Nitrogen loss in coastal sediments driven by anaerobic ammonium oxidation coupled to microbial reduction of Mn(IV)-oxide.

Coastal sediments play a central role in regulating the amount of land-derived reactive nitrogen (Nr) entering the ocean, and their importance becomes crucial in vulnerable ecosystems threatened by anthropogenic activities. Sedimentary denitrification has been identified as the main sink of Nr in marine environments, while anaerobic ammonium oxidation with nitrite (anammox) has also been pointed out as a key player in controlling the nitrogen pool in these locations. Collected evidence in the present work indicates that the microbial biota in coastal sediments from Baja California (northwestern Mexico) has the potential to drive anaerobic ammonium oxidation linked to Mn(IV) reduction (manganammox). Unamended sediment showed ammonification, but addition of vernadite (δMnO2 with nano-crystal size ∼15 Å) as terminal electron acceptor fueled simultaneous ammonium oxidation (up to ∼400 µM of ammonium removed) and production of Mn(II) with a ratio ∆[Mn(II)]/∆[NH4+] of 1.8, which is very close to the stoichiometric value of manganammox (1.5). Additional incubations spiked with external ammonium also showed concomitant ammonium oxidation and Mn(II) production, accounting for ∼30 % of the oxidized ammonium. Tracer analysis revealed that the nitrogen loss associated with manganammox was 4.2 ± 0.4 µg 30N2/g-day, which is 17-fold higher than that related to the feammox process (anaerobic ammonium oxidation linked to Fe(III) reduction, 0.24 ± 0.02 µg 30N2/g-day). Taxonomic characterization based on 16S rRNA gene sequencing revealed the existence of several clades belonging to Desulfobacterota as potential microorganisms catalyzing the manganammox process. These findings suggest that manganammox has the potential to be an additional Nr sink in coastal environments, whose contribution to total Nr losses remains to be evaluated.

210Pb geochronology and metal concentrations in sediment cores recovered in the Alvarado Lagoon system, Veracruz, Mexico.

Three sediment cores recovered from the Alvarado Lagoon System (ALS) in the Gulf of Mexico were used to reconstruct the history of metals and metalloids and their environmental importance. The sedimentary profiles were dated with 210Pb and verified with 137Cs. Maximum ages of 77 and 86 years were estimated. Sediment provenance was described by sedimentological and geochemical proxies. The chemical alteration index (CIA) and weathering index (CIW) revealed moderate to high intensity of weathering in the source area that is controlled tropical climatic conditions, runoff, and precipitation in the basin that feeds sediments to this coastal lagoon. The Al2O3/TiO2 ratios indicated that the sediments were derived from intermediate igneous rocks. The enrichment factor values revealed the lithogenic and anthropic contribution of metals and metalloids. Cd is classified under the category extremely severe enrichment; agricultural activities, fertilizers, herbicides, and pesticides containing Cd are expected to supply this metal to the ecosystem. Factor Analysis and Principal Components provided two main factors, terrigenous and biological origins; ANOVA indicated that there are significant differences between the cores for the parameters analyzed and revealed that there are differences in depositional environments between the recovery zones of the cores. The ALS presented natural variations associated with the climatic conditions, terrigenous input, and its relationship with the hydrological variations of the main rivers. The contribution of this work was to identify the magnitude of the natural component versus the human contribution, mainly of risk metals such as Cd, to support better management of the hydrological basin that affects the ALS.

Microbial indicators along a metallic contamination gradient in tropical coastal sediments.

The structure and diversity of microbial community inhabiting coastal sediments reflect the exposition to contaminants. Aiming to assess the changes in the microbiota from Sepetiba Bay (SB, Brazil) sediments, correlations between the 16S rRNA gene data (V4-V5 region), metal contamination factors (CF), and the ecological risk classification provided by the Quality Ratio (QR) index were considered. The results show that microbial diversity differs significantly between the less (SB external sector) and the most (SB internal sector) polluted sectors. Also, differences in the microbial community structure regarding the ecological risk classifications validated the QR index as a reliable tool to report the SB chronic contamination. Microbial indicator genera resistant to metals (Desulfatiglans, SEEP-SRB1, Spirochaeta 2, among others) presented mainly anaerobic metabolisms. These genera are related to the sulfate reducing and methanogenic metabolisms probably participating in the natural attenuation processes but also associated with greenhouse gas emissions. In contrast, microbial indicator genera sensitive to metals (Rubripirellula, Blastopirellula, Aquibacter, among others) presented mainly aerobic metabolisms. It is suggested that future works should investigate the metabolic functions to evaluate the influence of metallic contaminants on microbial community inhabiting SB sediment.

Textural characteristics and abundance of microplastics in Tecolutla beach sediments, Gulf of Mexico.

Abundance of microplastics in coastal sediments is considered an emerging pollution problem worldwide. In Mexico, studies focused on microplastics in coastal sediments are little. In this study, we analyzed the textural characteristics and investigated the abundance of microplastics in the Tecolutla beach sediments, SW Gulf of Mexico. The extraction of microplastics in sediments was done by density separation. Microplastics were identified by stereomicroscope and scanning electron microscopy, and were classified based on their morphology, color, length, texture, and abundance. Among 181 microplastics, fiber type is predominant (number of microplastics n = 166; 92%) and followed by film (n = 12; 6%) and fragment (n = 3; 2%) types. The most abundant color of microplastics is black (n = 81; 45%) and second dominant color is blue (n = 65; 36%); most of them are fiber type. Based on the textural characteristics of sediments, it was observed that microplastics were derived from the fluvial contribution of the Tecolutla River and were deposited in the coastal environment by ocean currents. This study revealed that the abundance of microplastics was high in fine-grained sediments and was directly proportional to skewness. The results of this study can act as a reference for understanding the abundance of microplastics in the Gulf of Mexico coastal sediments.

Inferring pollution records in sediment cores from transitional environments of Marquelia coast, Guerrero, Mexico.

The vertical distribution pattern and concentrations of elements (Fe, Al, Ca, Mg, Mn, Cr, Cu, Ni, Co, Pb, Zn, and As) in the estuarine and lagoon region of Marquelia coast, Guerrero, Mexico, were studied to comprehend the origin and pollutant phases of geochemical elements. Henceforth, two sediment core samples [C1 (127 cm) and C2 (110 cm)] were collected to assess the pollution status using geochemical indices, namely anthropogenic factor (AF), enrichment factor (EF), and geoaccumulation index (Igeo). Additionally, the elemental concentrations were compared with the sediment quality guidelines (SQGs) to examine the potential risks to biota. Among the two depositional environments, the sediments of lagoon Apozahualco exhibited higher concentrations of elements. The granulometry characteristics of sediment grains also attested that the concentration and mobilization of metals are largely governed by the fine-grained fractions. Major elemental concentration and grain size changes were identified at several depths (30-40, 60-70, and 90-100 cm) revealing the internal hydrodynamic condition. The overall assessment of geochemical indices revealed that the sediments were unpolluted to moderately polluted. The anthropogenic factor indicated that the upper portion of the sediments were affected by anthropogenic influences. The comparison of trace element concentration with SQGs denoted that Cr, Ni, and As could pose potential adverse effect to the organisms that live in and near the sedimentary environment. Factor analysis revealed the origin and behaviour of the studied elements during transportation and deposition processes in both the ecosystems (i.e. estuary and lagoon). The results of this study provided an in-depth understanding of variations in elemental concentration and pollution status of sediment profile in coastal transitional environments that would aid in sustainable management.

Relevance of carbon burial and storage in two contrasting blue carbon ecosystems of a north-east Pacific coastal lagoon.

Coastal vegetated ecosystems constitute very productive habitats, characterized by efficient Corg sequestration and long-term preservation in sediments, so they play an important role in climate change mitigation. The temporal evolution of Corg content, stocks and burial rates were evaluated in seagrass and salt marsh habitats in San Quintin Bay (northeast Pacific, Mexico) by using 210Pb-dated sediment cores. Salt marsh cores were characterized by fine-grained sediments, higher salinities, lower terrigenous input and lower mass accumulation rates (MAR: 0.01-0.03 g cm-2 yr-1) than seagrass cores (MAR: 0.02-3.21 g cm-2 yr-1). Accumulation rates in both habitats steadily increased throughout the past century most likely because of soil erosion promoted by land use changes in the surroundings. The Corg stocks were highest in salt marsh cores (12.2-53.6 Mg ha-1 at 10 cm depth; 259-320 Mg ha-1 at 1 m depth) than in seagrass cores (5.7-14.4 Mg ha-1, and 80-98, Mg ha-1, respectively), whereas Corg burial rates were considerably lower in salt marsh (13-60 g m-2 yr-1) than in seagrass (9-144 g m-2 yr-1) habitats, and the temporal variations observed in Corg burial rates were mostly driven by changes in the accumulation rates. The overall Corg stock (485 ±â€¯51 Gg C) for both habitats together was comparable to the carbon emissions of a major city nearby. Our results highlight the need to protect these environments as relevant carbon reservoirs.

Trace metal bioavailability in sediments from a reference site, Ribeira Bay, Brazil.

Surface sediments were collected near potential contamination sources impacting Ribeira Bay (Brazil), a system considered as a 'reference site' for trace metals. Physicochemical properties (pH and Eh), grain size and concentrations of total organic carbon (TOC), total phosphorus (TP), acid-volatile sulfides (AVS) and simultaneously-extracted metals (Fe, Mn, Cd, Cu, Ni, Pb and Zn) were analyzed. Although relatively low metal concentrations were found, correlations of Zn and Ni with high TP levels suggested an association with sewage inputs, while other metals presented associations with specific geochemical carriers (TOC, Fe and Mn compounds). AVS levels exceeding those of the sums of Cd, Cu, Ni, Pb and Zn (ΣSEM) by at least one order of magnitude and TOC-normalized differences between ΣSEM and AVS ((ΣSEM-AVS)/fOC) near to or below than -200µmolgOC(-1) indicated that there were sufficient AVS and TOC levels to control trace metal bioavailability in sediment pore water.

Diverse Bacterial Groups Contribute to the Alkane Degradation Potential of Chronically Polluted Subantarctic Coastal Sediments.

We aimed to gain insight into the alkane degradation potential of microbial communities from chronically polluted sediments of a subantarctic coastal environment using a combination of metagenomic approaches. A total of 6178 sequences annotated as alkane-1-monooxygenases (EC 1.14.15.3) were retrieved from a shotgun metagenomic dataset that included two sites analyzed in triplicate. The majority of the sequences binned with AlkB described in Bacteroidetes (32 ± 13 %) or Proteobacteria (29 ± 7 %), although a large proportion remained unclassified at the phylum level. Operational taxonomic unit (OTU)-based analyses showed small differences in AlkB distribution among samples that could be correlated with alkane concentrations, as well as with site-specific variations in pH and salinity. A number of low-abundance OTUs, mostly affiliated with Actinobacterial sequences, were found to be only present in the most contaminated samples. On the other hand, the molecular screening of a large-insert metagenomic library of intertidal sediments from one of the sampling sites identified two genomic fragments containing novel alkB gene sequences, as well as various contiguous genes related to lipid metabolism. Both genomic fragments were affiliated with the phylum Planctomycetes, and one could be further assigned to the genus Rhodopirellula due to the presence of a partial sequence of the 23S ribosomal RNA (rRNA) gene. This work highlights the diversity of bacterial groups contributing to the alkane degradation potential and reveals patterns of functional diversity in relation with environmental stressors in a chronically polluted, high-latitude coastal environment. In addition, alkane biodegradation genes are described for the first time in members of Planctomycetes.