Pedological Characteristics and Heavy Metals Contamination of the Paddy Soils in Taiwan

Extensive rice production on numerous alluviums and terraces in Taiwan has been done by the complete irrigation systems since the early and mid stages of the 20th century. Irrigation water and the fluctuation of groundwater play important roles in controlling the soil hydrology and redoximorphology. Redoximorphic features are consequently formed by the alternative wet and dry cycles, such as Fe soft masses, Fe and clay depletions and Fe-Mn nodules through the profiles of paddy soils. The saturated and reducing durations were specified associated with the definite redoximorphic features in the soils under a landscape unit. In the case studies of rice-growing Ultisols on red earth terrace in northwestern Taiwan, the optimum durations of saturation and reduction were about 50% of the year in the formation of redoxi-morphic features. This anthraquic condition could promote the formation of diverse redoximorphic features associated with plinthites. In the paddy soils of Taiwan, Entisols, Inceptisols, Alfisols, Ultisols, Mollisols and Oxisols are main Soil Orders based on Soil Taxonomy. On one hand considering by soil quality and food security of rice, heavy metal contamination is the main issue in rice production of Taiwan. On the other hand by rice market liberalization, changing the land use from paddy soils into non-waterlogged cropping has some problems in initial soil properties such as poor drainage and impeded root growth by the subsurface compacted layers for upland crops. Irrigation water for rice production in Taiwan has been contaminated by illegal discharges of industrial and livestock wastewater affecting the paddy soil qualities by heavy metals. According to the regulation for pollutants in Soil and Groundwater Pollution Remediation Act of Taiwan, the total seriously contaminated area by heavy metals is more than 300ha, especially by Cd, Cr, Cu, Ni and Pb contamination of rice in Taiwan. Due to the special profile morphology and hydrology of paddy soils, dilution by deep plowing and mixing, acid washing, chemical stabilization, and phytoremediation are major remediation technologies applied on the contaminated sites with pilot or field scales. However, the recovery of soil fertilities and ecological functions is needed to be evaluated after remediation.Special Revie

Effect of Sampling Density on Estimation of Regional Soil Organic Carbon Stock for Rural Soils in Taiwan

Accurately quantifying soil organic carbon (SOC) stocks in soils is considered necessary and important for studying the soil quality and productivity, modeling the global carbon cycle, and assessing the global climate change. The objectives of this chapter are (1) to evaluate the effects of sampling density and interpolation methods on spatial distribution of SOC density (SOCD) and (2) to estimate the SOC stocks in 0–30, 0–50, and 0–100 cm layer of Tainan rural soils (2192 km2), Taiwan. Ordinary kriging (OK), empirical Bayesian kriging (EBK), and inverse distance weighting (IDW) methods and four sampling densities (n = 7388, 1168, 370, or 77) were used for spatial interpolation. The results indicated that different sampling densities had significant effects on predicting the spatial patterns of SOCD, but no significant difference was found among three interpolation methods. Spatial pattern of SOCD obtained from the highest sampling density appeared to be the most detailed distribution, and the prediction accuracy showed a reducing trend with decreasing sampling density. At least 1 sample per 2 km × 2 km area was suggested. The estimates of SOC stocks in different layers of Tainan soils ranged from 8.03 to 8.08 million tons in 0–30 cm, 11.92 to 12.04 million tons in 0–50 cm, and 20.38 to 20.65 million tons in 0–100 cm

Health Risk-Based Assessment and Management of Heavy Metals-Contaminated Soil Sites in Taiwan

Risk-based assessment is a way to evaluate the potential hazards of contaminated sites and is based on considering linkages between pollution sources, pathways, and receptors. These linkages can be broken by source reduction, pathway management, and modifying exposure of the receptors. In Taiwan, the Soil and Groundwater Pollution Remediation Act (SGWPR Act) uses one target regulation to evaluate the contamination status of soil and groundwater pollution. More than 600 sites contaminated with heavy metals (HMs) have been remediated and the costs of this process are always high. Besides using soil remediation techniques to remove contaminants from these sites, the selection of possible remediation methods to obtain rapid risk reduction is permissible and of increasing interest. This paper discusses previous soil remediation techniques applied to different sites in Taiwan and also clarified the differences of risk assessment before and after soil remediation obtained by applying different risk assessment models. This paper also includes many case studies on: (1) food safety risk assessment for brown rice growing in a HMs-contaminated site; (2) a tiered approach to health risk assessment for a contaminated site; (3) risk assessment for phytoremediation techniques applied in HMs-contaminated sites; and (4) soil remediation cost analysis for contaminated sites in Taiwan

Functional composition drives ecosystem function through multiple mechanisms in a broadleaved subtropical forest

Understanding the role of biodiversity (B) in maintaining ecosystem function (EF) is a foundational scientific goal with applications for resource management and conservation. Two main hypotheses have emerged that address B-EF relationships: niche complementarity (NC) and the mass-ratio (MR) effect. We tested the relative importance of these hypotheses in a subtropical old-growth forest on the island nation of Taiwan for two EFs: aboveground biomass (ABG) and coarse woody productivity (CWP). Functional dispersion (FDis) of eight plant functional traits was used to evaluate complementarity of resource use. Under the NC hypothesis, EF will be positively correlated with FDis. Under the MR hypothesis, EF will be negatively correlated with FDis and will be significantly influenced by community-weighted mean (CWM) trait values. We used path analysis to assess how these two processes (NC and MR) directly influence EF and may contribute indirectly to EF via their influence on canopy packing (stem density). Our results indicate that decreasing functional diversity and a significant influence of CWM traits were linked to increasing AGB for all eight traits in this forest supporting the MR hypothesis. Interestingly, CWP was primarily influenced by NC and MR indirectly via their influence on canopy packing. Maximum height explained more of the variation in both AGB and CWP than any of the other plant functional traits. Together, our results suggest that multiple mechanisms operate simultaneously to influence EF, and understanding their relative importance will help to elucidate the role of biodiversity in maintaining ecosystem function