| Large quantities of deicing salts are applied in urban areas for clearing the pavement and ensuring the normal traffic flow during the winter seasons in Northeastern China. There have been many recent reports of high salt levels on aquatic systems and terrestrial vegetation. According to the different pathways by which salt ions may move after deicing salts application, studies of salt storage in soils are especially needed in urban environments. Compared to soils in other ecosystems, urban soils are more exposed to human activities. Urban areas are responsible for a large portion of deicing salts use. However, most previous studies of the effects of deicing salts have been on the soils beside remote, rural highways where salt effects are easily attributed to as single source (a road). It is still unclear how well results of rural studies apply to urban areas, where road and sidewalk density is high, total impervious cover is high. The most common deicing material used in Shenyang city, where the largest and oldest heavy industrial base city in China, is the chemical compounds including sodium chloride (NaCl), calcium chloride (CaCl2).In this paper, the possible alternative pathway by which salt ions (K, Ca, Na, Mg, Cl and SO42-) may move to soil, plants and aquatic systems after deicing chemicals applications was investigated. The distribution characteristics of the principal components in the urban environment showed that the high sodium and chloride concentration in roadside snow is extensively higher than thatin roadside snow samples collected far from urban roads. The salt from deicing operation has been observed to accumulate in roadside soil and inhibit the growth of vegetation (Pinus tabulaeformis). There was an obvious increasing of salt ions concentrations in stormwater runoff samples, especially Na and Cl. It is also found that readily soluble salts ions in stormwater runoff peaked at the first storm event after winter.It is evident that the application of deicing salts in cold regions of China every year has had adverse impacts on the aquatic ecology through stormwater runoff.Application of chemical road deicers has a negative impact on roadside vegetation. Every year, plants in cities suffer from direct and indirect effects of salt application for winter road maintenance.The effects of different concentrations of two typical deicing salts on seed germination and growth response of three kinds of cool-season turfgrasses(Poa pratensis cv. Merit, Lolium perenne cv. Green Emerald and Trifolium repens cv. Riverdel) were studied in this paper. The NaCl content of two typical deicing salts was45.2%and54.6%, respectively. The investigation of growth response in the turfgrass seedlings including length of roots and shoots, relative water content, relative conductivity of the plasma membrance, malondialdehyd (MDA) content and peroxidases (POD) activity. The results showed that the inhibition effect of seed germination and growth response in the three kinds of turfgrasses was increased with the increasing deicing salts concentration. Compared with No.1deicing salt, the inhibition effect of No.2deicing salt on seed germination and growth of three cool-season turfgrass species was stronger. The deicing salts tolerance was in the sequence Lolium perenne, Poa pratensis and Trifolium repens. The critical value of those was6.25-9.61g/L,4.99-6.17g/L and1.97-3.11g/L, respectively. The maximum value was12.89-16.85g/L,9.79-12.62g/L and5.71-8.26g/L, respectively. The deicing salts stress mainly inhibited water absorption, disturbed membrane function and induced MDA accumulation via the effect of osmotic and ion toxicity. However, POD enzyme of the three kinds of turfgrass seedlings played a significant role under the deicing salts stress.Pot experiments were performed in soil culture to test the effect of two typical deicing salts on the growth and K+and Na+transportation and distribution of Amelanchier alnifolia seedlings. The results showed that the biomass accumulation of roots, stems and leaves of seedlings was inhibited by the stress of two typical deicing salts. The treatment of0.4%deicing salts decreased the biomass accumulation significantly in comparison with the control seedlings. Compared with the No.2deicing salts, the seedling of Amelanchier alnifolia had the higher biomass accumulation, K+/Na+ratios and higher transportation selectivity of K+to Na+from root to stem and stem to leaves. In conclusion, the inhibition effect of No.2deicing salt was stronger. With the increasing concentration of deicing salts, the Na+content in the roots, stems and leaves of Amelanchier alnifolia increased while the K+content decreased, resulting in a decrease in the K+/Na+ratio. The ability of ion transporting from root to stem was enhanced, while K+to Na+from stem to leaves was decreased significantly under the increasing concentration of deicing salts. It was reported that the application of exogenous K+and salicylic acid (SA) could protect plants against abiotic stress. In this study, pot experiments were performed in soil culture to test the efficacy of two soil additives, potassium nitrate (KNO3) and SA, in alleviating the stress of deicing salts on growth and photosynthetic parameters of Pinus tabulaeformis seedlings. The results showed that the treatment of KNO320mmol/L and SA2mmol/L to0.2%deicing salts had high dry weight and water content. Meanwhile, the MDA content and leakage rates of electrolyte increased once exposure to0.2%deicing salts, and salts exposure also had an inhibitory effect on the activities of the POD. It was also found that the contents of Ci and Gs remained unchanged in leaves of Pinus tabulaeformis seedlings in all alleviation treatments, but the enhancing of chlorophyll contents played a key role in maintaining the leaf photosynthetic rate under the treatment of KNO3and SA. The results indicated that the salt tolerance of Pinus tabulaeformis seedlings was improved by using soil additives of KNO320mmol/L and SA2mmol/L. Exogenous K+and SA showed strong benefits against deicing salts-induced negative symptoms.Of several impacts of road salting on roadside soils, the potential disruption of the nitrogen cycle has been largely ignored. The effects of deicing salts on the activity and community structure of soil microorganisms, ammonification and nitrification in the soils were investigated. The results showed that the inhibition effect of microbial biomass, metabolic quotient, urease enzyme activiy, the content of mineralizable N and nitrate N growth response was increased with the increasing deicing salts concentration. All that indexes were inhibited significantly by the stress of0.5%deicing salts..The declining trend in biomass C/N with increasing salinity may reflect the baeterial dominanee in soil microbial biomass. The positive relationship between microbial biomass and the content of mineralizable N and nitrate N, indicated that the remarkable influence of deicing salts on the activity and community structure of soil microorganisms, and induced the decrease of soil nitrogen mineralization and nitrification in the soils.Widespread use of deicing salts on road in cold regions has been shown to mobilize heavy metals in roadside soils putting ground and surface waters at risk. Examining the accumulation of deicing salts and its short-term effect on metal mobility in urban roadside soils is important for understanding the distribution and movement of heavy metals in the environment of Northern China. The investigation results from41roadside soils not only showed a strong rise in deicing-salt related Na concentration (352-513mg/kg) and Cl concentration (577-2,353mg/kg), but also high Cd (1.2-7.6mg/kg) and Pb (28.7-101.6mg/kg) values. The most serious contaminated roadside soil was leached in columns alternately with de-icing salt solution and de-ionized water to simulate the runoff of deicing salts into roadside soils followed by snowmelt or rainwater. The results showed that an extensive mobilization of Cd (20.90%of the total Cd) occurred in the salt leachate and a high correlation with Cl showed that Cl complexes are important for the mobilization, although the cation exchange cannot be excluded. Conversely, only2.34%of the total amount of Pb was leached confirming the usual hypotheses about the high immobility of Pb in soils. However, the high Pb concentration coincided with peaks in Fe and TOC concentrations and the low proportion of Pb in the>0.45μm phase, implied an extensive mobilization of small-sized colloids. |
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