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The Wanshan mercury mine, which is an abandoned mine located in northeastern Guizhou Province in Southwest China, has introduced serious Hg pollution to the local ecosystem resulting from previous mining and smelting activities. However, it is not clear to date whether soil pollution has actually improved after treatment by related departments. Therefore, the present study investigates the vegetation community and heavy metal contents of the soil and plants in the Wanshan mercury mining area. The results showed that most of Hg, Cd, As, Cu, and Zn contents in soil samples were higher than those of Soil Environment Quality Risk Control Standard for Soil Contamination of Agricultural Land in China (GB15618-2018). The observed plant species mainly consisted of Compositae, followed by Leguminosae. Unfortunately, this investigation found that heavy metal concentrations in these plants were not extremely high and far below the standard of hyperaccumulator. Despite all this, the maximum values of bioaccumulation factor for Pb, Cd, Hg, As, Cu and Zn were Serissa japonica (Thunb.) Thunb., Rhus chinensis Mill., Potentilla sibbaldii Haller f., Erigeron canadensis L., Clerodendrum bungei var. bungei. and Rhus chinensis Mill., respectively. Regardless of the carcinogenic or noncarcinogenic risk index, the potential risk to urban children is higher. Our results suggest that heavy metal pollution was indeed relieved since their contents in soil significantly decreased in comparison with those reported in other previous studies. This finding provides a reference for the long-term treatment of heavy metal pollution in the local environment and other areas employing analogous environmental protection measures.

Tidal marsh wetlands in the Yellow River Delta provide valuable eco-services to the local population and global ecology. However, this area is suffering from serious degradation under the stresses of social development and climate change. Hydrological connectivity, a new framework in hydrology and ecology, has been proposed as the main factor affecting the ecological processes in coastal wetlands; however, its role in hydrology–soil–vegetation interactions remains unclear. In this study, the researchers parametrically quantified the hydrological connectivity in the tidal marsh wetlands and analyzed its relationship with Phragmites australis, one of the dominant species in this area. Our results showed threshold-like effects on the interaction between hydrological connectivity and P. australis on the plot scale. When biomass is lower than 2.2 kg/m2, the population density and structure size were found to increase with hydrological connectivity. When the biomass is higher than the threshold, the plots disconnected hydrologically because of high water consumption. Compared with soil chemistry, salinity, and water soil content, hydrological connectivity in the surface soil layer is more strongly linked to the plant traits and spatial structure in the tidal marsh wetlands due to the narrow ranges of other variables. Based on the authors’ analysis, the researchers do not recommend dense plantation of P. australis, especially near the freshwater sources in the tidal marsh, because of its high reproduction ability and competitive nature, which may cut the freshwater connectivity off, lowering the richness of plant species and habitat diversity.

Soil is a fundamental component to an ecological system. This study is aimed to clarify the spatial heterogeneity of soils in the Houzhai River basin and the factors controlling it. Overall, 2755 sites designed using ArcGIS were studied; soil thickness, vegetation, land use (human disturbance), and topographic characteristics were analyzed. Soils in the basin are characterized by the high spatial heterogeneity. Soils on the elevated convex elements of topography are thinner than those in the depressions and on flat lands. Soils in the western part of the Houzhai River basin are generally thicker than soils in the eastern part of the basin. The mean soil thickness of forestland, paddy fields, arid land, and grassland is 37.40, 84.43, 69.08 and 56.03 cm, respectively. Based on the present study, soil thickness in the Houzhai River basin is closely associated with landscape, land use, and vegetation. It is interesting that soils of croplands, including paddy fields and arid lands, are generally thicker than soils of other land uses under similar environmental conditions. The major reason for this—either the choice of soils with initially greater thickness for cropland or the result of soil protection measures by land owners—remains open to arguments and needs to be clarified.

In this study, an innovative method was used to assess the spatial and temporal patterns of the hydrological connectivity in soil profiles in the Yellow River Delta wetland. In this method, field dye-tracing experiments conducted in the study area (i.e., large [LWa] and small communities [LWb] of Phragmites australis and Suaeda glauca [JP]) were considered, and the root-soil interface in the region and the status of the wetland degradation were analyzed. The results revealed that the index of hydrological connectivity (IHC) significantly changed both spatially and temporally. The high IHC values reaching a 0.392 ± 0.209 gradient were concentrated in the middle and western parts of the study areas. The spatial distribution of the high hydrological connectivity has been extremely fragmented since 2010. The LWb (severely degraded wetland) and JP (extremely degraded wetland) were found to be more seriously degraded than the LWa (moderately degraded wetland) in the study area. The changes in the IHC were positively correlated with the principal component (PC) values of the wetland degradation. The IHC is a novel indicator of the status of wetland degradation. Furthermore, the soil holding capacity, soil non-capacity porosity, and soil ventilation were relatively important for the changes in the IHC. Compared with the soil properties, the hydrological responses of the roots systems can be neglected at the root-soil interface. Based on our results, we propose an alternative wetland restoration solution for the Yellow River Delta wetland: 1) a seepage layer in the surface soils (0–10 cm), shallow ploughing treatment, and litter or straw return to the soil surface should be conducted to increase the hydrological connectivity of the soil surface; 2) reeds should not be reaped every year to remove the nutrients from this area; and 3) appropriate freshwater inputs should be strengthened.

To explore the spatial heterogeneity of pH and cadmium (Cd) content in the soils of the tea gardens in the plateau mountain regions as well as its driving factors, the pH values, Cd content and other physical and chemical indicators from 423 soil samples were examined. A coefficient of variation method and a semivariance function model was adopted to explore the soils’ spatial heterogeneity, and a random forest approach was applied to evaluate the factors influencing environmental Cd under different pH values. The results show that the pH values of the soils of the tea gardens in the plateau mountain regions were within the appropriate range for the growth of tea plants, and soil samples with pH values falling between 4.5 and 6.0 account for 74% of all samples. A comparison against the criteria of risk screening values for the contamination of agricultural land, a component of quantifying soil environmental quality in China, was preformed; it was determined that the content of heavy metal Cd in the soil of the tea gardens did not exceed the limit. The content of soil pH in the research area gradually declined from southwest to northeast, exhibiting two distinct parallel distribution zones running along the southwest-northeast direction. The spatial distribution of the heavy metal Cd content in the soil showed a gradually decreasing trend from north to south, with low-value polygons dominantly appearing in the southeasternmost area and high-value polygons concentrated in the north. When the soil pH ≤ 5.5, it had the largest effect on the Cd content; when 5.5

Particulate matter (PM) in the atmosphere is a threat to human health. Wetland plants were confirmed to accumulate particles on the leaf surface; at the same time, rainfall could wash-off particles and accelerate the whole removal process, however, the dynamic processes occurring during rainfall events on wetland plants remain unclear. In order to provide sustainable strategies for authorities to take measures, we need to figure out how to reduce PM on leave surface by artificial rainfall efficiently. Four wetland species (Scirpus validus, Typha orientalis, Phragmites australis, and Iris wilsonii) were selected to examine for leave surface accumulation and simulate the experiment. We estimated the wash-off ability of rainfalls with three different intensities (15, 30, and 60 mm h−1) and determined the proportions of different PM size-fractions washed by the rains. The results showed that particles accumulated on the surface could be washed off efficiently (78% ∼ 89%) by the simulated rainfalls. The removal rates were high in the first 30 min and large particles comprised a large proportion of the removed particles. The rainfall with the intensity of 30 mm h−1 removed the most particles among three different rainfall intensities. When the rainfall intensity increased, fine particles (PM2.5) could be washed off more easily. Moreover, with a thinner wax layer, fine particles on wetland plants’ leaf surfaces might be more easily removed by the rains. While wash off the plants, spraying rains with the intensity of 30 mm h−1 for about 30 min every time (high intensity with shorter time) may be particle removal efficiency.

Wetland ecosystem, with their precious natural resources and important ecological functions, is an integral part of the global ecosystem. Preferential flow is a form of water and solute transport that is widely present in all types of soils and has a great impact on nutrient transport and environmental pollution in soils. In this paper, we observe the phenomenon of preferential flow within a wetland ecosystem and discuss the possible effects of preferential flow within a wetland on the wetland ecosystem as a background. We conducted dye tracing experiments outdoors. The preferential flow was qualitative analysis using soil composition. It was found that two types of preferential flow existed in the experimental area, namely finger flow and macropore flow. Quantitative analysis of the preferential flow was performed using PS and Image-Pro Plus software to obtain the intensity data of the preferential flow. The results show that the preferential flow phenomenon in the experimental area is obvious and the preferential-flow intensity data is high. We also found a clear correlation between initial soil–water content, which is an environmental factor characteristic of wetlands, and the preferential-flow data (p = 0.04

Growing populations and industrialization have led to raised wetland ecosystems nitrogen(N) loads. A micro constructed wetland planted with Lythrum salicaria L treating an artificial wastewater was used to investigate the short-term variations in the plant biomass and the removal efficiency of N. Our results showed that the biomass of Lythrum salicaria L. increased rapidly during the experiment due to their extensive root system and vigorous spread, and waterlogged conditions had little effect on the relationship between biomass and the concentration of TN in soil and effluent. Under different waterlogged conditions, the removal rates of TN in the water were all more than 60%, providing a reference for waterlogged conditions used in wetland eutrophication restoration.

Management intensity was considered an important factor in evaluating and regulating the anthropogenic restoration measures for a degraded ecosystem. By comparing selected conventional soil physicochemical, microbial and incorporating aggregate-associated indices between wetland plot with high-intensity freshwater replenishment (HI wetlands) and wetland plot with low-intensity freshwater replenishment (LI wetlands), edaphic responses of degraded estuarine wetlands to freshwater replenishment at different intensity were assessed in the present study. The results showed that high-intensity freshwater replenishment exerted better soil salinization and alkalization alleviation effects on degraded estuarine wetlands, which caused lower EC and pH values in HI wetlands than those in LI wetlands. And soil microbial biomass was promoted, with freshwater replenishment intensity increased, as indicated by MBC and total PLFAs. Minor alternation of soil microbial community composition was observed with an elevated abundance of arbuscular mycorrhizal fungi (AMF) in HI wetlands. On the other hand, freshwater replenishment at low intensity was found to contribute to organic matter accumulation, as indicated by both higher SOC concentrations and carbon stocks in LI wetlands than those in HI wetlands. And soil aggregate-associated indicators provided more scientific clues that freshwater replenishment at low intensity favored the formation of large macroaggregates, and thus supported higher soil aggregate stability. Moreover, a transfer of allocations of aggregate-associated carbon and nitrogen stocks from microaggregates to large macroaggregates was induced as the freshwater replenishment intensity decreased, and the principle governing factors were the proportion of large macroaggregates in soils, soil salinity and microbial decomposition rates based on multivariate statistical analysis. The findings of this study could provide basic data regarding soil physicochemical properties, microbial characteristics and soil structure stability in restored wetlands of the Yellow River Delta with freshwater replenishment at different intensity and guiding adaptive management strategies of freshwater replenishment to enhance the ecological functions of estuarine wetlands.

The main factors controlling plant litter decomposition rates are litter quality and environmental factors. We investigated how different salinity and inundation conditions influence the decomposition rate and how litter quality affects dynamic change during the decomposition process in the Yellow River Delta wetland in northeastern China. To do this, we designed a field experiment using the litter bag method to study two selected dominant halophyte species (Phragmites australis and Suaeda salsa). We found litter decomposed faster when inundated across a range of salinities. Both the water chemical oxygen demand and NH3-N concentration were inversely correlated with salinity. The ratio of nitrogen to phosphorous showed an upward trend during the process of decomposition. The decomposition rate increased during the later stage of the process. Under inundation conditions, the decomposition rate of only S. salsa showed a positive correlation with salinity. The study results suggest that moderately higher salinity would increase anaerobic decomposition owing to the combined effect of salinity and inundation. The implications of our findings may be used to further assess the impact of environmental parameters and litter quality on the decomposition rate in estuarine wetland and can help determine a strategy for wetland reparation and remediation.

Protecting soil from Pb contamination has been a programme for a long time in China. However, research on lead pollution in wetlands remains rare. To understand the characteristics of Pb pollution in Beijing and the sources of contamination of different soil samples in wetlands, we collected samples during all four seasons from two soil horizons and analyzed their Pb concentrations and Pb isotope ratios. The average concentrations of Pb varied from 65.44 mg/kg in spring to 106.11 mg/kg in winter. Concentrations in autumn were significantly lower than those in spring and summer and were notably different between A and B Horizons (59.42 and 71.47 mg/kg, respectively). The Pb isotopic compositions show that Pb pollution results from a mixing of geogenic and anthropogenic materials. The ratios of

Coastal wetlands are ecologically and economically important; however, they are currently faced with fragmentation and loss. Plants are a fundamental element of wetlands and previous researches have focused on wetland plant connectivity; however, these researches have been conducted at the landscape but not species level. Here, given that tidal flats are important areas in coastal wetlands, we investigated the connectivity characteristics of typical plant species and environmental factors in different wetland regions influenced by various tidal conditions to reveal vegetation connectivity and its relationship with environmental factors on a small-patch scale. We found that tides negatively affect plant connectivity because both the Tamarix chinensis and Suaeda salsa have the highest connectivity on river banks, which are not influenced by tides. Of two tidal regions, different tides conditions have different influence on two plant species. T. chinensis had higher connectivity in the supratidal zone, whereas S. salsa had higher connectivity in the intertidal zone. Besides, the soil water content and soil salinity were significantly different in the three regions, but the soil total nitrogen and phosphorous were not. Soil water content and soil salinity were two factors that significantly affected plant connectivity. Specifically, soil water content positively affected the connectivity of T. chinensis and S. salsa, whereas soil salinity negatively affected the connectivity of T. chinensis. Taken together, these results indicate that tidal conditions affect plant connectivity on a small-patch scale. River banks and supratidal zone are beneficial for the recovery and growth of T. chinensis, intertidal zone and river banks are more conducive to the recovery and growth of S. salsa. Based on the above research, this study provides insights that could be applied to vegetation restoration in coastal wetlands.

Today, particulate-matter (PM) pollution has become one of the most severe air-pollution problems. As the most commonly used method in daily life, phytoremediation can use plant organs (such as leaves) as biological filters for pollutants to repair the atmosphere. At the same time, rainfall can remove PM from plant-leaf surfaces and enable them to adsorb PM again. By simulating natural rainfall, the rainfall characteristics are quantified as rainfall intensity and rainfall duration, and we use the washout-weighing method to obtain the amount of PM removed from the leaf surface. Then, use a scanner to scan the leaves after rain to get their images, and use Image J software to process the images to obtain leaf area. Finally, the amount of PM removed by rain per unit leaf area can be calculated. It will be used to explore the impact of different rainfall intensity and duration on the removal of PM from the leaf surface of wetland plants. The results showed that under three rainfall intensities used in this experiment, the removal of PM from plant-leaf surfaces all increased with an increase in rainfall duration. When the particle size is 10-100-μm, and the rainfall intensity is 30 mm/h, the removal amount of plant particles tested in this experiment is the largest. With increased rainfall duration, the removal of PM from plant-leaf surfaces increased sharply at first, then slowly, and finally tended to be stable. The removal efficiency of PM on the blade surface is most apparent at the early stage of rainfall, and then gradually weakens. Among the four wetland plants tested in this experiment, in the range of 10-100-μm, the number of PM on the leaf surface of Scirpus validus is the largest, and the optimum rainfall intensity is 30 mm/h; in the range of 2.5–10-μm, the number of PM on the leaf surface of Typha orientalis is the largest, and the optimal rainfall intensity is 30 mm/h; in the range of 0.45–2.5-μm, the number of PM on the leaf surface of Iris wilsonii is the largest, and the optimal rainfall intensity is 15 mm/h. Wetland species with high particle accumulation capacity can provide references for vegetation restoration of degraded wetland plants and plant cultivation in constructed wetlands. At the same time, the best rainfall intensity and duration for removing particulate matter on the surface of plant leaves were obtained through experiments, which provided a reference for the design of automatic plant irrigation systems and dust removers in different scenarios.

The applicability of the ordinary kriging method for estimating the soil organic carbon (SOC) stored in karst regions was investigated. A total of 23,536 soil samples were analysed from 2755 soil profiles collected using a grid-based sampling method in a typical small karst basin of western Guizhou in Southwest China. Corrections for the gravel content and rock exposure rate were applied to the GIS-based spatial interpolation and simulation and were compared with the same approach with the addition of soil profiles. With the addition of the soil profile data, the SOC stored in the karst catchment was accurately calculated as follows: 1.48 × 108 kg at a depth of 10 cm, 2.65 × 108 kg at 20 cm, 3.43 × 108 kg at 30 cm, and 5.39 × 108 kg at 100 cm. With the interpolation that was corrected for the rock exposure rate and soil depth, the resulting carbon storage estimation was 1.14–1.19 times higher than the most accurate estimate (that with the soil profiles), with an error rate of 114%–119%. Since the conventional geostatistical method failed to accurately fit the data, including the spatial distribution, micro-geomorphic features, rock exposure rate, and depth of the soil patches in the highly sloped exposed bedrock, must be used to correct the estimation of the SOC storage and organic carbon density in karst areas. Keywords: Correction, Karst, Organic carbon storage, GIS spatial interpolation simulation, Applicability

The present article reports an assessment of afforestation potential and anticipation of carbon sequestration in the Houzhai River Basin in Guizhou Province in southwestern China. Total of 2755 soil profiles consisting of 22,057 soil samples were collected according to a grid-sampling method at a 150 m scale in the Houzhai River basin, and the SOC contents in soil samples were analyzed using a titration method. General information regarding the geographic characteristics of each sampling grid was recorded in the field. The results indicate that land use in the Houzhai River Basin is very complex. Land use status and land use change in the study area were closely associated with local geographic characteristics and variations in economic structures. There were approximately 15.26 km2 of land that could or should be rearranged as afforestation land in the Houzhai River Basin. The increased SOC storage (0.00–1.00 m soil horizon) would be up to 5.48 × 104 Mg, 6.42 × 104 Mg, 4.77 × 104 Mg and 3.18 × 104 Mg when all of the calculated lands became shrub-grass lands, shrub lands, arbor-shrub forest lands and arbor forest lands, respectively. The increased SOC percentages would be 52.16%, 61.13%, 45.39% and 30.32%, respectively, in comparison with the present SOC storage in these lands.

A better understanding of preferential water flow is important because water-related crises, i.e., water scarcity and security, are strongly associated with water retention rates in different landscapes. This review aims to evaluate significant advances in the main themes of preferential water flow to establish the inconsistent roles of preferential water flow in eco-hydrology and suggest promising areas for future work. Results showed that preferential water flow studies have made significant advances in our understanding of certain parameters functioning at multiple scales but that most studies focus on preferential water flow in the vadose zone, whereas few studies on the soil surface. Preferential water flow can have a positive effect on averting water crises, such as when it affects surface runoff soil erosion, soil formation as ecosystem services, nutrient cycling in root zone, and overall water regulation of the water cycle. Conversely, preferential water flow can have a negative effect on eco-hydrological issues via slope stability, gully erosion, geological disaster, waste treatment, water supply in root zone, and food production. Our review concludes that more information is required on preferential water flow before we can assess its role in mitigating water-related crisis events.

Dry deposition of particulate matter (PM) indicates the capacity of atmosphere self-depuration. To investigate seasonal dry deposition of PM in an urban forest, the concentration and ionic composition of PM2.5 (particulate matter with aerodynamic equivalent diameters less than 2.5 μm) and the deposition of PM and ions in PM at different layer were measured at three canopy heights in the Beijing Olympic Forest Park. Results showed that diurnal trends in PM concentration varied with height and that concentrations tended to be highest in the understory. During winter, when the absorption ability of plants, which withered, was reduced, and anthropogenic emissions, primarily from coal combustion, ion concentrations tended to be highest in the forest canopy. The anions SO42−, NO3−, and Cl− were the dominant ionic species, accounting for 82% of the total mass of water-soluble ions in PM2.5. Results showed a lower mass ratio of NO3−/SO42− (mean = 0.29, SD = 0.24), relative to previous studies, implying that vehicle emissions may have reduced in Beijing. The chemical forms of sulfate and nitrate were likely NH4NO3 and (NH4)2SO4; however, Ca(NO3)2 was the only chemical form detected based on the correlation coefficient between Ca2+ and NO3−. Concentrations of PM were negatively related to temperature and wind speed, and positively related to relative humidity. Within the forest canopy, the deposition velocity was low (high) during summer (winter). Furthermore, ion deposition fluxes were higher in the forest understory (1.5–6 m) during summer and in the canopy (6–10 m) during winter. This was attributed to seasonal trends in PM concentration.

Forests and wetlands, as two important ecosystems, play a crucial role in reducing the concentration of particulate matters. The main purpose of this study is to reveal the contribution of forest and wetland ecosystems to the reduction of particulate matter. We collected the concentration and meteorological data during the daytime in a forest and a wetland in the Olympic Park in Beijing. The main results are as follows: daily variation in the PM

In recent decades, China has experienced both rapid urbanization and heavy air pollution and the rapid urbanization trend would be continue in the next decade. Wetlands have been shown to be efficient in particle removal, primarily through dry deposition and leaf accumulation. Thus, a more comprehensive understanding of PM2.5 removal by wetlands during urbanization processes could inform urban planning. In the current study, three wetland plots, Cuihu Lake Park (CL), Summer Palace (SP), and Olympic Park (OP), were selected as low, medium, and highly degrees of urbanization site respectively based on the proportions of building and traffic district areas to compare the removal efficiencies. Results show the average dry deposition velocity in OP was significantly higher than CL and SP. Dry deposition is mainly influenced by meteorological conditions. Buildings and other infrastructure make the meteorological conditions conducive to deposition, resulting in higher wind velocity, higher temperature, and more intense turbulence between buildings. Variation in leaf accumulation was not statistically significant between the three plots, and plant species was the major factor affecting the amount of accumulation. The dry deposition contribution to particle removal increases with degree of urbanization. The average dry deposition accounted for 39.74%, 52.55%, and 62.75% at low, middle and high level respectively. Therefore, Wetlands with greater degree of urbanization improve PM2.5 removal efficiency primarily by accelerating the dry deposition process. The result emphasizes the importance of wetlands in particle removal in highly urbanized areas and thus more wetlands should be preserved and/or created during urban expansion.

Forests and vegetation are known to play an important role in capturing air pollutants, whereas the role of wetland plants in this context has been poorly understood. This study focused on particle accumulation in six common wetland plant species in a wetland in Beijing, China. The aim of the study was to show the capacity of the six plants species to accumulate particulates of two different size fractions (fine particles: diameter

To research soil organic carbon (SOC) in a typical small karst basin of western Guizhou in southwest China, data from the second national soil resource survey (1980) and data analysed in the labora...

The effects of preferential flow on plant root and soil have not been deeply studied. Research on the combination of wetland vegetation, hydrology, and soil can provide a theoretical basis for wetland vegetation restoration and soil salinization control. We integrated preferential flow, root, and soil to study the distribution characteristics of the root architecture and soil nutrient of two different ecotypes of Phragmites communis (P. communis) in the Yellow River Delta on a small scale. We found that both root architectures included root length, width, surface area, volume, and biomass and soil nutrients included soil organic carbon, organic matter and total nitrogen decreased with the increase of soil depth. Large P. communis (LP) not only had significantly larger root length, width, surface area, but also had significantly higher soil organic carbon, organic matter, total nitrogen, and available phosphorus than small P. communis (SP). The root architectures of SP in the preferential flow area (PFA) were significantly greater than those in the matrix flow area (MFA). The contents of soil organic carbon, organic matter, and total nitrogen in LP grown in the PFA were obviously higher than those in the MFA. Based on correlation analysis, root architectures had remarkably positive correlations with soil organic carbon, organic matter, and total nitrogen. These findings suggest that preferential flow improves the root-soil system. By artificially adding peat and biochar and changing irrigation methods, the possibility of preferential flow can be increased, plant root growth and soil nutrient can be improved, so as to resist the damage of soil salinization. In addition, different ecotypes of P. communis should be planted to improve soil salinization. LP and SP are suitable for slight and heavy soil salinization areas respectively.

Growing populations and industrialization have led to increased nitrogen (N) loads in wetland ecosystems. A micro-constructed wetland planted with Lythrum salicaria L. to treat artificial wastewater was used to investigate the short-term variations in the plant biomass and dynamics of total nitrogen (TN) content. Our results showed that the biomass of Lythrum salicaria L. rapidly increased during the experiment due to their extensive root system and vigorous spread, and waterlogged conditions had little effect on the relationship between biomass and the TN content in soil and effluent. Under different waterlogged conditions, the TN removal rates in the water were all greater than 60%, providing a reference for the waterlogged conditions used in wetland eutrophication restoration.

Apparently, plant leaf surface particulate matter (PM) can be effectively removed by rainfall, leaving space on the leaf surface to adsorb and retain PM again. At present, most of the relevant studies adopt the method of artificial rainfall simulation to quantify rainfall characteristics in terms of rainfall intensity, and mostly focus on one category of plants. Studies of rainfall intensity on different categories of plants are lacking. Therefore, in this study, common urban greenery plants were classified into four categories, namely, trees, shrubs, herbs, and aquatic plants. Artificial rainfall was used and three different gradients of rainfall intensity, 30 mm/h, 45 mm/h and 60 mm/h, were set. The mass of per unit leaf area PM removal was calculated using the elution weighing method and the filter membrane method was used to classify the PM into three particle sizes: coarse (10–100-μm), fine (3–10-μm) and ultrafine (0.4–3-μm). It was devoted to investigating the differences in the effect of rainfall intensity on the removal of PM from the leaf surfaces of different categories of common urban greenery. The results showed that the removal of coarse particles by rainfall was the highest under different rainfall intensities. At the same time, the removal effects of rainfall on leaf surface PM of herbs were the highest under different rainfall intensity, while that of trees was the lowest. Among the same category of plants, Salix matsudana had better particle retention capacity among trees, Buxus sinica among shrubs, Poa pratensis among herbs, and Acorus calamus among aquatic plants. In addition, all tested plants had the highest mass of PM removed from leaf surface units at high rainfall intensity (60 mm/h). However, at a higher rainfall intensity (45 mm/h), the mass of PM on plant unit leaf surface removed was lower than the minimum rainfall intensity (30 mm/h). The results of the above study can provide a basis and theoretical support for the selection of species for urban green space restoration, as well as a reference for the establishment of urban cleaning systems from the perspective of the relationship between rainfall intensity and PM on plant leaf surfaces.

Paddy rice, one of the most important food crops in Southeast Asia, is considered a main source of human exposure to heavy metal contamination because it efficiently accumulates heavy metals. In the present study, of Japonica rice grains, straw, roots, leaves, and husks and rhizosphere paddy soils (0–20 cm and 20–40 cm depth) were collected from Zunyi in northern Guizhou Province, China. The forms of heavy metals, including Cr, Cd, Pb, Cu, and Zn, in the two soil profiles were investigated using Tessier’s five-stage sequential extraction procedure. There was no heavy metal pollution in the study area based on the evaluation of the geo-accumulation index and the potential ecological risk index. Accumulation varied from one area to another, and the highest metal accumulation was found in the order of root > stems > leaves. The bioaccumulation factor (BCF) results revealed that during the grain-filling stage, the rice had high BCF values (> 1) for Cd and Zn. The target hazard quotient (THQ) of ingestion peaked for Cd and reached its minimum level for Zn in not only in adults but also in children. The THQ was ranked as Cd > Cu > Pb > Cr > Zn for both adults and children. The hazard index values for adults and children for the five heavy metals were 1.81 × 10−3 and 1.55 × 10−3, respectively, indicating that these metals have little effect on the human body. The lifetime carcinogenic risk values for local adults and children were 4.28 × 10−5 and 5.92 × 10−5, respectively, both of which were within the tolerable to acceptable risk range. In summary, obvious hazards for local adults and children were not observed in this study. Considering the total amount and chemical forms of Cd, it is necessary to notify the appropriate departments about the possible rice contamination caused by Cd in the soil.

With the rapid development of industry, studies on lead pollution in total suspended particulate matter (TSP) have received extensive attention. This paper analyzed the concentration and pollution sources of lead in the Cuihu Wetland in Beijing during the period of 2016–2017. The results show that the lead contents in TSP in the Cuihu Wetland were approximately equal in summer and spring, greater in winter, and greatest in autumn. The corresponding lead concentrations were 0.052, 0.053, 0.101, and 0.115 ng/m3, respectively. We compared the 206Pb/207Pb data with other materials to further understand the potential sources of atmospheric lead. The mean values of 206Pb/207Pb from spring to winter were 1.082, 1.098, 1.092, and 1.078, respectively. We found that the lead sources may be associated with coal burning, brake and tire wear, and vehicle exhaust emissions. We also calculated the enrichment factor values for the four seasons, and the values were all much greater than 10, indicating that the lead pollution is closely related to human activities.

The assessment of soil organic carbon (SOC) in mountainous karst areas is very challenging, due to the high spatial heterogeneity in SOC content and soil type. To study and assess the SOC storage in mountainous karst areas, a total of 22,786 soil samples were collected from 2,854 soil profiles in Guizhou Province in Southwest China. The SOC content in the soil samples was determined by the oxidation of potassium dichromate (K2Cr2O7), followed by titration with iron (II) sulfate (FeSO4). The SOC storage was assessed based on different land uses. The results suggested that the average SOC density in the top 1.00 m of soil associated with different land uses decreased in the following order: Croplands (9.58 kg m&minus, 2) &gt, garden lands (9.07 kg m&minus, grasslands (8.07 kg m&minus, forestlands (7.35 kg m&minus, uncultivated lands (6.94 kg m&minus, 2). The SOC storage values in the 0.00&ndash, 0.10 m, 0.00&ndash, 0.20 m, 0.00&ndash, 0.30 m and 0.00&ndash, 1.00 m soil layers of Guizhou Province were 0.50, 0.87, 1.11 and 1.58 Pg, respectively. The SOC in the top 0.30 m of soil accounted for 70.25% of the total within the 0.00&ndash, 1.00 m layer in Guizhou Province. It was concluded that assessing SOC storage in mountainous karst areas was more accurate when using land use rather than soil type. This result can supply a scientific reference for the accurate assessment of the SOC storage in the karst areas of southwestern China, the islands of Java, northern and central Vietnam, Indonesia, Kampot Province in Cambodia and in the general area of what used to be Yugoslavia, along with other karst areas with similar ecological backgrounds.

Structural hydrological connectivity has been proposed to describe the geological structure of the landscape as well as to explain hydrological behaviors. Indices based on the topological or soil condition were developed to interpret their relationships. While previous studies mainly focused on well-instrumented catchments which are narrow in humidity or temperate zone, the hydrological responses to structural connectivity at the plot and hill slope scale as well as in arid or semi-arid climate conditions remain unclear. This study was conducted in the semi-arid mountainous region of northern China in Haihe Basin which is the source of water of about 350 million people. Experiments were conducted during the rainy season in 2012 and 2013 using four runoff plots. Two indices, flow path length (FL) based on topography and integral connectivity scale length (ICSL) based on soil moisture conditions, developed to represent hydrological connectivity structure and the runoff response to rainfall were analyzed. The results showed that the surface runoff coefficient was strongly and positively linearly correlated to FL, and the correlation between subsurface flow and ICSLs was quadratic. Plots with shorter FL required more rainfall to generate surface runoff. In the shallow soil layer, when the ICSLs are relatively low, the soil can store more water and less rainfall feeds subsurface runoff. Further analysis indicated that improved shallow soil connectivity conditions might enhance the water-holding capacity and lead to lower water yields for each event. This study demonstrated that hydrological structure connectivity could explain the mechanism of runoff generation in semi-arid areas while further experiments should be undertaken to find the threshold-like relationship between FL and surface runoff as well as the influence of plant cover on hydrological behaviors.

As a transitional zone between aquatic and terrestrial ecosystems, the riparian buffer is an important control measure for non-point source pollution. The research presented here mainly discussed the interception efficiencies of different vegetation types for nitrogen and phosphorus pollution. The results showed that canopy, shrub, and grass interceptions basically accounted for about 80.0% of total interception, and therefore riparian buffer configurations should clearly distinguish three levels of vegetation types. (1) Canopy, shrub, grass, and litter interceptions of Pinus tabuliformis (YS) were the highest, up to about 71.1%. (2) Platycladus orientalis (CB) had the highest transportation and enrichment for the elements nitrogen (N) and phosphorus (P) throughout the process, which the value of TP decreased from 0.2 to 0.12 mg/L and the value of TN decreased from 5.0 to 2.5 mg/L. (3) The transportation of total phosphorus (TP) of the three tree species was higher than the transportation of total nitrogen (TN), showing that the enrichment of P was stronger than that of N. Thus, Pinus tabuliformis is the best configuration for rainfall interception, while Platycladus orientalis is the best configuration for N and P removals. Different forest configurations should also be considered to build a riparian buffer to remove nutrient in the future.

Hydrological connectivity is an essential driver of the stability, structure, and function of wetland ecosystems. Small-scale hydrological connectivity restricts large-scale hydrological cycle processes. This study aimed to investigate the response of soil and root properties to hydrological connectivity at the soil profile scale. Tamarix chinensis, which is a typical plant of the Yellow River Delta wetland, was sampled for analysis. We investigated soil and root properties in the three study plots where T. chinensis distributed and compared them at different soil depths and under different hydrological connectivity conditions. We found that the soil organic carbon (SOC), soil organic matter (SOM), and soil total nitrogen (STN) were significantly higher in shallow soil (0–10 cm deep), and that root architecture parameters such as root length and width at soil depth of 0–10 cm were also significantly higher than at other soil depths. Both the soil nutrients and root architecture parameters were significantly influenced by hydrological connectivity. Specifically, SOC, SOM, and STN were significantly higher in regions of high hydrological connectivity than in regions of low hydrological connectivity. Additionally, root length, root surface area, root projected area, and root volume were markedly higher in regions of high hydrological connectivity. Furthermore, root length and width had significant positive correlations with both SOC and SOM in regions of high hydrological connectivity. Taken together, these results indicate that higher hydrological connectivity promotes soil nutrients and root architecture at the soil profile scale. In the process of wetland protection and restoration, we should not only pay attention to hydrological connectivity at a watershed scale, but also to improving hydrological connectivity at smaller scales so as to restore soil nutrients and promote plant growth.

The dry deposition of particular matters from atmosphere to ecosystems is an undesirable consequence of this pollution while the deposition process is also influenced by different land use types. In current study, concentration of fine particles, coarse particles and meteorological data were collected during the daytime in an artificial forest, wetland and a water surface in the Beijing Olympic Park. Dry deposition velocity, fluxes and vegetation collection were calculated by different models and the results were compared. The results show: (1) the deposition velocity onto the forest canopy was higher than which onto the wetland and the water surface and the velocity varied in different seasons; (2) the fine particles deposited most in the winter while the coarse particles was in the spring; (3) the vegetation collection rates of fine particles were lower than coarse particles, and the forest collected more PMs than the wetland plants.

The speciation and activity of heavy metals in farmland were changed with the different soil properties and flooded environment, especially in the complex and rainy environment in soil of Guizhou Province. The objective of this study was to explore the concentrations of a variety of heavy metal activity and the speciation of those heavy metals in rhizosphere soil at different growth stages of Brassica campestris L. in a Karst mountainous area. Tessier's five-stage sequential extraction procedure, the potential ecological risk index, a Bayesian network, accumulation factors, translocation factors and a laboratory simulation experiment were applied in this study. The results showed that (1) no heavy metal concentrations (except the Cd concentration) exceeded the limits of the soil environmental quality risk control standards for soil contamination of agricultural land in China (GB15618-2018). (2) The orders of the accumulation factor and translocation factor values were Zn > Cd > Cu > Pb > Cr and Cd > Cu > Zn > Pb > Cr, respectively. The order of the heavy metal contents of different tissues during the whole growth period was roots > leaves > stems. (3) The indoor simulation test exhibited that the dry-wet alternation and flooding can reduce Cd activity in soil. (4) Redox potential (Eh), rather than pH or organic matter, was the main factor impacting the total content and chemical speciation of heavy metals in the soil, based on a dynamic Bayesian network. Based on the results, we suggest that the activity of heavy metals should be improved by using dry-wet alternation, whereas the proportions of ion-exchangeable forms of heavy metals are relatively low in the study area (except for Cd). Several measures may be taken to enhance soil acidity and reduce the Cd activity during Brassica campestris L. cultivation.

In order to provide useful and effective reference indicators for wetland protection and restoration, we are trying to understand the role of hydrological processes in wetlands with hydrological connectivity. To quantify hydrological connectivity at soil-profile scale with the soil-profile indexes, dye-tracing field tests were conducted in Yellow River Delta to determine the size and distribution of soil pores, as well as the trail of waterflow. After data analyses, the results showed: (1) where preferential pathways were rich, that is, where hydrological connectivity was strong, the dye coverage was larger (the dye coverage of CLa1 was 0.20 ± 0.08, when CLa2 was 0.22 ± 0.05 and CLa3 was 0.13 ± 0.02), and the dye coverage of preferential pathway was larger (the dye coverage of preferential pathway of CLa1 was 0.16 ± 0.07, when CLa2 was 0.19 ± 0.04 and CLa3 was 0.11 ± 0.02). (2) hydrological connectivity weakens non-linearly from about 30 cm deep. (3) hydrological barrier in soil made dye coverage increase at 10–20 cm deep and it would weaken the vertical hydrological connectivity and strengthen the horizontal hydrological connectivity by preventing the flow from infiltrating further down.

Due to the impacts of unwise industrial agriculture, extreme precipitation events are increasing in frequency and are accelerating the process of global warming in the karst area. The dynamic change in soil organic carbon (SOC) and its driving factors in cultivated land in the last 35 years were studied by using data from the second national soil survey of China and measurements made in 2015. The results indicated that the SOC per unit area of cultivated land increased by 32.45 &times, 103 t in the last 35 years in the study area, exhibiting basically the same levels and a slight increasing trend, and the annual average change rate was 0.02 kg C.hm&minus, 2.a&minus, 1. In terms of spatial distribution, carbon loss areas were mainly concentrated in the middle northern region, western region, and scattered eastern regions of the county. The main factors affecting the change in SOC in the cultivated land in the study area in the last 35 years include nitrogen fertilizer application, stubble, soil thickness, soil total nitrogen, C/N, rock coverage, gravel content, soil organic carbon density (SOCD1980), etc. This study will provide a database for the management of SOC in cultivated land in the future.

Decomposition of halophyte litter may considerably influence carbon cycling and energy flow in estuarine ecosystems. We examined water quality parameters, soil properties, and soil phospholipid fatty acid (PLFA) contents from the Yellow River Estuary, China, to investigate Phragmites australis and Suaeda glauca litter decomposition dynamics. Surface soils (0–10 cm) under three different salinity conditions were collected from six plots. Results showed that the litter decomposition rate of S. glauca (k = 0.0063) was significantly (p = 0.032) higher than that of P. australis (k = 0.0024). Litter decomposition rate had a significant (p

To increase our knowledge of PM2.5 concentrations near the surface in a forest park in Beijing, an observational study measured the concentration and composition of PM2.5 in Beijing Olympic Forest Park from 2014 to 2015. This study analyzed the meteorological factors and removal efficiency at 1.5 m above the ground (human breathing height) over the day in the forest. The results showed that the average concentrations of PM2.5 near the surface peaked at 07:00–09:30 and reached their lowest at 12:00–15:00. Besides, the results showed that the annual concentration of PM2.5 in the forest was highest during winter, followed by spring and fall, and was lowest during summer. The main chemical components of PM2.5 near the surface in the forest were SO42− and NO3−, which accounted for 68.72% of all water-soluble ions that we observed. The concentration of PM2.5 in the forest had a significant positive correlation with relative humidity and a significant negative correlation with temperature. The removal efficiency near the surface showed no significant variation through the day or year. In the forest, the highest removal efficiency occurred between 07:00 and 09:30 in summer, while the lowest occurred between 09:30 and 12:00 in winter.

Salt marshes are changeable and important ecosystems that currently face various threats, including global climate change and human activities. The influence of these factors can result in the degradation of salt marshes. Tidal creeks, which are an important source of nutrients and other substances for salt marsh vegetation, play an important role in the health of salt marshes. In this study, the morphological characteristics of tidal creeks and the characteristics of two typical plants, Suaeda glauca (SG) and Phragmites communis (PC), in the Yellow River Delta, China were investigated to determine the effect of tidal creeks on these plants. Aerial photography and field measurements of tidal creeks were carried out from May to July 2018 in the study area. At the same time, nine line-intercepts were set in the vertical direction of tidal creeks to investigate plants. The results showed that different grades of tidal creek exerted no significant influence on the growth of either S. glauca or P. communis. However, unlike grade, the size of a creek and the distance from it had marked effects on these plants. The cross-sectional area of a tidal creek had a significant positive impact on the density of S. glauca (r = 0.39, p = 0.02). For P. communis, the depth of a tidal creek had a strong correlation with this species’ density (r = 0.51, p = 0.04) and height (r = 0.63, p = 0.01). Meanwhile, there was a negative relationship between the distance from tidal creeks and the height of S. glauca (r = −0.52, p = 0.02). Conversely, the height (r = 0 0.90, p = 0.00) and density (r = 0.62, p = 0.01) of P. communis were positively affected by its vertical distance from tidal creeks. We found that the subtidal zone near a tidal creek was more conducive to the recovery and growth of S. glauca, and that areas further away from a tidal creek, located in the intertidal and subtidal zones, were more conducive to the recovery and growth of P. communis. The parameters associated with tidal creeks in the subtidal zone (cross sectional area 4.55 m2, distance 0–10 m) were beneficial for the growth of S. glauca. For P. communis, relevant features in the intertidal and subtidal zones (depth 0.40–0.45 m, distance 20–60 m) are useful. Our results suggest that attention should be paid to the effects of size and distribution of tidal creeks during the process of salt marsh restoration. This work also provides practical guidance for the restoration of native salt marshes in China.

The Yellow River Delta is one of the International Important Wetlands on the west coastline of the Pacific Ocean in China. Despite its importance for regional and global ecological security, it is vulnerable because of human activities and climate change. Local government is trying to identify a more efficient way to conserve the delta thereby reducing a potential environmental crisis. The framework of hydrological connectivity provides a new perspective to study hydrological related ecological processes, while the method is highly exclusive because of environment and scale heterogeneity. This study collaborated with managers to develop a new algorithm to parameterize the hydrological connectivity on plot, point and landscape scales. Then the interspecific and conspecific structures of two dominate species (Phragmites communis and Suaeda salsa) are linked to these indices. The results show: (1) According to the point and plot scale results, AP (semi-artificial pond) and IF (intertidal flat) has the strongest hydrological connectivity followed by TM (tidal marsh). The average positive point-scale index values in AP, IF RS (river side wetland) and TM are 0.610, 0.495, 1.162 and 1.217 and the average plot-scale index values in AP, IF RS and TM are 1.53, 0.87, 0.48 0.55. At the landscape scale, index values show high collinearity with plot density and lack of hydrological significance because of low data resolution and scale effects. (2) At the individual level, P. communis and S. salsa showed a higher interspecific and conspecific competitive strength to respond to environmental stress in the weak hydrological connectivity area. (3) At the community level, in higher salinity wetland classes, biomass, plant coverage and biodiversity showed a positive linear correlation with plot-scale indices. Future study will improve the current parametrization method at the landscape scale and reveal the response of other important plant species to hydrological connectivity in this area.

To study the spatial heterogeneity and effect factors of soil organic carbon density (SOCD) under different karst landforms, total of 1,173 samples were taken from different karst landforms including Puding (KP), Xingyi (KPCD), Guanling (KC), Libo (KVF) and Yinjiang (KTV) in Guizhou Province. SOCD characteristics in lands with different vegetation types, land uses and soil types under different karst landforms were analysed. The relationship between SOCD and environment factors was analysed via redundancy analysis. The results indicate that there is a larger discrepancy of SOCD among difference karst landforms types, and this distinction decreased gradually with the increasing of soil depth. The SOCD in soil horizons (0-100 cm) of KPCD, KP, KTV, KC and KVF were 11.10 kg·m−2, 8.43 kg·m−2, 8.13 kg·m−2, 7.06 kg·m−2 and 7.06 kg·m−2, respectively. Soil thickness and rock exposure rate are critical factors affecting SOCD in karst regions.

To understand the effect of forests and wetlands on air quality, the PM10 and PM2.5 concentration and meteorological data were collected in the forest and wetland in the Beijing Olympic Forest Park...

Studies dealing with water flow and preferential flow are of typically importance because there are still many unresolved water security and scarcity problems. It may indeed be a valuable idea to provide a special review of the progress in the water flow and preferential flow for the applied water science community and to identify what is still missing or unresolved to improve predictions of surface water and groundwater quality within multiscale. This paper aims to review the state of the art on water flow and preferential flow published per year from 1995 to 2015, respectively, and to present a discussion of perspectives and some significant advances in the main themes of water flow and preferential flow that have emerged in recent years, with insights, some promising areas for future work, and suggestions also being provided regarding potential research trends, requirements and solutions. Recorded reports show that it is of general interest in water flow in the period 1995–2015 and also there are clear significant trends from physical hydrology and socio-hydrology perspectives. The future trend of water flow which is predicted in some way indicates a general increase. The term of preferential flow, its significance and progress in the period 1995–2015, shows that despite the increasing number of papers published on preferential flow, there has not been as much attention paid to this topic as we have expected, given its vital role in soil hydrology, water sustainability, slope stability and agricultural management. Finally, existing love-hate relationship between water flow and preferential flow pathways is reviewed.

Karst areas are typical ecologically fragile areas, and stony desertification has become the most serious ecological and economic problems in these areas worldwide as well as a source of disasters and poverty. A reasonable sampling scale is of great importance for research on soil science in karst areas. In this paper, the spatial distribution of stony desertification characteristics and its influencing factors in karst areas are studied at different sampling scales using a grid sampling method based on geographic information system (GIS) technology and geo-statistics. The rock exposure obtained through sampling over a 150 m × 150 m grid in the Houzhai River Basin was utilized as the original data, and five grid scales (300 m × 300 m, 450 m × 450 m, 600 m × 600 m, 750 m × 750 m, and 900 m × 900 m) were used as the subsample sets. The results show that the rock exposure does not vary substantially from one sampling scale to another, while the average values of the five subsamples all fluctuate around the average value of the entire set. As the sampling scale increases, the maximum value and the average value of the rock exposure gradually decrease, and there is a gradual increase in the coefficient of variability. At the scale of 150 m × 150 m, the areas of minor stony desertification, medium stony desertification, and major stony desertification in the Houzhai River Basin are 7.81 km2, 4.50 km2, and 1.87 km2, respectively. The spatial variability of stony desertification at small scales is influenced by many factors, and the variability at medium scales is jointly influenced by gradient, rock content, and rock exposure. At large scales, the spatial variability of stony desertification is mainly influenced by soil thickness and rock content.