Wetlands For Removal Research Articles

Application of Floating Beds Constructed with Woodchips for Nitrate Removal and Plant Growth in Wetlands

Constructed wetlands and constructed floating wetlands are widely used for nitrogen (N) removal from surface water to combat eutrophication in freshwaters. Two main N removal pathways in freshwaters are plant biomass N uptake and denitrification, i.e. transformation of nitrate (NO3-) to nitrous oxide (N2O) or nitrogen gas (N2) by different microbes possessing nirK, nirS, nosZI, and nosZII genes. In this study, we tested woodchips-based floating beds (WFBs) as a nature-based and environment-friendly method to remove nitrate-nitrogen (NO3-N) from water. Moreover, we tested whether WFBs could support the growth of three selected plant species and the abundance of microbes on plant roots and woodchips as a proxy for WFBs’ denitrification potential. We conducted a greenhouse experiment for 90 days and measured NO3-N removal rates from water in WFBs mesocosms during five sampling occasions. Plant biomass production, biomass N uptake, and plant morphology related to N uptake and abundance of denitrifying organisms were measured at the end of the experiment. NO3-N removal rates were 29.17 ± 11.07, 28.18 ± 12.62, 25.28 ± 9.90, and 22.16 ± 7.79 mg L–1 d–1 m–2 (mean ± standard deviation) in Glyceria maxima, Juncus effusus, Filipendula ulmaria, and unplanted WFBs treatments, respectively for whole experimental period. N content in above- and belowground biomass of studied species ranged between 0.98 – 1.15 and 1.09 – 1.28 (% dry weight), respectively. Plant relative biomass production was 215 ± 61, 67 ± 18, and 7 ± 17 (% dry weight) for G. maxima, J. effusus and F. ulmaria, respectively. Denitrifiers were detected both on plant roots and woodchips, indicating WFBs’ denitrification potential. Our study highlights that WFBs could be applied to enhance NO3-N removal from surface water through plant biomass uptake and denitrification processes. Future studies should consider the long-term in situ application of WFBs for NO3-N removal from water.

Rhizosphere-Associated Anammox Bacterial Diversity and Abundance of Nitrogen Cycle-Related Functional Genes of Emergent Macrophytes in Eutrophic Wetlands.

Rhizospheric microbial community of emergent macrophytes plays an important role in nitrogen removal, especially in the eutrophic wetlands. The objective of this study was to identify the differences in anammox bacterial community composition among different emergent macrophytes and investigate revealed the the main factors affecting on the composition, diversity, and abundance of anammox bacterial community. Results showed that the composition, diversity, and abundance of the anammox community were significantly different between the vegetated sediments of three emergent macrophytes and unvegetated sediment. The composition of the anammox bacterial community was different in the vegetated sediments of different emergent macrophytes. Also, the abundance of nitrogen cycle-related functional genes in the vegetated sediments was found to be higher than that in the unvegetated sediment. Canonical correspondence analysis (CCA) and structural equation models analysis (SEM) showed that salinity and pH were the main environmental factors influencing the composition and diversity of the anammox bacterial community and NO2--N indirectly affected anammox bacterial community diversity by affecting TOC. nirK-type denitrifying bacteria abundance had significant effects on the bacterial community composition, diversity, and abundance of anammox bacteria. The community composition of anammox bacteria varies with emergent macrophyte species. The rhizosphere of emergent macrophytes provides a favorable environment and promotes the growth of nitrogen cycling-related microorganisms that likely accelerate nitrogen removal in eutrophic wetlands.

Detection of large-scale Spartina alterniflora removal in coastal wetlands based on Sentinel-2 and Landsat 8 imagery on Google Earth Engine

The invasion of Spartina alterniflora has posed significant threats to the ecosystem health and biodiversity in coastal wetlands in China. In recent years, China has enacted large-scale S. alterniflora removal projects. Accurate monitoring of the S. alterniflora removal dynamics is crucial for evaluating the effectiveness of the removal projects and coastal wetland management. In this study, we presented a novel method for automatic and rapid detection of S. alterniflora removal events and removal timing at large scale based on time series Sentinel-2 and Landsat 8 imagery on Google Earth Engine. The method first detected and reconstructed the tidal-inundation-related Normalized Difference Vegetation Index (NDVI) using a newly proposed Tide Gap Filling algorithm, aiming to alleviate the impact of tidal inundation on S. alterniflora removal detection; then, the potential removal period were extracted based on the reconstructed NDVI time series; finally, the removal event and the corresponding removal timing were identified and mapped within the potential removal period by considering the phenological characteristics of the undisturbed S. alterniflora. We took the Shandong Province in northern coastal China and Fujian Province in southern coastal China as our study areas, where large-scale S. alterniflora removal projects were carried out in 2021 and 2022, respectively. Accuracy assessment based on field surveys and high-spatial-resolution PlanetScope imagery showed that the method achieved good accuracies for removal detection, with overall accuracies of 88.89 % for Shandong and 81.33 % for Fujian, respectively. The mean absolute error day (MAED) between the detected removal timing and the reference removal timing was 6.77 days in Shandong and 13.75 days in Fujian. Both provinces have successfully implemented the S. alterniflora removal projects. In Shandong, 82.32 % (7,243.94 ha) of S. alterniflora were removed during July to December in 2021; in Fujian, 88.81 % (6,649.21 ha) of S. alterniflora were removed during July to December in 2022. We expect that the method has great potential to be applied at national scale to provide baseline data for coastal wetland restoration and management.

Addressing the C/N imbalance in the treatment of irrigated agricultural water by using a hybrid constructed wetland at field-scale

To mitigate excess of nitrate-N (NO3−-N) derived from agricultural activity, constructed wetlands (CWs) are created to simulate natural removal mechanisms. Irrigated agricultural drainage water is commonly characterized by an organic carbon/nitrogen (C/N) imbalance, thus, C limitation constrains heterotrophic denitrification, the main biotic process implicated in NO3−-N removal in wetlands. We studied a pilot plant with three series (169 m2) of hybrid CWs over the first two years of functioning to examine: i) the effect of adding different C-rich substrates (natural soil vs. biochar) to gravel on NO3−-N removal in a subsurface flow (Phase I), ii) the role of a second phase with a horizontal surface flow (Phase II) as a source of dissolved organic C (DOC), and its effect in a consecutive horizontal subsurface flow (Phase III) on NO3−-N removal, and iii) the contribution of each phase to global NO3−-N removal. Our results showed that the addition of a C-rich substrate to gravel had a positive effect on NO3−-N removal in Phase I, with mean efficiencies of 40% and 17% for soil and biochar addition, respectively, compared to only gravel (0.75%). In Phase II, the algae growth turned into a DOC concentration increase, but it did not enhance NO3−-N removal in Phase III. In series with C-rich substrate addition, the largest contribution to NO3−-N removal was found in Phase I. However, in series with only gravel, Phase II was the most effective on NO3−-N removal. Contribution of Phase III to NO3−-N removal was almost negligible.

Invasive Spartina alterniflora accelerates the increase in microbial nitrogen fixation over nitrogen removal in coastal wetlands of China

Salt marsh plants play a vital role in mediating nitrogen (N) biogeochemical cycle in estuarine and coastal ecosystems. However, the effects of invasive Spartina alterniflora on N fixation and removal, as well as how these two processes balance to determine the N budget, remain unclear. Here, simultaneous quantifications of N fixation and removal via 15N tracing experiment with native Phragmites australis, invasive S. alterniflora, and bare flats as well as corresponding functional gene abundance by qPCR were carried out to explore the response of N dynamics to S. alterniflora invasion. Our results showed that N fixation and removal rates ranged from 0.77 ± 0.08 to 16.12 ± 1.13 nmol/(g·h) and from 1.42 ± 0.14 to 16.35 ± 1.10 nmol/(g·h), respectively, and invasive S. alterniflora generally facilitated the two processes rates. Based on the difference between N removal and fixation rates, net N2 fluxes were estimated in the range of −0.39 ± 0.14 to 8.24 ± 2.23 nmol/(g·h). Estimated net N2 fluxes in S. alterniflora stands were lower than those in bare flats and P. australis stands, indicating that the increase in N removal caused by S. alterniflora invasion may be more than offset by N fixation process. Random forest analysis revealed that functional microorganisms were the most important factor associated with the corresponding N transformation process. Overall, our results highlight the importance of N fixation in evaluating N budget of estuarine and coastal wetlands, providing valuable insights into the ecological effect of S. alterniflora invasion.

Stable isotopes of nitrate (δ15N and δ18O) as functional indicators of nitrogen processing in constructed wetlands

The effectiveness of nitrogen removal in wetlands relies heavily on the biological processes that control its removal. Here, we used δ15N and δ18O of nitrate (NO3−) to assess the presence and the dominance of transformation processes of nitrogen in two urban water treatment wetlands in Victoria, Australia over two rainfall events. Laboratory incubation experiments were undertaken in both light and dark to measure the isotopic fractionation factor of nitrogen assimilation (by periphyton and algae) and benthic denitrification (using bare sediment). Highest isotopic fractionations were observed for nitrogen assimilation by algae and periphyton in the light, 15ε = −14.6 to −25 ‰ while the 15ε = −1.5 ‰ in bare sediment, consistent with that of benthic denitrification. Transect water samplings of the wetlands showed different rainfall patterns (discrete versus continuous) affect the removal capability of the wetlands. During the discrete event sampling, the observed 15ε of NO3− (an average of 3.0 to 4.3 ‰) within the wetland falls between the experimental 15ε of benthic denitrification and assimilation; coinciding with the decrease in NO3− concentrations, suggesting that both denitrification and assimilation were important removal pathways. Depletion of δ15N-NO3− throughout the whole wetland system also suggested the influence of water column nitrification during this time. In contrast, during continuous rain events, no fractionation effect was observed within the wetland and was consistent with limited NO3− removal. The difference in fractionation factors within the wetland during different sampling conditions suggested that nitrate removal was highly likely limited by changes in overall nutrient inputs, residence time and water temperature which impeded biological uptake or removal. These highlight that consideration of sampling condition is crucial when assessing the efficacy of a wetland in removing nitrogen.

An integrated watershed-scale framework to model nitrogen transport and transformations

Excess nitrogen in water bodies is associated with a number of environmental problems, including hypoxia and eutrophication. Originating from anthropogenic activities such as fertilizer application, and influenced by watershed characteristics such as the structure of the drainage network, stream discharge, temperature, and soil moisture, factors influencing nitrogen transport and transformation are many and interconnected. This paper describes the development and application of a process-oriented nitrogen model based on the modeling framework of PAWS (Process-based Adaptive Watershed Simulator) that can describe coupled hydrologic, thermal and nutrient processes. The integrated model was tested for an agricultural watershed with complex land use, namely the Kalamazoo River watershed in Michigan, USA. Nitrogen transport and transformations on the landscape were modeled by representing multiple sources and processes (fertilizer/manure application, point sources, atmospheric deposition, nitrogen retention and removal in wetlands and other lowland storage, etc.) across multiple hydrologic domains (streams, groundwater, soil water). The coupled model provides a tool to examine nitrogen budgets and to quantify the impacts of human activities and agricultural practices on the riverine export of nitrogen species. Model results indicate that the river network removed approximately 5.96 % of the total anthropogenic nitrogen input to the watershed, and that the riverine export of nitrogen accounted for 29.22 % of the total anthropogenic inputs during 2004–2009 while the groundwater contribution of nitrogen to the rivers during the same period was found to be 18.53 % highlighting the important role of groundwater within the watershed.

The effects of cold frozen conditions on nitrogen removal and transformation in wetlands purifying wastewater: Insights from combined full- and pilot-scale observations

In wastewater treatment, wetlands are regarded as cost-efficient and sustainable purification systems. Currently, different types of wetland are used for year-round treatment of municipal wastewater (the polishing step after the secondary or tertiary units) in cold climate regions. However, there is a lack of understanding regarding the effect of freezing cold conditions on pollutant removal processes, in particular regarding those linked to nitrogen cycling. This study evaluated the effect of cold winter conditions on contaminant removal, with a focus on nitrogen transformation and removal in a pond-type surface flow wetland with reed (Reed-SF) and a peat-based horizontal subsurface flow (Peat-HSSF) wetland. Year-round full-scale wetland monitoring was complemented with pilot-scale laboratory experiments, which allowed to follow the cold-climate induced effects on contaminant removal and nitrogen processes, along with other water quality, environmental, and microbial parameters. Overall, it was observed that the effect of cold climate conditions on nitrogen removal was dependent on the wetland type in combination with the quality of the inflow water. When treating ammonium (NH4) rich wastewater, removal of total nitrogen (Ntot), as well as NH4, was higher in the Peat-HSSF than in the Reed-SF wetland. Under frozen conditions, NH4 removal decreased slightly but remained positive in the pilot Peat-HSSF, whereas it declined and even turned into leaching in the pilot Reed-SF wetland. Conditions encountered in the Peat-HSSF wetlands (high abundances of active nitrifying bacteria, high levels of dissolved oxygen (DO) and redox potential) supported nitrification, which continued under cold conditions. Whereas in the Reed-SF, a low abundance of active nitrifying bacteria was found, especially in the water column under frozen conditions. DO here was low and decreased in cold conditions with ice cover.

Development of a novel sizing approach for passive mine water treatment systems based on ferric iron sedimentation kinetics

The removal of dissolved and particulate iron (Fe) from contaminated mine drainage is an omnipresent challenge in, and legacy of, the mining industry worldwide. The sizing of settling ponds and surface-flow wetlands for passive Fe removal from circumneutral, ferruginous mine water is based either on a linear (concentration-independent) area-adjusted removal rate or flat assignment of an experience-based retention time, neither of which reflects the underlying Fe removal kinetics. In this study, we evaluated the Fe removal performance of a pilot-scale passive system operating in three identical, parallel lines for treatment of mining-influenced, ferruginous seepage water to determine and parameterise a robust, application-orientated model approach for sizing of settling ponds and surface-flow wetlands, each. By systematically varying flow rates (and thus residence time), we were able to demonstrate that the sedimentation-driven removal of particulate hydrous ferric oxides in settling ponds may be approximated by a simplified first-order approach at low to moderate Fe levels. The first-order coefficient was found in the order of 2.1(±0.7) × 10−2 h−1, which corresponds well with previous laboratory studies. The sedimentation kinetics may be combined with the preceding Fe(II) oxidation kinetics to estimate the required residence time for pre-treatment of ferruginous mine water in settling ponds. In contrast, Fe removal in surface-flow wetlands is more complex due to the phytologic component, which is why we advanced the established area-adjusted Fe removal approach by parameterising the underlying concentration-dependency for polishing of pre-treated mine water. The quantitative results of this study provide a novel, conservative approach for customised sizing of settling ponds and wetlands in integrated passive mine water treatment systems.

Wetland Removal Mechanisms for Emerging Contaminants

In recent decades, previously unobserved trace compounds have become more widely detected in wastewater treatment effluents and freshwater ecosystems. Emanating from various sources and presenting potential human health and ecological risks at much lesser concentrations than traditional contaminants, detection of “emerging contaminants” has increased with improvements in analytical techniques. The behavior of emerging contaminants in wetlands is a topic of increasing interest, as natural wetlands are known to transform and sequester pollutants and constructed or treatment wetlands are widely utilized to address elevated concentrations of constituents of concern. Both natural and constructed wetlands are complex biogeochemical systems with interrelated abiotic and biotic mechanisms leading to the removal of emerging contaminants. A literature review was performed to assess the current state of knowledge of various wetland mechanisms involved in removing these contaminants from surface waters and effluents. The primary mechanisms discussed in the literature are sorption, photodegradation, microbial biodegradation and phytoremediation. The most influential mechanisms are dependent on the properties of the contaminants and wetland systems studied. Common trends exist for different constructed wetland designs to leverage various mechanisms based on hydrology, substrate and vegetation plantings. Much remains to be understood about the various processes occurring in wetlands as they relate to emerging contaminant removal. Improving the understanding of the potential role of wetland mechanisms can help manage this environmental challenge more effectively.

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

Documenting the impacts of increasing salinity in freshwater and coastal ecosystems: Introduction to the special issue

Low-level cadmium alleviates the disturbance of doxycycline on nitrogen removal and N2O emissions in ditch wetlands by altering microbial community and enzymatic activity

Excessive use of feed additives and chemical fertilizers leads to the accumulation of antibiotics and heavy metals in water environments. Studies have reported the toxicity of combined pollutants on the performance and microbial community in sequencing batch reactors. However, the influence of combined pollutants on nitrogen removal in wetlands remains unclear. Here, an 84 d exposure experiment was conducted to investigate the effects of cadmium (Cd) and doxycycline (DC) on nitrogen metabolism in ecological ditches using metagenomic analysis. The results showed that adding 50 mg L−1 DC at 5 mg L−1 Cd stress deteriorated nitrogen removal performance and significantly increased N2O emissions and lactate dehydrogenase release. However, a low level of Cd (0.5 mg L−1) significantly reduced N2O emissions under the high DC concentration pressure (50 mg L−1). The increasing Cd concentration markedly weakened the inhibition of DC (1 mg L−1) on the relative abundances of the dominant genera. Moreover, high concentrations of mixed Cd/DC showed stronger inhibitory effects on glucokinase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase. NADH had a higher tolerance to mixed Cd/DC than ATP. However, low levels of mixed Cd/DC led to a higher abundance of key denitrifying enzymes and genes. The assimilatory nitrate reduction pathway increased under the mixture of Cd/DC stress, accompanied by an increase in ferredoxin-nitrite/nitrate reductase and the abundance of nasA and nirA genes. Our results indicate that the presence of low-level Cd could alleviate the impact of DC on nitrogen removal and N2O emissions in ecological ditches by altering microbial community and enzymatic activity associated with transport, metabolism, and gene expression. However, the increasing Cd concentration at DC stress could intensify the combined toxicity. Overall, our findings provide new insights into the ecological toxicity of emerging combined pollutants and their impact on biological nitrogen transformation in wastewater treatment systems.

Assessing runoff sensitivity of North American Prairie Pothole Region basins to wetland drainage using a basin classification-based virtual modelling approach

Abstract. Wetland drainage has been pervasive in the North American Prairie Pothole Region. There is strong evidence that this drainage increases the hydrological connectivity of previously isolated wetlands and, in turn, runoff response to snowmelt and rainfall. It can be hard to disentangle the role of climate from the influence of wetland drainage in observed records. In this study, a basin-classification-based virtual modelling approach is described that can isolate these effects on runoff regimes. The basin class which was examined, entitled Pothole Till, extends throughout much of Canada's portion of the Prairie Pothole Region. Three knowledge gaps were addressed. First, it was determined that the spatial pattern in which wetlands are drained has little influence on how much the runoff regime was altered. Second, no threshold could be identified below which wetland drainage has no effect on the runoff regime, with drainage thresholds as low as 10 % in the area being evaluated. Third, wetter regions were less sensitive to drainage as they tend to be better hydrologically connected, even in the absence of drainage. Low flows were the least affected by drainage. Conversely, during extremely wet years, runoff depths could double as the result of complete wetland removal. Simulated median annual runoff depths were the most responsive, potentially tripling under typical conditions with high degrees of wetland drainage. As storage capacity is removed from the landscape through wetland drainage, the size of the storage deficit of median years begins to decrease and to converge on those of the extreme wet years. Model simulations of flood frequency suggest that, because of these changes in antecedent conditions, precipitation that once could generate a median event with wetland drainage can generate what would have been a maximum event without wetland drainage. The advantage of the basin-classification-based virtual modelling approach employed here is that it simulated a long period that included a wide variety of precipitation and antecedent storage conditions across a diversity of wetland complexes. This has allowed seemingly disparate results of past research to be put into context and finds that conflicting results are often only because of differences in spatial scale and temporal scope of investigation. A conceptual framework is provided that shows, in general, how annual runoff in different climatic and drainage situations will likely respond to wetland drainage in the Prairie Pothole Region.

Effect of erythromycin on epiphytic bacterial communities and water quality in wetlands

The occurrence of antibiotics such as erythromycin (ERY) under macrolide group, has long been acknowledged for negatively affecting ecosystems in freshwater environments. However, the effects of ERY on water quality and microbial communities in epiphytic biofilms are poorly understood. Here, Scanning Electron Microscopy (SEM), High-throughput sequencing, and physicochemical analytical methods were employed to unravel the impact of ERY on the water quality and bacterial morphology, biodiversity, composition, interaction, and ecological function in epiphytic biofilms attached to Vallisneria natans and artificial plants in mesocosmic wetlands. The study showed that ERY exposure significantly impaired the nutrient removal capacity (TN, TP, and COD) and altered the epiphytic bacterial morphology of V. natans and artificial plants. ERY did not affect the bacterial α-diversity. Notwithstanding ERY decreased the bacterial composition, but the relative abundance of Proteobacteria and Patescibacteria spiked by 62.2 % and 54 %, respectively, in V. natans, while Desulfobacteria and Chloroflexi increased by 8.9 % and 11.2 %, respectively, in artificial plants. Notably, ERY disturbed the food web structure and metabolic pathways such as carbohydrate metabolism, amino acid metabolism, energy metabolism, cofactor and vitamin metabolism, membrane transport, and signal transduction. This study revealed that ERY exposure disrupted the bacterial morphology, composition, interaction or food web structure, and metabolic functions in epiphytic biofilm. These data underlined that ERY negatively impacts epiphytic bacterial communities and nutrient removal in wetlands.

Crab bioturbation affects competition between microbial nitrogen removal and retention in estuarine and coastal wetlands

As the important benthic animal in coastal wetlands, crab bioturbation may significantly affect the nitrogen (N) budgets by regulating microbial N transformation processes. However, the response of interaction between different microbial N processes to crab bioturbation remains poorly understood. Here, a 30-day microcosmic experiment was conducted using sediment collected from the Yangtze Estuary wetland, followed by the determination of temporal variations of physicochemical parameters, N removal (denitrification plus anammox, which is defined as N2 production) and retention rates (nitrate dissimilatory reduction to ammonium, DNRA) as well as relevant gene abundances in response to different crabs densities. The results showed that crab bioturbation simultaneously promoted the rates of N2 production and DNRA processes. These two process rates were positively associated with the intensity of crab bioturbation, which was supported by molecular analysis of relevant functional gene abundance. Crab bioturbation was more beneficial to DNRA than N2 production. Due to this disproportionate stimulation, crab bioturbation increased the importance of DNRA, indicating that N retention was becoming more significant under crab bioturbation in estuarine and coastal wetlands. The variations of sediment total organic carbon and oxygen availability driven by crab bioturbation were the critical factors mediating the changes in microbial N removal and retention. Overall, our findings highlighted that crab bioturbation can affect the N budgets in estuarine and coastal wetlands by altering the competition between microbial N removal and retention.

Impacts of nano-titanium dioxide toward Vallisneria natans and epiphytic microbes

In this study, Vallisneria natans plants were exposed to 5 and 20 nm of titanium dioxide nanoparticles (TiO₂ NPs) anatase and 600–1000 nm of bulk at 5 and 20 mg/L for 30 days. SEM images and EDX spectra revealed that epiphytic biofilms were more prone to TiO₂ NPs adhesion than bare plant leaves. TiO₂ NPs injured plant leaf cells, ruptured epiphytic diatoms membranes and increased the ratio of free-living microbes. The TN, NH4⁺-N and NO3ˉ-N concentrations significantly decreased, respectively, by 44.9%, 33.6%, and 23.6% compared to bulk treatments after 30 days due to macrophyte damage and a decline in diversity of epiphytic bacterial community and abundance of nitrogen cycle bacteria. TiO₂ NPs size-dependent decrease in bacterial relative abundance was detected, including phylum Cyanobacteria, Planctomycetes, and Verrucomicrobia. Although TiO₂ NPs increased eukaryotic diversity and abundance, abundances of Bacillariophyceae and Vampyrellidae classes and Gastrotricha and Phragmoplastophyta phylum decreased significantly under TiO₂ NPs exposure compared to bulk and control. TiO₂ NPs reduced intensities of interaction relationships among epiphytic microbial genera. This study shed new light on the potential effects of TiO₂ NPs toxicity toward aquatic plants and epiphytic microbial communities and its impacts on nitrogen species removal in wetlands.

A framework to identify priority wetland habitats and movement corridors for urban amphibian conservation

Abstract Cities worldwide are expanding in area and human population, posing multiple challenges to amphibian populations, including habitat loss from removal of wetlands and terrestrial upland habitat, habitat fragmentation due to roads and the built environment, and habitat degradation from pollutants, extensive human use and introduced species. We developed an eight‐step urban amphibian conservation framework based on established monitoring, analytical methods and community engagement to enable amphibian conservation in a large urban centre. The framework outlines a process used to conserve biodiversity in a complex landuse and decision‐making environment supported by a series of successive complementary modelling techniques to measure amphibian presence, priority habitat and functional connectivity. We applied the framework in Calgary, Alberta, Canada to illustrate its potential. Here, urbanization has reduced wetlands by 90% and ecological knowledge on amphibians was poor. We improved knowledge on amphibian diversity and distribution, identified core wetlands and movement pathways for amphibian species and identified barriers in the wetland network where construction or restoration measures could re‐establish amphibians or increase their densities. This knowledge was shared with ecologists and city planners for implementation through appropriate policies and plans. Our framework provides a series of stepwise products to improve an urban municipality's ability to restore or conserve priority habitat and movement pathways necessary for amphibian survival under pressure from multiple land uses. The framework provides a platform to identify city plans, policy and or programmes and to derive necessary information to support amphibian conservation.

Disentangling the roles of plant functional diversity and plaint traits in regulating plant nitrogen accumulation and denitrification in freshwaters

Abstract There is a growing recognition that functional measures of diversity, based on quantification of functionally important species traits, are useful for explaining variation in ecosystem processes. However, the mechanisms linking functional diversity to different processes remain poorly understood, hindering development of a predictive framework for ecosystem functioning based on species traits. The current understanding of how the functional traits of aquatic plants (macrophytes) affect nitrogen (N) cycling by regulating microbial communities and their activity in freshwater habitats is particularly limited. Denitrifying bacteria are typically associated with the roots of both aquatic and terrestrial plants and denitrification is the main cause of loss of N from ecosystems. Disentangling the interplay between plants and microbial denitrifiers is key to understanding variation in rates of denitrification from local to landscape scales. In a mesocosm experiment, we varied the species richness (monocultures or two‐species mixtures) and composition of macrophytes. We quantified effects of both macrophyte functional diversity, quantified as functional trait dissimilarity, and functional trait composition, quantified as community weighted mean trait values, on N removal in wetlands. We used structural equation modelling to disentangle the direct and indirect influences of traits on N accumulation in plant biomass, denitrification activity and abundance of key bacterial denitrification genes (nirS and nirK). Both functional diversity and functional trait composition regulated N removal, explaining 70%–94% variation in the underlying ecosystem processes. Increased macrophyte functional diversity increased plant N accumulation, and indirectly enhanced denitrification by increasing denitrification gene abundance. Among traits, greater plant relative growth rates, specific leaf area and above‐ground biomass increased plant N accumulation. Denitrification activity increased with increasing below‐ground biomass but decreased with increasing root diameter. These findings improve our understanding of N removal in freshwater wetlands dominated by macrophytes, and have broad ecological implications for wetland management targeting enhanced ecosystem services. Our results highlight the potential for optimizing denitrification and plant N accumulation in wetlands and thereby improving water purification by increasing macrophyte functional diversity and ensuring the presence of key traits in macrophyte assemblages. A free Plain Language Summary can be found within the Supporting Information of this article.

Dynamics of nutrient release from solid carbon sources of wetland plants and its effect on the efficiency of nitrogen removal from artificial wetland water bodies

污水低碳氮比(C/N)是影响人工湿地氮去除效果限制因素，传统的碳源添加及利用存在成本较高、补充困难的局限性. 本研究契合“就地取材，原位处理”的废物利用原则，选择人工湿地常见的水生植物和农业废弃物(玉米芯、稻草)作为对照，对比了挺水植物(香蒲、美人蕉)、浮叶植物(莲)、沉水植物(菹草)、湿生植物(南荻、短尖苔草)的释碳能力，初步确定了以香蒲、美人蕉、南荻为代表的植物具有较好的释放碳能力，在中国湿地中分布广泛，且均对水体二次污染较小. 以南荻、美人蕉、玉米芯作为碳源添加的模拟人工湿地实验验证表明，在低碳氮比的模拟表流人工湿地投入植物碳源，能有效提高系统的脱氮效率，对照组、南荻组、美人蕉组和玉米芯组的出水总氮浓度分别为(5.24±0.07)、(4.50±0.10)、(3.75±0.17)和(2.97±0.18)mg/L，对应的去除率分别为58%、64%、70%和76%，确定南荻和美人蕉植物残体以及改性材料均残体和改性材料适合作为人工湿地中原位利用的外加碳源. 本研究探索了通过湿地植物配置解决人工湿地水体低C/N比的问题，为提高湿地脱氮效果提供了有意义的新途径.;The low carbon to nitrogen ratio (C/N) of wastewater is a limiting factor of nitrogen removal in artificial wetlands, and traditional carbon sources are costly and difficult to replenish. This study, taking aquatic plants and agricultural wastes (corn cobs and rice straw) which commonly exist in artificial wetlands as a reference, compared the carbon release capacity of water-supporting plants (Typha orientalis and Canna indica), floating-leaf plants (Nelumbo nucifera), submerged plants (Potamogeton crispus), and wet plants (Triarrhena lutarioriparia and Carex brevicuspis). The results show that the plants, such as Typha orientalis, Canna indica and Triarrhena lutarioriparia, which widely distribute in wetlands of China, have high carbon release capacities and have less secondary pollution to water bodies. The experiments of artificial wetlands added with Triarrhena lutarioriparia, Typha orientalis and corn cob as carbon source explored that addition of plant carbon source in the surface flow of artificial wetlands with low C/N ratio could effectively improve the denitrification efficiency of the system. Total nitrogen concentration of the control group, Triarrhena lutarioriparia group, Typha orientalis group and corn cob group were (5.24±0.07), (4.50±0.10), (3.75±0.17) and (2.97±0.18) mg/L, respectively. Correspondingly, the removal rates account for 58%, 64%, 70% and 76%, respectively. It is confirmed that plant residues and modified materials of Triarrhena lutarioriparia and Canna indica were appropriate as an in-situ source of additional carbon in artificial wetlands. Exploring the low C/N ratio in artificial wetlands through wetland plant configuration would provide a new way to improve wetland denitrification.

Seasonal impoundment management reduces nitrogen cycling but not resilience to surface fire in a tidal wetland

Hydrology and salinity regimes of many impounded wetlands are manipulated to provide seasonal habitats for migratory waterfowl, with little-known consequences for ecosystem structure and function. Managed hydrology can alter ecosystems by directly changing soil properties and processes and by influencing plant community dynamics. Additionally, management history may influence ecosystem response to disturbance, including fires. To better understand how wetland management regime influences ecosystem response to disturbance, we quantified elevation, soil nitrogen concentrations and process rates, and plant community structure and diversity in a natural experiment following the 2018 Branscombe Fire. We measured paired burned-unburned patches in both tidally-influenced and managed, seasonally-impounded wetlands in Suisun Marsh, California, USA. Unburned ecosystem structure and nutrient cycling differed by wetland management history; unburned impounded wetlands were ∼1 m lower in elevation and plant community composition was dominated by succulents whereas the unburned tidal wetland was dominated by graminoids. Unburned impounded wetland soil nitrogen cycling (potential nitrification and denitrification) rates were <28% of those measured in unburned tidal wetland soils and soil extractable nitrate, ammonium, and dissolved inorganic phosphorus concentrations were also substantially lower in unburned impounded than unburned tidal wetlands. Despite these differences in pre-disturbance (i.e., unburned) conditions, all soil processes recovered to baseline levels within 6 months after surface fire, and we found no evidence of plant community change 1 year after fire in either wetland management type. Overall, water management history exerted stronger control on ecosystem processes and structure than surface fire disturbance. Low extractable soil nitrate and potential denitrification rates may indicate limitation of soil nitrogen removal in impounded wetlands, with implications for downstream environmental quality and eutrophication across managed landscapes.