Dataset Information

Sulfate Reduction in Sediments Produces High Levels of Chromophoric Dissolved Organic Matter.

ABSTRACT: Sulfate reduction plays an important role in altering dissolved organic matter (DOM) in estuarine and coastal sediments, although its role in the production of optically active chromophoric DOM (CDOM) and a subset of fluorescent DOM (FDOM) has not been previously investigated in detail. Freshwater sediment slurries were incubated anaerobically with added sulfate and acetate to promote sulfate-reducing bacteria. Ultraviolet visible (UV-Vis) absorbance and 3-dimensional excitation emission matrix (EEM) fluorescence spectra were measured over a five weeks anaerobic dark incubation period. Parallel Factor Analysis (PARAFAC) of FDOM determined components that increased significantly during dark and anaerobic incubation matching three components previously considered of terrestrially-derived or humic-like origin published in the OpenFluor database. The observed FDOM increase was strongly correlated (R2?=?0.96) with the reduction of sulfate. These results show a direct experimental link between sulfate reduction and FDOM production, which impacts our understanding of coastal FDOM sources and early sediment diagenesis. As 3D fluorescence techniques are commonly applied to diverse systems, these results provide increasing support that FDOM can have many diverse sources not consistently captured by common classifications such as "humic-like" fluorescence.

SUBMITTER: Luek JL

PROVIDER: S-EPMC5562794 | biostudies-other | 2017 Aug

REPOSITORIES: biostudies-other

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Sulfate Reduction in Sediments Produces High Levels of Chromophoric Dissolved Organic Matter.

Luek Jenna L JL Thompson Kaitlyn E KE Larsen Randolph K RK Heyes Andrew A Gonsior Michael M

Scientific reports 20170818 1

Sulfate reduction plays an important role in altering dissolved organic matter (DOM) in estuarine and coastal sediments, although its role in the production of optically active chromophoric DOM (CDOM) and a subset of fluorescent DOM (FDOM) has not been previously investigated in detail. Freshwater sediment slurries were incubated anaerobically with added sulfate and acetate to promote sulfate-reducing bacteria. Ultraviolet visible (UV-Vis) absorbance and 3-dimensional excitation emission matrix ...[more]

PMID: 28821807

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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.

Project description:This study aimed to reveal the distribution characteristics and sources of dissolved organic matter (DOM) in sediments of typical lakes in the southeastern of the Hubei province and provide a reference for pollution control of eutrophic lakes. The sediments of four typical lakes (Liangzi, Baoan, Daye, and Qingshan) in the southeastern of the Hubei Province were investigated in May 2019. Ultraviolet-visible (UV-Vis) absorption spectroscopy and excitation-emission matrixes characteristics of DOM were obtained by UV-Vis spectrophotometry and three-dimensional fluorescence spectroscopy. Moreover, the DOM fluorescence components were resolved by parallel factor analysis (PARAFAC). The results showed that: (1) The absorption coefficient a350 in surface sediments followed the order: Baoan Lake (16.99 ± 3.82 m-1) > Qingshan Lake (15.37 ± 3.8 m-1) > Liangzi Lake (12.54 ± 5.58 m-1) > Daye Lake (12.43 ± 1.43 m-1). Specifically, with increasing depth in the sediment cores, a350 increased and then gradually decreased in Daye Lake and Baoan Lake, but fluctuated in Liangzi Lake and Qingshan Lake with a roughly decreasing trend. (2) Two humic-like components (C1, C2) and one protein-like component (C3) were identified via PARAFAC. This analysis also showed that the surface sediment fluorescent dissolved organic matter (FDOM) was dominated by protein-like, while the sediment core FDOM was dominated by humic-like in Liangzi Lake. The proportion of humic-like in FDOM was higher than protein-like in surface sediments and sediment cores of Baoan, Daye, and Qingshan Lakes. (3) The DOM of surface sediments in the Liangzi Lake comprised mostly autochthonous components, mainly produced by the vital activities of aquatic organisms. The DOM of surface sediments in Baoan Lake and Qingshan Lake showed weak humic and moderate autochthonous characteristics. The humification of DOM in sediment cores of Liangzi, Baoan, and Qingshan Lakes gradually decreased from depth to the surface. The DOM in surface sediments of Daye Lake had strong humic and moderate autochthonous characteristics. (4) In general, the DOM of lake sediments in southeastern Hubei Province has dual-contribution characteristics representing terrigenous and endogenous sources. In the restoration and treatment of lake ecology, both internal and terrestrial pollution should be considered. At the same time, it is noteworthy that cyanobacteria depletion and aquatic residues caused potential internal pollution.

Project description:The determination of copper (Cu) speciation and its bioavailability in natural waters is an important issue due to its specific role as an essential micronutrient but also a toxic element at elevated concentrations. Here, we report an improved anodic stripping voltammetry (ASV) method for organic Cu speciation, intended to eliminate the important problem of surface-active substances (SAS) interference on the voltammetric signal, hindering measurements in samples with high organic matter concentration. The method relies on the addition of nonionic surfactant Triton-X-100 (T-X-100) at a concentration of 1 mg L-1. T-X-100 competitively inhibits the adsorption of SAS on the Hg electrode, consequently 1) diminishing SAS influence during the deposition step and 2) strongly improving the shape of the stripping Cu peak by eliminating the high background current due to the adsorbed SAS, making the extraction of Cu peak intensities much more convenient. Performed tests revealed that the addition of T-X-100, in the concentration used here, does not have any influence on the determination of Cu complexation parameters and thus is considered "interference-free." The method was tested using fulvic acid as a model of natural organic matter and applied for the determination of Cu speciation in samples collected in the Arno River estuary (Italy) (in spring and summer), characterized by a high dissolved organic carbon (DOC) concentration (up to 5.2 mgC L-1) and anthropogenic Cu input during the tourist season (up to 48 nM of total dissolved Cu). In all the samples, two classes of ligands (denoted as L1 and L2) were determined in concentrations ranging from 3.5 ± 2.9 to 63 ± 4 nM eq Cu for L1 and 17 ± 4 to 104 ± 7 nM eq Cu for L2, with stability constants logK Cu,1 = 9.6 ± 0.2-10.8 ± 0.6 and logK Cu,2 = 8.2 ± 0.3-9.0 ± 0.3. Different linear relationships between DOC and total ligand concentrations between the two seasons suggest a higher abundance of organic ligands in the DOM pool in spring, which is linked to a higher input of terrestrial humic substances into the estuary. This implies that terrestrial humic substances represent a significant pool of Cu-binding ligands in the Arno River estuary.

Dataset Information

Sulfate Reduction in Sediments Produces High Levels of Chromophoric Dissolved Organic Matter.

Publications

Sulfate Reduction in Sediments Produces High Levels of Chromophoric Dissolved Organic Matter.

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