Dataset Information

Factors controlling the distributions of dissolved organic matter in the East China Sea during summer.

ABSTRACT: To determine the distribution of dissolved organic matter (DOM) in the East China Sea (ECS) during the summer, we measured the dissolved organic carbon (DOC) and nitrogen (DON), fluorescent dissolved organic matter (FDOM), and chlorophyll a (Chl. a) in the upper 100-m layer of this region during July and September 2015. The DOC (r² = 0.72 and 0.78 in July and September, respectively) and DON (r² = 0.43 and 0.33) were significantly correlated with salinity, suggesting that the river is the primary origin of DOM. However, we found that at a DOC "pulse" under a salinity ranging from 24 to 35, the extrapolating DOC values (304 ± 11 μM) were twice higher than those with a salinity of close to 0, as found in a previous study. The excess DOC concentration seemed to be attributed to the microbial metabolism during transport from the estuary based on the good relationships between DOC and marine humic-like FDOM (r² = 0.42 and 0.47), as well as the fluorescence, humification, and biological indexes, but showed no correlation with Chl. a. Thus, the results of our study indicate that microbial activities can be a significant factor controlling the distribution of DOM in the ECS during summer.

SUBMITTER: Kim J

PROVIDER: S-EPMC7366708 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Factors controlling the distributions of dissolved organic matter in the East China Sea during summer.

Kim Jeonghyun J Kim Tae-Hoon TH Park Sang Rul SR Lee Hyuk Je HJ Kim Jang Kyun JK

Scientific reports 20200716 1

To determine the distribution of dissolved organic matter (DOM) in the East China Sea (ECS) during the summer, we measured the dissolved organic carbon (DOC) and nitrogen (DON), fluorescent dissolved organic matter (FDOM), and chlorophyll a (Chl. a) in the upper 100-m layer of this region during July and September 2015. The DOC (r<sup>2</sup> = 0.72 and 0.78 in July and September, respectively) and DON (r<sup>2</sup> = 0.43 and 0.33) were significantly correlated with salinity, suggesting that t ...[more]

PMID: 32678257

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Project description:Analyzing the molecular composition change of dissolved organic matter (DOM) during transportation in estuaries can enhance our understanding of the fate of DOM. However, the impact of hydrologic conditions resulting from large river plumes on the DOM cycle are less explored, and previous studies were insufficient to capture the molecular fate that occur during the transportation process. In this study, we used a range of bulk and optical techniques, as well as Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), to determine the concentration and characteristics of DOM along two trajectories of downstream plumes of diluted water of the Yangtze (Changjiang) River estuary (YRE) during the high discharge season. These two plumes situated along the route of the summer Changjiang diluted water (CDW) have been identified and named CDW-North (CDW-N) and CDW-South (CDW-S), respectively. Despite having the same riverine end-member origin, the turbidity zone in YRE significantly modifies the molecular characteristics and composition of DOM. The results of FT-ICR MS indicated a spatial variation of DOM composition in the coastal zone of the two plumes. The relative intensities of the CHO, CHOS, and CHONS compounds are negatively correlated with salinity. In addition, the coastal zones of both CDW-N and CDW-S are characterized by more autochthonous DOM sources. More CHON compounds in CDW-N are probably due to the production of autochthonous DOM in offshore waters. The activity of phytoplankton increased the surface dissolved oxygen level of CDW-N in the coastal zone. However, the hypoxic zone formed at the bottom of the CDW-N due to microbial degradation of organic matter and may further benefit the preservation of CHON compounds. Our study emphasizes that the characteristics and composition of the estuarine DOM can be significantly shaped by distinct large river plumes. Furthermore, using FT-ICR MS in combination with complementary techniques can better assist in identifying the sources and transformation mechanisms of estuarine DOM in large river plume-affected systems and provide more valuable insights into the role of DOM in the estuarine biogeochemical cycle.

Project description:BackgroundMono-specific aquaculture effluents contain high concentrations of nutrients and organic matter, which affect negatively the water quality of the recipient ecosystems. A fundamental feature of water quality is its transparency. The fraction of dissolved organic matter that absorbs light is named chromophoric dissolved organic matter (CDOM). A sustainable alternative to mono-specific aquaculture is the multitrophic aquaculture that includes species trophically complementary named "extractive" species that uptake the waste byproducts. Sea cucumbers are recognized as efficient extractive species due to the consumption of particulate organic matter (POM). However, the effects of sea cucumbers on CDOM are still unknown.MethodsDuring more than one year, we monitored CDOM in two big-volume tanks with different trophic structure. One of the tanks (-holothurian) only contained around 810 individuals of Anemonia sulcata, whereas the other tank (+holothurian) also included 90 individuals of Holothuria tubulosa and Holothuria forskali. We routinely analyzed CDOM absorption spectra and determined quantitative (absorption coefficients at 325 nm) and qualitative (spectral slopes) optical parameters in the inlet waters, within the tanks, and in their corresponding effluents. To confirm the time-series results, we also performed three experiments. Each experiment consisted of two treatments: +holothurians (+H) and -holothurians (-H). We set up three +H tanks with 80 individuals of A. sulcata and 10 individuals of H. tubulosa in each tank and four -H tanks that contained only 80 individuals of A. sulcata.ResultsIn the time-series, absorption coefficients at 325 nm (a325) and spectral slopes from 275 to 295 nm (S275-295) were significantly lower in the effluent of the +holothurian tank (average: 0.33 m-1 and 16 µm-1, respectively) than in the effluent of the -holothurian tank (average: 0.69 m-1 and 34 µm-1, respectively), the former being similar to those found in the inlet waters (average: 0.32 m-1 and 22 µm-1, respectively). This reduction in the absorption of the dissolved organic matter appears to be mediated by the POM consumption by holothurians. The experiments confirmed the results observed in the time-series. The a325 and S275-295 values were significantly lower in the treatment with holothurians than in the treatment without holothurians indicating a reduction in the concentration of chromophoric organic compounds, particularly of low molecular weight.DiscussionConsequently, sea cucumbers appear to improve water transparency in aquaculture tanks. The underlying mechanism of this improvement might be related to the POM consumption by holothurians, which reduces the concentration of CDOM derived from POM disaggregation or to the direct assimilation of dissolved compounds of low molecular weight as chromophoric amino acids.

Dataset Information

Factors controlling the distributions of dissolved organic matter in the East China Sea during summer.

Publications

Factors controlling the distributions of dissolved organic matter in the East China Sea during summer.

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