Wetlands are among the most biologically active ecosystems on Earth, playing an important role in the global carbon cycle. Methane production in wetlands, resulting from anaerobic respiration of organic matter, accounts for an important part of natural sources of methane. In this work, we have evaluated the methane release rates of saline shallow lakes located in Central Spain, some of which maintain natural conditions, whereas others are hydrologically altered, with lowered salinity, or even presenting trophic alterations. We used sediment core plus water incubations to determine the release of methane from the studied lakes to the atmosphere, integrating both diffusion and ebullition processes, as well as the effects of temperature and salinity on methane production. The studied hypersaline lakes released methane at rates within the lowest range reported for temperate lakes and wetlands, whereas in hydrologically altered lakes that have dropped their salinity these rates were markedly higher. Models built with the specific response of methane release rates to temperature regarding the temperature changes expected according to the RCP climate scenarios predicted significant increases of these rates for the future, which could almost double current methane release for some of the studied lakes under the most pessimistic mitigation scenario (RCP8.5).

Deltaic wetlands are highly productive ecosystems, which characteristically can act as C-sinks. However, they are among the most threatened ecosystems, being very vulnerable to global change, and require special attention towards its conservation. Knowing their climate change mitigating potential, conservation measures should also be oriented with a climatic approach, to strengthen their regulatory services. In this work we studied the carbon biogeochemistry and the specific relevance of certain microbial guilds on carbon metabolisms of the three main types of deltaic wetlands located in the Ebro Delta, north-eastern Spain, as well as how they deal with human pressures and climate change effects. We estimated the metabolic rates of the main carbon-related metabolisms (primary production and respiration) and the resulting carbon and global warming potential balances in sites with a different salinity range and trophic status. With the results obtained, we tried to define the influence of possible changes in salinity and trophic level linked to the main impacts currently threatening deltaic wetlands, on the C-metabolisms and GHG emissions, for a better understanding of the mitigating capacity and their possible enhancement when applying specific management actions. Metabolic rates showed a pattern highly influenced by the salinity range and nutrients inputs. Freshwater and brackish wetlands, with higher nutrient inputs from agricultural runoff, showed higher C-capture capacity (around 220–250 g C m^-2 y^-1), but also higher rates of degradative metabolisms (aerobic respiration and CH₄ emissions). Contrastingly, the rates of C-related metabolisms and C-retention of Salicornia-type coastal salt marshes were lower (42 g C m^-2 y^-1). The study of the microbial metacommunity composition by the16S RNA gene sequencing revealed a significant higher presence of methanogens in the salt marsh, and also higher metabolic potential, where there was significantly more organic matter content in sediment. Salinity inhibition, however, explained the lower respiration rates, both aerobic and anaerobic, and prevented higher rates of methanogenesis despite the major presence of methanogens. Conservation measures for these wetlands would require, overall, maintaining the sediment contributions of the river basin intending to overcome the regression of the Delta and its salt marshes in a climate change scenario. Particularly, for reducing degradative metabolisms, and favour C-retention, nutrient inputs should be controlled in freshwater and brackish wetlands in order to reduce eutrophication. In salt marshes, the reduction of salinity should be avoided to control increases in methanogenesis and CH₄ emissions.

Permanent freshwater and brackish marshes are the typical wetland type of the Mediterranean Spanish coast. Historically, alterations to the original morphological and hydrological characteristics of some these ecosystems have increased their trophic status, which could influence the carbon (C) balance, while other ecosystems remain close to their natural condition. In this work, the main processes related to the C cycle were studied in several Mediterranean coastal marshes with different degrees of alteration and in sites restored and managed in different ways. Carbon associated with greenhouse gases (CO₂ and CH₄) was determined using gas exchange methods for plankton, benthos, and sediments, as well as net production estimations for helophytes, to determine the influence of wetland conservation status, restoration, and management practices on C balances. Freshwater and brackish marshes showed capacity for C capture, especially in the restored sites (∼950 g m⁻² yr⁻¹), with a paramount role of helophytes. Differences among the study sites revealed the importance of alterations and restoration for C exchange. Specifically, a highly altered site showed increased rates of aerobic respiration compared to undisturbed sites, with a decrease in C storage capacity to ∼50 g m⁻² yr⁻¹. Management practices resulting in instability of the organic sediments favoured degradative metabolism, with release of stored C and concomitant increases in CH₄ emissions. Our results indicate that the hydromorphological alterations in these sites may convert healthy ecosystems contributing to C sequestration and climate change mitigation into C-emitting ecosystems.

This work aims to validate the wide use of an algorithm developed using genetic programing (GP) techniques allowing to discern between water and non-water pixels using the near infrared band and different thresholds. A total of 34 wetlands and shallow lakes of 18 ecological types were used for validation. These include marshes, salt ponds, and saline and freshwater, temporary and permanent shallow lakes. Furthermore, based on the spectral matching between Landsat and Sentinel-2 sensors, this methodology was applied to Sentinel-2 imagery, improving the spatial and temporal resolution. When compared to other techniques, GP showed better accuracy (over 85% in most cases) and acceptable kappa values in the estimation of water pixels (κ ≥ 0.7) in 10 of the 18 assayed ecological types evaluated with Landsat-7 and Sentinel-2 imagery. The improvements were especially achieved for temporary lakes and wetlands, where existing algorithms were scarcely reliable. This shows that GP algorithms applied to remote sensing satellite imagery can be a valuable tool to monitor water coverage in wetlands and shallow lakes where multiple factors cause a low resolution by commonly used water indices. This allows the reconstruction of hydrological series showing their hydrological behaviors during the last three decades, being useful to predict how their hydrological pattern may behave under future global change scenarios.

The effluents from conventional wastewater treatment plants (WWTP), even if accomplishing quality regulations, substantially differ in their characteristics with those of waters in natural environments. Constructed wetlands (CWs) serve as transitional ecosystems within WWTPs, mitigating these differences and restoring natural features before water is poured into the natural environment. Our study focused on an experimental surface-flow CW naturalizing the WWTP effluent in a semiarid area in Eastern Spain. Despite relatively low pollutant concentrations entering the CW, it effectively further reduced settled organic matter and nitrogen. Dissolved organic matter (DOM) reaching the CW was mainly protein-like, yet optical property changes in the DOM indicated increased humification, aromaticity, and stabilization as it flowed through the CW. Flow cytometry analysis revealed that the CW released less abundant but more active bacterial populations than those received. MiSeq Illumina sequencing highlighted changes in the prokaryotic community composition, with phyla Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria dominating the CW outflow. Functional prediction tools (FaproTax and PICRUSt2) demonstrated a shift towards microbial guilds aligned with those of the natural aquatic environments, increased aerobic chemoheterotrophs, photoautotrophs, and metabolic reactions at higher redox potentials. Enhanced capabilities for degrading plant material correlated well with changes in the DOM pool. Our findings emphasize the role of CWs in releasing biochemically stable DOM and functionally suited microbial populations for natural receiving environments. Consequently, we propose CWs as a naturalization nature-based solution (NBS) in water-scarce regions like the Mediterranean, where reclaimed discharged water can significantly contribute to ecosystem's water resources compared to natural flows.

The features of lentic waterbodies largely depend on the surrounding environment. Mediterranean coastal lagoons have been historically altered, with their catchment being highly modified for agricultural, livestock, or urban uses. Changes in land uses induce pressures that impact the waterbodies and alter their ecological status. The objectives of this paper were: to develop a methodological approach (LUPLES: Land Uses for estimating Pressure Levels to approach the Ecological Status), to quantify the main pressures on the waterbodies and to forecast the possible impacts of these pressures on their ecological status. Corine-Land Cover maps and Geographic Information System technics were used to delineate and identify land uses in the catchments. Specific algorithms were created to quantify the main pressures from land uses in the catchment and hydro-morphological alterations in the immediate basin. The values of the estimated pressure levels were correlated with ecological status indicators using metrics developed for the European Water Framework Directive. Data were obtained from European and River Basin Authorities databases. Results showed statistically significant correlations between the pressure levels quantified by the LUPLES method and the impact level detected by biological, physical and chemical metrics. This method provides a useful approach to estimate the pressure levels affecting lentic waterbodies and could be applied to approach how they could affect their ecological status.