Planting richness affects the recovery of vegetation and soil processes in constructed wetlands following disturbance

Response of key nitrogen removal processes in estuarine salt marshes to different plant harvesting patterns varies significantly across different time scales

Estuarine wetlands are crucial in mitigating eutrophication in estuarine waters through plant uptake and microbial transformation. Nitrogen is one of the main nutrients removed. However, without proper plant harvesting, the nitrogen absorbed by plants can return to the water as litter during autumn and winter, potentially causing secondary pollution. This issue has been underexplored in natural estuarine wetlands. To address this, we conducted an in-situ survey at Chongming Dongtan to examine how nitrogen removal processes respond to different harvesting seasons and frequencies over time. The study found that the response of soil nitrification and denitrification to plant harvesting on tidal flats varied by time scales and harvesting patterns. Short-term responses of soil nitrification and denitrification depended on the harvesting season. Annually, combining plant uptake and soil denitrification, autumn and winter harvesting both improved nitrogen removal, with autumn being the most effective, boosting it by 73.0% and 61.7%, respectively, compared to no harvesting. While harvesting twice in summer and autumn significantly increased plant nitrogen uptake (p < 0.05), the overall removal (316.76 g N m-2) was less than with no harvesting (323.08 g N m-2) when soil denitrification was considered. Redundancy analysis and structural equation modelling indicated that, in the short term, harvesting impacted soil nitrification and denitrification through redox potential (Eh) and temperature, while, annually, the effects primarily depended on the balance between Eh and soil organic carbon (SOC). These results provide practical strategies for large-scale sustainable ecological management of plants in the Yangtze River estuary wetlands.

Relationships between denitrification rates and functional gene abundance in a wetland: The roles of single- and multiple-species plant communities

Wetland soil denitrification removes excess inorganic nitrogen (N) and prevents eutrophication in aquatic ecosystems. Wetland plants have been considered the key factors determining the capacity of wetland soil denitrification to remove N pollutants in aquatic ecosystems. However, the influences of various plant communities on wetland soil denitrification remain unknown. In the present study, we measured variations in soil denitrification under different herbaceous plant communities including single Phragmites karka (PK), single Paspalum thunbergia (PT), single Zizania latifolia (ZL), a mixture of Paspalum thunbergia plus Phragmites karka (PTPK), a mixture of Paspalum thunbergia plus Zizania latifolia (PTZL), and bare soil (CK) in the Estuary of Nantiaoxi River, the largest tributary of Qingshan Lake in Hangzhou, China. The soil denitrification rate was significantly higher in the surface (0-10 cm) than the subsurface (10-20 cm) layer. Wetland plant growth increased the soil denitrification rate by significantly increasing the soil water content, nitrate concentration, and ln(nirS) + ln(nirK). A structural equation model (SEM) showed that wetland plants indirectly regulated soil denitrification by altering the aboveground and belowground plant biomass, nitrate concentration, abundances of denitrifying functional genes, and denitrification potential. There was no significant difference in soil denitrification rates among PT, PK and ZL. The soil denitrification rate was significantly lower in PTZL than PTPK. Two-plant communities did not necessarily enhance the denitrification rate compared to single planting, the former had a greater competitiveness on N uptake and consequently reduced the amount of nitrate available for denitrification. As PTPK had the highest denitrification rate, co-planting P. thunbergia and P. karka could effectively improve N removal efficiency and help mitigate eutrophication in adjacent aquatic ecosystems. The results of this investigation provide useful information guiding the selection of appropriate wetland herbaceous plant species for wetland construction and the removal of N pollutants in aquatic ecosystems.

Exploring the most important indicators for environmental condition assessment using structural equation modeling and InVEST habitat quality model

Land degradation threatens the social welfare of human societies. In order to identify the most important indicators for land degradation assessment, this article quantified 36 vegetation and soil indicators. Ecosystem condition was determined based on the ecosystem threats using the InVEST habitat quality model, dividing the region to five degradation classes, i.e., negligible, little, medium, high, and very high degradation classes. The structural equation modeling showed that vegetation indicators were more important than soil indicators for land degradation assessment. Climate had a significant mediation on the relationships between soil and vegetation indicators and degradation (P < 0.05). Warning indicators were identified for each degradation stage. The mean changes of degradation indicators were 18, 35, 56, and 78% in little, medium, high, and very high degradation classes, respectively. Cold and semi-arid climates were more influenced by vegetation indicators which had the most variations in the early stages of degradation. Warm and arid regions were more affected by soil indicators, which had the most variations in the high and very high degradation stages. This approach provides comprehensive and necessary information about the condition of ecosystems by determining the severity of degradation in an area, the most important warning indicators of degradation, and the deviation of ecosystems from normal condition at each degradation classes, which helps a lot to managers to choose appropriate restoration plans.

Evapotranspiration from Horizontal Subsurface Flow Constructed Wetlands Planted with Different Perennial Plant Species

This paper presents the results of an experiment carried out in Southern Italy (Sicily) on the estimation evapotranspiration (ET) in pilot constructed wetlands planted with different species (Chrysopogon zizanioides, Myscanthus x giganteus, Arundo donax, Phragmites australis, and Cyperus papyrus). In the two monitored growing seasons, reference ET0 was calculated with the Penman-Monteith formula, while actual ET and crop coefficients were measured through a water balance and the FAO 56 approach, respectively. The highest average seasonal ET value was observed in Phragmites australis (17.31 mm d−1) followed by Arundo donax (11.23 mm day−1) Chrysopogon zizanioides (8.56 mm day−1), Cyperus papyrus (7.86 mm day−1), and Myscanthus x giganteus (7.35 mm day−1). For all plants, crop coefficient values showed different patterns in relation to growth stages and were strongly correlated with phenological parameters. Myscanthus x giganteus and Arundo donax showed a water use efficiency values significantly higher than those observed for the other tested species. Results of this study may contribute to select appropriate plant species for constructed wetlands located in semi-arid regions, especially when the use of reclaimed water and/or the use of aboveground biomass are planned.

Designing Wetlands as an Essential Infrastructural Element for Urban Development in the era of Climate Change

The increasing development of urban infrastructure has led to the significant loss of natural wetlands and their ecosystem services. Many novel urban development projects currently attempt to incorporate environmental sustainability, cross-disciplinary collaboration, and community engagement into the intricate challenges we all face in an era of climate change. This paper aims to communicate several key findings on design elements that can be adopted or incorporated in the design of created wetlands as infrastructural elements. Three major design elements—microtopography, hydrologic connectivity, and planting diversity—are presented, and their relations to restoring ecosystem services of urban wetlands, in particular water and habitat quality, are discussed. These design elements can be easily adopted or incorporated in the planning, designing, and construction stages of urban development. The success of urban infrastructure projects may require both better communication among stakeholders and a great deal of community engagement. The Rain Project, a floating wetland project on an urban college campus, demonstrates the role of interdisciplinary collaboration and community engagement as a model for sustainable stormwater management, a critical part of today’s urban development. Further efforts should be made to advance the science of designing urban wetlands and its communication to transform cultural attitudes toward sustainable urban development.