Search

Abstract Nitrous oxide (N 2 O) is a major greenhouse gas, with elevated emission being reported from subtropical forests that receive high nitrogen (N) deposition. After 10 years of monthly addition of ammonium nitrate (NH 4 NO 3) or sodium nitrate (NaNO 3) to a Mason pine forest at Tieshanping, near Chongqing city in Southwest China, the simulated N deposition was stopped in October 2014. The results of soil N 2 O emissions monitoring in different seasons during the nitrogen application period showed that nitrogen addition significantly increased soil N 2 O emission. In general, the N 2 O emission fluxes were positively correlated to nitrate (NO 3 −) concentrations in soil solution, supporting the important role of denitrification in N 2 O production, which was also modified by environmental factors such as soil temperature and moisture. After stopping the application of nitrogen, the soil N 2 O emissions from the treatment plots were no longer significantly higher than those from the reference plots, implying that a decrease in nitrogen deposition in the future would cause a decrease in N 2 O emission. Although the major forms of N deposition, NH 4 + and NO 3 −, had not shown significantly different effects on soil N 2 O emission, the reduction in NH 4 + deposition may decrease the NO 3 − concentrations in soil solution faster than the reduction in NO 3 − deposition, and thus be more effective in reducing N 2 O emission from N-saturated forest soil in the future. Graphical abstract Image 1 Highlights • Effects of increasing/decreasing N deposition on soil N 2 O emission were studied. • N deposition increases soil N 2 O emission from an N-saturated subtropical forest. • Soil N 2 O emissions were positively correlated to NO 3 − concentrations in soil water. Soil nitrate availability, other than soil temperature and moisture, is key factor determining soil N 2 O emission from an N-saturated subtropical forests. [ABSTRACT FROM AUTHOR]

Poor water and nutrient retention are the major soil fertility limitations in the low productivity agricultural soils of Nepal. The addition of biochar to these soils is one way these hindrances can be overcome. In the present study, six different biochar doses (control, 5 t ha −1 , 10 t ha −1 , 15 t ha −1 , 25 t ha −1 and 40 t ha −1 ) were applied to a moderately acidic silty loam soil from Rasuwa, Nepal and the effects on soil physicochemical properties and maize and mustard yield over three years (i.e., six cropping seasons), were investigated. Biochar addition did not show significant effects on maize and mustard grain yield in the first year, however significant positive effects (p   <   0.01) were observed during the second and third years. During the second year, maize grain yield significantly increased by 50%, 47% and 93% and mustard grain yield by 96%, 128% and 134% at 15 t ha −1 , 25 t ha −1 and 40 t ha −1 of biochar respectively. A similar significant increase in yield of both crops was observed in the third year. Yields for both maize and mustard correlated significantly (p   <   0.001 ) with plant available P, K + , pH, total OC%, CEC, base saturation, and increased as a function of biochar addition. On the basis of the measured crop yields for the various biochar doses, a cost-benefit analysis was carried out, and gross margin was calculated to optimize biochar dose for local farming practice. Total costs included financial cost (farm input, labor and biochar production cost), health cost and methane emission cost during biochar production. Health costs were a minor factor (<2% of total biochar preparation cost), whereas methane emission costs were significant (up to 30% of biochar cost, depending on the C price). Total income comprised sale of crops and carbon sequestration credits. The cost-benefit analysis showed that the optimal biochar application dose was 15 t ha −1 for all C price scenarios, increasing gross margin by 21% and 53%, respectively, for 0 and 42 US$ per ton CO 2 price scenarios. In the current situation, only the 0 US$ price scenario is realistic for rural farmers in Nepal, but this still gives benefits of biochar amendment, which are capped at a 15 t ha −1 biochar addition. [ABSTRACT FROM AUTHOR]

The influence of nitrogen (N) deposition on forest ecosystems largely depend on the N status. Developing threshold and practical indicators for N saturation in subtropical forests, with extremely high N deposition, would both enhance forest management and the assessments of global N balance and carbon (C) sequestration. Here, we quantified the N mass balance and assessed current N status at a number of subtropical forest sites in South China, using both N content, C/N ratio, and 15 N natural abundance (δ 15 N) as potential indicators of N saturation. Among the studied sites, N deposition ranged from 13.8 to 113 kg N ha −1 yr −1 in throughfall, and was dominated by ammonium (NH 4 + ). The threshold for N leaching in subtropical forest was first found to be 26–36 kg N ha −1 yr −1 , which was 160% higher than in temperate forest (based on prescribed minimum). This indicates that critical parameter inputs in global models of the impact of N deposition are in need of revision, based on specific ecosystem characteristics. We found a critical C/N ratio of 20 for the O/A horizon as indicator of N saturation. Foliar N content and δ 15 N were positively correlated with N deposition and were well suited to indicate regional N status. The δ 15 N enrichment factor ( Ɛ foli/So2 , δ 15 N foliage - δ 15 N Soil2 ) was between −10‰ and −1‰, and had similar trend to those obtained from other regions with increasing N deposition. These suggest that the enrichment factor could be used to investigate the influence of N deposition in forest ecosystems, regardless of spatial heterogeneity in δ 15 N of N input, soil N availability and geomorphology. [ABSTRACT FROM AUTHOR]

Soil erosion by water is one of the main causes of land degradation and reduced agricultural productivity in Africa leading to an estimated annual loss in crop yield of 280 million tons. To reverse this problem, various indigenous and recently introduced cross slope barrier soil and water conservation (CSB-SWC) techniques have been implemented. These include Fanya juu 1 1 A Kiswahili word referring to ‘throw uphill’, corresponding to the CSB-SWC structure built by throwing soil upslope from a ditch , soil bunds, stone bunds, bench terraces, vegetative barriers, and tied-ridges. In this review, we analyze and synthesize the results of various studies that focused on the effects of CSB-SWC techniques on runoff, soil loss, soil properties, crop yield, and biomass in Sub-Saharan Africa (SSA). Introduction of various CSB-SWC techniques was found to reduce runoff and soil loss by 13–71% and 39–83%, respectively. More than 80% of the reviewed scientific studies showed a positive effect on crop yield mainly due to retention of nutrients and moisture. The effect of CSB-SWC techniques on crop yield varies with rainfall and slope, with most of the CSB-SWC techniques improving crop yields in low rainfall areas. Fanya juu and soil bunds were effective on relatively gentle slopes while hedgerows and stone bunds were effective even on moderately steep slopes. However, studies across SSA indicate that some CSB-SWC techniques could have negative side effects such as waterlogging. Also, these techniques are associated with the occupation of significant areas of cultivable land. Thus, they require proper design and implementation. In most cases, CSB-SWC techniques are economically feasible, due to improved crop yield and low labor opportunity costs. However, implementation may be hampered by high construction costs, small landholding size, land tenure insecurity, and low short-term benefits. Effectiveness and benefits of CSB-SWC can be improved by their integration with other land management techniques such as soil fertility amendments and conservation tillage. [ABSTRACT FROM AUTHOR]

We studied the role of biochar in improving soil fertility for maize production. The effects of biochar on the alleviation of three potential physical-chemical soil limitations for maize growth were investigated, i.e. water stress, nutrient stress and acid stress. Experiments involved soils with two dosages of biochar (0.5% and 2% w:w), as well as ones without biochar, in combination with four different dosages of NPK fertilizer, water and lime. Biochar was produced from the invasive shrubby weed Eupatorium adenophorum using flame curtain kilns. This is the first study to alleviate one by one the water stress, nutrient stress and acid stress in order to investigate the mechanisms of biochar effects on soil fertility. Biochar addition increased soil moisture, potassium (K) and plant available phosphorous (P-AL), which all showed significant positive relationship ( p < 0.001) with above ground biomass of maize. However, biochar was much more effective at abundant soil watering (+ 311% biomass) than at water-starved conditions (+ 67% biomass), indicating that biochar did increase soil moisture, but that this was not the main reason for the positive biomass growth effects. Biochar addition did have a stronger effect under nutrient-stressed conditions (+ 363%) than under abundant nutrient application (+ 132%). Biochar amendment increased soil pH, but liming and pH had no effect on maize dry biomass, so acidity stress alleviation was not the mechanism of biochar effects on soil fertility. In conclusion, the alleviation of nutrient stress was the probably the main factor contributing to the increased maize biomass production upon biochar addition to this moderately acidic Inceptisol. [ABSTRACT FROM AUTHOR]

Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil organic matter (SOM) in forest soil is of major importance for cation binding and acid buffering, but its characteristics may differ among soils under different tree species. We investigated acidity, cation exchange properties and Al bonding to SOM in stands of Scots pine, pedunculate oak, Norway spruce, European beech and common hornbeam in southern Poland. The content of total carbon (C t ) was by far the major contributor to total cation exchange capacity (CEC t ) even in loamy soils and a strong relationship between C t and CEC t was found. The slope of the regression of CEC t to C t increased in the order hornbeam ≈ oak < beech < spruce ≈ pine, suggesting that the number of negatively charged sites of SOM at any value in the acid pH range was smallest for hornbeam and oak, and largest for spruce and pine soils. This was supported by the apparent dissociation constant (pK app ) values of SOM, which were largest in soils under oak. The maximum values of Al saturation were similar between the stands. However, maximum Al bonding to SOM occurred at higher pH values in soils under pine and spruce than under oak. Therefore, at any value in the acid pH range, the SOM in pine soil has less Al complexed and more adsorbed H + than SOM from oak soils. Such differences in Al and H bonding are not only important for pH buffering and metal solubility controls, but also for stabilization of SOM via saturation of functional groups by Al and H. [ABSTRACT FROM AUTHOR]

Highlights: [•] We show that different uncertainties, which can be of a fundamentally different nature, are directly related in cascades of interrelated uncertainties. [•] This interrelatedness opens new possibilities for coping with uncertainty. [•] Cascades of uncertainties can be a key tool to connect actors from different disciplines. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses and compares results of management interventions to remobilise dunes and obtain more autonomous changes in foredunes resulting from a change in coastal defence policy. In recent decades, nature conservation managers tried to restore aeolian dynamics and dune mobility landward of foredunes to maintain threatened, rare pioneer species. Results indicate that destabilisation activities yielded an important increase of blowing sand and its effects on ecology but with a limited effect on the desired integral remobilization of dunes. Roots remaining in the sand after removal of vegetation and soil is one of the main problems. Follow up removal of roots for 3 to 5years seems to be essential, but it is not clear whether the dunes will remain mobile in the long term. In 1990 the Dutch government decided to maintain the position of the coastline by artificial sand nourishment. An intensive management of the foredunes was no longer required. Consequently, natural processes in the foredunes revived, and the sediment budget of the beach–dune system changed. Two main types of responses are visible. In some areas, increased input of sand resulted in the development of embryonic dunes seaward of the former foredunes, leading to increased stabilisation of the former foredunes. In other areas, development of embryonic dunes was insignificant despite the increased sand input, but wind erosion features developed in the foredunes, and the environment was more dynamic. The reasons for the differences are not clear, and the interaction between shoreface, beach and dunes is still poorly understood. Until now, attempts to mobilise the inner dunes were independent of changes made to the foredunes. We argue that an integrated, dynamic approach to coastal management, taking account of all relevant functions (including safety and natural values) and the dune–beach system as a whole, may provide new and durable solutions. An integrated approach would ideally provide fresh sand to the system by sand nourishment; define a wide safety zone, which enables the transition zone of beach to foredunes to develop freely; reserve space for natural processes without restrictions; and stimulate natural redistribution of sand within the system and restore inland transport of sand by removing vegetation behind the foredunes. A long time scale (several decades) is needed for this approach to be successful. [Copyright &y& Elsevier]

Abstract: Subtropical forests in SW China, receiving high nitrogen (N) deposition, have been reported to show high N retention. N removal by denitrification may be one important process favored by warm and wet soils during monsoonal summer when most of the atmogenic N input occurs. Due to low pH soils which are common in this region, N removal by denitrification may entail substantial N2O emissions. In this study, we explored intrinsic denitrification characteristics of soils from different landscape elements of a forested headwater catchment in SW China (Tieshanping, Chongqing). Laboratory incubations were used to measure instantaneous denitrification rates, apparent specific denitrifier growth rates, denitrification product stoichiometries (N2O/(N2O + N2)) and response to carbon-addition as a function of soil depth and landscape position. The results revealed that potential denitrification and denitrifier growth rates were highest in top soils along a hill slope, and decreased strongly with soil depth due to C-limitation. A hydrologically connected, colluvial groundwater discharge zone showed equally high instantaneous denitrification rates which were more equally distributed with depth. Denitrifying communities in the top horizons of the hill slope were less efficient in expressing N2O reductase in response to anoxia resulting in higher N2O/(N2 + N2O) product ratios than found in soils of the groundwater discharge zone, suggesting that a significant share of the deposited N can be lost as N2O from the hill slopes. Differences in denitrification traits appeared to be linked to eco-hydrological conditions in the two landscape elements and to substrate availability along the hydrological flowpath. Our study supports the notion that denitrification plays an important role for observed N removal in SW Chinese forest ecosystems and illustrates how habitat functions constrain the amount of N2O emitted during N removal. [Copyright &y& Elsevier]

Abstract: The Netherlands is a low-lying country, in which 9 million people are living below sea level and 70% of the gross domestic product is being earned in areas below sea level. Therefore, protection against flooding is traditionally the primary focus of coastal policy in the Netherlands. Analysis shows that characteristics of Dutch coastal management very well comply with the recommendations and key concepts to support sustainable coastal management as issued by the EU in 2004 (EUROSION). Sediment management represents the core of erosion management in the Netherlands; key concepts like resilience, coastal sediment cells, favorable sediment status and strategic sediment reservoirs, are important building stones. Development and implementation of coastal erosion management in the Netherlands, has implicitly been guided by a systematic Frame-of-Reference. Characteristics of this approach are the definition of clear objectives at different levels (i.e. strategic, tactical and operational) and an operational decision recipe related to policy development and implementation. Application of the Frame-of-Reference to current problems and challenges in Dutch coastal management indicates its ability to reveal shortcomings of the existing approach, and to explore potential solutions. Where EUROSION offers important concepts to define coastal erosion management, the Frame-of-Reference offers a tool to discern different objectives and responsibilities. The combination of both strongly supports implementation of coastal erosion management. [Copyright &y& Elsevier]

Abstract: The main objective of the Conscience project was to develop and test concepts, guidelines and tools for the sustainable management of erosion along the European coastline, based on the best available scientific knowledge and on existing practical experience. Four concepts are potentially capable of providing the nexus between scientific knowledge and management: coastal resilience, coastal sediment cell, favourable sediment status and strategic sediment reservoir. The project has tested the use of these concepts and found that they are useful, provided that they are positioned and linked within a logical structure that we shall call the Conscience “Frame of Reference”, defined in time and space and supported through data and monitoring. Practical experience in six coastal sites in Europe has shown that the use of this Frame of Reference together with these concepts can make management objectives explicit and transparent. It can therefore support the design of an appropriate, resilience based coastal erosion management practice. [Copyright &y& Elsevier]

Here, we present one of the first studies investigating the mobility, solubility and the speciation-dependent in-situ bioaccumulation of antimony (Sb) in an active Sb mining area (Xikuangshan, China). Total Sb concentrations in soils are high (527–11,798 mg kg−1), and all soils, including those taken from a paddy field and a vegetable garden, show a high bioavailable Sb fraction (6.3–748 mg kg−1), dominated by Sb(V). Elevated concentrations in native plant species (109–4029 mg kg−1) underpin this. Both chemical equilibrium studies and XANES data suggest the presence of Ca[Sb(OH)6]2, controlling Sb solubility. A very close relationship was found between the citric acid extractable Sb in plants and water or sulfate extractable Sb in soil, indicating that citric acid extractable Sb content in plants may be a better predictor for bioavailable Sb in soil than total acid digestible Sb plant content. [Copyright &y& Elsevier]

Objectives: The aim was to describe causative agents and clinical characteristics in adult outpatients with upper airway symptoms during the 2009 H1N1 pandemic and to evaluate case definitions that are used in clinical practice.Methods: From August through December 2009, 964 symptomatic adult outpatients were included. RT-PCR was used to detect the following pathogens: influenza A (H1N1) and B, parainfluenza 1-4, adenovirus, respiratory syncytial virus, human rhinovirus, human metapneumovirus, human coronavirus (OC43, 229E, NL63), Chlamydia pneumoniae, Mycoplasma pneumoniae and Legionella species. The Dutch GHOR, American CDC and WHO, and British HPA case definitions were evaluated.Results: A respiratory pathogen was detected in 41% of tested patient samples; influenza A (H1N1) and human rhinovirus were both detected in 16%. Clinical presentation of influenza cases was significantly more serious when compared to rhinovirus or negative-tested cases. Test characteristics were almost similar for all 4 case definitions, with an average sensitivity of 66%, specificity of 70%, positive predictive value of 34% and negative predictive value of 90%.Conclusions: Influenza A (H1N1) and human rhinovirus were the major pathogens responsible for respiratory disease. The 2009 H1N1 pandemic in Amsterdam followed a mild course. Test characteristics of 4 different clinical case definitions seemed comparable but rather useless. [ABSTRACT FROM AUTHOR]

Copyright of Basic & Applied Ecology is the property of Urban & Fischer Verlag and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Coastal flood risk is defined as a product of probability of event and its effect, measured in terms of damage. The paper is focused on coastal management strategies aimed to decrease risk by decreasing potential damage. We review socio-economic literature to show that total flood damage depends on individual location choices in the housing market and on individual flood risk awareness. Low flood risk awareness leads to inefficient spatial developments and increased flood risk. We show that personal experience, risk communication, financial instruments like insurance from flooding and technical instruments like building on high elevations, are factors that increase individual risk awareness. Evidence that these factors indeed affect housing prices and land use patterns is provided. We discuss proactive instruments that can be used in coastal zone management in the Netherlands to increase individual risk awareness. We argue that policy-makers may create incentives giving individuals a possibility to make location choices that lead to less total flood risk in the coastal zone area. [ABSTRACT FROM AUTHOR]

Background & Aims: We investigated the long-term efficacy and renal safety of tenofovir disoproxil fumarate (TDF), administered to patients co-infected with human immunodeficiency virus and hepatitis B virus (HBV) as part of an antiretroviral therapy. Methods: We performed a multicenter, prospective cohort study of 102 patients co-infected with human immunodeficiency virus and HBV who were treated with TDF. Results: At baseline, 80% of patients had a detectable viral load (HBV DNA >20 IU/mL). Among patients positive for hepatitis B e antigen (HBeAg) (n = 67), 92% had a virologic response (HBV DNA <20 IU/mL) after 5 years of treatment. There was no difference between patients with or without lamivudine resistance at baseline (P = .39). Loss rates of HBeAg and hepatitis B s antigen (HBsAg) were 46% and 12%, respectively. Among HBeAg-negative patients (n = 15), 100% had a virologic response after 4 years of treatment and 2 (13%) lost HBsAg. Twenty subjects (20%, all HBeAg-negative) had undetectable HBV DNA at baseline; during a median follow-up period of 52 months (interquartile range, 41–63 mo), 19 (95%) maintained a virologic response and 2 (10%) lost HBsAg. Overall, one patient acquired a combination of resistance mutations for anti-HBV drugs and experienced a virologic breakthrough. Three (3%) patients discontinued TDF because of increased serum creatinine levels. The estimated decrease in renal function after 5 years of TDF therapy was 9.8 mL/min/1.73 m2, which was most pronounced shortly after TDF therapy was initiated. Conclusions: TDF, administered as part of antiretroviral therapy, is a potent anti-HBV agent with a good resistance profile throughout 5 years of therapy. Only small nonprogressive decreases in renal function were observed. [ABSTRACT FROM AUTHOR]

Abstract: Dissolved aluminium (Al) in soils, mobilized by acid deposition, is considered a threat to forest health through hampering root growth and nutrient uptake. Since the end of the 1980s dissolved Al in forest soil water plays a key role in the assessment of critical loads of acid deposition. So far, most evidence for toxicity of dissolved Al in forest soil water is based on nutrient solution studies and pot experiments. Here, we present results from one of the few in situ ecosystem-scale forest manipulation experiments to study the effect of Al on mature forest trees. A plotwise addition of dilute AlCl3 was conducted during seven years in an even-aged spruce forest (Picea abies) in an area in Norway with low acid deposition. Soil solution concentrations of Al were increased to potentially toxic levels (up to 500μmolL−1) and base cation (Ca+Mg+K) to inorganic Al ratios in the soil solution in the root zone were mostly below 1 in the Al-addition treatments. In the control treatment (only water addition) Al concentrations did not exceed 15μmolL−1 and base cation to inorganic Al ratios were above 1. The toxic effects of Al on fine root growth and plant growth found in hydroponic studies and pot trials are not confirmed by this field manipulation. However, magnesium (Mg) contents in needles decreased significantly and persistently in plots with elevated Al concentrations, whereas the needle Ca content did not respond. The depletion of the Mg content in needles is suggested to be due to antagonistic effects of high Al concentrations at the root surface, consistent with observed reductions in Mg to Al ratio of inner bark. This study clearly supports a role for Al in critical load functions for forests as dissolved Al causes a decrease in uptake of Mg. However, other signs of reduced forest vitality were not observed. Soil base cation status may need to be included in risk evaluations of forest health under acid deposition. [Copyright &y& Elsevier]

Purpose: To investigate the reproducibility of 3 different tracing methods to determine a reliable method to define the proper anatomical position of the mandibular canal based on cone beam computed tomography (CBCT) data. Materials and Methods: Five dentate and 5 edentate patients were selected at random from the CBCT database. Two independent observers traced both the left and the right mandibular canal using 3-dimensional image-based planning software (Procera System NobelGuide; Nobel Biocare, Göteborg, Sweden). All mandibular canals were traced using 3 different methods. Method I was based on coronal views, also known as cross-sections. Panorama-like reconstructions were the starting point for method II. The third method combined methods I and II. Results: With respect to interobserver reliability, no significant difference (P = .34) for the various methods was observed. The reproducibility was better in edentate than in dentate jaws (P = .0015). The difference between 2 tracings was the lowest for the combined method: within a range of 1.3 mm in 95% of the course of the canal. The most obvious deviations were mainly seen in the anterior part of the canal. Conclusions: The best reproducible method for mandibular canal tracing is the combined method III. Between observers, still a mean 95th percentile deviation threshold of 1.3 mm (SD 0.384) is noted, indicating that a safety zone of 1.7 mm should be respected. When planning surgery on CBCT-based data, surgeons should be aware of the obvious deviations located in the region of the anterior loop of the canal. [Copyright &y& Elsevier]

Abstract: The Dutch government wants to expand Mainport Rotterdam, one of the largest ports in the world, by land reclamation in the North Sea. This may affect the Wadden Sea, a unique wetlands area protected by the European Bird and Habitat Directives. To assess the impact of the port extension on the Wadden Sea, an Appropriate Assessment procedure was carried out. We investigated how stakeholders’ perceptions were dealt with and how knowledge was used in this decision-making process. Our findings form an argument for practitioners in marine and coastal management to choose a process-oriented approach to deal with complex issues. [Copyright &y& Elsevier]

Abstract: Objectives: This study aimed to test the following hypotheses: (1) a carry-over effect of EC40 does not occur in a split-mouth model, (2) two consecutive applications of EC40 varnish with an interval of 3 months per year has a better inhibiting effect on mutans streptococci in pit and fissure plaque of permanent first molars of 6–7-year olds than a repeated application at each 6 months and (3) EC40 exerts an inhibiting effect on mutans streptococci for at least a 6-month duration. Methods: Using a split-mouth design, test molars received EC40 on fissures and pits and control molars remained without treatment. One group of test molars received EC40 at baseline, 6, 12 and 18 months and another group at baseline, 3, 12 and 15 months. Plaque samples were taken from pits and fissures of test and control molars at baseline, 6, 9, 12 and 24 months. A mixed ANOVA model was used to analyze the data. Results: The first hypothesis was accepted, the second rejected and the third accepted. Conclusions: Twice a year EC40 application on pits and fissures of permanent first molars of 6–7-year-old children can significantly reduce mutans streptococci numbers for a 6-month period, but the reductions were small. [Copyright &y& Elsevier]

Elevated concentrations of reactive nitrogen (N) in precipitation have been reported for many cities in China. Due to increased use of fossil fuels and expansion in agriculture, further increases in deposition of ammonia (NH x ) and reactive N oxides (NO y ) are predicted. Increased deposition of reactive N is likely to affect N dynamics and N runoff in forest ecosystems. Yet, in China little work has been done to quantify the levels of atmospheric N deposition in such systems. Here, we assess the deposition of inorganic N (ammonium, NH4 + and nitrate, NO3 −) for five subtropical forest ecosystems in remote and urban areas of South China. Annual volume-weighted concentrations in bulk precipitation range from 0. 18 to 1. 55 mg NH4 +–N L−1 and from 0. 12 to 0. 74 mg NO3 −–N L−1. These values are large and several times greater than those reported for remote sites of the world. The fluxes of total inorganic N (TIN) in wet-only deposition range from 0. 8 to 2. 3 g N m−2 yr−1, with NH4 +–N contributing 54% to 77%. Both the tree canopy and the ground vegetation layer are important in determining the net N flux reaching the forest floor, but the net effect varies from site to site. At TieShanPing (TSP), close to Chongqing city, and at CaiJiaTang (CJT), near Shaoshan (Hunan province), the canopy represents a net source of N, probably due to dry deposition. At the other three sites (LiuChongGuan (LCG), LeiGongShan (LGS), both in Guizhou province, and LiuXiHe (LXH) in Guangdong), a net loss of reactive N from precipitation water occurs in the canopy, probably due to uptake processes. The total annual atmospheric TIN load is estimated to range from at least 0. 8 g N m−2 yr−1 to 4. 0 g N m−2 yr−1, with a considerable contribution from dry deposition. Concentrations and fluxes of inorganic N in tree canopy throughfall are greater than those in North America. Also the contribution of NH4 +–N to TIN fluxes in throughfall (40% to 70%) is greater than in North America. Our sites have N deposition levels and NH4 +–N contributions similar to those found in Northwest and central Europe. The TIN loads at TSP and CJT far exceed 2. 5 g N m−2 yr−1, which is the N deposition load above which NO3 − leaching is expected in temperate and boreal forests. [Copyright &y& Elsevier]