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1.
Sampling of the central region of the North Sea was carried out to study the spatial and seasonal changes of dissolved and
particulate organic C (DOC and POC, respectively). The surface waters were collected during four cruises over a year (Autumn
2004–Summer 2005). DOC and POC concentrations were measured using high temperature catalytic oxidation methods. The surface
water concentrations of DOC and POC were spatially and temporally variable. There were significantly different concentrations
of DOC and POC between the inshore and offshore waters in winter and summer only, with no clear trend in autumn and spring.
Highest mean concentrations of DOC were measured in spring with lower and similar mean concentrations for other seasons. POC
showed a clear seasonal cycle throughout the year with highest surface mean concentrations found in autumn and spring, but
lowest in winter and summer. The DOC distributions during autumn and spring were strongly correlated with chlorophyll suggesting
extracellular release from phytoplankton was an important DOC source during these two seasons. The lower concentrations of
DOC in summer were probably due to the heterotrophic uptake of labile DOC. The seasonal changes in the C:N molar ratios of
surface DOM (dissolved organic matter) resulted in higher mean C:N molar ratios in spring and lower ratios in winter. These
high ratios may indicate nutrient limitation of heterotrophic uptake immediately after the spring bloom. There is limited
data available for DOC cycling in these productive shelf seas and these results show that DOC is a major component of the
C cycle with partial decoupling of the DOC and DON cycling in the central North Sea during the spring bloom.
Handling editor: Luigi Naselli-Flores 相似文献
2.
Temporal and spatial distributions of dissolved organic carbon and nitrogen in two small lakes on the Southwestern China Plateau 总被引:6,自引:0,他引:6
Wen Li Fengchang Wu Congqiang Liu Pingqing Fu Jing Wang Yi Mei Liying Wang Jianyang Guo 《Limnology》2008,9(2):163-171
Temporal and spatial distributions of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), chlorophyll-a and inorganic nitrogen were investigated in two small mountainous lakes (Lake Hongfeng and Baihua), on the Southwestern China
Plateau, based on almost 2 years’ field observation. DOC concentrations ranged from 163 μM to 248 μM in Lake Hongfeng and
from 143 μM to 308 μM in Lake Baihua, respectively, during the study period. DON concentrations ranged from 7 μM to 26 μM
in Lake Hongfeng and from 14 μM to 47 μM in Lake Baihua. DOC showed vertical heterogeneity with higher concentrations in the
epilimnion than in the hypolimnion during the stratification period. The DON concentration profiles appeared to be more variable
than the DOC profiles. Apparent DON maxima occurred in the upper layer of water. In Lake Hongfeng, DOC concentration in the
surface water was highest at the end of spring and early summer. DON concentration was 2–5 μM higher in May 2003 and in June
2004 than in adjacent months. DOC and chlorophyll-a concentrations were significantly correlated (r = 0.79, P < 0.05). The period of highest concentrations of DOC in Lake Hongfeng was also the season of concentrated rainfall. Algae
activity and allochthonous input might result in an increase of DOC and DON concentrations together. In Lake Baihua, the maximum
concentrations of DOC and DON in the surface water occurred simultaneously in May 2003 and February 2004. DOC concentrations
were significantly correlated with DON (r = 0.90, P < 0.01), indicating the common sources. Allochthonous input, biological processes, stratification and mixing were the most
important factors controlling the distributions and cycling of dissolved organic matter (DOM) and inorganic nitrogen in these
two lakes. Inference from the corresponding vertical distributions of DOM and inorganic nitrogen indicated that DOM played
potential roles in the internal loading of nitrogen and metabolism in the water body in these small lakes. The carbon/nitrogen
(C/N) ratio showed a potential significance for tracing the source and biogeochemical processes of DOM in the lakes. These
results are of significance in the further understanding of biogeochemical cycling and environmental effects of DOM and nitrogen
in lake ecosystems. 相似文献
3.
Céline Guéguen Laodong Guo Deli Wang Noriyuki Tanaka Chin-Chang Hung 《Biogeochemistry》2006,77(2):139-155
Monthly (or bi-weekly) water samples were collected from the Yukon River, one of the largest rivers in North America, at a
station near the US Geological Survey Stevens Village hydrological station, Alaska from May to September 2002, to examine
the quantity and quality of dissolved organic matter (DOM) and its seasonal variations. DOM was further size fractionated
into high molecular weight (HMW or colloidal, 1 kDa–0.45 μm) and low molecular weight (LMW, <1 kDa) fractions. Dissolved organic
carbon (DOC), colored dissolved organic matter (C-DOM) and total dissolved carbohydrate (TCHO) species were measured in the
size fractionated DOM samples. Concentrations of DOC were as high as 2830 μmol-C l−1 during the spring breakup in May and decreased significantly to 508–558 μmol-C l−1 during open-water season (June–September). Within the DOC pool, up to 85% was in the colloidal fraction (1 kDa–0.45 μm) in
early May. As DOC concentration decreased, this colloidal portion remained high (70–85% of the bulk DOC) throughout the sampling
season. Concentrations of TCHO, including monosaccharides (MCHO) and polysaccharides (PCHO), varied from 722 μmol-C l−1 in May to 129 μmol-C l−1 in September, which comprised a fairly constant portion of bulk DOC (24±2%). Within the TCHO pool, the MCHO/TCHO ratio consistently
increased from May to September. The C-DOM/DOM ratio and the size fractionated DOM increased from May to September, indicating
that DOM draining into the Yukon River contained increased amounts of humified materials, likely related to a greater soil
leaching efficiency in summer. The average composition of DOM was 76% pedogenic humic matter and 24% aquagenic CHO. Characteristics
of soil-derived humic substances and low chlorophyll-a concentrations support a dominance of terrestrial DOM in Yukon River waters. 相似文献
4.
Composition and variations in the occurrence of dissolved free simple organic compounds of an unproductive lake ecosystem in northern Sweden 总被引:1,自引:0,他引:1
Low molecular weight organic carbon compounds are potentially important carbon and energy substrates to heterotrophic production
in the aquatic environment. We studied the occurrence of dissolved free amino acids (AA), monosaccharides (CHO), and carboxylic
acids (CA) in the subarctic Lake Diktar-Erik. The lake is unproductive with slightly humic water, and receives water via one
major inlet stream draining a birch forest environment. The concentration of dissolved organic carbon (DOC) in the inlet stream
was strongly correlated with the discharge. This relationship changed from season to season, indicating changes in the sources
of the DOC entering the stream. AA and CHO each accounted for an average of less than 0.5% of the DOC. After high discharge
events during the ice-free period, AA and CHO occurred in especially high concentrations. CA occurred in higher concentrations
during the ice-free period, when it generally accounted for 20–30% of the DOC pool. The CA content relative to the total DOC
pool was strongly inversely correlated with overall DOC concentration, and at low DOC levels the relative content of CA was
high and vice versa. This followed a seasonal trend, with CA accounting for a smaller proportion of the DOC in winter and
a larger part in spring/early summer. A conservative estimate suggested that the studied simple organic carbon compounds potentially
could cover 30% of the bacterial gross production in the lake and therefore potentially also was an important source of CO2 that occur in supersaturated concentrations in the lake. 相似文献
5.
Y. Tanaka T. Miyajima A. Watanabe K. Nadaoka T. Yamamoto H. Ogawa 《Coral reefs (Online)》2011,30(2):533-541
Dissolved organic matter (DOM) concentrations in a fringing coral reef were measured for both carbon and nitrogen with the
analytical technique of high-temperature catalytic oxidation. Because of high precision of the analytical system, not only
the concentrations of dissolved organic carbon and nitrogen (DOC and DON, respectively) but the C:N ratio was also determined
from the distribution of DOC and DON concentrations. The observed concentrations of DOC and DON ranged 57–76 and 3.8–5.6 μmol l−1, respectively. The C:N ratios of the DOM that was produced on the reef flat were very similar between seagrass- and coral-dominated
areas; the C:N ratio was 10 on average. The C:N ratio of DOM was significantly higher than that of particulate organic matter
(POM) that was produced on the reef flat. Production rates of DOC were measured on the reef flat during stagnant periods and
accounted for 3–7% of the net primary production, depending on the sampling site. The production rate of DON was estimated
to be 10–30% of the net uptake of dissolved inorganic N in the reef community. Considering that the DOM and POM concentrations
were not correlated with each other, a major source of the reef-derived DOM may be the benthic community and not POM such
as phytoplankton. It was concluded that a widely distributed benthic community in the coral reef released C-rich DOM to the
overlying seawater, conserving N in the community. 相似文献
6.
Sources of dissolved and particulate organic material in Loch Vale Watershed,Rocky Mountain National Park,Colorado, USA 总被引:6,自引:3,他引:3
The sources of both dissolved organic carbon (DOC) and particulate organic carbon (POC) to an alpine (Sky Pond) and a subalpine lake (The Loch) in Rocky Mountain National Park were explored for four years. The importance of both autochthonous and allochthonous sources of organic matter differ, not only between alpine and subalpine locations, but also seasonally. Overall, autochthonous sources dominate the organic carbon of the alpine lake, while allochthonous sources are a more significant source of organic carbon to the subalpine lake. In the alpine lake, Sky Pond, POC makes up greater than one third of the total organic matter content of the water column, and is related to phytoplankton abundance. Dissolved organic carbon is a product of within-lake activity in Sky Pond except during spring snowmelt and early summer (May–July), when stable carbon isotope ratios suggest a terrestrial source. In the subalpine lake, The Loch, DOC is a much more important constituent of water column organic material than POC, comprising greater than 90% of the spring snowmelt organic matter, and greater than 75% of the organic matter over the rest of the year. Stable carbon isotope ratios and a very strong relation of DOC with soluble Al(tot) indicate DOC concentrations are almost entirely related to flushing of soil water from the surrounding watershed during spring snowmelt. Stable carbon isotope ratios indicate that, for both lakes, phytoplankton is an important source of DOC in the winter, while terrestrial material of plant or microbial origin contributes DOC during snowmelt and summer. 相似文献
7.
During the unstratified (winter) and stratified (summer) periods of 1999 and 2000, we examined carbon (C) dynamics in the
upper water column of southern Lake Michigan. We found that (a) bacterial respiration (BR) and planktonic respiration (PR)
were major sinks for C, (b) C flux through bacteria (CFTB) was diminished in winter because of reduced bacterial production
(BP) and increased bacterial growth efficiency (BGE) at colder temperatures, and (c) PR exceeded primary production (PP) during
the spring–summer transition. Drawdown of dissolved organic C (DOC), resuspended organic matter from the lake floor, and riverine
organic matter likely provided organic C to compensate for this temporal deficit. DOC in the water column decreased between
winter and summer (29–91 mg C m2 d−1) and accounted for 20%–53% of CFTB and 11%–33% of PR. Sediment resuspension events supported elevated winter heterotrophy
in the years that they occurred with greatest intensities (1998 and 2000) and may be important to interannual variability
in C dynamics. Further, riverine discharge, containing elevated DOC (5×) and dissolved P (10×) relative to lake water, peaked
in the winter–spring season in southern Lake Michigan. Collectively, terrigenous inputs (river, stream, and groundwater discharges;
storm water runoff; and atmospheric precipitation) may support approximately 10%–20% of annual in-lake heterotrophy as well
as autotrophy. Terrestrial subsidies likely play a key role in the C balance of even very large lakes, representing a critical
linkage between terrestrial and aquatic ecosystems.
Received 11 June 2001; Accepted 14 December 2001. 相似文献
8.
9.
V. S. Kuwahara R. Nakajima B. H. R. Othman M. R. M. Kushairi T. Toda 《Coral reefs (Online)》2010,29(3):693-704
Biologically diverse coral-reef ecosystems are both directly and indirectly susceptible to changes in the spectral ultraviolet
radiation (UVR) distribution. The purpose of this study was to (1) measure the variability of UVR and photosynthetically active
radiation (PAR) penetration in the water above coral reefs around the Malaysian peninsula, (2) measure the variability and
distribution of UVR-specific biogeochemical factors, and (3) determine the impact of biogeochemical variability as it affects
the UVR:PAR ratio. Downwelling UVR and PAR irradiance and bio-optically derived biogeochemical factors were measured at 14
coral survey stations around the Malaysian peninsula from August 10–29, 2007. The West Coast was characterized by relatively
shallow mean 10% UV-B (320 nm) penetration (1.68 ± 1.12 m), high chlorophyll (3.00 ± 4.72 μg l−1), high chromophoric dissolved organic matter (CDOM; 6.61 ± 3.31 ppb), high particulate organic carbon (POC; 190.65 ± 97.99 mg m−3), and low dissolved organic carbon (DOC; 1.34 ± 0.65 mg m−3). By contrast, the East Coast was characterized by relatively deep mean 10% UV-B penetration (5.03 ± 2.19 m), low chlorophyll
(0.34 ± 0.22 μg l−1), low CDOM (1.45 ± 0.44 ppb), low POC (103.21 ± 37.93 mg m−3), and relatively high DOC (1.91 ± 1.03 mg m−3). The UVR:PAR ratio was relatively higher on the East Coast relative to the West Coast, suggesting variable concentrations
of UVR-specific absorbing components. At all sites, UVR attenuation coefficients showed significant correlations with CDOM,
but were spatially dependent with regard to chlorophyll a, POC, and DOC. The results suggest that bio-optically significant CDOM and DOC factors are uncoupled in coral-reef communities
of Malaysia. Furthermore, the results support prior studies that show chromophorically active concentrations of DOM and POC
are significantly altering the amount of UVR penetration above coral reefs and may be notable factors in regulating intricate
biogeochemical cycles around benthic coral communities in Malaysia. 相似文献
10.
Colloidal and dissolved organic matter in lake water: Carbohydrate and amino acid composition,and ability to support bacterial growth 总被引:3,自引:1,他引:2
Bacterial utilization of dissolved organic matter (DOM) was studied in water from a humic and a clearwater oligotrophic lake. Indigenous bacteria were inoculated into either 0.2 m natural filtered lake water, or lake water enriched fivefold with colloidal DOM >100 kD but below 0.2 m. Consumption of DOM was followed from changes in concentrations of total dissolved organic carbon (DOC), dissolved combined and free carbohydrates and amino acids (DCCHO and DFCHO, and DCAA and DFAA, respectively) and by uptake of monosaccharide and amino acid radioisotopes. DCCHO and DCAA made up 8% (humic lake) to 33–44% (clear-water lake) of the natural DOC pools, while DFCHO and DFAA contributed at most 1.7% to the DOC pools. Addition of >100 kD DOM increased the DOC concentrations by 50% (clearwater lake) to 92% (humic lake), but it only resulted in a higher bacterial production (by 63%) in the humic lake. During the incubations 13 to 37% of the DOC was assimilated by the bacteria, at estimated growth efficiencies of 4–8%. Despite the measured reduction of DOC, statistically significant changes of specific organic compounds, especially of DCCHO and DCAA, generally did not occur. Probably the presence of high molecular weight DOC interfered with the applied analytical procedures. Addition of radiotracers indicated, however, that DFAA sustained 17–58% and 29–100% of the bacterial carbon and nitrogen requirements, respectively, and that glucose met 1–3% of the bacterial carbon requirements. Thus, our experiments indicate that radiotracers, rather than measurements of concentration changes, should be used in studies of bacterial utilization of DOC in freshwaters with a high content of humic or high molecular weight organic matter. 相似文献
11.
Influence of hydrology and seasonality on DOC exports from three contrasting upland catchments 总被引:2,自引:0,他引:2
J. J. C. Dawson C. Soulsby D. Tetzlaff M. Hrachowitz S. M. Dunn I. A. Malcolm 《Biogeochemistry》2008,90(1):93-113
Variation in dissolved organic carbon (DOC) concentrations of surface waters is a consequence of process changes in the surrounding
terrestrial environment, both within annual cycles and over the longer term. Long-term records (1987–2006) of DOC concentrations
at six catchments (0.44–10.0 km2) across a climatic transect in Scotland were investigated for intra-annual relationships to evaluate potential long-term
seasonal patterns. The intra-annual mode of DOC export contrasted markedly between catchments and appeared dependent on their
hydrological characteristics. Catchments in wetter Central Scotland with high rainfall–runoff ratios, short transit times
and well-connected responsive soils show a distinct annual periodicity in DOC concentrations throughout the long-term datasets.
Increased DOC concentrations occurred between June and November with correspondingly lower DOC concentrations from December
to May. This appears unrelated to discharge, and is dependent mainly on higher temperatures driving biological activity, increasing
decomposition of available organic matter and solubility of DOC. The drier eastern catchments have lower rainfall–runoff ratios,
longer transit times and annual drying–wetting regimes linked to changing connectivity of soils. These are characterised by
seasonal DOC concentration–discharge relationships with an autumnal flush of DOC. Temperature influences the availability
of organic matter for DOC transport producing a high DOC concentration–discharge relationship in summer/autumn and low DOC
concentration–discharge relationship in winter/spring. These two distinct modes of seasonal DOC transport have important implications
for understanding changes in DOC concentrations and export brought about by climate change (temperature and precipitation)
and modelling of aquatic carbon losses from soil-types under different hydrological regimes. 相似文献
12.
Concentrations of plankton, suspended particles 0.74–87 μm equivalent spherical diameter and dissolved organic carbon (DOC)
were measured from May to February at an Antarctic coastal site. Bacteria-sized particles 0.74–1 μm diameter, and bacterial
cells and heterotrophic protists all exhibited a seasonal minimum during winter and maxima in summer. Bacteria composed <10%
of the bacteria-sized particles. Release of autotrophic protists from the ice caused water column biomass of autotrophs to
reach maximum concentrations in October and November, but maximum cell concentration in the water column was reached in January.
Microheterotroph biomass weakly reflected the release of the ice algal community but reached maximum concentration during
the water column bloom in January. Total DOC concentrations varied from 0.36 mg C l−1 in July to 3.10 mg C l−1 in October, with a yearly average of 1.51 mg C l−1. Ultrafiltration of DOC revealed that the molecular weight composition of the DOC differed greatly through the year. DOC
<5 kDa molecular weight reached a maximum of 1.25 mg C l−1 in October and accounted for up to 60% of total DOC in July. Concentrations of high molecular weight DOC (>100 kDa) were
highest in July and November, with the DOC (100 kDa–0.5 μm) fraction reaching a maximum of 1.22 mg C l−1 in November and composing 82% of the total DOC in January. Wet chemical oxidation and high-temperature catalytic oxidation
organic carbon analyses were compared. Good correlation was observed between methods during summer but no significant correlation
existed in winter, indicating that winter DOC may be refractory.
Accepted: 21 March 2000 相似文献
13.
Particulate and Dissolved Organic Carbon Production by the Heterotrophic Nanoflagellate Pteridomonas danica Patterson and Fenchel 总被引:1,自引:0,他引:1
Abstract
We established a budget of organic carbon utilization of a starved heterotrophic nanoflagellate, Pteridomonas danica, incubated in batch cultures with Escherichia coli as model prey. The cultures were sampled periodically for biomass determinations and total organic carbon dynamics: total
organic carbon, total organic carbon <1 μm, and dissolved organic carbon (DOC, <0.2 μm). During the 22 h incubation period,
P. danica underwent biovolume variations of 3.2-fold. Gross growth efficiency was 22% and net growth efficiency 40%. P. danica respired 33% and egested 44% of the ingested E. coli carbon during lag and exponential growth phases. The form of the organic carbon egested varied. Of the total ingested carbon,
9% was egested in the form of DOC and occurred mainly during the exponential growth phase; 35% was egested in the form of
particulate organic carbon (POC), ranging in size from 0.2 to 1 μm, and took place during the lag phase. P. danica could have reingested as much of 58% of this previously produced POC during the exponential growth phase as food scarcity
increased. We concluded that POC egestion by flagellates could represent a significant source of submicrometric particles
and colloidal organic matter. In addition, flagellate reingestion of egested POC could play a nonnegligible role in the microbial
food web. Finally, the methodology reported in this study has proved to be a useful tool in the study of carbon metabolism
in aquatic microorganisms.
Received: 31 July 1998; Accepted: 2 March 1999 相似文献
14.
T. Yoshioka S. Ueda T. Khodzher N. Bashenkhaeva I. Korovyakova L. Sorokovikova L. Gorbunova 《Limnology》2002,3(3):0159-0168
Concentrations of dissolved organic carbon (DOC) in Lake Baikal ranged from 90 to 110 μM C, considerably higher than those
in oceanic environments. The DOC concentrations in the epilimnion were higher than those in the hypolimnion. Since particulate
organic carbon (POC) concentrations in the pelagic waters of Lake Baikal were <10–40 μM C in the epilimnion and 2–5 μM C in
the hypolimnion, DOC constitutes a major component of the organic carbon pool in Lake Baikal, especially in the deep layers.
The DOC concentrations downstream of the Barguzin and Selenga Rivers were quite high (400–500 μM C). Probably because of the
high concentrations of DOC in these rivers, the DOC levels in Barguzin Bay and offshore at the mouth of the Selenga River
were higher than those in the pelagic regions of the central and south basins of Lake Baikal. The relationship between DOC
and electric conductivity revealed the transport of DOC from rivers to the pelagic area in Lake Baikal. The spatial distribution
of DOC suggested that a major part of DOC in the lake was allochthonous (land-derived).
Received: July 26, 2002 / Accepted: September 16, 2002
Present address:Research Institute for Humanity and Nature, 335 Takashima-cho, Marutamachi Kawaramachi, Kamigyo-ku, Kyoto 602-0878, Japan
Tel. +81-75-229-6167; Fax +81-75-229-6150 e-mail: yos@chikyu.ac.jp
Acknowldgments The authors wish to thank Director Prof. M. Grachev and Dr. O. Timoshkin of the Limnological Institute, Siberian Branch,
Academy of Science, Russia, for arranging the cruise on Lake Baikal. We are also indebted to Drs. V. Sinyukovich, I. Khanaev,
and A. Zhdanov for their kind assistance during the expeditions. We wish to thank Ms. Y. Ito for measuring the DOC concentrations.
This work was supported and financed by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan (No. 09041159) and for Scientific Research of Priority Area B (No. 11213101) and by the
International Geosphere-Biosphere Programme (IGBP) at Nagoya University.
Correspondence to:T. Yoshioka 相似文献
15.
M. S. Naumann A. Haas U. Struck C. Mayr M. el-Zibdah C. Wild 《Coral reefs (Online)》2010,29(3):649-659
Particulate organic matter (POM) and dissolved organic carbon (DOC) release by six dominant hermatypic coral genera (Acropora, Fungia, Goniastrea, Millepora, Pocillopora and Stylophora) were measured under undisturbed conditions by laboratory incubations during four seasonal expeditions to the Northern Red
Sea. In addition, the influence of environmental factors (water temperature, light availability and ambient inorganic nutrient
concentrations) was evaluated. Particulate organic carbon (POC) and particulate nitrogen (PN) release were always detectable
and genus-specific, with Stylophora releasing most POM (6.5 mg POC and 0.5 mg PN m−2 coral surface area h−1) during all seasons. The fire coral Millepora released significantly less POM (0.3 mg POC and 0.04 mg PN m−2 coral surface area h−1) than all investigated anthozoan genera. The average POC:PN ratio of POM released by all coral genera was 12 ± 1, indicating
high carbon/low nitrogen content of coral-derived organic matter. POM release showed little seasonal variation, but average
values of POC and PN release rates correlated with water temperature, light availability and ambient nitrate concentrations.
DOC net release and elevated DOC:POC ratios were detectable for Acropora, Goniastrea and Millepora, revealing maximum values for Acropora (30.7 mg DOC m−2 coral surface area h−1), whilst predominant DOC uptake was observed for Pocillopora, Fungia and Stylophora. Depth-mediated light availability influenced DOC fluxes of Acropora and Fungia, while fluctuations in water temperature and ambient inorganic nutrient concentrations showed no correlation. These comprehensive
data provide an important basis for the understanding of coral reef organic matter dynamics and relevant environmental factors. 相似文献
16.
Seasonal dynamics of suspended minerals, organic matter, particulate, and dissolved organic carbon (DOC), chlorophyll, and
their vertical fluxes were studied in a small Arctic fjord (Adventfjorden, Spitsbergen) from November 2006 to October 2007.
The fjord was usually covered with fast ice in winter, but remained open throughout the year since 2005. The open-water winter
period caused increased wave action and resuspension of organic and mineral particles. The lack of sea-ice in spring accelerated
the onset of the productive season. The earlier light signal also caused an earlier appearance of mesozooplanktonic organisms,
accompanied by a significant increase of the DOC pool in the water. In the cold period (winter and spring) 47% of the annual
organic matter settled on the sampling site, a lot coming from the spring diatom bloom in April. Summer melt (July, August)
resulted in turbid and brackish fjord surface water with stratification and increase of both suspended particles and sedimentation,
causing 60% of the annual minerals and 53% of the annual organic matter to settle at the sampling site. Increased dissolved
organic carbon (DOC) through sloppy feeding on the mixo- and heterotrophic protista by the abundant mesozooplankton indicated
intensive secondary production, resulting in a maximum fecal pellets flux of >5 mg C m−2 day−1. A warmer climate with reduced sea-ice cover in fjords will advance the onset of the spring bloom and will also result in
a larger input of turbid melt water in summer, restricting the light availability and enhancing flocculation and thereby sedimentation. 相似文献
17.
This study considers the cycling of nitrogen in the waters of the North Sea, particularly focussing on organic nitrogen. Dissolved
inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and particulate organic nitrogen (PON) were measured in the North
Sea over a one-year period (autumn 2004–summer 2005). The surface water concentrations of nitrate, ammonium, DON and PON during
the present study ranged from <0.1–7.2 μM, <0.1–2.0 μM, 1.9–11.2 μM and 0.3–5.6 μM, respectively, with DON the dominant fraction
of total nitrogen at all times. These nutrients concentrations were significantly lower compared to previous studies in the
southern North Sea. The seasonal variations showed high mean surface concentrations of nitrate (4.7 ± 0.6 μM) and DON (8.9 ± 0.9 μM),
low ammonium (<0.1 μM) and PON (0.8 ± 0.1 μM) in winter, shifting to low nitrate (0.3 ± 0.3 μM) and DON (4.2 ± 1.2 μM) in
summer, with high ammonium (0.8 ± 0.4 μM) in autumn and PON (2.5 ± 1.2 μM) in spring. Highest mean surface DON concentration
was measured in winter and may be due to resuspension of the organic matter from the bottom sediments. For autumn and spring,
phytoplankton DON release was likely to be the most significant source of DON as shown by high concentrations of low molecular
weight (LMW) DON and its positive correlation to chlorophyll a. Low total and LMW DON concentrations during summer were likely to be due to the uptake of the LMW DON fraction by phytoplankton
and bacteria and the stratification of the water column. DON is therefore shown to be a potentially important source of nitrogen
in shelf seas especially after the spring bloom has depleted nitrate to limiting concentrations.
Handling editor: L. Naselli-Flores 相似文献
18.
Roberto Bertoni Cristiana Callieri Gianluca Corno Serena Rasconi Emanuele Caravati Mario Contesini 《Hydrobiologia》2010,644(1):279-287
We analysed the long-term dynamics (1980–2007) of hypolimnetic and epilimnetic bacterial abundances and organic carbon concentrations,
both dissolved (DOC) and particulate (POC), in the deep holo-oligomictic Lake Maggiore, included in the Southern Alpine Lakes
Long-Term Ecological Research (LTER) site. During the 28 years of investigation, bacterial abundance and POC concentrations
did not decrease with declining phosphorus concentrations, while DOC concentrations showed a pronounced decrease in the epi-
and hypolimnion. We used the annual mean total lake heat content and total annual precipitation as climate-related variables,
and in-lake total phosphorus as a proxy for trophic state. The model (forward stepwise regression, FSR) showed that reduced
anthropogenic pressure was more significant than climate change in driving the trend in DOC concentrations. Bacterial dynamics
in the hypolimnion mirrored the fluctuations observed in the epilimnion, but average cell abundance was three times lower.
The FSR model indicates that bacterial number variability was dependent on POC in the epilimnion and DOC in the hypolimnion.
In the hypolimnion, cell biovolumes for rod and coccal morphotypes were significantly larger than in the epilimnion. 相似文献
19.
Colleen T. E. Kellogg Shelly D. Carpenter Alisha A. Renfro Am��lie Sallon Christine Michel J. Kirk Cochran Jody W. Deming 《Polar Biology》2011,34(12):2007-2023
Export of autochthonously produced particulate organic carbon (POC) is a globally important mechanism for sequestering carbon
in the deep sea. The role of microbial hydrolytic activity in attenuating POC flux is generally understudied, and particularly
complex on Arctic continental shelves influenced by other sources of POC. To evaluate this role, we used fluorogenic substrate
analogs to measure extracellular enzyme activity (EEA) associated with particle size fractions considered suspended (1–70 μm)
and sinking (>70 μm). Samples were collected by in situ filtration at depths of 25–100 m at ten stations (156–1,142 m deep)
in the Amundsen Gulf and Beaufort Sea in June–July, 2008, during the Circumpolar Flaw Lead project. Significant positive correlations
observed between EEA and both chlorophyll a and δ13CPOC suggest that EEA is elevated in waters dominated by marine-derived POC. No difference in bulk EEA was observed between size
fractions, but POC- and cell-specific EEA was significantly elevated on sinking aggregates. Calculations show that 2–44% of
carbon retention in surface waters could be attributed to mobilization by enzymes associated with sinking aggregates, and
up to 57% if enzymes associated with suspended particles are included. Model results suggest that microbial attenuation of
POC below the euphotic zone is a quantitatively important mechanism for carbon loss, especially when particles are sinking
slowly. The role of microbes in attenuating POC flux on Arctic shelves appears to have been underestimated previously and
may become increasingly important if climate warming brings increased marine productivity. 相似文献
20.
Differences in temperature, organic carbon and oxygen consumption among lowland streams 总被引:1,自引:0,他引:1
1. Temperature, organic carbon and oxygen consumption were measured over a year at 13 sites in four lowlands streams within the same region in North Zealand, Denmark with the objectives of determining: (i) spatial and seasonal differences between open streams, forest streams and streams with or without lakes, (ii) factors influencing the temperature dependence of oxygen consumption rate, (iii) consequences of higher temperature and organic content in lake outlets on oxygen consumption rate, and (iv) possible consequences of forecasted global warming on degradation of organic matter. 2. High concentrations of easily degradable dissolved (DOC) and particulate organic carbon (POC) were found in open streams downstream of plankton‐rich lakes, while high concentrations of recalcitrant DOC were found in a forest brook draining a forest swamp. Concentrations of predominantly recalcitrant POC and DOC were low in a groundwater‐fed forest spring. Overall, DOC concentration was two to 18 times higher than POC concentrations. 3. Oxygen consumption rate at 20 °C was higher during summer than winter, higher in open than shaded streams and higher in lake outlets than inlets. Rate was closely related to concentrations of chlorophyll and POC but not to DOC. The ratio of oxygen consumption rate to total organic concentrations (DOC + POC), serving as a measure of organic degradability, was highest downstream of lakes, intermediate in open streams and lowest in forest streams. 4. Temperature coefficients describing the exponential increase of oxygen consumption rate between 4 and 20 °C averaged 0.121 °C?1 (Q10 of 3.35) in 70 measurements and showed no significant variations between seasons and stream sites or correlations with ambient temperature and organic content. 5. Oxygen consumption rate was enhanced downstream of lakes during summer because of higher temperature and, more significantly, greater concentrations of degradable organic carbon. Oxygen consumption rates were up to seven times higher in the stream with three impoundments than in a neighbouring unshaded stream and 21 times higher than in the groundwater‐fed forest spring. 6. A regional climate model has calculated a dramatic 4–5 °C rise in air temperature over Denmark by 2070–2100. If this is realised, unshaded streams are estimated to become 2–3 °C warmer in summer and winter and 5–7 °C warmer in spring and, thereby, increase oxygen consumption rates at ambient temperature by 30–40% and 80–130%, respectively. Faster consumption of organic matter and dissolved oxygen downstream of point sources should increase the likelihood of oxygen stress of the stream biota and lead to the export of less organic matter but more mineralised nutrients to the coastal waters. 相似文献