Significant loss of soil inorganic carbon at the continental scale.

Widespread soil acidification due to atmospheric acid deposition and agricultural fertilization may greatly accelerate soil carbonate dissolution and CO2 release. However, to date, few studies have addressed these processes. Here, we use meta-analysis and nationwide-survey datasets to investigate changes in soil inorganic carbon (SIC) stocks in China. We observe an overall decrease in SIC stocks in topsoil (0-30 cm) (11.33 g C m-2 yr-1) from the 1980s to the 2010s. Total SIC stocks have decreased by ∼8.99 ± 2.24% (1.37 ± 0.37 Pg C). The average SIC losses across China (0.046 Pg C yr-1) and in cropland (0.016 Pg C yr-1) account for ∼17.6%-24.0% of the terrestrial C sink and 57.1% of the soil organic carbon sink in cropland, respectively. Nitrogen deposition and climate change have profound influences on SIC cycling. We estimate that ∼19.12%-19.47% of SIC stocks will be further lost by 2100. The consumption of SIC may offset a large portion of global efforts aimed at ecosystem carbon sequestration, which emphasizes the importance of achieving a better understanding of the indirect coupling mechanisms of nitrogen and carbon cycling and of effective countermeasures to minimize SIC loss.

Spatial-temporal evolution and prediction of urban landscape pattern and habitat quality based on CA-Markov and InVEST model.

The change of urban landscape caused by human activities is one of the most important factors affecting terrestrial ecosystem. The distribution of urban landscape pattern has great impacts on the service function of regional biodiversity. To reveal the variation of landscape pattern and habi-tat quality in cities and its driving factors, we extracted landscape type information of Wuhan in 2005, 2010, 2015, and analyzed spatial-temporal evolution of landscape pattern using Markov transition model. The CA-Markov model was used to simulate the landscape pattern in 2020 under the natural growth scenario. The driving factor for landscape variation was analyzed using Logistic regression model. Combined with InVEST model, spatial pattern of habitat quality and its variation in three phases were calculated and evaluated. The simulated habitat quality in 2020 was obtained and its distribution characteristics were analyzed. The relationship between variation of landscape pattern and human activities was explored. The results showed that cultivated land and manufactured surface were the landscape types with highest variations between 2005 and 2015. The area of cultivated land continued to decline, with most of the area being transferred into manufactured surface. The area of manufactured surface continued to increase, most of which was transferred from paddy field and dry land. From 2005 to 2015, the habitat quality declined, with a large number of landscapes with high habitat quality level being changed to low habitat quality level. The overall index of habitat quality decreased and the biodiversity service function declined, indicating the degeneration of habitat quality. In 2015-2020, the evolutionary trend of landscape pattern and habitat quality would keep consistent with the past decade, with an increasing area of artificial surface, decreasing index of habitat quality, weakening biodiversity service function, and degenerating habitat quality. The most important factor accounted for the landscape pattern change in the study area was the changes in Gross Domestic Product (GPD) and regional fiscal revenue. Human socio-economic activities were the key driving force for the spatial variation of landscape and degeneration of habitat quality. Urbanization and land reclamation by filling lakes were the main reasons for landscape pattern variation in Wuhan.

The effects of rainfall regimes and terracing on runoff and erosion in the Three Gorges area, China.

Changes in natural rainfall regimes have taken place and are expected to become more pronounced in future decades. These changes are also likely to be accompanied by changes in crop management practices. The main purpose of this study was to analyze runoff and soil loss in relation to rainfall regimes and terracing in the Three Gorges area, China. Based on 10 years of field observation and k-mean clusters, 101 rainfall events were grouped into three rainfall regimes. Rainfall regime I was the group of events with strong rainfall intensity, high frequency, and short duration. Rainfall regime III consisted of events with low intensity, long duration, and high rainfall amount. Rainfall regime II was the aggregation of events of high intensity and amount, and less frequent occurrence. The results showed that event runoff coefficients were not significantly different among rainfall regimes. However, the average soil erosion rates in rainfall regimes I and II were significantly higher than that in regime III. The average erosion rates under rainfall regimes I, II, and III were 21.6, 39.7, and 9.8 g m-2, respectively. The effect of rainfall regime on soil erosion also was changed by terracing. On unterraced cropland, soil erosion rate in rainfall regime I is significantly higher than that in regime III. However, the situation did not exist in unterraced orchard. Terracing significantly reduced runoff and soil erosion, and compensated the effects of rainfall regime on soil erosion, which indicated that runoff and erosion in terraced system may be little influenced by climate change. Based on these results, it was suggested more attention should be paid to the timing of rainfall events in relation to crop development and the high erosion on unterraced citrus orchard to control soil erosion in this area.

[Oxidation Process of Dissolvable Sulfide by Manganite and Its Influencing Factors].

As one of the manganese oxides, which are easily generated and widely distributed in supergene environment, manganite participates in the oxidation of dissolvable sulfide (S²â»), and affects the migration, transformation, and the fate of sulfides. In the present work, the redox mechanism was studied by determining the intermediates, and the influence of initial pH and oxygen atmosphere on the processes were studied. The chemical composition, crystal structures and micromorphologies were characterized by XRD, FTIR and TEM. The concentration of S²â» and its oxidation products were analyzed using spectrophotometer, high performance liquid chromatograph and ion chromatograph. The results indicated that elemental sulfur was formed as the major oxidation product of S²â» oxidation, and decreased pH could accelerate the oxidation rate of S²â» in the initial stage, however, there was no significant influence on final products. Elemental S could be further oxidized to S2O3²â» when the reaction system was bubbled with oxygen, and manganite exhibited excellent catalytic performance and chemical stability during the oxidation of dissolvable sulfide by oxygen. After reaction of more than 10 h, the crystal structure of manganite remained stable.

Effects of vegetation on runoff generation, sediment yield and soil shear strength on road-side slopes under a simulation rainfall test in the Three Gorges Reservoir Area, China.

Vegetation recolonization has often been used to control roadside slope erosion, and in this paper, four restoration models - Natural Restoration, Grass, Grass & Shrub, Sodded Strip - were chosen to recolonize the plants on a newly built unpaved roadside slope in the Three Gorges Reservoir Area. After eight months growth, eight rainfall simulations (intensity of 90 mm h(-1) for 60 min) and in-situ soil shear strength test were then carried out to identify the impacts of vegetation on roadside slope erosion and soil shear strength. The erosion on cutslopes was higher than that on fillslopes. The runoff coefficient and soil detachment rate were significantly lower on the Grass & Shrub model (4.3% and 1.99 g m(-2) min(-1), respectively) compared with the other three, which had the highest surface cover (91.4%), aboveground biomass (1.44 kg m(-2)) and root weight density (3.94 kg m(-3)). The runoff coefficient and soil detachment rate on roadside slopes showed a logarithmic decrease with the root weight density, root length density and aboveground biomass. The soil shear strength measured before and after the rainfall was higher on Grass & Shrub (59.29 and 53.73 kPa) and decreased on Grass (46.93 and 40.48 kPa), Sodded Strip (31.20 and 18.87 kPa) and Natural Restoration (25.31 and 9.36 kPa). Negative linear correlations were found between the soil shear strength reduction and aboveground biomass, root weight density and root length density. The variation of soil shear strength reduction was closely related to the roadside slope erosion, a positive linear correlation was found between runoff coefficient and soil shear strength reduction, and a power function was shown between soil detachment rate and soil shear strength reduction. This study demonstrated that Grass and Grass & Shrub were more suitable and highly cost-effective in controlling initial period erosion of newly built low-volume unpaved road.

[Effects of different vegetation protection measures on erosion prevention of unpaved roadside slopes in Three Gorges Reservoir Area].

One of the main impacts of road construction is the creation of bare and steep slopes when lack of vegetation protection, which usually generates serious soil loss, a major erosion source in mountainous areas. In this study, six treatments including planting grass (GRA), grass and bush (GBC), building terrace combined with grass and bush (TGB), planting sod strip (SS), building sloping farmland (SFL), and building sloping farmland combined with grass (SFLG) were installed on the newly constructed unpaved roadside slopes in Three Gorges Reservoir Area to investigate the effects of these measures on the erosion prevention of the unpaved roadside slopes under natural rainfall. Among the six treatments, GBC had the best effect, which had the quickest revegetation rate (the mean vegetation coverage increased from 20.2% to 91.6%), decreased the soil bulk density by 9.5%, and increased the saturated hydraulic conductivity by 678.1%, followed by GRA and SS. TGB had the greatest potential in mitigating soil loss and runoff, with the efficiency in trapping sediment and runoff reached 80.2% and 72.3%, respectively, being appropriate for the cut slopes with a gradient greater than 45 degrees, followed by GBC and GRA. GRA had a higher efficiency on fill slope than on cut slope, while GBC showed greater applicability on cut slope. On the fill slope with a moderate gradient 15 degrees, SFLG had a potential of trapping 23.0% of sediment, which was equivalent to that of GRA and GBC, but the efficiency in trapping runoff was only 2.0%. When the fill slopes with a gradient less than 15 degrees were utilized as farmland, a grass buffer strip of 2 m length was needed on the upslope for erosion control.

The effects of land use change on environmental quality in the red soil hilly region, China: a case study in Xianning County.

Land use and land cover change is gaining recognition as a key driver of environmental change. Rapid change of land use has occurred in the red soil hilly region of southeast China in the past three decades due to rural land reform, population pressure and rapid economic growth. In this paper, land use change and its impacts on environmental quality of Xianning County were investigated using technologies of remote sensing (RS), geographic information systems (GIS), and spatial principal components analysis (SPCA). It was indicated that the area of paddy field and upland decline rapidly while the area of woodland, horticulture farm and residential land increased sharply between 1978 and 2002. The driving forces probably were land use policy of the State government, structural adjustment of agricultural sectors and implementation of environmental conservation measures. Based on the assessment of environmental implications of land use practices, the environmental quality of some land use types (i.e. Woodland, sparse woodland, and paddy field) tended to improve, while horticulture farms, water body, and residential land showed a deterioration trend of environmental quality during 1978-2002. Perhaps the most significant finding of this study is that environment appears a negative tendency in the study area from 1991 to 2002, because little attention has been paid to the status and management of agricultural lands, which account for a substantial proportion of total land area. Therefore, for further improving environment in red soil hilly region in China, urgent action is required to improve the advisory services support to farmers on new tillage practices, soil and water conservation practices, raising the efficiency of fertilizer and manure use.

[Dynamic changes of forest vegetation coverage in letianxi basin of Three Gorges Reservoir Area: a study based on multi-source data].

Based on the multi-temporal and multi-source sensor images of 1987-2005, the dynamic changes of forest vegetation coverage in Letianxi basin of Three Gorges Reservoir Area were investigated by the methods of color balancing, image fusion, and radiometric normalization. The results showed that in 1987-2005, the forest area in the basin increased from 265.82 km2 to 346.45 km2. Vegetation coverage also had an increasing trend, but the increment was not uniform in the whole basin. The change process of the forest vegetation could be divided into three stages, i.e., slight destroying, starting restoration, and complete restoration. The gravity center of the forests in different coverage classes changed significantly, e.g., the gravity center of the forests with vegetation coverage less than 45% transferred to the north before 1987, but moved back to the south thereafter, while that of the forests with vegetation coverage greater than 45% moved constantly from northwest to southeast. The changes of forest vegetation coverage in the study area were deeply affected by the human disturbance, regional economic development, and national comprehensive management measures. Through 10 years ecological restoration, human disturbance was decreasing, and the forest area with vegetation coverage above 60% reached 217.88 km2, occupying about 62.9% of the total forest area, which implied that the ecological environment was improved gradually.