Abstract: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).
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.
Deltaic wetlands are highly productive ecosystems, which characteristically can act as Csinks. 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, northeastern 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 CH 4 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.
Constructed wetlands are commonly used for sewage treatment. However, as the natural processes operate, these artificial ecosystems can also be used to enhance the equalization of water features to those of the receiving environments, thus reducing the impacts of the treated water on the natural systems. Here, we studied, by a year-round survey, the simultaneous and separated operation of two subsurface wetlands that were used as a tertiary treatment to enhance the naturalization of wastewaters that had already been treated in a waste water treatment plant (WWTP). These wetlands were operating serially, with the first wetland being covered by the riparian plant Helosciadum nodiflorum, which has not been described so far as being used in treatment wetland, whereas the second was covered by Typha latifolia. The changes in the concentrations and transformation among the different types of pollutants and other physical and chemical parameters, as well as in the bacterial abundance and activity, were studied under different operational conditions of serial cooperation or of separately-operating wetlands. Both wetlands were differentially efficient in the reduction and transformation of the remaining pollutants, with very active nitrification and denitrification processes, which reduced the ammonium concentrations by more than 65%, although they changed according to the operational status of each wetland. They also reduced the already low organic matter contents by around 30% and promoted slight shifts in the dominant types of dissolved organic matter to less labile compounds. To a certain extent, the Typha-covered wetland also contributed to phosphorus removal, by up to 35%. Noticeably, both of the wetlands contributed greatly to the reduction of bacterial abundance, which was even 50% lower after the wetland transit, although the resulting community increased its activity, thus keeping the capacity for pollutant removal and transformation. Overall, the wetlands' operation increased the similarity between the poured waters and those of the receiving stream, thus diminishing its environmental impact.
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