Spatiotemporal patterns and co-occurrence patterns of dissimilatory nitrate reduction to ammonium community in sediments of the Lancang River cascade reservoirs.

Dissimilatory nitrate reduction to ammonium (DNRA) is an important nitrate reduction pathway in freshwater sediments. Many studies have focused on the DNRA process in various natural habitats. However, the joint operation of cascade reservoirs will affect the physical and chemical properties of sediments, which may change the DNRA process and bacterial community pattern in the surface sediments of cascade reservoirs. Our study was the first to investigate the spatiotemporal distribution patterns of potential DNRA rate, nrfA gene abundances, and DNRA bacterial community diversity in surface sediments of the Lancang River cascade reservoirs. The results of slurry incubation experiments combined with the 15N isotope tracer experiment ascertained that the potential rates of DNRA were 0.01-0.15 nmol-N cm-3 h-1, and qPCR results indicated that the abundance range of nrfA was 1.08 × 105-2.51 × 106 copies g-1 dry weight. High throughput sequencing of the nrfA gene revealed that the relative abundance of Anaeromyxobacter (4.52% on average), Polyangium (4.09%), Archangium (1.86%), Geobacter (1.34%), and Lacunisphaera (1.32%) were high. Pearson and RDA correlation analysis exhibited that nrfA gene abundance was positively correlated with altitude, pH, OC, and sand concentration. Anaeromyxobacter was positively correlated with reservoir age and DNRA potential rate. The deterministic environmental selection process plays a crucial role in the formation of the DNRA bacterial community. Network analysis displayed that the dominant DNRA genus was the key population of the DNRA microbial community in the sediments of Lancang River cascade reservoirs. This study reveals that the variation of DNRA bacterial activity and community structure is largely driven by the construction of cascade reservoirs, and provides a new idea for further understanding the characteristics of the DNRA community in the cascade reservoir ecosystem.

Study on the planning and influential factors of the safe width of riparian buffer zones in the upper and middle reaches of the Ziwu River, China.

In this study, we employed the random forest model to identify the riparian buffer zone in the upper and middle reaches of the Ziwu River, used the Soil and Water Assessment Tool (SWAT) to simulate and calculate the nonpoint source pollution load in the riparian buffer zone, and used empirical formulas to estimate the pollutant concentration when surface runoff passes the edge of the riparian buffer zone. Moreover, through correlation analysis, we identified the main factors that affect the safe width of the riparian buffer zone. By combining these factors with the characteristic parameters of the riparian buffer zone and the water quality demand, we analyzed and calculated the safe width of the riparian buffer zone. Our findings are as follows: ① the simulated values of the SWAT model were highly consistent with the measured values. Specifically, the calibration and verification results of the hydrological station achieved Ens ≥ 0.65, RE < ± 15%, and R2 ≥ 0.85, while the overall total nitrogen and total phosphorus loads achieved Ens ≥ 0.65, RE < ± 15%, and R2 > 0.65. ② We found that the total nitrogen (TN) and total phosphorus (TP) loads in the riparian buffer zone gradually increased from upstream to downstream. Among these loads, the normal season had the largest TN and TP concentrations reaching the edge of the riparian buffer zone, while the dry season had the minimum concentrations. ③ The factors affecting the safe width of the riparian buffer zone included the connectivity, slope of the buffer zone, cultivated land area, and regional population density. For the effective protection of water quality, it is recommended that the upstream, midstream, and downstream buffer zones be at least 77.9 m, 33.37 m, and 60.25 m wide, respectively.

Defining the sources and the fate of nitrate by using dual isotopes and a Bayesian isotope mixing model: Water-nitrate management in cascade dams of Lancang river.

A multi-isotopes approach involving the use of stable nitrate isotopes (δ15N-NO3- and δ18O-NO3-) combined with stable water isotopes (δD-H2O and δ18O-H2O) and SIAR model as tracers can help identify the nitrogen source and understand the transformation process in a river-cascade reservoirs system. In this study, we identify the potential impact of the N source in the Lancang River basin, clarified the seasonal variations in the isotope values and estimated the probability distribution and proportional contribution of multi-terminal NO3--N sources using Bayesian isotope mixing model. In addition, we investigate the factors that led to the seasonal variations of the stable isotopes and evaluated the relationship between the uncertainty of the contribution ratio of the N sources and isotopic variations in the river-cascade reservoirs system. The NO3--N is the main component of DIN (dissolved inorganic nitrogen), accounting for 68.1 % of DIN. The ratios of δ15N-NO3- and δ18O-NO3- ranged from +4.2 ‰ to +10.3 ‰, and from +5.9 ‰ to +9.3 ‰ in the Lancang River. The δD-H2O and δ18O-H2O of the surface waters ranged from -109.47 ‰ to -76.44 ‰, and from -15.13 ‰ to -11.61 ‰, respectively. The SIAR model analysis results show that nitrification of livestock and poultry manure is the main source of NO3--N in the upstream natural reach, accounting for 40.2 %. There is little difference between the wet season and the dry season. Nitrification of soil organic nitrogen is the main source of NO3--N in the cascade development reach, accounting for 42.3 %. The contribution rate of atmospheric precipitation to nitrate concentration in both sampling periods is low (<5 %). This study provides a useful insight for reservoir water environmental managers to verify cascade development river pollution contributors and to better apply remedial solutions.

Spatial and Seasonal Patterns of Sediment Bacterial Communities in Large River Cascade Reservoirs: Drivers, Assembly Processes, and Co-occurrence Relationship.

Sediment bacteria play an irreplaceable role in promoting the function and biogeochemical cycle of the freshwater ecosystem; however, little is known about their biogeographical patterns and community assembly mechanisms in large river suffering from cascade development. Here, we investigated the spatiotemporal distribution patterns of bacterial communities employing next-generation sequencing analysis and multivariate statistical analyses from the Lancang River cascade reservoirs during summer and winter. We found that sediment bacterial composition has a significant seasonal turnover due to the modification of cascade reservoirs operation mode, and the spatial consistency of biogeographical models (including distance-decay relationship and covariation of community composition with geographical distance) also has subtle changes. The linear regression between the dissimilarity of bacterial communities in sediments, geographical and environmental distance showed that the synergistic effects of geographical and environmental factors explained the influence on bacterial communities. Furthermore, the environmental difference explained little variations (19.40%) in community structure, implying the homogeneity of environmental conditions across the cascade reservoirs of Lancang River. From the quantification of the ecological process, the homogeneous selection was recognized as the dominating factor of bacterial community assembly. The co-occurrence topological network analyses showed that the key genera were more important than the most connected genera. In general, the assembly of bacterial communities in sediment of cascade reservoirs was mediated by both deterministic and stochastic processes and is always dominated by homogeneous selection with the seasonal switching, but the effects of dispersal limitation and ecological drift cannot be ignored.

Carbon dioxide (CO2) partial pressure and emission from the river-reservoir system in the upper Yellow River, northwest China.

The exchange of carbon dioxide (CO2) flux between rivers and the atmosphere is an important part of the global carbon cycle. Reservoir development and environmental changes gradually transform rivers into river-reservoir systems. However, the current estimates of CO2 exchange flux at the water-air interface in river-reservoir systems, especially in ecologically fragile regions, are still largely uncertain. In this study, the CO2 partial pressure (ρCO2) and exchange flux (FCO2) from river-reservoir systems in the upper reaches of the Yellow River (YeUR) were investigated using the CO2SYS system and a boundary layer approach. The spatiotemporal dynamics and driving factors of the partial pressure of ρCO2 and FCO2 were revealed. Our results demonstrated that, driven by the freeze-thaw cycle of the permafrost active layer and the development of cascade reservoirs, the average ρCO2 in the two water periods was higher in the cascade reservoir section (CR) than in the source region section (SR) and higher in the flood period than in the dry period. Driven by water temperature stratification and light conditions, the ρCO2 of each reservoir in the CR exhibited seasonal variations along with water depth. The environmental factors TN, TP, T, DO, and DOC were the main influencing factors of ρCO2 distribution and could be used as predictors of ρCO2 in the dry period (R2 = 0.40 P < 0.01). In the dry period, the FCO2 in the SR was - 112.91 ± 165.94 mmol/(m2·d), which was a sink of CO2, and the FCO2 in the CR was 131.02 ± 156.77 mmol/(m2·d), which was a source of CO2. In the flood period, the FCO2 in the SR was 686.54 ± 624.33 mmol/(m2·d), and the FCO2 in the CR was 466.10 ± 366.67 mmol/(m2·d). Both the SR and the CR were sinks of CO2. Our results contribute to the understanding of CO2 exchange in river-reservoir systems and carbon cycle processes.

Source Analysis and Contamination Assessment of Potentially Toxic Element in Soil of Small Watershed in Mountainous Area of Southern Henan, China.

In this study, the concentrations of potentially toxic elements in 283 topsoil samples were determined. Håkanson toxicity response coefficient modified matter element extension model was introduced to evaluate the soil elements contamination, and the results were compared with the pollution index method. The sources and spatial distribution of soil elements were analyzed by the combination of the PMF model and IDW interpolation. The results are as follows, 1: The concentration distribution of potentially toxic elements is different in space. Higher concentrations were found in the vicinity of the mining area and farmland. 2: The weight of all elements has changed significantly. The evaluation result of the matter-element extension model shows that 68.55% of the topsoil in the study area is clean soil, and Hg is the main contamination element. The evaluation result is roughly the same as that of the pollution index method, indicating that the evaluation result of the matter-element extension model with modified is accurate and reasonable. 3: Potentially toxic elements mainly come from the mixed sources of atmospheric sedimentation and agricultural activities (22.59%), the mixed sources of agricultural activities and mining (20.26%), the mixed sources of traffic activities, nature and mining (36.30%), the mixed sources of pesticide use and soil parent material (20.85%).

Community structure, distribution pattern, and influencing factors of soil Archaea in the construction area of a large-scale photovoltaic power station / Estructura de la comunidad, patrón de distribución y factores influyentes del suelo Archaea en el área de construcción de una central fotovoltaica a gran escala

The photovoltaic power station in Qinghai has been built for 8 years; however, its impact on the regional soil ecological environment has not been studied in depth. To reveal the structure and distribution pattern of archaeal communities in desert soil under the influence of a large photovoltaic power station, a comparative study was carried out between the soil affected by photovoltaic panels and the bare land samples outside the photovoltaic station in Gonghe, Qinghai Province. The abundance, community structure, diversity, and distribution characteristics of archaea were analyzed by quantitative PCR and Illumina-MiSeq high-throughput sequencing, and the main environmental factors affecting the variation in soil archaeal community were identified by RDA. The contribution rate of environmental factors and human factors to microbial community diversity was quantitatively evaluated by VPA. The results showed that there was no significant difference in soil nutrients and other physicochemical factors between the photovoltaic power station and bare land. Thaumarchaeota was the dominant archaeal phylum in the area, accounting for more than 99% of archaeal phylum, while at the level of genus, Nitrososphaera was the dominant archaeal genera. There was no significant difference in archaeal community structure between and under different types of PV panels. The analysis has shown that the construction of a photovoltaic station has little effect on the community structure of soil archaea in a desert area, and it was speculated that the selection of niche played a leading role in the distribution pattern of soil archaeal community. This study provides the basis for a scientific understanding of the characteristics and distribution patterns of soil archaeal communities affected by the construction of a photovoltaic power station.(AU)

Community structure, distribution pattern, and influencing factors of soil Archaea in the construction area of a large-scale photovoltaic power station.

The photovoltaic power station in Qinghai has been built for 8 years; however, its impact on the regional soil ecological environment has not been studied in depth. To reveal the structure and distribution pattern of archaeal communities in desert soil under the influence of a large photovoltaic power station, a comparative study was carried out between the soil affected by photovoltaic panels and the bare land samples outside the photovoltaic station in Gonghe, Qinghai Province. The abundance, community structure, diversity, and distribution characteristics of archaea were analyzed by quantitative PCR and Illumina-MiSeq high-throughput sequencing, and the main environmental factors affecting the variation in soil archaeal community were identified by RDA. The contribution rate of environmental factors and human factors to microbial community diversity was quantitatively evaluated by VPA. The results showed that there was no significant difference in soil nutrients and other physicochemical factors between the photovoltaic power station and bare land. Thaumarchaeota was the dominant archaeal phylum in the area, accounting for more than 99% of archaeal phylum, while at the level of genus, Nitrososphaera was the dominant archaeal genera. There was no significant difference in archaeal community structure between and under different types of PV panels. The analysis has shown that the construction of a photovoltaic station has little effect on the community structure of soil archaea in a desert area, and it was speculated that the selection of niche played a leading role in the distribution pattern of soil archaeal community. This study provides the basis for a scientific understanding of the characteristics and distribution patterns of soil archaeal communities affected by the construction of a photovoltaic power station.

Multiple isotopic tracing for sulfate and base cation sources of precipitation in Hangzhou city, Southeast China: Insights for rainwater acidification mechanism.

Acid deposition has been regarded as a serious factor in the deteriorative water environment and ecosystems. Despite the powerful acid emission control measures have been implemented by the Chinese government, many areas (especially Southeast China) are still suffering from acid deposition. The chemical and isotopic (δ34S and 87Sr/86Sr) compositions of rainwater in Hangzhou, a typical megacity in Southeast China with serious acid rain problem, for one year were studied with the aim to better constrain potential sources and explore the causes of rainwater acidification. Most rainwater samples were acidic, with a VWM pH value of 4.65. SO42- was the dominant anion and the main acid ion in rainwater. Sulfur isotope and the quantity equilibrium model revealed that sea salt, crustal, biogenic, and anthropogenic sulfur represented 2.3%, 0.1%, 16.7%, and 80.8% of the SO42- source in rainwater, respectively. The back trajectory and strontium isotopes indicated that the base cations (BCs) in rainwater originated mainly from anthropogenic sources. The relatively low neutralizing capacity caused by limited BCs input and emission control measures undermines some efforts to reduce rainwater acidity. This case study demonstrated that a valuable tool to probe the source of acid rain and unravel the mechanism of rainwater acidification can be provided by multiple lines of evidence, including rainwater chemical compositions, stable sulfur isotopes, and stable strontium isotopes.

Nitrous oxide (N2O) emissions from the high dam reservoir in longitudinal range-gorge regions on the Lancang-Mekong River, southwest China.

Nitrous oxide (N2O) is a greenhouse gas that should not be overlooked, and its emissions from plain reservoirs as well as small- and medium-sized reservoirs have been extensively studied; however, N2O emission patterns from high-dam reservoirs in longitudinal range-gorge regions remain unclear. In this study, the N2O concentration and emission flux from the high-dam Xiaowan Reservoir were investigated using static headspace gas chromatography and a boundary layer approach in the Lancang River. The factors influencing N2O production and emissions, especially the influence of damming, were explored. Our results demonstrated that the Xiaowan Reservoir, a source of N2O emissions, had an N2O emission flux of 15.48 ± 2.87 µmol m2·d-1 in 2019; the N2O concentration and emission flux exhibited an increasing trend along the flow direction within the Xiaowan Reservoir but decreased downstream of the dam. During the two water seasons, water temperature, the concentration of DO, NO3- and NH4+are all influencing factors of the N2O concentration in the XWR. the N2O in the XWR during the wet season was produced by nitrification, during the dry season the production mechanism of N2O was relatively complicated, but mainly produced by nitrification. This study advances our knowledge of N2O emissions from high-dam reservoirs in longitudinal range-gorge regions.

Spatial-temporal dynamics and influencing factors of archaeal communities in the sediments of Lancang River cascade reservoirs (LRCR), China.

The spatial and temporal distribution of the archaeal community and its driving factors in the sediments of large-scale regulated rivers, especially in rivers with cascade hydropower development rivers, remain poorly understood. Quantitative PCR (qPCR) and Illumina MiSeq sequencing of the 16S rRNA archaeal gene were used to comprehensively investigate the spatiotemporal diversity and structure of archaeal community in the sediments of the Lancang River cascade reservoirs (LRCR). The archaeal abundance ranged from 5.11×104 to 1.03×106 16S rRNA gene copies per gram dry sediment and presented no temporal variation. The richness, diversity, and community structure of the archaeal community illustrated a drastic spatial change. Thaumarchaeota and Euryyarchaeota were the dominant archaeal phyla in the sediments of the cascade rivers, and Bathyarchaeota was also an advantage in the sediments. PICRUSt metabolic inference analysis revealed a growing number of genes associated with xenobiotic metabolism and carbon and nitrogen metabolism in downstream reservoirs, indicating that anthropogenic pollution discharges might act as the dominant selective force to alter the archaeal communities. Nitrate and C/N ratio were found to play important roles in the formation of the archaeal community composition. In addition, the sediment archaeal community structure was also closely related to the age of the cascade reservoir and hydraulic retention time (HRT). This finding indicates that the engineering factors of the reservoir might be the greatest contributor to the archaeal community structure in the LRCR.

Effects of photovoltaic panels on soil temperature and moisture in desert areas.

Photovoltaic power generation is an important clean energy alternative to fossil fuels. To reduce CO2 emissions, the Chinese government has ordered the construction of a large number of photovoltaic (PV) panels to generate power in the past two decades; many are located in desert areas because of the sufficient light conditions. Large-scale PV construction in desert areas can alter the local microclimate and soil conditions, thereby affecting the growth of vegetation. However, few studies have focused on the effects of PV panels on the environment of desert areas. In this study, we investigated the effects of PV panels on soil moisture and temperature via a whole-year field experiment at a PV power plant in a desert area in western China. The in situ soil moisture and temperature at a depth of 0-0.4 m were measured under three types of PV shading conditions: shaded by fixed-tilt (FIX) PV panels, shaded by oblique single-axis (OSA) PV panels, and no shading. The results showed that the soil temperature and moisture at sites under PV shading were significantly affected compared with those at sites without shading. PV panels increased the average soil temperature during winter but decreased it during the other three seasons. Moreover, the warming effect of FIX PV panels on the soil is more apparent than that of OSA PV panels. PV panels have positive effects on soil moisture. Compared with that at the sites without shaded areas, the average soil moisture under the FIX PV panels and under the OSA PV panels increased by 14.7% and by 11.1%, respectively. These data provide support for future studies on vegetation restoration around PV power plants in desert areas.

[Red Mud-activated Peroxymonosulfate for Ciprofloxacin Degradation: Efficiency and Mechanism].

In this paper, the effects and mechanism of ciprofloxacin (CIP) degradation with peroxymonosulfate (PMS) catalyzed by solid waste red mud (RM) was firstly studied. The results indicated that RM has large specific surface area (10.96 m2·g-1) and complex pore structure, containing ferric, alumina and calcium oxide, which enhanced ciprofloxacin degradation by PMS effectively. Radical quenching experiments revealed that SO4-·and HO·were contributed to ciprofloxacin oxidation, and the reaction was mainly occurred on RM's surface. An increase in temperature could accelerate CIP degradation, and the corresponding reaction activation energy Ea was about 5.74 kJ·mol-1. Meanwhile, CIP degradation rate increased with PMS concentration and the optimal dosage of RM was 1.0 g·L-1. Eight degradation intermediates were identified using HPLC/MS/MS, and consequently, CIP was degraded mainly through two pathways; the piperazine groups were preferentially attacked by active free radicals. This study further indicated that RM is a cheap catalyst and can be potentially used in the treatment of antibiotic contaminated wastewater.

Spatiotemporal variations of nitrate sources and dynamics in a typical agricultural riverine system under monsoon climate.

Nitrogen pollution is a serious environmental issue in the Danjiangkou Reservoir region (DRR), the water source of the South-to-North Water Diversion Project of China. In this research, seasonal surveys and a bi-weekly time series survey were conducted in the Qihe River Basin, one of the most densely populated agricultural basins in the DRR. Hydrochemical compositions (NO3- and Cl-), dual isotopes (δD-H2O, δ18O-H2O, δ15N-NO3-, and δ18O-NO3-), and a Markov Chain Monte Carlo isotope mixing model were jointly applied to unravel the sources, migrations, and transformations of the nitrate (NO3-) in the basin. It was revealed that the mixing between different sources was the main process controlling the isotopic compositions of the riverine NO3- in the upper-middle reaches. In contrast, denitrification occurred in the lower reaches. For the first time, the sources of NO3- were quantified at a basin scale in the DRR. Overall, the river transported 484.2 tons/year of NO3-N to the reservoir, of which 32.6%, 36.4%, 28.0%, and 3.0% was from soil organic nitrogen, chemical fertilizer, residential sewage and atmospheric precipitation, respectively. The NO3-N fluxes of the different sources were regulated by the monsoon climate and anthropogenic activities. For example, high precipitation and intense fertilization resulted in severe nonpoint source pollution. Denitrification thrived in soils and reservoirs in wet seasons. Temperature could regulate the migration, nitrification and denitrification processes. Based on the results, we suggest that the management strategies dealing with nitrogen pollution issue in the DRR should follow the specific spatiotemporal characteristics of NO3- sources, migration and transformation mechanisms.

Reservoir effects on the variations of the water temperature in the upper Yellow River, China, using principal component analysis.

Water temperature is an important factor that affects the number and variety of river species. After a reservoir is built, a river's thermal regime changes significantly. Analyzing and evaluating river water temperature variation trends caused by damming can provide scientific support for developing effective water management strategies for reservoirs. This paper aimed to construct an index system of water temperatures in high and cold areas of the Upper Yellow River, and a method was proposed for identifying river water temperature variation based on principal component analysis (PCA). The variation degree in the river water temperature caused by large reservoirs was analyzed quantitatively. A three-dimensional water temperature model was developed to simulate the effect of a stratified intake on the alleviation of low-temperature water. The results indicated that (1) the water temperature decreased in summer and increased in winter, seasonal temperature changes decreased, there was a time delay in water temperature processes and a time fluctuation in the temperature threshold. (2) Certain indices were obtained that considered fish spawning and breeding, thermal condition changes and interactions between the organisms influenced by the reservoirs. (3) A stratified intake has a good effect on mitigating the impact of low water temperatures on fish spawning to some extent. The index system of the water temperature and its gradient changes effectively analyzed the influence of the reservoirs on river water temperature variations.

Occurrence and risk assessment of antibiotics in the Xi'an section of the Weihe River, northwestern China.

Fifteen antibiotics, including seven sulfonamides (SAs); three macrolides (MLs); three quinolones (QNs); one lincosamide, lincomycin (LIN); and one tetracycline (TC), were detected in the surface water of the Xi'an section of the Weihe River by using high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS). The detection rates were 12.50-100%, and the detected concentrations were in the range of nd-270.60 ng/L. The average detected concentrations of the SAs, MLs, QNs, LIN and TC were 113.68, 111.79, 20.55, 23.81 and 25.66 ng/L, respectively. Among these, SAs and MLs were the dominant antibiotics detected in the Weihe River. Compared with those in other water bodies in China and abroad, the antibiotic residues in the Weihe River were at a moderate contamination level. The SAs concentration distribution followed upstream > midstream > downstream, while the MLs concentration distribution was midstream < downstream < upstream. The correlation analysis and principal component analysis (PCA) indicated that domestic sewage, livestock discharge, and aquaculture and pharmaceutical wastewater are the main sources of antibiotic residues in the Weihe River. In addition, the detected ciprofloxacin (CFX), ofloxacin (OFX) and sulfamethoxazole (SMX) pose high ecological risk in the short and long term.

Chemical composition of precipitation in Shenzhen, a coastal mega-city in South China: Influence of urbanization and anthropogenic activities on acidity and ionic composition.

Rainwater samples from Shenzhen in south China were collected over the period of a year, and the chemical compositions were measured with the main purpose of understanding the acidification of rainwater and the controlling factors. The pH value of precipitation ranged from 3.72 to 6.77, with a volume-weighted mean (VWM) value of 4.29, and the acid rain frequency was 97%. The VWM concentrations of anions and cations followed the order of SO42- > Cl- > NO3- and Na+ > Ca2+ > NH4+ > Mg2+ > K+, respectively. Air mass back-trajectory and positive matrix factorization analyses indicated that sources of ions in rainwater were mainly from sea salt, soil dust and anthropogenic activities. Compared with other areas in China, the rainwater of Shenzhen has the lowest values of the NP/AP, ∆pH and NF values of Ca2+ and NH4+, indicating that the lack of the capacity for neutralization could be the main reason for the severe acid rain problem. It is noteworthy that the rain acidification tendency is obvious, and the pH value has reduced by 1.0 units since the 1980s. Based on a comparison of the chemical compositions of the rainwater from different historical periods, the NO3- concentration was found to have increased consistently, whereas the NH4+ concentration maintained a decreasing trend since 1980. On the other hand, the nss-SO42- and nss-Ca2+ concentrations increased after 1980 and then decreased after 1994. Meanwhile, the decreasing pH was accompanied by a decreasing NP/AP ratio. These results suggest that the changes in human activities at different stages of urban development can lead to a synergistic change in the chemical characteristics of precipitation. Both an increase in the acidic species emissions (especially NOX) due to rapid economic development and a decrease in the alkaline ions concentration due to urbanization have resulted in the rain acidification tendency in Shenzhen.

[Progress in the Studies of Precipitation Chemistry in Acid Rain Areas of Southwest China].

The precipitation data for nine sites in the acid rain area of southwest China were analyzed. The data included pH and the concentrations of major ions (Cl-, SO42-, NO3-, Ca2+, NH4+, Mg2+, K+, and Na+). SO42- and NO3- were the main anions, whereas Ca2+ and NH4+ were the main cations in the precipitation. The concentrations of acidic ions, alkaline ions, and total ions in this area were significantly higher than those reported in southeast China, but much lower than those in northern China. About 58% of the total precipitation has a pH value ranging from 4.5 to 5.6. According to the correlation of acidic and alkaline ions as well as the results of the neutralization factor, the rainwater in this area has been neutralized. Ca2+ and NH4+ are the dominant neutralization substances in rainwater. Comparisons of pH and the main ion components with other areas showed that rainfall neutralization in this area was stronger than that in southeast China but poorer than that in northern China. Calculation of enrichment factors for rainwater components relative to soil and seawater indicated that Ca2+ and Mg2+ mainly originated from terrestrial sources and SO42- and NO3- were mostly attributed to the anthropogenic activities in this area. In addition, approximately 99.7% of Ca2+ and 84.0% of Mg2+ were attributed to terrestrial sources and were closely related to the widespread distribution of carbonate rocks in the southwest of China.

Land use change and its effects on water quality in typical inland lake of arid area in China.

Land-use change is very important for determining and assessing the influence of human activity on aquatic environment of rivers and lakes. The present work with Bosten River basin as the subject, analyzes features of dynamic land-use change of the basin from 1993 to 2013, in order to study the influence of land-use pattern change on the basin water quality, according to the land-use/land-cover(LUCC) chart from 2000 to 2013 made by ArcGIS and ENVI. It shows cultivated land, wetland and forestland constitute most of Bosten River basin, taking up over 41.7% of the total; from 1993-2000, LUCC of the basin is relatively small, with an increase of cultivated land, residential-industry land, water wetlands by 15.09%-18.33%,most of which are transformed from forestland, grassland and unused land; from 2000-2013, LUCC of the basin is relatively significant, with a continuing and bigger increase of cultivated land and Residential-industry area, most of which are transformed from water wetlands and unused land. Based on analysis of landuse pattern and water quality index, it can be told that water pollution is positively correlated to cultivated land and residential-industry area and negatively correlated to water and grassland. Also, the influence of land-use pattern change on water quality has been discussed, whose finding can serve as the scientific evidence for land-use optimization and water pollution control.

Nitrogen impacts on atrazine-degrading Arthrobacter strain and bacterial community structure in soil microcosms.

The objective of this study was to investigate the impacts of exogenous nitrogen on a microbial community inoculated with the atrazine-degrading Arthrobacter sp. in soil amended with a high concentration of atrazine. Inoculated and uninoculated microcosms for biodegradation tests were constructed. Atrazine degradation capacity of the strain DAT1 and the strain's atrazine-metabolic potential and survival were assessed. The relative abundance of the strain DAT1 and the bacterial community structure in soils were characterized using quantitative PCR in combination with terminal restriction fragment length polymorphism. Atrazine degradation by the strain DAT1 and the strain's atrazine-metabolic potential and survival were not affected by addition of a medium level of nitrate, but these processes were inhibited by addition of a high level of nitrate. Microbial community structure changed in both inoculated and uninoculated microcosms, dependent on the level of added nitrate. Bioaugmentation with the strain DAT1 could be a very efficient biotechnology for bioremediation of soils with high concentrations of atrazine.