Soil Type, Topography, and Land Use Interact to Control the Response of Soil Respiration to Climate Variation

The effects of soil and topography on the responses of soil respiration (Rs) to climatic variables must be investigated in the southeastern mountainous areas of China due to the rapid land-use change from forest to agriculture. In this study, we investigated the response of Rs to soil temperature (ST), precipitation over the previous seven days (AP7), and soil water content (SWC) across two hillslopes that had different land uses: a tea garden (TG) and a bamboo forest (BF). Meanwhile, the roles of soil properties including soil clay content and total nitrogen (TN), and topography including elevation, profile curvature (PRC), and slope on the different responses of Rs to these climatic variables were investigated. Results showed that mean Rs on the BF hillslope (2.21 umol C m−2 s−1) was 1.71 times of that on the TG hillslope (1.29 umol C m−2 s−1). Soil clay content, elevation, and PRC had negative correlations (p \u3c 0.05) with spatial variation of Rs, and ST was positively correlated (p \u3c 0.01) with temporal variation of Rs on both hillslopes. Across both hillslopes ST explained 33%–73% and AP7 explained 24%–38% of the temporal variations in Rs. The mean temperature sensitivities (Q10s) of Rs were 2.02 and 3.22, respectively, on the TG and BF hillslopes. The Q10 was positively correlated (p \u3c 0.05) with the temporal mean of SWC and TN, and negatively correlated (p \u3c 0.05) with clay and slope. The mean AP7 sensitivities (a concept similar to Q10) were greatly affected by clay and PRC. When Rs was normalized to that at 10 °C, power or quadratic relationships between Rs and SWC were observed in different sites, and the SWC explained 12%–32% of the temporal variation in Rs. When ST and SWC were integrated and considered, improved explanations (45%–81%) were achieved for the Rs temporal variation. In addition, clay and elevation had vital influences on the responses of Rs to SWC. These results highlight the influences of soil, topographic features, and land use on the spatial variations of the Rs, as well as on the responses of Rs to different climatic variables, which will supplement the understanding of controlling mechanisms of Rs on tea and bamboo land-use types in Southeastern China

Environmental impact assessments of the Three Gorges Project in China: issues and interventions

The paper takes China's authoritative Environmental Impact Statement for the Yangzi (Yangtze) Three Gorges Project (TGP) in 1992 as a benchmark against which to evaluate emerging major environmental outcomes since the initial impoundment of the Three Gorges reservoir in 2003. The paper particularly examines five crucial environmental aspects and associated causal factors. The five domains include human resettlement and the carrying capacity of local environments (especially land), water quality, reservoir sedimentation and downstream riverbed erosion, soil erosion, and seismic activity and geological hazards. Lessons from the environmental impact assessments of the TGP are: (1) hydro project planning needs to take place at a broader scale, and a strategic environmental assessment at a broader scale is necessary in advance of individual environmental impact assessments; (2) national policy and planning adjustments need to react quickly to the impact changes of large projects; (3) long-term environmental monitoring systems and joint operations with other large projects in the upstream areas of a river basin should be established, and the cross-impacts of climate change on projects and possible impacts of projects on regional or local climate considered. © 2013 Elsevier B.V.Xibao Xu, Yan Tan, Guishan Yan

Coupling soil water processes and nitrogen cycle across spatial scales: Potentials, bottlenecks and solutions

Interactions among soil water processes and the nitrogen (N) cycle govern biological productivity and environmental outcomes in the earth’s critical zone. Soil water influences the N cycle in two distinct but interactive modes. First, the spatio-temporal variation of soil water content (SWC) controls redox coupling among oxidized and reduced compounds, and thus N mineralization, nitrification, and denitrification. Secondly, subsurface flow controls the movement of water and dissolved N. These two processes interact such that subsurface flow dynamics control the occurrence of relatively static, isolated soil solution environments that span a range of reduced to oxidized conditions. However, the soil water-N cycle is usually treated as a black box. Models focused on N cycling simplify soil water parameters, while models focused on soil water processes simplify N cycling parameters. In addition, effective ways to deal with upscaling are lacking. New techniques will allow comprehensive coupling of the soil water-N cycle across time and space: 1) using hydrogeophysical tools to detect soil water processes and then linked to electrochemical N sensors to reveal the soil N cycle, (2) upscaling small-scale observations and simulations by constructing functions between soil water-N cycle and ancillary soil, topography and vegetation variables in the hydropedological functional units, and (3) integrating soil hydrology models with N cycling models to minimize the over-simplification of N biogeochemistry and soil hydrology mechanisms in these models. These suggestions will enhance our understanding of soil water processes and the N cycle and improve modeling of N losses as important sources of greenhouse gas emission and water pollution.This is a manuscript of an article published as Qing Zhu, Michael J. Castellano, Guishan Yang , Coupling soil water processes and nitrogen cycle across spatial scales: Potentials, bottlenecks and solutions. Earth-Science Reviews (2018), doi:10.1016/j.earscirev.2018.10.005. Posted with permission.</p

Measuring the Pattern of High Temperature Areas in Urban Greenery of Nanjing City, China

Most studies are concerned with the cooling effect of urban greenery, but some have also revealed that some patches changed from normal temperature areas (NTAs) into high temperature areas (HTAs). Landsat TM images and ArcGIS software are used to analyze the HTA patterns in Nanjing, China. The HTAs’ lower limit temperature was defined as the 30.26 °C and the percentage of the HTAs in all greenery was 24.87%. The disturbance on the cooling effect existed but not evidently. The average impervious ratio (IR) and surface temperature (ST) of HTAs, respectively, were 3.76 times and higher 2.86 °C than those of NTAs. The structure of NTAs’ IR levels was extremely uneven but the HTAs’ were relatively even. However, the co-coefficient between the IR and ST in the whole greenery was small. Sampling analysis with the same ST and IR revealed that the complex environment in green buffer affected temperature differences; The adjacent HTAs, with its 89.78% in the study area, largely along the green patch, were far more than independent HTAs and presented a ring shape. Thus, the significantly heterogeneous urban environment inevitably resulted in diverse factors forming HTAs

Three Gorges Project: effects of resettlement on nutrient balance of the agroecosystems in the reservoir area

This paper reports on the effects of human resettlement on the nutrient balance of the agroecosystems in Three Gorges Reservoir Area (TGRA) of China. The analysis used is the OECD (Organisation for Economic Co-operation and Development) 'Soil Surface Nitrogen Balance Model' and agricultural statistical data for the county level in 1985-2005. Spatial and temporal changes of nutrient balance and the impacts of resettlement on such changes were examined. The results demonstrate that rural resettlement has significantly increased soil surface nitrogen and phosphorous surplus since 2000. The structural transformation of agricultural activities from grain production to horticulture or forestry should be encouraged, and more people may need to be moved out of the TGRA to reduce nutrient water pollution.Three Gorges Project, resettlement, nutrient balance, agroecosystems,

Urban Land Pattern Impacts on Floods in a New District of China

Urban floods are linked to patterns of land use, specifically urban sprawl. Since the 1980s, government-led new districts are sweeping across China, which account for many of the floods events. Focuses of urbanization impact on floods are extending gradually from hydraulic channels, to imperviousness ratio, to imperviousness pattern in urban areas or urbanized basins. Thus, the paper aims to explore how urban land pattern can affect floods in urban areas to provide decision makers with guidance on land use and stormwater management. Imperviousness was generally correlated with spatial variations in land use, with lower imperviousness in less dense, new districts, and higher imperviousness in more dense, uniform/clustered development in local areas adjacent to hot nodes. The way imperviousness and channel are organized, and the location of imperviousness within a catchment, can influence floods. Local government’s approach to new district planning, in terms of zoning provisions, has only considered some development aspects and has not adequately integrated flood management. A key issue for the planning should been done to adequately cater for flooding, particularly considering the benefits of keeping natural conveyance systems (rivers) and their floodplains to manage flood waters