Chun-Chih Tsui

Digestion Methods for Total Heavy Metals in Sediments and Soils

The objectives of this study were to analyze the total contents of Cd, Cr, Cu, Ni, Pb, and Zn in the freshwater sediments and the arable and non-arable soils of Taiwan, and to compare the different digestion methods for their determination. Two hundred and thirty-nine freshwater sediments were collected from the Fei-Tsui Reservoir Watershed (FTRW) in northern Taiwan. Forty-two surface (0–15 cm) and subsurface (15–30 cm) soil samples were likewise collected from 21 representative arable soils derived from various parent materials and with varying weathered degrees in different regions of Taiwan. In addition, one hundred and ninety-four non-arable soils were collected from the different forest regions, industrial parks, resident areas, and commercial areas. Several digestion methods including the aquaregia and different combinations of concentrated acids (HClO4, HNO3, H2SO4, or HF) were compared. All samples were digested both by the aqua regia method and the Baker and Amacher method for Cd, Cr, Cu, Ni, Pb, and Zn. The Reisenauer method was used for Cr and the Burau method for Pb further. The results indicate that the best digestion methods to analyze the total contents of heavy metals in the sediments and soils were recommended as follows: the Baker and Amacher method for Cd, Cr,Cu, Ni, and Zn; the Reisenauer method for Cr, but for simplicity the Baker and Amacher method is also recommended as the flexible method for the total analysis of Cr; the aqua regia method for Cu, Ni, and Zn; and the Burau method for Pb.

Net nitrogen mineralization and nitrification of different landscape positions in a lowland subtropical rainforest in Taiwan

Abstract Measurements of soil nitrogen (N) transformation rate are needed to be able to assess the plant availability and forest ecosystem losses of N, but little is known about lowland subtropical rainforests. The objectives of the present study were to determine the rates of N mineralization and nitrification in different seasons (January and August 2006) and in different landscape positions (footslope and summit) in the Nanjenshan forest of southern Taiwan, where vegetation types and soil properties vary among different landscape positions. Net N mineralization and nitrification were measured using 28-day in-situ open core and capped core incubations. The results from January 2006 showed that the concentrations of ammonium-N (NH4 +-N), mineral N (NH4 +-N plus NO3 −-N) and nitrate-N (NO3 −-N) were not significantly different between open and capped cores, or between summit and footslope. However, the results of August 2006 showed that the NH4 +-N concentrations of the summit soils were significantly higher than those of the footslope soils (P < 0.05), and that NO3 −-N concentrations in the open cores were significantly lower than those in the capped cores because of higher rainfall in the summer. In general, concentrations of mineral N and NO3 −-N in August were higher than those in January (both P = 0.0003), and NH4 +-N concentrations were significantly different between the different landscape positions (P < 0.05). There were larger soil C and N and microbial N pools at the summit position; however, footslope soils showed higher net N mineralization and nitrification rate as expressed on the basis of per unit C or N. Our results suggested that the substrate properties of the footslope position contributed to the higher net N mineralization and nitrification rate, and that the differences in N transformation rates between the landscape positions appeared to be related to vegetation type.

Food Safety and Bioavailability Evaluations of Four Vegetables Grown in the Highly Arsenic-Contaminated Soils on the Guandu Plain of Northern Taiwan

Arsenic contamination in a large area of agricultural fields on the Guandu Plain of northern Taiwan was confirmed in a survey conducted in 2006, but research concerning the relationship between bioavailable As concentrations in contaminated soils and crop production in Taiwan is not available. Pot experiments were conducted to examine the growth and accumulation of As in four vegetable crops grown in As-contaminated soils and to assess As intake through consumption. The phytotoxic effects of As in soils were not shown in the pot experiments in which vegetable crops were grown in soils contaminated with different As levels in situ collected from Guandu Plain (120–460 mg/kg) or artificially spiked As-contaminated soils (50–170 mg/kg). Experimental results showed that the bioavailable As extracted with 5 M NaHCO3 from soils can be used to estimate As concentrations in vegetables. The As concentrations in the vegetables were compared with data shown in the literature and As limits calculated from drinking water standards and the provisional tolerance weekly intake (PTWI) of inorganic As established by the Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO). Although the As levels in the vegetables were not high and the bioavailability of As in the soils was quite low, long-term consumption may result in higher As intake in the human body.

BASELINE CONCENTRATIONS OF TEN METALS IN THE FRESHWATER SEDIMENTS OF A WATERSHED IN TAIWAN

ABSTRACT Freshwater sediments and water samples were quarterly collected at different sampling stations from August 1996 to April 1998 in the Fei-Tsui reservoir watershed (FTRW) of northern Taiwan. The sediment and soil samples were digested using mixture of inorganic acids to analyze the total concentration of ten metals. The baseline concentrations of ten metals in the sediments of FTRW were calculated from the geometric mean (GM) values and the geometric standard deviation (GSD). The baseline concentrations of 10 metals in the 239 sediments of this watershed are listed as followings (mg/kg, only % for Fe): As 1.80–51.5, Cd 0.04–7.54, Cr 5.25–273, Cu 2.65–91.7, Hg 0.03–0.26, Mn 18.6–2310, Ni 3.95–167, Pb 1.10–75.4, Zn 6.46–327, and Fe 0.47–9.63%. However, the GMs of 10 metal concentrations in the sediments were lower than the regulated threshold concentrations in Taiwan rural soils. Highly correlations among different metals in the sediments of FTRW indicate that very similar sediments of formation process control the metal content associated with the parent materials. Inadequate land use results in As, Cr, Mn, and Ni accumulated in the sediment to show potentially contamination risk in the study area associated with accelerated erosion and runoff.

Estimation of Soil Carbon Stock in Taiwan Arable Soils by Using Legacy Database and Digital Soil Mapping

Since the Kyoto Protocol [1] was adopted, recent concerns about global warming have driv‐ en many effort been paid to develop methods to quantify both current and future carbon (C) stocks in different ecosystems. In global assessment, the current C stock contained in the plant and microbial biomass is estimated 560 Gt and 110 Gt, respectively, while soil C pool amounts to 2500 Gt, includes 1550 Gt of soil organic carbon (SOC) and 950 Gt of soil inor‐ ganic carbon (SIC) [2-6]. The soil C pool is 3.3 times the size of the atmospheric C pool of 760 Gt and 4.5 times of the biotic pool [4]. Therefore, soils are particularly important, as they are the largest reservoir of C in the terrestrial biosphere [2-3]. The SOC pool represent a dynam‐ ic equilibrium of C gains from plant production and loss through decomposition [7-8]. Car‐ bon stock in soils is influenced by climate condition, soil properties, vegetation, land use and soil management [9-13].

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.