Ecological restoration of mined-out areas of dry tropical environment, India

The objective of the present study was to evince the long-term changes after natural revegetation and experimental revegetation of the coal mine spoils with respect to total plant biomass, available plant nutrients, nitrogen transformation and microbial biomass N (MBN) in dry tropical environment of India. Total plant biomass (above- and below-ground), plant available nitrogen, soil nitrogen mineralization and microbial biomass N (MBN) were studied for 2 years in 5 and 10 years old naturally vegetated and revegetated coal mine spoils, and dry tropical forest ecosystem of India. In forest ecosystem, the above ground biomass values ranged from 3,520 to 3,630 kg ha(-1) and belowground from 6,280 to 6,560 kg ha(-1). Plant available nitrogen ranged from 16.76 to 23.21 microg g(-1), net N-mineralization from 9.8 to 48.53 microg g(-1) month(-1) and MBN from 26.4 to 80.02 microg g(-1). In naturally revegetated mine spoil, the above ground biomass values ranged from 1,036 to 1,380 kg ha(-1) and belowground from 2,538 to 3,380 kg ha(-1). Plant available nitrogen ranged from 7.33-17.14 microg g(-1), net N-mineralization from 3.1 to 12.46 microg g(-1) month(-1) and MBN from 14.2 to 35.44 microg g(-1). In revegetated mine spoil, the above ground biomass values ranged from 1,224 to 1,678 kg ha(-1) and belowground from 2,870 to 4,130 kg ha(-1). Plant available nitrogen ranged from 9.4 to 18.83 microg g(-1), net N-mineralization from 4.2 to 16.2 microg g(-1) month(-1) and MBN from 21.6 to 42.6 microg g(-1). The mean plant biomass values in 5 and 10 years mine spoils was lower compared to forest ecosystem by 2.5 and 2 times, respectively. N-mineralization value in 5 year mine spoil was 3.5 times lower and in 10 years mine spoil 2 times lower compared to forest ecosystem. The MBN value was about 2 times lower in both 5 and 10 year mine spoils compared to native forest. MBN was positively related to the re-vegetation age of the mine spoil.     

Soil organic carbon and nitrogen accumulation on coal mine spoils reclaimed with maritime pine (Pinus pinaster Aiton) in Agacli–Istanbul

Mining operations on open coal mines in Agacli-Istanbul have resulted in the destruction of vast amounts of land. To rehabilitate these degraded lands, plantations on this area began in 1988. Twelve tree species were planted, however, the most planted tree species was maritime pine (Pinus pinaster Aiton). This study performed on 14 sample plots randomly selected in maritime pine plantations on coal mine soil/spoils in 2005. Soil samples were taken from eight different soil layers (0-1, 1-3, 3-5, 5-10, 10-20, 20-30, 30-40 and 40-50 cm) into the soil profile. On soil samples; fine soil fraction (<2 mm), soil acidity (pH), organic carbon (C(org)) and total nitrogen (N(t)) contents were investigated, and results were compared statistically among soil layers. As a result, 17 years after plantations, total forest floor accumulation determined as 17,973.20 kg ha(-1). Total nitrogen and organic matter amounts of forest floor were 113.90 and 14,640.92 kg ha(-1) respectively. Among soil layers, the highest levels of organic carbon (1.77%) and total nitrogen (0.096%) and the lowest pH value (pH 5.38) were found in 0-1 cm soil layer, and the variation differs significantly among soil layers. Both organic carbon and total nitrogen content decreased, pH values increased from 0-1 to 5-10 cm layer. In conclusion, according to results obtained maritime pine plantations on coal mine spoils; slow accumulation and decomposition of forest floor undergo simultaneously. Depending on these changes organic carbon and total nitrogen contents increased in upper layer of soil/spoil.     

Are Nitrogen-Fertilized Forest Soils Sinks or Sources of Carbon?

We developed a simple conceptual model that tracks nitrogen and carbon jointly through an N fertilized forest ecosystem. The stimulation of growth increases the litterfall and imports substrate for soil microorganisms. Microbial biomass forms according to the supply of C and N. The formation of microbial biomass is accompanied by respiratory C losses. The quantity of CO₂ efflux depends on the C use efficiency of microbes. When excess N is available, the microbial activity is accelerated and the demand for substrate is high. Litterfall supplies an insufficient amount of C to the soil. In such a case, labile soil C is mineralized and the net effect of N fertilization is a loss of soil C. A strong N fertilization effect on the aboveground biomass can offset the soil C loss. In the case of a low N dosage or high N losses due to leaching or emission of nitrogen oxides, the soil C loss is small. The conceptual model was applied to a case study. The field data, collected over a time span of several decades, could not support sound conclusions on the temporal trend of soil C because the spatial and temporal variability of the chemical data was high. The conceptual model allowed to give an evaluation of the fertilization effect on soil C based on reproducible principles.     

Soil Type and Forest Vegetation Influences on Forest Floor Nitrogen Dynamics at the Bear Brook Watershed in Maine (BBWM)

The paired watershed experiment at the Bear Brook Watershed in Maine (BBWM) provided an opportunity to study changes in forest soil O horizon properties as a result of experimental, chronic N additions. The West Bear brook watershed received elevated N and S inputs since November 1989 as bimonthly applications of (NH4)2SO4. Forest floor samples (O horizon) were collected in July of 1992 from three dominant stand and five soil types at BBWM. The (NH4)2SO4 amendments in the treated watershed (West Bear) stimulated potential net nitrification, but significant increases were found only in hardwood O horizons after three years of treatment. Hardwood stand forest floor soil materials had the lowest C:N ratios (mean=23), compared with mixedwood (mean=27) and softwood stands (mean=33). NH4-N accounted for over 95% of the inorganic N in the forest floor. The lack of a strong relationship between soil type and potential net N mineralization at BBWM, coupled with conflicting results in the literature, suggested that stand characteristics were more important than conventional soil nomenclature based on pedogenetic features, or 2.5 years of treatments, in defining differences in soil N dynamics and responses to increased N inputs.     

Some soil properties on coal mine spoils reclaimed with black locust (Robinia pceudoacacia L.) and umbrella pine (Pinus pinea L.) in Agacli-Istanbul

This study performed on randomly selected seven sample plots in leguminous black locust (Robinia pceudoacacia L.) plantations and five sample plots in umbrella pine (Pinus pinea L.) plantations on coal mine soil/spoils. Soil samples were taken from eight different soil depths (0–1, 1–3, 3–5, 5–10, 10–20, 20–30, 30–40, and 40–50 cm) into the soil profile. On soil samples, bulk density, fine soil fraction (Ø < 2 mm), sand, silt and clay rates, soil acidity (pH), organic carbon (C_org), and total nitrogen (N_t) contents were investigated. Also, some forest floor properties (unit mass, organic matter, and total nitrogen) were determined, and results were compared statistically between umbrella pine and black locust. As a result, 17 years after plantations, total forest floor accumulation determined as 6,107 kg ha^???1 under black locust compared to 13,700 kg ha^???1 under umbrella pine. The more rapid transformation of leguminous black locust forest floor creates organic carbon that migrates further into the mineral profile, and rapid accumulation of C and N in the soil profile was registered. Slower transformation processes of forest floor under umbrella pine result in lower soil N ratio and greater quantity of forest floor. Higher soil pH under leguminous black locust was determined significantly than umbrella pine. In conclusion, the composition of symbiotic nitrogen fixation of black locust appears to be a possible factor favoring carbon and nitrogen accumulation and, consequently, soil development. Clearly, both tree species have favorable impacts on initial soil formation. The umbrella pine generates the more forest floor layer; in contrast, black locust forest floor incorporates into the soil more rapidly and significantly increases soil nitrogen in upper soil layers.     

Non-target effect of organic insecticides: effect of two plant extracts on soil microbial biomass and enzymatic activities in soil

Efficacious botanical derivatives can provide an alternative to synthetic pesticides for organic farming systems. However, there is lack of information regarding the side effects of organic pesticides on key soil ecological processes. In this study, we investigated the effects of aqueous extracts from Urginea maritima and Euphorbia myrsinites exhibiting translaminar and systemic activity against pests on microbial biomass and enzymatic activities in soil. Two grams of plant material was extracted with 100 ml of water and then diluted 1:100, 2:100, and 4:100 with distilled water. Diluted plant extracts were applied around hypocotyl of tomato by soil drench. The effect of both plant extracts on microbial biomass C, amount of total N and organic C, and enzymatic activity in soil was significant. After the last application, the highest microbial biomass C was determined in the lowest U. maritima concentration (U 1:100). Soils treated with the highest concentration of U. maritima (U 4:100) had always lower SMBC content than control soil. All concentrations of E. myrsinites decreased microbial biomass C by 18% to 27% compared to the control. Total nitrogen and organic carbon decreased in soils without (control) and with treated U. maritima extract from first application to last application. Phosphatase, urease, and β-glucosidase activities were monitored in plant extract-treated soils. Except U. maritima 1:100 treatments of second and fourth applications, the other treatments of plant extracts negatively affected enzymatic activity in soil. U. maritima and E. myrsinites plant extracts exhibited different effects on soil microbial biomass and activity, probably because of their different chemical contents.     

Temporal changes of soil respiration under different tree species

Soil respiration rates were measured monthly (from April 2007 to March 2008) under four adjacent coniferous plantation sites [Oriental spruce (Picea orientalis L.), Austrian pine (Pinus nigra Arnold), Turkish fir (Abies bornmulleriana L.), and Scots pine (Pinus sylvestris L.)] and adjacent natural Sessile oak forest (Quercus petraea L.) in Belgrad Forest—Istanbul/Turkey. Also, soil moisture, soil temperature, and fine root biomass were determined to identify the underlying environmental variables among sites which are most likely causing differences in soil respiration. Mean annual soil moisture was determined to be between 6.3 % and 8.1 %, and mean annual temperature ranged from 13.0°C to 14.2°C under all species. Mean annual fine root biomass changed between 368.09 g/m² and 883.71 g/m² indicating significant differences among species. Except May 2007, monthly soil respiration rates show significantly difference among species. However, focusing on tree species, differences of mean annual respiration rates did not differ significantly. Mean annual soil respiration ranged from 0.56 to 1.09 g?C/m²/day. The highest rates of soil respiration reached on autumn months and the lowest rates were determined on summer season. Soil temperature, soil moisture, and fine root biomass explain mean annual soil respiration rates at the highest under Austrian pine (R ²?=?0.562) and the lowest (R ²?=?0.223) under Turkish fir.     

Fluctuations of Climatic Conditions, Elemental Cycling and Forest Growth at the Watershed Scale

The relationships between fluctuations in climatic conditions,forest productivity and elemental cycling were studied from 1994 to 1997 in a headwater catchment of the southern Laurentians dominated by sugar maple (Acer saccharumMarsh.) growing on podzolic soils. Annual budgets show that H⁺, K, and NO₃ were retained in the watershed whileCa, Mg and Na were lost. The magnitude of the net annual budget for Ca, Mg and Na was correlated to annual variationsin precipitation with the absolute budget value decreasing during dry years. Stemwood (r² = 0.85) and total tree biomass production (r² = 0.99) were correlated with mean annual temperature but fine roots and leaf litter werenot. During the growing season, the pH of the organic horizons(FH) decreased as the volumetric water content of soildecreased. A positive association was also found between airtemperature and H₂O-soluble (r² = 0.88) and PO₄-extractable (r² = 0.99) SO₄ in the upper B horizon. On a multi-year scale, we suspect that the decreasein the storage of inorganic SO₄ in the soil results from the cumulative effects of annual variations in climatic conditions superimposed on the long-term decrease in SO₄deposition from the atmosphere. These soil changes were reflected by a decline in SO₄, Ca and Mg concentrationsin the stream. The generalisation of the observed short-term patterns to longer time scales must be approached with caution. Yet, our results indicate that the associations between climatic variations and the biogeochemistry of the ecosystem occur at different spatial and temporal scales and integrate abroad range of chemical components and ecosystem compartments. This reflects the inherent complexity of natural systems and offers a vast palette of indicators of the response of terrestrial ecosystems to variations in the intensity of environmental factors such as climatic conditions.     

Assessment of biological and biochemical indicators in soil under transgenic Bt and non-Bt cotton crop in a sub-tropical environment

There is concern that transgenic Bt-crops carry genes that could have undesirable effects on natural and agro-ecosystem functions. We investigated the effect of Bt-cotton (expressing the Cry 1Ac protein) on several microbial and biochemical indicators in a sandy loam soil. Bt-cotton (MRC-6301Bt) and its non-transgenic near-isoline (MRC-6301) were grown in a net-house on a sandy clay loam soil. Soil and root samples were collected 60, 90, and 120 days after sowing. Soil from a control (no-crop) treatment was also included. Samples were analysed for microbial biomass C, N and P (MBC, MBN, MBP), total organic carbon (TOC), and several soil enzyme activities. The microbial quotient (MQ) was calculated as the ratio of MBC-to-TOC. The average of the three sampling events revealed a significant increase in MBC, MBN, MBP and MQ in the soil under Bt-cotton over the non-Bt isoline. The TOC was similar in Bt and non-Bt systems. Potential N mineralization, nitrification, nitrate reductase, and acid and alkaline phosphatase activities were all higher in the soil under Bt-cotton. Root dry weights were not different (P > 0.05), but root volume of Bt-cotton was higher on 90 and 120 days than that of non-Bt cotton. The time of sampling strongly affected the above parameters, with most being highest on 90 days after sowing. We concluded from the data that there were some positive or no negative effects of Bt-cotton on the studied indicators, and therefore cultivation of Bt-cotton appears to be no risk to soil ecosystem functions.     

Soil response to a 3-year increase in temperature and nitrogen deposition measured in a mature boreal forest using ion-exchange membranes

The projected increase in atmospheric N deposition and air/soil temperature will likely affect soil nutrient dynamics in boreal ecosystems. The potential effects of these changes on soil ion fluxes were studied in a mature balsam fir stand (Abies balsamea [L.] Mill) in Quebec, Canada that was subjected to 3 years of experimentally increased soil temperature (+4 °C) and increased inorganic N concentration in artificial precipitation (three times the current N concentrations using NH₄NO₃). Soil element fluxes (NO₃, NH₄, PO₄, K, Ca, Mg, SO₄, Al, and Fe) in the organic and upper mineral horizons were monitored using buried ion-exchange membranes (PRS? probes). While N additions did not affect soil element fluxes, 3 years of soil warming increased the cumulative fluxes of K, Mg, and SO₄ in the forest floor by 43, 44, and 79 %, respectively, and Mg, SO₄, and Al in the mineral horizon by 29, 66, and 23 %, respectively. We attribute these changes to increased rates of soil organic matter decomposition. Significant interactions of the heating treatment with time were observed for most elements although no clear seasonal patterns emerged. The increase in soil K and Mg in heated plots resulted in a significant but small K increase in balsam fir foliage while no change was observed for Mg. A 6–15 % decrease in foliar Ca content with soil warming could be related to the increase in soil-available Al in heated plots, as Al can interfere with the root uptake of Ca.     

Deposition of Inorganic Particulate Aerosols to Vegetation - A New Method of Estimating

A new, direct method was developed for quantifying inorganic particulate aerosols trapped by the forest canopy, and for determining the resulting input of elements to a forest ecosystem. The method is based on direct measurements of only six parameters. Using this method, it is possible to determine the load of aerosols trapped by the forest canopy and deposited to leaves, as well as the load of aerosols falling to the forest floor by impaction on plants. It is also possible to estimate the aerosol input of soluble and insoluble elements to an ecosystem. With this new method it has been found that the load of aerosols trapped by the canopy of a mixed forest located in the Rybnik Coal Basin averaged 189.0 kg x ha-1 x growing season-1, or 39.3% of the total inorganic particles reaching the ecosystem. The trapped aerosols provided 13.4 kg x ha-1 of soluble nitrogen and 0.91 kg x ha-1 of insoluble nitrogen over the growing season. At the same time, the input of soluble nitrogen from the atmosphere with rainfall to an open area averaged 13.9 kg x ha-1, and the input of insoluble nitrogen with inorganic dusts averaged 1.4 kg x ha-1.     

An assessment of the relationship between potential chemical indices of nitrogen saturation and nitrogen deposition in hardwood forests in southern Ontario

Southern Ontario receives the highest levels of atmospheric nitrogen (N) deposition in Canada and there are concerns that forests in the region may be approaching a state of ‘N saturation’. In order to evaluate whether potential chemical indices provide evidence of N saturation, 23 hardwood plots were sampled along a modeled N-deposition gradient ranging from 9.3 to 12.8 kg/ha/year. All plots were dominated by sugar maple (Acer saccharum Marsh.) and foliar N and foliar δ¹⁵N were positively correlated with modeled N deposition. However, forest floor N content and the C:N ratio were unrelated to N deposition, but were instead related to soil pH and annual temperature; lower C:N ratios and higher N content in the forest floor were found at the most acidic sites in the cooler, northern part of the study region despite lower N deposition. Likewise, δ¹⁵N values in surface mineral soil and the ¹⁵N enrichment factor of foliage (δ¹⁵N foliage ? δ¹⁵N soil) are correlated to soil pH and temperature and not N deposition. Further, potential N mineralization, ammonification, and nitrification in Ontario maple stands were highest in the northern part of the region with the lowest modeled N deposition. Nitrogen cycling in soil appears to be primarily influenced by the N status of the forest floor and other soil properties rather than N deposition, indicating that chemical indices in soil in these hardwood plots may not provide an early indicator of N saturation.     

The impact of point source pollution on shallow groundwater used for human consumption in a threshold country

Many developing and threshold countries rely on shallow groundwater wells for their water supply whilst pit latrines are used for sanitation. We employed a unified strategy involving satellite images and environmental monitoring of 16 physico-chemical and microbiological water quality parameters to identify significant land uses that can lead to unacceptable deterioration of source water, in a region with a subtropical climate and seasonally restricted torrential rainfall in Northern Argentina. Agricultural and non-agricultural sources of nitrate were illustrated in satellite images and used to assess the organic load discharged. The estimated human organic load per year was 28.5 BOD(5) tons and the N load was 7.5 tons, while for poultry farms it was 9940-BOD(5) tons and 1037-N tons, respectively. Concentrations of nitrates and organics were significantly different between seasons in well water (p values of 0.026 and 0.039, respectively). The onset of the wet season had an extraordinarily negative impact on well water due in part to the high permeability of soils made up of fine gravels and coarse sand. Discriminant analysis showed that land uses had a pronounced seasonal influence on nitrates and introduced additional microbial contamination, causing nitrification and denitrification in shallow groundwater. P-well was highly impacted by a poultry farm while S-well was affected by anthropogenic pollution and background load, as revealed by Principal Component Analysis. The application of microbial source tracking techniques is recommended to corroborate local sources of human versus animal origin.     

Controls on N Retention and Exports in a Forested Watershed

We conducted a 15N-tracer study in a fertilized, forested catchment at the Bear Brook Watersheds in Maine (BBWM), USA, in order to characterize N cycling processes, identify sinks for ammonium-N additions, and determine the contribution of the experimental ammonium additions to nitrate exports from the treated catchment. Distributions of 15N in plant tissues, soils, precipitation and streamwater collected before adding tracers showed that nitrate-N (the dominant form of inorganic N deposition at the site) inputs under ambient conditions were depleted in 15N relative to plants and that soil was enriched in 15N relative to plants. The 15N content of streamwater nitrate was within the range of 15N contents in natural plant tissues, suggesting that nitrate deposited from the atmosphere is reduced and assimilated into soil and plant N pools before being leached as nitrate from the catchment. Variations in 15N natural abundances also suggested that most N uptake by trees is from the forest floor and that nitrification occurs in soils at this catchment under ambient conditions. Changes in 15N contents of plant tissues, soils and streamwater after adding a 15N tracer to the ammonium sulfate fertilizer applied to the treated catchment showed that soils were the dominant sink for the labeled ammonium. Surface soils (Oca horizon plus any underlying mineral soil to 5cm depth) assimilated 19 to 31 percent of the 42 kg ha-1 of 15N-labelled ammonium-N during the tracer study. Aboveground biomass assimilated 8 to 17 percent of the labeled ammonium-N additions. Of the three forest types on the catchment, the soil:biomass assimilation ratio of labeled-N was highest in the spruce forest, intermediate in the beech-dominated hardwood forest and lowest in the mixed hardwood-spruce forest. Although ammonium sulfate additions led to increases in streamwater nitrate, only 2 of the 13 kg ha-1 of nitrate-N exported from the catchment during the 2 years of tracer additions was derived from the 42 kg ha-1 of labeled ammonium-N additions.     

Seasonal baseline of nutrients and stable isotopes in a saline lake of Argentina: biogeochemical processes and river runoff effects

The seasonal variability of inorganic and organic nutrients and stable isotopes and their relations with plankton and environmental conditions were monitored in Lake Chasicó. Principal component analysis evidenced the strong influence of the river runoff on several biogeochemical variables. Silicate concentrations were controlled by diatom biomass and river discharge. Higher values of nitrate and soluble reactive phosphorus (SRP) indicated agricultural uses in the river basin. Elevated pH values (～9) inhibiting nitrification in the lake explained partially the dominance of ammonium: ～83 % of dissolved inorganic nitrogen (DIN). The low DIN/SRP ratio inferred nitrogen limitation, although the hypotheses of iron and CO₂ limitation are relevant in alkaline lakes. Particulate organic matter (POM) and dissolved organic matter (DOM) were mainly of autochthonous origin. The main allochthonous input was imported by the river as POM owning to the arid conditions. Dissolved organic carbon was likely top-down regulated by the bacterioplankton grazer Brachionus plicatilis. The δ¹³C signature was a good indicator of primary production and its values were influenced probably by CO₂ limitation. The δ¹⁵N did not evidence nitrogen fixation and suggested the effects of anthropogenic activities. The preservation of a good water quality in the lake is crucial for resource management.     

Soil microbial characteristics at the monitoring plots on windthrow areas of the Tatra National Park (Slovakia): their assessment as environmental indicators

This study focused on the responses of soil microorganisms to different management regimes on disturbed windthrow areas. Microbial parameters potentially serving as indicators of environmental changes within a long-term monitoring of forest development after large-scale disturbance events were assessed. Basal and substrate-induced respiration, N mineralisation, catalase activity, microbial biomass as well as functional diversity based on Biolog assay were determined in soil samples from three disturbed plots and an undisturbed reference plot in the Tatra National Park (Slovakia) since 2006. A relative congruence of inter-annual trends of microbial activity indicators at all plots results from a common response of microbiota to changes of climate at the landscape level after forest stands were destroyed. While catalase activity and functional diversity proved to be useful indicators of temporal trends, microbial biomass seems to reflect different management regimes at the disturbed plots.     

Water quality assessment using integrated modeling and monitoring in Narva Bay, Gulf of Finland

A coupled three-dimensional hydrodynamic–ecological model was used for the assessment of water quality in Narva Bay during one biologically active season. Narva Bay is located in the south-eastern Gulf of Finland. Narva River with a catchment’s area covering part of Russia and Estonia discharges water and nutrients to Narva Bay. The ecological model includes phytoplankton carbon, nitrogen and phosphorus, chlorophyll a, zooplankton, detritus carbon, nitrogen and phosphorus, inorganic nitrogen, inorganic phosphorus and dissolved oxygen as state variables. Both the hydrodynamic and ecosystem models were validated using a limited number of measurements. The hydrodynamic model validation included comparison of time series of currents and temperature and salinity profiles. The ecological model results were compared with the monitoring data of phytoplankton biomass, total nitrogen and phosphorus and dissolved oxygen. The comparison of hydrodynamic parameters, phytoplankton biomass, surface layer total phosphorus and dissolved oxygen and near-bottom layer total nitrogen was reasonable. Time series of spatially mean values and standard deviations of selected parameters were calculated for the whole Narva Bay. Combining model results and monitoring data, the characteristic concentrations of phytoplankton biomass, total nitrogen and phosphorus and near-bottom dissolved oxygen were estimated. Phytoplankton biomass and total phosphorus showed seasonal variations, of 0.6–1.1 and 0.022–0.032 mg/l, respectively, during spring bloom, 0.1–0.3 and 0.015–0.025 mg/l in summer and 0.2–0.6 and 0.017–0.035 mg/l during autumn bloom. Total nitrogen and near-bottom oxygen concentrations were rather steady, being 0.25–0.35 and 2–6 mg/l, respectively. The total nitrogen and phosphorus concentrations show that according to the classification of Estonian coastal waters, Narva Bay water belongs to a good water quality class.     

Effects of wetland recovery on soil labile carbon and nitrogen in the Sanjiang Plain

Soil management significantly affects the soil labile organic factors. Understanding carbon and nitrogen dynamics is extremely helpful in conducting research on active carbon and nitrogen components for different kinds of soil management. In this paper, we examined the changes in microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) to assess the effect and mechanisms of land types, organic input, soil respiration, microbial species, and vegetation recovery under Deyeuxia angustifolia freshwater marshes (DAMs) and recovered freshwater marsh (RFM) in the Sanjiang Plain, Northeast China. Identifying the relationship among the dynamics of labile carbon, nitrogen, and soil qualification mechanism using different land management practices is therefore important. Cultivation and land use affect intensely the DOC, DON, MBC, and MBN in the soil. After DAM soil tillage, the DOC, DON, MBC, and MBN at the surface of the agricultural soil layer declined significantly. In contrast, their recovery was significant in the RFM surface soil. A long time was needed for the concentration of cultivated soil total organic carbon and total nitrogen to be restored to the wetland level. The labile carbon and nitrogen fractions can reach a level similar to that of the wetland within a short time. Typical wetland ecosystem signs, such as vegetation, microbes, and animals, can be recovered by soil labile carbon and nitrogen fraction restoration. In this paper, the D. angustifolia biomass attained natural wetland level after 8 years, indicating that wetland soil labile fractions can support wetland eco-function in a short period of time (4 to 8 years) for reconstructed wetland under suitable environmental conditions.     

Monitoring nitrogen deposition in typical forest ecosystems along a large transect in China

The nitrogen (N) deposition fluxes were investigated in eight typical forest ecosystems along the North–South Transect of Eastern China (NSTEC; based on the ChinaFLUX network) by ion-exchange resin (IER) columns from May 2008 to April 2009. Our results demonstrated that the method of IER columns was both labor cost saving and reliable for measuring dissolved inorganic nitrogen (DIN) deposition at the remote forest stations. The deposition of DIN in the throughfall ranged from 1.3 to 29.5 kg N ha^?1 a^?1, increasing from north to south along NSTEC. The relatively high average ratio of ammonium to nitrate in deposition (1.83) indicated that the N deposition along the NSTEC in China mostly originated in farming and animal husbandry rather than in industry and vehicle activities. For seasonal variability, the DIN deposition showed a single peak in the growing season in the northern part of NSTEC, while, in the southern part, it exhibited double-peaks in the early spring and the mid-summer, respectively. On the annual scale, the DIN deposition variations of the eight sites could be mainly explained by precipitation and the distances from forest stations to provincial capital cities.     

Nutrients in the Changjiang River

N, P and SiO3-Si in the Changjiang mainstream and its major tributaries and lakes were investigated in the dry season from November to December, 1997, and in the flood season in August and October, 1998. An even distribution of SiO3-Si was found along the Changjiang River. However, the concentrations of total nitrogen, total dissolved nitrogen, dissolved inorganic nitrogen, nitrate and total phosphorus, total particulate phosphorus increased notably in the upper reaches, which reflected an increasing impact from human activities. Those concentrations in the middle and lower reaches of the Changjiang River were relatively constant. Dissolved N was the major form of N and the particulate P was the major form of P in the Changjiang River. The molar ratio of dissolved N to dissolved P was extremely high (192.5-317.5), while that of the particulate form was low (5.6-37.7). High N/P ratio reflected a significant input of anthropogenic N such as N from precipitation and N lost from water and soil etc. Dissolved N and P was in a quasi-equilibrium state in the process from precipitate to the river. In the turbid river water, light limitation, rather than P limitation, seemed more likely to be a controlling factor for the growth of phytoplankton. A positive linear correlationship between the concentration of dissolved N and the river's runoff was found, mainly in the upper reaches, which was related to the non-point sources of N. Over the past decades, N concentration has greatly increased, but the change of P concentration was not as significant as N. The nutrient fluxes of the Changjiang mainstream and tributaries were estimated, and the result showed that the nutrient fluxes were mainly controlled by the runoff, of which more than a half came from the tributaries. These investigations carried out before water storage of the Three Gorges Dam will supply a scientific base for studying the influences of the Three Gorges Dam on the ecology and environment of the Changjiang River and its estuary.