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1.
One of the most important challenges in global climate change research is balancing the carbon budget within the global carbon cycle. Carbon burial in sediments at the land–ocean interface has been difficult to quantify and model because it represents non-steady-state boundary conditions that are also affected by human activities. In this study, we document carbon burial rates in the Yangtze River (1.6–4.9 × 1012 gC year?1) and Hudson River (1.8–3.6 × 1010 gC year?1) estuaries and integrate our results with carbon burial rates determined by others in the world’s 25 largest river-estuarine systems (6–11 × 1013 gC year?1). Our results indicate that carbon burial in estuaries, bays, coves, lagoons, mud flats, marshes, mangroves, and other highly productive or protected low-energy areas at the land–ocean interface along the entirety of the world’s coastlines may serve as an unrecognized sink within the global carbon budget. 相似文献
2.
The paper presents the molybdenum isotope data, along with the trace element content, to investigate the geochemical behavior
of authigenic Mo during long-term burial in sediments in continental margin settings of the Yangtze block, as well as their
indication to the burial of original organic carbon. The burial rate of original organic carbon was estimated on the basis
of the amount of sedimentary sulfur (TS content), whilst the carbon loss by aerobic degradation was estimated according to
calculated Mn contents. On these points, the original organic carbon flux was calculated, exhibiting a large range of variation
(0.17–0.67 mmol/m2/day). The strong correlation between sedimentary Mo isotope values and organic carbon burial rates previously proposed on
the basis of the investigations on modern ocean sediments, was also used here to estimate the organic carbon burial rate.
The data gained through this model showed that organic carbon burial rates have large variations, ranging from 0.43–2.87 mmol/m2/day. Although the two sets of data gained through different geochemical records in the Yangtze block show a deviation of
one order of magnitude, they do display a strong correlation. It is thus tempting to speculate that the Mo isotope signature
of sediments may serve as a tracer for the accumulation rate of original organic carbon in the continental margin sediments.
__________
Translated from Earth Science—Journal of China University of Geosciences, 2007, 32(6) [译自: 地球科学—中国地质大学学报] 相似文献
3.
Ana Carolina Ruiz-Fernández José Luis Marrugo-Negrete Roberth Paternina-Uribe Libia Hascibe Pérez-Bernal 《Estuaries and Coasts》2011,34(6):1117-1128
With the aim of evaluating temporal changes in sedimentation and organic carbon (Corg) supplied over the last ~100 years, a sediment core was collected at Soledad Lagoon, a costal ecosystem surrounded by mangroves,
located in the Cispatá Estuary (Caribbean coast of Colombia). The core sediments were characterized by low concentrations
of calcium carbonate (0.2–2.9%), organic matter (3–8%), total nitrogen (0.11–0.38%), and total phosphorus (0.19–0.65 mg g−1). Fe and Al concentrations ranged from 4% to 5%, and Mn from 356 to 1,047 μg g−1. The 210Pb-derived sediment and mass accumulation rates were 1.54 ± 0.18 mm year−1 and 0.08 ± 0.01 g cm−2 year−1, respectively. The sediment core did not provide evidence of human impact, such as enhancement of primary production or nutrient
enrichment, which may result from recent land uses changes or climate change. The Corg fluxes estimated for Soledad Lagoon core lay in the higher side of carbon fluxes to coastal ecosystems (314–409 g m−2 year−1) and the relatively high Corg preservation observed (~45%) indicate that these lagoon sediments has been a net and efficient sink of Corg during the last century, which corroborate the importance of mangrove areas as important sites for carbon burial and therefore,
long-term sequestration of Corg. 相似文献
4.
Release of CO2 from surface ocean water owing to precipitation of CaCO3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface
water to sedimentary storage was studied by means of a quotient θ = (CO2 flux to the atmosphere)/(CaCO3 precipitated). θ depends not only on water temperature and atmospheric CO2 concentration but also on the CaCO3 and organic carbon masses formed. In CO2 generation by CaCO3 precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric
CO2 concentration (195–375 ppmv), and increasing CaCO3 precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic
carbon counteracts the CO2 production by carbonate precipitation and it results in lower CO2 emissions from the surface layer. When atmospheric CO2 increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO2 transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric
CO2. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon
from land, the calculated CO2 flux to the atmosphere is a function of the CaCO3 and Corg net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO2 flux near the Last Glacial Maximum is 17 to 7×1012 mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time
it is 38–42×1012 mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic
emissions of CO2 to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total
alkalinity owing to the CaCO3 storage and consequent emission of CO2. These results are in agreement with the conclusions of a number of other investigators. As the CO2 uptake in mineral weathering is a major flux in the global carbon cycle, the CO2 weathering pathway that originates in the CO2 produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large
imbalances of the atmosphere and land organic reservoir at 102–104-year time scales. 相似文献
5.
In the past several decades, the techniques used to discern the different sedimentary fractions of P have been refined. This
has allowed for a better understanding of P burial of the different P fractions and diagenetic reactions and, ultimately,
the constraining of P residence time in the oceans. P sequential extraction was performed on eight sediment cores (between
16 and 24 cm deep) collected along a salinity gradient from the Ojo de Liebre Lagoon and the salt evaporation saltern of Guerrero
Negro, Baja California Sur, Mexico in order to determine, under purely diagenetic conditions (in the absence of anthropogenic
activities and biogenic sediment reworking), the fractionation and flux of P to the sediments. The majority of P was found
in the authigenic fraction (37 ± 5.4% to 53 ± 8.9%), with P associated to organic matter comprising the overall smallest percentage
(0.25 ± 0.43% to 21 ± 6.0%) relative to total P. The average flux of total P to the sediments for all the sites was found
to be (451 ± 127) × 10−4 mol m−2 year−1, up to several orders of magnitude greater than those found in other studies. It is concluded that P is most likely transformed
from P associated to organic matter to the authigenic mineral phase and that P was retained in the sediments in its mineral
form rather than in reactive forms. This particular study area has the ability to retain large quantities of P in the sediments. 相似文献
6.
The eastern Alaska Beaufort Sea coast is characterized by numerous shallow (2–5 m) estuarine lagoons, fed by streams and small
rivers that drain northward from the Brooks Range through the arctic coastal plain, and bounded seaward by barrier islands
and shoals. Millions of birds from six continents nest and forage during the summer period in this region using the river
deltas, lagoons, and shoreline along with several species of anadromous and marine fish. We examined biogeochemical processes
linking the benthic community to the overall food web structure of these poorly studied but pristine estuaries, which are
largely covered by 1.8 m of ice for 10 months annually. In summer, these lagoons are relatively warm with brackish salinities
(5–10°C, S = 10–25) compared to more open coastal waters (0–5°C, S > 27). The stable isotopic composition of organic materials in sediments (i.e., benthic particulate organic matter) and water
column suspended particulate organic matter from both streams and lagoons are largely indistinguishable and reflect strong
terrestrial contributions, based upon δ13C and δ15N values (−25.6‰ to −27.4‰ and 1.4‰ to 3.3‰, respectively). By comparison, shifts toward more heavy isotope-enriched organic
materials reflecting marine influence are observed on the adjacent coastal shelf (−24.8‰ to −25.4‰ and 3.4‰ to 5.3‰, respectively).
The isotopic composition of lagoon fauna is consistent with a food web dominated by omnivorous detritovores strongly dependent
on microbial processing of terrestrial sources of carbon. Biomagnification of 15N in benthic organisms indicate that the benthic food web in lagoons support up to four trophic levels, with carnivorous gastropod
predators and benthic fishes (δ15N values up to 14.4‰) at the apex. 相似文献
7.
The quantification of carbon burial in lake sediments, and carbon fluxes derived from different origins are crucial to understand modern lacustrine carbon budgets, and to assess the role of lakes in the global carbon cycle. In this study, we estimated carbon burial in the sediment of Lake Qinghai, the largest inland lake in China, and the carbon fluxes derived from different origins. We find that: (1) The organic carbon burial rate in lake sediment is approximately 7.23 g m−2 a−1, which is comparable to rates documented in many large lakes worldwide. We determined that the flux of riverine particulate organic carbon (POC) is approximately 10 times higher than that of dissolved organic carbon (DOC). Organic matter in lake sediments is primarily derived from POC in lake water, of which approximately 80% is of terrestrial origin. (2) The inorganic carbon burial rate in lake sediment is slightly higher than that of organic carbon. The flux of riverine dissolved inorganic carbon (DIC) is approximately 20 times that of DOC, and more than 70% of the riverine DIC is drawn directly and/or indirectly from atmospheric CO2. (3) Both DIC and DOC are concentrated in lake water, suggesting that the lake serves as a sink for both organic and inorganic carbon over long term timescales. (4) Our analysis suggests that the carbon burial rates in Lake Qinghai would be much higher in warmer climatic periods than in cold ones, implying a growing role in the global carbon cycle under a continued global warming scenario. 相似文献
8.
By combining the carbon cycle model with the records of carbonate and organic (kerogen) carbon isotope, this paper presents
the calculation of the fraction of organic carbon burial (f
org) of beds 23–40 at the global boundary stratotype section and point (GSSP) of the Permian-Triassic boundary at Meishan, Zhejiang
Province. The resulting calculation produces two episodes of f
org maxima observed to occur at beds 23–24 and 27–29, which respectively corresponds to the two episodic anoxic events indicated
by the flourish of green sulfur bacteria. Two episodic f
org minima occurred at beds 25–26 and 32–34, generally coincident with the flourish of cyanobacteria (bed 26 and upper part of
beds 29 to 34) as shown by the high value of 2-melthyhopnoanes. It appears that the f
org is related to the redox conditions, with greater f
org values observed under the reductive condition. The relationship between f
org and the total organic carbon (TOC) content was complex. The f
org value was low at some beds with a high TOC content (such as bed 26), while high observed at some beds with a low TOC content
(e.g. bed 27). This association infers the important contribution of primary productivity to the TOC content. The original
organic burial could be thus calculated through the configuration of the function of the primary productivity and f
org, which can be used to correct the residual TOC measured today. This investigation indicates that compiling the organic-inorganic
carbon isotopes with the carbon cycle model favors to understand the fraction of organic carbon burial, providing information
for the reconstruction of the coupling among biota, environments and organic burial.
Journal of China University of Geosciences, 2007, 32(6): 767–773 [译自: 地球科学—中国地质大学学报] 相似文献
9.
河流系统是连接陆地和海洋的纽带,在全球碳循环中起着重要的作用。河流中的颗粒有机碳(POC)主要由来源于土壤和植被的生物有机碳和来源于岩石的化石有机碳组成,POC的侵蚀、搬运、氧化和埋藏对不同时间尺度的碳循环有着重要的意义。本研究统计了我国31条主要河流(包括台湾12条)的POC含量、碳同位素和悬浮物通量等数据,获得生物POC和化石POC的年通量,探讨了我国河流POC来源和通量的控制因素。结果表明,这些河流的POC的来源和通量表现出明显的差异:黄河和长江侵蚀大量的年老生物POC,而台湾河流主要为化石POC;我国河流POC来源与通量主要受控于物理侵蚀、气候、地质地貌和人类活动等因素的影响。这些河流的流域面积占我国国土面积的47%,近10年其生物POC和化石POC的总年通量分别为4.25±0.78Mt C/a和2.04±0.22Mt C/a,各占世界河流通量的2.7+1.3/-0.9%和4.7+6.6/-2.8%,表现出对全球海洋有机碳的一定贡献。过去几十年,我国河流输沙量显著减少,改变了河流有机碳氧化和水库埋藏过程及通量,其过程和通量的进一步监测和研究对理解有机碳侵蚀、输运、氧化和埋藏及其在全球碳循环中的作用至关重要。
相似文献10.
Hydrogeologic data of 455 water wells comprising geologic logs, water qualities, and aquifer test results are analyzed to
determine hydrogeological characteristics, water quality, and sustainable yield of the groundwater resources of Cheju volcanic
island. The groundwater of the island occurs in unconsolidated pyroclastic deposits and clinkers interbedded in highly jointed
basaltic and andesitic rocks as high-level, basal, and parabasal groundwater under unconfined conditions. The total storage
of groundwater is estimated at about 44 billion m3. The average transmissivity and specific yield of the aquifer are at about 0.34 m2 s–1(29300 m2 day–1) and 0.12, respectively. The average annual precipitation is about 3.39 billion m3, of which 1.49 billion m3– equivalent to 44.0% of the total annual precipitation – is recharged into aquifers, with 0.638 billion m3 year–1 of runoff and 1.26 billion m3 year–1 of evapotranspiration. Based on a groundwater budget analysis, the sustainable yield is estimated at about 0.62 billion m3 year–1, equivalent to 41.6% of annual recharge. A low-permeability marine sedimentary formation (Sehwari formation), composed of
loosely cemented sandy silt, was recently found to be situated at 120±68 m below mean sea level. If the said marine sediment
is distributed as a basal formation of the freshwater zone of the island, most of its groundwater will be of parabasal type.
So the marine sediment is one of the most important hydrogeological boundaries and groundwater occurrences in the area.
Received: 16 January 1997 / Accepted: 16 June 1997 相似文献
11.
Analysis of 3-m sediment cores revealed that profiles of carbon (C), sulfur (S), and iron (Fe) varied with relative distance from marine and terrestrial sediment sources in Tomales Bay California. Despite relatively high sedimentation rates throughout the bay (historically 3–30 mm yr−1), sulfate reduction of deposited organic matter led to free-sulfide accumulation in sediments only at the location farthest from terrestrial runoff, the source of reactive iron. Acid-volatile sulfide concentrations in all sediments (<10 μmol g−1) were low relative to concentrations of chromiumreducible sulfide (up to 400 μmol g−1 farthest from the reactive iron source). A calculated index of iron availability, used to describe sediment resistance to build-up of free sulfide, was lowest at this location. Recent, upward shifts in reactive Fe concentration and in the relative contribution of terrestrial orgnic carbon (measured as a shift in δ13C of bulk sediment organic matter) in all cores indicated that erosion and transport of sediments from the watershed surrounding Tomales Bay increased after European settlement in the 1850s. 相似文献
12.
C. Christiansen F. Gertz M. J. C. Laima L. C. Lund-Hansen T. Vang C. Jürgensen 《Environmental Geology》1997,29(1-2):66-77
The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of
P. This is only few percent of the supply from adjacent marine areas, as the yearly transport through the study area is 218 000
tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m–2 yr–1) and 477 ton of P (on average 0.9 g m–2 yr–1). Shallow-water parts of the study area have no net deposition because of frequent (>35% of the year) resuspension. Resuspension
frequency in deep water is <1% of the year. Resuspension rates, as averages for the study area, are 10–17 times higher than
net deposition rates. Because of resuspension, shallow-water sediments are coarse lag deposits with small amounts of organic
matter (1.1%) and nutrients (0.04% N and 0.02% P). Deep-water sediments, in contrast, are fine grained with high levels of
organic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive
sediment water fluxes of nutrients, oxygen consumption, and penetration into the sediment. Fluxes of dissolved reactive phosphate
from sediment to water after resuspension were negative in organic-rich sediments (13.2% organic matter) with low porosity
(56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Fluxes of inorganic
N after resuspension were reduced to 70% and 0–20% in relation to the rates before resuspension, respectively.
Received: 10 July 1995 · Accepted: 19 January 1996 相似文献
13.
N. Ramaiah V. V. S. S. Sarma Mangesh Gauns M. Dileep Kumar M. Madhupratap 《Journal of Earth System Science》2000,109(4):443-451
Bacterial abundance and production, numbers, sizes and concentrations of transparent exopolymer particles (TEP) and total
organic carbon (TOC) were measured during the 1996 summer monsoon to understand the relationship between TEP, the most labile
particulate organic carbon, and bacteria. While high regional variability in the vertical distribution of TOC was discernible,
TEP concentrations were high in surface waters at 18–20°N along 64°E with concentrations well over 25 mg alginic acid equivalents
I−1 due to upwelling induced productivity. Their concentrations decreased with depth and were lower between 200 and 500 m. Bacterial
concentrations were up to 1.99 × 108 I–1 in the surface waters and decreased by an order of magnitude or more at depths below 500 m. A better relationship has been
found between bacterial abundance and concentrations of TEP than between bacteria and TOC, indicating that bacterial metabolism
is fueled by availability of TEP in the Arabian Sea. Assuming a carbon assimilation of 33%, bacterial carbon demand (BCD)
is estimated to be 1.017 to 4.035 g C m–2 d–1 in the surface waters. The observed TEP concentrations appear to be sufficient in meeting the surface and subsurface BCD
in the northern Arabian Sea. 相似文献
14.
David R. Griffith William R. Martin Timothy I. Eglinton 《Geochimica et cosmochimica acta》2010,74(23):6788-6800
Long-term carbon cycling and climate change are strongly dependent on organic carbon (OC) burial in marine sediments. Radiocarbon (14C) has been widely used to constrain the sources, sinks, and processing of sedimentary OC. To elucidate the dominant controls on the radiocarbon content of total organic carbon (14CTOC) accumulating in surface sediments we construct a box model that predicts 14CTOC in the sediment mixed layer (measured as fraction modern, Fm). Our model defines three distinct OC pools (“degradable,” “semi-labile,” and “refractory”) and assumes that 14CTOC flux to sediments is exclusively derived from surface ocean primary productivity, and hence follows a “generic” surface ocean dissolved inorganic carbon (DIC) bomb curve. Model predictions are compared to a set of 75 surface sediment samples, which span a wide geographic range and reflect diverse water column and depositional conditions, and for which sedimentation rate and mixed-layer depth are well characterized. Our model overestimates the Fm value for a majority (65%) of these sites, especially at shallow water depths and for sites characterized by depleted δ13CTOC values. The model is most sensitive to sedimentation rate and mixed-layer depth. Therefore, slight changes to these parameters can lead to a match between modeled and measured Fm values at many sites. Yet, in some cases, we find that measured Fm values cannot be simulated without large and unrealistic changes to sedimentation rate and mixed-layer depth. These results point to sources of pre-aged OC to surface sediments and implicate soil-derived terrestrial OC, reworked marine OC, and/or anthropogenic carbon as important components of the organic matter present in surface sediments. This approach provides a valuable framework within which to explore controls on sedimentary organic matter composition and carbon burial over a range of spatial and temporal scales. 相似文献
15.
Recent data were summarized on the concentration and mass of inorganic and organic carbon in reservoirs of the Earth’s hydrosphere. We compared carbon masses and accumulation conditions in the surface hydrosphere and waters of the sedimentary shell and proportions between carbonate, dissolved, and suspended particulate organic carbon. It was shown that the total masses of carbon in the surface hydrosphere and in the waters of the sedimentary shell are approximately equal to 80 × 1018 g C at an organic to carbonate carbon ratio of 1 : 36 and 1 : 43, respectively. Three main forms of organic compounds in the ocean (living organisms, suspended particles, and dissolved species) occur in the proportion 1 : 13 : 250 and form the pyramid of masses 4 × 1015 g, 50 × 1015 g, and 1000 × 1015 g Corg. The descending sequence of the organic to carbonate carbon ratio in water, ocean (1 : 36) > glaciers (1 : 8) > lakes (1 : 2) > rivers (1 : 0.6) > wetlands (1 : 0.3), is in general consistent with an increase in the same direction in the mean concentrations of organic matter: 0.77 mg Corg/L in the ocean, 0.7 mg Corg/L in glaciers, 6–30 mg Corg/L in lakes, 15 mg Corg/L in rivers, and 75 mg Corg/L in wetlands. Both the mean concentrations and masses of dissolved organic matter in the pore waters of oceanic sediments and in the waters of the sedimentary shell are similar: 36–37 mg/L and 5 × 1018 and 5.6 × 1018 g, respectively. The mass of carbonate carbon in the pore waters of the ocean, (19–33) × 1018 g, is comparable with its mass in the water column, 38.1 × 1018 g. 相似文献
16.
Amber Hardison Craig Tobias Jennifer Stanhope Elizabeth Canuel Iris Anderson 《Estuaries and Coasts》2011,34(2):243-255
The water–sediment interface is a dynamic zone where the benthic and pelagic environments are linked through exchange and
recycling of organic matter and nutrients. However, it is often difficult to measure rate processes in this zone. To that
end, we designed an experimental apparatus for continuous and homogeneous perfusion of sediment porewater with dissolved conservative
(SF6, Rhodamine WT dye) and isotopic (H13CO3− and 15NH4+) tracers to study nitrogen and carbon cycling by the sediment microbial community of shallow illuminated sediments. The perfusionator
consists of a 60-cm ID × 60-cm high cylinder that includes a reservoir for porewater at the base of the sediment column. Porewater
amended with conservative and stable isotopic tracers was pumped through a mixing reservoir and upward through the overlying
sediments. We tested the perfusionator in a laboratory setting, as part of an outdoor mesocosm array, and buried in coastal
sediments. Conservative and isotopic tracers demonstrated that the porewater tracers were distributed homogeneously through
the sediment column in all settings. The perfusionator was designed to introduce dissolved stable isotope tracers but is capable
of delivering any dissolved ionic, organic, or gaseous constituent. We see a potentially wide application of this technique
in the aquatic and marine sciences in laboratory and field settings. 相似文献
17.
Worldwide Typology of Nearshore Coastal Systems: Defining the Estuarine Filter of River Inputs to the Oceans 总被引:1,自引:0,他引:1
Hans H. Dürr Goulven G. Laruelle Cheryl M. van Kempen Caroline P. Slomp Michel Meybeck Hans Middelkoop 《Estuaries and Coasts》2011,34(3):441-458
We present a spatially explicit global overview of nearshore coastal types, based on hydrological, lithological and morphological
criteria. A total of four main operational types act as active filters of both dissolved and suspended material entering the
ocean from land: small deltas (type I), tidal systems (II), lagoons (III) and fjords (IV). Large rivers (V) largely bypass
the nearshore filter, while karstic (VI) and arheic coasts (VII) act as inactive filters. This typology provides new insight
into the spatial distribution and inherent heterogeneity of estuarine filters worldwide. The relative importance of each type
at the global scale is calculated and types I, II, III and IV account for 32%, 22%, 8% and 26% of the global coastline, respectively,
while 12% have a very limited nearshore coastal filter. As an application of this typology, the global estuarine surface area
is re-estimated to 1.1 × 106 km2 instead of 1.4 × 106 km2 in earlier work. 相似文献
18.
Unit-cell dimensions of a natural phlogopite from Pargas, Finland, have been determined in the temperature interval of 27–1050 °C
by X-ray powder diffraction technique. Expansion rates vary discontinuously with temperature with a break at 412 °C. Below
this temperature, the linear expansions (α) for a, b and c axis lengths are 3.74 × 10−5 K−1, 1.09 × 10−5 K−1, and 1.19 × 10−5 K−1, respectively, and above that they are 0.86 × 10−5 K−1, 0.80 × 10−5 K−1, and 1.93 × 10−5 K−1. The volume thermal expansion coefficients are 6.26 × 10−5 K−1 and 3.71 × 10−5 K−1 for low-temperature and high-temperature intervals, respectively. The observed kink in the rate of thermal expansions with
temperature could be due to the different mode of structural changes. Thermogravimetric analysis of the sample indicates the
oxidation of iron in the temperature range of 500–600 °C and dehydroxylation as well as decomposition of phlogopite in the
temperature range of 900–1200 °C.
Received: 8 September 1998 / Accepted: 28 February 2000 相似文献
19.
May-Linn Paulsen Andreas J. Andersson Lihini Aluwihare Tyler Cyronak Sydney D’Angelo Charlie Davidson Hany Elwany Sarah N. Giddings Heather N. Page Magali Porrachia Stephen Schroeter 《Estuaries and Coasts》2018,41(4):1050-1068
Estuaries are important subcomponents of the coastal ocean, but knowledge about the temporal and spatial variability of their carbonate chemistry, as well as their contribution to coastal and global carbon fluxes, are limited. In the present study, we measured the temporal and spatial variability of biogeochemical parameters in a saltmarsh estuary in Southern California, the San Dieguito Lagoon (SDL). We also estimated the flux of dissolved inorganic carbon (DIC) and total organic carbon (TOC) to the adjacent coastal ocean over diel and seasonal timescales. The combined net flux of DIC and TOC (FDIC?+?TOC) to the ocean during outgoing tides ranged from ??1.8±0.5?×?103 to 9.5±0.7?×?103?mol C h?1 during baseline conditions. Based on these fluxes, a rough estimate of the net annual export of DIC and TOC totaled 10±4?×?106?mol C year?1. Following a major rain event (36 mm rain in 3 days), FDIC?+?TOC increased and reached values as high as 29.0 ±?0.7?×?103?mol C h?1. Assuming a hypothetical scenario of three similar storm events in a year, our annual net flux estimate more than doubled to 25 ±?4?×?106?mol C year?1. These findings highlight the importance of assessing coastal carbon fluxes on different timescales and incorporating event scale variations in these assessments. Furthermore, for most of the observations elevated levels of total alkalinity (TA) and pH were observed at the estuary mouth relative to the coastal ocean. This suggests that SDL partly buffers against acidification of adjacent coastal surface waters, although the spatial extent of this buffering is likely small. 相似文献
20.
The hydroelectric reservoir of Petit Saut, French Guiana, was created in 1994–1995 by flooding 350 km2 of tropical forest. When sampled in 1999, the lake exhibited a permanent stratification separating the 3–5 m thick, oxygenated
epilimnion from the anoxic hypolimnion. The rate of anaerobic organic carbon mineralization below the oxycline was on the
order of 1 μmol C m−2 s−1 and did not show a pronounced difference between wet and dry seasons. Methanogenesis accounted for 76–83% of anaerobic carbon
mineralization, with lesser contributions of sulfate reduction and dissimilatory iron reduction. Upward mixing of reduced
inorganic solutes explained 90% of the water column O
2 demand during the dry season, while most O
2 consumption during the wet season was coupled to aerobic respiration of organic matter synthesized in the surface waters.
Inorganic mercury species represented 10–40% of total dissolved mercury in the epilimnion, but were of relatively minor importance
(≤10%) in the anoxic portion of the water column. Net production of soluble organic mercury compounds in the flooded soils
and anoxic water column did not vary significantly between wet and dry seasons. Methylmercury accounted for about 15% of total
dissolved mercury below the oxycline. Its estimated net production rate, 0.04 mg m−2 yr−1, is of the same order of magnitude as values reported for contaminated lakes and flooded terrestrial ecosystems. 相似文献