Junhong Bai

Assessment of heavy metal pollution in wetland soils from the young and old reclaimed regions in the Pearl River Estuary, South China.

Soils were sampled in three types of wetlands from the young (A) and old (B) reclaimed regions of the Pearl River Estuary. They were analyzed for total concentrations of heavy metals to investigate their distributions and pollution levels in both regions. Results showed that most heavy metals in ditch and riparian wetlands did not significantly differ from those in reclaimed wetlands in A region, while significantly lower for Cd, Cu, Pb, and Zn in reclaimed wetlands in B region, suggesting higher effects of long-term reclamation. Iron, Cr and Cu were identified as metal pollutants of primary concern and had higher contributions to the total toxic units compared to other metals. Almost all metals exceeded their lowest effect levels and Fe and Cr even exceeded the severe effect levels. Multivariate analysis shows that Fe and Mn are controlled by parent rocks and other metals mainly originate from anthropogenic source.

Wetland Degradation and Ecological Restoration

Wetlands are among the most important ecosystems on earth and functioned as the “kidneys” of the earth, which play an important role in maintaining ecological service functions. However, with the rapid growth in human populations, wetlands worldwide are suffering from serious degradation or loss as affected by wetland pollution, wetland reclamation, civilization and land use changes, and so forth. Wetland degradation has potential influences on human health, biodiversity, regional climate, and regional ecological security. Therefore, it is an urgent task to recover these degraded wetlands. In recent years, wetland protection, restoration, and its reasonable exploitation have been paid much more attention to by most governments and researchers. Moreover, wetland restoration has become the frontier fields of wetlands science, which has been listed as one of important themes in these recent international wetlands and ecological conferences. Understanding wetland degradation processes can contribute to better effective wetland restoration. Therefore, we organized this special issue on “wetland degradation and ecological restoration.” The objective of this special issue is to emphasize the effects of human activities on wetland ecosystems, the relationships between soil, water, and plant in wetlands, and wetland restoration issues and applications.

Distribution and pollution, toxicity and risk assessment of heavy metals in sediments from urban and rural rivers of the Pearl River delta in southern China

Sediments were collected from the upper, middle and lower reaches of both urban and rural rivers in a typical urbanization zone of the Pearl River delta. Six heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) were analyzed in all sediment samples, and their spatial distribution, pollution levels, toxicity and ecological risk levels were evaluated to compare the characteristics of heavy metal pollution between the two rivers. Our results indicated that the total contents of the six metals in all samples exceeded the soil background value in Guangdong province. Based on the soil quality thresholds of the China SEPA, Cd levels at all sites exceeded class III criteria, and other metals exhibited pollution levels exceeding class II or III criteria at both river sites. According to the sediment quality guidelines of the US EPA, all samples were moderately to heavily polluted by Cr, Cu, Ni, Pb and Zn. Compared to rural river sites, urban river sites exhibited heavier pollution. Almost all sediment samples from both rivers exhibited moderate to serious toxicity to the environment, with higher contributions from Cr and Ni. A “hot area” of heavy metal pollution being observed in the upper and middle reaches of the urban river area, whereas a “hot spot” was identified at a specific site in the middle reach of the rural river. Contrary metal distribution patterns were also observed along typical sediment profiles from urban and rural rivers. However, the potential ecological risk indices of rural river sediments in this study were equal to those of urban river sediments, implying that the ecological health issues of the rivers in the undeveloped rural area should also be addressed. Sediment organic matter and grain size might be important factors influencing the distribution profiles of these heavy metals.

Fractionation, transfer, and ecological risks of heavy metals in riparian and ditch wetlands across a 100-year chronosequence of reclamation in an estuary of China

The effect of reclamation on heavy metal concentrations and the ecological risks in ditch wetlands (DWs) and riparian wetlands (RWs) across a 100-year chronosequence in the Pearl River Estuary of China was investigated. Concentrations of 4 heavy metals (Cd, Cu, Pb, and Zn) in soil and plant samples, and sequential extracts of soil samples were determined, using inductively coupled plasma atomic absorption spectrometry. Results showed that heavy metal concentrations were higher in older DW soils than in the younger ones, and that the younger RW soils contained higher heavy metal concentrations compared to the older ones. Although the increasing tendency of heavy metal concentrations in soil was obvious after wetland reclamation, the metals Cu, Pb, and Zn exhibited low or no risks to the environment based on the risk assessment code (RAC). Cd, on the other hand, posed a medium or high risk. Cd, Pb, and Zn were mainly bound to Fe-Mn oxide, whereas most of Cu remained in the residual phase in both ditch and riparian wetland soils, and the residual proportions generally increased with depth. Bioconcentration and translocation factors for most of these four heavy metals significantly decreased in the DWs with older age (p<0.05), whereas they increased in the RWs with younger age (p<0.05). The DW soils contained higher concentrations of heavy metals in the organic fractions, whereas there were more carbonate and residual fractions in the RW soils. The non-bioavailable fractions of Cu and Zn, and the organic-bound Cd and Pb significantly inhibited plant growth.

Spatial variability of soil carbon, nitrogen, and phosphorus content and storage in an alpine wetland in the Qinghai–Tibet Plateau, China

This study considers the spatial variability of soil organic carbon, nitrogen, and phosphorus storage in a drained alpine wetland and the possible relationships with soil properties. Top 0-0.30 m soil samples were collected in a typical alpine wetland in the south-eastern Qinghai-Tibet plateau using grid sampling. There was high spatial variability for soil organic carbon density (SOCD), soil total nitrogen density (STND), and soil total phosphorous density (STPD) in the drained alpine wetland. Spherical models best described the structure of the semivariograms for SOCD and STPD, and an exponential model for STND, with the range parameter of <4 m. Similar spatial distribution with lower or higher patches of C, N, and P storage were observed. SOCD, STND, and STPD were significantly negatively correlated with soil moisture (P<0.01), and significantly positively correlated with bulk density (P<0.01). However, no significant correlations were observed between SOCD, STND, and STPD and soil pH values. Wetland drainage might lead to higher C, N, and P densities in top 0.30 m soils due to peat compaction; thus, it is necessary to incorporate water table fluctuations or the whole depth of peat layers to estimating precisely C, N and P storage.

Landscape pattern evolution processes of alpine wetlands and their driving factors in the Zoige Plateau of China

Zoige Plateau wetlands are located in the northeastern corner of the Qinghai-Tibet Plateau. The landscape pattern evolution processes in the Zoige Plateau and their driving factors were identified by analyzing the dynamic changes in landscape modification and conversion and their dynamic rates of alpine wetlands over the past four decades. The results showed that the landscape conversion between wetlands and non-wetlands mainly occurred during the period from 1966 to 1986. The marsh wetland area converted from lake and river wetlands was larger because of swamping compared to other wetland landscapes. Meanwhile, the larger area of marsh wetlands was also converted to lake wetlands more than other types of wetlands. The modification processes mainly occurred among natural wetland landscapes in the first three periods. Obvious conversions were observed between wetland and non-wetland landscapes (i.e., forestland, grassland, and other landscapes) in the Zoige Plateau. These natural wetland landscapes such as river, lake and marsh wetlands showed a net loss over the past four decades, whereas artificial wetland landscapes (i.e., paddy field and reservoir and pond wetlands) showed a net decrease. The annual dynamic rate of the whole wetland landscape was 0.72%, in which the annual dynamic rate of river wetlands was the highest, followed by lake wetlands, while marsh wetlands had the lowest dynamic rate. The integrated landscape dynamic rate showed a decreasing trend in the first three periods. The changes in wetland landscape patterns were comprehensively controlled by natural factors and human activities, especially human activities play an important role in changing wetland landscape patterns.

China’s Coastal Wetlands: Understanding Environmental Changes and Human Impacts for Management and Conservation

Anthropogenic activities are substantially changing coastal wetland ecosystems globally. In developing countries such as China, a number of anthropogenic factors associated with rapid population growth and economic development threaten coastal wetlands. In China, notably, coastal wetlands have been increasingly lost to reclamations that are widely adopted to meet the increasing demand for land under rapid economic development. Coastal wetland management requires understanding the patterns of and the mechanisms underlying such human impacts. In this special issue, we synthesize current understanding of environmental changes and human impacts on China’ coastal wetlands, focusing on reclamation. Coastal human activities in China are found to change shoreline evolution and wetland hydrology, to deteriorate soil and water quality, to alter vegetation succession, benthic animal and microbial communities, and fisheries, and to impair ecosystem functioning and services. For some of those impacts, new models and indices are developed or applied. We also outline key research areas that should be further studied for effective management of coastal wetlands and successful wetland restoration. We suggest that developing a multi-objective, multi-scenario, and multi-scale framework of integrated management will be crucial to the success of China’s coastal wetland conservation with increasing human dominance of the nation’s coasts.

Polycyclic aromatic hydrocarbons (PAHs) in wetland soils under different land uses in a coastal estuary: toxic levels, sources and relationships with soil organic matter and water-stable aggregates.

The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in the soils from industrial, wharf, cropland, milldam and natural wetland sites to characterize their distributions, toxic levels and possible sources in the Pearl River Estuary and identify their relationships with soil organic matter (SOM) and water-stable aggregates (WSAs). Our results indicate that the average concentration of total PAHs in this region reached a moderate pollution level, which was higher than that in other larger estuaries in Asia. The average level of total PAHs in industrial soils was 1.2, 1.5, 1.6 and 2.3 times higher than those in soils from wharf, cropland, milldam and natural wetland sites, respectively. Greater accumulation of PAHs occurred in the middle and/or bottom soil layers where 3-ring PAHs were dominant. Industrial soils also exhibited the highest toxic levels with the highest toxic equivalent concentrations of PAHs, followed by wharf and milldam soils, and the cropland and wetland soils had the lowest toxicity. The diagnostic ratios suggested that PAHs primarily originated from biomass and coal combustion at industrial and milldam sites, and petroleum combustion was determined to be the primary source of PAHs at the wharf, cropland and wetland sites. Both 3-ring and 4-ring PAHs in the milldam and wharf soils were significantly positively correlated with the SOM, whereas the 4,5,6-ring PAHs and total PAHs in industrial soils and the 2-ring PAHs in cropland soils were significantly negatively correlated with the SOM. In addition, large WSAs also exhibited a significant positive correlation with PAHs.

Five-year changes in soil organic carbon and total nitrogen in coastal wetlands affected by flow-sediment regulation in a Chinese delta.

Changes in the sources and sinks of soil organic carbon (SOC) and total nitrogen (TN) in wetland soils as indicators of soil quality and climate change have received attention worldwide. Soil samples were collected in 2007 and 2012 in the coastal wetlands of the Yellow River Delta and the SOC and TN were determined to investigate a five-year change in their content and stock in these wetlands as affected by flow-sediment regulation. Our results revealed that the soils in 2007 exhibited greater electrical conductivities, SOC content and density, and ammonium nitrogen (NH4+-N) levels in the top 10 cm soils (p < 0.05) compared with the soils in 2012. In general, the SOC and TN contents decreased with increasing soil depth. However, the highest ratios of soil organic carbon and total nitrogen (molar C/N ratios) were observed in the 30–40 cm soil layer. A significant SOC loss occurred (p < 0.05) in top 10 cm soils, but only a small change in SOC in the top 50 cm soils. Comparatively, TN levels did not show significant differences in the study period.

Temporal–spatial variation and partitioning prediction of antibiotics in surface water and sediments from the intertidal zones of the Yellow River Delta, China

As special zones, the intertidal zones of the Yellow River Delta (YRD) are highly variable along with time and space. Fluvial-marine and land-ocean interactions which frequently occur in these areas have a great impact on the fate of pollutants. Antibiotics, which contribute to antibiotic-resistant genes (ARGs), are widely detected in wastewater, natural water, soil, sediments, and even drinking water. Therefore, it is meaningful to investigate the occurrence and fate of antibiotics in these special zones. In this study, eight antibiotics belonging to tetracyclines (TCs), fluoroquinolones (FQs), and macrolides (MLs) were detected in the surface water and sediments from the intertidal zones of YRD during two seasons. Two models were established to predict the partitioning coefficients of norfloxacin (NOR) and erythromycin (ETM) using physicochemical properties of sediments, respectively. The total concentrations of these antibiotics were 82.94-230.96ng·L(-1) and 40.97-207.44ng·g(-1), respectively, in the surface water and sediments. Seasonal variation was mainly influenced by the frequency of antibiotics use and environment factors. The regions with river supply exhibited the highest concentrations of antibiotics in surface water and sediments. Meanwhile, particle-size fractions, cation exchange capability (CEC), and metal ions content played dominant roles in the partitioning behaviors of NOR and ETM between the surface water and sediments. Both models established in this study featured accuracy and feasibility, which provided the methods for predicting the partitioning coefficients of emerging contaminants similar in structures to NOR and ETM in the intertidal zones.