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Inmaculada de Vicente Eva Ortega-Retuerta Ignacio P. Mazuecos Michael L. Pace Jonathan J. Cole Isabel Reche 《Aquatic Sciences - Research Across Boundaries》2010,72(4):443-453
In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences
for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in
biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength
and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located
in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low
color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean
(36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L−1 in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems
and ranged from 66 to 9,038 μg GX eq L−1. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl
a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the
positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables
tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly
driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes,
the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above
which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column. 相似文献
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Par Mauricette Feuillade Ph. Dufour J. Feuillade J. P. Pelletier 《Aquatic Sciences - Research Across Boundaries》1986,48(1):18-33
The release of soluble organic carbon by the phytoplankton in the trophogenic layer of Lake Geneva has been investigated by14C method from March to November 1984. The carbon excretion rate varied from 0.01 to 0.5 mg C·m−3·h−1 and depended primarily upon the rate of its photosynthetic assimilation. The carbon excretion rate varied generally between
2 and 5% of photoassimilated carbon and exceptionally exceeded 6%. These values were underestimated from part of heterotrophic
reassimilation. The study of the carbon balance over 24 hours has shown that night excretion represents less than 10% of losses
due to respiration.
Heterotrophic activity measured by14C glucose assimilation exhibited seasonal variations following the same general pattern as excretion. The quantity of phytoplankton
excretion products appeared to be superior to the needs in organic compounds of heterotrophic organisms in the trophogenic
layer.
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Naomi Greenwood Rodney M. Forster Veronique Créach Suzanne J. Painting Anna Dennis Stewart J. Cutchey Tiago Silva David B. Sivyer Tim Jickells 《Ocean Dynamics》2012,62(2):307-320
The seasonal and interannual variability in the phytoplankton community in Liverpool Bay between 2003 and 2009 has been examined
using results from high frequency, in situ measurements combined with discrete samples collected at one location in the bay.
The spring phytoplankton bloom (up to 29.4 mg chlorophyll m−3) is an annual feature at the study site and its timing may vary by up to 50 days between years. The variability in the underwater
light climate and turbulent mixing are identified as key factors controlling the timing of phytoplankton blooms. Modelled
average annual gross and net production are estimated to be 223 and 56 g C m−2 year−1, respectively. Light microscope counts showed that the phytoplankton community is dominated by diatoms, with dinoflagellates
appearing annually for short periods of time between July and October. The zooplankton community at the study site is dominated
by copepods and use of a fine mesh (80 μm) resulted in higher abundances of copepods determined (up to 2.5 × 106 ind. m−2) than has previously reported for this location. There is a strong seasonal cycle in copepod biomass and copepods greater
than 270 μm contribute less than 10% of the total biomass. Seasonal trends in copepod biomass lag those in the phytoplankton
community with a delay of 3 to 4 months between the maximum phytoplankton biomass and the maximum copepod biomass. Grazing
by copepods exceeds net primary production at the site and indicates that an additional advective supply of carbon is required
to support the copepod community. 相似文献
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Sediment cores and sediment traps were collected twice a month in two 35 m deep stations of Lake Geneva (Switzerland). The
organic input sedimenting to the bottom is equal to 157 g C m−2y−1 in station 1, to 214 g C in station 2. In spite of this difference, the oxygen uptake by the sediment (OUS) is similar in
both locations (46–47 g C m−2y−1). The oxygen uptake by the matter sedimenting to the bottom (OUSM) is respectively 45 g C m−2y−1 and 41 g C in stations 1 and 2. The equivalence between OUS and OUSM implies that most of the sedimented matter arriving
to the bottom is directly oxidized at the sediment surface. In station 1, OUS is positively correlated to OUSM, and OUSM is
positively correlated to chlorophyll-a concentrations in the water column (0–20 m) one week before sediment sampling. In location
2, OUS is positively correlated to the percentage of organic carbon and nitrogen in the sedimented matter, negatively to its
C:N ratio. Increasing allochthonous inputs have a negative influence on benthic respiration. At both sites, OUS is not directly
related to macrobenthic biomass or to temperature of bottom water. 相似文献
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Tao Zhen Shen ChengDe Gao QuanZhou Sun YanMin Yi WeiXi Li YingNian 《中国科学D辑(英文版)》2007,50(7):1103-1114
High-resolution sampling, measurements of organic carbon contents and 14C signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau, and application
of 14C tracing technology were conducted in an attempt to investigate the turnover times of soil organic carbon and the soil-CO2 flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12×104 kg C hm−2 to 30.75×104 kg C hm−2 in the alpine meadow ecosystems, with an average of 26.86×104 kg C hm−2. Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of
years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO2 flux ranges from 103.24 g C m−2 a−1 to 254.93 gC m−2 a−1, with an average of 191.23 g C m−2 a−1. The CO2 efflux produced from microbial decomposition of organic matter varies from 73.3 g C m−2 a−1 to 181 g C m−2 a−1. More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%281.23% of total CO2 emitted from organic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming, the storage, volume of flow and fate of the soil organic carbon in the alpine meadow
ecosystem of the Tibetan Plateau will be changed, which needs further research.
Supported by the National Natural Science Foundation of China (Grant Nos. 40231015, 40471120 and 40473002) and the Guangdong
Provincial Natural Science Foundation of China (Grant No. 06300102) 相似文献
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FANG JingYun LIU GuoHua ZHU Biao WANG XiaoKe & LIU ShaoHui Department of Ecology College of Environmental Sciences and Key Laboratory for Earth Surface Processes of the Ministry of Education Peking University Beijing China Research Center for Eco-Environmental Sciences Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2007,50(1):92-101
There is a general agreement that forest ecosystems in the Northern Hemisphere function as signifi-cant sinks for atmospheric CO2; however, their magnitude and distribution remain large uncertainties. In this paper, we report the carbon (C) stock and its change of vegetation, forest floor detritus, and mineral soil, annual net biomass increment and litterfall production, and respiration of vegetation and soils between 1992 to 1994, for three temperate forest ecosystems, birch (Betula platyphylla) forest, oak (Quercus liaotungensis) forest and pine (Pinus tabulaeformis) plantation in Mt. Dongling, Beijing, China. We then evaluate the C budgets of these forest ecosystems. Our results indicated that total C density (organic C per hectare) of these forests ranged from 250 to 300 t C ha-1, of which 35―54 t C ha-1 from vegetation biomass C and 209―244 t C ha-1 from soil organic C (1 m depth, including forest floor detritus). Biomass C of all three forests showed a net increase, with 1.33―3.55 t C ha-1 a-1 during the study period. Litterfall production, vegetation autotrophic respiration, and soil heterotrophic respira-tion were estimated at 1.63―2.34, 2.19―6.93, and 1.81―3.49 t C ha-1 a-1, respectively. Ecosystem gross primary production fluctuated between 5.39 and 12.82 t C ha-1 a-1, about half of which (46%―59%, 3.20―5.89 t C ha-1 a-1) was converted to net primary production. Our results suggested that pine forest fixed C of 4.08 t ha-1 a-1, whereas secondary forests (birch and oak forest) were nearly in balance in CO2 exchange between the atmosphere and ecosystems. 相似文献
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A critical factor controlling changes in the acidity of coastal waters is the alkalinity of the water. Concentrations of alkalinity
are determined by supply from rivers and by in situ processes such as biological production and denitrification. A 2-year
study based on 15 cruises in Liverpool Bay followed the seasonal cycles of changing concentrations of total alkalinity (TA)
and total dissolved inorganic carbon (DIC) in relation to changes caused by the annual cycle of biological production during
the mixing of river water into the Bay. Consistent annual cycles in concentrations of nutrients, TA and DIC were observed
in both years. At a salinity of 31.5, the locus of primary production during the spring bloom, concentrations of NO
x
decreased by 25 ± 4 μmol kg−1 and DIC by 106 ± 16 μmol kg−1. Observed changes in TA were consistent with the uptake of protons during primary biological production. Concentrations of
TA increased by 33 ± 8 μmol kg−1 (2009) and 33 ± 15 μmol kg−1 (2010). The impact of changes in organic matter on the measured TA appears likely to be small in this area. Thomas et al.
(2009) suggested that denitrification may enhance the CO2 uptake of the North Sea by 25%, in contrast we find that although denitrification is a significant process in itself, it
does not increase concentrations of TA relative to those of DIC and so does not increase buffer capacity and potential uptake
of CO2 into shelf seawaters. For Liverpool Bay historical data suggest that higher concentrations of TA during periods of low flow
are likely to contribute in part to the observed change in TA between winter and summer but the appropriate pattern cannot
be identified in recent low-frequency river data. On a wider scale, data for the rivers Mersey, Rhine, Elbe and Weser show
that patterns of seasonal change in concentrations of TA in river inputs differ between river systems. 相似文献
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22 annual layered samples of coral from 1977 to 1998 were collected from Daya Bay, South China Sea, their bomb-14C (nuclear weapons testing14C) concentrations were determined and studied, and the atmosphere-sea exchange rate and diffusion thickness were estimated
and found to be 17 mol · m−2 · a−1 and 32 μm, respectively. The interannual variation of coral Δ14C is mainly controlled by oceanic factors. In ENSO years, the coastwise upwelling current of South China Sea gets intensified,
hence the coral Δ14C displays its bottom value. The coral Δ14C does no respond vividly to the variation of the solar radiation energy. In the past 20 years or so, the genera situation
and the oceanic thermal structure of South China Sea are still stable even though inter annual variation occurs in the atmosphere-sea
interaction and the upwelling current driven by the tropical energy. 相似文献
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William F. James 《Aquatic Sciences - Research Across Boundaries》2010,72(1):61-69
Backwaters connected to large rivers retain nitrate and may play an important role in reducing downstream loading to coastal
marine environments. A summer nitrogen (N) inflow-outflow budget was examined for a flow-regulated backwater of the upper
Mississippi River in conjunction with laboratory estimates of sediment ammonium and nitrate fluxes, organic N mineralization,
nitrification, and denitrification to provide further insight into N retention processes. External N loading was overwhelmingly
dominated by nitrate and 54% of the input was retained (137 mg m−2 day−1). Ammonium and dissolved organic N were exported from the backwater (14 and 9 mg m−2 day−1, respectively). Nitrate influx to sediment increased as a function of increasing initial nitrate concentration in the overlying
water. Rates were greater under anoxic versus oxic conditions. Ammonium effluxes from sediment were 26.7 and 50.6 mg m−2 day−1 under oxic and anoxic conditions, respectively. Since anoxia inhibited nitrification, the difference between ammonium anoxic–oxic
fluxes approximated a nitrification rate of 29.1 mg m−2 day−1. Organic N mineralization was 64 mg m−2 day−1. Denitrification, estimated from regression relationships between oxic nitrate influx versus initial nitrate concentration
and a summer lakewide mean nitrate concentration of 1.27 mg l−1, was 94 mg m−2 day−1. Denitrification was equivalent to only 57% of the retained nitrate, suggesting that another portion was assimilated by biota.
The high sediment organic N mineralization and ammonium efflux rate coupled with the occurrence of ammonium export from the
system suggested a possible link between biotic assimilation of nitrate, mineralization, and export. 相似文献
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Young-Joo Lee 《中国科学D辑(英文版)》2006,49(8):872-880
Serious interest has been directed toward natural gas hydrate as a potential energy resource; factor in global climate change, and submarine geohazard since naturally occurring gas-hydrate deposits were found in the 1960s. Hydrate Ridge, Cascadia convergent mar- gin, is characterized by abundant methane hydrates at and below the seafloor, active venting of fluids and gases, chemosynthetic communities, and some of the highest methane oxidation rates ever found in the ma-rine environment. All of… 相似文献
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Black carbon aerosols and their radiative properties in the Pearl River Delta region 总被引：13，自引：0，他引：13
Dui Wu JieTai Mao XueJiao Deng XueXi Tie YuanHang Zhang LiMin Zeng Fei Li HaoBo Tan XueYan Bi XiaoYing Huang Jing Chen Tao Deng 《中国科学D辑(英文版)》2009,52(8):1152-1163
The climatic and environmental effects of atmospheric aerosols are a hot topic in global science community, and radiative
properties of the aerosols are one of the important parameters in assessing climatic change. Here we studied the black carbon
concentration and absorption coefficient measured with aethalometers, scattering coefficient measured with nephelometers,
and single scattering albedo derived at an atmospheric composition watch station in Guangzhou from 2004 to 2007. Our main
results are as follows. The data of black carbon concentration and absorption coefficients measured with instruments cannot
be directly used until they are measured in parallel with internationally accepted instruments for comparison, calibration,
and reduction. After evaluation of the data, the result shows that the monthly mean of BC concentration varies 3.1–14.8 μg·m−3 and the concentration decreases by about 1 μg·m−3 in average over the four years; It is higher in the dry season with a multi-year mean of 8.9 μg/m3 and lower in the rainy season with a multi-year mean of 8.0 μg·m−3; The extreme maximum of monthly mean concentration occurred in December 2004 and extreme minimum in July 2007, and a 4-year
mean is 8.4 μg·m−3. It is also shown that monthly mean scattering coefficient derived varies 129 −565 Mm−1, monthly mean absorption coefficient 32–139 Mm−1, and monthly mean single scattering albedo 0.71–0.91, with annual mean values of 0.80, 0.82, 0.79 and 0.84 for 2004, 2005,
2006 and 2007, respectively. Three instruments were used to take simultaneous measurements of BC in PM10, PM2.5, and PM1 and the results showed that PM2.5 took up about 90% of PM10 and PM1 accounted for about 68% of PM2.5, and BC aerosols are mainly present in fine particulates. The variability of BC concentrations is quite consistent between
the Nancun station (141 m above sea level) and the Panyu station (13 m above sea level), which are 8 km apart from each other.
The concentration in higher altitude station (Panyu) is consistently lower than the lower altitude station (Nancun), and the
difference of annual mean is about 4 μg·m−3.
Supported by Natural Science Foundation of China (Grant Nos. U0733004, 40375002, 40418008, 40775011), National High Technology
R & D Program of China (Grant Nos. 2006AA06A306 and 2006AA06A308) and National Basic Research Program of China (Grant No.
2005CB422207) 相似文献