scholarly journals Intra-annual variability of carbon and nitrogen stable isotopes in suspended organic matter in waters of the western continental shelf of India

2011 ◽  
Vol 8 (11) ◽  
pp. 3441-3456 ◽  
Author(s):  
M. V. Maya ◽  
S. G. Karapurkar ◽  
H. Naik ◽  
R. Roy ◽  
D. M. Shenoy ◽  
...  
Keyword(s):  
Organic Matter ◽  
Continental Shelf ◽  
Phytoplankton Production ◽  
Terrestrial Organic Matter ◽  
Monsoon Period ◽  
Isotopic Signatures ◽  
Carbon And Nitrogen ◽  
Annual Variability ◽  
Post Monsoon ◽  
Sw Monsoon

Abstract. Intra-annual variations of δ13C and δ15N of water-column suspended particulate organic matter (SPOM) have been investigated to understand the biogeochemical cycling of C and N in the Western Continental Shelf of India (WCSI). The key issues being addressed are: how the δ15N of SPOM is affected by seasonally varying processes of organic matter production and respiration and how it relates to the δ15N of sedimentary organic matter that appears to show a decreasing trend despite an apparent intensification of seasonal oxygen deficiency over the past few decades? A secondary objective was to evaluate the sources of organic carbon. Elemental carbon and nitrogen concentrations, C/N ratios in SPOM, along with ancillary chemical and biological variables including phytoplankton pigment abundance were also determined on a seasonal basis (from March 2007 to September 2008), with the partial exception of the southwest (SW) monsoon period. The results reveal significant shifts in isotopic signatures, especially δ15N, of SPOM before and after the onset of SW monsoon. Very low δ15N values, reaching a minimum of −4.17 ‰, are found during the pre-monsoon period. Our results provide the first direct evidence for the addition of substantial amounts of isotopically light nitrogen by the diazotrophs, especially Trichodesmium, in the region. The δ15N of SPOM is generally lower than the mean value (7.38 ‰) for surficial sediments, presumably because of diagenetic enrichment. The results support the view that sedimentary δ15N may not necessarily reflect denitrification intensity in the overlying waters due to diverse sources of nitrogen and variability of its isotopic composition. The observed intra-annual variability of δ13C of SPOM during the pre-monsoon and post-monsoon periods is generally small. Phytoplankton production and probably species composition could drive some of the observed changes. The largest changes (depletion of δ13C and increase in C/N) appear to occur during the pre- and post-monsoon seasons, presumably through episodic deposition of terrestrial organic matter from the atmosphere. During the SW monsoon, when a large input of terrestrial organic matter is expected through runoff from land, the C/N ratio remains low, but significant difference is observed between δ13C data in 2007 and 2008. Inputs of soil organic matter that may have elemental and isotopic signatures different from those of the conventional (C3 plant derived) organic matter could explain the constancy of the C/N ratio.

scholarly journals Intra-annual variability of carbon and nitrogen stable isotopes in suspended organic matter in waters of the western continental shelf of India

2011 ◽  
Vol 8 (2) ◽  
pp. 3923-3951
Author(s):  
M. V. Maya ◽  
S. G. Karapurkar ◽  
H. Naik ◽  
R. Roy ◽  
D. M. Shenoy ◽  
...  
Keyword(s):  
Organic Matter ◽  
Water Column ◽  
Phytoplankton Production ◽  
Monsoon Period ◽  
Δ13c And Δ15n ◽  
Carbon And Nitrogen ◽  
Annual Variability ◽  
Post Monsoon ◽  
Biological Variables ◽  
Sw Monsoon

Abstract. The δ13C and δ15N of water-column suspended particulate organic matter (SPOM), elemental carbon and nitrogen concentrations, and C/N ratios in SPOM, along with ancillary chemical and biological variables including phytoplankton pigment abundance, were determined every month, with the partial exception of the southwest (SW) monsoon period, from March 2007 to September 2008 at a fixed site located off Goa (central west coast of India). The results reveal significant shifts in isotopic signatures, especially δ15N, of SPOM before and after the onset of the SW monsoon. Very low δ15N values, reaching a minimum of −4.17‰, are found during the pre-monsoon period. Although the average δ15N values for the SW monsoon (6.55‰) and post-monsoon (6.19‰) are substantially higher, these values are lower than expected from a region that experiences intense water-column denitrification, as well as those reported previously from the open Arabian Sea. Our results provide the first direct evidence for the addition of substantial amounts of isotopically light nitrogen by the diazotrophs, especially Trichodesmium, in the region. The δ15N of SPOM is generally lower than the mean value (7.38‰) for surficial sediments in the region, presumably because of diagenetic enrichment. The results support the notion that sedimentary δ15N may not necessarily reflect denitrification intensity in the overlying waters due to diverse sources of nitrogen and variability of its isotopic composition. The observed intra-annual variability of δ13C of SPOM is small (seasonal averages: pre-monsoon: −21.40‰, SW monsoon: −20.41‰ and post-monsoon: −22.15‰). Phytoplankton production and probably species composition could drive the observed changes. Occasional shifts in δ13C toward more negative values are suggestive of terrestrial inputs, but by and large the SPOM in the region seems to be of marine origin with relatively low and constant C/N ratios (5.8–6.5) occurring throughout the study period.

Stable Carbon and Nitrogen Isotopes in the Tidal Flat Sediments of Northern Yellow Sea

2013 ◽  
Vol 316-317 ◽  
pp. 223-226
Author(s):  
Bao Zhan Liu ◽  
Yu Liu ◽  
Ying Li ◽  
Hai Xia Wang
Keyword(s):  
Organic Matter ◽  
Tidal Flat ◽  
Yellow Sea ◽  
Nitrogen Isotopes ◽  
Stable Carbon ◽  
Terrestrial Organic Matter ◽  
Δ13c And Δ15n ◽  
Carbon And Nitrogen Isotopes ◽  
Carbon And Nitrogen ◽  
Northern Yellow Sea

Stable carbon and nitrogen compositions (δ13C, δ15N) of sedimentary organic matter were determined in the tidal flat of northern Yellow sea. The results showed that stable carbon and nitrogen isotopes compositions of the sediment samples ranged from −24.669～−19.457‰ and 2.125～7.043‰, respectively. The highest value was in St.DLD, and the lowest was in St.Z. Similar δ13C values were observed in St.H (−21.996±0.651‰) and St.P (−22.021±0.187‰), and similar δ15N values were between St.DLJ (5.502±0.223‰) and St.P (5.310±0.294‰). The δ13C and δ15N values did not show any significant regularity. The δ13C and δ15N signatures showed some fluctuation, no obvious regularity. The major source of terrestrial organic matter was from the emissions of river and human pollutant.

scholarly journals Evidence for the offshore transport of terrestrial organic matter due to the rise of sea level: The case of the East China Sea Continental Shelf

2000 ◽  
Vol 27 (23) ◽  
pp. 3893-3896 ◽  
Author(s):  
Kazumasa Oguri ◽  
Eiji Matsumoto ◽  
Yoshiki Saito ◽  
Makio C. Honda ◽  
Naomi Harada ◽  
...  
Keyword(s):  
Organic Matter ◽  
Continental Shelf ◽  
Sea Level ◽  
East China Sea ◽  
East China ◽  
The East China Sea ◽  
Terrestrial Organic Matter ◽  
China Sea ◽  
Offshore Transport

scholarly journals The Response of Dissolved Organic Matter during Monsoon and Post-Monsoon Periods in the Regulated River for Sustainable Water Supply

2020 ◽  
Vol 12 (13) ◽  
pp. 5310
Author(s):  
Mei-Yan Jin ◽  
Hye-Ji Oh ◽  
Kyung-Hoon Shin ◽  
Min-Ho Jang ◽  
Hyun-Woo Kim ◽  
...  
Keyword(s):  
Land Use ◽  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Heavy Rainfall ◽  
Urban Land Use ◽  
Regulated River ◽  
Regulated Rivers ◽  
Monsoon Period ◽  
Post Monsoon ◽  
Sustainable Water Supply

Dissolved organic matter (DOM) in rivers are an important factor in pollution management due to the abundance of stored carbon. Using fluorescent spectroscopy, we investigated the temporal and spatial dynamics of DOM compositions, as well as their properties, for two of the major four regulated rivers—Han River (HR) and Geum River (GR) in South Korea. We collected eight sampling sites, four from each of the two rivers (from close to the weirs) in order to observe the integrated effects of different land use (terrestrial input) during the monsoon (July) and post-monsoon periods (September). High integral values of DOM compositions (July: 30.81 ± 9.71 × 103 vs. September: 1.78 ± 0.66 × 103) were present in all eight sites after heavy rainfall during the monsoon period, which indicated that Asian monsoon climates occupy a potent role in the DOM compositions of the rivers. Regarding DOM compositions, tryptophan-like and fulvic acid-like components were predominant in HR and GR, especially in GR with high integral values of protein-like and humus components. However, the properties of terrestrial DOM between HR and GR are markedly different. These results considered due to the different land use, where the terrestrial DOM shows a low degree of humification due to a high percentage of agriculture and urban land use in GR. Furthermore, these two rivers are typical regulated rivers, due to their weir constructions. High values of DOM components were present in the downstream of the weirs; however, increasingly high patterns appeared in the HR because of heavy rainfall (511.01 mm in HR; 376.33 mm in GR). In addition, a lower increasing trend of humic-like component was present in the GR due to a low percentage of forest land use/cover. These results suggest that the effect of the weir on rivers can be highlighted by the different percentages of land use/cover under the conditions of the monsoon period. Hence, DOM fluorescence can serve as an effective indicator for providing an early signal for the complex impacts of the different land use and rainfall in the regulated river systems.

Mercury and methylmercury along a transect from the Lena river estuary across the Laptev Sea Shelf

2020 ◽  
Author(s):  
Van Liem Nguyen ◽  
Birgit Wild ◽  
Örjan Gustafsson ◽  
Igor Semiletov ◽  
Oleg Dudarev ◽  
...  
Keyword(s):  
Organic Matter ◽  
Continental Shelf ◽  
Arctic Ocean ◽  
River Delta ◽  
The Arctic ◽  
Laptev Sea ◽  
Terrestrial Organic Matter ◽  
Lena River ◽  
The Arctic Ocean ◽  
The Laptev Sea

<p>Widespread accelerated permafrost thawing is predicted for this century and beyond. This threatens to remobilize the large amounts of Mercury (Hg) currently ‘locked’ in Arctic permafrost soils to the Arctic Ocean and thus potentially lead to severe consequences for human and wildlife health. Future risks of Arctic Hg in a warmer climate are, however, poorly understood. One crucial knowledge gap to fill is the fate of Hg once it enters the marine environment on the continental shelves. Arctic rivers are already today suggested to be the main source of Hg into the Arctic Ocean, with dissolved and particulate organic matter (DOM and POM, respectively) identified as important vectors for the land to sea transport.</p><p>In this study, we have investigated total Hg (HgT) and monomethylmercury (MeHg) concentrations in surface sediments from the East Siberian Arctic Shelf (ESAS) along a transect from the Lena river delta to the Laptev Sea continental slope. The ESAS is the world’s largest continental shelf and receives large amounts of organic carbon by the great Arctic Russian rivers (e.g., Lena, Indigirka and Kolyma), remobilized from continuous and discontinuous permafrost regions in the river catchments, and from coastal erosion. Data on HgT and MeHg levels in ESAS sediments is however limited. Here, we observed concentrations of Hg ranging from 30 to 96 ng Hg g<sup>-1</sup> d.w. of HgT, and 0.03 to 9.5 ng Hg g<sup>-1</sup> d.w. of MeHg. Similar concentrations of HgT were observed close to the river delta (54 ± 19 ng Hg g<sup>-1</sup> d.w.), where >95 % of the organic matter is of terrestrial origin, and the other section of the transect (42 ± 7 ng Hg g<sup>-1</sup> d.w.) where the terrestrial organic matter is diluted with carbon from marine sources. In contrast, we observed higher concentrations of MeHg close to the river delta (0.72 ± 0.71 ng Hg g<sup>-1</sup> d.w. as MeHg) than further out on the continental shelf (0.031 ± 0.71 ng Hg g<sup>-1</sup> d.w. as MeHg). We also observed a positive correlation between the MeHg:Hg ratio and previously characterized molecular markers of terrestrial organic matter (Bröder et al. Biogeosciences (2016) & Nature Com. (2018)). We thus suggest riverine inputs, rather than in situ MeHg formation, to explain observed MeHg trends.</p>

Changes in the planktonic food web of a new experimental reservoir

1997 ◽  
Vol 54 (5) ◽  
pp. 1088-1102 ◽  
Author(s):  
M J Paterson ◽  
D Findlay ◽  
K Beaty ◽  
W Findlay ◽  
E U Schindler ◽  
...  
Keyword(s):  
Organic Matter ◽  
Bacterial Biomass ◽  
Zooplankton Community ◽  
Zooplankton Biomass ◽  
Phytoplankton Production ◽  
First Year ◽  
Terrestrial Vegetation ◽  
Terrestrial Organic Matter ◽  
Planktonic Food ◽  
Before And After

Changes in plankton community structure were examined in an experimental reservoir (Lake 979) before and after impoundment. The role of allochthonous organic matter in planktonic food webs is unclear, and reservoir creation can be viewed as an extreme manipulation of terrestrial organic matter inputs. After impoundment of Lake 979, concentrations of phosphorus, nitrogen, and dissolved organic carbon increased as a result of decomposition of flooded terrestrial organic matter. In the first year of impoundment, mean bacterial biomass increased 10 times , and individual bacterial cell volumes increased 2 times over pre-flooding averages. Phytoplankton production and biomass decreased to approximately 25% of pre-flooding levels. Zooplankton biomass and production by Cladocera increased 10 times , and zooplankton community composition changed from dominance by small-sized Bosmina longirostris to dominance by large Daphnia rosea. In the first year of impoundment, production by Cladocera usually exceeded phytoplankton14C productivity, suggesting that the main pathway of carbon flow to secondary producers shifted from an autochthonous to an allochthonous base derived from flooded terrestrial vegetation. In the second year of flooding, bacterial biomass decreased and phytoplankton biomass was higher than in the two previous years of study.

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