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1.
Spatial variability of the photosynthetic parameters and biomass of the Gulf of California phytoplankton 总被引:2,自引:0,他引:2
Gaxiola-Castro G; Alvarez-Borrego S; Lavin M; Zirino A; Najera-Martinez S 《Journal of plankton research》1999,21(2):231-245
Spatial variability of the central Gulf of California (CGC) phytoplankton
biomass and photosynthetic parameters in relation to physical forcing was
studied. Sampling was carried out in November, and the surface
TC range was
20-27.5°C. Strong tidal mixing in the midrift islands regions
injects relatively cool, nutrient-rich waters to the euphotic zone. Some of
this water is transported via jets and cool filaments throughout the Gulf.
In general, chlorophyll a (Chl) of small phytoplankton
(<8 m) (up to >2.5 mg
m-3) was higher than that of large phytoplankton.
Highest values of phytoplankton assimilation numbers
(PBm) [3.17 mg C (mg
Chla)-1
h-1], and photosynthetic efficiency B) [0.23 mg C (mg
Chl a)-1
h-1 (W
m-2)-1] were determined for
the large phytoplankton cells (>8 m). Our hypothesis that
PBm values increase
from cooler to warmer waters is not supported by the data. We found a
27-fold spatial difference of Chl, compared with a 10-fold difference of
PBm and a 6-fold
difference of B. Thus, in our study
area, the major source of variability for primary productivity (PP) comes
from Chl, and not from
PBm and
B. Therefore, we propose that it is
possible to estimate late-fall PP for the CGC using average photosynthetic
parameters. Average values for
PBm and
B of total phytoplankton were 0.72
mg c (mg Chl a)-1
h-1 and 0.12 mg C (mg Chl
a-1 h-1,
(W m-2)-1, with standard
errors of 0.07 and 0.03, respectively.
相似文献
2.
Observations on the first red tide off Kuwait, Arabian Gulf, yielded high
biomass [55.4-262.7 g chlorophyll (Chl)
a l-1] and primary production
(507.9-571.2 g C
h-1l-1), comparable with some
of the highest values reported. There were contrasting changes in the
carbon assimilation ratios, composition of the phytoplankton and the
contribution of nanoplankton (<20 m) between 11 and 12 May.
On 11 May, carbon assimilation by nanoplankton was 2.2 g C
(g Chl a)-1
h-1, but increased to 9.2 g C (g C
(g Chl a)-1
h-1 the following day. Nanoplankton contributed 56
and 9% of Chl a and production, respectively, on 11
May, while net plankton (>20 m) accounted for >65%
of the biomass and primary production on 12 May. Picoplankton (<3
m) contributed <8% of Chl a and
<3% of production. Frequent sampling will be necessary to capture
such dynamic changes and ephemeral events in these waters.
相似文献
3.
Egg production of a brackish water calanoid copepod Acartia
bifilosa was measured in the laboratory in different chlorophyll
(Chl) a concentrations (0-24 mgr;
l-1) and temperatures 4-24C), and the cephalothorax length and carbon content
of females were determined. Egg production was positively correlated both
with Chl a concentration and with temperature; highest
egg production was obtained with 14-20 g Chl
a l-1 and at 13-18°C.
There was also a significant positive correlation between egg production
and female length-specific carbon content (g C
m-1). However, no correlation was observed
between egg production and cephalothorax length of females. Female carbon
content changed during the 3 day experiments; carbon content was positively
related to Chl a concentration and negatively related
to temperature. We conclude that food availability (Chl
a concentration), rather than temperature, limits the
egg production of A.bifilosa in the present study area
in the northern Baltic Sea. Further, both food concentration and
temperature affect egg production not only through the direct effect on the
numbers of eggs produced per female, but also through their effect on
female carbon content.
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4.
Long-term phytoplankton studies in the Bahí Blanca estuary
showed a seasonal pattern characterized by a winter-early spring bloom of
diatoms dominated by Thalassiosira curviseriata.
Laboratory experiments were carried out to elucidate the influence of
irradiance, temperature and salinity on the growth rate of
T.curviseriata. The maximum daily growth rate was 1.93
divisions at 20C. The compensation point
(Ic) varied from approaching zero to 3.08 mol m-2
s-1, values were
-0.020-0.070 divisions mol-1, and the
calculated Ik (the irradiance at which initial slope
line reaches the maximum rate of growth) varied between 32 and 36
mol m-2 s-1. Growth
became light saturated (when max) between 70 and 80
mol m-2 s-1, and was
inhibited at -150 mol m-2
s-1 at all temperatures (5-20°C). The range
of temperatures at which T.curviseriata can grow
(5-20°C) coincides with the temperature range over which it is
found in the field. In contrast, the thermal optimum for growth,
20°C, was higher than the range of temperatures (between 5 and
10°C) characteristic of the winter-early spring bloom in
Bahí Blanca estuary. The mean specific growth rate of
T.curviseriata was not affected by salinity over the
tested range between 25 and 40 p.p.t. Field observations and experimental
data support the characterization of T.curviseriata as
a eurythermal and euryhaline species adapted to growth at relatively low
light intensity. These characteristics may explain the ability of
T.curviseriata to flourish seasonally when light
conditions are apparently limiting and its presence almost year round under
variable conditions of temperature and salinity.
相似文献
5.
Assimilation and release of 14C in a tropical strain of Cryptomonas obovata (Cryptophyceae) exposed to several irradiances 总被引:1,自引:0,他引:1
Carbon assimilation (14C) and dissolved organic
carbon (DO14C) release by a tropical strain of
Cryptomonas obovata was studied. Cells were exposed to
a range of irradiances (0-2000 mol
m-2 s-1) using axenic batch
cultures in the laboratory (Ek = 180 mol
m-2s-1). At up to 2000
mol m-2s-1, carbon
assimilation was not inhibited and an acclimation to low irradiances was
observed. DO14C release was dependent on carbon
fixation and no increase was detected under high irradiances. To determine
particulate organic carbon (PO14C) loss and
CO14C release cells acclimated to 350 mol
m-2 s-1 were incubated during
4 h at 35, 350, 850 and 1900 mol m-2
s-1. DO14C release was
responsible for 30% of the PO14C loss at 1900
mol m-2s-1. High-
and low-molecular-weight (HMW, LMW) compounds were released by
C.obovata under all irradiance conditions. However,
increased release with exposure time was observed only for the HMW
compounds.
相似文献
6.
The raphidophyte flagellate Chattonella marina was
successfully cultured from Boston Bay (South Australia), coincident with
mass mortality of farmed bluefin tuna (Thunnus
maccoyii) in April 1996. Grown under laboratory conditions at
150 mol m-2
s-1 irradiance, optimal growth (>0.5
day-1) occurred at a temperature of 25C and a salinity of 30 p.s.u., but good growth
(>0.3 day-1) also occurred between a
temperature of 10 and 30°C and at a salinity of 15-45 p.s.u.
However, cultures grow much faster at an irradiance of 450 mol
m-2 s-1 (1.08
day-1). While Australian
C.marina had similar temperature and salinity
requirements as well-studied Japanese cultures from the Seto Inland Sea,
the Australian strains exhibited a light saturation level for growth four
times higher than that reported from Japan (150 mol
m-2 s-1). An adaptation to
higher light intensities was reflected in higher concentrations of
microsporine-like amino acids in the Australian strains. The different
light adaptation phenotypes were still apparent after long-term culturing
under similar physiological conditions. Potential growth habitats for this
ichthyotoxic flagellate in the Australian region and implications for
finfish aquaculture industries are discussed.
相似文献
7.
Viral lysis and grazing loss of bacteria in nutrient- and carbon-manipulated brackish water enclosures 总被引:1,自引:0,他引:1
A 3 week enclosure experiment was carried out at the Gulf of Finland, the
Baltic Sea. After additions of inorganic nutrients [nitrogen (N) +
phosphorus (P)] and a carbon source (sucrose), we followed bacterial, viral
and heterotrophic nanoflagellate (HNF) abundances, as well as bacterial
production and the frequency of bacteria visibly infected with viruses.
Furthermore, the decay rate of virus particles was measured three times
during the enclosure experiment from the KCN-treated water samples.
Bacterial mortality caused by viral lysis was estimated using the decay
rates and the fraction of bacteria infected. Nutrient (N + P) additions
stimulated phytoplankton growth [the chlorophyll (Chl)
a concentration increased from <5 g l-1 up to 19 g
l-1], while sucrose additions increased bacterial
production (from 4-6 x 107
l-1 h-1). The phytoplankton
blooms affected bacterial production only slightly. Bacterial mortality
that was explained by viruses ranged from <2% to 13% when estimated
from the visibly infected cells, and from 8% to 808% when the decay rates
(range 0.052-0.765 h-1) were used. Assuming a
clearance rate of 5 nl flagellate-1
h-1, the HNF community could graze 16-135% of total
bacterial loss.
相似文献
8.
The occurrence of early larval stages of Brama brama
and Coryphaena hippurus is reported for the first time
in Adriatic waters. Two larvae of B.brama between 4.36
and 5.00 mm, and two larvae of C.hippurus between 4.75
and 4.95 mm standard length, were found in ichthyoplankton collections
taken off the River Neretva estuary (43010N,
17°250E) and station Stoncica, island Vis
(43°000N,
16°20E) (eastern middle Adriatic),
respectively. The capture of both species (B.brama) in
August 1998; C.hippurus in May 1998) is in agreement
with their proposed seasonal life cycle in the Adriatic Sea.
相似文献
9.
Are copepods important grazers of the spring phytoplankton bloom in the western Irish Sea? 总被引:3,自引:0,他引:3
Gowen R; McCullough G; Kleppel G; Houchin L; Elliott P 《Journal of plankton research》1999,21(3):465-483
The spring phytoplankton bloom and copepod grazing were studied at a
coastal and offshore station in the western Irish Sea during 1997. Maximum
chlorophyll standing stocks of 132.8 mg m-2 inshore
and 199.4 mg m-2 offshore were measured in late
April. At that time, mean water column temperatures were 10 and 8C at the coastal and offshore station, respectively.
Spring bloom production at the coastal station was estimated as 31.2 g C
m-2 and was dominated by the diatom
Guinardia delicatula. Offshore, production was 28.2 g
C m-2 and the bloom was composed of small (10 m) phytoflagellates
and the silicoflagellate Dictyocha speculum. Maximum
copepod abundance (189 and 544 x 103 individuals
m-2, inshore and offshore, respectively) coincided
with the spring bloom. Pseudocalanus and
Temora ingestion rates were derived from measurements
of gut pigment fluorescence, and were found to vary during the course of
the spring bloom as a result of changes in gut content. Grazing by late
copepodite and adult Pseudocalanus and
Temora was variable inshore, but overall accounted for
17% of bloom production. Offshore, 22% of bloom production was grazed with
maximum grazing (76% of daily production) occurring at the end of the
bloom. Large copepod species were not major grazers of the spring bloom.
Greater utilization of spring bloom production by copepods in the western
Irish Sea compared to regions of the North Sea is attributed to differences
in population size at the time of the bloom.
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10.
Light-limited photosynthetic carbon incorportion is expectedto be directly proportional to the scalar quantum irradiance.The proportionality constant is , where mis the maximum quantum yield (mol C Einstein1 absorbed)and $$\stackrel{\¯}{{\hbox{ k }}_{\hbox{ c }}}$$ isthe mean spectral absorption coefficient (m2 mg1 chla). Recent efforts to evaluate of in situphytoplankton photosynthesis are variously flawed. Lack of evidenceof proportionality and lack of correction of cosine to scalarirradiance are common deficiencies. Most data, as we interpretthem, indicate values in the range 0.0003 0.0006 mol C m2 Einstein1 abs mg1 chl a. New determinationsin lrondequoit Bay, New York, lie in this range. Most estimatesof at depth have been about 0.010 m2 mg1chl a. Similar values are being obtained for total particulatesfrom lrondequoit Bay; whether detritus contributes significantlyis not yet known. Published data, in our view, all point tovalues of m in situ in the range 0.030.07 mol C Einstein1abs. Published values >0.10 are almost certainly due to imprecisionor systematic error.
*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP) First International Workshop heldat the Limnological Institute, University of Konstanz, in April1982. 相似文献
11.
Llewellyn Carole A.; Tarran Glen A.; Galliene Chris P.; Cummings Denise G.; De Menezes Alex; Rees Andy P.; Dixon Jo L.; Widdicombe Claire E.; Fileman Elaine S.; Wilson Willie H. 《Journal of plankton research》2008,30(3):261-273
The microbial dynamics during a spring diatom bloom declinewas monitored in the Northeast Atlantic during a 5-day Lagrangianstudy (8–12 April 2002). Phytoplankton abundance, compositionand health status were related to viral and bacterial abundance,zooplankton abundance and grazing rates, as well as bacterialproduction. Phytoplankton reached maximum concentration on Day3 (Chl a >5 µg L–1) and declined on Day 5 (Chla 2 µg L–1) and was dominated (70% of Chl a) bydiatoms. Bacterial production increased substantially to >20µg C L–1 day–1 on Day 3 and concomitantlylarge viruses decreased in number by half to <10 x 103 mL–1.This was followed by a 5-fold increase in large viruses on Day5, indicating infection and subsequent lysis on Days 3 and 5,respectively. Micro- and mesozooplankton grazing were not theprincipal cause for the decline of the bloom and pheophorbide-ashowing little variation in concentration from Days 1–4(100 ng L–1) although doubled on Day 5. The poor physiologicalstatus of the diatoms, indicated by the high chlorophyllide-aconcentrations (50–480 ng L–1), likely promoteda series of closely interrelated events involving bacteria andviruses leading to the demise of the diatom bloom. 相似文献
12.
Abundance and biogeography of tintinnids (Ciliophora) and associated microzooplankton in the Southwestern Atlantic Ocean 总被引:4,自引:1,他引:3
Absolute abundances of foraminifers, polycystine and phaeodarian
radiolarians, tintinnids, pteropods and early crustacean larvae and moults
were assessed in a collection of 57 vertically stratified (0-100 m) net
microplankton samples from 22 stations located between 34 and 58S (along 51-56°W), covered on 8-16 November
1994. Tintinnids were identified to species and measured in order to
estimate their biomass from biovolume to carbon conversions. The
distribution of the microzooplanktonic groups assessed was irregular and
patchy, both geographically and vertically, and their abundances were
characteristic of oceanic low to medium productivity environments.
Tintinnid biomass was also generally low (0.05-0.40 g Cl-1). With the exception of
the tintinnids, associations between microzooplanktonic numbers and
chlorophyll a were generally loose. Eighty-eight
tintinnid taxa were recorded, yet only five accounted for 53% of the
specimens identified. Multivariate (cluster) analysis of tintinnid specific
distribution patterns clearly showed several distinct zones. From north to
south, these are: Transition Zone (TZ), with three subzones, TZ north
(34°S-38°S), TZ central
(39°44S-44°S) and TZ south (46°S);
Subantarctic Zone (SZ; 48-55°S); Polar Front Zone
(55°30S); Antarctic Zone (AZ;
58-59°36S). Each of these was characterized by distinct
tintinnid assemblages, abundance and biomass. With few exceptions,
tintinnid cells were fairly evenly distributed throughout the upper 50 m.
Taxonomic composition usually changed little with depth. Mean population
depths were calculated for a subset of 35 tintinnids; 29 of these dwell
preferably above 40 m. The spatial distribution of tintinnid species
richness showed a more or less gradual decrease from north to south.
Specific diversity and equitability generally increased with depth, and
were higher in antarctic waters than the southern transitional and
subantarctic ones; this trend is tentatively attributed to higher water
column vertical stability south of the Polar Front.
相似文献
13.
In situ light measurements were used to obtain information oninherent and apparent optical properties. The average verticalattenuation coefficient Kd(ave) varied from 1.1 to 4.6 In unitsm1 During three periods the variation in Kd(ave) correlatedwith changes in chlorophyll a concentration and specific attenuationcoefficients Ks, of 0.013, 0.014 and 0.022 m2 mg Chl a1were calculated. Chlorophyll-specific diffuse absorption coefficients(A,) for these periods were 0.012. 0.013 and 0.017 m2 mg Chla1 and only varied significantly from estimates of Ksin the period when scattering was intense. Absorption coefficientsa(zmid) and scattering coefficients b(zmid) calculated for themid-point of the euphotic zone ranged between 0.45 and 2.9 mand 3.552.0 m respectively. Chlorophyll-specific absorptioncoefficients Ka, of 0.005, 0.006 and 0.007 m2 mg Chl a1and scattering coefficients Kb of 0.05. 0.09 and 0.191 m2 mgChl a1 were measured during the three periods. The highKb value occurred when gas-vacuolate cyanobactena were dominant.Algal photosynthesis and light absorption were related throughthe maximum quantum yield m which varied between 0.019 and 0.11mol C Einstein1 while average quantum yields a, variedbetween 0.006 and 0.024 with a mean of 0.013 mol C Einstein1A comparison of changes in the mean irradiance of the mixedzone and chlorophyll concentration indicated that growth waslight limited below 0.040.05 Einsteins absorbed mg Chla1 day1. 相似文献
14.
The goal of this study was to provide temporal information on the
generation time of Dolioletta gegenbauri and some of
the life cycle's components. At 20C and
90 g C l-1 of
ingestible phytoplankton. D.gegenbauri's life cycle is
completed in 20.5 days. Phorozooids 5 mm produce on average 11.0
gonozooids day-1 over a period of 8-18 days.
Utilizing field data on the abundance and size distribution of an
assemblage of phorozooids and nurses, in conjunction with experimentally
obtained rates, indicates that asexual production per cubic meter by
phorozooids with that of nurses should result in rapid colonization of a
wide shelf by doliolids, as observed during July and August 1981 on the
southeastern continental shelf of the USA.
相似文献
15.
Short communication. Carbon:nitrogen ratios of Baltic Sea copepods-indication of mineral limitation?
The carbon (C) and nitrogen (N) content and the C:N ratio of two common
calanoid copepods, Eurytemora affinis and
Acartia bifilosa were measured during spring and
summer at the SW coast of Finland, northern Baltic Sea. The C:N ratio of
both copepod species was slow and stable (4-4.5), irrespective of sampling
time, which implies N limitation at least during intermediate to high food
concentrations in spring and early summer. In addition, experiments were
conducted to reveal whether the diet of copepods affects their C and N
content. Adding green algae Brachiomonas submarina in
concentrations of 50-500 g C
l-1 to <100-m-filtered sea water did
not significantly increase copepod C or N content in 3 day experiments.
However, the C and N contents of E.affinis eggs were
2 times higher in high food concentration, which may increase
survival of eggs and nauplii.
相似文献
16.
Growth and toxin production of a highly toxic clone of the marine
dinoflagellate Alexandrium tamarense, isolated from
the lower St Lawrence estuary (Quebec) in eastern Canada, were studied in
unialgal batch cultures under different conditions. Controlled experiments
were conducted on the production of paralytic shellfish poisoning (PSP)
toxins under conditions of varying light (40, 60, 150, 230 and 470 mol m-21
s-1), salinity (10, 15, 20, 25 and 30)
and nitrate concentrations (0, 88, 364, 528 and 880 mol
l-1). The effects of variable environmental factors
on both toxin composition (% molar) and cell toxicity [pg STXeq (saxitoxin
equivalents) cell-1] were determined through the
culture cycle. The toxin profile (% molar; mean SD), determined by high-performance liquid
chromatography with fluorescence detection (HPLC-FD), remained stable and
was consistently dominated by the low-potency
N-sulfocarbamoyl toxins C1/C2 (64.0 ± 3%).
There were also substantial relative amounts of the high-toxicity carbamate
derivatives gonyautoxin 1-4 (GTX1-4) (1.7 ± 0.5%), neosaxitoxin
(NEO) (16.2 ± 2%) ans saxitoxin (STX) (17.8 ± 2%).
The cellular toxicity (mean ± SD: 58.8 ± 7 pg STXeq
cell-1) was essentially independent of light,
salinity and nitrate concentration throughout the exponential growth phase,
but varied over the growth stages in cultures. A positive correlation was
observed between cellular toxicity and salinity-dependent growth rate,
indicating that cell toxin quota may be affected by extrinsic factors, but
it is not always a direct functional response to specific environmental
stress.
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17.
The Faroe shelf water is separated from the offshore water by a persistent
tidal front, which surrounds the islands. This shelf water contains a
neritic zooplankton community, which, regarding species composition,
production, seasonal development and environmental conditions, is quite
different from that in the surrounding ocean. While during spring and
summer the zooplankton in the oceanic environment are dominated by the
copepod Calanus finmarchicus, the zooplankton in the
shelf water are largely dominated by neritic copepods, mainly
Acartia longiremis and Temora longicornis.
Calanus finmarchicus occurs in interannually highly variable
abundance in the Faroe shelf ecosystem. Meroplanktonic larvae, mainly
Balanus spp, and decapod larvae, are also common in
the shelf water during spring and summer. During the period presented
(1989-1997), the Faroe shelf ecosystem has undergone very large changes in
abundance of different zooplankton species. The midsummer abundance of
C.finmarchicus, which originally is advected into the
shelf from the open ocean, fluctuated from 400 copepods
m-3 in 1989 to 25 copepods
m-3 in 1994, and at the same time the neritic
zooplankton increased from 120 m-3 in 1989
to 450 m-3 in 1994. Consequently, the midsummer
biomass in the shelf fluctuated by a factor of 10 during the same period.
It is presumed that this variability between oceanic- and neritic-dominated
zooplankton, their sizes and their biomass has greatly affected the entire
pelagic ecosystem.
相似文献
18.
Egg production rates of eight calanoid copepod species during summer 1997 off Newport, Oregon, USA 总被引:3,自引:0,他引:3
Measurements of hydrography, water transparency, chlorophyll (Chl)
a and egg production rates (EPRs) by females of
Calanus marshallae Frost, Calanus
pacificus Brodsky, Eucalanus californicus
Johnson, Epilabidocera longipedata Sato,
Pseudocalanus mimus Frost, Centropages
abdominalis Sato, Acartia longiremis
Lilljerborg and Paracalanus parvus (Claus) were
estimated at weekly intervals between 17 July and 2 September 1997.
Production of eggs was determined in 24 h incubations to examine the
effects of environmental variability on EPR, to detect the possibility of
food limitation of EPR, and to evaluate the hypothesis that growth rates of
females are size dependent. During the study, an anomalous downwelling
event occurred, possibly in response to the 1997 El Niño, which
allowed us to determine how El Niño events affect EPRs of
coastal copepods. The larger copepods Calanus marshallae, Calanus
pacificus and Centropages abdominalis
showed the highest egg production and specific growth rates during the
period of active upwelling (18 July-13 August, water temperatures
8-13C, Chl a
concentration 4.7-16.2
l-1 and water transparency 3-5 m). After 27 August,
the 1997-98 El Niño arrived off Oregon, creating a downwelling
situation. Upwelling winds ceased, the thermocline intensified, temperature
and transparency increased (to >18°C and 16 m), and Chl
a declined to <2 g
l-1. Densities of the common coastal species
declined greatly as well. Paracalanus parvus became
the dominant species, and Eucalanus californicus, Epilabidocera
longipedata and Corycaeus anglicus became
common in our samples. EPRs for the larger boreal copepods
(Calanus and Centropages)
declined greatly during El Niño;; the smaller copepods,
Pseudocalanus mimus, A.longiremis and
Paracalanus parvus, showed low but relatively constant
egg production and specific growth rates during both upwelling and
downwelling events. Over the entire study period, only three species
produced eggs at its maximum rate (24-28 eggs
female-1 day-1),
Pseudocalanus mimus which averaged 4 eggs
day-1. All other species had EPRs that were two or
five times below their maximum EPR. Thus, EPRs were not related to body
size, contrary to our expectations. Hatching success was variable among
species. Values as low as 20-40% were found for all species at least once
during the study period, suggesting that occasionally a substantial portion
of egg production may not be viable.
相似文献
19.
Temporal and spatial variations in phytoplankton carbon isotopes in a polymictic subtropical lake 总被引:2,自引:0,他引:2
Stable carbon isotopes (13C) were determined for phytoplanktonand dissolved inorganic carbon (DIC) from Lake Apopka, a shallow,polymictic and hypereutrophic lake in Florida, USA. Bulk planktondominated by pico- and nanqanobacteria were enriched in 13(13.1± 1.1%) as a result of assimilation of extremely 13C-richDIC (13C = 9.6 ± 3.0%). Diatoms (Aulacoseira spp.) hada 13C of 14.3 ± 0.6% that was slightly more negativethan that of small cyanobacteria. Meroplanktonic diatoms hada 13C (13.6 ± 1.8%), similar to their planktoniccounterparts. The 13C of a colonial cyanobacterium (Microcystisincerta) was exceptionally heavy (3.0 ± 1.0%)and attributed to localized carbon limitation. Seasonal variationin 13C of bulk plankton was small (4%) relative to reports forother lacustrine systems No difference in the 13C of bulk planktonhorn surface water between stratified and non-stratified periodswas found. No measurable changes in 13C of bulk plankton wereindicated in light and dark incubation experiments Frequentwind mixing of the water column, high DIC concentration, andconsistently high lake productivity were used to explain thetemporal and spatial isotope consistency of phytoplankton inthis lake. 相似文献
20.
Effects of UVB radiation on freshwater autotrophic and heterotrophic picoplankton in a subalpine lake 总被引:1,自引:0,他引:1
The effects of UVB radiation on the activity of heterotrophic (HPP) and
autotrophic (APP) picoplankton (0.2-2 m) and
of autotrophic assemblages >2 m has been measured and
compared. Under natural UVB irradiance in a large, deep, oligotrophic
subalpine lake (Lago Maggiore, 4555N) with mean dissolved organic carbon
(DOC) concentrations of 1 mg Cl-1, the
microorganisms of the two size fractions were not significantly
photoinhibited in their autotrophic and heterotrophic activities. The
vertical attenuation coefficient (Kd) for irradiance
at 305 nm ranged from 1.45 to 1.67 during spring and summer. The mixing
layer extended to a greater depth than the layer affected by UVB radiation
(z1% < zmix), thus
enabling the microorganisms living there to photoadapt. As the assimilation
numbers of APP and nanoplankton were higher at 2 m depth than near the
surface, we suspected that the influence of longer wavelength (UVA,
photosynthetically active radiation) could be stronger than UVB in
affecting the photosynthetic efficiency of natural populations. The
artificial increase in UVB irradiance had a higher detrimental effect on
HPP due to their smaller size, less protection and indirect effects through
autotrophic cell inhibition. Picocyanobacteria were percentually more
affected by UVB than nanoplankton during April due to the presence of
diatoms, which are more resistant than other algal groups to solar UVB
irradiance. Furthermore, picocyanobacteria had lower assimilation numbers
with respect to larger phytoplankton in the quartz tubes during
stratification.
相似文献