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1.
Arctic landscapes are believed to be highly sensitive to climate change and accelerated disturbance of permafrost is expected to significantly impact the rate of carbon cycling. While half the global soil organic matter (SOM) is estimated to reside in Arctic soils, projected warmer temperatures and permafrost disturbance will release much of this SOM into waterways in the form of dissolved organic matter (DOM). The spring thaw and subsequent flushing of soils releases the highest contributions of DOM annually but has historically been undersampled due to the difficulties of sampling during this period. In this study, passive samplers were placed throughout paired High Arctic watersheds during the duration of the 2008 spring flush in Nunavut, Canada. The watersheds are very similar with the exception of widespread active layer detachments (ALDs) that occurred within one of the catchments during a period of elevated temperatures in the summer of 2007. DOM samples were analyzed for structural and spectral characteristics via nuclear magnetic resonance (NMR) and fluorescence spectroscopy as well as vulnerability to degradation with simulated solar exposure. Lignin-derived phenols were further assessed utilizing copper(II) oxide (CuO) oxidation and gas chromatography/mass spectrometry (GC/MS). The samples were found to have very low dissolved lignin phenol content (∼0.07% of DOC) and appear to originate from primarily non-woody angiosperm vegetation. The acid/aldehyde ratios for dissolved vanillyl phenols were found to be high (up to 3.6), indicating the presence of highly oxidized lignin. Differences between DOM released from the ALD vs. the undisturbed watershed suggest that these shallow detachment slides have significantly impacted the quality of Arctic DOM. Although material released from the disturbed catchment was found to be highly oxidized, DOM in the lake into which this catchment drained had chemical characteristics indicating high contributions from microbial and/or primary productivity. The resulting pool of dissolved carbon within the lake appears to be more biologically- and photochemically-labile than material from the undisturbed system. These disturbances may have implications for projected climate warming; sustained elevated temperatures would likely perpetuate widespread ALDs and further affect carbon cycling in this environment.  相似文献   

2.
鲁宗杰  邓娅敏  杜尧  沈帅  马腾 《地球科学》2017,42(5):771-782
水体中溶解性有机质(dissolved organic matter, DOM)是含水层中砷释放的主控因素之一.江汉平原河湖众多、沟渠广布,地表水体与浅层地下水的交互作用使得DOM的组分特征及其强度有显著差异.为查明江汉平原地下水中溶解性有机质在砷迁移转化过程中的作用,对江汉平原地表水和浅层地下水进行三维荧光光谱分析,使用平行因子分析法提取水体中有机质的分子组成、功能特点和荧光特征,并分析各组分相对含量与地下水中砷与铁的关联.江汉平原水体中DOM包括3种主要组分,组分C1、C2为类腐殖质,C2是生物降解过程中产生的小分子,C3为类蛋白物质.地下水DOM以类腐殖质组分C1、C2为主,地表水以类蛋白类物质C3和小分子腐殖质C2为主.高砷地下水中DOM以陆源为主,主要通过两种途径促进As的迁移转化:(1) DOM的腐殖质组分充当微生物群落的电子运输工具,促进微生物作用下的有机质氧化和铁氧化物的还原,并伴随As的释放及大量溶解性有机碳(dissolved organic carbon, DOC)和HCO3-的产生;(2) As以铁等金属阳离子为桥接物与腐殖质结合,通过形成As-Fe-DOM络合物,导致地下水中砷的迁移.   相似文献   

3.
The delivery of organic carbon (C) from rivers to the coastal ocean via estuaries is recognized as an important component of the global C budget however, smaller river systems are often overlooked and modern flux estimates are not very different from historical estimates. Here, the seasonal (wet vs. dry) concentration and fluxes of dissolved organic C (DOC) were measured in five small sub-tropical rivers that drain into the Tampa Bay (FL, USA) estuary. DOC distributions were highly variable among riverine, mesohaline, and marine end-member samples in all river catchments and no significant differences were observed among or between DOC concentrations with respect to river catchment, season, or year of sampling. In general, DOC mixed non-conservatively during the wet seasons, and conservatively during the dry seasons, with the estuarine reaches of each river serving as a sink of DOC. Fluxes were strongly tied to discharge irrespective of season, and the estuaries removed 15–65% of DOC prior to export to coastal Bay and Gulf of Mexico waters. DOC concentrations were similar to others reported for low-elevation sub-tropical rivers, and a combination of elevation, residence time, and climate appear to control the abundance and variability of DOC in sub-tropical vs. tropical river systems. The characterization of DOC in small, sub-tropical rivers, which share characteristics with both their temperate and tropical counterparts, is critical for quantitatively constraining the importance of these systems in local-to-regional scale ocean C budgets. In addition to geomorphic properties, the role of past, present, and future land cover and other environmental change in small coastal rivers also exerts control on the quantity and flux of DOC in these systems.  相似文献   

4.
Dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) optical properties were analyzed along two estuarine river transects during the wet and dry seasons to better understand DOM dynamics and quantify mangrove inputs. A tidal study was performed to assess the impacts of tidal pumping on DOM transport. DOM in the estuaries showed non-conservative mixing indicative of mangrove-derived inputs. Similarly, fluorescence data suggest that some terrestrial humic-like components showed non-conservative behavior. An Everglades freshwater-derived fluorescent component, which is associated with soil inputs from the Northern Everglades, behaved conservatively. During the dry season, a protein-like component behaved conservatively until the mid-salinity range when non-conservative behavior due to degradation and/or loss was observed. The tidal study data suggests mangrove porewater inputs to the rivers following low tide. The differences in quantity of DOM exported by the Shark and Harney Rivers imply that geomorphology and tidal hydrology may be a dominant factor controlling the amount of DOM exported from the mangrove ecotone, where up to 21 % of the DOC is mangrove-derived. Additionally, nutrient concentrations and other temporal factors may control DOM export from the mangroves, particularly for the microbially derived fluorescent components, contributing to the seasonal differences. The wet and dry season fluxes of mangrove DOM from the Shark River is estimated as 0.27?×?109 mg C d?1 and 0.075?×?109 mg C d?1, respectively, and the Harney River is estimated as 1.9?×?109 mg C d?1 and 0.20?×?109 mg C d?1.  相似文献   

5.
The patterns of dissolved organic matter (DOM) fluorescence properties were examined in a Precambrian shield stream over a seven-month field study. Unique spatial and temporal patterns of simultaneous changes were observed in dissolved organic carbon concentration (DOC), humic-like fluorescence intensity, maximum excitation and emission wavelengths and fluorescence index (the ratio of the emission intensity at a wavelength of 450 nm to that at 500 nm at an excitation wavelength of 370 nm). The spatial change indicates the alteration of DOM along the length of the stream, and temporal change corresponded to a drought event in August. In contrast to humic-like fluorescence, the protein-like fluorescence shows considerable variability, suggesting its ephemeral nature. There were strong relationships between humic-like fluorescence intensity, fluorescence index, maximum Ex/Em wavelengths, DOC concentration and molecular size of DOM. This study has significant implications to the understanding of the nature and biogeochemical cycling of DOM.  相似文献   

6.
Analytical methods of dissolved Se species in river water and seawater were established and applied to study dissolved Se speciation in the Kaoping and Erhjen rivers and estuaries, southwestern Taiwan. The Kaoping and Erhjen rivers and estuaries were respectively in relatively oxygenated and oxygen-deficient conditions as revealed from the distributions of dissolved oxygen, DOC, nutrients, and dissolved Mn. Concentrations of dissolved total Se increased downstream in the riverine sections, ranging from 0.6 nM to 1.2 nM for the Kaoping River and from 0.8 nM to 1.05 nM for the Erhjen River. The dissolved total Se was only slightly higher in the Erhjen middle estuary than in the Kaoping middle estuary in spite of heavier pollution in the former. The dissolved total Se behaved rather conservatively in the Kaoping estuary but nonconservatively in the Erhjen estuary resulting from anthropogenic inputs, and in this respect showed similarities with the behavior of redox-sensitive Mn. The predominant species of selenium were Se(VI) and organic Se in the Kaoping River and Se(VI) in the Kaoping estuary. The elevated concentration of Se(VI) in the Kaoping estuary may stem from the degradation of organic Se and oxidation of Se(IV). On the other hand, Se(IV) and organic Se were equally dominant in the Erhjen River, and Se(IV) was predominant through most of the Erhjen estuary. The elevated distribution of Se(IV) in the Erhjen middle estuary may result mostly from partial decomposition of organic Se, but further oxidation of Se(IV) was inhibited in reducing waters. However, Se(VI) became dominant at Erhjen outer estuary where water was oxygenated by the replacement of intruded coastal seawater. Apparently, the speciation of dissolved Se was mainly controlled by the biological and redox processes in the Kaoping and Erhjen rivers and estuaries.  相似文献   

7.
Inputs of dissolved carbon, nitrogen, and phosphorus were assessed for an estuary and its catchment (Horsens, Denmark). Seasonal patterns in the concentrations of DOM in the freshwater supply to the estuary differed depending on the soil and drainage characteristics of the area. In streams draining more natural areas the, patterns observed were largely driven by seasonal temperature fluctuations. The material exported from agricultural areas was more variable and largely controlled by precipitation events. Positive exponential relationships were found between the nitrogen and phosphorus loading, and the percentage of catchment area used for agriculture. Colored DOM (CDOM) loading measurements were found to be a good predictor of dissolved organic carbon (DOC) loading across the different subcatchments, offering a rapid and inexpensive alternative of operationally monitoring DOC export. For all the dissolved nutrient inputs to the estuary, dissolved inorganic nitrogen (DIN) and dissolved organic phosphorus dominated the loadings. Although 81% of the nitrogen annually supplied to the estuary was DIN, 83% of the nitrogen exported from the estuary was dissolved organic nitrogen (DON). Results show that increasing the area of the catchment covered by forest and natural pastures would have a positive effect on the trophic status of the estuary, leading to a considerable decrease in the phosphorus loading and a shift in the nitrogen loading from DIN to DON. Such a change in land use would also increase the export of DOC and CDOM to the estuary having the potential to increase oxygen consumption and reduce the photic depth.  相似文献   

8.
Maatouk  E.  Samrani  A. El  Sawan  R.  Salameh  R. Bou Ghosn  Kazpard  V.  Matar  Z. 《Aquatic Geochemistry》2022,28(2):111-133

This work focuses on the characterization of a typical coastal karst watershed by addressing its physico-chemical parameters. The concentrations of the main ions clearly indicate the dominance of Ca2+ and HCO3? with a carbonate weathering rate equivalent to 230t/Km2/year; that is a typical weathering of karst watersheds. The spatio-temporal variability of dissolved organic matter (DOM) is also assessed in the watershed. Many samples were collected under different hydrological conditions from three representative sites. The evolution of OM composition along an urbanization gradient from upstream to downstream Kadisha watershed reveals the very strong impact of urban discharges on the receiving waters. Substantial differences in DOC results are highlighted in relation to the urban or natural origin of the DOM. Upstream OM flux is quantified and compared to downstream OM flux showing that, during the low flow period, the downstream flux is 29 times higher than the upstream. Also, a large fraction of non-humic substances, including hydrophilic organic matter HPI, is detected in the downstream section impacted by urban discharges. The higher values of SUVA noticed for DOM at upstream compared to downstream, reflects the low aromaticity and non-humic character of DOM in downstream. These outcomes show the impact of the Tripoli urban discharges on the quality and quantity of OM in the receiving waters downstream of the Kadisha catchment. This is typical at low water period when the dilution factor of urban discharges in the receiving waters is the least.

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9.
Here we report on the temporal changes in the composition of dissolved organic carbon (DOC) collected in the tidal freshwater region of the lower Mississippi River. Lignin-phenols, bulk stable carbon isotopes, compound-specific isotope analyses (CSIA) and 13C nuclear magnetic resonance (NMR) spectrometry were used to examine the composition of high molecular weight dissolved organic matter (HMW DOM) at one station in the lower river over 6 different flow regimes in 1998 and 1999. It was estimated that the annual input of DOC delivered to the Gulf of Mexico from the Mississippi River was of 3.1 × 10−3 Pg, which represents 1.2% of the total global input of DOC from rivers to the ocean. Average DOC and HMW DOC were 489 ±163 and 115 ± 47 μM, respectively. 13C-NMR spectra revealed considerably more aliphatic structures than aromatic carbons in HMW DOC. Lignin phenols were significantly 13C-depleted with respect to bulk HMW DOM indicating that C4 grass inputs to the HMW DOM were not significant. It is speculated that C4 organic matter in the river is not being converted (via microbial decay) to HMW DOM as readily as C3 organic matter is, because of the association of C4 organic matter with finer sediments. The predominantly aliphatic 13C NMR signature of HMW DOM suggests that autochthonous production in the river may be more important as a source of DOC than previously thought. Increases in nutrient loading and decreases in the suspended load (because of dams) in the Mississippi River, as well as other large rivers around the world, has resulted in significant changes in the sources and overall cycling of riverine DOC.  相似文献   

10.
《Geochimica et cosmochimica acta》1999,63(19-20):3311-3319
Copper speciation was determined monthly at seven sites on four rivers in southern New England to understand which geochemical factors control free metal ion concentrations in river water. Samples were conventionally filtered (<0.45 μm) and then ultrafiltered (3.000 molecular weight cut-off) to determine Cu speciation in the truly dissolved size fraction. Differential pulse anodic stripping voltammetry (DPASV) was used to quantify natural organic complexation and cathodic stripping square wave voltammetry (CSSWV) to measure directly both Cu sulfide complexes and total EDTA concentrations. The results showed both dissolved organic matter (DOM) and sulfide complexation dominate Cu speciation and control the concentrations of free ion. Free Cu2+ was calculated to be in the subnanomolar range for the majority of the year. Only in the winter months, when concentrations of DOM and metal sulfides complexes were at a minimum were free metal ions directly measurable by DPASV at low nanomolar concentrations. The extent of sulfide complexation appears to be dominated by the size of headwater marshes (upstream sampling sites) and by the amount of sewage treatment plant effluent (downstream sites). DOM complexation was related to the organic matter composition and followed model organic ligands. Indirect evidence suggests variations in river water pH and Ca2+ (metal competition) has only a minor role in Cu complexation. Measured concentrations of total EDTA suggest this synthetic ligand can control Cu speciation in some highly developed watersheds; however, competition from Ni (and possibly Fe) limits the extent of this complexation.  相似文献   

11.
Benthic dissolved organic carbon (DOC) flux rates and changes in DOC isotope ratios, along with nutrient fluxes, phospholipid fatty acids concentration and carbon isotope ratios were measured in productive estuarine sediments over a diel cycle to determine the mechanisms driving benthic-pelagic coupling of DOC. There was uptake of DOC during the dark and efflux during the light at all sites. DOC uptake rates were related to benthic respiration (dark O2 uptake) and effluxes were coupled to the trophic status (ratio of production to respiration) of the sediments. Highest uptake and efflux rates were observed at two high nutrient concentration sites. The DOC:DON ratio of water column dissolved organic matter (DOM) decreased during the dark and increased during the light indicating preferential uptake and release of carbon rich dissolved organic matter. The calculated carbon isotope ratio of the DOC taken up by the benthos was significantly more depleted than the bulk water column DOC pool, suggesting preferential uptake of selected components of the water column DOC pool. Generally the isotope ratio of the DOC released during the light was more enriched than that taken up during the dark, which suggests that the benthos has the potential to significantly alter the estuarine DOC pool. Uptake and efflux were coupled to respiration and algal grazing/mineralization, therefore increased nutrient loading may shift the composition of the estuarine DOC pool through changes in the magnitude of benthic DOC fluxes. A combination of biological (diel shifts in DOC production and consumption) and abiotic processes (flocculation) appear to be driving the observed benthic DOC dynamics at the study sites. This study was the first to measure carbon isotopic changes in the water column DOC pool due to benthic processes, and shows that the benthos can alter the estuarine DOC pool through diel differences in DOC uptake and efflux.  相似文献   

12.
Defining the control that hydrology exerts on organic carbon (OC) export at the watershed scale is important for understanding how the source and quantity of OC in streams and rivers is influenced by climate change or by landscape drainage. To this end, molecular (lignin phenol), stable carbon isotope, and dissolved organic carbon (DOC) data were collected over a range of flow conditions to examine the influence of hydrology on annual OC export from an 850 km2 Midwestern United States agricultural watershed located in west central Indiana. In years 2002 and 2003, modeled annual DOC loads were 19.5 and 14.1 kg ha−1yr−1, while 71% and 85%, respectively, of the total annual OC was exported in flow events occurring during less than 20% of that time. These results highlight the importance of short-duration, high-discharge events (common in smaller watersheds) in controlling annual OC export. Based on reported increases in annual stream discharge coupled with current estimates of DOC export, annual DOC loads in this watershed may have increased by up to 40% over the past 50 years. Molecular (lignin phenol) characterization of quantity and relative degradation state of terrestrial OC shows as much temporal variability of lignin parameters (in high molecular weight dissolved organic carbon) in this one watershed as that demonstrated in previously published studies of dissolved organic matter in the Mississippi and Amazon Rivers. These results suggest that hydrologic variability is at least as important in determining the nature and extent of OC export as geographic variability. Moreover, molecular and bulk stable carbon isotope data from high molecular weight dissolved organic carbon and colloidal organic carbon showed that increased stream flow from the study watershed was responsible for increased export of agriculturally derived OC. When considered in the context of results from other studies that show the importance of flood events and in-stream processing of terrestrial organic carbon, our results show how hydrologic variability in smaller watersheds can reflect landscape-scale carbon dynamics in ways that cannot necessarily be measured at the outlets of large rivers due to multiple source signals and attenuated hydrology.  相似文献   

13.
This project examined concentrations, composition and turnover neutral sugars in the Delaware estuary to gain insights into dissolved inorganic nitrogen (DIN) use by heterotrophic bacteria and into the lability and diagenetic state of dissolved organic material (DOM) during passage through the estuary. Dissolved free monosaccharides were not measurable (<5 nM) in the estuary whereas concentrations of dissolved combined neutral sugars (DCNS) were high, much higher than observed in oceanic waters. DCNS made up a similar fraction of dissolved organic carbon (DOC) as in the oceanic waters examined to date, and the monosaccharide composition of the DCNS pool was similar to that of oceanic waters. The composition did not vary substantially within the estuary or seasonally, but it did vary among three size fractions of the organic matter pool. Glucose was enriched in the low molecular weight fraction of DOC and in particulate material, whereas the high molecular weight DOC fraction was slightly depleted in glucose. Depletion experiments indicated that DCNS is not used extensively on the day time scale in the Delaware estuary, although freshly-produced polysaccharides may still be important carbon sources for heterotrophic bacteria. The very low concentrations of free monosaccharides in the Delaware estuary help to explain why DIN use by heterotrophic bacteria is relatively low in this estuary. Although DOC-DIN interactions in the Delaware apparently differ from oceanic waters, the portion of DOM traced by DCNS, which is thought to be the labile fraction, appears to be similar to that of oceanic DOM, suggesting that organic material in the estuary is degraded extensively before being exported to the coastal ocean.  相似文献   

14.
Activities of man in rivers and their watersheds have altered enormously the timing, magnitude, and nature of inputs of materials to estuaries. Despite an awareness of large-scale, long-term changes in river-estuarine watersheds, we do not fully understand the consequences to estuarine ecosystems of these activities. Deforestation, urbanization, and agriculturalization have changed the timing and nature of material inputs to estuaries. Conversion of land from forest to almost any other land use promotes overland flow of storm runoff; increases the timing, rate and magnitude of runoff; and increases sediment, organic matter, and inorganic nutrient export. It has been estimated that total organic carbon levels in rivers have increased by a factor of 3–5 over natural levels. Man’s activities have also changed the magnitude of particulate organic carbon relative to dissolved organic carbon export and the lability of the organic matter. Historically, rivers and streams had different features than they do today. Two of man’s activities that have had pronounced effects on the timing and quality of river water are channelization and damming. Agricultural drainage systems, channelized and deepened streams, and leveeing and prevention of overbank flooding have had the combined effect of increasing the amplitude and rate of storm runoff, increasing sediment load, increasing nutrient delivery downstream, and decreasing riparian wetland productivity. Dams on the other hand have altered natural discharge patterns and altered the downstream transfer of sediments, organic matter, and nutrients. Patterns of estuarine community metabolism are sensitive to variations, in the timing, magnitude, and quality of material inputs from watersheds. The autotrophic-heterotrophic nature of an estuary is determined by three primary factors: the ratio of inorganic to organic matter inputs, water residence time, and the overall lability of allochthonous organic matter inputs. A simulation model is used to explore the effects of man’s activities in watersheds on the spatial patterns of production and respiration in a generalized estuarine system. Examined are the effects of variations in the ratios of inorganic and organic nitrogen loading, the residence time of water in the estuary, the degradability of allochthonous organic matter, and the ratio of dissolved to particulate organic matter inputs. Simulations suggest that the autotrophic-heterotrophic balance in estuaries is more sensitive to variations in organic matter loading than inorganic nutrient loading. Water residence time and flocculation-sedimentation of organic matter are two physical factors that most effect simulated spatial patterns of metabolism in estuaries.  相似文献   

15.
The biological turnover of riverine dissolved organic carbon (DOC) discharged into five southeastern United States estuaries was examined in long-term respiration bioassays. Measures of bacterial oxygen consumption indicated surprisingly large differences in the inherent biodegradability of DOC among the five estuaries, despite their close geographic proximity. Differences of up to 13-fold in biodegradation rates were also found temporally within a single estuary. For most of the southeastern United States estuaries, measured rates of riverine DOC biodegradation were low relative to rates reported for other freshwater and marine environments. This was particularly true for the coastal plain (“blackwater”) rivers that contribute about 35% of the riverine DOC exported to coastal marine environments in this region; extrapolation of biodegradation rates to the adjacent continental shelf predict biodegradation of a maximum of 11% of exported blackwater DOC within the estuary-shelf system (with transit times of up to 140 d). DOC from Piedmont rivers was more biologically labile, with maximum losses of 30% predicted within the estuary and adjacent shelf. Short exposures to natural sunlight increased the lability of the riverine DOC and enhanced biodegradation rates by over 3-fold in some cases, although significant inter-estuary differences in susceptibility of riverine DOC to photolysis were also evident. *** DIRECT SUPPORT *** A01BY085 00007  相似文献   

16.
Water samples from eight major Texas rivers were collected at different times during 1997–1998 to determine the dissolved and particulate trace metal concentrations, expected to show differences in climate patterns, river discharge and other hydrochemical conditions, and human activities along the different rivers. Specifically, two eastern Texas rivers (Sabine, Neches) lie in a region with high vegetation, flat topography, and high rainfall rates, while four Central Texas rivers (Trinity, Brazos, Colorado, and San Antonio) flow through large population centers. Relatively high dissolved organic carbon (DOC) concentrations in the eastern Texas rivers and lower pH led to higher Fe and Mn concentrations in river waters. The rivers that flow through large population centers showed elevated trace metal (e.g., Cd, Pb, Zn) concentrations partly due to anthropogenically produced organic ligands such as ethylenediaminetetraacetic acid (EDTA) present in these rivers. Trace metal levels were reduced below dams/reservoirs along several Texas rivers. Statistical analysis revealed four major factors (suspended particulate matter [SPM], EDTA, pH, and DOC) that can explain most of the observed variability of trace metal concentrations in these rivers. SPM concentrations directly controlled particulate metal contents. Variation in pH correlated with changes of dissolved Co, Fe, Mn, and Ni, and particulate Mn concentrations, while DOC concentrations were significantly related to dissolved Fe concentrations. Most importantly, it was found that, more than pH, EDTA concentrations exerted a major control on dissolved concentrations of Cd and Zn, and, to a lesser extent, Cu, Ni, and Pb.  相似文献   

17.
The composition and metabolic capability of bacterioplankton communities were examined over seasonal and spatial gradients and related to the source, composition, and quantity of dissolved organic matter (DOM) in the blackwater estuary Winyah Bay, Georgetown County, SC, USA and its tributary rivers. Bacterial community composition (BCC) was measured by terminal restriction fragment length polymorphism, and bacterial metabolic capability (BMC) was measured by defined substrate utilization patterns (Biolog GN2 plates). Spatial patterns were not important, despite the anticipated watershed effects and the well-documented influence of salinity gradients on estuarine bacterioplankton, but DOM, BCC, and BMC all showed varying degrees of temporal patterns; DOM-based groupings differentiated BCC samples better than spatiotemporal categories, but not BMC. BCC was closely related to properties describing DOM composition, particularly those related to DOM source (i.e., cypress swamps vs. in situ phytoplankton production, indicated by chlorophyll a, colored DOM spectral slope, α355/dissolved organic carbon (DOC), and DOC concentration), and to associated physicochemical variables, such as temperature, pH, and salinity. BMC was more strongly related to abiotic factors, such as temperature and dissolved nutrients, as well as to chlorophyll a and percent bioavailable DOC. In contrast with previous studies, BCC and BMC were significantly correlated in this highly heterotrophic estuary, suggesting that DOM source variability may select for specialist phylotypes above a background of generalists. This study, therefore, supports a causative pathway from DOM to BMC to BCC while suggesting that BCC and BMC may be simultaneously influenced by different suites of DOM characteristics and physicochemical parameters.  相似文献   

18.
In the present study, we explored the use of various optical parameters to detect differences in the composition of the dissolved organic matter (DOM) in a set of lakes that are all located on the Canadian Precambrian Shield, but within which Cu and Ni speciation predictions were previously shown to diverge from measured values in some lakes but not in others. Water samples were collected with in situ diffusion samplers in 2007 (N = 18 lakes) and 2008 (N = 8 lakes). Significant differences in DOM quality were identified between the sampling regions (Rouyn-Noranda, Québec and Sudbury, Ontario) and among lakes, based on dissolved organic carbon concentrations ([DOC]), specific UV absorbance (SUVA254), fluorescence indices (FI), and excitation–emission matrix (EEM) fluorescence measurements. Parallel factor analysis (PARAFAC) of the EEM spectra revealed four components, two of which (C3, oxidized quinone fluorophore of allochthonous origin, and C4, tryptophan-like protein fluorescence of autochthonous origin) showed the greatest inter-regional variation. The inter-lake differences in DOM quality were consistent with the regional watershed characteristics as determined from satellite imagery (e.g., watershed-to-lake surface area ratios and relative percentages of surface water, rock outcrops vegetative cover and urban development). Source apportionment plots, built upon PARAFAC components ratios calculated for our lakes, were used to discriminate among DOM sources and to compare them to sources identified in the literature. These results have implications for other areas of research, such as quantifying lake-to-lake variations in the influence of organic matter on the speciation of trace elements in natural aquatic environments.  相似文献   

19.
卤水中溶解性有机质(dissolved organic matter,DOM)会对盐田日晒工艺和产品质量产生不利影响,如盐田卤水的蒸发速率减缓、蒸发度减小以及提取的矿物产品带有刺鼻的气味、浓重的颜色等。因此,对具有资源开发利用价值的卤水体系中DOM结构和性质的研究可以为后续DOM的有效去除或在DOM共存体系中调控无机盐结晶工艺路线提供有效的指导意见。本文以自然界中广泛存在的两种不同类型的卤水体系,即盐湖卤水DOM(SLDOM)和油田卤水DOM(OFDOM)为研究对象,采用溶解性有机碳(dissolved organic carbon,DOC)分析、光谱学分析和平行因子分析等手段对DOM的含量、分子量分布特征、光谱学结构和光降解行为开展了研究。DOC和荧光分析表明SLDOM和OFDOM的DOC含量和生物指数(BIX)值相似;与OFDOM相比,SLDOM的腐质化指数(HIX)值和高分子量组分(HMW)比例偏高;特别吸收光谱(SUVA254)和糖类化合物含量检测结果表明,SLDOM和OFDOM的HMW组分中含有的芳香类和糖类化合物所占比例比低分子量组分(LMW)高;三维荧光谱图分析(EEM)结果表明,SLDOM主要以腐殖质类物质为主,而OFDOM以蛋白质类组分为主。此外,DOM的荧光组分在不同分子量中的分布也存在明显差异:对于SLDOM,富里酸主要分布在HMW DOM中,而腐殖酸主要在LMW DOM中;对于OFDOM,芳香胺类蛋白组分主要分布在HMW DOM中,色氨酸和酪氨酸类蛋白组分主要分布在LMM DOM中。在光降解实验中,SLDOM和OFDOM的DOC含量随光照时间增加而逐渐减少,分别下降了29.32%和15.11%。进一步的分析表明,光照过程中两种卤水中糖类化合物均减少,小分子量的DOM优先分解。此外,在光照过程中SLDOM芳香类化合物增加,腐质化程度基本不变;OFDOM芳香类化合物减少,腐质化程度增加。EEM平行因子分析(PARAFAC)结果表明,SLDOM荧光组分在光降解过程中荧光强度增加,而OFDOM荧光强度减少。  相似文献   

20.
Aureococcus anophagefferens, the pelagophyte responsible for brown tide blooms, occurs in coastal bays along the northeast coast of the United States. This species was identified in Chincoteague Bay, Maryland, in 1997 and has bloomed there since at least 1998. Time series of dissolved organic matter (DOM) concentrations and characteristics are presented for two sites in Chincoteague Bay: one that experienced a brown tide bloom in 2002 and one that did not. Characteristics of the bulk DOM pool were obtained using dissolved organic carbon (DOC) and ultraviolet-visible (UV-Vis) measurements (spectral slope and specific UV absorbance). High molecular weight DOM (HMW-DOM) was characterized in terms of DOC concentration, carbon: nitrogen (C:N) ratio, isotopic signature, and molecular-level characteristics as determined by direct temperature resolved mass spectrometry (DT-MS). Compositional changes in the DOM pool are associated with brown tide blooms, although a direct relationship between DOM characteristics and bloom development could not be confirmed. DOC measurements suggest that during the brown tide bloom, HMW-DOM was released into the surface water. UV-Vis analysis on the bulk DOM and molecular-level characterization of the HMW-DOM using DT-MS show that this material was optically active and more aromatic in nature. Based upon C:N ratio and HMW-DOC measurements, it appears that this HMW-DOM was more nitrogen enriched. Whether this material was released as exudates or was due to lysis ofA. anophagefferens could not be determined.  相似文献   

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