Wei-Yu Shi

Progress in the remediation of hazardous heavy metal-polluted soils by natural zeolite

Hazardous heavy metal pollution of soils is an increasingly urgent problem all over the world. The zeolite as a natural amendment has been studied extensively for the remediation of hazardous heavy metal-polluted soils with recycling. But its theory and application dose are not fully clear. This paper reviews the related aspects of theory and application progress for the remediation of hazardous heavy metal-polluted soils by natural zeolite, with special emphasis on single/co-remediation. Based on the comments on hazardous heavy metal behavior characteristics in leaching and rhizosphere and remediation with zeolite for heavy metal-polluted soils, it indicated that the research of rhizosphere should be strengthened. Theory of remediation with natural zeolite could make breakthroughs due to the investigation on synthetic zeolite. Co-remediation with natural zeolite may be applied and studied with more prospect and sustainable recycling.

The remediation of the lead-polluted garden soil by natural zeolite.

The current study investigated the remediation effect of lead-polluted garden soil by natural zeolite in terms of soil properties, Pb fraction of sequential extraction in soil and distribution of Pb in different parts of rape. Natural zeolite was added to artificially polluted garden soil to immobilize and limit the uptake of lead by rape through changing soil physical and chemical properties in the pot experiment under greenhouse conditions. Results indicated that the addition of natural zeolite could increase soil pH, CEC, content of soil organic matter and promote formation of soil aggregate. The application of zeolite decreased the available fraction of Pb in the garden soil by adjusting soil pH rather than CEC, and restrained the Pb uptake by rape. Data obtained suggested that the application of a dose of zeolite was adequate (>or=10 g kg(-1)) to reduce soluble lead significantly, even if lead pollution is severe in garden soil (>or=1000 mg kg(-1)). An appropriate dose of zeolite (20 g kg(-1)) could reduce the Pb concentration in the edible part (shoots) of rape up to 30% of Pb in the seriously polluted soil (2000 mg kg(-1)).

Co-remediation of the lead-polluted garden soil by exogenous natural zeolite and humic acids

The current study reported the co-remediation effect on the lead-polluted garden soil by zeolite and humic acids (HA), which was from comparing with the remediation of single zeolite in term of the lead fraction of sequential extraction in the soil and the distribution of lead in different parts of rape. Mixed treatment (zeolite and HA) and single treatment (zeolite) were, respectively, applied to the artificially polluted garden soil to examine the difference of their remediation effects in pot experiment. Results indicated that the co-remediation led to significantly greater (p<0.01) reduction in the lead concentration in plants than by singly adding to zeolite. The co-application of zeolite and HA reduced the available fraction of lead compounds, but slightly increased (p<0.01) the water-soluble fraction of lead compounds in the garden soil, compared with the application of single zeolite, especially in the severe lead-polluted soil (> or =1000 mg kg(-1)). This method might be an efficient way to remediate the lead-polluted soils on a large scale, although zeolite is a kind of hazardous material.

How many check dams do we need to build on the Loess Plateau

F more than 400 years, check dams have been constructed on the Loess Plateau of China. Over the past several hundred years, people have increasingly realized the advantages of check dams for capturing sediments, improving gully slope stabilities, and increasing croplands. In Environmental Science and Technology, Wang et al. summarized the advantages of check dams for environmental services and food security. The report demonstrated that about 110,000 check dams have been built on the Loess Plateau over the past 50 years and approximately 21 billion m of sediments have been captured by these dams. Moreover, the filled check dams can be reclaimed as croplands, and by 2002, approximately 320,000 hectares of dam croplands had been created. The significant role of check dams in soil conservation and cropland expansion inspires the passions of policy makers. As early as 2003, the Ministry of Water Resources of P.R. China (CMWR) initiated a program for check dams in the Loess Plateau, and 163,000 check dams are planned and an investment of 83.06 billion RMB of funding is required for the period 2003−2020. Policy makers consider that the Loess Plateau has the capacity to allow the construction of as many as 334,000 check dams and will therefore require an even greater amount of investment. The Loess Plateau is currently undergoing a great leap forward in check dam construction. The CMWR has set a target of 47,000 check dams, built at an investment of more than 20 billion RMB, from 2010 to 2015. Increasing numbers of environmental scientists are concerned about the negative effects of such large-scale engineering on the balance of the water cycle and sediment load in the Yellow River. The CMWR projects that, by 2020, check dam construction will lead to a 4.3−5.5 billion m decrease in water yield to the Yellow River. However, the amount of this decrease is highly uncertain. The actual amount may exceed the projected amount due to trends in climate warming and extensive human activities. The sediment load and streamflow in the Yellow River have dramatically decreased in recent years. Huang et al. reported that the sediment load delivered from the Yellow River to the sea decreased sharply to 0.15 billion tons per year between 2000 and 2005, representing only 14% of the widely cited estimate of 1.08 billion tons per year. The data released by the Yellow River Sediment Bulletin show that the sediment load gauged by the Huayuankou hydrologic station decreased substantially to 0.107 billion tons per year between 2000 and 2010. This value represents only 10% of the sediment load of 1.054 billion tons per year occurring between 1950 and 2000. Moreover, the annual streamflow in the Yellow River averaged 40.05 billion m between 1950 and 2000, whereas it decreased to 22.65 billion m during the past decade. Many scientists conclude that human intervention is the primary factor that caused the decrease in the sediment load and streamflow in the Yellow River. However, we still have not determined a suitable sediment load and streamflow that would keep the Yellow River healthy, and therefore determine the appropriate number of check dams that should be built on the Loess Plateau. The Loess Plateau covers an area of 648,700 km, including 200,000 km of highplain plateau, 140,000 km of hilly plateau, 107,200 km of rocky mountains, 63,600 km of Fen River− Wei River fault depression valley, 79,2000 km of deserts, and 58,700 km of Hetao alluvial plains (Figure 1). The different geographical regions play different roles in soil and water conservation and ecosystem services. The hilly plateau regions suffer the most severe soil erosion in the Loess Plateau and should therefore be considered critical areas for check dam engineering. The rocky mountain regions are appropriate for planting and should therefore be considered critical areas for afforestation and water conservation. We suggest that the planning of check dam engineering should comply with the landforms and geographical function zones. Currently, many significant problems occur in the planning and engineering of check dams. First, there is a lack of critical discussion on the appropriate density and distribution of check dams. The contiguous area of Shanxi-Shaanxi-Inner Mongolia is the central erosion area of the hilly plateau and is therefore the most critical target area for check dam construction. However, a large number of check dams are still planned for construction in the highplain plateau and rocky mountains. Second, effective soil and water conservation measures and climate change significantly decreased soil erosion in the Loess Plateau and

Land-use types and soil chemical properties influence soil microbial communities in the semiarid Loess Plateau region in China

Similar land-use types usually have similar soil properties, and, most likely, similar microbial communities. Here, we assessed whether land-use types or soil chemical properties are the primary drivers of soil microbial community composition, and how changes in one part of the ecosystem affect another. We applied Ion Torrent sequencing to the bacterial and fungal communities of five different land-use (vegetation) types in the Loess Plateau of China. We found that the overall trend of soil quality was natural forest > plantation > bare land. Dominant bacterial phyla consisted of Proteobacteria (42.35%), Actinobacteria (15.61%), Acidobacteria (13.32%), Bacteroidetes (8.43%), and Gemmatimonadetes (6.0%). The dominant fungi phyla were Ascomycota (40.39%), Basidiomycota (38.01%), and Zygomycota (16.86%). The results of Canonical Correspondence Analysis (CCA) and Redundancy Analysis (RDA) based on land-use types displayed groups according to the land-use types. Furthermore, the bacterial communities were mainly organized by soil organic carbon (SOC). The fungal communities were mainly related to available phosphorus (P). The results suggested that the changes of land use type generated changes in soil chemical properties, controlling the composition of microbial community in the semiarid Loess Plateau region. The microbial community could be an indicator for soil quality with respect to ecological restoration.

Dynamics of ecosystem carbon stocks during vegetation restoration on the Loess Plateau of China

In the last few decades, the Loess Plateau had experienced an extensive vegetation restoration to reduce soil erosion and to improve the degraded ecosystems. However, the dynamics of ecosystem carbon stocks with vegetation restoration in this region are poorly understood. This study examined the changes of carbon stocks in mineral soil (0–100 cm), plant biomass and the ecosystem (plant and soil) following vegetation restoration with different models and ages. Our results indicated that cultivated land returned to native vegetation (natural restoration) or artificial forest increased ecosystem carbon sequestration. Tree plantation sequestered more carbon than natural vegetation succession over decades scale due to the rapid increase in biomass carbon pool. Restoration ages had different effects on the dynamics of biomass and soil carbon stocks. Biomass carbon stocks increased with vegetation restoration age, while the dynamics of soil carbon stocks were affected by sampling depth. Ecosystem carbon stocks consistently increased after tree plantation regardless of the soil depth; but an initial decrease and then increase trend was observed in natural restoration chronosequences with the soil sampling depth of 0–100 cm. Moreover, there was a time lag of about 15–30 years between biomass production and soil carbon sequestration in 0–100 cm, which indicated a long-term effect of vegetation restoration on deeper soil carbon sequestration.

Net primary production, nitrogen cycling, biomass allocation, and resource use efficiency along a topographical soil water and nitrogen gradient in a semi-arid forest near an arid boundary

AimsThe objective of this study was to investigate how plants maintain productivity under a limited supply of water and N along the topographical soil water and N gradients in semi-arid forests.MethodsWe investigated forest structure and productivity, N cycling, and water and N use by plants at three different slope positions in a forested area near an arid boundary on a loess plateau in China.ResultsNet primary production (NPP) and aboveground N uptake decreased as soil water and/or N availability decreased on upper slopes; however, NPP and aboveground N uptake were only slightly lower than those of more humid forest ecosystems. Water use efficiency (WUE), N use efficiency (NUE), and fine root biomass increased as soil water and/or N supply decreased with altitude. High NUE was linked to higher N mean residence time, caused by higher N resorption efficiency rather than increasing N productivity.ConclusionsOur results suggest that NPP and N uptake can be maintained by increasing WUE and NUE and increasing fine root biomass in water and N co-limited semi-arid forest ecosystems near arid boundaries. Such changes in resource use and acquisition strategy can affect production and N cycling via plant-soil feedback systems.

A Monte Carlo approach to estimate the uncertainty in soil CO2 emissions caused by spatial and sample size variability.

Abstract The soil CO2 emission is recognized as one of the largest fluxes in the global carbon cycle. Small errors in its estimation can result in large uncertainties and have important consequences for climate model predictions. Monte Carlo approach is efficient for estimating and reducing spatial scale sampling errors. However, that has not been used in soil CO2 emission studies. Here, soil respiration data from 51 PVC collars were measured within farmland cultivated by maize covering 25 km2 during the growing season. Based on Monte Carlo approach, optimal sample sizes of soil temperature, soil moisture, and soil CO2 emission were determined. And models of soil respiration can be effectively assessed: Soil temperature model is the most effective model to increasing accuracy among three models. The study demonstrated that Monte Carlo approach may improve soil respiration accuracy with limited sample size. That will be valuable for reducing uncertainties of global carbon cycle.