Low water level drives high nitrous oxide emissions from treatment wetland

Global environmental change mediated response of wetland plants: Evidence from past decades

Wetland ecosystems are critically affected by global environmental changes, yet understanding the impact of these changes on wetland plants remains a challenge. This review article employs a comprehensive approach, including bibliographic analysis, utilization of various climate models for historical data retrieval, and extensive literature survey, to investigate the response of wetland plants to environmental shifts over the past decades. The analysis conducted in this study uncovers a multitude of climatic parameters that exhibit an influence on the dynamics of wetland vegetation. Results indicated a significant positive trend in atmospheric CO2 concentration, leading to increased water use efficiency in some plant species, particularly C3 plants. However, C4 plants did not show the same positive response. Nitrous oxide growth rate showed a weaker, less consistent trend than CO2, highlighting the need for further investigation into the complex factors influencing Nitrous oxide emissions from wetlands. Methane growth rate and global mean sea level demonstrated a strong positive linear trend. Ocean pH exhibited a statistically significant downward trend (acidification), while sea surface temperature showed a moderate but statistically significant upward trend. Glacier mass balance revealed a significant negative trend. Although some plants may benefit from increased CO2 initially, but the combined effects of rising sea levels, ocean acidification, and temperature changes pose substantial threats to the overall health and diversity of wetland plant life.

Research Status and Development Trend of Greenhouse Gas in Wetlands: A Bibliometric Visualization Analysis

With the intensification of global warming, wetland greenhouse gas (GHG) emissions have attracted worldwide attention. However, the scientific understanding of wetland GHGs is still limited. To gain a comprehensive and systematic understanding of the current research status and development trends in wetland GHGs. We selected 1627 papers related to wetland GHG research from the Web of Science Core Collection database and used the bibliometric visualization analysis method to reveal the annual publication, main core research forces, research hotspots, and trends in this field. The results showed that the research in this field shows a steady upward trend. United States research institutions and scholars play a key role in this field. The research on "climate change" based on three major wetland GHGs (carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)) has been continuously gaining popularity. In recent years, "water" has become an emerging core topic. More and more studies have focused on enhancing wetland pollutant treatment capacity, improving wetland ecosystem productivity, maintaining water level stability, strengthening blue carbon sink function, exploring remote sensing applications in wetlands, and promoting wetland restoration to reduce GHG emissions. Furthermore, we discussed the influencing factors of the emission of CO2, CH4, and N2O in wetlands and summarized the potential methods to reduce GHG emissions. The findings provide scientific guidance and reference on wetland sustainable development and GHG emission reduction.

Assessment of nutrient storage and translocation in winter harvested Typha latifolia from free-water surface treatment wetland mitigating diffuse agricultural pollution

Wetland macrophytes play a critical role in the performance of treatment wetlands (TWs), primarily through nutrient uptake. However, this retention is temporary, as nutrients are released back into the water upon the decomposition of plant litter. The removal of stored nutrients from TWs can be efficiently achieved by harvesting plants during the peak of the growing season, albeit with significant ecological disturbance. Therefore, winter harvesting is recommended, although the specific amounts of nitrogen (N) and phosphorus (P) removed during this period remain uncertain. This study aimed to evaluate the effectiveness of winter harvesting in removing substantial nutrient amounts compared to belowground storage. Experimental harvesting was conducted over five winters (2018, 2019, 2021, 2022, and 2023) at the Vända free-water surface TW system in Estonia, focusing on above-ice biomass (stems, leaves, flowers) and below-ice biomass (roots and rhizomes). The dry weight and nutrient content of these biomasses were analysed. Findings indicated a gradual increase in nutrient pools within Typha latifolia plants, without significant differences between the two subsequent wetlands or a clear correlation with vegetation cover. Winter harvesting of above-ice biomass removed approximately 50 % of plant biomass, and about 30 % of N and P accumulated in the macrophytes, as most nutrients were already stored in the rhizomes by the end of the growing season.

Mitigating N2O emissions in land treatment systems: Mechanisms, influences, and future directions

Land treatment systems (LTS) are widely used in decentralized domestic wastewater treatment due to low energy requirements and effective treatment outcomes. However, LTS operations are also a significant source of N2O emissions, a potent greenhouse gas threatening the ozone layer and posing risks to human health. Despite the importance of understanding and controlling N2O emissions, existing literature lacks comprehensive analyses of the mechanisms driving N2O generation and effective control strategies within LTS. This study addresses this gap by reviewing current research and identifying key factors influencing N2O emissions in LTS. This review reveals that in addition to traditional nitrification and denitrification processes, co-denitrification and complete ammonia oxidation are crucial for microbial nitrogen removal in LTS. Plant selection is primarily based on their nitrogen absorption capacity while using materials such as biochar and iron can provide carbon sources or electrons to support microbial activities. Optimizing operational parameters is essential for reducing N2O emissions and enhancing nitrogen removal efficiency in LTS. Specifically, the carbon-to‑nitrogen ratio should be maintained between 5 and 12, and the hydraulic loading rate should be kept within 0.08-0.2 m3/(m2·d). Dissolved oxygen and oxidation-reduction potential should be adjusted to meet the aerobic or anaerobic conditions the microorganisms require. Additionally, maintaining a pH range of 6.5-7.5 by adding alkaline substances is crucial for sustaining nitrous oxide reductase activity. The operating temperature should be maintained between 20 and 30 °C to support optimal microbial activity. This review further explores the relationship between environmental factors and microbial enzyme activity, community structure changes, and functional gene expression related to N2O production. Future research directions are proposed to refine N2O flux control strategies. By consolidating current knowledge and identifying research gaps, this review advances LTS management strategies that improve wastewater treatment efficiency while mitigating the environmental and health impacts of N2O emissions.

Assessing methane emissions and soil carbon stocks in the Camargue coastal wetlands: Management implications for climate change regulation

Coastal wetlands are crucial in climate change regulation due to their capacity to act as either sinks or sources of carbon, resulting from the balance between greenhouse gas (GHG) emissions, mainly methane (CH4), and soil carbon sequestration. Despite the paramount role of wetlands in climate regulation few studies investigate both aspects. The Camargue is one of the largest wetlands in Europe, yet the ways in which environmental and anthropic factors drive carbon dynamics remain poorly studied. We examined GHG emissions and soil organic carbon (SOC) stocks and accumulation rates in twelve representative wetlands, including two rice fields, to gain insights into the carbon dynamics and how it is influenced by hydrology and salinity. Mean CH4 rates ranged between - 87.0 and 131.0 mg m-2 h-1and the main drivers were water conductivity and redox, water table depth and soil temperature. High emission rates were restricted to freshwater conditions during summer flooding periods whereas they were low in wetlands subjected to summer drought and water conductivity higher than 10 mS cm-1. Nitrous oxide emissions were low, ranging from - 0.5 to 0.9 mg N2O m-2 h-1. The SOC stocks in the upper meter ranged from 17 to 90 Mg OC ha-1. Our research highlights the critical role of low-saline wetlands in carbon budgeting which potentially are large sources of CH4 but also contain the largest SOC stocks in the Camargue. Natural hydroperiods, involving summer drought, can maintain them as carbon sinks, but altered hydrology can transform them into sources. Artificial freshwater supply during summer leads to substantial CH4 emissions, offsetting their SOC accumulation rates. In conclusion, we advocate for readjusting the altered hydrology in marshes and for the search of management compromises to ensure the compatibility of economic and leisure activities with the preservation of the inherent climate-regulating capacity of coastal wetlands.

Regulating greenhouse gas dynamics in tidal wetlands: Impacts of salinity gradients and water pollution

Tidal wetlands play a critical role in emitting greenhouse gases (GHGs) into the atmosphere; our understanding of the intricate interplay between natural processes and human activities shaping their biogeochemistry and GHG emissions remains lacking. In this study, we delve into the spatiotemporal dynamics and key drivers of the GHG emissions from five tidal wetlands in the Scheldt Estuary by focusing on the interactive impacts of salinity and water pollution, two factors exhibiting contrasting gradients in this estuarine system: pollution escalates as salinity declines. Our findings reveal a marked escalation in GHG emissions when moving upstream, primarily attributed to increased concentrations of organic matter and nutrients, coupled with reduced levels of dissolved oxygen and pH. These low water quality conditions not only promote methanogenesis and denitrification to produce CH4 and N2O, respectively, but also shift the carbonate equilibria towards releasing more CO2. As a result, the most upstream freshwater wetland was the largest GHG emitter with a global warming potential around 35 to 70 times higher than the other wetlands. When moving seaward along a gradient of decreasing urbanization and increasing salinity, wetlands become less polluted and are characterized by lower concentrations of NO3-, TN and TOC, which induces stronger negative impact of elevated salinity on the GHG emissions from the saline wetlands. Consequently, these meso-to polyhaline wetlands released considerably smaller amounts of GHGs. These findings emphasize the importance of integrating management strategies, such as wetland restoration and pollution prevention, that address both natural salinity gradients and human-induced water pollution to effectively mitigate GHG emissions from tidal wetlands.

Greenhouse gas production from an intermittently dosed cold-climate wastewater treatment wetland

This study explores the greenhouse gas (GHG) fluxes of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) from a two-stage, cold-climate vertical-flow treatment wetland (TW) treating ski area wastewater at 3 °C average water temperature. The system is designed like a modified Ludzack-Ettinger process with the first stage a partially saturated, denitrifying TW followed by an unsaturated nitrifying TW and recycle of nitrified effluent. An intermittent wastewater dosing scheme was established for both stages, with alternating carbon-rich wastewater and nitrate-rich recycle to the first stage. The system has demonstrated effective chemical oxygen demand (COD) and total inorganic nitrogen (TIN) removal in high-strength wastewater over seven years of winter operation. Following two closed-loop, intensive GHG winter sampling campaigns at the TW, the magnitude of N2O flux was 2.2 times higher for denitrification than nitrification. CH4 and N2O emissions were strongly correlated with hydraulic loading, whereas CO2 was correlated with surface temperature. GHG fluxes from each stage were related to both microbial activity and off-gassing of dissolved species during wastewater dosing, thus the time of sampling relative to dosing strongly influenced observed fluxes. These results suggest that estimates of GHG fluxes from TWs may be biased if mass transfer and mechanisms of wastewater application are not considered. Emission factors for N2O and CH4 were 0.27 % as kg-N2O-N/kg-TINremoved and 0.04 % kg-CH4-C/kg-CODremoved, respectively. The system had observed seasonal emissions of 600.5 kg CO2 equivalent of GHGs estimated over 130-days of operation. These results indicate a need for wastewater treatment processes to mitigate GHGs.