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The change in the community structure of phytoplankton and bacterioplankton, and in the degree of coupling between them as well as the environmental conditions, have substantial impacts on the transfer of energy to higher trophic levels and finally on the fate of organic matter. The microbial community structure, usually described only by the abundance of the different taxonomic or functional groups, can be extended to include other levels of descriptors, like physiological state and single-cell properties. These features play a role in the ecological regulation of microbial communities but are not generally studied as additional descriptors of the community structure. Here, we show the changes in abundance and single-cell characteristics based on flow cytometry measurements of picocyanobacteria, photoautotrophic pico- and nanoeukaryotes, and heterotrophic bacteria during the rainy and dry seasons along the estuarine gradient of the inner Gulf of Nicoya. The spatiotemporal distribution of these microbial assemblages showed different patterns in surface and bottom waters along the estuarine gradient and seasonally, both in their abundances and single-cell traits, which suggest differences in their ecological regulation. The changes in the structure of the microbial community along the estuary correlated most significantly with the changes in environmental variables during the dry season. This seems to occur due to changes in salinity, concentration and lability of DOC, concentration of DIN and PO 4 3- and net community production, largely affected by the differences in the river flow. In addition, during the dry season, small-size phytoplankton and bacterioplankton assemblages, characterised by abundance and single-cell traits, presented a higher level of coupling, leading to a more complex ecological network with respect to the rainy season., (Copyright © 2024. Published by Elsevier B.V.)

This study examines long-term burial rates of organic carbon (OC), organic nitrogen (ON), and total sulphur (TS) in a tidal-dominated coastal wetland with a high spatial heterogeneity and habitat diversity, and long history of human impacts, Cádiz Bay (SW Spain). Using replicate sediment cores, we quantified fluxes of these elements over a transect, extending from the lower saltmarsh (Spartina maritima, ~0.3 m mean sea level, MSL) to the lower intertidal region (Zostera noltei, ~ - 0.7 m MSL). Potential organic matter (OM) sources to the sediment were examined using an extensive dataset on carbon and nitrogen stable isotopes, and C:N molar ratios of primary producers in the region. OC burial rates decreased from the sites below MSL (~80 gC·m -2 ·y -1 ) to the lower saltmarsh (~50 gC·m -2 ·y -1 ), whereas ON burial rates showed an opposite pattern (~3 gN·m -2 ·y -1 and ~4 gN·m -2 ·y -1 observed below and above MSL, respectively). TS burial rates (0.5-46 gS·m -2 ·y -1 ) did not show any trend along the sea-land gradient. Hence, (tidal) elevation appeared to be an important determinant of sediment biogeochemical properties, and predictor of OM burial rates. The Bayesian mixing model suggested a well-mixed combination of subtidal and terrestrial/high-marsh OM sources to the surface sediments, with no clear indication of an increased contribution from the particular vegetation species inhabiting the sediments. The indication that there is substantial transport, remineralization and cycling of OM between habitats, suggests diversity may play an important role in maintaining this function, reinforcing the idea that a holistic, catchment-scale view is appropriate for understanding and preserving the long-term burial of OM in coastal wetlands., Competing Interests: Declaration of competing interest The authors declare no actual or potential conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The discharge of acid mine drainage (AMD) into a reservoir may seriously affect the water quality. To investigate the metal transfer between the water and the sediment, three cores were collected from the Sancho Reservoir (Iberian Pyrite Belt, SW Spain) during different seasons: turnover event; oxic, stratified period; anoxic and under shallow perennially oxic conditions. The cores were sliced in an oxygen-free atmosphere, after which pore water was extracted by centrifugation and analyzed. A sequential extraction was then applied to the sediments to extract the water-soluble, monosulfide, low crystallinity Fe(III)-oxyhydroxide, crystalline Fe(III)-oxide, organic, pyrite and residual phases. The results showed that, despite the acidic chemistry of the water column (pH<4), the reservoir accumulated a high amount of autochthonous organic matter (up to 12 wt.%). Oxygen was consumed in 1mm of sediment due to organic matter and sulfide oxidation. Below the oxic layer, Fe(III) and sulfate reduction peaks developed concomitantly and the resulting Fe(II) and S(II) were removed as sulfides and probably as S linked to organic matter. During the oxic season, schwertmannite precipitated in the water column and was redissolved in the organic-rich sediment, after which iron and arsenic diffused upwards again to the water column. The flux of precipitates was found to be two orders of magnitude higher than the aqueous one, and therefore the sediment acted as a sink for As and Fe. Trace metals (Cu, Zn, Cd, Pb, Ni, Co) and Al always diffused from the reservoir water and were incorporated into the sediments as sulfides and oxyhydroxides, respectively. In spite of the fact that the benthic fluxes estimated for trace metal and Al were much higher than those reported for lake and marine sediments, they only accounted for less than 10% of their total inventory dissolved in the column water., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The effect of macroalgal blooms on the abundance and community structure of intertidal sediment meiofauna was studied using an in situ enclosure experiments (Bay of Cádiz, Spain). Meiofaunal abundance (3500-41,000 ind 10 cm⁻²) was three to sevenfold higher in the presence of macroalgae. Nematoda were the dominant taxon both in Control (52-82%) and Macroalgae plots (92-96%), followed by Harpacticoida Copepoda and Ostracoda. Non-metric Multi-Dimensional Scaling (MDS) analysis clearly separated the meiofaunal community from Control and Macroalgae plots. Organic matter, organic carbon, total nitrogen, chlorophyll a and freeze-lysable inorganic nutrients were higher in Macroalgae plots, and were highly correlated with the horizontal MDS axis separating Control and Macroalgae meiofaunal communities. Meiofaunal abundance and taxonomic composition in the Bay of Cádiz seem to be bottom-up controlled either through a grazer system based on microphytobenthos in bare sediments or through a decomposer system in macroalgae affected sediments., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The effects of floating macroalgae (250 g DW m(-2)) on photoautotrophic microbenthos were studied in a flow-through mesocosm with a parallel mesocosm without macroalgae serving as Control. Vertical microprofiles of O(2) at the sediment-water interface showed a immediate and complete suppression of photosynthetic activity of microphytobenthos (MPB) under the macroalgal canopy, resulting in a shift of benthic metabolism from autotrophic to heterotrophic. MPB abundance and chlorophyll a content decreased and a change from a diatom-dominated to cyanobacteria-dominated community was observed. Inorganic nitrogen nutrients' concentrations increased in the porewater as a result of the inhibition of MPB nutrient demand, leading to an increase in net ammonification and anaerobic NO(x)(-) consumption rates. No organic matter transfer from macroalgae to the sediment was detected, resulting in a net consumption of the carbon and nitrogen stored in the sediment. In consequence, sediment was progressively impoverished in nitrogen, reducing sediment nutrient regeneration., (Copyright © 2011 Elsevier Ltd. All rights reserved.)