scholarly journals Migration and transformation of dissolved carbon during accumulated cyanobacteria decomposition in shallow eutrophic lakes: a simulated microcosm study

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5922 ◽  
Author(s):  
Zhichun Li ◽  
Yanping Zhao ◽  
Xiaoguang Xu ◽  
Ruiming Han ◽  
Mingyue Wang ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Carbon Cycling ◽  
Dissolved Inorganic Carbon ◽  
Eutrophic Lakes ◽  
Overlying Water ◽  
Dissolved Carbon ◽  
Laboratory Microcosm ◽  
Transformation Mechanisms ◽  
Diffusive Fluxes ◽  
Sediment Interface

The decomposition processes of accumulated cyanobacteria can release large amounts of organic carbon and affect the carbon cycling in shallow eutrophic lakes. However, the migration and transformation mechanisms of dissolved carbon (DC) require further study and discussion. In this study, a 73-day laboratory microcosm experiment using suction samplers (Rhizon and syringe) was conducted to understand the migration and transformation of DC during the cyanobacteria decomposition. The decomposition of cyanobacteria biomass caused anoxic and reduction conditions, and changed the acid-base environment in the water column. During the early incubation (days 0–18), a large amount of cyanobacteria-derived particulate organic matter (POM) was decomposed into dissolved organic carbon (DOC) in the overlying water, reaching the highest peak value of 1.82 g L−1 in the treatment added the high cyanobacteria biomass (470 g). After 18 days of incubation, the mineralization of increased DOC to dissolved inorganic carbon (DIC) maintained a high DIC level of overlying water in treatments added cyanobacteria biomass. The treatment added the medium cyanobacteria biomass (235 g) presented the lower DOC/total dissolved carbon ratio than the high cyanobacteria biomass associated with the lower mineralization from DOC to DIC. Due to the concentration differences of DIC at water-sediment interface, the main migration of DIC from pore water to overlying water occurred in the treatment without added cyanobacteria biomass. However, the treatments added the cyanobacteria biomass presented the obvious diffusion of DOC and the low migration of DIC at the water-sediment interface. The diffusive fluxes of DOC at the water-sediment interface increased with the cyanobacteria biomass added, reaching the maximum value of 411.01 mg/(m2·d) in the treatment added the high cyanobacteria biomass. In the overlying water, the group added the sediment and medium cyanobacteria biomass presented a faster degradation of cyanobacteria-derived POM to DOC and a higher mineralization level of DOC to DIC than added the medium cyanobacteria biomass without sediment. Therefore, during accumulated cyanobacteria decomposition, the biomass of accumulated cyanobacteria and sediment property can influence the migration and transformation of DC, playing an important role in carbon cycling in shallow eutrophic lakes.

scholarly journals Carbon cycling on the East Siberian Arctic Shelf – a change in air-sea CO<sub>2</sub> flux induced by mineralization of terrestrial organic carbon

2017 ◽  
Author(s):  
Erik Gustafsson ◽  
Christoph Humborg ◽  
Göran Björk ◽  
Christian Stranne ◽  
Leif G. Anderson ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Organic Carbon ◽  
Carbon Cycling ◽  
Dissolved Inorganic Carbon ◽  
Carbon Sources ◽  
Atmospheric Co2 ◽  
Arctic Shelf ◽  
The Arctic ◽  
Biogeochemical Model ◽  
Siberian Arctic

Abstract. Measurements from the SWERUS-C3 and ISSS-08 Arctic expeditions were used to calibrate and validate a new physical-biogeochemical model developed to quantify key carbon cycling processes on the East Siberian Arctic Shelf (ESAS). The model was used in a series of experimental simulations with the specific aim to investigate the pathways of terrestrial dissolved and particulate organic carbon (DOCter and POCter) supplied to the shelf. Rivers supply on average 8.5 Tg C yr−1 dissolved inorganic carbon (DIC), and further 8.5 and 1.1 Tg C yr−1 DOCter and POCter respectively. Based on observed and simulated DOC concentrations and stable isotope values (δ13CDOC) in shelf waters, we estimate that only some 20 % of the riverine DOCter is labile. According to our model results, an additional supply of approximately 14 Tg C yr−1 eroded labile POCter is however required to describe the observed stable isotope values of DIC (δ13CDIC). Degradation of riverine DOCter and POCter results in a 1.8 Tg C yr−1 reduction in the uptake of atmospheric CO2, while degradation of eroded POCter results in an additional 10 Tg C yr−1 reduction. Our calculations indicate nevertheless that the ESAS is an overall small net sink for atmospheric CO2 (1.7 Tg C yr−1). The external carbon sources are largely compensated by a net export from the shelf to the Arctic Ocean (31 Tg C yr−1), and to a smaller degree by a permanent burial in the sediments (2.7 Tg C yr−1).

scholarly journals Pore water geochemistry along continental slopes north of the East Siberian Sea: inference of low methane concentrations

2017 ◽  
Vol 14 (12) ◽  
pp. 2929-2953 ◽  
Author(s):  
Clint M. Miller ◽  
Gerald R. Dickens ◽  
Martin Jakobsson ◽  
Carina Johansson ◽  
Andrey Koshurnikov ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Pore Water ◽  
Dissolved Inorganic Carbon ◽  
Sediment Cores ◽  
Turnover Rates ◽  
Water Geochemistry ◽  
Geochemical Environment ◽  
East Siberian Sea ◽  
Continental Slopes ◽  
Diffusive Fluxes

Abstract. Continental slopes north of the East Siberian Sea potentially hold large amounts of methane (CH4) in sediments as gas hydrate and free gas. Although release of this CH4 to the ocean and atmosphere has become a topic of discussion, the region remains sparingly explored. Here we present pore water chemistry results from 32 sediment cores taken during Leg 2 of the 2014 joint Swedish–Russian–US Arctic Ocean Investigation of Climate–Cryosphere–Carbon Interactions (SWERUS-C3) expedition. The cores come from depth transects across the slope and rise extending between the Mendeleev and the Lomonosov ridges, north of Wrangel Island and the New Siberian Islands, respectively. Upward CH4 flux towards the seafloor, as inferred from profiles of dissolved sulfate (SO42−), alkalinity, and the δ13C of dissolved inorganic carbon (DIC), is negligible at all stations east of 143° E longitude. In the upper 8 m of these cores, downward SO42− flux never exceeds 6.2 mol m−2 kyr−1, the upward alkalinity flux never exceeds 6.8 mol m−2 kyr−1, and δ13C composition of DIC (δ13C-DIC) only moderately decreases with depth (−3.6 ‰ m−1 on average). Moreover, upon addition of Zn acetate to pore water samples, ZnS did not precipitate, indicating a lack of dissolved H2S. Phosphate, ammonium, and metal profiles reveal that metal oxide reduction by organic carbon dominates the geochemical environment and supports very low organic carbon turnover rates. A single core on the Lomonosov Ridge differs, as diffusive fluxes for SO42− and alkalinity were 13.9 and 11.3 mol m−2 kyr−1, respectively, the δ13C-DIC gradient was 5.6 ‰ m−1, and Mn2+ reduction terminated within 1.3 m of the seafloor. These are among the first pore water results generated from this vast climatically sensitive region, and they imply that abundant CH4, including gas hydrates, do not characterize the East Siberian Sea slope or rise along the investigated depth transects. This contradicts previous modeling and discussions, which due to the lack of data are almost entirely based on assumption.

Carbon and phosphorus losses from dairy pasture in South Australia

Soil Research ◽  
2001 ◽  
Vol 39 (5) ◽  
pp. 969 ◽  
Author(s):  
N. K. Fleming ◽  
J. W. Cox
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Overland Flow ◽  
Dissolved Inorganic Carbon ◽  
South Australia ◽  
Annual Rainfall ◽  
Carbon Loss ◽  
Dissolved Carbon ◽  
Time Of Year ◽  
Phosphorus Losses

Runoff (overland flow and A/B horizon interflow) was measured from 2 grazed dairy pastures at Flaxley, South Australia, from 1996 to 1998. Runoff ranged from 0.4% to 10% of annual rainfall and >90% of this was overland flow. Phosphorus and carbon were measured in runoff. As much as 2.3 kg/ha of phosphorus and 10.7 kg/ha of total dissolved carbon were lost from the subcatchments in the wettest year. Over the study period, 98% of total phosphorus and 86% of total dissolved carbon were lost in overland flow. Around 45% of phosphorus was dissolved and 69% of total dissolved carbon was dissolved organic carbon. The proportion of phosphorus present in the particulate form decreased during each runoff season, and was highest in the wettest year. There was no consistent trend in the proportion of total dissolved carbon present as dissolved organic carbon because the factors found to affect dissolved organic carbon loss were different from those affecting dissolved inorganic carbon loss. Predictive relationships based on factors such as the time of year when the storm occurred and runoff volume have been developed from the 3 years of data and they explain a high proportion of variability of phosphorus and carbon loads.

Sources of Dissolved Inorganic Carbon in Two Small Streams with Different Bedrock Geology: Insights from Carbon Isotopes

Radiocarbon ◽  
2015 ◽  
Vol 57 (3) ◽  
pp. 439-448 ◽  
Author(s):  
Naoto F Ishikawa ◽  
Ichiro Tayasu ◽  
Masako Yamane ◽  
Yusuke Yokoyama ◽  
Saburo Sakai ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Carbon Cycling ◽  
Carbonate Rock ◽  
Dissolved Inorganic Carbon ◽  
Stable Carbon Isotope ◽  
The Other ◽  
Biological Degradation ◽  
Small Streams ◽  
Limestone Bedrock

Radiocarbon natural abundances (Δ14C) are being increasingly used to trace carbon cycling in stream ecosystems. To understand the ultimate sources of carbon, we determined the stable carbon isotope ratios (δ13C) and Δ14C values of dissolved inorganic and organic carbon (DIC and DOC, respectively) and of particulate organic carbon (POC) in two small streams in central Japan, one of which flows over limestone bedrock (Seri) and the other does not (Fudoji). Investigations over four seasons revealed that the Δ14C values of the DIC (from −238‰ to −174‰ for Seri and −23‰ to +10‰ for Fudoji) were less variable than those of the other carbon fractions (DOC: from −400‰ to −138‰ for Seri and −2‰ to +103‰ for Fudoji; POC: from −164‰ to −60‰ for Seri and −55‰ to +37‰ for Fudoji). Based on mass balance calculations using the δ13C and Δ14C values, the proportions of carbon in the DIC originated from (1) atmospheric CO2 were 47% to 57% for Seri and 74% to 90% for Fudoji, (2) organic matter degradation were 29% to 35% for Seri and 4% to 21% for Fudoji, and (3) carbonate rock were 14% to 22% for Seri and 4% to 6% for Fudoji. We compared the results with previous studies that had been conducted in larger rivers and showed that in small streams, the dissolution of atmospheric CO2 and weathering of carbonate rock are more important factors in the carbon cycling than the biological degradation of organic matter.

scholarly journals Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the brine-seawater interface

2012 ◽  
Vol 9 (12) ◽  
pp. 17913-17937
Author(s):  
S. R. Shah ◽  
S. B. Joye ◽  
J. A. Brandes ◽  
A. P. McNichol
Keyword(s):  
Organic Carbon ◽  
Isotopic Composition ◽  
Source Region ◽  
Microbial Control ◽  
Carbon Isotopic Composition ◽  
Overlying Water ◽  
Large Reservoir ◽  
Dissolved Carbon ◽  
Carbon Isotopic ◽  
Orca Basin

Abstract. Orca Basin, an intraslope basin on the Texas–Louisiana continental slope, hosts a hypersaline, anoxic brine in its lowermost 200 m. This brine contains a large reservoir of reduced and aged carbon, and appears to be stable at decadal time scales: concentrations and the isotopic composition of dissolved inorganic (DIC) and organic carbon (DOC) are similar to previous reports. Both DIC and DOC are more "aged" within the brine pool than in overlying water, and the isotopic contrast between brine carbon and seawater carbon is much greater for DIC than DOC. While the stable carbon isotopic composition of brine DIC points towards a combination of methane and organic carbon re-mineralization as its source, radiocarbon and box model results point to the brine interface as the major source region for DIC with oxidation of methane diffusing upwards from sediments supplying only limited DIC to the brine. This conclusion is consistent with previous studies reporting microbial activity focused at the seawater-brine interface. Isotopic similarities between DIC and DOC suggest a different relationship between these two carbon reservoirs than is typically observed in deep ocean basins. Radiocarbon values implicate the seawater-brine interface region as the likely source region for DOC as well as DIC. Further investigations of the seawater-brine interface are needed to advance our understanding of the specific microbial processes contributing to dissolved carbon storage in the Orca Basin brine.

scholarly journals Dissolved Carbon Transport and Processing in North America’s Largest Swamp River Entering the Northern Gulf of Mexico

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1395
Author(s):  
Emily M. DelDuco ◽  
Y. Jun Xu
Keyword(s):  
Gulf Of Mexico ◽  
Carbon Cycling ◽  
Mississippi River ◽  
Dissolved Inorganic Carbon ◽  
Isotope Composition ◽  
River System ◽  
Floodplain Wetland ◽  
Co2 Partial Pressure ◽  
River Waters ◽  
Dissolved Carbon

Transport and transformation of riverine dissolved carbon is an important component of global carbon cycling. The Atchafalaya River (AR) flows 189 kilometers through the largest bottomland swamp in North America and discharges ~25% of the flow of the Mississippi River into the Gulf of Mexico annually, providing a unique opportunity to study the floodplain/wetland impacts on dissolved carbon. The aim of this study is to determine how dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in the AR change spatially and seasonally, and to elucidate which processes control the carbon cycling in this intricate swamp-river system. From May 2015 to May 2016, we conducted monthly river sampling from the river’s inflow to its outflow, analyzing samples for concentrations and δ13C stable isotope composition of DOC and DIC. We found that DIC concentrations in the AR were three times higher than the DOC concentrations on average, and showed more pronounced downstream changes than the DOC. During the study period, the river discharged a total of 5.35 Tg DIC and a total of 2.34 Tg DOC into the Gulf of Mexico. Based on the mass inflow–outflow balance, approximately 0.53 Tg (~10%) of the total DIC exported was produced within the floodplain/wetland system, while 0.24 Tg (~10%) of the DOC entering the basin was removed. The AR’s water was consistently oversaturated with CO2 partial pressure (pCO2) above the atmospheric pCO2 (with pCO2 varying from 551 µatm to 6922 µatm), indicating a large source of DIC from river waters to the atmosphere as well as to the coastal margins. Largest changes in carbon constituents occurred during periods of greatest inundation of the swamp-river basin and corresponded with shifts in isotopic composition. This effect was particularly pronounced during the initial flood stages, supporting the hypothesis that subtropical floodplains can act as effective enhancers of the biogeochemical cycling of dissolved carbon.

scholarly journals Spatio-temporal Variation in Nutrient Profiles and Exchange Fluxes at the Sediment-Water Interface in Yuqiao Reservoir, China

2019 ◽  
Vol 16 (17) ◽  
pp. 3071 ◽  
Author(s):  
Wen ◽  
Wu ◽  
Yang ◽  
Jiang ◽  
Zhong
Keyword(s):  
Pore Water ◽  
Water Source ◽  
Water Soluble ◽  
Drinking Water Source ◽  
Eutrophic Lakes ◽  
Overlying Water ◽  
Total N ◽  
Yuqiao Reservoir ◽  
Nutrient Profiles ◽  
Main Component

Nutrients released from sediments have a significant influence on the water quality in eutrophic lakes and reservoirs. To clarify the internal nutrient load and provide reference for eutrophication control in Yuqiao Reservoir, a drinking water source reservoir in China, pore water profiles and sediment core incubation experiments were conducted. The nutrients in the water (soluble reactive P (SRP), nitrate-N (NO3−-N), nitrite-N (NO2−-N), and ammonium-N (NH4+-N)) and in the sediments (total N (TN), total P (TP) and total organic carbon (TOC)) were quantified. The results show that NH4+-N was the main component of inorganic N in the pore water. NH4+-N and SRP were higher in the pore water than in the overlying water, and the concentration gradient indicated a diffusion potential from the sediment to the overlying water. The NH4+-N, NO3−-N, and SRP fluxes showed significant differences amongst the seasons. The NH4+-N and SRP fluxes were significantly higher in the summer than in other seasons, while NO3−-N was higher in the autumn. The sediment generally acted as a source of NH4+-N and SRP and as a sink for NO3−-N and NO2−-N. The sediments release 1133.15 and 92.46 tons of N and P, respectively, to the overlying water each year.

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