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1.
Transport and fate of organic carbon by the fluvial system play a significant role in the global biogeochemical cycle of carbon. Previous studies show that the transportation of modern organic carbon from the Himalayan River system accounts for 10–20% of the total global flux to the oceans. Till date, no study has been published which dealt with the transport of organic carbon in the headwaters of the Ganga River. The Alaknanda River is a headwater stream of the Ganga, which flows in the Western Himalayas of India. Water and freshly deposited channel sediment samples were collected during the months of March 2014 and August 2014 and analysed for dissolved organic carbon (DOC), particulate organic carbon (POC) and channel organic carbon (COC). The observed variability of organic carbon concentration was correlated with factors such as discharge, physiography and suspended sediment concentration (SSC). The results show that seasonal erosivity in the basin influences its DOC concentration and physiography, thus acting as a key parameter which controls transportation, oxidation and residence time of the organic matter. The allochthonous input of sediments from the erosional activities is the major source of organic carbon. At Devprayag, Alaknanda contributes 66% of the total DOC flux carried by the Ganga River. The comparison with the previously published values indicate that due to differences in physiography and chemical weathering rate, the Ganga River transports organic carbon mainly as a dissolved load in its upstream and predominantly as POC down the Himalayan foothills. 相似文献
2.
Joel C. Hoffman Gregory S. Peterson Anne M. Cotter John R. Kelly 《Estuaries and Coasts》2010,33(6):1391-1405
We characterized stable isotope mixing along a river-Great Lake transition zone in the St. Louis River, an important fish
nursery in western Lake Superior, and used it to identify food web linkages supporting young fish production. We observed
a broad, spatial pattern in the carbon stable isotope ratio (δ13C); downriver enrichment in particulate organic carbon and aquatic vegetation δ13C, as well as pelagic, benthic and littoral invertebrate δ13C, reflected isotope mixing along the river-lake transition zone. Fishes with similarly enriched δ13C were used to identify benthopelagic and littoral trophic pathways. River and Lake Superior organic matter (OM) sources contributed
to both pathways. Differences between the δ13C in fishes and invertebrate prey revealed that fish production was supported at multiple spatial scales. The result was that
the food web specific to any location along the transition zone incorporated multiple OM sources from across the watershed. 相似文献
3.
We summarize rates of metabolism and major sources and sinks of organic carbon in the 148-k long, tidally influenced, freshwater Hudson River. The river is strongly heterotrophic, with respiration exceeding gross primary production (GPP). The P:R ration averages 0.57 (defined as the ratio of GPP to total ecosystem respiration) if only the aquatic portion of the ecosystem is considered and 0.70 if the emergent marshes are also included. Gross primary production (GPP) by photoplankton averages approximately 300 g C m?2 yr?1 and is an order of magnitude greater than that by submersed macrophytes. However, the river is deep, well mixed, and turbid, and phytoplankton spend a majority of their time in the dark. As a result, respiration by living phytoplankton is extremely high and net primary production (NPP) by phytoplankton is estimated to be only some 6% of GPP. NPP by phytoplankton and submersed macrophytes are roughly equal (approximately 20 g C m?2 yr?1 each) when averaged over the river. Emergent marshes are quite productive, but probably less than 16 g C m?2 yr?1 enters the aquatic portion of the ecosystem from these marshes. Heterotrophic respiration and secondary production in the river are driven primarily by allochthonous inputs of organic matter from terrestrial sources. Rates of metabolism vary along the river, with depth being a critical controlling factor. The P:R ratio for the aquatic portion of the ecosystem varies from 1 in the mid-river to 0.2 in the deeper waters. NPP is actually negative in the downstream waters where average depths are greater since phytoplankton respiration exceeds GPP there; the positive rates of NPP occurring upriver support a downstream advection of phytoplankton to the deeper waters where this C is largely respired away by the algae themselves. This autotrophic respiration contributes significantly to oxygen depletion in the deeper waters of the Hudson. The tidally influenced freshwater Hudson largely fits the patterns predicted by the river continuum model for larger rivers. However, we suggest that the continuum model needs to more clearly distinguish between GPP and NPP and should include the importance of autotrophic respiration by phytoplankton that are advected along a river. The organic carbon budget for the tidally influenced freshwater Hudson is balanced to within a few percent. Respiration (54%) and downstream advection into the saline estuary (41%) are the major losses of organic carbon from the ecosystem. Allochthonous inputs from nonpoint sources on land (61%) and GPP by phytoplankton (28%) are the major sources to the system. Agricultural erosion is the major source of allochthonous inputs. Since agricultural land use increased dramatically in the last century, and has fallen in this century, the carbon cycle of the tidally influenced freshwater Hudson River has probably changed markedly over time. Before human disturbance, the Hudson was probably a less heterotrophic system and may even have been autotrophic, with gross primary production exceeding ecosystem respiration. 相似文献
4.
We quantified temporal and spatial variability in diets of 950 juvenile (age-0) striped bass in the Hudson River estuary.
We used canonical correspondence analysis to assess the roles of temporal and spatial habitat variability in juvenile diet
variation. We found that juvenile striped bass diets in the Hudson River were only modestly comparable to diets in other east
coast estuaries. Among-year differences (51.4%) and spatial differences (41.9%) were substantially associated with juvenile
striped bass diet. We found ontogeny (2.8%) and within-season variation (9.5%) to only weakly associate with diet variation.
Our results indicate that an understanding of the temporal and spatial variation within the Hudson River estuary is vital
in understanding variation in feeding by resident juvenile fish. 相似文献
5.
6.
Florian Einsiedl Norbert Hertkorn Moritz Frommberger Boris P. Koch 《Geochimica et cosmochimica acta》2007,71(22):5474-5482
The study of molecular transformation processes of dissolved organic carbon (DOC) in the environment significantly contributes to a better understanding of the global biogeochemical organic matter cycle. In an oxic karst groundwater system, in which the most powerful abiotic DOC degradative reactions, photodegradation and metal-mediated redox chemistry, are at best marginal contributors, a near complete turnover of fulvic acids (FAs) has been observed within decades (∼60 years). Depletion of oxygen for a very extensive range of aliphatic and aromatic carbon chemical environments has been confirmed as well as the formation of novel classes of compounds, suggesting a major contribution from biotic processes. From these results we infer that FAs must be perceived as a rather active participant in the global carbon cycle. Molecular-level alterations of such magnitude and rapidity on such short-time scales ought to be considered as widespread in the processing of “refractory” DOC in the environment. 相似文献
7.
River systems play an important role in the global carbon cycle. Rivers transport carbon to the ocean and also affect the carbon cycle in the coastal ocean. The flux from land to the ocean is thought to be a very important part of the land carbon budget. To investigate the effect of dam-building on dissolved organic carbon (DOC) in rivers, three reservoirs of different trophic states in the Wujiang basin, Guizhou Province, were sampled twice per month between May 2011 and May 2012. Temporal and spatial distributions of DOC in the reservoirs and their released waters were studied. It was found that different factors controlled DOC in river water, reservoir water, and released water. DOC in the rivers tended to be affected by primary production. For reservoirs, the main controlling factors of DOC concentration varied by trophic state. For the mesotrophic Hongjiadu Reservoir, the effect of primary production on DOC concentration was obvious. For the eutrophic Dongfengdu Reservoir and the hypereutrophic Wujiangdu Reservoir, primary production was not significant and DOC came instead from soil and plant litter. 相似文献
8.
Dissolved rare earth elements in a seasonally snow-covered, alpine/subalpine watershed, Loch Vale, Colorado 总被引：1，自引：0，他引：1
Alan M. Shiller 《Geochimica et cosmochimica acta》2010,74(7):2040-49
Dissolved rare earth elements (REEs) were determined in a four-year time series at the outlet of Loch Vale. The Loch Vale watershed is a seasonally snow-covered alpine/subalpine basin in Rocky Mountain National Park, USA. The time series was mainly distinguished by an annual early spring peak in the concentrations of all REEs. REE concentrations at this time were as much as 8-fold greater than at other times of the year. This annual peak was coincident with an early spring peak in dissolved organic carbon (DOC) which results from flushing of soils at the beginning of spring snow melting. The REE/DOC peak occurs as discharge starts to increase from wintertime lows but well before the spring peak in discharge. Speciation considerations suggest complexation of the REEs by DOC. The Ce anomaly also increases (i.e., is less fractionated) during the spring flush indicating that the most reducing (or least oxidizing) REE sources in the system are comparatively more important at that time. Mn data and the La/Yb ratio also support this. The behavior of REEs in the Loch Vale system has additionally been compared with metal and DOC behavior in other systems. Hydrologic and climatic differences can be important especially with regard to timing and duration of the spring flush peak. Damping of hydrologic events in the lower floodplain of major rivers may also partially result in the differences observed between Loch Vale and the lower Mississippi River. However, comparison with the Amazon River system additionally suggests that seasonal flooding of wetlands may be an important regulator of REE concentrations. Chemical differences are also important for these systems. This includes pH and suspended matter concentrations which affect the balance between adsorption and complexation. Additionally, the relative complexing ability of DOC in different systems is a factor needing further consideration. 相似文献
9.
P. W. Lehman 《Estuaries and Coasts》2004,27(2):311-324
Significant coherence among time series of environmental and biological production variables suggested mechanistic pathways
through which climate contributed to the downward shift in estuarine production (biomass) in northern San Francisco Bay estuary,
1975–1993. Climate directly and indirectly affected physical processes in the estuary through precipitation and its subsequent
impact on streamflow and physical variables affected by streamflow. Climate also directly influenced air temperature and wind
velocity. The influence if climate was evaluated through a climate index based on sea level pressure. A shift in this climate
index in the early 1980s coincided with changes in many environmental variables including water transparency, water temperature,
wind velocity, and rainfall. These physical changes were accompanied by a decrease in diatom, total zooplankton, andNeomysis mercedis carbon at the base of the food web throughout the estuary. Box-Jenkins time series coherence analysis was used to quantify
associations among these physical, chemical, and biological time series for nine regions of the estuary. These associations
were used to develop a conceptual model of mechanistic pathways that directly linked food web carbon production to climate.
Strong coherence among diatom, zooplankton, andN. mercedis carbon time series suggested climate also had an indirect impact on food web production through trophic cascade. Differing
mechanistic pathways among the nine regions of the estuary suggested climate was an important contributor to the spatial variability
in total food web production and trophic structure. 相似文献
10.
The role of hydrology in annual organic carbon loads and terrestrial organic matter export from a midwestern agricultural watershed 总被引：1，自引：0，他引：1
Brent J. Dalzell Timothy R. Filley Jon M. Harbor 《Geochimica et cosmochimica acta》2007,71(6):1448-1462
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
11.
The relationship between nitrogen (N) and phytoplankton chlorophyll a (Chl) establishes a basis for understanding eutrophication in coastal marine ecosystems. A substantial literature exists
on cross-ecosystem analysis of this relationship, but there is little information on cross-scale patterns. A collection of
observational records in Bedford Basin (Canada) was used to construct the N–Chl relationship at four time scales: intra-day,
intra-annual, interannual, and interdecadal. Additionally, a dataset of contingent observations from 16 biogeochemical ocean
provinces was used to construct the N–Chl relationship at large spatial scale. In Bedford Basin, N statistically predicts
Chl at time scales that are short (intra-day, intra-annual) and long (interdecadal) but not intermediate (interannual). There
is an apparent stoichiometric regularity in the dependence of Chl on N that crosses time scales. Further, an apparent similitude
exists between the local pattern at long time scale and the global pattern at large space scale. 相似文献
12.
《Geochimica et cosmochimica acta》1999,63(3-4):427-448
Numerous studies of marine environments show that dissolved organic carbon (DOC) concentrations in sediments are typically tenfold higher than in the overlying water. Large concentration gradients near the sediment–water interface suggest that there may be a significant flux of organic carbon from sediments to the water column. Furthermore, accumulation of DOC in the porewater may influence the burial and preservation of organic matter by promoting geopolymerization and/or adsorption reactions. We measured DOC concentration profiles (for porewater collected by centrifugation and “sipping”) and benthic fluxes (with in situ and shipboard chambers) at two sites on the North Carolina continental slope to better understand the controls on porewater DOC concentrations and quantify sediment–water exchange rates. We also measured a suite of sediment properties (e.g., sediment accumulation and bioturbation rates, organic carbon content, and mineral surface area) that allow us to examine the relationship between porewater DOC concentrations and organic carbon preservation. Sediment depth-distributions of DOC from a downslope transect (300–1000 m water depth) follow a trend consistent with other porewater constituents (ΣCO2 and SO42−) and a tracer of modern, fine-grained sediment (fallout Pu), suggesting that DOC levels are regulated by organic matter remineralization. However, remineralization rates appear to be relatively uniform across the sediment transect. A simple diagenetic model illustrates that variations in DOC profiles at this site may be due to differences in the depth of the active remineralization zone, which in turn is largely controlled by the intensity of bioturbation. Comparison of porewater DOC concentrations, organic carbon burial efficiency, and organic matter sorption suggest that DOC levels are not a major factor in promoting organic matter preservation or loading on grain surfaces. The DOC benthic fluxes are difficult to detect, but suggest that only 2% of the dissolved organic carbon escapes remineralization in the sediments by transport across the sediment-water interface. 相似文献
13.
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
14.
Junyu Zou 《Journal of Earth System Science》2017,126(1):6
Carbon (POC, DOC) and carbon isotopes (δ13C) within two headwater tributaries to the Xi River Basin, southwest China were analyzed to document the geochemical characteristics and sources of organic carbon (C) within basins characterized by a monsoonal climate and karst landforms. δ13 C POC value and C/N ratio data indicate that suspended soil organic carbon (SOC) was an important source of POC in both the Nanpan and Beipan rivers (i.e., the studied tributaries). However, differences in C sources exist between the Nanpan and Beipan River Basins. Higher terrestrial plants supplied a portion of the POC within the Beipan River. In contrast, the Nanpan River was characterized by an inverse correlation between POC and DOC, and a positive relationship between the δ13C values. These trends indicate that DOC within the Nanpan River was partly derived from the degradation of soil C within the water column. In addition, the interception of C by hydrological projects (e.g., dams) positioned along the Nanpan River led to higher DOC/POC ratios. In contrast, within the Beipan River δ13C DOC values range from ?20 to ?25.2 ‰ and are consistent with ratios associated with soil C, suggesting that leaching of C from catchment soil was the dominant source of DOC. Organic C in tributaries to the Beipan River may also have been derived from intense upland soil erosion, a process that resulted in the lowest DOC/POC ratios. The collected data indicate that land-use changes have potentially influenced regional- to local-scale organic C budgets within subtropical basins subjected to karstification. 相似文献
15.
Relationships between DOC concentration,molecular size and fluorescence properties of DOM in a stream 总被引：1，自引：0，他引：1
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
16.
A. S. Prokushkin O. S. Pokrovsky M. A. Korets A. V. Rubtsov S. V. Titov I. V. Tokareva R. A. Kolosov R. M. W. Amon 《Doklady Earth Sciences》2018,480(2):763-766
The spatial and temporal variations in concentrations of dissolved organic carbon in the Yenisei River and its major tributaries are analyzed. The results obtained suggest that the maximal contribution to the flows of dissolved organic carbon in the Yenisei River is made by cryohydromorphic forest landscapes of the Central Siberian Plateau. 相似文献
17.
The flood zone of the Ob River, the largest (in watershed area) river of the Arctic Ocean basin, is tens of km wide and, after the Amazon's Varzea, is the world's second largest flooding territory. To better understand the biogeochemistry of the Ob River and adjacent surface waters, we studied, in May and July 2014, the dissolved and colloidal organic carbon and trace metals in small rivers, lakes, and flooded water bodies connected and disconnected with the mainstream as well as the Ob River itself. All major and trace elements were distributed among two major categories depending on their pattern of dependence on the dissolved organic carbon (DOC) concentration. Dissolved inorganic carbon (DIC), Na, Mg, Ca, sulfate, Sr, Mo, Sb and U exhibited a general decrease in concentration with the increase of the [DOC]. The lowest concentration of these elements was observed in DOC-rich humic, acidic (4.9 ≤ pH ≤ 6.1) upland lakes fed by surrounding bogs. These elements marked the influence of underground feeding in July during summer baseflow, which was most visible in flood lakes in the Ob riparian zone and the Ob River itself. In May, the flood lakes were statistically similar to the Ob River. The elevated concentration of DOC (up to 60 mg/L) in the upland lakes was not correlated with groundwater-related elements, suggesting a lack of significant groundwater feeding in these lakes. In contrast, insoluble, usually low mobile elements (Al, Fe, other trivalent hydrolysates, Ti, Zr, Hf) and some metals (Cr, Zn, Ni, Pb) demonstrated a steady increase in concentration with increasing DOC, with the lowest values observed in the Ob River and the highest values observed in small tributaries and organic-rich upland lakes in July. It follows that these elements are limited by their main carriers – organic and organo-ferric colloids, rather than by the availability of the source, peat and mineral soil or plant litter. While for the majority of non-colloidal, groundwater-fed elements with high mobility (DIC, Na, Mg, Ca, K, Sr…) the small tributaries can be used as representatives of the Ob main stream, this is not the case for low mobility “insoluble” elements, such as Fe, Al, trivalent and tetravalent hydrolysates, and metal micronutrients (Cu, Zn, and Mn). The low soluble elements and divalent metals exhibited a much lower concentration in the river mainstream compared to that in the flood lakes, upland lakes and small rivers. This difference is significantly more pronounced in the baseflow in July compared to the spring flood in May. Presumably, autochthonous processes, such as the photo-oxidation and bio-oxidation of organo-ferric colloids and phytoplankton uptake are capable decreasing the concentration of these elements in the river mainstream. 相似文献
18.
Landscape scale controls on the vascular plant component of dissolved organic carbon across a freshwater delta 总被引：1，自引：0，他引：1
Robert S. Eckard Brian A. Bergamaschi Carol Kendall 《Geochimica et cosmochimica acta》2007,71(24):5968-5984
Lignin phenol concentrations and compositions were determined on dissolved organic carbon (DOC) extracts (XAD resins) within the Sacramento-San Joaquin River Delta (the Delta), the tidal freshwater portion of the San Francisco Bay Estuary, located in central California, USA. Fourteen stations were sampled, including the following habitats and land-use types: wetland, riverine, channelized waterway, open water, and island drains. Stations were sampled approximately seasonally from December, 1999 through May, 2001. DOC concentrations ranged from 1.3 mg L−1 within the Sacramento River to 39.9 mg L−1 at the outfall from an island drain (median 3.0 mg L−1), while lignin concentrations ranged from 3.0 μg L−1 within the Sacramento River to 111 μg L−1 at the outfall from an island drain (median 11.6 μg L−1). Both DOC and lignin concentrations varied significantly among habitat/land-use types and among sampling stations. Carbon-normalized lignin yields ranged from 0.07 mg (100 mg OC)−1 at an island drain to 0.84 mg (100 mg OC)−1 for a wetland (median 0.36 mg (100 mg OC)−1), and also varied significantly among habitat/land-use types. A simple mass balance model indicated that the Delta acted as a source of lignin during late autumn through spring (10-83% increase) and a sink for lignin during summer and autumn (13-39% decrease). Endmember mixing models using S:V and C:V signatures of landscape scale features indicated strong temporal variation in sources of DOC export from the Delta, with riverine source signatures responsible for 50% of DOC in summer and winter, wetland signatures responsible for 40% of DOC in summer, winter, and late autumn, and island drains responsible for 40% of exported DOC in late autumn. A significant negative correlation was observed between carbon-normalized lignin yields and DOC bioavailability in two of the 14 sampling stations. This study is, to our knowledge, the first to describe organic vascular plant DOC sources at the level of localized landscape features, and is also the first to indicate a significant negative correlation between lignin and DOC bioavailability within environmental samples. Based upon observed trends: (1) Delta features exhibit significant spatial variability in organic chemical composition, and (2) localized Delta features appear to exert strong controls on terrigenous DOC as it passes through the Delta and is exported into the Pacific Ocean. 相似文献
19.
Temporal variability in sources of dissolved organic carbon in the lower Mississippi river 总被引：2，自引：0，他引：2
Thomas S. Bianchi Timothy Filley Patrick G. Hatcher 《Geochimica et cosmochimica acta》2004,68(5):959-967
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.
Jimena Samper-Villarreal Peter J. Mumby Megan I. Saunders Chris Roelfsema Catherine E. Lovelock 《Estuaries and Coasts》2018,41(6):1732-1743
Blue carbon initiatives require accurate monitoring of carbon stocks. We examined sources of variability in seagrass organic carbon (Corg) stocks, contrasting spatial with short temporal scales. Seagrass morphology and sediment Corg stocks were measured from biomass and shallow sediment cores collected in Moreton Bay, Australia. Samples were collected between 2012 and 2013, from a total of 77 sites that spanned a gradient of water turbidity. Environmental measures of water quality between 2000 and 2013 revealed strong seasonal fluctuations from summer to winter, yet seagrass biomass exhibited no temporal variation. There was no temporal variability in Corg stocks, other than below ground biomass stocks were slightly higher in June 2013. Seagrass locations were grouped into riverine, coastal, and seagrass loss locations and short temporal variability of Corg stocks was analysed within these categories to provide clearer insights into temporal patterns. Above ground Corg stocks were similar between coastal and riverine meadows. Below ground Corg stocks were highest in coastal meadows, followed by riverine meadows. Sediment Corg stocks within riverine meadows were much higher than at coastal meadows and areas of seagrass loss, with no difference in sediment Corg stocks between these last two categories. Riverine seagrass meadows, of higher turbidity, had greater total Corg stocks than meadows in offshore areas irrespective of time. We suggest that Corg stock assessment should prioritise sampling over spatial gradients, but repeated monitoring over short time scales is less likely to be warranted if environmental conditions remain stable. 相似文献