The vegetation in constructed wetlands (CWs) plays an important role in wastewater treatment. Popularly, the common emergent plants in CWs have been vegetation of natural wetlands. However, there are ornamental flowering plants that have some physiological characteristics similar to the plants of natural wetlands that can stimulate the removal of pollutants in wastewater treatments; such importance in CWs is described here. A literature survey of 87 CWs from 21 countries showed that the four most commonly used flowering ornamental vegetation genera were Canna, Iris, Heliconia and Zantedeschia. In terms of geographical location, Canna spp. is commonly found in Asia, Zantedeschia spp. is frequent in Mexico (a country in North America), Iris is most commonly used in Asia, Europe and North America, and species of the Heliconia genus are commonly used in Asia and parts of the Americas (Mexico, Central and South America). This review also compares the use of ornamental plants versus natural wetland plants and systems without plants for removing pollutants (organic matter, nitrogen, nitrogen and phosphorous compounds). The removal efficiency was similar between flowering ornamental and natural wetland plants. However, pollutant removal was better when using ornamental plants than in unplanted CWs. The use of ornamental flowering plants in CWs is an excellent option, and efforts should be made to increase the adoption of these system types and use them in domiciliary, rural and urban areas.

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Abstract:The high costs involved in treating wastewater are problems that developing countries confront, mainly in rural areas. Therefore, Constructed Wetlands (CWs), which are composed of substrate, vegetation, and microorganisms, are an economically and ecologically viable option for wastewater treatment in these places. There is a wide variety of possibilities for substrates and ornamental plants that have not yet been evaluated to be implemented in future CW designs. The goal of this study was to evaluate the process of adaptation and removal of wastewater pollutants in CW microcosms using different terrestrial ornamental plants (Lavandula sp., Spathiphyllum wallisii, and Zantedeschia aethiopica). Those plants were sown in two types of substrate: red volcanic gravel (RVG) and polyethylene terephthalate (PET). CWs with vegetation reduced 5-day biochemical oxygen demand (BOD 5 ) by 68% with RVG substrate and 63% with PET substrate, nitrates 50% in RVG substrate and 35% in PET substrate, phosphates 38% in RVG substrate and 35% in PET substrate, and fecal coliforms 64% in RVG and 59% in PET substrate). In control microcosms without vegetation, reductions were significantly lower than those in the presence of plants, with reduction of BOD 5 by 61% in RVG substrate and 55% in PET substrate, nitrates 26% in RVG substrate and 22% in PET substrate, phosphates 27% in RVG substrate and 25% in PET substrate. Concerning fecal coliforms 62% were removed in RVG substrate and 59% in PET substrate. Regarding the production of flowers, Lavandula sp. did not manage to adapt and died 45 days after sowing and did not produce flowers. Spathiphyllum wallisii produced 12 flowers in RVG and nine flowers in PET, while Zantedeschia aethiopica produced 10 in RVG and 7 in PET. These results showed that the use of substrates made of RVG and PET is a viable alternative to be implemented in CWs. In addition, the reuse of PET is an option that decreases pollution by garbage. The plants Spathiphyllum wallisii and Zantedeschia aethiopica remarkably contribute in the removal of pollutants in wastewater. Additionally, the use of ornamental plants, with commercial interest such as those evaluated, enables an added value to the CW to be given, which can be used for flower production purposes on a larger scale and favor its acceptance within rural communities.

Wetlands play an important role in carbon cycling. Perturbation of these ecosystems by human activities causes changes in the soil carbon storage and carbon gaseous emissions. These changes might have important repercussions for global warming. The aim of this study was to investigate whether the conversion of freshwater forested wetlands (FW) to flooded grasslands (FGL) has affected soil carbon cycling. Soil carbon pools and soil organic carbon (SOC) fractions (water-soluble carbon (WSC), hot-water-soluble carbon (HWSC), and HCl/HF soluble carbon (HCl/HF-SC)) were compared between FW and FGL. Additionally, the seasonal dynamic of methane (CH 4) and carbon dioxide (CO 2) fluxes were monitored in both ecosystems located in the coastal plain of Veracruz State Mexico. In FW, soil organic matter (SOM) concentrations were significantly (P ≤ 0.05) higher than FGL. Soil bulk density (BD) was slightly higher in FGL than FW but it was not significantly different (P ≥ 0.05). The average of WSC and HWSC in FW were not significantly (P ≤ 0.05) different. Total carbon pools (44 cm deep) were not significantly different (P = 0.735). During the dry season, CO 2 fluxes (26.38 ± 4.45 g m −2 d −1) in FGL were significantly higher (P = 0.023) than in FW (14.36 ± 5.77 g m −2 d −1). During the rainy and windy seasons, both CH 4 and CO 2 fluxes were significantly higher (P = 0.000 and P = 0.001) in FGL compared with FW. It was concluded that converting FW to FGL causes loss of SOC and increases carbon gaseous fluxes.