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1.
Spatial changes of small nanoplankton (2–10 μm) were investigated in relation to sea-ice conditions, hydrography and receding
ice processes in the Ross Sea (Antarctica) during spring 1994. Abundance and biomass of heterotrophic and autotrophic nanoplankton,
as well as bacterioplankton, were determined along a south-north transect from the open waters polynya towards the pack ice.
Autotrophic and heterotrophic nanoplankton biomass ranged from 758 to 4570 mgC m−2 and from 3 to 387 mgC m−2, respectively. Heterotrophic nanoplankton accounted, on average, for about 9% of the total (i.e. autotrophic plus heterotrophic)
nanoplankton biomass. The size structure of both auto- and heterotrophic nanoplankton in the Ross Sea continental shelf receding
ice edge was different from that of nanoplankton associated with the shelf break and open Antarctic ice-edge area. Generally,
the highest heterotrophic biomass was found in the pack-ice zone on the continental shelf, while the highest heterotrophic
contribution to the total nanoplankton biomass (up to 25%) was encountered at the shelf break where phytoplankton was largely
dominated by 2- to 3-μm-size cells.
Accepted: 2 May 1999 相似文献
2.
We conducted a 1-year survey in two humic shallow lakes from the floodplain of the Lower Paraná River, Laguna Grande Lake (LGL) and a relictual oxbow lake (ROL). We aimed to test two hypotheses: (1) the efficiency in light use of picoplankton (0.2–3 μm) is greater as light restriction increases and (2) the contribution of picoplankton to the total productivity is higher when the total photosynthetic biomass is lower. We performed P–E curves for picoplankton and nano- and microplankton (>3 μm) using the 14C assimilation technique. The light environments of the water bodies differed mainly owing to the development of free floating plants on the surface of the ROL and the dominance of phytoplankton in LGL. Primary productivity patterns in LGL were seasonality driven whilst in the ROL they were related to the coverage of floating macrophytes, which promoted light limitation and a lower productivity. In LGL, nano- and microplankton were in general more productive and the relative contribution of picoplankton to the total phytoplankton production decreased with the increase in total photosynthetic biomass. Hence, our study extends previously observed patterns to subtropical shallow lakes, where seasonality and free floating plants may influence the dynamics of phytoplankton production. 相似文献
3.
Production rates, abundance, chlorophyll a (Chl a) concentrations and pigment composition were measured for three size classes (<2 μm, 2–11 μm and >11 μm) of phytoplankton
from May to December 2000 in deep, mesotrophic, alpine lake Mondsee in Austria. The study focuses on differences among phytoplankton
size fractions characterised by their surface area to volume ratio ([mm2 l−1: mm3l−1]), pigment distribution patterns and photosynthetic rates. Particular attention was paid to autotrophic picophytoplankton
(APP, fraction <2 μm) since this size fraction differed significantly from the two larger size fractions. Among the three
fractions, APP showed the highest surface area to volume ratios and a high persistence in the pattern of lipophilic pigments
between temporarily and spatially successive samples (about 80% similarity of pigment composition between samples over seasons
and depths). The epilimnetic abundance of APP varied seasonally with an annual maximum of 180 × 103 cells ml−1 in June (at 4–9 m). The minimum (October at 12 m) was more than an order of magnitude lower (4.9 × 103 ml−1). APP peaked during autumn and contributed between 24% and 42% to the total area-integrated Chl a (10–23 mg m−2) and between 16% and 58% to total area-integrated production (5–64 mg m−2 h−1) throughout seasons. 相似文献
4.
Luz Allende Guillermo Tell Horacio Zagarese Ana Torremorell Gonzalo Pérez José Bustingorry Roberto Escaray Irina Izaguirre 《Hydrobiologia》2009,624(1):45-60
Shallow lakes often alternate between two possible states: one clear with submerged macrophytes, and another one turbid, dominated
by phytoplankton. A third type of shallow lakes, the inorganic turbid, result from high contents of suspended inorganic material,
and is characterized by low phytoplankton biomass and macrophytes absence. In our survey, the structure and photosynthetic
properties (based on 14C method) of phytoplankton were related to environmental conditions in these three types of lakes in the Pampa Plain. The
underwater light climate was characterized. Clear-vegetated lakes were more transparent (K
d 4.5–7.7 m−1), had high DOC concentrations (>45 mg l−1), low phytoplankton Chl a (1.6–2.7 μg l−1) dominated by nanoflagellates. Phytoplankton productivity and photosynthetic efficiency (α ~ 0.03 mgC mgChla
−1 h−1 W−1 m2) were relatively low. Inorganic-turbid lakes showed highest K
d values (59.8–61.4 m−1), lowest phytoplankton densities (dominated by Bacillariophyta), and Chl a ranged from 14.6 to 18.3 μg l−1. Phytoplankton-turbid lakes showed, in general, high K
d (4.9–58.5 m−1) due to their high phytoplankton abundances. These lakes exhibited the highest Chl a values (14.2–125.7 μg l−1), and the highest productivities and efficiencies (maximum 0.56 mgC mgChla
−1 h−1 W−1 m2). Autotrophic picoplankton abundance, dominated by ficocianine-rich picocyanobacteria, differed among the shallow lakes independently
of their type (0.086 × 105–41.7 × 105 cells ml−1). This article provides a complete characterization of phytoplankton structure (all size fractions), and primary production
of the three types of lakes from the Pampa Plain, one of the richest areas in shallow lakes from South America.
Handling editor: J. Padisak 相似文献
5.
This study has two main objectives, the first being the determination of net phytoplankton primary production to explain the
phytoplankton’s function in a wetland carbon cycle, while the second objective is to relate this function with the phytoplankton
assemblage composition. The annual variation in the phytoplankton production was monitored monthly for more than a year (2007–2008)
in the semiarid eutrophic, hydrologically-perturbed “Tablas de Daimiel” National Park wetland. The phytoplankton fraction
considered in this study comprised all organisms between the size 3 and 100 μm. The total biomass of phytoplankton was obtained
by counting algae and calculating their volume, while net primary production and respiration were quantified by in situ incubations
with the Winkler method. The respiration ranged from undetectable to 0.07 mgO2 l−1 h−1; net photosynthesis reached 0.20 mgO2 l−1 h−1. Net primary production was maximum at the end of the warm period (October 2007), and other peaks occurred at the start of
summer (July 2007) or spring (March 2008). When maximum production took place, phytoplankton was mainly composed of small
fast-growing chlorophytes (Tetraselmis cf. fontiana or Chlamydomonas sp.), in addition to some of the large, S-strategist algae (Peridinium
umbonatum, Microcystis flos-aquae, Euglena sp.). The phytoplankton metabolism in “Tablas de Daimiel” was autotrophic as a whole due to changing contributions of algal
groups. Only chlorophyte biomass was statistically related to net primary production. The conclusion reached is that this
shallow eutrophic semiarid wetland possessed an annual net autotrophic production of phytoplankton fraction resulting from
the small, fast-growing algae enhanced by hydrological perturbations that interrupted the autogenic course of S strategists. 相似文献
6.
Primary production by phytoplankton in the eutrophic Mikawa Bay, Japan, was studied by simultaneous measurements of natural
carbon isotope ratio (δ
13C) and short-term carbon uptake rates (13C tracer study) of size-fractionated nannoplankton (<10 μm) and net plankton (>10 μm) samples. Short-term photosynthetic rates,
which represent the physiological state of algae, were variable regardless of standing stock sizes. Theδ
13C values of particulate organic carbon (POC) in June and July displayed horizontal variations for both the net plankton fraction
(−19.8 to −12.7‰) and the nannoplankton fraction (−22.0 to −12.8‰). For both fractions, low concentrations of POC had more
negativeδ
13C values (−22 to −18‰). Highδ
13C values for the net plankton were found when POC concentrations were much higher, due to red tide. This suggests that the
increase in algal standing crop for the net plankton fraction resulted from accelerated photosynthetic activity. However the
nannoplankton fractions with higher POC values have relatively lowδ
13C values. 相似文献
7.
The influence of brackish phytoplankton cell classes upon the response of urea decomposition was investigated in Lake Nakaumi.
The urea decomposition rate was 5 to 350 μmol urea m−3 h−1 in the light and 3 to 137 μmol urea m−3 h−1 in the dark. The urea decomposition rates in the light were obviously higher than in the dark. An extremely high rate (350
μmol urea m−3 h−1) was observed in Yonago Bay. The rate in the smaller fraction (<5 μm) exceeded that in the middle (5–25 μm) and larger fractions
(>25 μm). The chlorophyll- and photosynthesis-specific rates for urea decomposition in the light were 0.5 to 3.9 μmol urea
mg chl.a
−1 h−1 and 0.3 to 1.3 μmol urea mg photo.C−1. The specific urea decomposing activities were higher in the smaller fraction than in the other two fractions. The present
results suggest that in brackish waters urea decomposition occurred with coupling to the standing crop and photosynthetic
activity of phytoplankton.
Received: May 22, 1999 / Accepted: August 15, 1999 相似文献
8.
Effects of hydrologic and water quality drivers on periphyton dynamics in the southern Everglades 总被引:2,自引:2,他引:0
David M. Iwaniec Daniel L. Childers Damon Rondeau Christopher J. Madden Colin Saunders 《Hydrobiologia》2006,569(1):223-235
Everglades periphyton mats are tightly-coupled autotrophic (algae and cyanobacteria) and heterotrophic (eubacteria, fungi
and microinvertebrates) microbial assemblages. We investigated the effect of water column total phosphorus and nitrogen concentrations,
water depth and hydroperiod on periphyton of net production, respiration, nutrient content, and biomass. Our study sites were
located along four transects that extended southward with freshwater sheetflow through sawgrass-dominated marsh. The water
source for two of the transects were canal-driven and anchored at canal inputs. The two other transects were rain-driven (ombrotrophic)
and began in sawgrass-dominated marsh. Periphyton dynamics were examined for upstream and downstream effects within and across
the four transects. Although all study sites were characterized as short hydroperiod and phosphorus-limited oligotrophic,
they represent gradients of hydrologic regime, water source and water quality of the southern Everglades. Average periphyton
net production of 1.08 mg C AFDW−1 h−1 and periphyton whole system respiration of 0.38 mg C AFDW−1 h−1 rates were net autotrophic. Biomass was generally highest at ombrotrophic sites and sites downstream of canal inputs. Mean
biomass over all our study sites was high, 1517.30 g AFDW m−2. Periphyton was phosphorus-limited. Average periphyton total phosphorus content was 137.15 μg P g−1 and average periphyton total N:P ratio was 192:1. Periphyton N:P was a sensitive indicator of water source. Even at extremely
low mean water total phosphorus concentrations ( ≤ 0.21 μmol l−1), we found canal source effects on periphyton dynamics at sites adjacent to canal inputs, but not downstream of inflows.
These canal source effects were most pronounced at the onset of wet season with initial rewetting. Spatial and temporal variability
in periphyton dynamics could not solely be ascribed to water quality, but was often associated with both hydrology and water
source. 相似文献
9.
An investigation into the changing phytoplankton biomass and total water column production during autumn sea ice formation
in the eastern Weddell Sea, Antarctica showed reduced biomass concentrations and extremely low daily primary production. Mean
chlorophyll-a concentration for the entire study period was extremely low, 0.15±0.01 mg.m−3 with a maximum of 0.35 mg.m−3 found along the first transect to the east of the grid. Areas of low biomass were identified as those either associated with
heavy grazing or with deep mixing and corresponding low light levels. In most cases phytoplankton in the <20-μm size classes
dominated. Integrated biomass to 100 m ranged from 7.1 to 28.0 mg.m−2 and correlated positively with surface chlorophyll-a concentrations. Mean PBmax (photosynthetic capacity) and αB (initial slope of the photosynthesis-irradiance curve) were 1.25±0.19 mgC. mgChla
−1.h−1 and 0.042±0.009 mgC.mgChla
−1.h−1.(μmol.m−2.s−1)−1 respectively. The mean index of photoadaptation,I
k, was 32.2±4.0 μmol.m−2.s−1 and photoinhibition was found in all cases. Primary production was integrated to the critical depth (Z
cr) at each production station and ranged from 15.6 to 41.5 mgC.m−2.d−1. It appears that, other than grazing intensity, the relationship between the critical depth and the mixing depth (Z
mix) is an important factor as, ultimately, light availability due both to the late season and growing sea ice cover severely
limits production during the austral autumn. 相似文献
10.
Amâncio Sara Rebordão João Paulo Chaves Maria Manuela 《Plant Cell, Tissue and Organ Culture》1999,58(1):31-37
Grapevine plantlets multiplied in vitro were acclimatized at 40 or 90 μmol m−2 s−1 photon flux density for 12 or 16 h per day, respectively. In the high-light regime a decrease in total chlorophyll and an
increase in chlorophyll a/chlorophyll b ratio occurred. However, at high-light intensity lower photosynthetic capacities and higher apparent photosynthesis were
measured than at the low-light regime. In leaves expanded during acclimatization, the light compensation point was higher
in plantlets under high-light while quantum yield was higher in low-light conditions. High-light also gave rise to an increase
in carbohydrate concentration. As a whole, the results suggest that high-light increases carbon assimilation and growth although
with a low investment in the photosynthetic apparatus.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
We compared on eight dates during the ice-free period physicochemical properties and rates of phytoplankton and epipelic primary
production in six arctic lakes dominated by soft bottom substrate. Lakes were classified as shallow ( < 2.5 m), intermediate in depth (2.5 m < < 4.5 m), and deep ( > 4.5 m), with each depth category represented by two lakes. Although shallow lakes circulated freely and intermediate and
deep lakes stratified thermally for the entire summer, dissolved oxygen concentrations were always >70% of saturation values.
Soluble reactive phosphorus and dissolved inorganic nitrogen (DIN = NO3
−–N + NH4
+–N) were consistently below the detection limit (0.05 μmol l−1) in five lakes. However, one lake shallow lake (GTH 99) periodically showed elevated values of DIN (17 μmol l−1), total-P (0.29 μmol l−1), and total-N (33 μmol l−1), suggesting wind-generated sediment resuspension. Due to increased nutrient availability or entrainment of microphytobenthos,
GTH 99 showed the highest average volume-based values of phytoplankton chlorophyll a (chl a) and primary production, which for the six lakes ranged from 1.0 to 2.9 μg l−1 and 0.7–3.8 μmol C l−1 day−1. Overall, however, increased resulted in increased area-based values of phytoplankton chl a and primary production, with mean values for the three lake classes ranging from 3.6 to 6.1 mg chl a m−2 and 3.2–5.8 mmol C m−2 day−1. Average values of epipelic chl a ranged from 131 to 549 mg m−2 for the three depth classes, but levels were not significantly different due to high spatial variability. However, average
epipelic primary production was significantly higher in shallow lakes (12.2 mmol C m−2 day−1) than in intermediate and deep lakes (3.4 and 2.4 mmol C m−2 day−1). Total primary production (6.7–15.4 mmol C m−2 day−1) and percent contribution of the epipelon (31–66%) were inversely related to mean depth, such that values for both variables
were significantly higher in shallow lakes than in intermediate or deep lakes.
Handling editor: L. Naselli-Flores 相似文献
12.
We report the effect of UV-B radiation (0.8 ± 0.1 mW cm−2) and UV-B radiation supplemented with low-intensity PAR (∼80 μmol photons m−2 s−1) on the photosynthesis, photosynthetic pigments, phosphoglycolipids, oxidative damage, enzymatic antioxidants, and UV-absorbing
compounds in Phormidium tenue, a marine cyanobacterium. UV-B radiation resulted in a decline in photosynthesis and photosynthetic pigments leading to lower
biomass. P. tenue synthesized UV-absorbing compounds like mycosporine-like amino acids (MAAs) and scytonemin in response to UV-B radiation.
Quantity of MAAs and scytonemin was higher when UV-B was supplemented with low-level PAR. UV-B treatment also resulted in
quantitative changes in phosphoglycolipids of the membrane. The UV-B treatment resulted in a slight increase in the level
of peroxidation of cell membrane and very little increase in the activity of superoxide dismutase (SOD). Results indicate
that UV-B affected photosynthesis and that the main protective system was the synthesis of MAAs and scytonemin-like compounds
rather than antioxidant enzymes such as SOD. 相似文献
13.
Photosynthetic Response of Carrots to Varying Irradiances 总被引:7,自引:3,他引:4
Response to irradiance of leaf net photosynthetic rates (P
N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled
environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m−2 s−1 at 20 °C and 350 μmol (CO2) mol−1(air). The values of P
N were fitted to a rectangular hyperbolic nonlinear regression model. P
N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P
N than CC. None of the cultivars reached saturation at 1 000 μmol m−2 s−1. The predicted P
N at saturation (P
Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO2) m−2 s−1, respectively. The compensation irradiance (I
c) occurred at 54 μmol m−2 s−1 for Cascade, 36 μmol m−2 s−1 for CC, 45 μmol m−2 s−1 for Oranza, and 25 μmol m−2 s−1 for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO2) mol−1(PAR) and did not differ. Dark respiration varied from 2.66 μmol m−2 s−1 for Cascade to 0.85 μmol m−2 s−1 for RCC. As P
N increased with PAR, intercellular CO2 decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between
600 and 800 μmol m−2 s−1 followed by a steep decline resulting in sharp increases in water use efficiency.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
Norbert Kemka Serge Hubert Zébazé Togouet Robert Patrick Djogo Kinfack Moïse Nola Samuel Foto Menbohan Thomas Njiné 《Hydrobiologia》2009,625(1):91-103
This study carried out within the framework of a multi-disciplinary project, aimed at highlighting the fundamental processes
governing the functioning of the hypertrophic Yaoundé Municipal Lake. It was based on the hypothesis that, even within a small
range of lake trophic status, important variations can occur in the species composition, biomass and photosynthetic activity
of the phytoplankton size-fractions. For this purpose, samples were taken at weekly intervals from November 1996 to December
1997 at a fixed set of depths in the water column. Spatial-temporal fluctuations of some physical–chemical variables, associated
with biological variables such as phytoplankton size-class species composition, phytoplankton size-class biomass, phytoplankton
primary production and chlorophyll-a were analysed. The water transparency was low and rarely exceeded 100 cm. Conductivity values relatively higher increased
generally from the top to the lake bottom. The oxygen deficiency, and sometimes anoxia, recorded from 2.5 m depth resulted
in high quantities of ammonium nitrogen. Total phosphorus and total Kjeldahl nitrogen concentrations were characteristics
of hypertrophic lakes. The fertility of this biotope favoured the development of a high phytoplanktonic community with remarkable
physiological adaptations to the variations of the nutritive potentials of the lake, characterized by the size-structure of
these organisms. Cells of small size (<12 μm) contributed up to 11.42% of the total phytoplanktonic biomass. Species with
average size (12–45 μm), dominated by Chlamydomonas spp., represented a more significant contribution reaching up to 69.85%, whereas the cells of big size (>45 μm), mainly Euglenophyta,
maintained the relatively most important biomass, accounting for up to 89.85% of the total phytoplanktonic biomass. Chlorophyll-a concentrations are among the highest reported for both fresh water and sea water, being a consequence of high proportions
of Chlorophyta and Euglenophyta. This led to intense phytoplanktonic photosynthetic activity which continued throughout the
year, even though it was confined to the upmost first meter of the water column. Analyses pointed out the allogenic nature
of the functioning of this urban lake ecosystem, due to a poor waste management on the surrounding landscape.
Handling editor: J. Padisak 相似文献
15.
Primary production of organic matter and phototrophic communities in the soda lakes of the Kulunda steppe (Altai krai) 总被引:1,自引:0,他引:1
E. I. Kompantseva A. V. Komova I. I. Rusanov N. V. Pimenov D. Yu. Sorokin 《Microbiology》2009,78(5):643-649
The rates of photosynthesis and dark CO2 fixation were determined in 12 soda lakes of the Kulunda steppe. Characterization of the phototrophic communities was given,
and the cell numbers of anoxygenic phototrophic bacteria (APB) were determined. The photosynthetic production in different
lakes was substantially different, constituting from 0.01 to 1.32 g C m−2 day−1. The main part of carbon dioxide was assimilated in the process of oxygenic photosynthesis. Anoxygenic photosynthesis was
recorded only in 5 of the 12 lakes studied. Its values varied between 0.06 and 0.42 g C m−2 day−1, constituting from 8 to 34% of the total photosynthetic activity. Anoxygenic photosynthesis was revealed in the lakes where
the number of APB reached 107–109 CFU cm−3. Dark CO2 fixation constituted 0.01–0.15 g C m−2 day−1. Positive correlation was observed between the primary production value and water alkalinity. No relationship between productivity
and water mineralization was revealed in the 30–200 g l−1 range, whereas an increase in salinity above 200 g l−1 suppressed the photosynthetic activity. The mechanisms of influence of the environmental factors on the rate of photosynthesis
are discussed. 相似文献
16.
Ciliate and bacterial densities and their link with eutrophication were studied in fourteen shallow lakes in northwest Spain.
Total phosphorus (TP) in these lakes varied between 30 μg l−1 and 925 μg l−1 and chlorophyll a concentration (chla) between 0.5 μg l−1 and 107 μg l−1. Bacterial abundance ranged from 1 × 106 to 14 × 106 cells ml−1, while ciliate abundance ranged from 0.6 cells ml−1 to 229 cells ml−1. Lakes were classified into three trophic types from their TP and chla concentrations. Bacterial abundance was significantly
correlated with trophic type, as well as with TP and with chla separately, whereas ciliate abundance was only correlated with
chla. No significant relationship could be established between bacterial and ciliate abundance across the trophic gradient.
A general pattern was observed in the ratios of bacterial abundance to TP and chla concentrations, of decreasing ratios with
increases in the nutrient loading. This pattern was not found for ciliates. The dominant zooplankton group in 13 of the 14
lakes studied was Rotifera, which accounted for a mean of 71% of total zooplankton abundance (41% of zooplankton biomass).
The positive correlation between bacteria and ciliates with this group, and the absence of any relationship with Cladocera
suggest that top down control by cladocerans was weaker in our lakes than previously shown in northern European shallow lakes.
Rotifers could be important predators of bacteria in the high-nutrient lakes of our study. Higher slopes of regressions on
bacterial abundance towards the hypertrophic range indicate that top-down control was weaker in our lakes than in northern
European shallow lakes. 相似文献
17.
The ability of photoautotrophic picoplankton Synechococcus to degrade urea was examined in the euphotic zone of Lake Biwa. Samples were divided into pico (0.2–2.0 μm) and larger (>2.0
μm) size fractions by filtration. The rates of urea degradation (the sum of the rates of incorporation of carbon into phytoplankton
cells and of liberation of CO2 into water) measured by radiocarbon urea were 8 and 17 μmol urea m−3 day−1 in June and July, respectively, for the picophytoplankton in the surface water, and 196 and 96 μmol urea m−3 day−1, respectively for the larger phytoplankton. The rates decreased with depth, somewhat similar to the vertical profiles of
the photosynthetic rate. The urea degradation rates were obviously high under light conditions. In daylight, urea was degraded
into two phases, carbon incorporation and CO2 liberation, whereas in the dark it was degraded only into the CO2 liberation phase. The contribution of picophytoplankton to total phytoplankton in urea degradation was high in the subsurface
to lower euphotic layer. Urea degradation activity was higher in the picophytoplankton fraction than in the larger phytoplankton
fraction. Shorter residence times of urea were obtained in the upper euphotic zone. The contribution of picophytoplankton
to urea cycling was 4% to 35%. The present results suggest that the picophytoplankton Synechococcus is able to degrade urea and effectively makes use of regenerated urea as a nitrogen source in the euphotic layer, and that
picophytoplankton play an important role in the biogeochemical nitrogen cycle in Lake Biwa.
Received: June 25, 1998 / Accepted: February 10, 1999 相似文献
18.
In order to provide a better understanding of the dynamics of phytoplankton in the coastal regions of high latitudes, a study
was carried out to estimate the dynamics of carbon biomass of autotrophic and heterotrophic algal groups over the austral
spring-summer 1997/1998 period. At a fixed station located in the central basin (Paso Ancho) of the Straits of Magellan (53°S),
surface water samples were collected at least once a week from September 1997 (early spring) to March 1998 (late summer).
Quantitative analysis of biomass of phytoplankton was estimated from geometric volumes, using non-linear equations, and converted
to biomass. The pattern of chlorophyll a showed a strong temporal variability, with maximum values (mean 2.8 mg m−3) at the austral spring phytoplankton increase or bloom (October/November) and minimum values during early spring (September:
<0.5 mg m−3) and summer (January/March: 0.5–1.0 mg m−3). During the spring bloom, diatoms made up to 90% of the total phytoplankton carbon (0.01–189 μg l−1), followed by a maximum of thecate dinoflagellates (0.08–34 μg l−1), and sporadic high biomass of phytoflagellates during summer. Heterotrophic algal groups such as Gymnodinium and Gyrodinium spp. dominated (70%, in the 5- to 25-μm size range) shortly before the main diatom bloom, and small peaks were observed within
spring and early summer periods (0–0.4 μg l−1). Phytoflagellates dominated earlier (spring) with higher carbon biomass (8 μg l−1) and post-bloom periods (summer) when carbon biomass ranged between 1 and 4 μg l−1.
Accepted: 6 September 2000 相似文献
19.
Phytoplankton populations in perennially ice-covered Lake Bonney, Antarctica grow in a unique non-turbulent environment. The
absence of turbulence generated by winds or major streams, combined with strong vertical gradients in temperature and nutrients,
create vertically stratified environmental conditions that support three discrete phytoplankton populations in the east lobe
of this lake. Phytoplankton biomass and photosynthesis were measured in the east lobe of Lake Bonney during the winter-spring
transicion (September) to mid-summer (January). During this period, irradiance beneath the ice increased from 0.03 to 1.9
mol quanta m−2 d−1. Chlorophylla concentrations ranged from 0.03 to 3.8 μl−1 within the trophogenic zone (just beneath the permanent ice cover to 20 m) and photosynthesis ranged from below detection
to 3.2 μg Cl−1 d−1. Our results indicate: (1) phytoplankton photosynthesis began in late winter (before 9 September, our earliest sampling date);
(2) maxima for phytoplankton biomass and production developed sequentially in time from the top to the bottom of the trophogenic
zone, following the seasoral increase in irradiance; and (3) the highest photosynthetic efficiencies occurred in early spring,
then decreased over the remainder of the phytoplankton growth season. The spring decrease in photosynthetic rates for shallower
phytoplankton appeared to be related to nutrient availability, while photosynthesis in the deeper populations was solely lightdependent. 相似文献
20.
Benthic algal communities can play an important role in matter and energy flux of shallow lakes. Their contribution to total
primary production of lakes has been largely unexplored. The aim of this study was to estimate the primary production of the
epipsammic algal communities at different water depths in Lake Balaton (Hungary) with photosynthetic measurements performed
in laboratory. The photosynthesis of the benthic algae of different origin was studied at nine different irradiance levels,
in three replicates. The maximum photosynthetic rate (P
max) was always higher in samples from the shallow parts than those from the deeper regions of the lake. Along the west–east
longitudinal axis of the lake P
max decreased in the southern part and increased in the middle of the lake as a consequence of differences in the chlorophyll-a concentrations. Knowing P
max, I
k, global radiation and extinction coefficient, the primary production (mg C m−2 day−1) of the epipsammic algal community was calculated at different water depths. In the shallow regions at 0.5 and 1 m water
depth 75–95% and 60–85% of the production was attributable to the epipsammon. The percentage contribution of epipsammon was
at 2 m water depth 20–65%. In the deeper pelagic region (>3 m) more than 85% of the primary production originated from the
phytoplankton. 相似文献