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1.
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
2.
Untangling the complex issue of dissolved organic carbon uptake: a stable isotope approach 总被引:1,自引:0,他引:1
LOUIS A. KAPLAN TRACY N. WIEGNER J. D. NEWBOLD PEGGY H. OSTROM HASAND GANDHI 《Freshwater Biology》2008,53(5):855-864
1. We estimated uptake of stream water dissolved organic carbon (DOC) through a whole-stream addition of a 13 C-DOC tracer coupled with laboratory measurements of bioavailability of the tracer and stream water DOC.
2. The tracer, a leachate of13 C-labelled tree tissues, was added to the head waters of White Clay Creek, Pennsylvania, U.S.A., over a 2-h period and followed 1.27 km downstream to generate mass transfer coefficients for DOC lability classes within the tracer.
3. From the longitudinal13 C uptake curve, we resolved labile and semi-labile DOC classes within the 13 C-DOC tracer comprising 82% and 18% of the tracer respectively.
4. Plug-flow laboratory bioreactors colonized and maintained with stream water were used to determine the concentration of stream water DOC fractions that had a similar lability to the labile and semi-labile classes within the tracer and we assumed that stream water DOC and tracer DOC with comparable lability fractions in the bioreactors behaved similarly in the stream, i.e. they had the same mass transfer coefficients.
5. A small fraction (8.6%) of the stream water DOC was labile, travelling 238 m downstream before being taken up. The remaining bioavailable stream water DOC was semi-labile and transported 4.5 km downstream before being taken up. These uptake lengths suggest that the labile DOC is an energy source within a stream reach, while the semi-labile DOC is exported out of the reach to larger rivers and the downstream estuary, where it may provide energy for marine microbial communities or simply be exported to the oceans. 相似文献
2. The tracer, a leachate of
3. From the longitudinal
4. Plug-flow laboratory bioreactors colonized and maintained with stream water were used to determine the concentration of stream water DOC fractions that had a similar lability to the labile and semi-labile classes within the tracer and we assumed that stream water DOC and tracer DOC with comparable lability fractions in the bioreactors behaved similarly in the stream, i.e. they had the same mass transfer coefficients.
5. A small fraction (8.6%) of the stream water DOC was labile, travelling 238 m downstream before being taken up. The remaining bioavailable stream water DOC was semi-labile and transported 4.5 km downstream before being taken up. These uptake lengths suggest that the labile DOC is an energy source within a stream reach, while the semi-labile DOC is exported out of the reach to larger rivers and the downstream estuary, where it may provide energy for marine microbial communities or simply be exported to the oceans. 相似文献
3.
1. The δ13 C and δ15 N signatures of zooplankton vary with dissolved organic carbon (DOC), but inconsistent and limited taxonomic resolution of previous studies have masked differences that may exist among orders, genera or species and are attributable to dietary and/or habitat differences. Here we investigate differences among the isotopic signatures of five zooplankton taxa ( Daphnia , Holopedium , large Calanoida, small Calanoida and Cyclopoida) in Precambrian shield lakes with a sixfold range of DOC concentration.
2. δ13 C signatures of Daphnia , small calanoids and large calanoids became more depleted with increasing lake DOC, whereas Holopedium and cyclopoid δ13 C became enriched with increasing DOC concentration.
3. The variability of δ13 C and δ15 N isotopic signatures among zooplankton groups was reduced in high-DOC, compared to low-DOC lakes, especially for δ13 C. Differences in δ13 C and POM-corrected δ15 N accounted for up to 33.7% and 19.5% of the variance, respectively, among lakes of varying DOC concentration.
4. The narrow range of signatures found in higher DOC lakes suggests that different taxa have similar food sources and/or habitats. In contrast, the wide range of signatures in low-DOC lakes suggests that different taxa are exploiting different food sources and/or habitats. Together with the variable trends in zooplankton isotopic signatures along our DOC gradient, these results suggest that food web dynamics within the zooplankton community of temperate lakes will change as climate and lake DOC concentrations change. 相似文献
2. δ
3. The variability of δ
4. The narrow range of signatures found in higher DOC lakes suggests that different taxa have similar food sources and/or habitats. In contrast, the wide range of signatures in low-DOC lakes suggests that different taxa are exploiting different food sources and/or habitats. Together with the variable trends in zooplankton isotopic signatures along our DOC gradient, these results suggest that food web dynamics within the zooplankton community of temperate lakes will change as climate and lake DOC concentrations change. 相似文献
4.
富营养化湖泊溶解性有机碳生物可利用性研究进展 总被引:3,自引:0,他引:3
富营养化湖泊溶解性有机碳(DOC)包括内源和外源性碳源,不同来源碳源在物质化学结构组成和分子量级等方面具有显著差异,进而影响到对细菌的生物可利用性和碳素在食物网中的传递效率。根据国内外文献,综述了内外源DOC在碳稳定同位素值域上的显著差异,建议通过对DOC碳稳定同位素的分析来识别富营养化湖泊中DOC的主要来源;通过对比内外源DOC在碳水化合物、结合态中性糖和腐殖质含量上的差异,并结合细菌生长参数如细菌二级生产力、细菌呼吸作用及细菌生长效率来分析内外源DOC对细菌的生物可利用性。从富营养化湖泊DOC来源的角度探讨其生物可利用性和碳素传递效率,有助于了解富营养化湖泊食物网中碳素循环特征,加强对湖泊生态学的认识,为湖泊环境治理与保护提供科学依据。 相似文献
5.
Concentrations of dissolved organic carbon (DOC) and color were measuredas a function of time in enclosures and lakes at the Experimental Lakes Area,to calculate their net loss rates. Loss rates in enclosures werefirst order for both DOC and color, with half-times for loss of 166and 122 d, respectively. Thus, the colored, light-attenuating componentof the DOC pool is lost from water more rapidly than is bulk DOC. Loss ratesin lakes, calculated from a steady state model, were similar to values forcolor in enclosures, but for DOC in lakes were four times slower than inenclosures. In lakes, loss rate for DOC increased rapidly with decreasingwater residence time (w) but was independent ofw when it was greater than 3 years. In lakes, theloss rate for color was independent of water residence time. Thedifference in losses of DOC and color between lakes and enclosurescould be from release of low-color DOC from sediments. 相似文献
6.
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
7.
Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition 总被引:12,自引:1,他引:11
We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (13CPOC) and suspended matter (13CPOC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest 13CDIC values are observed due to enhanced input of CO2 from decomposition of 13C-depleted terrestrial plant detritus (average 13CDIC = –/14.3). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative 13CDIC values (average 13CDIC = –9.9). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a < 4.5 gl–1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 gl–1. Furthermore, in winter the very narrow range of 13CPOC (from –26.5 to –27.6) is associated with relatively high C/N ratios (C/N > 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer 13CPOC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N < 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in 13C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of 13C/12C fractionation by phytoplankton is attempted. 相似文献
8.
【目的】惰性溶解有机碳(refractory dissolved organic carbon,RDOC)是海洋总有机碳的主体组分,RDOC在深海中可保存数千年,构成了巨大的碳储库,在调节气候变化中有重要作用。但RDOC的定量评估尚未有统一的标准方法。通过测定环境中能被异养细菌利用的溶解有机碳(biodegradable DOC,BDOC)可以反过来评估RDOC的量。本文对BDOC测定中一些关键步骤进行验证,为制定海洋RDOC评估标准奠定基础。【方法】本文评估了3种过滤方式及5种滤膜对DOC测定的影响,并评估了瓶子效应和稀释效应对细菌生长和DOC利用的影响。【结果】研究发现,(1) GF/F滤膜、GF-75滤膜、聚四氟乙烯(PTFE)滤膜(孔径0.2μm)、聚碳酸酯(PC)滤膜(孔径0.2μm)和聚四氟乙烯材质针孔过滤器(HA)(孔径0.2μm) 5种滤膜不会引入DOC污染;抽滤过滤和重力过滤方式过滤效果稳定、无污染,而在线过滤效果不稳定,易污染;(2)不同大小培养体系(30–480 mL;表面积/体积比为:1.64–0.67 cm–1)之间的细菌生长速率和DOC利用量没有显著性差异;(3)培养体系稀释度越高,细菌生长速率越高,对数生长期细菌丰度及DOC利用量越低。【结论】综合考虑,建议BDOC和RDOC测定实验中采用抽滤过滤的方式及不进行稀释的培养体系;常用的滤膜和培养体积对BDOC评估无显著影响。结合研究结果,我们提出了评估海洋RDOC的方法。 相似文献
9.
The quantitative importance of photosynthetically produced dissolved organic carbon (PDOC) released from phytoplankton as
a source of carbon for pelagic, heterotrophic bacteria was investigated in four temperate Swedish lakes, of which two had
low (≈20 mg Pt 1−1), and two moderately high (60–80 mg Pt 1−1) humic content. The bacterial assimilation of PDOC was estimated with the 14C method, and the total production of the heterotrophic bacteria was estimated with the [3H]thymidine incorporation method.
The release of PDOC from natural communities of phytoplankton was not restricted to periods of photosynthesis, but often continued
during periods of darkness. Heterotrophic bacteria often assimilated the labile components of the PDOC at high rates (up to
73% of the released PDOC was assimilated during the incubation in our experiments). The contribution of PDOC to bacterial
production exhibited large within-lake seasonal variations, but PDOC was at certain times, both in humic and non-humic lakes,
a quantitatively very important carbon source for the heterotrophic bacteria. Under periods of comparatively low primary production,
heterotrophic bacteria in humic lakes appear to utilize allochthonous, humic substances as a substrate. 相似文献
10.
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
11.
12.
Chris D. Evans Tim G. Jones Annette Burden Nick Ostle Piotr Zieliński Mark D. A. Cooper Mike Peacock Joanna M. Clark Filip Oulehle David Cooper Chris Freeman 《Global Change Biology》2012,18(11):3317-3331
Dissolved organic carbon (DOC) concentrations in surface waters have increased across much of Europe and North America, with implications for the terrestrial carbon balance, aquatic ecosystem functioning, water treatment costs and human health. Over the past decade, many hypotheses have been put forward to explain this phenomenon, from changing climate and land management to eutrophication and acid deposition. Resolution of this debate has been hindered by a reliance on correlative analyses of time series data, and a lack of robust experimental testing of proposed mechanisms. In a 4 year, four‐site replicated field experiment involving both acidifying and deacidifying treatments, we tested the hypothesis that DOC leaching was previously suppressed by high levels of soil acidity in peat and organo‐mineral soils, and therefore that observed DOC increases a consequence of decreasing soil acidity. We observed a consistent, positive relationship between DOC and acidity change at all sites. Responses were described by similar hyperbolic relationships between standardized changes in DOC and hydrogen ion concentrations at all sites, suggesting potentially general applicability. These relationships explained a substantial proportion of observed changes in peak DOC concentrations in nearby monitoring streams, and application to a UK‐wide upland soil pH dataset suggests that recovery from acidification alone could have led to soil solution DOC increases in the range 46–126% by habitat type since 1978. Our findings raise the possibility that changing soil acidity may have wider impacts on ecosystem carbon balances. Decreasing sulphur deposition may be accelerating terrestrial carbon loss, and returning surface waters to a natural, high‐DOC condition. 相似文献
13.
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
14.
Pelagic and benthic net production of dissolved inorganic carbon in an unproductive subarctic lake 总被引:2,自引:0,他引:2
JAN ÅBERG MATS JANSSON JAN KARLSSON KLOCKAR-JENNY NÄÄS ANDERS JONSSON 《Freshwater Biology》2007,52(3):549-560
1. Both the pelagic and benthic net dissolved inorganic carbon (DIC) productions were measured in situ on four occasions from June to September 2004, in the unproductive Lake Diktar-Erik in subarctic Sweden. The stable isotopic signal ( δ 13 C) of respired organic material was estimated from hypolimnion water data and data from a laboratory incubation using epilimnion water.
2. Both pelagic and benthic habitats were net heterotrophic during the study period, with a total net DIC production of 416 mg C m−2 day−1 , of which the pelagic habitat contributed approximately 85%. The net DIC production decreased with depth both in the pelagic water and in the sediments, and most of the net DIC production occurred in the upper water column.
3. Temporal variations in both pelagic and benthic DIC production were small, although we observed a significant decrease in pelagic net DIC production after the autumn turnover. Water temperature was the single most important factor explaining temporal and vertical variations in pelagic DIC production. No single factor explained more than 10% of the benthic net DIC production, which probably was regulated by several interacting factors.
4. Pelagic DIC production, and thus most of the whole-lake net production of DIC, was mainly due to the respiration of allochthonous organic carbon. Stable isotope data inferred that nearly 100% of accumulated DIC in the hypolimnion water had an allochthonous carbon source. Similarly, in the laboratory incubation using epilimnion water, c. 85% of accumulated DIC was indicated to have an allochthonous organic carbon source. 相似文献
2. Both pelagic and benthic habitats were net heterotrophic during the study period, with a total net DIC production of 416 mg C m
3. Temporal variations in both pelagic and benthic DIC production were small, although we observed a significant decrease in pelagic net DIC production after the autumn turnover. Water temperature was the single most important factor explaining temporal and vertical variations in pelagic DIC production. No single factor explained more than 10% of the benthic net DIC production, which probably was regulated by several interacting factors.
4. Pelagic DIC production, and thus most of the whole-lake net production of DIC, was mainly due to the respiration of allochthonous organic carbon. Stable isotope data inferred that nearly 100% of accumulated DIC in the hypolimnion water had an allochthonous carbon source. Similarly, in the laboratory incubation using epilimnion water, c. 85% of accumulated DIC was indicated to have an allochthonous organic carbon source. 相似文献
15.
Alternative explanations for rising dissolved organic carbon export from organic soils 总被引:8,自引:0,他引:8
CHRISTOPHER D. EVANS PIPPA J. CHAPMAN† JOANNA M. CLARK† DON T. MONTEITH‡ MALCOLM S. CRESSER§ 《Global Change Biology》2006,12(11):2044-2053
Since 1988, there has been, on average, a 91% increase in dissolved organic carbon (DOC) concentrations of UK lakes and streams in the Acid Waters Monitoring Network (AWMN). Similar DOC increases have been observed in surface waters across much of Europe and North America. Much of the debate about the causes of rising DOC has, as in other studies relating to the carbon cycle, focused on factors related to climate change. Data from our peat‐core experiments support an influence of climate on DOC, notably an increase in production with temperature under aerobic, and to a lesser extent anaerobic, conditions. However, we argue that climatic factors may not be the dominant drivers of DOC change. DOC solubility is suppressed by high soil water acidity and ionic strength, both of which have decreased as a result of declining sulphur deposition since the 1980s, augmented during the 1990s in the United Kingdom by a cyclical decline in sea‐salt deposition. Our observational and experimental data demonstrate a clear, inverse and quantitatively important link between DOC and sulphate concentrations in soil solution. Statistical analysis of 11 AWMN lakes suggests that rising temperature, declining sulphur deposition and changing sea‐salt loading can account for the majority of the observed DOC trend. This combination of evidence points to the changing chemical composition of atmospheric deposition, particularly the substantial reduction in anthropogenic sulphur emissions during the last 20 years, as a key cause of rising DOC. The implications of rising DOC export for the carbon cycle will be very different if linked primarily to decreasing acid deposition, rather than to changes in climate, suggesting that these systems may be recovering rather than destabilising. 相似文献
16.
17.
Role of dissolved organic carbon in the attenuation of photosynthetically active and ultraviolet radiation in Adirondack lakes 总被引:5,自引:0,他引:5
1. We surveyed eighty-five lakes located in the Adirondack Mountain Region of New York State, U.S.A., to characterize the attenuation of photosynthetically active (PAR) and ultraviolet radiation (UVR) in relation to dissolved organic carbon (DOC) concentrations and pH. Attenuation of PAR was quantified in situ . Attenuation was also inferred by measuring the light absorption of filtered lake water samples at wavelengths (300, 340 and 440 nm) representing UV-B, UV-A and PAR.
2. Substantial variation in transparency was observed among lakes in this region. Attenuation depths ( z1% ) for PAR ranged from 0.5 to greater than 20 m, while inferred values for UV-B and UV-A ranged from a few centimetres to > 5 m. Median values of UV-A penetration (0.75 m) and UV-B penetration (0.45 m) corresponded to 11% (UV-A) and 6% (UV-B) of lake maximum depth.
3. Much of the variation in PAR and UVR attenuation was explained by differences in lake DOC. Univariate power models based solely on DOC accounted for 85% (PAR), 90% (UV-A) and 91% (UV-B) of the variation in absorption.
4. Attenuation and absorption coefficients were generally lower for recently acidified lakes compared to acidic and circumneutral lakes which have not undergone recent acidification. However, differences among these three groups of lakes were not statistically significant. Our results suggest that the effects of acidification on the optical properties of a regional population of lakes, even in an area experiencing widespread acidification, are relatively subtle in comparison with other factors contributing to inter-lake variability.
5. The presence of near-shore wetlands is probably a key factor influencing regional variability in DOC and light climate among Adirondack lakes. Temporal variability in climatic factors influencing wetland DOC production and export may mask more subtle influences on lake DOC associated with anthropogenic acidification. 相似文献
2. Substantial variation in transparency was observed among lakes in this region. Attenuation depths ( z
3. Much of the variation in PAR and UVR attenuation was explained by differences in lake DOC. Univariate power models based solely on DOC accounted for 85% (PAR), 90% (UV-A) and 91% (UV-B) of the variation in absorption.
4. Attenuation and absorption coefficients were generally lower for recently acidified lakes compared to acidic and circumneutral lakes which have not undergone recent acidification. However, differences among these three groups of lakes were not statistically significant. Our results suggest that the effects of acidification on the optical properties of a regional population of lakes, even in an area experiencing widespread acidification, are relatively subtle in comparison with other factors contributing to inter-lake variability.
5. The presence of near-shore wetlands is probably a key factor influencing regional variability in DOC and light climate among Adirondack lakes. Temporal variability in climatic factors influencing wetland DOC production and export may mask more subtle influences on lake DOC associated with anthropogenic acidification. 相似文献
18.
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
19.
Reductions in the global stratospheric ozone layer arethought to be increasing the amount of ultraviolet B (UV-B) radiationreaching the planets surface and may be affecting the chemistry ofdissolved organic carbon (DOC) in surface waters. We studied theabundance of chromophores in DOC collected in four different aquaticenvironments in southwestern Nova Scotia using 13C nuclearmagnetic resonance (13C NMR) spectroscopy. We showed a clearseasonal pattern in the distribution of structural carbon related tolight-sensitive chromophores. There seemed to be little variation in theUV-B related chemical structure of DOC between lakes and streams, thoughwater from a bog pool showed large differences from the other samples. Thesepatterns of potential UV-B reactivity tend to be dampened however, byvariations in DOC concentrations which also occur seasonally. 相似文献
20.
1. Agricultural and urban land use may increase dissolved inorganic nitrogen (DIN) concentrations in streams and saturate biotic nutrient demand, but less is known about their impacts on the cycling of organic nutrients. To assess these impacts we compared the uptake of DIN (as ammonium, NH4+), dissolved organic carbon (DOC, as acetate), and dissolved organic nitrogen (DON, as glycine) in 18 low‐gradient headwater streams in southwest Michigan draining forested, agricultural, or urban land‐use types. Over 3 years, we quantified uptake in two streams in each of the three land‐use types during three seasons (spring, summer and autumn). 2. We found significantly higher NH4+ demand (expressed as uptake velocity, Vf) in urban compared to forested streams and NH4+Vf was greater in spring compared to summer and autumn. Acetate Vf was significantly higher than NH4+ and glycine Vf, but neither acetate nor glycine Vf were influenced by land‐use type or season. 3. We examined the interaction between NH4+ and acetate demand by comparing simultaneous short‐term releases of both solutes to releases of each solute individually. Acetate Vf did not change during the simultaneous release with NH4+, but NH4+Vf was significantly higher with increased acetate. Thus, labile DOC Vf was not limited by the availability of NH4+, but NH4+Vf was limited by the availability of labile DOC. In contrast, neither glycine nor NH4+Vf changed when released simultaneously indicating either that overall N‐uptake was saturated or that glycine and NH4+ uptake were controlled by different factors. 4. Our results suggest that labile DOC and DON uptake can be equivalent to, or even higher than NH4+ uptake, a solute known to be highly bioreactive, but unlike NH4+ uptake, may not differ among land‐use types and seasons. Moreover, downstream export of nitrogen may be exacerbated by limitation of NH4+ uptake by the availability of labile DOC in headwater streams from the agricultural Midwestern United States. Further research is needed to identify the factors that influence cycling of DOC and DON in streams. 相似文献