Ditch Wetlands Research Articles

Cadmium contamination decreased bacterial network complexity and stability in coastal reclamation areas

Cadmium(Cd) contamination can exert significantly adverse effects on soil microbiota in reclaimed areas, however, its effects on bacterial network structure are still limitedly understood. Here we collected soil samples from typical reclaimed wetlands (RW) and ditch wetlands (DW) in coastal reclamation areas and examined the effects of Cd contamination on the bacterial network complexity and stability. The results showed that the bacterial networks were destabilized by the Cd contamination, while bacteria in DW soils showed robust invulnerability characterized by higher node constancy and compositional stability compared with RW soils. Soil bacteria resisted Cd stress by forming a network with intensive connections in the module but sparser connections among the modules. Especially, network modularity was higher in DW soils than in RW soils, but made it more vulnerable to nodes removal. In addition, Cd contamination promoted bacterial positive cohesion but decreased negative cohesion in RW soils. Flavobacteriaceae, Xanthomonadaceae, and Alcaligenaceae were identified as core phylotypes, which played pivotal roles in regulating interspecies interactions due to higher contributions to cohesion and significant correlations with soil nutrients. The findings of this work indicate the changes of bacterial network structure and the indispensable role of core phylotypes in regulating interactions and maintaining network sustainability under Cd contamination.

Effect of combined cadmium and doxycycline pollution on the nitrogen cycle in constructed ditch wetlands

Effect of combined cadmium and doxycycline pollution on the nitrogen cycle in constructed ditch wetlands

Preservation of Soil Iron-Bound Organic Carbon in a Karst Ditch Wetland: A Case Study in Caohai Lake, China

Preservation of Soil Iron-Bound Organic Carbon in a Karst Ditch Wetland: A Case Study in Caohai Lake, China

A study of typical plant growth changes in response to drainage water and salt in ditch wetland in arid area

Agricultural drainage significantly affected the changes of soil moisture and salinity in ditch wetlands. These changes can profoundly impact the spatial distribution and evolution of ditch wetland vegetation, thereby affecting the ecological environmental effects of these wetlands. Consequently, it is imperative to investigate the response of typical plant growth to drainage and soil salt in ditch wetlands in arid regions. Based on the classical metapopulation conceptual framework model (Levins model), this study established a new model of plant growth change in ditch wetlands, incorporating the key variables (water level and soil salinity) of arid area ditch wetlands. The application of the Gaussian model facilitates the resolution of species growth rates and mortality rates within this model. The study focused on the main drainage ditch (ditch M) and the drainage bucket ditch (ditch N) in the Lubotan saline-alkali land in Fuping, Shaanxi Province. The results revealed the following key findings: 1) the model effectively simulates the response of plant growth changes to water level and soil salinity in ditch wetlands in arid regions, particularly plants in the reed area and transition area disturbed by single factors such as water level and soil salinity; 2) the germination period of Phragmites australis in the reed area thrives in a shallow moisture environment, and adjusting the water level of the drainage ditch can maintain optimal growth conditions for Phragmites australis; 3) during the germination period of Suaeda salsa in the transition area, soil salinity should not be excessively high, though a moderate increase in soil salinity can promote the germination and growth of Suaeda salsa; and 4) Suaeda salsa in the symbiotic area has a higher adaptability to the soil salinity, with change in biomass consistent with plants in the transition area. The model provides an explanation and prediction for the growth changes of plant communities in ditch wetlands under drainage conditions. By integrating this model with the impact of farmland drainage on water level and soil salinity in drainage ditches, effective drainage management measures can be formulated, offering scientific support for the construction of ecological irrigation areas.

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.

The diversity and function of the in-situ fungal communities in response to polycyclic aromatic hydrocarbons in the urban wetland.

PAHs (polycyclic aromatic hydrocarbons) increases the potential harm to ecosystem and human health. The fungi is considered as a powerful choice for degradation of PAHs. The researches on the effect of PAHs on fungal population in sediment/soil mostly stayed in the laboratory simulation that is based on extreme pollution. This study investigated the fungal population of the urban wetland by high-throughput sequencing in-situ micro-pollution state. Our statistical analysis revealed significant difference in the whole fungal population at the phylum among three land use types in typical urban wetland. Among them, Ascomycota was the dominant fungi at the phyla in three land use types. Fungal genus of degrading PAHs were significantly correlated with Dibenz[a, h]anthracene (P = 0.018) in ditch wetland, Total Organic Carbon (P = 0.02) and Fluoranthene (P = 0.04) in riverine wetland, and ElectricalConductivity (P = 0.018) in agricultural land. PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) suggested that 20 enzymes were present related to PAHs metabolism in three land use types. Specifically, monoxygenase, dehydrogenase, and laccase were most abundant among inferred enzymes, indicating that the urban wetland had potential for the degradation of PAHs. This study contributed to in-depth understanding of the structure and function of fungal population and provided a theoretical basis for PAHs microbial remediation in the in-situ environment.

Abundance and characteristics of sediment-bound magnetic minerals and trace elements in karst ditch wetland: A case study from Guizhou Province, China

This study investigated sediment-bound magnetic properties and selected trace elements level in the karst ditch wetland, Caohai National Nature Reserve, Guizhou Province, China. Sediment-bound magnetic signals were quantified using low-frequency mass magnetic susceptibility (χLF), anhysteretic remanent magnetization susceptibility (χARM), saturation isothermal remanent magnetization (SIRM), and percentage frequency-dependent susceptibility (χfd%). Concentrations of Cd, Cr, Sb and Zn were determined using inductively coupled plasma mass spectrometry. Sediment χLF, χARM, SIRM, and χfd% were higher than those of bedrocks and mainly altered by the pedogenic processes. The estimated χfd% ranged from 6.15 % to 14.62 % and reflected the magnetic grain sizes were largely concentrated in the range of superparamagnetic particles. The elevated concentrations of sediment-bound Cd, Cr, Sb, and Zn supported the significant contribution of the anthropogenic sources in the karst ditch wetlands. The weak relationship between magnetic signals and selected trace elements (p < 0.05) suggested the occurrence of few sediment-bound iron-containing minerals associated with selected trace elements. These results indicated that a minor contribution of anthropogenic sources of selected trace elements to the elevated sediment magnetic signals in the karst ditch wetlands.

Optimizing aeration pattern to improve nitrogen treatment performance of ditch wetlands in polder areas around Chaohu Lake, China

Ditch wetlands in polders are planned to attenuate the nitrogen load from paddy fields, mainly resulting in eutrophication of Chaohu Lake, China. The nitrogen treatment performance of ditch wetlands is poor because of the low dissolved oxygen (DO) concentration observed in field. Aeration is often used to improve both DO concentration and nitrogen treatment performance, but aeration pattern needs to be optimized for better treatment performance. A dynamic model was constructed to explore the nitrogen transformation with the DO effect. The simulation results show that through an optimal aeration pattern, the treatment performance of total nitrogen (TN) increased from 3.9% to 23.9% when TN was dominated by ammonium and organic nitrogen (NH4 + ON). The optimal aeration pattern was that the ratio of aeration time to non-aeration time was approximately 1:1, and the aeration cycle period was equal to the experimental period (10 d). The essence of aeration is to ensure that the mass of nitrogen nitrified from NH4 is denitrified, which means that the rate of nitrification is close to that of denitrification. The concentration ratio of (NH4 + ON)/NO3 was a reasonable indicator to determine the aeration time for various composition of TN. Finally, guidelines for drainage water recycling within polders from the point of DO are provided to achieve the objective of nitrogen load reduction in polders.

Co-selective Pressure of Cadmium and Doxycycline on the Antibiotic and Heavy Metal Resistance Genes in Ditch Wetlands.

Abuse of heavy metals and antibiotics results in the dissemination of metal resistance genes (MRGs) and antibiotic resistance genes (ARGs). Ditch wetlands are important sinks for heavy metals and antibiotics. The relationships between bacterial communities and MRG/ARG dissemination under dual stresses of heavy metals and antibiotics remain unclear. The responses of MRGs and ARGs to the co-selective pressure of cadmium (Cd) and doxycycline (DC) in ditch wetlands were investigated after 7-day and 84-day exposures. In ecological ditches, residual rates of Cd and DC varied from 0.4 to –5.73% and 0 to –0.61%, respectively. The greatest total relative abundance of ARGs was observed in the Cd 5 mg L–1 + DC 50 mg L–1 group. A significant level of DC (50 mg L–1) significantly reduced the total relative abundances of MRGs at a concentration of 5 mg L–1 Cd stress. Redundancy analysis indicated that Cd and DC had strong positive effects on most ARGs and MRGs after a 7-day exposure. Meanwhile, the class 1 integron gene (intI1) exhibited strong positive correlations with most ARGs and cadmium resistance genes (czcA) after an 84-day exposure. Network analysis showed that Acinetobacter and Pseudomonas were the potential dominant host genera for ARGs and MRGs, and tetracycline resistance genes (tetA), czcA, and intI1 shared the same potential host bacteria Trichococcus after an 84-day exposure.

Nitrogen and Phosphorus Pollutants Removal from Rice Field Drainage with Ecological Agriculture Ditch: A Field Case

Excessive nitrogen and phosphorus in agricultural drainage can cause a series of water environmental problems such as eutrophication of water bodies and non-point source pollution. By monitoring the water purification effect of a paddy ditch wetland in Gaochun, Nanjing, Jiangsu Province, we investigated the spatial and temporal distribution patterns of N and P pollutants in paddy drains during the whole reproductive period of rice. Then, the dynamic changes of nitrogen and phosphorus in time and space during the two processes of rainfall after basal fertilization and topdressing were analyzed after comparison. At last, the effect of the ditch wetland on nutrient purification and treatment mechanism, along with changing flow and concentration in paddy drains, was clarified. The results of this study showed that the concentrations of various nitrogen and phosphorus in the ditch basically reached the peak on the second and third days after the rainfall (5.98 mg/L for TN and 0.21 mg/L for TP), which provided a response time for effective control of nitrogen and phosphorus loss. The drainage can be purified by the ecological ditch, about 89.61%, 89.03%, 89.61%, 98.14%, and 79.05% of TN, NH4+-N, NO3−-N, NO2−-N, and TP decline. It is more effective than natural ditches for water purification with 80.59%, 40%, 12.07%, 91.06% and 18.42% removal rates, respectively. The results of the study can provide a theoretical basis for controlling agricultural non-point source pollution and improving the water environment of rivers and lakes scientifically.

Combined Pollution of Cadmium and Doxycycline Reduces Denitrification and Anammox Rates But Increases N2o Emission in Constructed Ditch Wetlands

Combined Pollution of Cadmium and Doxycycline Reduces Denitrification and Anammox Rates But Increases N2o Emission in Constructed Ditch Wetlands

Study on drainage strategy of ditch wetland in semi-arid area under the influence of inflow from the upstream irrigation area

Salt drainage from farmlands can potentially degrade the ecological function of ditch wetlands in arid and semi-arid irrigation areas. However, such ditch wetlands may accept different quantities and salt concentrations of upstream inflows, which may have positive or negative effects on the water and salt dynamics of ditch wetland systems and, therefore, on the associated water and salt management measures. In this paper, we propose a new theoretical analysis model that enables us to study the influence of different upstream inflows on the water–salt dynamics and drainage strategies for ditch wetland in the study area. The research carried out by us has revealed that upstream inflow is one of the most important factors influencing ditch wetlands under the current conditions. An increase in salinity or a decrease in flow will negatively affect the ecology of the ditch wetland. In contrast, which will improve the ditch wetland environment. Nevertheless, wetlands are more sensitive to changes in salinity than to the volume of upstream inflow. Based on the combined effects of the salinity and quantity of its inflow on the wetlands, it can be divided into four categories: no-risk, low-risk, medium-risk, and high-risk. The inflow with no risk and low risk will have a positive effect on the ditch wetland system and drainage management, while medium-risk and high-risk conditions will increase the difficulty of drainage management, These results provide the insights needed to guide the design of drainage management practices for ditch wetlands in semi-arid regions that receive upstream inflows to maximize the benefits to the agricultural system and the environment.

Influence of different controlled drainage strategies on the water and salt environment of ditch wetland: A model-based study

Ditch wetlands reduce agricultural nonpoint source pollution and protect the water environment in drainage areas. One effective management option is controlled drainage. However, for ditch wetlands receiving salt-laden drainage water in arid or semi-arid irrigation areas, controlled drainage may lead to eventual build up of salinity to critical levels that are detrimental to the ecological services and agricultural production of wetland systems. In order to evaluate the positive and negative impacts of agricultural practice of using controlled drainage to manage ditch wetlands water quality in arid or semi-arid irrigation area, based on the principle of water-salt balance we constructed an analysis model. A ditch wetland as a case example in semi-arid irrigation area was then used to display model predictions of salinity variations over time under different watertable control depths. The ditch wetland area to farmland area ratio is 0.091, and the input sources of water and salt are not unique. The results showed that the model established by considering various inflows and outflows has higher simulation accuracy. The water stored in the wetland is key to affecting the salt concentration of the wetland, and the amount of water can be regulated by controlled drainage. Controlled drainage changes the hydrological process of farmland and ditch wetlands, reduces drainage output and damage by high concentrations of salt. But this management measure also increases the risk of medium salt concentrations that may cause an increase in salt output. Considering agricultural production and environmental protection of ditch wetlands, the drainage water table controlled at 1.2 m is a suitable drainage management measure in this irrigation area. The results provide the underlying insights needed to guide the design of drainage management practices in ditch wetlands that receive drainage discharge in semi-arid regions that can be sustained to the maximum benefit of the agricultural system and the environment.

Pathways regulating nitrogen removal in constructed ditch wetlands: effects of different inflow ratios and artificial aeration.

Constructed ditch wetland (CDW) is a combination of idle ditch and constructed wetland, which is typically used in rural areas to remove pollutants from domestic wastewater. However, its low total nitrogen (TN) removal remains a pressing issue. To enhance total nitrogen removal, an approach of supplying water at two locations in the CDW at different influent flow ratios, combined with artificial aeration, was proposed to adjust carbon and oxygen distribution in the system. The highest average TN removal was achieved at low influent concentration (CDW4; influent flow ratio 1:2). The removal of TN in winter and spring were 58.93 and 83.26%, respectively. The distribution of carbon sources in the back zone enhanced denitrification. Of the high influent concentration treatments, CDW2 (2:1) achieved 16.97% more TN removal on average compared with CDW1 (3:0), after extra artificial aeration was applied in the front zone. However, nitrification was a limiting step in the system, which became the primary problem preventing pollutant purification. Moreover, nitrifying bacteria abundance was negatively correlated to the influent flow ratio and autotrophic denitrifying bacterial abundance was positively correlated to the influent flow ratios. Graphical abstract.

Effects of coastal reclamation history on heavy metals in different types of wetland soils in the Pearl River Delta: Levels, sources and ecological risks

The human activity of coastal reclamation for agriculture production has caused serious environmental pollution problems and threatened the sustainable development of coastal delta area. Top soils (0–10 cm) were collected to clarify the effects of reclamation years (100y, 40y, 30y and 10y) on heavy metal pollution in reclaimed wetlands and ditch wetlands in Nansha District of the Pearl River Delta. Three parallel samples were also collected from each sampling site. As, Cd, Zn, Cu and Pb were analyzed to assess their concentration levels compared with other deltas. Geoaccumulation index, enrichment factor values, new toxicity evaluation index and principal component analysis were also used in this study. Compared with the reclaimed wetland soils, the highest concentrations of the selected elements were observed in the ditch wetland soils, with the value of Cd (1.97 ± 0.38 mg/kg), As (18.21 ± 4.61 mg/kg), Pb (68.56 ± 6.28 mg/kg), Cu (103.98 ± 23.38 mg/kg) and Zn (250.89 ± 52.35 mg/kg). Meanwhile, the elevated concentrations of heavy metals under the reclamation periods of 10y and 30y were found in two types of wetland soils except for As and Cd, which indicated that the comprehensive interactions of physical and chemical properties of soil, geographical factors, river network transportation and human activities jointly regulated the changes of heavy metal accumulation with wetland types and reclamation years. The highest potential ecological risks of Cd and Cu were observed in ditch wetlands. The sum of the toxic units were lower than 4. The contributing ratios of As (18.66 ± 3.23%) and Cd (12.97 ± 1.73%) were enhanced according to the new toxicity evaluation index compared with the ratios of As (14.70 ± 2.57%) and Cd (11.39 ± 2.35%). All the enrichment factor values of Cd, Zn and Cu exceeded 1.5, implying a large anthropogenic origin. However, the sources of As and Pb in the ditch and reclaimed wetland soils of the Pearl River Delta were generally controlled by the comprehensive effect of the natural, industrial and agricultural sources. Based on the results, key strategies including reducing the amount of pesticide and fertilizer and developing environment-friendly modern agriculture and clean production process were proposed for healthy development of the wetland ecosystems in the Pearl River Delta.

Seeking the hotspots of nitrogen removal: A comparison of sediment denitrification rate and denitrifier abundance among wetland types with different hydrological conditions

Wetlands play a vital role in removing nitrogen (N) from aquatic environments via the denitrification process, which is regulated by multiple environmental and biological factors. Until now, the mechanisms by which environmental factors and microbial abundance regulate denitrification rates in wetlands under different hydrological conditions remain poorly understood. Here, we investigated sediment potential denitrification rate (PDR) and unamended denitrification rate (UDR), and quantified denitrifier abundance (nirS, nirK, and nosZ genes) in 36 stream, river, pond, and ditch wetland sites along the Dan River, a nitrogen–rich river in central China. The result indicated that ditches had the highest denitrification rates and denitrifier abundance. Both PDR and UDR showed strong seasonality, and were observed to be negatively correlated with water velocity in streams and rivers. Moreover, denitrification rates were significantly related to denitrifier abundance and many water quality parameters and sediment properties. Interestingly, PDR and UDR were generally positively associated with N and carbon (C) availability in streams and rivers, but such correlations were not found in ponds and ditches. Using a scaling analysis, we found that environmental parameters, including Reynolds number, sediment total C ratio, and interstitial space, coupled with relative nirS gene abundance could predict the hotspots of denitrification rates in wetlands with varying hydrologic regimes. Our findings highlight that hydrological conditions, especially water velocity and hydrologic pulsing, play a nonnegligible role in determining N biogeochemical processes in wetlands.

Polycyclic aromatic hydrocarbons (PAHs) in surface soils from reclaimed and ditch wetlands along a 100-year chronosequence of reclamation in a Chinese estuary: Occurrence, sources, and risk assessment

The coastal reclamation for agricultural exploitation have caused serious pollution to the soil environment in coastal wetlands. However, few studies have been conducted on the persistent organic pollutants and ecological risks commonly existing in reclaimed coastal wetlands with different reclamation ages, which is of vital importance to alleviate agricultural soil organic pollution and warrantee food safety. Surface soils (0–10 cm) were collected in reclaimed wetlands (RW) and ditch wetlands (DW) along a 100-year chronosequence of intermittent reclamation (i.e., 100-yr, 40-yr, 30-yr, and 10-yr) in the Pearl River Estuary (PRE) of China. The concentrations of 16 Polycyclic aromatic hydrocarbons (PAHs) in soil samples were determined on a GC–MS 2010 QP-plus to investigate their occurrences, sources, and ecotoxic risk levels. The results showed that the total concentrations of PAHs at eight sampling sites ranged from 67.6 to 1172.8 ng·g−1, with a mean of 466.08 ng·g−1. The concentrations of ∑16PAHs in DW soils increased gradually, whereas the concentrations showed a “decreasing before increasing then decreasing” tendency in RW soils along the chronosequence of reclamation. The highest value occurred in the 30-yr soils of RW, which was heavily polluted, and the rest soils were slightly contaminated except for 40R and 100D soils (no pollution). The PAHs were predominantly composed of 2-, 3-, and 5-ring PAHs (the total accounting for >70% of the total 16 PAHs) at most of sampling sites. And the isomers of PAHs were predominantly composed of naphthalene (Nap), phenanthrene (Phe) and benzo(a)pyrene (Bap), and some PAHs isomers (i.e., Nap, Phe, Bap, fluorene (Fle), benz(a)an-thracene (Baa), and dibenz (a,h) anthracene (Daa) occurred predictable toxicity according to the sediment quality guidelines. A significant positive correlation was observed among the heavy Polycyclic aromatic hydrocarbons (HPAHs, including 4-, 5-, and 6-ring PAHs) and total nitrogen (TN), soil moisture and soil organic matter (SOM) in RW soils (p < 0.05), however, most of PAHs isomers were significantly negatively correlated with soil moisture content in DW soils (p < 0.05). According to the ratios of isomers, the combustion of fossil fuels and petroleum emissions were the major sources of PAHs. The highest value of toxic equivalent concentrations (TEQs)/∑PAHs ratios and TEQs appeared in 10-yr DW soils, followed by 100-yr and 30-yr RW soils, which showed higher potential ecological risks mainly because of certain PAH isomers (Bap and Daa) had higher TEQs and ecological risks.

Polycyclic Aromatic Hydrocarbons in Sediments/Soils of the Rapidly Urbanized Lower Reaches of the River Chaohu, China.

Polycyclic aromatic hydrocarbons (PAHs) are highly teratogenic, persistent carcinogens, and ubiquitous environmental pollutants. To determine the impact of rapid urbanization on sediment/soil PAHs, we collected 30 cm soil cores in ditch wetlands, riverine wetlands, and agricultural lands along the lower reaches of the Shiwuli River feeding Chaohu Lake, China. Ecological risk effects were evaluated by two models based upon Benzo[a]pyrene toxic equivalency (TEQ-BaP) and total toxic units (TUs). The presence of PAHs, such as BbF, BkF, InP, and BgP, that are known pollutants of concern, suggests certain ecological risks. The concentration of PAHs in the surface layer followed in the order of: ditch wetlands (617.2 ng/g average), riverine wetlands (282.1 ng/g average), agricultural lands (103.7 ng/g average). PAHs in ditch sediments were vertically distributed evenly, and PAHs in agricultural soils were concentrated in the surface soil. In riverine wetland sediments, the 2-, 3-, and 4-ring PAHs had a uniform distribution, whereas the 5- and 6-ring PAHs were concentrated in the surface soil. Redundancy analysis (RDA) explored the correlation between the environmental properties and the occurrence of PAHs. Total organic carbon (p = 0.010), percent clay (p = 0.020), and distance (p = 0.020) were the primary factors in ditch wetlands. Depth (p = 0.010) and distance (p = 0.006) were the main factors in agricultural lands. There were no significant correlations in riverine wetlands. The correlation between the distance from the built-up urban areas and pollutant concentration showed that the closer the distance, the greater the concentration of PAHs.

Rural domestic wastewater treatment in constructed ditch wetlands: Effects of influent flow ratio distribution

Constructed wetlands (CWs) are a sustainable technology used to remove pollutants from wastewater; however, their low total nitrogen (TN) removal efficiency remains a pressing issue. Constructed ditch wetland systems (CDWs) differ from CWs in being narrow and shallow. This study observed the performance of CDWs throughout their operational period and investigated the causes of their low TN removal rates. To enhance TN removal, we propose an approach where the inflow is divided into two parts with different influent flow ratios. Four systems were trialed in parallel to examine the effects of the influent flow ratio distribution on organics removal and nitrogen transformation. A flow ratio of 1:2 was considered optimal following comparison of the four experimental CDWs. The removal efficiencies of chemical oxygen demand (COD) and TN in the control CDW (influent flow ratio 3:0) during winter were 91.15% and 25.87%, respectively, whereas the removal efficiencies of the best-performing CDW (influent flow ratio 1:2) were 91.59% and 50.40%, respectively. Based on an analysis of nitrogen transformation, a model of effluent TN and nitrate nitrogen concentration in the four CDWs was constructed.

Comprehensive assessment of soil quality for different wetlands in a Chinese delta

AbstractSoil quality is usually considered a powerful tool to reveal soil degradation status and wetland ecosystem health. It is insufficient to reflect actual soil quality based on soil fertility or heavy metal pollution assessment, respectively. A comprehensive assessment was performed to combine soil fertility and heavy metal contamination together, on the basis of 13 soil physical, chemical, biological indicators and six heavy metals, in the Pearl River Delta of China including urban river wetland (URW), ditch wetland (DW), riparian wetland (RiW), and reclaimed wetland (ReW). The moderate fertility level was observed according to the minimum data set, including total nitrogen (TN), microbial biomass carbon (MBC), total phosphorus, total potassium, sand, and salinity. DW soils had significantly higher soil fertility index values than RiW and ReW soils. Low TN, soil organic carbon (SOC), MBC levels, and sandy loam texture revealed potential chemical, biological and physical degradation risks, especially for ReW. In addition, wetland soils were heavily contaminated by heavy metals, particularly for Cd, according to Nemerow Pollution Index. URW soils exhibited significantly higher pollution levels than ReW soils. According to the methodology of comprehensive assessment, soil quality belonged to moderate and low grades because of severe heavy metal pollution, following with moderate nutrition level. Consequently, pollution treatment, fertility (e.g., SOC, N, P, and K), and soil texture improvement are crucial to improving soil quality, preventing further degradation and promoting ecological conservation and sustainability of coastal wetlands in the Pearl River Delta.