Roadside Soils Research Articles

Soil organic carbon distribution in roadside soils of Singapore

Soil is the largest pool of organic carbon in terrestrial systems and plays a key role in carbon cycle. Global population living in urban areas are increasing substantially; however, the effects of urbanization on soil carbon storage and distribution are largely unknown. Here, we characterized the soil organic carbon (SOC) in roadside soils across the city-state of Singapore. We tested three hypotheses that SOC contents (concentration and density) in Singapore would be positively related to aboveground tree biomass, soil microbial biomass and land-use patterns. Overall mean SOC concentrations and densities (0–100 cm) of Singapore's roadside soils were 29 g kg−1 (4–106 g kg−1) and 11 kg m−2 (1.1–42.5 kg m−2) with median values of 26 g kg−1 and 10 kg m−2, respectively. There was significantly higher concentration of organic carbon (10.3 g kg−1) in the top 0–30 cm soil depth compared to the deeper (30–50 cm, and 50–100 cm) soil depths. Singapore's roadside soils represent 4% of Singapore's land, but store 2.9 million Mg C (estimated range of 0.3–11 million Mg C). This amount of SOC is equivalent to 25% of annual anthropogenic C emissions in Singapore. Soil organic C contents in Singapore's soils were not related to aboveground vegetation or soil microbial biomass, whereas land-use patterns to best explain variance in SOC in Singapore's roadside soils. We found SOC in Singapore's roadside soils to be inversely related to urbanization. We conclude that high SOC in Singapore roadside soils are probably due to management, such as specifications of high quality top-soil, high use of irrigation and fertilization and also due to an optimal climate promoting rapid growth and biological activity.

Traffic-related metal(loid) status and uptake by dominant plants growing naturally in roadside soils in the Tibetan plateau, China

To understand traffic-related metal(loid) status and uptake by dominant plants growing naturally in roadside soils in the Tibetan plateau, China, aboveground parts and root samples of three dominant plant species (Kalidium slenderbranch, Stipa purpurea, Kobresia pygmaea) were collected along the Qinghai–Tibet highway, and were analyzed for concentrations of traffic-related metal(loid)s such as chromium (Cr), zinc (Zn), copper (Cu), cadmium (Cd), arsenic (As), and lead (Pb). The results indicated that concentrations of metal(loid)s in plant tissues varied greatly among plant species and sites. Tissue distribution of metal(loid)s was significantly related to distance and demonstrated variability as an exponential function of traffic proximity. It was deduced that Cd in Kalidium slenderbranch and Cu and Zn in S. purpurea were mainly derived from soil; Kalidium slenderbranch and Kobresia pygmaea absorbed Zn, and S. purpurea absorbed Cd, mainly through stomata, from atmospheric deposition; enrichments of Pb and As in S. purpurea presented similar characteristics to those of Cd and Pb in Kobresia pygmaea and were affected by both soil and atmospheric deposition. After excluding the effects of the traffic, the highest value obtained for metal(loid)-translocation capacity (7.51 for translocation factor, TF) was observed for S. purpurea collected from Tuotuohe, while the lowest value for metal(loid)-uptake capacity (0.015 for bioaccumulation factor, BF) was for Kalidium slenderbranch collected from Golmud. The three plant species showed limited soil-to-root transfer of metal(loid)s, possibly due to the high soil pH along the Qinghai–Tibet highway, but demonstrated great potential for metal(loid) transfer from roots to aboveground parts.

Level of Cd in different types of soil of Rohtak district and its bioremediation

Soil samples were collected in the year 2013 and 2014 from different locations to study the comparative level of Cd in the soil samples. The concentration of cadmium in industrial, agricultural and roadside soils, depends on the amount of Cd present in the rocks from which the soils form, the amount added in the form of fertilizers, the amount added to soils from the vehicular exhaust and industrial waste. It is found that, on an average, industrial soil contains greater concentrations of Cd than either of agricultural and roadside soil. In the case of agricultural soil, the phosphorous fertilizer used soil contains an elevated level of Cd. Results also show that long-term use of fertilizers and industrial waste will increase the level of Cd in the surface soils. The study reveals that the topsoil in the study area is more polluted with Cd. The average concentration of Cd exceeds the guideline value, therefore, the soil of different sites is said to have an elevated level of Cd. Variation of Cd in the soil depends on several factors like pH of the soil and season. To check the remediation process, pre-cultured media was sprayed on the soil samples and it has been found that S. cerevisiae has the capability to remove Cd. When the pH of the soil was maintained at 5.5, it was observed that 65–82% of Cd2+ got removed within 30days.

Highway increases concentrations of toxic metals in giant panda habitat.

The Qinling panda subspecies (Ailuropoda melanoleuca qinlingensis) is highly endangered with fewer than 350 individuals inhabiting the Qinling Mountains. Previous studies have indicated that giant pandas are exposed to heavy metals, and a possible source is vehicle emission. The concentrations of Cu, Zn, Mn, Pb, Cr, Ni, Cd, Hg, and As in soil samples collected from sites along a major highway bisecting the panda's habitat were analyzed to investigate whether the highway was an important source of metal contamination. There were 11 sites along a 30-km stretch of the 108th National Highway, and at each site, soil samples were taken at four distances from the highway (0, 50, 100, and 300m) and at three soil depths (0, 5, 10cm). Concentrations of all metals except As exceeded background levels, and concentrations of Cu, Zn, Mn, Pb, and Cd decreased significantly with increasing distance from the highway. Geo-accumulation index indicated that topsoil next to the highway was moderately contaminated with Pb and Zn, whereas topsoil up to 300m away from the highway was extremely contaminated with Cd. The potential ecological risk index demonstrated that this area was in a high degree of ecological hazards, which were also due to serious Cd contamination. And, the hazard quotient indicated that Cd, Pb, and Mn especially Cd could pose the health risk to giant pandas. Multivariate analyses demonstrated that the highway was the main source of Cd, Pb, and Zn and also put some influence on Mn. The study has confirmed that traffic does contaminate roadside soils and poses a potential threat to the health of pandas. This should not be ignored when the conservation and management of pandas is considered.

Contamination status and assessment of urban and non-urban soils in the region of Sulaimani City, Kurdistan, Iraq

Soil contamination, especially in urban areas, is a globally increasing threat. Yet, knowledge on the status of urban soils in recently and rapidly developing regions and semiarid areas is still scarce. In this study, soils were investigated from Sulaimani city that underwent rapid growth and urbanization in past decades. Properties and contamination of 91 topsoils from 11 areas of different anthropogenic impact were determined. Differences between urban and non-urban soils were attributed by principal component analysis to differences in contents of pedogenic oxides, carbonate, organic nitrogen and carbon, pH and CEC. Also total contents of potentially toxic elements (PTE) were higher; mean contents of Cd, Pb, Cu and Zn in urban soils were 0.35, 51.8, 78.6 and 163.0 mg kg−1. The PTE contents increased with traffic volume and industrial emissions. The anthropogenic origin of contamination was further evidenced by significant enrichment of PTE in the top 0–5 cm compared to deeper topsoil layers. Additionally, mobility of PTEs was low in the clayey, alkaline soils. Contamination was substantially lower compared to many other cities, being explained by the short history of urban development in Sulaimani. Correspondingly, contents of polycyclic aromatic hydrocarbons were mostly not detectable. Contamination with PTEs was assessed using pollution indices and classified as ‘moderate’ to ‘considerable’ in roadside soils and significant’ to ‘very high’ in soils from industrial areas, depending on the single element. Toxicity indices >0.5 revealed that adverse effects on ecosystem functions must be expected at several urban and especially industrial sites.

Heavy metal migration along a rural highway route: Ilesha-Akure roadside oil, Southwestern, Nigeria

<div> <p>This paper present migration of some selected heavy metal (zinc, lead, copper, chromium and nickel) of roadside soil samples from along Ilesa-Akure highway with a view to assess the degree of contamination such soils contain and the likelihood that this contamination can be remobilized. Soil samples were collected from 5 locations (Ilesa, Ipetu-ijesa, JABU, Ilara-mokin and FUTA north gate) at depths of 0-5, 15-20, 35-40 and 55-60cm and analysed for the five selected heavy metals in the bulk sample and clay fraction. Their concentrations and distributions in four different road verge zones (5m, 30m, 60m and 110m) were determined. The 5m zone had the highest mean concentration of the five metals whereas the 110m zone exhibited the lowest mean concentration. Zinc and lead exhibited a significant decrease in the roadside soils with the increasing distance from the road while chromium and nickel showed significant increase, copper on the other hand showed no significant difference. Quantitative assessment of the heavy metal contamination using the I<sub>geo </sub>and <em>PI</em> indexes showed that the selected heavy metals were in the order of Cu < Pb < Zn < Ni <Cr for both Indexes. Soil characteristics (which include pH, Cation exchange capacity {CEC}, organic matter and other basic geotechnical tests) responsible for the mobility and vertical distributions of these heavy metals from the road side soil were also assessed.</p> </div> <p> </p>

Insights into the chemical partitioning of trace metals in roadside and off-road agricultural soils along two major highways in Attica’s region, Greece

We report in this study the magnetic properties and partitioning patterns of selected trace metals (Pb, Zn, Cu, Cd, Ni) in roadside and off-road (>200m distance from the road edge) agricultural soils collected along two major highways in Greece. Sequential extractions revealed that the examined trace metals for the entire data set were predominantly found in the residual fraction, averaging 37% for Cd up to 80% for Cu. Due to the strong influence of lithogenic factors, trace metal pseudototal contents of the roadside soils did not differ significantly to those of the off-road soils. Magnetic susceptibility and frequency dependent magnetic susceptibility determinations showed a magnetic enhancement of soils; however, it was primarily related to geogenic factors and not to traffic-derived magnetic particles. These results highlight that in areas characterized by strong geogenic backgrounds, neither pseudototal trace metal contents nor magnetic properties determinations effectively capture traffic-related contamination of topsoils. The vehicular emission signal was traced by the increased acid-soluble and reducible trace metal contents of the roadside soils compared to their off-road counterparts. In the case of Cu and Zn, changes in the partitioning patterns were also observed between the roadside and off-road soils. Environmental risks associated with agricultural lands extending at the margins of the studied highways may arise from the elevated Ni contents (both pseudototal and potentially mobile), and future studies should investigate Ni levels in the edible parts of plants grown on these agricultural soils.

Evaluation of accumulation and concentration of heavy metals in different urban roadside soil types in Miranda Park, Sydney

The overall objectives of this study were to examine the relationship between the concentrations of heavy metals such as Pb, Zn, Cu, and Cd in roadside soil derived from three different geological parent materials, Hawkesbury Sandstone, Wianamatta Shale, and Mittagong Formation and also to examine the influence of rainfall events on heavy metal concentrations in both the topsoil and the subsoil in all three soil types. In this paper, the focus is on lead and zinc. The results obtained from the samples taken from an initial transect were used to select the location of the study sites. Soil samples were collected using a stainless steel auger at distances of 1, 5, and 10 m from the edge of two major roads of similar traffic volumes bordering a suburban park. At each of five study sites, samples were collected at depths of 0–10 and 10–30 cm, three times pre-rainfall (after extended periods of no rain) and three times post-rainfall (after intensive rainfall periods). The modified aqua regia digestion method was applied for heavy metal concentrations measurement. To determine the temporal dynamics of trace elements in the soils, sequential extractions were applied to all the topsoil samples according to the modified three-step sequential extraction procedure. The corresponding concentrations of Pb and Zn were different for the soil derived from Hawkesbury Sandstone and Wianamatta Shale and also Mittagong Formation. The highest concentration of Pb was in the soil from Wianamatta Shale, 159.32 mg/kg and the highest concentration of Zn was in the soil from the Mittagong Formation, 254.12 mg/kg, all at a distance of 1 m from the roadside. From the sequential chemical extraction results, the rainfall substantially influenced the exchangeable fraction (F1) of Pb at a distance from the road of 1 m. A significant reduction of F1 was found for the soil derived from Mittagong Formation which also had the most significant reduction of total Zn concentration. The interpretation of the results showed that there was a clear correlation between the concentration of Pb and Zn with the distance from the roadside and depth in all soil types. However, the results also showed that there are variable concentrations between the soil types. The heavy metal concentrations at the same distance for the three soil types are different. The rainfall events do influence the heavy metal concentration differently in both topsoil and subsoil of the three soil types at the same distance from the roadside.

Long-term ferrocyanide application via deicing salts promotes the establishment of Actinomycetales assimilating ferrocyanide-derived carbon in soil.

SummaryCyanides are highly toxic and produced by various microorganisms as defence strategy or to increase their competitiveness. As degradation is the most efficient way of detoxification, some microbes developed the capability to use cyanides as carbon and nitrogen source. However, it is not clear if this potential also helps to lower cyanide concentrations in roadside soils where deicing salt application leads to significant inputs of ferrocyanide. The question remains if biodegradation in soils can occur without previous photolysis. By conducting a microcosm experiment using soils with/without pre‐exposition to road salts spiked with 13C‐labelled ferrocyanide, we were able to confirm biodegradation and in parallel to identify bacteria using ferrocyanide as C source via DNA stable isotope probing (DNA‐SIP), TRFLP fingerprinting and pyrosequencing. Bacteria assimilating 13C were highly similar in the pre‐exposed soils, belonging mostly to Actinomycetales (Kineosporia, Mycobacterium, Micromonosporaceae). In the soil without pre‐exposition, bacteria belonging to Acidobacteria (Gp3, Gp4, Gp6), Gemmatimonadetes (Gemmatimonas) and Gammaproteobacteria (Thermomonas, Xanthomonadaceae) used ferrocyanide as C source but not the present Actinomycetales. This indicated that (i) various bacteria are able to assimilate ferrocyanide‐derived C and (ii) long‐term exposition to ferrocyanide applied with deicing salts leads to Actinomycetales outcompeting other microorganisms for the use of ferrocyanide as C source.

Occurrence and Distribution of Heavy Metals in Roadside Soils and Plants along Major Urban Roads of Zanzibar

Occurrence and Distribution of Heavy Metals in Roadside Soils and Plants along Major Urban Roads of Zanzibar

Traffic-related heavy metals uptake by wild plants grow along two main highways in Hunan Province, China: effects of soil factors, accumulation ability, and biological indication potential.

This study was performed to investigate pollution of traffic-related heavy metals (HMs-Zn, Pb, Cu, Cr, and Cd) in roadside soils and their uptake by wild plants growing along highways in Hunan Province, China. For this, we analyzed the concentration and chemical fractionation of HMs in soils and plants. Soil samples were collected with different depths in the profile and different distances from highway edge. And leaves and barks of six high-frequency plants were collected. Results of the modified European Community Bureau of Reference (BCR) showed that the mobile fraction of these HMs was in the order of Cd > Pb > Zn > Cu > Cr. A high percentage of the mobile fraction indicates Cd, Pb, and Zn were labile and available for uptake by wild plants. The total concentration and values of risk assessment code (RAC) showed that Cd was the main risk factor, which were in the range high to very high risk. The accumulation ability of HMs in plants was evaluated by the biological accumulation factor (BAF) and the metal accumulation index (MAI), and the results showed that all those plant species have good phyto-extraction ability, while accumulation capacity for most HMs plants tissues was bark > leaf. The highest MAI value (5.99) in Cinnamomum camphora (L) Presl indicates the potential for bio-monitoring and a good choice for planting along highways where there is contamination with HMs.

Spatial distribution and temporal trends of farmland soil PBDEs: processes and crop rotation effects.

The concentration and temporal trend of PBDEs in farmland soil during a circle of crop rotation period within an e-waste dismantling area of South China were investigated. The averaged current concentration of total PBDEs in the farmland soil was averaged 19.1 ± 20.7ng/g dry weight, which was much lower than the PBDE level in roadside soil and in topsoil near e-waste dismantling sites. Spatial distribution of total PBDEs concentration in the study area showed higher level at the field near e-waste workshops and lower at the distanced farmland area. Soil organic carbon content was significantly correlated with concentration of BDE209 (r = 0.704, p < 0.01), but not related with the sum concentration of other PBDE compounds (r = 0.097, p > 0.1). During the whole crop rotation circle, the temporal concentration of PBDEs in the farmland soil was highest (25.3 ± 11.4ng/g dry wt.) in April when early paddy had been transplanted for 1 or 2weeks. When the crop rotated to autumn peanut in August and the land is turning dry, the PBDEs concentration in farmland soil reached the lowest level which was 8.1 ± 1.2ng/g dry wt. The temporal trend of PBDEs in farmland soil was not consistent with that of atmospheric PBDEs and soil total organic carbon (TOC) content during the rotation cycle. It was concluded that the dynamics of PBDEs in the farmland soil is influenced by multiple, interacting factors, and not clearly related to neither the atmospheric deposition nor the organic carbon content of the soil, but possibly related to the micro-environmental conditions changed by crop rotation process.

Physiological and Structural Abnormalities of Coconut Plants (&lt;i&gt;Cocos nucifera&lt;/i&gt; L.) at Different Stages of Growth and Plantation Sites under Low Temperature Condition in Bangladesh

Physiological and structural changes of coconut plants at different growth stages and plantation sites under low temperature conditions was investigated during 1997-98, 2002-03, 2005-06 and 2009-10 in the northern region of Bangladesh. Three growth stages viz. &lt; 7, 7-15 and &gt; 15 years and three locations viz. road side, near pond and near drain were selected for this study. Leaf area damage with characteristics lesions categorized into mildly damaged, moderately damaged and dead plants. Age and planting site revealed very significant differences. The highest percent of dead (49.84-58.49 %), moderately damaged (37.20-46.21 %) and mildly damaged plants (65.70-74.79 %) were found in road side, while the highest percent of dead plants (39.93-45.58 %), moderately (20.18-26.68 %) and mildly damaged plants (69.46-70.37 %) were found in above 15 years old plants. The lowest percent dead of plants (20.82, 18.27 and 19.55 %) were found in pond side and (11.74, 12.53 and 13.31 %) in the 7-15 years old plants. The mean temperature, sunshine hours and total precipitations remained below 16.88 °C, 10.25 hours and 11.7 cm, respectively during 1997-98, 2002-03 and 2009-10. The highest amount of potassium (0.57 me/100 g soil) was found in pond side soil, whereas the lowest amount of potassium (0.11 me/100g soil) was found in road side soil. It has been concluded that low temperature (below 16.88 °C), mean precipitation 11.7 cm and amount of potassium 0.11me/100 g in soil were responsible for severe damage of the coconut plants in the study area.The Agriculturists 2015; 13(2) 113-119

Polycyclic Aromatic Hydrocarbons in Road-Deposited Sediments and Roadside Soil in Tijuana, Mexico

ABSTRACTRoad-deposited sediment and roadside soil in the urban area of the city of Tijuana were collected and analyzed for 16 polycyclic aromatic hydrocarbons (PAHs). The ΣPAH concentration for road-deposited sediment (RDS) ranged between 460 and 2027 µg/kg with an average of 933 µg/kg. The ΣPAH concentration in roadside soil was lower than in RDS, with a range between 54 and 1863 µg/kg and a mean value of 308 µg/kg. The diagnostic ratios showed that the PAHs originated mostly from pyrogenic sources such as gasoline and diesel combustion. The results show that PAH concentration in RDS and roadside soils is low when compared with other published studies. The low PAH levels found in this study are possibly related to differences in climate, urban features, and anthropogenic activities conducted in the studied areas. The toxicity equivalent concentrations (TEQ) of PAH calculated were also low in comparison with other studies. This is probably due to the lower concentration of total PAHs and the highly toxic high-molecular-weight PAHs.

Assessment of Heavy Metals Contamination in Roadside Soil Dust in Doon Valley, Uttarakhand

The accumulation of heavy metals in soil at roadside has been studied by the analysis of top soil/dust samples. Concentration of the elements Co, Cr, Pb and Cd were measured on 39 top soil/dust samples collected from near the highways, industrial area and control site. The samples were analysed for Zn, Cu, Fe, Mn, Pb, Cd, Ni, and Cr by using atomic absorption spectrophotometer (AAS). The mean concentrations of Co, Cr, Pb and Cd were 0.390, 0.090, 2.195 and 0.094 mg kg-1, respectively. Data obtained from analysis, were statistically examined to know the distribution of metals in different highways and industrial area. The results showed that the topsoil/dust near the highway and industrial sites had significantly enrichment particularly Pb than control sites.

Monitoring of Contaminant Input into Roadside Soil from Road Runoff and Airborne Deposition

Non-point sources of traffic-related pollution become a major concern as they – compared to the point-source inputs – are more difficult to be defined or controlled. It is crucial to evaluate the fraction of traffic-related contamination that is transported to the road surroundings as it could negatively impact soil, surface water and groundwater. This study describes two means through which pollutants leave the road to the surrounding environment. Three German motorways were selected (A4, A555, and A61), where runoff and deposits were analyzed to determine pollutant load moving into the roadside soil or into the drainage system. Each of the three motorways carries approximately 70,000 vehicles a day on 4 to 6 driving lanes; and they cover a broad range of truck participation in the total traffic load ranging from 5.4% to 19.8%. The three motorways represent several topographical and landscape features as forest with noise barrier and parallel as well as perpendicular orientation to the main wind direction. Sampling of runoff and deposition was done on monthly basis. Bulk deposition was collected in Bergerhoff vessels at two heights (1.5 m and 0.3 m above the ground) and in 1 m, 2.5 m, 5 m and 10 m distances from the road edge. The results showed that heavy metals as well as large amounts of mineral compounds are moving from the driving lanes into the roadside environment. This includes sodium from applying deicing salts in winter seasons, which could be found in soil, dust and water samples. Calcium and iron were also detected in almost comparable concentrations. The annual deposition flow (bulk deposition) measured at a height of 1.5 m was higher than the comparative values for urban areas and background measuring points. The spatial distribution of material deposition showed clear differences between the three motorways. The pollutant load in deposition measured near the ground surface was higher than those measured at 1.5 m above the land surface. At all three sites, a clear negative correlation between pollutant load and the distance from the roadside could be found. Nearly 90% of the concentration values of heavy metals in road runoff were below or in the range of the test values for seepage water in the German Soil Protection and Contamination Ordinance. The pH-values around 7 in runoff and adjacent soil provide a good retention capacity in the soil for the heavy metal input.

An Evaluation Performance of Potential Pollution of Arsenic, Chromium and Cadmium in the Road Side Soil of Kirkuk City, Northern Iraq

The present work is to evaluate and investigate the distribution of heavy metals (As, Cr and Cd) and to assess the road side samples contamination using an Index (SEPI), (CPI), (GAI), (CF) and (PLI). From right and left Khasa in Kirkuk city, road soil samples were collected in order to estimate the probable contamination level of heavy metals (Cd), (As) and (Cr) in the study area. The heavy metal concentrations were determined in the way side samples by using (ICP-MS) technique. The 22 samples have collected in August, 2013. The results of average levels of heavy metals revealed Cr, As and Cd recorded the highest concentration of (178.6 ppm, 10.4 ppm and 0.599 ppm) in right Khasa respectively. These heavy metals are recorded the lowest value (165.8, 8.29 and 0.4 ppm) in left Khasa respectively. However, the concentration of Cr and As was higher than the studied worldwide permissible of contaminated soil. The highest (SEPI) for As in right Khasa and Cr in left in Khasa seems therefore to be that this road side soil is the most polluted in the city of Kirkuk classified moderately contamination. The accounted of (CPI) for As, Cd and Cr ranged from 0.82 to 1.30 with average 1.01 and 0.6 to 1.12 with an average 0.78 in right and left Khasa respectively. The highest values in the right Khasa which suggest multi-elements contamination and suggested this area of study area received more heavy metals comes from manmade and industrial activities. The GAI showed a moderate contaminated with Cd in right Khasa of study area, while the other metals are in their uncontaminated level. The CF results has been showed by a considerable contamination metals (As, Cr and Cd) in of right Khasa, but low to moderate contamination in left Khasa. The results of (PLI) revealed a deterioration of site quality in all samples of Kirkuk city. Thus the evaluation methods revealed that the studied areas especially right Khasa impacted with heavy industrial activity, phosphate fertilizer, emission of gasses from automobile manufacture tire abrasion and workshop causing an increasing in metal concentrations towards the right Khasa.

Traffic-Related Heavy Metal Contamination in Urban Areas and Correlation with Traffic Activity in China

In this study, a detailed investigation was conducted to collect the concentrations of heavy metals—including cadmium, copper, nickel, lead and zinc—from five geographic areas to reflect the different land use and traffic conditions in Zhaoyuan, China. Analytical results of heavy metal concentrations showed that the mean and median values of these elements in soils were clearly higher than the corresponding background values, indicating pollution from the urban area. To generate a continuous surface from the collected discrete samples, Kriging interpolation was introduced to determine the spatial distribution patterns of heavy metal contamination. As a major source of urban heavy metal contamination, the traffic area was carefully analyzed. Interelemental relationships showed that most heavy metals in the traffic area had similar anthropogenic origins. In addition, the research team explored the relationships between heavy metals and traffic characteristics. The results indicated that heavy metal concentrations in roadside soils not only decreased with rising altitude and increasing distance from the trunk and branch roads on both sides but also could be affected by traffic volume. Finally, three evaluation methods—including the geoaccumulation index, the pollution index, and the improved pollution index—were introduced to assess heavy metal contamination levels fully in the traffic area. The pollution index evaluation method produced results indicating more severe levels of contamination than the other two evaluation methods.

Spatial patterns and determinants of species richness of alien and native plants in the Nujiang River valley

Biological invasion has attracted widespread attention because invasive species threaten native biodiversity and weaken ecosystem services. Based on field investigation of vegetation in Nujiang River valley, Northwest Yunnan, we analyzed the spatial patterns of native and invasive species richness, and the effects of topography, climate, and roadside habitat disturbance on the invasive versus native plant species richness. We recorded 26 exotic invasive plant species that belong to 13 families and 21 genera, and 1,145 native plant species, belonging to 158 families and 628 genera. Along the Nujiang River valley, species richness of invasive plants decreased with increasing latitude and altitude, while species richness of native plants increased with increasing latitude, and showed a hump-shaped pattern with elevation. A generalized linear model was used to estimate the roles of roadside disturbance, climate, topography and soil nutrients on the distribution of both native and invasive species richness. Results of hierarchical variation partitioning revealed that roadside habitat disturbance had primary impact on the distribution of two groups of species. Pre·研究报告· 390 生 物 多 样 性 Biodiversity Science 第 24 卷 cipitation was the climatic determinant of invasive species diversity, and small-scale topographic factors, especially aspect, mainly affected native species diversity. It is likely that native species became drought-resistant in the evolutionary process while invasive species failed to adapt themselves to the local arid environments due to the short colonization time. This research supports the hypothesis that resource availability is the main factor limiting plant invasion, and highlights the negative effects of human activity on biodiversity. In addition, results of structural equation modelling revealed that native communities aren’t resistant to plant invasion. The negative relationship between invasive and native species richness reflects the different responses of the two group species to environmental factors.

Roadside soils show low plant available zinc and copper concentrations

Vehicle combustion and component wear are a major source of metal contamination in the environment, which could be especially concerning where road ditches are actively farmed. The objective of this study was to assess how site variables, namely age, traffic (vehicles day−1), and percent carbon (%C) affect metal accumulation in roadside soils. A soil chronosequence was established with sites ranging from 3 to 37 years old and bioavailable, or mobile, concentrations of Zinc (Zn) and Copper (Cu) were measured along major highways in North Carolina using a Mehlich III extraction. Mobile Zn and Cu concentrations were low overall, and when results were scaled via literature values to “total metal”, the results were still generally lower than previous roadside studies. This could indicate farming on lands near roads would pose a low plant toxicity risk. Zinc and Cu were not correlated with annual average traffic count, but were positively correlated with lifetime traffic load (the product of site age and traffic count). This study shows an often overlooked variable, site age, should be included when considering roadside pollution accumulation. Zinc and Cu were more strongly associated with %C, than traffic load. Because vehicle combustion is also a carbon source, it is not obvious whether the metals and carbon are simply co-accumulating or whether the soil carbon in roadside soils may facilitate previously overlooked roles in sequestering metals on-site.