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1.
The distributions of dissolved organic carbon (DOC) in the warm season were elucidated in ten lakes of different trophic types in Japan, Russia, and China. DOC showed similar vertical distributions in all the lakes in summer when thermal stratification occurred. DOC in the epilimnion was higher than the value of 0.8mgCl–1 found in the hypolimnion. In three Japanese lakes, hypolimnion DOC was negatively correlated with apparent oxygen utilization (AOU), reflecting the net oxidation of DOC using the dissolved oxygen in lake water. The DOC:O2 ratios (0.115–0.179), calculated by the slopes of the regression lines of DOC versus AOU in hypolimnion water, were as low as those of deep-sea water, which indicates low bioavailability of lake water DOC for heterotrophic bacteria. DOC and conductivity did not correlate well except in two Japanese lakes: one showed a positive correlation and the other a negative correlation, indicating DOC loading from the inflowing rivers. Eutrophic lakes tended to have higher DOC values than meso- and oligotrophic lakes, and DOC values in the surface water negatively correlated with Secchi depths. 相似文献
2.
Distribution of dissolved organic carbon and dissolved fulvic acid in mesotrophic Lake Biwa, Japan 总被引:1,自引:0,他引:1
The dissolved organic carbon (DOC) concentrations in mesotrophic Lake Biwa were determined by a total organic carbon (TOC)
analyzer, and DOC molecular size distributions were determined by size exclusion chromatography (SEC) using a fluorescence
detector at excitation/emission (Ex/Em) levels of 300/425 nm with the eluent at pH 9.7. The fluorescence wavelengths for detection
were chosen from the result of excitation–emission matrix spectrometry (EEM) analysis for dissolved fulvic acid (DFA) extracted
from Ado River (peak A, Ex/Em = 260–270/430–440 nm; peak B, Ex/Em = 300–310/420–430 nm). Ado River DFA was eluted with a retention
time (RT) of 7.4–8.9 min and the apparent molecular weight was estimated at 22–87 kDa based on the elution curve for the spherical
protein molecular weight standard. A DFA peak eluted at the same retention time as Ado River DFA also appeared in all the
samples of Lake Biwa water. From the linear relationship between the peak areas with an RT of 7.4–8.9 min by SEC analysis
and DOC values of DFA by TOC analysis of a series of DFA samples (r2 = 0.9995), the concentrations of DFA in the lake water were roughly calculated. DFA was distributed within the range 0.25–0.43 mg C l−1 and accounted for 15%–41% of DOC, with the highest ratios observed at a depth of 70 m in August and the lowest at 2.5 m in
May. 相似文献
3.
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
4.
Sources and fates of dissolved organic carbon in lakes as determined by whole-lake carbon isotope additions 总被引:3,自引:0,他引:3
Darren L. Bade Stephen R. Carpenter Jonathan J. Cole Michael L. Pace Emma Kritzberg Matthew C. Van de Bogert Rose M. Cory Diane M. McKnight 《Biogeochemistry》2007,84(2):115-129
Four whole-lake inorganic 13C addition experiments were conducted in lakes of differing trophic status. Inorganic 13C addition enriched algal carbon in 13C and changed the C-DOC by +1.5‰ to +9.5‰, depending on the specific lake. This change in C-DOC represented a significant input of algal DOC that was not completely consumed by bacteria. We modeled the dynamics in
C-DOC to estimate the fluxes of algal and terrestrial carbon to and from the DOC pool, and determine the composition of the
standing stock. Two experiments in lightly stained, oligotrophic lakes indicated that algal production was the source of about
20% of the DOC pool. In the following year, the experiment was repeated in one of these lakes under conditions of nutrient
enrichment, and in a third, more humic lake. Algal contributions to the DOC pool were 40% in the nutrient enriched lake and
5% in the more humic lake. Spectroscopic and elemental analyses corroborated the presence of increased algal DOC in the nutrient
enriched lake. Natural abundance measurements of the C of DOC in 32 lakes also revealed the dual contributions of both terrestrial and algal carbon to DOC. From these results,
we suggest an approach for inferring the contribution of algal and terrestrial DOC using easily measurable parameters. 相似文献
5.
To determine the chemical and physicochemical characteristics of dissolved organic carbon in the Ado River and the Yasu River,
the main rivers flowing into Lake Biwa, the adsorption behavior onto hydrous iron oxide (HIO) and the reactivity to KMnO4 oxidant were investigated in parallel with measurement of the distribution profiles of dissolved organic carbon (DOC) along
the rivers. In one year of observation at the mouths of the two rivers, DOC concentrations were found to vary in the Ado over
the range 0.28–1.21 mg C l−1 and in the Yasu over the range 1.01–2.68 mg C l−1. Act-DOC, one of the fractions separated from the total DOC by its adsorption-active character onto HIO at pH 4, was thought
primarily to control the variation of total DOC, as in Lake Biwa. The int-DOC, another fraction separated by its adsorption-inert
or -inactive character onto HIO, remained at almost a steady value around 0.18 ± 0.07 mg C l−1 in the Ado, which was lower than that (0.35 ± 0.05 mg C l−1) in Lake Biwa. The act-DOC in river waters was reactive to KMnO4 oxidant, showing a linear relation with the amount of permanganate consumed for the reaction (chemical oxygen demand: COD).
In river waters, the relation can be approximated by a straight line expressed as COD (mg O2 l−1) = 0.64 × act-DOC (mg C l−1) − 0.02. In contrast, in the lake water the relation was COD (mg O2 l−1) = 0.97 × act-DOC (mg C l−1) − 0.50.
Received: March 3, 1999 / Accepted: December 2, 1999 相似文献
6.
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
7.
The impact of conservation tillage practices on soil carbon has been of great interest in recent years. Conservation tillage might have the potential to enhance soil carbon accumulation and alter the depth distribution of soil carbon compared to conventional tillage based systems. Changes in the soil organic carbon (SOC) as influenced by tillage, are more noticeable under long-term rather than short-term tillage practices. The objective of this study was to determine the impacts of long-term tillage on SOC and dissolved organic carbon (DOC) status after 19 years of four tillage treatments in a Hydragric Anthrosol. In this experiment four tillage systems included conventional tillage with rotation of rice and winter fallow system (CTF), conventional tillage with rotation of rice and rape system (CTR), no-till and ridge culture with rotation of rice and rape system (NT) and tillage and ridge culture with rotation of rice and rape system (TR). Soils were sampled in the spring of 2009 and sectioned into 0–10, 10–20, 20–30, 30–40, 40–50 and 50–60 cm depth, respectively.Tillage effect on SOC was observed, and SOC concentrations were much larger under NT than the other three tillage methods in all soil depths from 0 to 60 cm. The mean SOC concentration at 0–60 cm soil depth followed the sequence: NT (22.74 g kg?1) > CTF (14.57 g kg?1) > TR (13.10 g kg?1) > CTR (11.92 g kg?1). SOC concentrations under NT were significantly higher than TR and CTR (P < 0.01), and higher than CTF treatment (P < 0.05). The SOC storage was calculated on equivalent soil mass basis. Results showed that the highest SOC storage at 0–60 cm depth presented in NT, which was 158.52 Mg C ha?1, followed by CTF (106.74 Mg C ha?1), TR (93.11 Mg C ha?1) and CTR (88.60 Mg C ha?1). Compared with conventional tillage (CTF), the total SOC storage in NT increased by 48.51%, but decreased by 16.99% and 12.77% under CTR and TR treatments, respectively. The effect of tillage on DOC was significant at 0–10 cm soil layer, and DOC concentration was much higher under CTF than the other three treatments (P < 0.01). Throughout 0–60 cm soil depth, DOC concentrations were 32.92, 32.63, 26.79 and 22.10 mg kg?1 under NT, CTF, CTR and TR, and the differences among the four treatments were not significant (P > 0.05). In conclusion, NT increased SOC concentration and storage compared to conventional tillage operation but not for DOC. 相似文献
8.
Jennifer Lawson Knoepfle Peter T. Doran Fabien Kenig W. Berry Lyons V. F. Galchenko 《Hydrobiologia》2009,632(1):139-156
In perennially ice-covered lakes of Taylor Valley, Antarctica, “legacy”, a carryover of past ecosystem events, has primarily
been discussed in terms of nutrient and salinity concentrations and its effect on the current ecology of the lakes. In this
study, we determine how residual pools of ancient carbon affect the modern carbon abundance and character in the water columns
of Lakes Fryxell, Hoare, and Bonney. We measure the stable carbon isotopic compositions and concentrations of particulate
organic carbon (POC) and dissolved inorganic carbon (DIC) in the water column of these lakes over four seasons (1999–2002).
These data are presented and compared with all the previously published Taylor Valley lacustrine carbon stable isotopic data.
Our results show that the carbon concentrations and isotopic compositions of the upper water columns of those lakes are controlled
by modern processes, while the lower water columns are controlled to varying degrees by inherited carbon pools. The water
column of the west lobe of Lake Bonney is dominated by exceptionally high concentrations of DIC (55,000–75,000 μmol l−1) reflecting the long period of ice-cover on this lake. The east lobe of Lake Bonney has highly enriched δ13CDIC values resulting from paleo-brine evaporation effects in its bottom waters, while its high DIC concentrations provide geochemical
evidence that its middle depth waters are derived from West Lake Bonney during a hydrologically connected past. Although ancient
carbon is present in both Lake Hoare and Lake Fryxell, the δ13CDIC values in bottom waters suggest dominance by modern primary productivity-related processes. Anaerobic methanogenesis and
methanotrophy are also taking place in the lower water column of Lake Fryxell with enough methane, oxidized anaerobically,
to contribute to the DIC pool. We also show how stream proximity and high flood years are only a minor influence on the carbon
isotopic values of both POC and DIC. The Taylor Valley lake system is remarkably stable in both inter-lake and intra-lake
carbon dynamics.
Handling editor: K. Martens 相似文献
9.
Dynamics of dissolved organic carbon concentration (DOC) and capacity toabsorb light (color) are determined by in-lake and external properties andprocesses. In this study, the influence of external factors such as rainfallandsolar radiation on DOC and color dynamics was assessed for a small forestedlake. DOC and absorption coefficients at 440 nm (a440)ranged 4-fold from 0.46 to 1.62 mM and from 3.4 to 14.8m–1, respectively. DOC and a440 variedsynchronously, but an important percentage of the variability (26%) ina440 was not explained by DOC. The resulting twofold variation inthemolar absorption coefficient of DOC suggested significant seasonal changes inchromophoric content. Both DOC and a440 were positive andsignificantly related to cumulative rainfall. Solar radiation, however, onlyappeared to influence a440 dynamics. This influence was mediated byphotobleaching. Photobleaching coefficients (kb) were higher in falland spring relative to the summer. This seasonal variability in kbvalues was related to monthly rainfall. The influence of photobleaching ona440 dynamics was evaluated by comparing the half life ofa440 in the water column with water residence time (WRT). For thestudy lake, photobleaching contributed notably to a440 dynamicsduring the dry periods when WRT was longer than the a440 half life .DOC dynamics, however, were not related to solar radiation becausephotomineralization was considerably slower than photobleaching. 相似文献
10.
Dissolved organic carbon (DOC) plays an important role in surface water chemistry and ecology and trends in DOC concentration have been also associated with shifts in terrestrial carbon pools. Numerous studies have reported long-term trends in DOC concentration; however, some studies consider changes in average measured DOC whereas other compute discharge weighted concentrations. Because of differences in reporting methods and variable record lengths it is difficult to compare results among studies and make regional generalizations. Furthermore, changes in stream discharge may impact long-term trends in DOC concentration and the potentially subtle effect of shifts in stream flow may be missed if only measured DOC concentrations are considered. In this study we compare trends in volume-weighted vs. average measured DOC concentration between 1980 and 2001 at seven headwater streams in south-central Ontario, Canada that vary in wetland coverage and DOC (22-year mean vol. wt.) from 3.4 to 10.6 mg l−1. On average, annual measured DOC concentrations were 13–34% higher than volume-weighted values, but differences of up to 290% occurred in certain years. Estimates of DOC flux were correspondingly higher using measured concentration values. Both measured and volume-weighted DOC concentrations increased significantly between 1980 and 2001, but slopes were larger in measured data (0.04–0.35 mg l−1 year−1 compared with 0.05–0.15 mg l−1 year−1) and proportional increases at the most wetland-influenced sites ranged from 32 to 43% in volume-weighted DOC and from 52 to 75% in measured DOC. In contrast, DOC flux did not change with time when estimated using either method, because of the predominant influence of stream flow on DOC export. Our results indicate that changes in stream flow have an important impact on trends in DOC concentration, and extrapolation of trend results from one region to another should be made cautiously and consider methodological and reporting differences among sites. 相似文献
11.
David W. Schindler P. Jefferson Curtis Suzanne E. Bayley Brian R. Parker Ken G. Beaty Michael P. Stainton 《Biogeochemistry》1997,36(1):9-28
During 20 years of climatic warming, drought and increased forest firesbetween 1970 and 1990, DOC concentrations declined by 15--25%in lakesof the Experimental Lakes Area, northwestern Ontario, allowing increasedpenetration of both UV and photosynthetically-active radiation (PAR), andcausing deeper euphotic zones and thermoclines. Decreased input to thelakes of DOC from terrestrial catchments and upstream lakes was theprimary reason for the decline, although in-lake removal also increasedslightly. Decreased streamflow caused by drought was more important thanforest fires in affecting DOC exports from catchments. Experimentalacidification of lakes caused even greater losses in DOC, by enhancing ratesof in-lake removal. DOC in Lake 302S, acidified to pH 4.5 during the1980s, declined to less than 10% of preacidificationvalues. 相似文献
12.
A stable carbon isotope study of dissolved inorganic carbon cycling in a softwater lake 总被引:3,自引:0,他引:3
Andrew L. Herczeg 《Biogeochemistry》1987,4(3):231-263
The dissolved inorganic carbon (DIC) cycle in a softwater lake was studied using natural variations of the stable isotopes of carbon,12C and13C. During summer stratification there was a progressive decrease in epilimnion DIC concentration with a concomitant increase in 13CDIC), due to preferential uptake of12C by phytoplankton and a change in the dominant CO2 source from inflow andin situ oxidation to invasion from the atmosphere. There was an increase in hypolimnion DIC concentration throughout summer with a concomitant general decrease in 13CDIC from oxidation of the isotopically light particulate organic carbon that sank down through the thermocline from the epilimnion.Mass balance calculations of DI12C and DI13C in the epilimnion for the summer (June 23–September 25) yield a mean rate of net conversion of DIC to organic carbon (Corg) of 430 ± 150 moles d-1 (6.5 ± 1.8 m moles m-2 d-1. Net CO2 invasion from the atmosphere was 420 ± 120 moles d-1 (6.2 ± 1.8 m moles m-2 d-1) with an exchange coefficient of 0.6 ± 0.3m d-1. These results imply that at least for the summer months the phytoplankton obtained about 90% of their carbon from atmosphere CO2. About 50% of CO2 invasion and conversion to Corg for the summer occurred during a two week interval in mid-summer.DIC concentration increased in the hypolimnion at a rate of 350 ± 70 moles DIC d-1 during summer stratification. The amount of DIC added to the hypolimnion was equivalent to 75 ± 20% of net conversion of DIC to Corg in the euphotic zone over spring and summer implying rapid degradation of POC in the hypolimnion. The 13C of DIC added to the deep water (-22.) was too heavy to have been derived from oxidation of particulate organic carbon alone. About 20% of the added DIC must have diffused from hypolimnetic sediments where relatively heavy CO2 (-7) was produced by a combination of POC oxidation and as a by-product of methanogenesis. 相似文献
13.
W. Ellis Penning Marit Mjelde Bernard Dudley Seppo Hellsten Jenica Hanganu Agnieszka Kolada Marcel van den Berg Sandra Poikane Geoff Phillips Nigel Willby Frauke Ecke 《Aquatic Ecology》2008,42(2):237-251
Aquatic macrophytes are one of the biological quality elements in the Water Framework Directive (WFD) for which status assessments
must be defined. We tested two methods to classify macrophyte species and their response to eutrophication pressure: one based
on percentiles of occurrence along a phosphorous gradient and another based on trophic ranking of species using Canonical
Correspondence Analyses in the ranking procedure. The methods were tested at Europe-wide, regional and national scale as well
as by alkalinity category, using 1,147 lakes from 12 European states. The grouping of species as sensitive, tolerant or indifferent
to eutrophication was evaluated for some taxa, such as the sensitive Chara spp. and the large isoetids, by analysing the (non-linear) response curve along a phosphorous gradient. These thresholds
revealed in these response curves can be used to set boundaries among different ecological status classes. In total 48 taxa
out of 114 taxa were classified identically regardless of dataset or classification method. These taxa can be considered the
most consistent and reliable indicators of sensitivity or tolerance to eutrophication at European scale. Although the general
response of well known indicator species seems to hold, there are many species that were evaluated differently according to
the database selection and classification methods. This hampers a Europe-wide comparison of classified species lists as used
for the status assessment within the WFD implementation process. 相似文献
14.
B. Michalzik E. Tipping J. Mulder J.F. Gallardo Lancho E. Matzner C.L. Bryant N. Clarke S. Lofts M.A. Vicente Esteban 《Biogeochemistry》2003,66(3):241-264
DyDOC describes soil carbon dynamics, with a focus on dissolved organic carbon (DOC). The model treats the soil as a three-horizon profile, and simulates metabolic carbon transformations, sorption reactions and water transport. Humic substances are partitioned into three fractions, one of which is immobile, while the other two (hydrophilic and hydrophobic) can pass into solution as DOC. DyDOC requires site-specific soil characteristics, and is driven by inputs of litter and water, and air and soil temperatures. The model operates on hourly and daily time steps, and can simulate carbon cycling over both long (hundreds-to-thousands of years) and short (daily) time scales. An important feature of DyDOC is the tracking of 14C, from its entry in litter to its loss as DO14C in drainage water, enabling information about C dynamics to be obtained from both long-term radioactive decay, and the characteristic 14C pulse caused by thermonuclear weapon testing during the 1960s ("bomb carbon"). Parameterisation is performed by assuming a current steady state. Values of a range of variables, including C pools, annual DOC fluxes, and 14C signals, are combined into objective functions for least-squares minimisation. DyDOC has been applied successfully to spruce forest sites at Birkenes (Norway) and Waldstein (Germany), and most of the parameters have similar values at the two sites. The results indicate that the supply of DOC from the surface soil horizon to percolating water depends upon the continual metabolic production of easily leached humic material. In contrast, concentrations and fluxes of DOC in the deeper soil horizons are controlled by sorption processes, involving comparatively large pools of leachable organic matter. Times to reach steady state are calculated to be several hundred years in the organic layer, and hundreds-to-thousands of years in the deeper mineral layers. It is estimated that DOC supplies 89% of the mineral soil carbon at Birkenes, and 73% at Waldstein. The model, parameterised with "steady state" data, simulates short-term variations in DOC concentrations and fluxes, and in DO14C, which are in approximate agreement with observations. 相似文献
15.
John E. Hobbie 《Hydrobiologia》1992,229(1):169-180
The dissolved organic carbon (DOC) of lakes dominates any budget of organic carbon in these systems. Limnologists are still limited by techniques and particularly by the lack of measurements of rates of microbial transformation and use of this DOC. There are now four different approaches to the study of the microbial control of DOC in lakes. The first is through measurements of the total DOC. Recent advances in measurement with high temperature combustion will likely lead to higher and more consistent measurements in freshwaters than previously. It is possible that a biologically active fraction may be identified. The second approach is through measurements of microbial incorporation and respiration of 14C-labeled organic matter. The kinetics of this process are well known but advances in measurement of the size of the substrate pool are still being made. The third approach is to use bacterial growth in batch or continuous flow experiments in order to understand how much of the total DOC can be decomposed by microbes. The assay in this approach may be microbial growth (thymidine incorporation, biomass changes) or change in the DOC (total concentrations, specific compounds, or fractions of the DOC by molecular weight). These methods are promising but are not developed enough for routine use. For example, growth measurements in the laboratory are all subject to experimental artifacts caused by changes in the DOC and in the bacterial populations. Finally, the fourth approach is through the use of isotopes of the natural DOC. In the sea this approach has given the age of the bulk DOC (14C data). In freshwaters it has great potential for differentiating between bacterial use of terrestrial DOC vs. use of algal-derived DOC (13C data). Stable isotopes are also useful for experimentally labeling DOC produced by algae and following the use of this material by bacteria. 相似文献
16.
Jeffrey N. Houser Darren L. Bade Jonathan J. Cole Michael L. Pace 《Biogeochemistry》2003,64(2):247-269
We investigated the effect of dissolved organic carbon (DOC) on hypolimnetic metabolism (accumulation of dissolved inorganic carbon (DIC) and methane (CH4)) in 21 lakes across a gradient of DOC concentrations (308 to 1540 mol C L–1). The highly colored nature of the DOC in these lakes suggests it is mostly of terrestrial origin. Hypolimnetic methane accumulation was positively correlated with epilimnetic DOC concentration (Spearman rank correlation = 0.67; p < 0.01), an indicator of allochthonous DOC inputs, but not with photic zone chlorophyll a concentration (Spearman rank correlation = 0.30; p = 0.22). Hypolimnetic DOC concentrations declined in 19 of 21 lakes during the stratified period at rates that ranged from 0.06 to 53.9 mmol m–2 d–1. The hypolimnetic accumulation of DIC + CH4 was positively correlated with, and, in most cases of comparable magnitude to, this DOC decline suggesting that DOC was an important substrate for hypolimnetic metabolism. The percentage of surface irradiance reaching the thermocline was lower in high DOC lakes (0.3%) than in low DOC lakes (6%), reducing hypolimnetic photosynthesis (as measured by the depth and magnitude of the deep dissolved oxygen maxima) in the high DOC lakes. In June, the hypolimnia of lakes with < 400 mol L–1 DOC had high concentrations of dissolved oxygen and no CH4, while the hypolimnia of lakes with DOC > 800 mol L–1 were completely anoxic and often had high CH4 concentrations. Thus, DOC affects hypolimnetic metabolism via multiple pathways: DOC was significant in supporting hypolimnetic metabolism; and at high concentrations depressed photosynthesis (and therefore oxygen production and DIC consumption) in the hypolimnion. 相似文献
17.
Dissolved organic carbon (DOC) and NO3– are important forms of C and N in stream water. Hypotheses concerning relationships between DOC and NO3– concentrations have been proposed, but there are no reports demonstrating a relationship between them in stream water. We observed 35 natural streams in the Lake Biwa watershed, central Japan, and found an inverse relationship between DOC and NO3– concentrations. This relationship was also found in observations of their seasonal variations in the Lake Biwa watershed. Moreover, this relationship was also found to apply to watersheds in other regions in Japan. These results suggest that forest biogeochemical processes which control DOC and NO3– concentrations in Japanese streams are closely related. Excess N availability together with a C (energy) deficit in a soil environment may explain this relationship. DOC and NO3– concentrations in streams will thus be a useful index indicating C and N availability in catchments. 相似文献
18.
Characterization and origin of polar dissolved organic matter from the Great Salt Lake 总被引:2,自引:0,他引:2
Jerry A. Leenheer Ted I. Noyes Colleen E. Rostad M. Lee Davisson 《Biogeochemistry》2004,69(1):125-141
Polar dissolved organic matter (DOM) was isolated from a surface-water sample from the Great Salt Lake by separating it from colloidal organic matter by membrane dialysis, from less-polar DOM fractions by resin sorbents, and from inorganic salts by a combination of sodium cation exchange followed by precipitation of sodium salts by acetic acid during evaporative concentration. Polar DOM was the most abundant DOM fraction, accounting for 56% of the isolated DOM. Colloidal organic matter was 14C-age dated to be about 100% modern carbon and all of the DOM fractions were 14C-age dated to be between 94 and 95% modern carbon. Average structural models of each DOM fraction were derived that incorporated quantitative elemental and infrared, 13C-NMR, and electrospray/mass spectrometric data. The polar DOM model consisted of open-chain N-acetyl hydroxy carboxylic acids likely derived from N-acetyl heteropolysaccharides that constituted the colloidal organic matter. The less polar DOM fraction models consisted of aliphatic alicyclic ring structures substituted with carboxyl, hydroxyl, ether, ester, and methyl groups. These ring structures had characteristics similar to terpenoid precursors. All DOM fractions in the Great Salt Lake are derived from algae and bacteria that dominate DOM inputs in this lake. 相似文献
19.
A comparative study of dissolved organic carbon transport and stabilization in California forest and grassland soils 总被引:2,自引:0,他引:2
For soil carbon to be effectively sequestered beyond a timescale of a few decades, this carbon must become incorporated into
passive reservoirs or greater depths, yet the actual mechanisms by which this occurs is at best poorly known. In this study,
we quantified the magnitude of dissolved organic carbon (DOC) leaching and subsequent retention in soils of a coniferous forest
and a coastal prairie ecosystem. Despite small annual losses of DOC relative to respiratory losses, DOC leaching plays a significant
role in transporting C from surface horizons and stabilizing it within the mineral soil. We found that DOC movement into the
mineral soil constitutes 22% of the annual C inputs below 40 cm in a coniferous forest, whereas only 2% of the C inputs below
20 cm in a prairie soil could be accounted for by this process. In line with these C input estimates, we calculated advective
transport velocities of 1.05 and 0.45 mm year−1 for the forested and prairie sites, respectively. Radiocarbon measurements of field-collected DOC interpreted with a basic
transport-turnover model indicated that DOC which was transported and subsequently absorbed had a mean residence time of 90–150 years.
Given these residence times, the process of DOC movement and retention is responsible for 20% of the total mineral soil C
stock to 1 m in the forest soil and 9% in the prairie soil. These results provide quantitative data confirming differences
in C cycles in forests and grasslands, and suggest the need for incorporating a better mechanistic understanding of soil C
transport, storage and turnover processes into both local and regional C cycle models. 相似文献
20.
Although dissolved organic matter (DOM) released from the forest floor plays a crucial role in transporting carbon and major nutrients through the soil profile, its formation and responses to changing litter inputs are only partially understood. To gain insights into the controlling mechanisms of DOM release from the forest floor, we investigated responses of the concentrations and fluxes of dissolved organic carbon (DOC) and nitrogen (DON) in forest floor leachates to manipulations of throughfall (TF) flow and aboveground litter inputs (litter removal, litter addition, and glucose addition) at a hardwood stand in Bavaria, Germany. Over the two-year study period, litter manipulations resulted in significant changes in C and N stocks of the uppermost organic horizon (Oi). DOC and DON losses via forest floor leaching represented 8 and 11% of annual litterfall C and N inputs at the control, respectively. The exclusion of aboveground litter inputs caused a slight decrease in DOC release from the Oi horizon but no change in the overall leaching losses of DOC and DON in forest floor leachates. In contrast, the addition of litter or glucose increased the release of DOC and DON either from the Oi or from the lower horizons (Oe + Oa). Net releases of DOC from the Oe + Oa horizons over the entire manipulation period were not related to changes in microbial activity (measured as rates of basal and substrate-induced respiration) but to the original forest floor depths prior to manipulation, pointing to the flux control by the size of source pools rather than a straightforward relationship between microbial activity and DOM production. In response to doubled TF fluxes, net increases in DOM fluxes occurred in the lower forest floor, indicating the presence of substantial pools of potentially soluble organic matter in the Oe + Oa horizons. In contrast to the general assumption of DOM as a leaching product from recent litter, our results suggest that DOM in forest floor leachates is derived from both newly added litter and older organic horizons through complex interactions between microbial production and consumption and hydrologic transport. 相似文献