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Submarine mud volcanoes as a source of chromophoric dissolved organic matter to the deep waters of the Gulf of Cadiz.

ABSTRACT: Seafloor structures related to the emission of different fluids, such as submarine mud volcanoes (MVs), have been recently reported to largely contribute with dissolved organic matter (DOM) into the oceans. Submarine MVs are common structures in the Gulf of Cádiz. However, little is known about the biogeochemical processes that occur in these peculiar environments, especially those involving DOM. Here, we report DOM characterization in the sediment pore water of three MVs of the Gulf of Cádiz. Estimated benthic fluxes of dissolved organic carbon (DOC) and chromophoric DOM (CDOM) were higher than in other marine sediments with an average of 0.11?±?0.04 mmol m^-2 d^-1 for DOC and ranging between 0.11 and 2.86 m^-1 L m^-2 d^-1, for CDOM. Protein-like components represented?~?70% of the total fluorescent DOM (FDOM). We found that deep fluids migration from MVs (cold seeps) and anaerobic production via sulfate-reducing bacteria represent a source of DOC and FDOM to the overlying water column. Our results also indicate that fluorescent components can have many diverse sources not captured by common classifications. Overall, MVs act as a source of DOC, CDOM, and FDOM to the deep waters of the Gulf of Cádiz, providing energy to the microbial communities living there.

SUBMITTER: Amaral V

PROVIDER: S-EPMC7865021 | biostudies-literature | 2021 Feb

REPOSITORIES: biostudies-literature

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Submarine mud volcanoes as a source of chromophoric dissolved organic matter to the deep waters of the Gulf of Cádiz.

Amaral Valentina V Romera-Castillo Cristina C Forja Jesús J

Scientific reports 20210205 1

Seafloor structures related to the emission of different fluids, such as submarine mud volcanoes (MVs), have been recently reported to largely contribute with dissolved organic matter (DOM) into the oceans. Submarine MVs are common structures in the Gulf of Cádiz. However, little is known about the biogeochemical processes that occur in these peculiar environments, especially those involving DOM. Here, we report DOM characterization in the sediment pore water of three MVs of the Gulf of Cádiz. E ...[more]

PMID: 33547356

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Project description:Background:Mono-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. Methods:During 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. Results:In 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. Discussion:Consequently, 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

Submarine mud volcanoes as a source of chromophoric dissolved organic matter to the deep waters of the Gulf of Cadiz.

Publications

Submarine mud volcanoes as a source of chromophoric dissolved organic matter to the deep waters of the Gulf of Cádiz.

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