Much research has been published regarding the relation between major gas hydrate accumulations and the global carbon cycle. In this context, the determination of the sulfate/methane interface (SMI) depth is of primary importance in order to understand the dynamics of methane flux in the shallow section. This paper identifies the depth of the SMI in sediments based on sulfate and methane concentration profiles in cores recovered in the Rio Grande Cone Gas Hydrate Province, Pelotas Basin, southern Brazil. The shape of methane and sulfate concentration profiles in the sediments can be linked to the local methane flux rate as follows: (i) near linear, high upward-diffusing methane flux coupled with high sulfate diffusion from seawater; (ii) irregular, variable methane flux rates; and (iii) kink-type profile, which is indicative of variable rather than strictly high upward methane flux. The areas in which a high methane flux was identified are spatially associated with gas chimneys in sediments within pockmarks, whereas profiles with low methane flux are present in adjacent areas. These chimneys appear as acoustic blankings in seismic records and can therefore be mapped in subsurface. The wavy-like seismic reflection following the SMI coincides with the occurrence of authigenic carbonate nodules and concretions. In addition, high methane fluxes and the occurrence of concretions and nodules carbonates were correlated by stratigraphic position of the concretions bearing intervals and sulfate profiles.

The search for low-cost and sustainable adsorbents for dye removal has driven the valorization of agro-industrial residues. In this study, pecan nutshells (PNSs) were evaluated as a biosorbent for methylene blue (MB) removal. The material was prepared by drying, grinding, and alkaline treatment with NaOH, which led to an increase in the apparent surface area (0.974 m²·g^–1) and pore volume (0.0014 cm³·g^–1). Surface characterization revealed the involvement of hydroxyl, carboxyl, and aromatic functional groups in the interaction with the dye molecules. The adsorption of MB by PNSs exhibited high efficiency, even at low dosages, and optimal performance was observed at 1.5 g·L^–1. The process remained essentially pH-independent across the 4–10 range. Equilibrium data were analyzed using the Langmuir, Freundlich, Dubinin–Radushkevich, and Sips isotherm models. Among them, the Sips model provided the best fit to the experimental data, yielding a maximum adsorption capacity of 317.5 mg·g^–1 at 25 °C, which is consistent with a heterogeneous surface presenting finite saturation. The thermodynamic parameters (ΔH° = +12.32 kJ·mol^–1; ΔG° = −13.43 kJ·mol^–1 at 25 °C; ΔS° = +86.27 J·mol^–1·K^–1) indicate that the adsorption process is spontaneous and endothermic, with an enthalpy change characteristic of weak to moderate interactions. Kinetic data were best described by the pseudo-second-order model, with equilibrium reached within approximately 180 min. Intraparticle diffusion analysis revealed a multistep adsorption involving an initial boundary-layer diffusion followed by a slower pore diffusion. Overall, the adsorption mechanism is interpreted as multifactorial, governed by hydrogen bonding, π–π stacking, and van der Waals forces, consistent with a physisorption-dominated process strengthened by structural heterogeneity. These results demonstrate that PNS combines high capacity with operational simplicity, representing a scalable and sustainable alternative for the treatment of dye-contaminated wastewater.