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

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

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

Preparation of Sea-buckthorn Oil Microcapsule Composite Film and the Preservation Effect of Hand-grabbed Mutton

In order to explore the preservation effect of microcapsule composite film with sea-buckthorn oil on hand-grabbed mutton, this study used gelatin/acacia to coat sea-buckthorn oil, and prepared microcapsule composite film with sea-buckthorn oil using gelatin as membrane substrate and glycerin as plasticizer. The mechanical properties, surface morphology and antioxidant and antibacterial activities of the composite film were measured, and the film was fitted on the surface of hand-grabbed mutton. The effects of composite membrane on color, pH, weight loss, TVB-N, total number of bacterial colonies and sensory indexes were analyzed to evaluate the fresh-keeping effect of hand-grabbed mutton. Results showed that the embedding rate and yield of sea buckthorns oil microcapsules were 88.94% and 76.28%, respectively, and the optimum conditions for preparing the membrane were 6 g/100 mL gelatin concentration. The ratio of gelatin to glycerin was 1:0.4 and the drying conditions were 20 ℃ for 48 h. The thickness of the composite film was 0.36±0.01 cm, the percentage of breaking elongation was 50.56%±0.55%, the tensile strength was 27.81±0.22 N, and the permeability coefficient was 2.50±0.10 ×10−12 g·cm/(cm2·Pa·s), indicating that it had good mechanical properties. Compared with coating treatment, DPPH and ABTS+ free radical scavenging rates decreased by 18.95% and 19.84% after 15 d. The antibacterial zone diameter was 3±0.5 cm. Compared with the blank group and the coated group, the composite film could reduce the weight loss rate, inhibit the growth of TVB-N, maintain the color and extend the shelf life for 5 d. This study proved that microcapsule composite film with sea-buckthorn oil has good preservation effect, providing theoretical guidance for meat preservation

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