Environmental protection measures mitigate Pb but not Cd accumulation in soils: Evidence from a 49-year soil chronosequence in an industrial and mining city in Southwest China.

To address severe soil Pb and Cd contamination from anthropogenic activities, governments have implemented various environmental management measures. However, the extent to which these measures have constrained Pb and Cd accumulation in industrial and mining city soils remains unclear. Here, we investigated Pb and Cd accumulation patterns in soils of Panzhihua City, Southwest China, and determined their dominant anthropogenic drivers using Pb and Cd isotopes. Pb accumulation initially slowed and then increased, while Cd showed a continuous acceleration. Traffic and coal-burning power generation were the dominant anthropogenic forcings for Pb and Cd accumulation in the soils, respectively. Environmental protection measures, particularly the ban on leaded gasoline, significantly reduced Pb accumulation by decreasing traffic-related Pb contributions to soils from 1980 to 2008. However, environmental management measures could not practically mitigate Cd accumulation in the soils owing to the high Cd content in consumed coal, poor efficiency of air pollutant control measures, and steep rise in coal-burning power generation. This study thus indicates the criticality of controlling Cd emissions from thermal power generation. Additionally, the challenges faced by small industrial and mining cities during economic transformation and environmental policy implementation warrant more attention.

Fungal community determines soil multifunctionality during vegetation restoration in metallic tailing reservoir.

Microorganisms are pivotal in sustaining soil functions, yet the specific contributions of bacterial and fungal succession on the functions during vegetation restoration in metallic tailing reservoirs remains elusive. Here, we explored bacterial and fungal succession and their impacts on soil multifunctionality along a ∼50-year vegetation restoration chronosequence in China's largest vanadium titano-magnetite tailing reservoir. We found a significant increase in soil multifunctionality, an index comprising factors pertinent to soil fertility and microbially mediated nutrient cycling, along the chronosequence. Despite increasing heavy metal levels, both bacterial and fungal communities exhibited significant increase in richness and network complexity over time. However, fungi demonstrated a slower succession rate and more consistent composition than bacteria, indicating their relatively higher resilience to environmental changes. Soil multifunctionality was intimately linked to bacterial and fungal richness or complexity. Nevertheless, when scrutinizing both richness and complexity concurrently, the correlations disappeared for bacteria but remained robust for fungi. This persistence reveals the critical role of the fungal community resilience in sustaining soil multifunctionality, particularly through their stable interactions with powerful core taxa. Our findings highlight the importance of fungal succession in enhancing soil multifunctionality during vegetation restoration in metallic tailing reservoirs, and manipulating fungal community may expedite ecological recovery of areas polluted with heavy metals.

Nano-enabled strategies to promote safe crop production in heavy metal(loid)-contaminated soil.

Nanobiotechnology is a potentially safe and sustainable strategy for both agricultural production and soil remediation, yet the potential of nanomaterials (NMs) application to remediate heavy metal(loid)-contaminated soils is still unclear. A meta-analysis with approximately 6000 observations was conducted to quantify the effects of NMs on safe crop production in soils contaminated with heavy metal(loid) (HM), and a machine learning approach was used to identify the major contributing features. Applying NMs can elevate the crop shoot (18.2 %, 15.4-21.2 %) and grain biomass (30.7 %, 26.9-34.9 %), and decrease the shoot and grain HM concentration by 31.8 % (28.9-34.5 %) and 46.8 % (43.7-49.8 %), respectively. Iron-NMs showed a greater potential to inhibit crop HM uptake compared to other types of NMs. Our result further demonstrates that NMs application substantially reduces the potential health risk of HM in crop grains by human health risk assessment. The NMs-induced reduction in HM accumulation was associated with decreasing HM bioavailability, as well as increased soil pH and organic matter. A random forest model demonstrates that soil pH and total HM concentration are the two significant features affecting shoot HM accumulation. This analysis of the literature highlights the significant potential of NMs application in promoting safe agricultural production in HM-contaminated agricultural lands.

Microbial nutrient limitation and carbon use efficiency changes under different degrees of litter decomposition.

Alpine ecosystems are important terrestrial carbon (C) pools, and microbial decomposers play a key role in litter decomposition. Microbial metabolic limitations in these ecosystems, however, remain unclear. The objectives of this study aim to elucidate the characteristics of microbial nutrient limitation and their C use efficiency (CUE), and to evaluate their response to environmental factors. Five ecological indicators were utilized to assess and compare the degree of microbial elemental homeostasis and the nutrient limitations of the microbial communities among varying stages of litter decomposition (L, F, and H horizon) along an altitudinal gradient (2800, 3000, 3250, and 3500 m) under uniform vegetation (Abies fabri) on Gongga Mountain, eastern Tibetan Plateau. In this study, microorganisms in the litter reached a strictly homeostatic of C content exclusively during the middle stage of litter decomposition (F horizon). Based on the stoichiometry of soil enzymes, we observed that microbial N- and P-limitation increased during litter degradation, but that P-limitation was stronger than N-limitation at the late stages of degradation (H horizon). Furthermore, an increase in microbial CUE corresponded with a reduction in microbial C-limitation. Additionally, redundancy analysis (RDA) based on forward selection further showed that microbial biomass C (MBC) is closely associated with the enzyme activities and their ratios, and MBC was also an important factor in characterizing changes in microbial nutrient limitation and CUE. Our findings suggest that variations in MBC, rather than N- and P-related components, predominantly influence microbial metabolic processes during litter decomposition on Gongga Mountain, eastern Tibetan Plateau.

Soil heavy metal pollution promotes extracellular enzyme production by mediating microbial community structure during vegetation restoration of metallic tailing reservoir.

Vegetation restoration in metallic tailing reservoirs is imperative to restore the post-mining degraded ecosystems. Extracellular enzymes determine microbial resource acquisition in soils, yet the mechanisms controlling the enzyme activity and stoichiometry during vegetation restoration in metallic tailing reservoirs remain elusive. Here, we investigated the variations and drivers of C-, N- and P-acquiring enzymes together with microbial community along a 50-year vegetation restoration chronosequence in the China's largest vanadium titano-magnetite tailing reservoir. We found a parabolic pattern in the enzyme activity and efficiency along the chronosequence, peaking at the middle restoration stage (∼30 years) with approximately six-fold increase relative to the initial 1-year site. The enzyme ratios of C:P and N:P decreased by 33 % and 68 % along the chronosequence, respectively, indicating a higher microbial demand of C and N at the early stage and a higher demand of P at the later stage. Soil nutrients directly determined the enzyme activities and stoichiometry, whereas microbial biomass and community structure regulated the temporal pattern of the enzyme efficiency. Surprisingly, increased heavy metal pollution imposed a positive effect on the enzyme efficiency indirectly by altering microbial community structure. This was evidenced by the increased microbial diversity and the conversion of copiotrophic to oligotrophic and stress-tolerant taxa along the chronosequence. Our findings provide new insights into microbial functioning in soil nutrient dynamics during vegetation restoration under increasing heavy metal pollution.

Microplastic pollution promotes soil respiration: A global-scale meta-analysis.

Microplastic (MP) pollution likely affects global soil carbon (C) dynamics, yet it remains uncertain how and to what extent MP influences soil respiration. Here, we report on a global meta-analysis to determine the effects of MP pollution on the soil microbiome and CO2 emission. We found that MP pollution significantly increased the contents of soil organic C (SOC) (21%) and dissolved organic C (DOC) (12%), the activity of fluorescein diacetate hydrolase (FDAse) (10%), and microbial biomass (17%), but led to a decrease in microbial diversity (3%). In particular, increases in soil C components and microbial biomass further promote CO2 emission (25%) from soil, but with a much higher effect of MPs on these emissions than on soil C components and microbial biomass. The effect could be attributed to the opposite effects of MPs on microbial biomass vs. diversity, as soil MP accumulation recruited some functionally important bacteria and provided additional C substrates for specific heterotrophic microorganisms, while inhibiting the growth of autotrophic taxa (e.g., Chloroflexi, Cyanobacteria). This study reveals that MP pollution can increase soil CO2 emission by causing shifts in the soil microbiome. These results underscore the potential importance of plastic pollution for terrestrial C fluxes, and thus climate feedbacks.

Occurrence and fate of current-use pesticides in Chinese forest soils.

Pesticides play a crucial role in securing global food production to meet increasing demands. However, because of their pervasive use, they are now ubiquitous environmental pollutants that have adverse effects on both ecosystems and human health. In this study, the environmental occurrence and fate of 16 current-use pesticides (CUPs) were investigated in 93 forest soil samples obtained from 11 distinct mountains in China. The concentrations of the target pesticides ranged from 0.36 to 55 ng/g dry weight. Cypermethrin, dicofol, chlorpyrifos, chlorothalonil, and trifluralin were the most frequently detected CUPs. The CUP concentrations were generally higher in the O-horizon than in the A-horizon. Chlorpyrifos, chlorothalonil, and dicofol were detected in most deep layers in soil profiles from three mountains selected to represent distinct climate zones. No clear altitudinal trend in organic carbon-normalized concentrations of CUPs was observed in the O- or A-horizons within individual mountains. A negative correlation was noted between the CUP concentrations and the altitudes across all sampling sites. This indicated that proximity to emission sources was a key factor affecting the spatial distribution of CUPs in mountain forest soil on a national scale. The ecological risk assessment showed that dicofol and cypermethrin pose potential risks to earthworms. This study emphasizes the importance of source control when setting management strategies for CUPs.

Warming-induced shifts in alpine soil microbiome: An ecosystem-scale study with environmental context-dependent insights.

Climate warming is a pressing global issue with substantial impacts on soil health and function. However, the influence of environmental context on the responses of soil microorganisms to warming remains largely elusive, particularly in alpine ecosystems. This study examined the responses of the soil microbiome to in situ experimental warming across three elevations (3850 m, 4100 m, and 4250 m) in the meadow of Gongga Mountain, eastern Tibetan Plateau. Our findings demonstrate that soil microbial diversity is highly resilient to warming, with significant impacts observed only at specific elevations. Furthermore, the influence of warming on the composition of the soil microbial community is also elevation-dependent, underscoring the importance of local environmental context in shaping microbial evolution in alpine soils under climate warming. Notably, we identified soil moisture at 3850 m and carbon-to-nitrogen ratio at 4250 m as indirect predictors regulating the responses of microbial diversity to warming at specific elevations. These findings underscore the paramount importance of considering pre-existing environmental conditions in predicting the response of alpine soil microbiomes to climate warming. Our study provides novel insights into the intricate interactions between climate warming, soil microbiome, and environmental context in alpine ecosystems, illuminating the complex mechanisms governing soil microbial ecology in these fragile and sensitive environments.

Pollution and mobility of heavy metals in the soils of a typical agricultural zone in eastern China.

The pollution of heavy metals (HMs) in agricultural soils profoundly threatens national food safety, and the mobility and environmental behaviors of HMs are closely implicated in crop safety. Here, we assessed the pollution level and mobility of ten HMs and explored their environmental behaviors in the soils of three different land uses from a main crop production zone in eastern China. The concentrations of HMs in the soils were higher in the farmland than the woodland and wasteland, and Cd showed a relatively higher pollution and ecological risk levels compared to other metals. Cadmium was dominated by the reducible (41%) and exchangeable (23%) fractions, and the rest of HMs were mainly in the residual fraction (> 60%). The significant correlation between the exchangeable and DGT-labile Cd indicates relatively higher mobility of Cd in the soils. Soil pH, organic matters and mineral elements had significant correlation with the exchangeable and reducible fractions of most of the HMs (e.g., Cd, Co, Mn, Ni, Pb and V; p < 0.05), indicating their good predictors of the HMs mobility. However, this was not the case for the DGT-labile fraction, which suggests a marked difference in the controlling mechanisms of the mobility versus potential bioavailability of HMs in the soils. The results of this study indicate that both the chemically extracted fractions and the bioavailable fractions of HMs need be considered when effectively assessing the safety of agricultural soils.

New perspectives on microbiome and nutrient sequestration in soil aggregates during long-term grazing exclusion.

Grazing exclusion alters grassland soil aggregation, microbiome composition, and biogeochemical processes. However, the long-term effects of grazing exclusion on the microbial communities and nutrient dynamics within soil aggregates remain unclear. We conducted a 36-year exclusion experiment to investigate how grazing exclusion affects the soil microbial community and the associated soil functions within soil aggregates in a semiarid grassland. Long-term (36 years) grazing exclusion induced a shift in microbial communities, especially in the <2 mm aggregates, from high to low diversity compared to the grazing control. The reduced microbial diversity was accompanied by instability of fungal communities, extended distribution of fungal pathogens to >2 mm aggregates, and reduced carbon (C) sequestration potential thus revealing a negative impact of long-term GE. In contrast, 11-26 years of grazing exclusion greatly increased C sequestration and promoted nutrient cycling in soil aggregates and associated microbial functional genes. Moreover, the environmental characteristics of microhabitats (e.g., soil pH) altered the soil microbiome and strongly contributed to C sequestration. Our findings reveal new evidence from soil microbiology for optimizing grazing exclusion duration to maintain multiple belowground ecosystem functions, providing promising suggestions for climate-smart and resource-efficient grasslands.

Spatial redistribution and enantiomeric signatures of hexachlorocyclohexanes in Chinese forest soils: Implications to environmental behavior and influencing factors.

Hexachlorocyclohexanes (HCHs) are a group of highly persistent pesticides. The concentrations of HCHs and the enantiomeric fractions of α-HCH in the O- and A-horizons from 30 mountains across China were analyzed in this study. The concentrations of total HCHs ranged from 0.061 to 46.9 ng/g (mean 2.12 ng/g) and 0.046 to 16.1 ng/g (mean 0.792 ng/g) in the O- and A-horizons, respectively. The HCH residues were mainly derived from the historical applications of technical HCH and lindane. Higher concentrations of HCHs were typically found in northern China, and no significant correlations were found between historical technical HCH usage and HCH isomer concentrations in either the O- or A-horizons (p > 0.05). Conversely, the concentrations of HCH isomers were significantly correlated with the environmental parameters (temperature and precipitation), thus indicating a typical secondary distribution pattern. Some HCH isomers tended to be transported northward under the long-term effect of monsoon. Chiral α-HCH was non-racemic in soils and showed preferential degradation of (-) α-HCH in both the O- and A-horizons. The transformation from γ-HCH to α-HCH might alter the enantiomeric signatures of α-HCH in soils. Moreover, the deviation from racemic of α-HCH was positively correlated with the C/N ratio in the A-horizon (p < 0.01), thus suggesting that the C/N ratio could alter the microbial activity and significantly affect the enantioselective degradation extent of α-HCH in soils.

Soil covering measure mitigates vanadium loss during short-term simulated rainfall in the vanadium titano-magnetite tailings reservoir.

Soil covering is an operative measure to decline pollutant release in tailings reservoirs and promote vegetation restoration, yet urgent research still needs to probe into pollutant leaching and migration in the artifact technology under extreme precipitation. Here, a soil column leaching experiment was designed to explore the migration and behaviors of vanadium (V) in the system of vanadium titano-magnetite tailings (VTMTs) covered by soils with different depths (5 cm, 10 cm, and 15 cm). Chemical fractions of V in the VTMTs and covered soils were analyzed to decipher the mechanisms underlying the V migration. We found a limited V leaching (0.26-0.52 µg/L, <0.01% of total V) in the columns during the experiments, and V in the VTMTs was not apt to be leached or migrate upward to the overlying soils. The soil volumes overlaid had nonsignificant effect on the V behaviors in the VTMTs (P > 0.05), because of the dominant and stable residual V (96.4% of total V) in the tailings. Although acid soluble V might be transformed to oxidizable V, it was resupplied by the fractions of weak-bound V in the solid phases during the leaching experiments. The mineral metal (hydr)oxides (e.g., aluminum, iron) determined the V behaviors in the VTMTs via absorption effect, and the high affinity of V to organic matters probably prevented its migration throughout the overlying soils. The results indicate that soil covering measure in the VTMTs reservoirs effectively reduces V migration or release from the tailings through leaching or upward migration, which provides a significant guidance for vegetation restoration in V-rich tailings reservoirs.

Novel ecological ditch system for nutrient removal from farmland drainage in plain area: Performance and mechanism.

The loading of nitrogen (N) and phosphorus (P) from agricultural drainage as the non-point sources is a worldwide environmental issue for aquatic ecosystem. However, how to remove these nutrients effectively from agricultural drainage remains a big challenge with increasing cemented ditches for better management. Here, we designed a novel ecological ditch system which integrated an earth ditch and a cemented ditch with iron-loaded biochar in the Chengdu Plain to reduce the loss of N and P from farmland. After a two-year monitoring, the removal efficiency of total N and total P reached 24.9% and 36.1% by the earth ditch and 30.7% and 57.8% by the integrated ditch system, respectively. The water quality was evidently improved after passing through the ditch system with the marked decrease in the concentrations of N and P. Dissolved organic N, nitrate, and particulate P became the dominant fractions of N and P loss. Rainfall soon after fertilization increased the concentrations of N and P in the ditch system and markedly affected their removal efficiency. The iron-loaded biochar effectively removed N and P from the drainage, especially at the high concentrations, which was mainly attributed to its high adsorption of the dissolved N and P fractions and the interception of the particulate nutrients. Our results indicate that the designed ecological ditch system has a high potential for alleviating agricultural non-point source pollution in the plain area and can be extended to other lowland agricultural ecosystems.

Dam construction attenuates trace metal contamination in water through increased sedimentation in the Three Gorges Reservoir.

Dam construction has a far-reaching impact on trace metal accumulation and the metal-induced quality of the aquatic environment. However, the long-term impacts of dam construction and impoundments on the spatial distribution of trace metals and water quality remain poorly understood. Here, we found that the concentrations of trace metals in the mainstream water of the world's largest reservoir, Three Gorges Reservoir (TGR), decreased after impoundment, while their concentrations and contamination in the sediments of the water-level fluctuation zone increased significantly, especially for anthropogenic sources of metals such as cadmium, lead, and zinc. The spatial and temporal variations of anthropogenic metals in the sediments revealed increased anthropogenic dominance in their distribution under current hydrological management, especially for the urban area of the upper TGR. Sediment fluxes, particle composition, and extreme climate modulated the distribution of trace metals in the sediments. The results demonstrate that human activities have increasingly determined the distribution and contamination state of trace metals in the mainstream TGR. However, in contrast to our previously thought, the anthropogenic discharge of trace metals did not adversely affect water quality. Our results indicate that dam construction in riverine systems attenuates trace metal contamination in water through sediment sorting and deposition.

Predicting soil cadmium uptake by plants in a tailings reservoir during 48-year vegetation restoration.

Plant uptake can reduce soil cadmium (Cd) pollution, while how to exactly predict plant Cd uptake in industrial or mining areas during vegetation restoration remains unexplored. Taking Heteropogon contortus as the object plant, we predicted plant Cd uptake in the Majiatian tailings reservoir during 48-year vegetation restoration by the methods of soil total Cd, DGT (diffusive gradients in thin films technique) and acetic acid (HAc) extraction. Meanwhile, we explored the effects of soil properties on the accuracy of the prediction. Total Cd concentrations in the soils exhibited a better prediction of plant Cd uptake relative to the methods of HAc extraction and DGT. However, the DGT method effectively predicted plant Cd uptake at low Cd supply (lower than 0.42 µg/L), probably because of the dominant diffusion limitation by plants. The prediction of plant Cd uptake by HAc extraction was improved when combined with soil pH. Our results indicate that with increasing external Cd inputs during the vegetation restoration, soil total Cd and traditional extraction method in combination with soil properties are effective ways to predict plant Cd uptake, especially when the Cd fractions cannot be measured by DGT. However, the DGT method works once plant Cd uptake dominated by diffusion limitation despite the interference in soil properties.

A novel framework to predict water turbidity using Bayesian modeling.

High water turbidity in aquatic ecosystems is a global challenge due to its harmful impacts. A cost-effective manner to rapidly and accurately measure water turbidity is thus of particular useful in water management with limited resources. This study developed a novel framework aiming to predict water turbidity in various aquatic ecosystems. The framework predicted water turbidity and quantified the uncertainty of the prediction through Bayesian modeling. To improve model performance, a model-update method was implemented in the framework to update the model structure and parameters once more measured data were available. 120 paired records (an image from smartphone and a measured water turbidity value by standard turbidimeters for each record) were collected from rivers, lakes and ponds across China to evaluate the performance of the developed framework. Our cross-validation results revealed a well prediction of water turbidity with Nash-Sutcliffe efficiency (NS) >0.87 (p<0.001) during the training period and NS>0.73 (p<0.001) during the validation period. The model-update method (in case of more measured data) for the developed Bayesian models in the framework resulted in a decreasing trend of model uncertainty and a stable mode fit. This study demonstrated a high value of the Bayesian-based framework in predicting water turbidity in a robust and easy manner.

Contamination, sources and health risk of heavy metals in soil and dust from different functional areas in an industrial city of Panzhihua City, Southwest China.

The contamination of heavy metals in urban soil and dust is closely related to anthropogenic emissions, while to what extent the metal contamination varies among different functional areas in industrial cities remains unclear. In this study, the contamination and health risk of seven heavy metals in the soil and dust were assessed at different functional areas of Panzhihua City, Southwest China, and their sources were identified by the spatial divisions and Pb isotopes. The results showed that the contamination of V and Cr in the vanadium/steel plant (VsA) and the contamination of Cd, Pb and Zn in the iron-ore smelting (IsA) were significantly higher relative to other functional areas. The sources of the contaminated heavy metals in the soil and dust were mainly from smelting and manufacturing vanadium/steel products, coal combustion and traffic. Vanadium and Cr were the major metals primarily contributing to the noncarcinogenic and carcinogenic risks, despite the low contamination level of Cr. The results indicate that the VsA is the priority control area in the Panzhihua City, and besides V, more attention should be paid in the future to monitor Cr risk in the soil and dust because of its high contribution to the health risk.

Vanadium accumulation mode of Heteropogon contortus and its driving factors in Majiatian tailing reservoir in Panzhihua, Southwestern China.

Native plants in metal pollution sites have great potentials for mine rehabilitation. In the presented work, we investigated Vanadium (V) concentrations of soils and plants (Heteropogon contortus) in Majiatian V-Ti magnetite tailing reservoir in Panzhihua, Southwestern China. The objectives were to explore the V accumulation mode of H. contortus and its driving factors, as well as the phytoremediation potential of H. contortus. As the results, H. contortus accumulated 37.53 mg/kg and 8.69 mg/kg of V in root and aerial part, respectively. With the increase of rehabilitation age, root V concentrations decreased, while aerial part V concentrations remained constant. The significant negative correlations between root V and soil V, acid-soluble V (VHAc) (P < 0.05) indicated that increasing soil V and VHAc concentrations drove the V accumulation mode of H. contortus. Soil properties had a little influence on the V accumulation mode of H. contortus. Therefore, H. contortus might be not the suitable plant extractant to remove V from mine tailing for its lower V accumulation capacity. On the other hand, it can tolerate high V stress through elimination and detoxification/isolation V. Furthermore, the settlement of H. contortus increased the content of soil organic matter and might thus improve the soil quality. The cover of H. contortus is also beneficial to reduce the dispersion of the tailings and prevent contaminating surrounding soil. Therefor it showed a great potential to serve as a pioneer plant in the remediation of V-rich tailing reservoirs and other V-contaminated sites with similar poor soil condition.

Characterizing the river water quality in China: Recent progress and on-going challenges.

Food production systems, urbanization, and other anthropogenic activities dramatically alter natural hydrological and nutrient cycles, and are primarily responsible for water quality impairments in China's rivers. This study compiled a 16-year (2003-2018) dataset of river water quality (161,337 records from 2424 sites), watershed/landscape features, and meteorological conditions to investigate the spatial water quality patterns and underlying drivers of river impairment (defined as water quality worse than Class V according to China's Environmental Quality Standards for Surface Waters, GB3838-2002) at a national scale. Our analysis provided evidence of a distinct water quality improvement with a gradual decrease in the frequency of prevalence of anoxic conditions, an alleviation of the severity of heavy metal pollution, whereas the cultural eutrophication has only been moderately mitigated between 2003 and 2018. We also identified significant spatial variation with relatively poorer water quality in eastern China, where 17.2% of the sampling sites registered poor water quality conditions, compared with only 4.6% in western China. Total phosphorus (TP) and ammonia-nitrogen (NH3-N) are collectively responsible for >85% of the identified incidences of impaired conditions. Bayesian modelling was used to delineate the most significant covariates of TP/NH3-N riverine levels in six large river basins (Liao, Hai, Yellow, Yangtze, Huai, and Pearl). Water quality impairments are predominantly shaped by anthropogenic drivers (82.5% for TP, 79.5% for NH3-N), whereas natural factors appear to play a secondary role (20.5% for TP, 17.5% for NH3-N). Two indicator variables of urbanization (urban areal extent and nighttime light intensity) and farmland areal extent were the strongest predictors of riverine TP/NH3-N levels and collectively accounted for most of the ambient nutrient variability. We concluded that there is still a long way to go in order to eradicate eutrophication and realize acceptable ecological conditions. The design of the remedial measures must be tailored to the site-specific landscape characteristics, meteorological conditions, and should also consider the increasing importance of non-point source pollution and internal nutrient loading.

Terrain-modulated deposition of atmospheric lead in the soils of alpine forest, central China.

Alpine ecosystem has a potential to intercept the transport of atmospheric metals, while the regulation mechanisms with variations in altitude and slope direction remain unclear. In this study, the soil and moss samples on the northern and southern slopes of Shennongjia Mountain were collected with altitude to quantitatively identify the sources of lead (Pb) and to decipher the regulation mechanisms of altitude and slope on the Pb distribution. The results showed that the concentrations of Pb decreased evidently with soil depth, and in the O (organic soils) and A (surface mineral soils) horizons they increased with altitude. The Pb isotopes and moss biomonitoring revealed that Pb was mainly from atmospheric deposition, and the sources included fossil fuel combustion, ore mining and smelting. Based on a binary mixing model of Pb isotopes, the percentage of atmospheric Pb in the O and A horizons and mosses averaged 58.8%, 43.7% and 71.0%, respectively. Atmospheric wet deposition strikingly controlled the distribution of soil Pb along the altitude. Canopy filtering and leaching also impacted the accumulation of Pb in the forest floor. The significant difference in the atmospheric Pb accumulation in the soils between the two slopes was not observed as expected, since atmospheric dry deposition from northwestern China contributed to the Pb accumulation on the northern slope according to the Pb isotopic ratios and air mass trajectories. The results of this study indicate that altitude determines the distribution pattern of atmospheric Pb, while slope direction screens the source region of Pb in alpine ecosystems.