (20–30 cm). Live fine root
mass showed a seasonal peak at the end of the major rainy season but fell to its lowest value during the dry or short rainy
season. The difference between the peak and low periods were significant (p ≤ 0.05). Fine root nitrogen (N) use showed significant seasonal variation where the mean monthly fine root N use was highest
during the major rainy season. There were significant effects on N use due to depths and in-growth periods, but not due to
clones. Enset fine root production and turnover ranged from 2,339 to 2,451 kg ha−1 year−1 and from 1.55 to 1.80 year−1, respectively. Root N return, calculated from fine root turnover, was estimated at 64–65 kg ha−1 year−1. Fine root production, vertical distribution and temporal dynamics may be related to moisture variations and nutrient (N)
fluxes among seasons and along the soil depth. The study showed that fine root production and turnover can contribute considerably
to the carbon and nitrogen economy of mature enset plots. 相似文献
20.
Characterization of phosphorus fractions in the sediments of a tropical intertidal mangrove ecosystem 总被引:2,自引:0,他引:2
Solid phases of phosphorus fractions in the surface and core sediments were studied to understand the biogeochemical cycling
and bioavailability of phosphorus in the Pichavaram intertidal mangrove sediments of India. Total P in surface and core sediments
ranged between 451–552 and 459–736 μg g−1 respectively and Fe bound P was the dominant fraction. Low levels of Fe bound P in the mangrove zone than the two estuarine
zones may be because of high salinity inhibition of phosphate adsorption onto the Fe-oxides/hydroxides. Post-depositional
reorganization of P was observed in surface sediments, converting organic P and Fe bound P into the authigenic P. High levels
of organic P in the mangrove zone is primarily due to intensive cycling and degradation of organic matter and adsorption of
phosphate on the organic molecules. The burial rates and regeneration efficiency of P in the intertidal mangrove ecosystem
ranged from 5.41 to 7.27 μmol P cm−2 year−1 and 0.122 to 0.233 μmol P cm−2 year−1, respectively. High burial efficiency (≈99%) of P proves the earlier observation of limiting nature of P for the biological
productivity. Further, bioavailable P (exchangeable P + Fe bound P + organic P) constituted a considerable proportion of sedimentary
P pool of which an average accounted for 55 and 50% in surface and core sediments respectively. The results indicate that
significant amount of P is locked in sediments in the form of authigenic P and detrital P which makes P as a limiting nutrient
for the biological productivity. 相似文献