Effects of decaying wood on eluviation,podzolization, acidification,and nutrition in soils with different moisture regimes

One possible impact of large accumulations of decaying wood on forest sites is an increase in (1) eluviation, podzolization and acidification of, and (2) leaching and loss of nutrients from, the soil directly under decaying wood. As an exploratory investigation, we sampled soils beneath forest floors with and without large accumulations of decaying wood (lignic and algnic forest floors respectively) on three soil moisture regimes. Nine sites were located, three in each of central British Columbia, east Vancouver Island, and east of Vancouver. Among the moist sites, there were no differences in Ae horizon thickness between the alignic and lignic forest floors. However, the Ae horizon was thicker beneath the lignic forest floors (mean 4.2 cm) compared to the alignic forest floors (mean 0.7 cm) in slightly dry and fresh sites. Lignic and alignic forest floors differed (p<0.01) in pH, total C, total N, mineralizable N, available S, available P, extractable Mg, K and Ca, lipids, C in fraction B (soluble polysaccharide fraction), C in humic acid, C in fulvic acid, and polyphenol C in fulvic acid for all soil moisture regimes. There were no significant differences in the measures of nutrients or indicators of podzolization as measured by organically complexed Fe and Al, the total non-crystalline Fe and Al, and the poorly crystalline Fe and Al, in the underlying 10 cm of the Bf horizon between the two substrates regardless of the soil moisture regime. Further investigations are needed to establish the relationships between soil productivity and the observed soil chemical measures.     

Temporal changes of soil respiration under different tree species

Soil respiration rates were measured monthly (from April 2007 to March 2008) under four adjacent coniferous plantation sites [Oriental spruce (Picea orientalis L.), Austrian pine (Pinus nigra Arnold), Turkish fir (Abies bornmulleriana L.), and Scots pine (Pinus sylvestris L.)] and adjacent natural Sessile oak forest (Quercus petraea L.) in Belgrad Forest—Istanbul/Turkey. Also, soil moisture, soil temperature, and fine root biomass were determined to identify the underlying environmental variables among sites which are most likely causing differences in soil respiration. Mean annual soil moisture was determined to be between 6.3 % and 8.1 %, and mean annual temperature ranged from 13.0°C to 14.2°C under all species. Mean annual fine root biomass changed between 368.09 g/m² and 883.71 g/m² indicating significant differences among species. Except May 2007, monthly soil respiration rates show significantly difference among species. However, focusing on tree species, differences of mean annual respiration rates did not differ significantly. Mean annual soil respiration ranged from 0.56 to 1.09 g?C/m²/day. The highest rates of soil respiration reached on autumn months and the lowest rates were determined on summer season. Soil temperature, soil moisture, and fine root biomass explain mean annual soil respiration rates at the highest under Austrian pine (R ²?=?0.562) and the lowest (R ²?=?0.223) under Turkish fir.     

Water use sources of desert riparian Populus euphratica forests

Desert riparian forests are the main body of natural oases in the lower reaches of inland rivers; its growth and distribution are closely related to water use sources. However, how does the desert riparian forest obtains a stable water source and which water sources it uses to effectively avoid or overcome water stress to survive? This paper describes an analysis of the water sources, using the stable oxygen isotope technique and the linear mixed model of the isotopic values and of desert riparian Populus euphratica forests growing at sites with different groundwater depths and conditions. The results showed that the main water source of Populus euphratica changes from water in a single soil layer or groundwater to deep subsoil water and groundwater as the depth of groundwater increases. This appears to be an adaptive selection to arid and water-deficient conditions and is a primary reason for the long-term survival of P. euphratica in the desert riparian forest of an extremely arid region. Water contributions from the various soil layers and from groundwater differed and the desert riparian P. euphratica forests in different habitats had dissimilar water use strategies.     

Occurrence, distribution, and source of polybrominated diphenyl ethers in soil and leaves from Shenzhen Special Economic Zone, China

Polybrominated diphenyl ethers (PBDEs) were measured in soil and three plant species samples taken at different land use areas in Shenzhen China. The concentrations of ??₇BDEs (BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, and BDE-183) and BDE-209 in the surface soils ranged from 0.23 to 271 and 8.9 to 5,956 ng/g dry weight (dw), respectively. These figures are comparable to that in the soils of electronic waste dismantling sites. BDE-209 was the predominant congener (contributes 85?C99% of ??₈PBDEs (??₇PBDEs plus BDE-209)) in soils. The regression slopes of total organic carbon and individual BDE congeners were rather gentle, indicating that factors other than soil organic matter regulated the soil concentrations. Proximity to sources of deposition processes might be the major factors. In the plant leaves, ??₇BDEs and BDE-209 concentrations ranged from 1.29 to 5.91 and 5.49 to 28.2 ng/g dw, respectively. BDE-209 is also the dominant component, but the contribution was much lower compared with that in soils. Bauhinia purpurea Linn. and Michelia alba DC. show some similarities on the uptake of PBDEs, while Ficus microcarpa var. pusillifolia is different from them. The correlations between plant leaf concentrations and predicted gaseous concentrations were moderate, indicating that gaseous concentration did not influence the leaf concentration significantly.     

Ecosystem types of boreal forest in the North Klondike River Valley,Yukon Territory,Canada, and their productivity potentials

Vegetation, environmental characteristics, and forest productivity were studied in the boreal forest in the North Klondike River Valley, Yukon Territory, Canada. The concept and approach of biogeoclimatic ecosystem classification were followed. For the treed vegetation, five ecosystem types were distinguished based on vegetation structure and physical and chemical properties of soils. They were: 1) spruce-lichen type, 2) spruce-moss type, 3) spruce-Equisetum type, 4) spruce-willow type, and 5) bog forest type. These types were differentiated mainly by moisture regime and base status of soils. The sequence of the ecosystem types reflected their topographical position from slope summit to valley bottom. The spruce-lichen type developed in the driest and nutritionally impoverished habitats, the spruce-Equisetum type occurred in moist and nutritionally enriched sites, and the spruce-moss type was found in between them. The bog forest type occurred where peat had accumulated sufficiently to generate ombrotrophic conditions in habitats of high water table underlain with permafrost. The spruce-willow type developed along small creeks where substrates were very coarse. Tree growth characteristics were measured, except for the bog forest type that did not have trees over 5 m tall. Total volume of standing trees ranged from 29 to 582 m³/ha, with an overall mean of 216.9 m³/ha. The spruce-Equisetum type exhibited the highest figure, 413.5 m³/ha, while spruce-lichen type the lowest one, 87.7 m³/ha. Mean annual increment ranged from 0.15 to 2.66 m³/ha, with an overall mean of 1.10 m³/ha. A similar tendency was noted for all other forestry characteristics, i.e., the spruce-Equisetum type showed the highest productivity while the spruce-lichen type the lowest. This tendency was considered to be attributed to the availability of moisture and basic cations in soils.     

Classification of moisture and aeration regimes in sub-boreal forest soils

One hundred and two white spruce (Picea glauca (Moench) Voss) stands were studied in the Sub-boreal Spruce zone of British Columbia and were quantitatively classified into seven soil moisture regimes (moderately dry, slightly dry, fresh, moist, very moist, wet, and very wet) according to actual/potential evapotranspiration ratio, depth to gleyed layer or prominent mottling, and depth to groundwater table. The delineated soil moisture regimes demonstrated strong relationships with the composition of understory vegetation and white spruce foliar nutrients and site index. These relationships implied that the three differentiating characteristics used in the classification provided a good estimation of growing-season soil water supply. In addition to soil moisture regimes, three soil aeration regimes (adequate, restricted, and deficient) were delineated according to presence or absence of gleyed horizons and groundwater table, slope gradient, and soil texture. These soil aeration regimes helped in explaining the variation in white spruce site index, especially on water-surplus sites. Thus, an integrated classification of soil moisture-aeration regimes was proposed to explain the effect of soil moisture and aeration on white spruce productivity.The results of this study gave further evidence that soil moisture and aeration regimes, differentiated on the basis of climatic data and soil morphological properties, are useful measures of soil moisture and aeration conditions in sub-boreal forest soils.     

Can adaptive modulation of traits to urban environments facilitate Ricinus communis L. invasiveness?

This paper addresses the phenotypic variation among Ricinus communis L. populations in four urban habitat types (road verges, garbage dumps, construction debris, and natural area) in Delhi, India, by evaluating important traits such as plant height, basal circumference, seeds per plant, seed size, seed weight, specific leaf area, and reproductive index. An important biochemical marker, proline, considered as a good plant performance indicator under stress was also quantified in leaves of R. communis to evaluate its response in different habitats. Interestingly, the species showed significant variation in plant height, specific leaf area, seed size, seed weight, and leaf proline content in different habitat types. Leaf proline content was positively related to plant height, specific leaf area, and seed size while negatively related to the total number of seeds/plant. Interestingly, reproductive index, calculated as a ratio of the total number of seeds to the plant height also showed a negative relation with leaf proline content. Results indicated that R. communis exhibits adaptive modulation of growth, reproductive traits, and leaf proline content in various urban habitats which contributes to invasiveness, range expansion, and establishment of the species. The study also gives evidence of how morphological and physiological traits could directly affect invasiveness of R. communis.     

Mercury accumulation in selected tissues of shrimp Penaeus merguiensis from Musa estuary,Persian Gulf: variations related to sex,size, and season

The levels of mercury in tissues of Penaeus merguiensis from Musa estuary, northwest of the Persian Gulf, were investigated. This study assessed the relationship between mercury levels in hepatopancrea, gill, and muscle with sex, size, and season. The order of mercury concentrations in tissues of the shrimp P. merguiensis was as follows: hepatopancreas > gill > muscle. There was a positive correlation between mercury concentrations in shrimp species with sex and size of its food items. We expected to see higher mercury levels in tissues of female species because they are larger and can eat larger food items. Also, there was a positive correlation between mercury concentrations in shrimp species with its food source. Therefore, female species feed more on shrimp and plant and are contaminated with high levels of mercury. There was significant difference (p?<?0.05) in mercury levels between different seasons; higher mercury levels were found in July (summer season).     

Negative effect of litter of invasive weed Lantana camara on structure and composition of vegetation in the lower Siwalik Hills,northern India

Lantana camara, an aromatic shrub, native to tropical America, was introduced into India for ornamental hedging, but later escaped and became a serious invasive weed. This study assessed the quantitative and qualitative status of plant community richness and diversity in areas invaded by L. camara in the Siwalik Hills (Himachal Pradesh, India), and explored allelopathy as a possible mechanism of interference. We measured species diversity, richness and evenness of the vegetation in areas invaded and uninvaded by L. camara. Allelopathic effects of L. camara rhizosphere soil and litter were assessed against two native plants—Achyranthes aspera (a herb) and Albizia lebbeck (a tree). Density, biomass and indices of diversity, richness and evenness were reduced by L. camara, indicating a significant alteration in composition and structure of native communities. Seedling growth of the test species was reduced in L. camara rhizosphere- and litter-amended soil. The inhibitory effect was ameliorated by the addition of activated charcoal, indicating the presence of organic inhibitors (quantified as phenolics) in the soil. Lantana invasion greatly reduces the density and diversity of the vegetation in the invaded area, and chemical interference of its litter plays an important role in invasion.     

Soil characteristics and heavy metal accumulation by native plants in a Mn mining area of Guangxi,South China

Revegetation and ecological restoration of a Mn mineland are important concerns in southern China. To determine the major constraints for revegetation and select suitable plants for phytorestoration, pedological and botanical characteristics of a Mn mine in Guangxi, southern China were investigated. All the soils were characterized by low pH and low nitrogen and phosphorus levels except for the control soil, suggesting that soil acidity and poor nutrition were disadvantageous to plant growth. In general, the studied mine soils had normal organic matter (OM) and cation exchange capacity (CEC). However, OM (8.9 g/kg) and CEC (7.15 cmol/kg) were very low in the soils from tailing dumps. The sandy texture and nutrient deficiency made it difficult to establish vegetation on tailing dumps. Mn and Cd concentrations in all soils and Cr and Zn concentrations in three soils exceeded the pollution threshold. Soil Mn and Cd were above phytotoxic levels, indicating that they were considered to be the major constraints for phytorestoration. A botanical survey of the mineland showed that 13 plant species grew on the mineland without obvious toxicity symptoms. High Mn and Cd concentrations have been found in the aerial parts of Polygonum pubescens, Celosia argentea, Camellia oleifera, and Solanum nigrum, which would be interesting for soil phytoremediation. Miscanthus floridulus, Erigeron acer, Eleusina indica, and Kummerowia striata showed high resistance to the heavy metal and harsh condition of the soils. These species could be well suited to restore local degraded land in a phytostabilization strategy.     

Effects of crude oil residuals on soil chemical properties in oil sites, Momoge Wetland, China

Crude oil exploration and production has been the largest anthropogenic factor contributing to the degradation of Momoge Wetland, China. To study the effects of crude oil on wetland soils, we examined the total petroleum hydrocarbon (TPH), total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP), as well as pH and electricity conductivity (EC) from oil sites and uncontaminated areas in the Momoge Wetland. All contaminated areas had significantly higher (p < 0.05) contents of TPH and TOC, but significantly lower (p < 0.05) TN contents than those of the uncontaminated areas. Contaminated sites also exhibited significantly higher (p < 0.05) pH values, C/N and C/P ratios. For TP contents and EC, no significant changes were detected. The level of soil contamination and impact of oil residuals on soil quality greatly depended on the length of time the oil well was in production. Oil residuals had caused some major changes in the soils’ chemical properties in the Momoge Wetland.     

The Influence of Linear Elements on Plant Species Diversity of Mediterranean Rural Landscapes: Assessment of Different Indices and Statistical Approaches

This paper mainly aims to study the linear element influence on the estimation of vascular plant species diversity in five Mediterranean landscapes modeled as land cover patch mosaics. These landscapes have several core habitats and a different set of linear elements -habitat edges or ecotones, roads or railways, rivers, streams and hedgerows on farm land- whose plant composition were examined. Secondly, it aims to check plant diversity estimation in Mediterranean landscapes using parametric and non-parametric procedures, with two indices: Species richness and Shannon index.Land cover types and landscape linear elements were identified from aerial photographs. Their spatial information was processed using GIS techniques. Field plots were selected using a stratified sampling design according to relieve and tree density of each habitat type. A 50×20 m² multi-scale sampling plot was designed for the core habitats and across the main landscape linear elements. Richness and diversity of plant species were estimated by comparing the observed field data to ICE (Incidence-based Coverage Estimator) and ACE (Abundance-based Coverage Estimator) non-parametric estimators.The species density, percentage of unique species, and alpha diversity per plot were significantly higher (p < 0.05) in linear elements than in core habitats. ICE estimate of number of species was 32% higher than of ACE estimate, which did not differ significantly from the observed values. Accumulated species richness in core habitats together with linear elements, were significantly higher than those recorded only in the core habitats in all the landscapes. Conversely, Shannon diversity index did not show significant differences.     

Seed bank of Cu-contaminated topsoils at a wood preservation site: impacts of copper and compost on seed germination

Is identification of seed bank (SB) species useful for sustainable management of vegetation restoration on Cu-contaminated soils? How does Cu contamination of the soil affect the SB and can incorporating compost into Cu-contaminated soils counter the effects of Cu? The topsoil SB was investigated at seven contaminated sub-sites of a wood preservation site. The germination parameters of the seeds were recorded using three substrates: a washed river sand (Sand), the same sand spiked with CuSO₄ to reach the same Cu concentrations as in the soil pore water (0.3 to 3.2 mg Cu/L) (Cu), and the same Cu-spiked sand amended with compost (CPM). The total number of germinated seeds (NGS) was 1,081. The whole seedling dataset enabled 12 plant species and eight families to be identified in the SB. Species richness and Shannon indexes were low. The addition of Cu in the germination substrate enhanced total NGS at one sub-site and the addition of CPM increased plant diversity at three sub-sites. SB composition varied with the sub-site but did not correlate with total soil Cu or with the Cu concentration in the soil pore water. Three species belonging to the Poaceae family dominated. In terms of total NGS, the dominant species were Portulaca oleracea and Agrostis capillaris. Similarities between SB and established vegetation were low but increased when the soil bulk density was reduced. The Cu-tolerant species P. oleracea and A. capillaris dominated in both the SB and the established vegetation. However, the pattern of SB and established vegetation differed and consequently SB was not a sufficient indicator to predict the future vegetation.     

Effects of long-term irrigation with treated wastewater on soil quality,soil-borne pathogens,and living organisms: case study of the vicinity of El Hajeb (Tunisia)

Medium (i.e. 15 years) and long-term (i.e. 20 years) impact of irrigation using secondary-treated municipal wastewater (TWW) was assessed on two agricultural soil samples, denoted by E and G, respectively, in the vicinity of El Hajeb region (Southern Tunisia). Soil pH, electrical conductivity particle size grading, potential risk of salinity, water holding capacity and chemical composition, as well as organic matter content, pathogenic microorganisms and heavy metal concentrations in the TWW-irrigated (E and G) and rainwater-irrigated (T) soils at various depths, were monitored and compared during a 5-year experiment. Our study showed that bacterial abundance is higher in sandy–clayey soil, which has an enhanced ability to retain moisture and nutrients. The high level of bacterial flora in TWW-irrigated soils was significantly (p?<?0.05) correlated (r?=?~0.5) with the high level of OM. Avoidance assays have been used to assess toxic effects generated by hazards in soils. The earthworms gradually avoided the soils from the surface (20 cm) to the depth (60 cm) of the G transect and then the E transect, preferring the T transect. The same behaviour was observed for springtails, but they seem to be less sensitive to the living conditions in transects G and E than the earthworms. The avoidance response test of Eisenia andrei was statistically correlated with soil layers at the sampling sites. However, the avoidance response test of Folsomia candida was positively correlated with silt-clay content (+0.744*) and was negatively correlated with sand content (?0.744*).     

Spatial variability of soil total and DTPA-extractable cadmium caused by long-term application of phosphate fertilizers, crop rotation, and soil characteristics

Increasing cadmium (Cd) accumulation in agricultural soils is undesirable due to its hazardous influences on human health. Thus, having more information on spatial variability of Cd and factors effective to increase its content on the cultivated soils is very important. Phosphate fertilizers are main contamination source of cadmium (Cd) in cultivated soils. Also, crop rotation is a critical management practice which can alter soil Cd content. This study was conducted to evaluate the effects of long-term consumption of the phosphate fertilizers, crop rotations, and soil characteristics on spatial variability of two soil Cd species (i.e., total and diethylene triamine pentaacetic acid (DTPA) extractable) in agricultural soils. The study was conducted in wheat farms of Khuzestan Province, Iran. Long-term (27-year period (1980 to 2006)) data including the rate and the type of phosphate fertilizers application, the respective area, and the rotation type of different regions were used. Afterwards, soil Cd content (total or DTPA extractable) and its spatial variability in study area (400,000 ha) were determined by sampling from soils of 255 fields. The results showed that the consumption rate of di-ammonium phosphate fertilizer have been varied enormously in the period study. The application rate of phosphorus fertilizers was very high in some subregions with have extensive agricultural activities (more than 95 kg/ha). The average and maximum contents of total Cd in the study region were obtained as 1.47 and 2.19 mg/kg and DTPA-extractable Cd as 0.084 and 0.35 mg/kg, respectively. The spatial variability of Cd indicated that total and DTPA-extractable Cd contents were over 0.8 and 0.1 mg/kg in 95 and 25 % of samples, respectively. The spherical model enjoys the best fitting and lowest error rate to appraise the Cd content. Comparing the phosphate fertilizer consumption rate with spatial variability of the soil cadmium (both total and DTPA extractable) revealed the high correlation between the consumption rate of P fertilizers and soil Cd content. Rotation type was likely the main effective factor on variations of the soil DTPA-extractable Cd contents in some parts (eastern part of study region) and could explain some Cd variation. Total Cd concentrations had significant correlation with the total neutralizing value (p?<?0.01), available P (p?<?0.01), cation exchange capacity (p?<?0.05), and organic carbon (p?<?0.05) variables. The DTPA-extractable Cd had significant correlation with OC (p?<?0.01), pH, and clay content (p?<?0.05). Therefore, consumption rate of the phosphate fertilizers and crop rotation are important factors on solubility and hence spatial variability of Cd content in agricultural soils.     

Effect of urbanization on the structure and functional traits of remnant subtropical evergreen broad-leaved forests in South China

We investigated the effects of major environmental drivers associated with urbanization on species diversity and plant functional traits (PFTs) in the remnant subtropical evergreen broad-leaved forests in Metropolitan Guangzhou (Guangdong, China). Twenty environmental factors including topography, light, and soil properties were used to quantify the effects of urbanization. Vegetation data and soil properties were collected from 30 400-m² plots at 6 study sites in urban and rural areas. The difference of plant species diversity and PFTs of remnant forests between urban and rural areas were analyzed. To discern the complex relationships, multivariate statistical analyses (e.g., canonical correspondence analysis and regression analysis) were employed. Pioneer species and stress-tolerant species can survive and vigorously establish their population dominance in the urban environment. The native herb diversity was lower in urban forests than in rural forests. Urban forests tend to prefer the species with Mesophanerophyte life form. In contrast, species in rural forests possessed Chamaephyte and Nanophanerophyte life forms and gravity/clonal growth dispersal mode. Soil pH and soil nutrients (K, Na, and TN) were positively related to herb diversity, while soil heavy metal concentrations (Cu) were negatively correlated with herb diversity. The herb plant species diversity declines and the species in the remnant forests usually have stress-tolerant functional traits in response to urbanization. The factors related to urbanization such as soil acidification, nutrient leaching, and heavy metal pollution were important in controlling the plant diversity in the forests along the urban–rural gradients. Urbanization affects the structure and functional traits of remnant subtropical evergreen broad-leaved forests.     

Efficient control of air pollution through plants, a cost-effective alternative: studies on Dalbergia sissoo Roxb

Plants can be used as both passive biomonitors and biomitigators in urban and industrial environments to indicate the environmental quality and to ameliorate pollution level in a locality. Many studies reveal that plants are negatively affected by the ambient levels of air pollutants. The present study was conducted to evaluate the impact of air pollution on comparative basis with reference to changes in photosynthetic pigments, plant height, leaves, as well as, biochemical parameters of plants of different sites around Udaipur city receiving varying levels of pollution load. The investigated tree species Dalbergia sissoo Roxb. (Family: Fabaceae) exhibited a reduction in various physiological and biochemical growth parameters that correspond with air pollution levels at different sites. The tree species growing in polluted and control areas were compared with respect to foliar dust load, leaf area, and chlorophyll and total carbohydrate and total protein concentration in the leaves. Our studies suggest that D. sissoo Roxb. can successfully be grown in an area for monitoring air pollution, where it is mild and droughts are common. It will prove as an ideal tree species to control pollution effectively beside acting as a shade tree and being a source of food for birds and animals. By plantation of D. sissoo Roxb., mitigative measure at the polluted sites to control generation of particulate matter and the air quality required can be ensured. Our results also confirm that industrial and vehicular air pollution level in Udaipur city is shifting beyond limits.     

The Chemistry of Soils, Rocks and Plant Bioindicators in Three Ecosystems of the Holy Cross Mountains, Poland

In June of 2000, biogeochemical study was carried out in three ecosystems of the Holy Cross Mountains (south-central Poland). This paper presents element concentrations and stable sulfur (and in one site lead) isotope ratios in rocks, detailed soil profiles, and plant bioindicators including epiphytic lichen Hypogymnia physodes (L.) Nyl., mosses (Pleurozium schreberi (Brid.) Mitt., Hypnum cupressiforme Hedw. S. Str., Hylocomium splendens (Hedw.) B.S.G.), Scots pine (Pinus sylvestris L.), common birch (Betula pendula Roth.), aspen (Populus tremula L.) and English oak (Quercus robur L.). Chemical analyses were performed with ICP-AES and AAS methods in the accredited laboratory (Central Chemical Laboratory of the Polish Geological Institute in Warsaw). The principal objective of this study was to compare the chemical composition of rocks, soils and selected plant bioindicators between investigation sites using the same methods of sample collection, preparation and analyses. The results of this study have shown that there is a high variability in concentrations of elements in plant bioindicators from the same sites that can not be explained only by soil properties or anthropogenic influence. This conclusion indicates that for biomonitoring purposes (especially with vascular plants) we cannot neglect individual features of the species examined.     

Assessing and Monitoring the Health of Western Rangeland Watersheds

The most important function of watersheds in the western U.S. is the capacity to retain soil and water, thereby providing stability in hydrologic head and minimizing stream sediment loads. Long-term soil and water retention varies directly with vegetation cover. Data on ground cover and plant species composition were collected from 129 sites in the Rio Grande drainage of south-central New Mexico. This area was previously assessed by classification of Advanced Very High Resolution Radiometry (AVHRR) imagery. The classification of irreversibly degraded sites failed to identify most of the severely degraded sites based on size of bare patches and 35% of the sites classified as degraded were healthy based on mean bare patch size and vegetation cover. Previous research showed that an index of unvegetated soil (bare patch size and percent of ground without vegetative cover) was the most robust indicator of the soil and water retention function. Although the regression of mean bare patch size on percent bare ground was significant (p < 0.001), percent bare ground accounted for only 11% of the variability in bare patch size. Therefore bare patch size cannot be estimated from data on percent bare ground derived from remote sensing. At sites with less than 25% grass cover, and on sites with more than 15% shrub cover, there were significant relationships between percent bare soil and mean bare patch size (p < 0.05). Several other indicators of ecosystem health were related to mean bare patch size: perennial plant species richness (r = 0.6, p < 0.0001), percent cover of increaser species (r = 0.5, p < 0.0001) and percent cover of forage useable by livestock (r = 0.62, p < 0.0001). There was no relationship between bare patch size and cover of species that are toxic to livestock. In order to assess the ability of western rangeland watersheds to retain soil and water using remote sensing, it will be necessary to detect and estimate sizes of bare patches ranging between at least 0.5 m in diameter to several meters in diameter.     

An investigation of arsenic contamination in Peninsular Malaysia based on Centella asiatica and soil samples

The first objective of this study was to provide data of arsenic (As) levels in Peninsular Malaysia based on soil samples and accumulation of As in Centella asiatica collected from 12 sampling sites in Peninsular Malaysia. The second objective was to assess the accumulation of As in transplanted C. asiatica between control and semi-polluted or polluted sites. Four sites were selected which were UPM (clean site), Balakong (semi-polluted site), Seri Kembangan (semi-polluted site) and Juru (polluted site). The As concentrations of plant and soil samples were determined by Instrumental Neutron Activation Analysis. The As levels ranged from 9.38 to 57.05 μg/g dw in soils, 0.21 to 4.33 μg/g dw in leaves, 0.18 to 1.83 μg/g dw in stems and 1.32–20.76 μg/g dw in roots. All sampling sites had As levels exceeding the CCME guideline (12 μg/g dw) except for Kelantan, P. Pauh, and Senawang with P. Klang having the highest As in soil (57.05 μg/g dw). In C. asiatica, As accumulation was highest in roots followed by leaves and stems. When the As level in soils were higher, the uptake of As in plants would also be increased. After the transplantation of plants to semi-polluted and polluted sites for 3 weeks, all concentration factors were greater than 50 % of the initial As level. The elimination factor was around 39 % when the plants were transplanted back to the clean sites for 3 weeks. The findings of the present study indicated that the leaves, stems and roots of C. asiatica are ideal biomonitors of As contamination. The present data results the most comprehensive data obtained on As levels in Malaysia.