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1.
Understanding how the concentration and chemical quality of dissolved organic matter (DOM) varies in soils is critical because
DOM influences an array of biological, chemical, and physical processes. We used PARAFAC modeling of excitation–emission fluorescence
spectroscopy, specific UV absorbance (SUVA254) and biodegradable dissolved organic carbon (BDOC) incubations to investigate the chemical quality of DOM in soil water collected
from 25 cm piezometers in four different wetland and forest soils: bog, forested wetland, fen and upland forest. There were
significant differences in soil solution concentrations of dissolved organic C, N, and P, DOC:DON ratios, SUVA254 and BDOC among the four soil types. Throughout the sampling period, average DOC concentrations in the four soil types ranged
from 9–32 mg C l−1 and between 23–42% of the DOC was biodegradable. Seasonal patterns in dissolved nutrient concentrations and BDOC were observed
in the three wetland types suggesting strong biotic controls over DOM concentrations in wetland soils. PARAFAC modeling of
excitation–emission fluorescence spectroscopy showed that protein-like fluorescence was positively correlated (r
2 = 0.82; P < 0.001) with BDOC for all soil types taken together. This finding indicates that PARAFAC modeling may substantially improve
the ability to predict BDOC in natural environments. Coincident measurements of DOM concentrations, BDOC and PARAFAC modeling
confirmed that the four soil types contain DOM with distinct chemical properties and have unique fluorescent fingerprints.
DOM inputs to streams from the four soil types therefore have the potential to alter stream biogeochemical processes differently
by influencing temporal patterns in stream heterotrophic productivity. 相似文献
2.
Quantification and characterization of dissolved organic carbon and iron in sedimentary porewater from Green Bay,WI, USA 总被引:3,自引:1,他引:3
Both dissolved organic carbon (DOC) and iron play an important role in biogeochemical processes in lacustrine benthic environments. Moreover, recent evidence has shown that both substances can act as active reductants in the redox transformation of organic pollutants. This paper examines the nature and abundance of DOC and dissolved ferrous iron (FeII) in porewaters from a sediment core collected in Green Bay, WI, USA. The concentration of dissolved FeII and the abundance, absorbance at 280 nm (A
280 nm), molar absorptivities (280 nm), molecular weights, and polydispersities of DOC were measured as a function of depth in porewaters. Dissolved FeII concentrations increased from 3.6 M near the sediment–water interface to 163 M at a depth of 11 cm, then gradually declined. The DOC distribution varied with sediment depth, with the greatest variation in porewater DOC content and properties occurring in the transitional zone between oxic and suboxic conditions. The down-core porewater DOC profile was characterized by an increase in DOC concentration with depth from 0.64 mM OC at 1 cm to 1.23 mM OC at 13 cm, below which it remained relatively constant. A strong correlation was observed between FeII and DOC concentrations, suggesting that these constituents co-accumulate in these porewaters. The correlation between the DOC concentration of the porewaters and A
280 nm was significant, making this parameter a good predictor for DOC concentrations in these waters. The molecular weight distributions of the porewater DOC were primarily monomodal, with relatively low polydispersivities. Weight-average molecular weights ranged from 1505 to 1949 Da. This data set is unique in that it is the first detailed study of a relatively highly resolved DOC profile of benthic porewater in surficial sediment from the Laurentian Great Lakes. 相似文献
3.
Redox Changes of Iron Caused by Erosion,Resuspension and Sedimentation in Littoral Sediment of a Freshwater Lake 总被引:1,自引:0,他引:1
Depth profiles of oxygen concentration and the redox status of acid-extractable iron were measured in littoral sediment cores
of Lake Constance after mechanical removal of surface sediment, mixing, and re-deposition. In undisturbed sediment cores,
oxygen penetrated down to 2.9±0.4 mm or 4.6±0.4 mm depth, respectively, after 12 h of incubation in the dark or light; causing
a net diffusive flux of 108±20 nmol cm−2 h−1 oxygen into or 152±35 nmol cm−2 h−1 out of the sediment. The uppermost 20 mm layer of the undisturbed sediment cores contained 10.2± 0.7 μmol cm−3 ferrous and 3.8±1.1 μmol cm−3 ferric iron. After erosion, the oxic–anoxic interface in the newly exposed sediment was shifted to about 2 mm depth within
30 min, causing an oxygen flow into the sediment. During the following 12 h, oxygen penetrated deeper into the sediment, and
in the light oxygen was produced photosynthetically. Ferrous iron was largely oxidized within two days after erosion. The
oxidation rates were higher in oxic than in anoxic sediment layers, and decreased with time. This oxidation process took the
longer and was confined closer to the surface the more reduced the exposed sediment had been before. Resuspension of eroded
sediment in aerated lake water did not cause a significant oxidation or reduction of iron. After re-deposition, the oxic–anoxic
interface in the re-sedimented material shifted to about 2 mm depth within 30 min, causing an oxygen flow into the sediment.
During the following 12 h, the oxygen penetration depth and the oxygen flow rate into the re-deposited sediment did not change
any further, and no oxygen was produced in the light. Ferric iron was reduced during the first day after re-deposition, and
partly re-oxidized during the second day. The extent of reduction was stronger and the extent of oxidation weaker the more
reduced the resuspended sediment was before. Oxic conditions in the sediment surface were established faster and ferrous iron
was oxidized to a larger extent after erosion of sediment than after resuspension and sedimentation. 相似文献
4.
Mangroves represent a major environment of tropical coasts. They are highly productive, and act both as a source and a sink of organic carbon. Concentrations and characteristics (fluorescence and hydrophobic–hydrophilic fractions) of dissolved organic matter (DOM) were investigated in relation to the organic content of sediments and to the chemistry of pore waters along the coastline of French Guiana. The pore waters studied were extracted (centrifugation, soil moisture sampler) from sediments cored beneath A. germinans mangrove stands representative of development stages: pioneer, mature and senescent. In order to asses the effects of seasonal changes, two cores were performed in each location, just after dry and wet seasons, respectively. Dissolved organic carbon (DOC) concentrations in pore waters of the upper sediment were found to increase, from 0.7 mmol l−1 under the pioneers to 9 under senescent mangroves. The evolution of sedimentary organic carbon (SedOC) in the same sediment paralleled that of DOC, increasing from 0.7 to 28%. On the contrary, in the lower parts of sediment cores SedOC and DOC displayed contrasting vertical trends: SedOC decreased sharply with depth while DOC increased, reaching concentrations up to 30 mmol l−1 at 50 cm in the older, senescent mangroves. In addition, the Fluorescence/DOC ratios and the hydrophobic contents of DOC were higher at greater depths in most cores, expressing changes in the DOC composition. These results suggest that the DOC of the upper layers originated directly from the SedOC of the enclosing sediment, while the hydrophobic and fluorescent DOC accumulated in the anoxic bottom layer. The mechanisms responsible for this accumulation at depth requires additional research to be fully understood. However, the anoxic conditions and high pH values prevailing in the lower sediment, by lessening DOM sorption and enhancing SedOC dissolution, may be partly responsible for the high DOC concentrations and fluorescences at depth. In addition, seasonal variation may be involved. During the rainy season, water sources were mixed resulting in lower DOC concentrations in the upper sediment, whereas during the dry season, increased evapotranspiration concentrate salts and DOC, which are transported vertically with percolating water. 相似文献
5.
Depth profiles of oxygen concentration and the redox status of acid-extractable iron were measured in littoral sediment cores
of Lake Constance incubated under a light–dark regimen of 12 h. While oxygen penetrated to 3.4±0.2 mm depth in the dark, photosynthetic
oxygen production shifted the oxic–anoxic interface down to 4.0±0.2 mm or 5.9±1.6 mm depth, at low or high light intensity,
respectively, and caused a net oxygen efflux into the water column. After a light–dark or dark–light transition, the oxygen
concentration at the sediment surface reached a new steady state within about 20 min. The redox state of the bioavailable
iron was determined in 1-mm slices of sediment subcores. After a dark period of 12 h, 85% of the acid-extractable iron (10.5 μmol cm−3 total) in the uppermost 8 mm was in the reduced state. Within 12 h at low or high light intensity, the proportion of ferrous
iron decreased to 82 or 75%, respectively, corresponding to net rates of iron oxidation in the range of 244 and 732 nmol cm−3 h−1, respectively. About 55 or 82% of the iron oxidation at low or high light intensity occurred in the respective oxic zone
of the sediment; the remaining part was oxidized in the anoxic zone, probably coupled to nitrate reduction. The areal rates
of iron oxidation in the respective oxic layer (21 or 123 nmol cm−2 h−1 at low or high light intensity, respectively) would account for 4 and 23% of the total electron flow to oxygen, respectively.
Light changes caused a rapid migration of the oxic–anoxic interface in the sediment, followed by a slow redox reaction of
biologically available iron, thus providing temporal niches for aerobic iron oxidizers and anaerobic iron reducers. 相似文献
6.
Stream dissolved organic matter bioavailability and composition in watersheds underlain with discontinuous permafrost 总被引:1,自引:0,他引:1
Kelly L. Balcarczyk Jeremy B. JonesJr. Rudolf Jaffé Nagamitsu Maie 《Biogeochemistry》2009,94(3):255-270
We examined the impact of permafrost on dissolved organic matter (DOM) composition in Caribou-Poker Creeks Research Watershed
(CPCRW), a watershed underlain with discontinuous permafrost, in interior Alaska. We analyzed long term data from watersheds
underlain with varying degrees of permafrost, sampled springs and thermokarsts, used fluorescence spectroscopy, and measured
the bioavailabity of dissolved organic carbon (DOC). Permafrost driven patterns in hydrology and vegetation influenced DOM
patterns in streams, with the stream draining the high permafrost watershed having higher DOC and dissolved organic nitrogen
(DON) concentrations, higher DOC:DON and greater specific ultraviolet absorbance (SUVA) than the streams draining the low
and medium permafrost watersheds. Streams, springs and thermokarsts exhibited a wide range of DOC and DON concentrations (1.5–37.5 mgC/L
and 0.14–1.26 mgN/L, respectively), DOC:DON (7.1–42.8) and SUVA (1.5–4.7 L mgC−1 m−1). All sites had a high proportion of humic components, a low proportion of protein components, and a low fluorescence index
value (1.3–1.4), generally consistent with terrestrially derived DOM. Principal component analysis revealed distinct groups
in our fluorescence data determined by diagenetic processing and DOM source. The proportion of bioavailable DOC ranged from
2 to 35%, with the proportion of tyrosine- and tryptophan-like fluorophores in the DOM being a major predictor of DOC loss
(p < 0.05, R
2 = 0.99). Our results indicate that the degradation of permafrost in CPCRW will result in a decrease in DOC and DON concentrations,
a decline in DOC:DON, and a reduction in SUVA, possibly accompanied by a change in the proportion of bioavailable DOC. 相似文献
7.
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
8.
Matthias Koschorreck Andreas Kleeberg Peter Herzsprung Katrin Wendt-Potthoff 《Hydrobiologia》2007,592(1):387-397
Natural alkalinity generation by microbial sulphate reduction in acidic lakes is usually inhibited by the low pH and a low
primary production which results in a lack of suitable organic carbon sources. In some acidic mining lakes mass developments
of filamentous benthic algae occur. The effects of this periphyton layer on the biogeochemistry of the sediment–water interface
were investigated by in situ microsensor measurements and laboratory incubations in Mining Lake Grünewalder Lauch (Germany).
Microsensor measurements showed that the oxic–anoxic boundary was located in the periphyton layer and was moving up and down
depending on light triggered photosynthesis. The sediment itself was permanently anoxic. The diurnal redox shift and the maintenance
of neutral conditions in the periphyton layer lead to an effective precipitation of iron and phosphorus. Under the periphyton
layer very high sulphate reduction rates up to 265 nmol cm−3 d−1 were measured in the sediment. These are the highest rates reported for mining lakes so far. The microbial activity was high
enough to keep the pH in the surface sediment neutral and contributed to natural alkalinity production.
Handling editor: L. Naselli-Flores 相似文献
9.
Takahito Yoshioka Khan M. G. Mostofa Eiichi Konohira Eiichiro Tanoue Kazuhide Hayakawa Mikio Takahashi Shingo Ueda Masanori Katsuyama Tamara Khodzher Nadezhda Bashenkhaeva Irina Korovyakova Larisa Sorokovikova Ludomira Gorbunova 《Limnology》2007,8(1):29-44
Distributions of molecular size and fluorescence properties of dissolved organic matter (DOM) in the Lake Biwa and Lake Baikal
watersheds were investigated using the cross-flow ultrafiltration technique and three-dimensional fluorescence measurements.
From the fluorescence properties, protein-like substances were usually found in the 0.1 μm-GF/F fraction (the Durapore membrane
retentate of the GF/F filtrate) of the lake DOM. The results indicated autochthonous production of protein-like organic-matters
in the lake environment. Fulvic acid (FA)-like components were composed of two fractions with respect to fluorescence properties
and molecular size. Two FA-like fluorescence peaks, which showed different fluorescence peak positions in the excitation-emission
matrix (EEM), were partly fractionated by the molecular size of 5000 daltons (5 kDa). The FA-like fluorescence peak position
of the <5-kDa fraction was observed at the shorter wavelength region compared with that of the fraction between 5 kDa and
0.1 μm (5 kDa20.1 μm fraction). A blue shift of the FA-like fluorescence peak position as well as a decrease in the molecular
size of the DOM was observed in lake samples. The relative contribution of the <5 kDa fraction to the DOC concentration was
high in lake waters (68%–79%) compared with river waters (44%–68%), suggesting characteristic changes in molecular size between
riverine and lacustrine DOM. DOM of the 5 kDa–0.1 μm fraction was relatively higher in river waters than in lake waters. These
findings coincided with in situ distributions of the fluorescence properties and molecular size of DOM found in both stream
and lake environments. These results indicate that FA-like substances from forested watersheds are decomposed qualitatively
and quantitatively in the river-lake environment by photochemical and biological processes. 相似文献
10.
Sarah L. Woodruff W. Alan House Maureen E. Callow Barry S. C. Leadbeater 《International Review of Hydrobiology》1999,84(5):509-532
The development of a diatom biofilm on a river sediment was studied using a fluvarium channel with intensive investigations over a total duration of 16 days. The overlying solution was monitored for dissolved calcium, silicon and soluble reactive phosphorus, pH, dissolved oxygen and temperature. The surface of the sediment was sampled for chlorophyll a, algal cell density and porewater profile measurements of calcium concentration, pH and dissolved oxygen were made using microelectrodes. At the end of the experiment the sediment was longitudinally sectioned and porewaters isolated and analysed. A diatom biofilm developed within approximately 5 days leading to a decrease in the concentrations of dissolved silicon and phosphorus in the overlying solution. After approximately 270 hours, the dissolved silicon concentration remained low (average of 6.7 μM). As the diatom numbers increased, photosynthetic activity was evident from increases in dissolved oxygen and pH at the interface. By the end of the experiment diurnal changes in the overlying solution of dissolved calcium, alkalinity and soluble reactive phosphorus were evident. Vertical concentration gradients in dissolved calcium, phosphorus and silicon in the sediment porewater were found at the end of the experiment. The results are consistent with the development of a photosynthetically active diatom biofilm that acted as a barrier to the diffusion of silicon from the porewater. It also induced precipitation and dissolution of calcite and co-precipitation of phosphate with calcite. Chemical fluxes of silicon, calcium and phosphorus were estimated from concentration gradients in the sediment and found to be much smaller than fluxes measured from changes in the bulk solution indicating that processes at the sediment-water interface and biofilm mainly control the flux to the overlying solution. 相似文献
11.
In a brackish, temperate, 24-m-deep Lake Shira, the profiles of salinity, temperature, oxygen and sulfide concentrations were
measured on a seasonal basis from 2002 to 2009. The lake was shown to be meromictic with autumnal overturn restricted to mixolimnion.
The depth of mixolimnion and position of oxic–anoxic interface varied annually. The spring mixing processes contribute to
the formation of mixolimnion in autumn. The exceptionally windy spring of 2007 caused the deepening of mixolimnion in the
winter of 2008. The winter position of oxic–anoxic interface was affected by the position of lower boundary of mixolimnion
in all winters. The salinity in the winter mixolimnion increased compared with the autumn because of freezing out of salts
from the upper water layers meters during ice formation and their dissolution in water below. The profiles of salinity and
temperature were simulated by the mathematical 1-D model of temperature and salinity conditions taking into account ice formation.
The simulated profiles generally coincided with the measured ones. The coincidence implies that simplified one-dimensional
model can be applied to roughly describe salinity and density profiles and mixing behavior of Lake Shira. 相似文献
12.
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
13.
E. Tipping M. F. Billett C. L. Bryant S. Buckingham S. A. Thacker 《Biogeochemistry》2010,100(1-3):121-137
Monitoring data over the period 1994–2007 were analysed for three streams (Cottage Hill Sike, CHS; Rough Sike, RS; Trout Beck, TB) draining blanket peat underlain by glacial clay and limestone-rich sub-strata at Moor House (Northern England). Dissolved organic carbon concentration, [DOC], showed complex relationships with both discharge and calcium concentration, [Ca]. A model based on [Ca] was constructed to simulate stream [DOC] by mixing dissolved organic matter (DOM) from shallow peat, quantified by measured [DOC] (15–30 mg l?1) in peat porewater, with DOM assumed to be present at a constant concentration (c. 5 mg l?1) in groundwater. A temperature-based adjustment to the measured porewater [DOC] was required to account for relatively low streamwater [DOC] during winter and spring. The fitted model reproduced short-term variation in streamwater [DOC] satisfactorily, in particular variability in RS and TB due to groundwater contributions. Streamwater DOM is largely derived from surface peat, which accounts for more than 96% of the total DOC flux in both RS and TB, and 100% in CHS. Model outputs were combined with streamwater and porewater DO14C data to estimate the 14C contents, and thereby the ages, of DOM from peat and groundwater. The peat-derived DOM is 5 years old on average, with most of it very recently formed. The derived age of groundwater DOM (8,500 years) is comparable to the 4,000–7,000 years estimated from the DO14C of water extracts of clay underlying the peat, suggesting that the clay is the source of groundwater DOM. 相似文献
14.
The impact of sediment coring on measured rates of sulfate reduction(SRR) by the whole core 35S-injection technique was assessed inmarshsediment vegetated by Spartina anglica. Simultaneously,therole of extraction method (centrifugation vs. sippers) for determination ofporewater DOC in vegetated sediment was evaluated. SRR was measuredinsitu with radiotracer injected directly into the sediment and in atime series from 1 to 24 h after coring. SRR incubations carriedout within 6 h (June) or 12 h (August) of coringyielded up to an order of magnitude higher rates than measured insitu. The enhancement of SRR was instantaneous but temporary andcorrelated with measured porewater DOC concentrations. Cores sampled fromrootedsediments should therefore not be used for sulfate reduction incubations withinthe first 12 h due to the effect of DOC leaching from roots cutduring the coring procedure. The labile fraction of leached DOC appears to beexhausted after a pre-incubation period of at least 12 h.Measurement of porewater DOC is also problematic in vegetated sediment.Porewater extraction by centrifugation of sediment may result in up to oneorderof magnitude higher DOC concentrations than in porewater obtained by anondestructive sipper technique. DOC is probably forced out of roots duringcentrifugation resulting in erroneously high porewater DOC concentrations. 相似文献
15.
Sources and seasonal patterns of dissolved organic matter (DOM) in the hyporheic zone 总被引:1,自引:0,他引:1
The hyporheic zone is a region underneath streambeds that integrates surface and groundwater. Although its location is central
to biogeochemical linkages between the riparian zone, dissolved nutrients, and benthic biota, the seasonal quality and likely
sources of dissolved organic matter (DOM) in the hyporheic zone are not well understood. To investigate DOM characteristics
in the hyporheic zone, water from the surface and subsurface (at depths 20, 60, and 100 cm below the streambed) was sampled
every 4 weeks from 2007 to 2008 in a third-order stream in southern Ontario. Using UV spectroscopy, measures of spectral slopes,
aromaticity, and A
254/A
365 ratios (molecular weight) were obtained. Temporal changes in these measures were consistent with watershed processes such
as shedding of leaf litter in the fall, and photochemical and biofilm influence in the spring and summer. The fluorescence
index (a measure of relative DOM source) suggested that at the surface and in the downwelling zone, DOM microbial sources
increased with depth in the sediment, regardless of the season. Excitation–emission matrices (EEMs) showed seasonally distinct,
protein-like DOM components of bacterial origin that were stronger in the fall. Leachates from specific allochthonous DOM
sources—leaf litter from Betula papyrifera (white birch) and Thuja occidentalis (white cedar)—and an autochthonous source, biofilm, were isolated and incubated with unfiltered surface water. EEMs from
these leachates indicated that these sources could indeed help explain observed patterns of DOM in surface and subsurface
waters. These results suggest that although DOM sources were relatively constant, biogeochemical processing within the hyporheic
zone resulted a DOM pool that was temporally dynamic and altered the nature of organic matter transported downstream into
lakes and rivers. 相似文献
16.
Absorption of solar ultraviolet radiation (UVR) in aquatic ecosystems is primarily controlled by dissolved organic carbon
(DOC). The role of iron (Fe) has also been suggested to contribute to UVR attenuation either directly or by interactions with
DOC. Here we present findings from three laboratory manipulations of Fe and DOC on changes to the dissolved UVR absorption
(ad,320) in a mid-latitude, dimictic, humic lake. In a laboratory simulation of lake turnover where anoxic, hypolimnetic water was
oxygenated ad,320 significantly increased from 23.3 to 81.7 m−1 (p<0.0001). In a second laboratory experiment, addition of ferrous Fe to deoxygenated lake water increased ad,320 upon reoxygenation up to a concentration of 1.0 mg l−1 Fe, where a solubility saturation threshold may have been reached. In situ lake experiments were designed to simulate release of UV absorbing substances from anoxic sediments by placing 20-l carboys
(open at the bottom, sealed at the top) onto the lake bottom. UV absorption at 320 nm increased over time for samples from
within the experimental carboys. Finally, samples from several lake profiles and sediment experiments were analyzed for ad,320, total Fe, and DOC. UV absorption of dissolved substances at 320 nm and total Fe concentration both increased with depth,
however DOC remained relatively constant over depth. Furthermore, total Fe and spectral slope showed tight coupling up to
1 mg l−1 total Fe in our survey analysis. Our results provide evidence for the importance of anoxic sediments as a source of ferrous
iron and UV absorbing substances and suggest a role for ferric iron in increasing UVR and PAR absorption in lake water. We
suggest that as this ferrous Fe oxidizes, its absorptive properties increase, and it may bind with dissolved organic matter,
enabling it to remain in solution and thus increasing the dissolved absorption of lake water for extended periods of time. 相似文献
17.
Dissolved organic matter (DOM) is an important component of aquatic food webs. We compare the uptake kinetics for NH4–N and different fractions of DOM during soil and salmon leachate additions by evaluating the uptake of organic forms of carbon
(DOC) and nitrogen (DON), and proteinaceous DOM, as measured by parallel factor (PARAFAC) modeling of DOM fluorescence. Seasonal
DOM slug additions were conducted in three headwater streams draining a bog, forested wetland, and upland forest using DOM
collected by leaching watershed soils. We also used DOM collected from bog soil and salmon carcasses to perform additions
in the upland forest stream. DOC uptake velocity ranged from 0.010 to 0.063 mm s−1 and DON uptake velocity ranged from 0.015 to 0.086 mm s−1, which provides evidence for the whole-stream uptake of allochthonous DOM. These findings imply that wetlands could potentially
be an important source of DOM to support stream heterotrophic production. There was no significant difference in the uptake
of DOC and DON across the soil leachate additions (P > 0.05), although differential uptake of DOM fractions was observed as protein-like fluorescence was removed from the water
column more efficiently than bulk DOC and DON (P < 0.05). Moreover, PARAFAC analysis of DOM fluorescence showed that protein-like fluorescence decreased downstream during
all DOM additions, whereas humic-like fluorescence did not change. This differential processing in added DOM suggests slow
and fast turnover pools exist for aquatic DOM. Taken together, our findings argue that DON could potentially fill a larger
role in satisfying biotic N demand in oligotrophic headwater streams than previously thought.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Author contributions J.B.F. conceived of or designed study, performed research, analyzed data, contributed new methods or models, and wrote the
paper. E.H. conceived of or designed study and analyzed data. R.T.E. conceived of or designed study and analyzed data. J.B.J.
contributed new methods or models and analyzed data. 相似文献
18.
Dissolved organic matter (DOM) in sediment pore waters from Yangtze estuary of China based on abundance, UV absorbance, molecular weight distribution and fluorescence were investigated using a combination of various parameters of DOM as well as 3D fluorescence excitation emission matrix spectra (F-EEMS) with the parallel factor and principal component analysis (PARAFAC-PCA). The results indicated that DOM in pore water of Yangtze estuary was very variable which mainly composed of low aromaticity and molecular weight materials. Three humic-like substances (C1, C2, C4) and one protein-like substance (C3) were identified by PARAFAC model. C1, C2 and C4 exhibited same trends and were very similar. The separation of samples on both axes of the PCA showed the difference in DOM properties. C1, C2 and C4 concurrently showed higher positive factor 1 loadings, while C3 showed highly positive factor 2 loadings. The PCA analysis showed a combination contribution of microbial DOM signal and terrestrial DOM signal in the Yangtze estuary. Higher and more variable DOM abundance, aromaticity and molecular weight of surface sediment pore water DOM can be found in the southern nearshore than the other regions primarily due to the influence of frequent and intensive human activities and tributaries inflow in this area. The DOM abundance, aromaticity, molecular weight and fluorescence intensity in core of different depth were relative constant and increased gradually with depth. DOM in core was mainly composed of humic-like material, which was due to higher release of the sedimentary organic material into the porewater during early diagenesis. 相似文献
19.
Wetlands are known to be important sources of dissolved organic matter (DOM) to rivers and coastal environments. However,
the environmental dynamics of DOM within wetlands have not been well documented on large spatial scales. To better assess
DOM dynamics within large wetlands, we determined high resolution spatial distributions of dissolved organic carbon (DOC)
concentrations and DOM quality by excitation–emission matrix spectroscopy combined with parallel factor analysis (EEM–PARAFAC)
in a subtropical freshwater wetland, the Everglades, Florida, USA. DOC concentrations decreased from north to south along
the general water flow path and were linearly correlated with chloride concentration, a tracer of water derived from the Everglades
Agricultural Area (EAA), suggesting that agricultural activities are directly or indirectly a major source of DOM in the Everglades.
The optical properties of DOM, however, also changed successively along the water flow path from high molecular weight, peat-soil
and highly oxidized agricultural soil-derived DOM to the north, to lower molecular weight, biologically produced DOM to the
south. These results suggest that even though DOC concentration seems to be distributed conservatively, DOM sources and diagenetic
processing can be dynamic throughout wetland landscapes. As such, EEM–PARAFAC clearly revealed that humic-enriched DOM from
the EAA is gradually replaced by microbial- and plant-derived DOM along the general water flow path, while additional humic-like
contributions are added from marsh soils. Results presented here indicate that both hydrology and primary productivity are
important drivers controlling DOM dynamics in large wetlands. The biogeochemical processes controlling the DOM composition
are complex and merit further investigation. 相似文献
20.
Photooxidation of wetland and riverine dissolved organic matter: altered copper complexation and organic composition 总被引:1,自引:0,他引:1
In natural waters, the uptake of transition metals such as copper (Cu) by aquatic biota depends on the activity of the free
cupric ion ({Cu2+}) rather than on total Cu concentration. Thus, an important ecological function of dissolved organic matter (DOM) in aquatic
ecosystems is Cu–DOM complexation, which greatly decreases the {Cu2+}. However, Cu bioavailability is greatly modified by source and environmental history of DOM because DOM affinity for Cu
varies by orders of magnitude among DOM sources; moreover, DOM is photochemically unstable. During 72-h irradiation experiments
at intensities approximating sunlight with DOM from a palustrine wetland and a third-order river, we investigated photooxidative
effects on DOM complexation of Cu as well as spectral and chemical changes in DOM that might explain altered Cu complexation.
Irradiation decreased Cu complexation by riverine DOM, but unexpectedly increased Cu complexation by wetland DOM, resulting
in 150% greater {Cu2+} in riverine DOM at the same dissolved organic carbon concentrations. The specific ultraviolet absorption (SUVa) and humic substances tracked photochemical changes in the conditional stability constants of Cu–DOM complexes, suggesting
that the aromaticity of DOM influences its affinity for Cu. Carbonyl concentration in 13C nuclear magnetic resonance spectra (13C-NMR) covaried directly with Cu binding-site densities in DOM. However, no aspect of Cu–DOM complexation consistently covaried
with fluorophores (i.e., the fluorescence index) or low molecular weight organic acids. Our results suggest that global increases
in UV radiation will affect Cu–DOM complexation and subsequent Cu toxicity depending on light regime as well as DOM source.
Handling editor: K. Martens 相似文献