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1.
Arctic rivers typically transport more than half of their annual amounts of water and suspended sediments during spring floods. In this study, the Sagavanirktok, Kuparuk and Colville rivers in the Alaskan Arctic were sampled during the spring floods of 2001 to determine levels of total suspended solids (TSS) and dissolved and particulate metals and organic carbon. Concentrations of dissolved organic carbon (DOC) increased from 167 to 742 μmol/L during peak discharge in the Sagavanirktok River, at about the same time that river flow increased to maximum levels. Concentrations of dissolved Cu, Pb, Zn and Fe in the Sagavanirktok River followed trends observed for DOC with 3- to 25-fold higher levels at peak flow than during off-peak discharge. Similar patterns were found for the Kuparuk and Colville rivers, where average concentrations of dissolved trace metals and DOC were even higher. These observations are linked to a large pulse of DOC and dissolved metals incorporated into snowmelt from thawing ponds and upper soil layers. In contrast with Cu, Fe, Pb and Zn, concentrations of dissolved Ba did not increase in response to increased discharge of water, TSS and DOC. Concentrations of particulate Cu, Fe, Pb and Zn were more uniform than observed for their respective dissolved species and correlated well with the Al content of the suspended particles. However, concentrations of particulate Al were poorly correlated with particulate organic carbon. Results from this study show that >80% of the suspended sediment and more than one-third of the annual inputs of dissolved Cu, Fe, Pb, Zn and DOC were carried to the coastal Beaufort Sea in 3 and 12 d, respectively, by the Kuparuk and Sagavanirktok rivers.  相似文献   

2.
Dissolved (<1 kDa) and colloidal (1 kDa-0.45 μm) size fractions of sulfate, organic carbon (OC), phosphate and 17 metals/metalloids were investigated in the acidic Vörå River and its estuary in Western Finland. In addition, geochemical modelling was used to predict the formation of free ions and complexes in these waters. The sampling was carried out during high-water flow in autumn and in spring when the abundantly occurring acid sulfate (AS) soils in the catchment area are extensively flushed. Based on the high concentrations of sulfate, acidity and several metals, it is clear that the Vörå River and its estuary is strongly affected by AS soils. The high dissolved form of metals limits also the existence of fish and other organisms in this estuary, and certainly also in other similar shallow brackish estuaries elsewhere in the Gulf of Bothnia. However, generally already <20% saline sea water reduces the concentration for OC and several elements (Al, Cu, Cr, Fe, Pb, PO4 and U) by half and c. 20–30% saline sea water is needed to halve concentrations of Cd, Co, Mn, Ni and Zn. Consequently, these elements as well as organic matters were rapidly precipitated in the estuary, even after mixing with fairly small amounts of the alkaline brackish sea water. Aluminium, Cu, Fe and U most likely precipitate together with organic matter closest to the river mouth. Manganese is relatively persistent in solution and, thus, precipitates further down the estuary as Mn oxides, which concomitantly capture Ba, Cd, Co, Cu, Ni and Zn. In the inner estuary, the high contents of Al is as important than Fe in removing PO4 and, thus, also reducing the risk of algae blooms in near coastal areas influenced by AS soils in the Gulf of Bothnia. Moreover, the dispersion of metals far out in the estuary is dependent on hydrological conditions, i.e. with high flows the plume of metal-rich water will spread further out in the estuary. Furthermore, the extensive drainage of the catchment and subsequent artificial enlargement of the river channel during recent decades has not only enabled oxidation of sulfidic sediments, but strongly increased flow peaks that reach further out in the estuary.  相似文献   

3.
The Kola River in the northern part of the Kola Peninsula, northwestern Russia, flows into the Barents Sea via the Kola Bay. The river is a unique place for reproduction of salmon and an important source of drinking water for more than 500,000 people in Murmansk and the surrounding municipalities. To evaluate the environmental status of the Kola River water, sampling of the dissolved (<0.22 μm) and suspended (>0.22 μm) phases was performed at 12 sites along the Kola River and its tributaries during 2001 and 2002. Major (Ca, K, Mg, Na, S, Si, HCO3 and Cl) and trace (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr, Ti, and Zn) elements, total and particulate organic C (TOC and POC), N and P were analysed. Comparison with the boreal pristine Kalix River, Northern Sweden, shows that, except for Na, Cl, Al, Cu and Ni, which exceed the concentrations in the Kalix River by as much as 2–3 times, the levels of other major and trace elements are close to or even below the levels in the Kalix River. However, the results also demonstrate that pollutants from the three major sources: (1) the Cu–Ni smelter in Monchegorsk, (2) the open-pit Fe mine and ore concentration plant in Olenegorsk, and (3) the Varlamov, the Medveziy and the Zemlanoy creeks, draining the area of the large agricultural enterprises in the lower part of the watershed, have a major influence on the water quality of the Kola River.  相似文献   

4.
Chen  Jingsheng  Wang  Feiyue 《GeoJournal》1996,40(1-2):31-37
A total of 42 aquatic particulate sample:, (suspended matter and < 63 m surficial sediments) was collected from 11 large rivers in eastern China. Contents of both major elements (Al, Si, Ca, Mg, K, Na, Ti, Fe, Mn) and trace elements (Cu, Pb, Zn, Cd, Cr, Co, Ni, V) in the particulate samples were analyzed. The geographic variations of river particulate compositions were studied. The results showed that the Yellow River particulates contained a notably high content of Ca and a low content of Al. Except for the Yellow River, A1 contents in particulates increased from the northern rivers to the southern rivers, while K and Na decreased. Trace elements were relatively enriched in the southern river particulates. The geographic variations seemed to be related to the weathering types and geological background within the river basins. The average composition of river particulates in China was then estimated. Based on the Chinese river data from this paper, as well as on the literature data for other main world rivers, a new estimation of the global average particulate composition was reported. Since the earlier estimations in the literature were not concerned with or at best concerned only with few of the Chinese rivers which contribute a major proportion to the global load of river particulates, this new estimation may be more reasonable.  相似文献   

5.
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   

6.
The Tinto and Odiel rivers drain 100 km from the Rio Tinto sulphide mining district, and join at a 20-km long estuary entering the Atlantic Ocean. A reconnaissance study of heavy metal anomalies in channel sand and overbank mud of the river and estuary by semi-quantitative emission dc-arc spectrographic analysis shows the following upstream to downstream ranges in ppm (μg g?1): As 3,000 to <200, Cd 30 to <0.1, Cu 1,500 to 10, Pb 2,000 to <10, Sb 3000 to <150, and Zn 3,000 to <200. Organic-rich (1.3–2.6% total organic carbon, TOC), sandysilty overbank clay has been analyzed to represent suspended load materials. The high content of heavy metals in the overbank clay throughout the river and estuary systems indicates the importance of suspended sediment transport for dispersing heavy metals from natural erosion and anthropogenic mining activities of the sulfide deposit. The organic-poor (0.21–0.37% TOC) river bed sand has been analyzed to represent bedload transport of naturally-occurring sulfide minerals. The sand has high concentrations of metals upstream but these decrease an order of magnitude in the lower estuary. Although heavy metal contamination of estuary mouth beach sand has been diluted to background levels estuary mud exhibits increased contamination apparently related to finer grain size, higher organic carbon content, precipitation of river-borne dissolved solids, and input of anthropogenic heavy metals from industrial sources. The contaminated estuary mud disperses to the inner shelf mud belt and offshore suspended sediment, which exhibit metal anomalies from natural erosion and mining of upstream Rio Tinto sulphide lode sources (Pb, Cu, Zn) and industrial activities within the estuary (Fe, Cr, Ti). Because heavy metal contamination of Tinto-Odiel river sediment reaches or exceeds the highest levels encountered in other river sediments of Spain and Europe, a detailed analysis of metals in water and suspended sediment throughout the system, and epidemiological analysis of heavy metal effects in humans is appropriate.  相似文献   

7.
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8.
《Applied Geochemistry》2005,20(1):69-88
Surface sediments of the NW Aegean Sea were analyzed for clay mineral composition (94 samples), organic C and carbonate content, and major and minor elements (112 samples). Illite is the most abundant clay mineral, followed by smectite, chlorite and kaolinite. Clay minerals are preferentially deposited within the continental shelf and slope environment, due to the prevailing cyclonic circulation and the formation of flocs in the rivers’ pro-delta areas. The spatial distribution of major lithogenic elements (Si, Al, Ti, Fe) is substantially biased by the presence of relict sands located in the central-eastern part of the Thermaikos Gulf continental shelf. Biogenic elements (Ca, Sr) are noticeably pronounced on the northern flank of the North Sporades Islands. Organic C content and minor elements Cu, Zn, As and Pb are enriched markedly over the Thessaloniki Bay and Gulf suggesting substantial human impact, deriving largely from untreated or partly treated domestic and industrial effluents. The terrigenous component of the elements is preferentially contributed from the Axios River (Zn and Pb), the Aliakmon River (Cr, Co, Ni, Cu and As), and to a lesser extent from the Pinios River (V, Co, Ni and Cu); a considerable part of the metals originates in ultra-mafic and volcanic formations, which are abundant in the rivers’ catchment basins. Carbonate content exhibits great variability, with the highest values observed in biogenic sediments of the Sporades Basin. In the latter area, Mn (and Fe) oxides and hydroxides were found as coatings on calcite. The coatings were enriched in Cr, Co, Ni, Zn, As, Mo and Pb, due to adsorption or ion-exchange during early diagenesis. The combined influence of the river systems, the Thessaloniki metropolis, and the diverse sedimentological background, generates great patchiness in the distribution of major and minor elements.  相似文献   

9.
The bioavailability of metals and their potential for environmental pollution depends not simply on total concentrations but on their chemical form. Consequently, knowledge of aqueous metal speciation is essential in investigating potential metal toxicity and mobility. Dissolved (<1 kDa), colloidal (1 kDa–0.45 μm) and particulate (>0.45 μm) size fractions of sulfate, organic C (OC) and 18 metals/metalloids were investigated in the extremely acidic Vörå River system in Western Finland, which is strongly affected by acid sulfate (AS) soils. In addition, geochemical modelling was used to predict the formation of free ions and complexes in these acidic waters. The most important finding of this study is that the very large amounts of elements known to be released from AS soils (including Al, Ca, Cd, Co, Cu, Mg, Mn, Na, Ni, Si and U) occur and can prevail mainly in toxic forms throughout acidic river systems; as free ions and/or sulfate-complexes. This has serious effects on the biota and particularly dissolved Al can be expected to have acute effects on fish and other organisms. In the study area, only the relatively forested upstream area (higher pH and contents of OC) had significant amounts of a few bioavailable elements (including Al, Cu, Ni and U) due to complexation with the more abundantly occurring colloidal OC in the upstream area. It is, however, notable that some of the colloidal/particulate metals were most likely associated with metal bearing phyllosilicates eroded from clay soils. Moreover, the mobilisation of Fe and As was small and As was predicted to be associated with Fe oxides, indicating a considerable influence of Fe oxides on the mobilisation/immobilisation processes of As. Elements will ultimately be precipitated in the recipient estuary, where the acidic metal-rich river water will gradually be diluted/neutralised with brackish seawater in the Gulf of Bothnia. According to speciation modelling, such a pH rise may first cause precipitation of Al, Cu and U together with organic matters closest to the river mouth, in line with previous sediment studies from the estuary.  相似文献   

10.
《Applied Geochemistry》2005,20(7):1391-1408
Surface water samples from the St. Lawrence River were collected in order to study the processes controlling minor and trace elements concentrations (Al, Fe, Mn, Cd, Co, Cu, Ni and Zn), and to construct mass balances allowing estimates of the relative importance of their natural and anthropogenic sources. The two major water inputs, the upper St. Lawrence River, which drains waters originating from the Lake Ontario, and the Ottawa River were collected fortnightly over 18 months. In addition, other tributaries were sampled during the spring floods. The output was monitored near Quebec City at the river mouth weekly between 1995 and 1999. Dissolved metal concentrations in the upper St. Lawrence River carbonated waters were lower than in the acidic waters of the tributaries draining the crystalline rocks of the Canadian shield and the forest cover. Biogeochemical and hydrodynamic processes occurring in Lake Ontario drive the seasonal variations observed in the upper St. Lawrence River. Biogeochemical processes relate to biological uptake, regeneration of organic matter (for Cd and Zn) and oxyhydroxide formation (for Mn and Fe), while hydrodynamic processes mainly concern the seasonal change in vertical stratification (for Cd, Mn, and Zn). In the Ottawa River, the main tributary, oxyhydroxide formation in summer governs seasonal patterns of Al, Fe, Mn, Cd, Co and Zn. The downstream section of the St. Lawrence River is a transit zone in which seasonal variations are mainly driven by the mixing of the different water masses and the large input of suspended particulate matter from erosion. The budget of all dissolved elements, except Fe and Zn, was balanced, as the budget of particulate elements (except Cd and Zn). The main sources of metals to the St. Lawrence River are erosion and inputs from tributaries and Lake Ontario. Direct anthropogenic discharges into the river accounted for less than 5% of the load, except for Cd (10%) and Zn (21%). The fluxes in transfer of dissolved Cd, Co, Cu and Zn species from the river to the lower St. Lawrence estuary were equal to corresponding fluxes calculated for Quebec City since the distributions of dissolved concentrations of these metals versus salinity were conservative. For Fe, the curvature of the dilution line obtained suggests that dissolved species were removed during early mixing.  相似文献   

11.
Fractionation by ultra-filtration of the dissolved organic material (DOM) in the River Beaulieu, with typical concentrations of dissolved organic carbon (DOC) of 7–8 mg C/l, showed it to be mainly in the nominal molecular weight range of 103–105, with 16–23% of the total DOC in the fraction > 105. The molecular weight distribution of DOM in the more alkaline River Test (average DOC, 2 mg C/l) was similar. In the River Beaulieu water, containing 136–314 βg Fe/l in ‘dissolved’ forms, 90% or more of this Fe was in the nominal molecular weight fraction > 105. Experiments showed that DOM of nominal molecular weight <105 could stabilize Fe(III) in ‘dissolved’ forms. The concentrations of ‘dissolved’ Fe in the river water probably reflect the presence of colloidal Fe stabilized by organic material and this process may influence the apparent molecular weight of the DOM. Dissolved. Mn (100–136 βg/l) in the River Beaulieu was mainly in true solution, probably as Mn(II), with some 30% in forms of molecular weight greater than ca 104.During mi xing in the Beaulieu Estuary, DOC and dissolved Mn behave essentially conservatively. This contrasts with the removal of a large fraction of the dissolved Fe (Holliday and LISS, 1976, Est. Coastal Mar. Sci. 4, 349–353). Concentrations of lattice-held Fe and Mn in suspended particulate material were essentially uniform in the estuary, at 3.2 and 0.012%, respectively, whereas the non-lattice held fractions decreased markedly with increase in salinity. For Mn the decrease was linear and could be most simply accounted for by the physical mixing of riverborne and marine participates, although the possibility that some desorption occurs is not excluded. The non-linear decrease in the concentration of non-lattice held Fe in particulates reflected the more complex situation in which physical mixing is accompanied by removal of material from the ‘dissolved’ fraction.  相似文献   

12.
The distribution of Mn was examined in the bottom sediments and water column (suspended paniculate matter) of the Laurentian Trough. Gulf of St. Lawrence. A characteristic profile of Mn with depth in the sediment consisted of a Mn-enriched surface oxidized zone, less than 20 mm thick, and a Mn-depleted subsurface reducing zone. A subsurface Mn maximum occurred within the oxidized zone. Below this maximum the concentration dropped sharply to nearly constant residual levels in the reducing zone. The accumulating estuarine sediments are deficient in Mn compared to the river input of suspended matter and are definitely not the ultimate sink for manganese. Manganese escapes from the sediment by diffusion and resuspension, forming Mn-enriched, fine-grained particles which are flushed out in the estuarine circulation. 5.0 × 109gyr?1 of Mn, or 50% more than the river input of dissolved Mn. are exported to the open ocean. In spite of the efficient mobilization and export of Mn, the quantity exported is a small fraction (0.2%) of the total flux to the deep-sea sediments. This is related to the low levels of paniculate matter transported by the St. Lawrence River. The export phénomenon, however, is probably true of many coastal regions of muddy sediments and thus has interesting implications for the oceanic budget of Mn.  相似文献   

13.
This study was designed to determine the amount of particulate organic carbon (POC) introduced to the Gulf of Mexico by the Mississippi River and assess the influence of POC inputs on the development of hypoxia and burial of organic carbon on the Louisiana continental shelf. Samples of suspended sediment and supporting hydrographic data were collected from the river and >50 sites on the adjacent shelf. Suspended particles collected in the river averaged 1.8±0.3% organic carbon. Because of this uniformity, POC values (in μmol l?1) correlated well with concentrations of total suspended matter. Net transport of total organic carbon by the Mississippi-Atchafalaya River system averaged 0.48×1012 moles y?1 with 66% of the total organic carbon carried as POC. Concentrations of POC decreased from as high as 600 μmol l?1 in the river to <0.8 μmol l?1 in offshore waters. In contrast, the organic carbon fraction of the suspended matter increased from <2% of the total mass in the river to >35% along the shelf at ≥10 km from the river mouth. River flow was a dominant factor in controlling particle and POC distributions; however, time-series data showed that tides and weather fronts can influence particle movement and POC concentrations. Values for apparent oxygen utilization (AOU) increased from ～60 μmol l?1 to >200 μmol l?1 along the shelf on approach to the region of chronic hypoxia. Short-term increases in AOU were related to transport of more particle-rich waters. Sediments buried on the shelf contained less organic carbon than incoming river particles. Orgamic carbon and δ13C values for shelf sediments indicated 3 that large amounts of both terrigenous and marine organic carbon are being decomposed in shelf waters and sediments to fuel observed hypoxia.  相似文献   

14.
《Applied Geochemistry》1998,13(4):451-462
Water, suspended matter, and sediment samples were taken from 8 locations along the Yangtze River in 1992. The concentration and speciation (exchangeable, bound to carbonates, bound to Fe–Mn oxides, bound to organic matter, and residual forms) of rare earth elements (La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu) were determined by instrumental neutron activation analysis (INAA).The contents of the soluble fraction of REEs in the river are low, and REEs mainly reside in particulate form. In the particles, the chondrite-normalized distribution patterns show significant LREE enrichment and Eu-depletion. While normalized to shales, both sediments and suspended matter samples show relative LREE enrichment and HREE depletion. REEs are relatively enriched in fine-grained fractions of the sediments.The speciation characteristics of REEs in the sediments and suspended matter are very similar. The amount of the five forms follows the order: residual>>bound to organic matter∼bound to Fe–Mn oxides>bound to carbonates>>exchangeable. About 65 to 85% of REEs in the particles exist in the residual form, and the exchangeable form is very low. High proportions of residual REEs reveal that REEs in sediments and suspended matter are controlled by their abundances in the earth's crust. Carbonate, Fe–Mn oxide and organic fractions of REEs in sediments account for 2.4–6.9%, 5.2–11.1%, and 7.3–14.0% of the total contents respectively. They are similar to those in the suspended matter. This shows that carbonates, Fe–Mn oxides and organic matter play important roles during the particle-water interaction processes. By normalization to shales, the 3 forms of REEs follow convex shapes according to atomic number with middle REE (Sm, Eu, and Tb) enrichment, while light REE and heavy REE are depleted.  相似文献   

15.
Recent studies have suggested that rivers may present an isotopically light Fe source to the oceans. Since the input of dissolved iron from river water is generally controlled by flocculation processes that occur during estuarine mixing, it is important to investigate potential fractionation of Fe-isotopes during this process. In this study, we investigate the influence of the flocculation of Fe-rich colloids on the iron isotope composition of pristine estuarine waters and suspended particles. The samples were collected along a salinity gradient from the fresh water to the ocean in the North River estuary (MA, USA). Estuarine samples were filtered at 0.22 μm and the iron isotope composition of the two fractions (dissolved and particles) were analyzed using high-resolution MC-ICP-MS after chemical purification. Dissolved iron results show positive δ56Fe values (with an average of 0.43 ± 0.04‰) relative to the IRMM-14 standard and do not display any relationships with salinity or with percentage of colloid flocculation. The iron isotopic composition of the particles suspended in fresh water is characterized by more negative δ56Fe values than for dissolved Fe and correlate with the percentage of Fe flocculation. Particulate δ56Fe values vary from −0.09‰ at no flocculation to ∼0.1‰ at the flocculation maximum, which reflect mixing effects between river-borne particles, lithogenic particles derived from coastal seawaters and newly precipitated colloids. Since the process of flocculation produces minimal Fe-isotope fractionation in the dissolved Fe pool, we suggest that the pristine iron isotope composition of fresh water is preserved during estuarine mixing and that the value of the global riverine source into the ocean can be identified from the fresh water values. However, this study also suggests that δ56Fe composition of rivers can also be characterized by more positive δ56Fe values (up to 0.3‰) relative to the crust than previously reported. In order to improve our current understanding of the oceanic iron isotope cycling, further work is now required to determine the processes controlling the fractionation of Fe-isotopes during continental run-off.  相似文献   

16.
Few studies have examined the dynamics of sediments and suspended organic matter and their export from headwater basins in the Andes Mountains to the Amazon River, despite the fact that the Andes are the primary source of sediments to the lower Amazon basin. We measured river discharge as well as the concentration, δ15N, δ13C, %N, and %OC of coarse and fine suspended sediments (CSS and FSS) in the Chorobamba River, located in the central Andean Amazon of Peru. Samples were taken at least weekly over an entire year (July 2004-July 2005), with additional sampling during storms. Concentrations of particulate organic matter (POM) were generally low in the study river, with concentrations increasing by up to several orders of magnitude during episodic rain events. Because both overall flow volumes and POM concentrations increased under stormflow conditions, the export of POM was enhanced multiplicatively during these events. We estimated that a minimum of 80% of annual suspended sediment transfer occurred during only about 10 days of the year, also accounting for 74% of particulate organic carbon and 64% of particulate organic nitrogen transport. Significant differences occurred between seasons (wet and dry) for δ13C of coarse and fine POM in the Chorobamba River, reflecting seasonal changes in organic matter sources. The time series data indicate that this Andean river exports approximately equal amounts of fine and coarse POM to the lower Amazon. The observation that the vast majority of sediments and associated OM exported from Andean rivers is mobilized during short, infrequent storm events and landslides has important implications for our understanding of Amazon geochemistry, especially in the face of incipient global change.  相似文献   

17.
The concentrations of total suspended sediments (TSS), dissolved organic carbon (DOC) and particulate organic carbon (POC) were measured in water samples taken monthly in the Apure, Caura and Orinoco rivers during a hydrological cycle (between Sept. 2007 and Aug. 2008). The DOC concentration values ranged between 1.5 and 6.8 mgC l−1 in the Apure River; 2.07 and 4.9 mgC l−1 in the Caura River and 1.66 and 5.35 mgC l−1 in the Orinoco River. The mean concentration of DOC was 3.9 mgC l−1 in the Apure River, 3.24 mgC l−1 in the Caura River and 2.92 mgC l−1 in the Orinoco River at Puerto Ordaz. The three rivers showed a similar temporal pattern in the concentrations of DOC, with higher DOC values during the increasing branch of the hydrograph due to wash-out processes of the organic material stored in soils. The mean concentration values of POC were 1.33 mgC l−1; 0.77 mgC l−1 and 0.91 mgC l−1 in the Apure, Caura and Orinoco rivers, respectively. The inverse relationship found between the percentage in weight of the POC and the concentrations of TSS in the three rivers fits a logarithmic model, as it has been previously reported for other worldwide rivers. The POC concentrations in the Orinoco River showed a positive relationship with the TSS, suggesting that the POC in the Orinoco is the result of terrestrially organic matter. Although the fluxes of organic carbon (OC) in the three studied rivers are dependent on the values of water discharge, the fluxes of DOC during the increasing branch of the hydrograph are higher than those found during the decreasing stage, due to the yield of organic material accumulated in soils during the preceding dry season. The mean annual flux of total organic carbon (TOC) of the Orinoco River at Puerto Ordaz was about 4.27 × 106 TonC yr−1. Of this, 3.28 × 106 TonC yr−1 (77%) represents the flux of DOC and about 0.99 TonC yr−1 (23%) represents the flux of POC. The mean annual input of TOC from the Apure River to the Orinoco River was about 4.92 × 105 TonC yr−1 (11.5%), while the contribution of TOC from the Caura River to the Orinoco River was estimated at 3.05 × 105 TonC yr−1 (7.1%).The values of annual transport of TOC calculated for the Apure, Caura and Orinoco rivers were lower than those reported twenty years ago. This could be related to interannual variations of precipitation in the Orinoco Basin, due to runoff variations can have a strong effect on the fluxes of OC from land to rivers.  相似文献   

18.
The vertical variability in mineralogical, chemical and isotopic compositions observed in large river suspended sediments calls for a depth-integration of this variability to accurately determine riverine geochemical fluxes. In this paper, we present a method to determine depth-integrated chemical particulate fluxes of large rivers, based on river sampling along depth-profiles, and applied to the Amazon Basin lowland tributaries. The suspended particulate matter (SPM) concentration data from depth-profiles is modeled for a number of individual grain size fractions using the Rouse model, which allows to predict the grain size distribution of suspended sediment throughout the whole river cross-section. Then, using (1) the relationship between grain size distribution and the Al/Si ratio (2) relationships between the Al/Si ratio and the chemical concentrations, the chemical composition of river sediment is predicted throughout the river cross-section, and integrated to yield the depth-integrated chemical particulate flux for a number of chemical elements (e.g. Si, Al, Fe, Na, REEs, …). For elements such as Al, Fe, REEs, Th, the depth-integrated flux is around twice as high as the one calculated from river surface sample characteristics. For Na and Si, the depth-integrated flux is three times higher than the “surface” estimate, due to the enrichment of albite and quartz at the bottom of the river. Depth-integrated 87Sr/86Sr composition of suspended sediment, also predictable using this method, differs by more than 10−3 from the surface sample composition.Finally, potential implications of depth-integrated estimates of Amazon sediment chemistry are explored. Depth-integration of particulate 87Sr/86Sr isotopic ratios is necessary for a reliable use of Sr isotopes as a provenance tracer. The concept of steady-state weathering of a large river basin is revisited using depth-integrated sediment composition. This analysis shows that, in the Amazon Basin river, the previously observed discrepancy between (1) weathering intensities of channel surface sediment and (2) silicate-derived dissolved fluxes is only slightly accounted for by the vertical variability of suspended sediment weathering intensities. This observation confirms that most large rivers basins are not eroding at steady-state.  相似文献   

19.
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   

20.
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