Wildfire risk inferred from tree rings in the Central Laurentians of boreal Quebec,Canada

Recent fire years 2002 and 2005 have been, in the context of the past 40 years, exceptional in Quebec, with area burned totalling over 1.8 million hectares. Without prolonged fire statistics and meteorological records, it remains difficult to place these events in the contexts of climate change and variability. How frequently does this type of year occur? In this study, chronologies of radial increment measurements of Pinus spp., considered reliable back to at least 1821, were calibrated to develop an index of past moisture in ground surface fuels in the Baie-Comeau area of the Central Laurentians ecoregion, Quebec (namely the Canadian Drought Code (CDC)). Over 37% of the variance in CDC observations (period 1901–2000) was recovered by the tree-ring estimates. These estimates in turn correlated well (R²=0.39) with annual area burned (AAB) by large forest fires (size >200 ha; 1959–1999) in the Central Laurentians ecoregion. The smoothed reconstruction showed the prevalence of periods of drier conditions than average from the 1840s to the 1920s, followed by an episode of moister conditions from the 1930s to the 1960s. The minimum occurrence rate of years of extreme wildfire risk in the Baie-Comeau area was estimated in the 1940s at 0.04 yr^?1, while the maximum was estimated in the 1910s at 0.21 yr^?1. Occurrence rate at the turn of the 21st century (0.21 yr^?1) was closely similar to that recorded during the 1890–1910s (within the uncertainty bands). These long-term variations matched temporal variations in a previously published time-since-fire distribution. The combined information from these ecological sources of data provides meaningful insights for future management of wildfire risk in the Baie-Comeau area, notably to increasing adaptation capacity in response to climate change.     

Treatment of domestic wastewater in tropical,subsurface flow constructed wetlands planted with Canna and Heliconia

Constructed wetlands have a good potential for wastewater treatment in developing countries due to the simple operation and low implementation costs. Ornamental plants like Canna and Heliconia are used in the wetlands to increase their aesthetic value and these two species were compared in this study. Six pilot scale horizontal subsurface flow constructed wetland units were constructed at the Asian Institute of Technology (AIT) campus in Bangkok, Thailand, of which three were planted with Heliconia psittacorum L.f. × H. Spathocircinata (Aristeguieta) and three with Canna × generalis L. Bailey. The beds were loaded with domestic wastewater in four trials with hydraulic loading rates ranging from 55 to 440 mm d^?1 corresponding to nominal detention times between 12 h and 4 days. Both plant species grew well in the systems and especially Canna had high growth rates (3100 ± 470 g DW m^?2 yr^?1) compared to Heliconia (550 ± 90 g DW m^?2 yr^?1). TSS mass removal rates were very high with efficiencies >88% even at hydraulic loading rates of 440 mm d^?1. COD mass removal rates varied between 42 and 83% depending on the loading rates. The removal rate constants for COD as fitted by the first-order k–C^* model were estimated to be 0.283 and 0.271 m d^?1 for Canna and Heliconia beds, respectively (C^* = 28.1 and 26.7 mg l^?1). Removals of nitrogen (N) and phosphorus (P) were low compared to the loading rates, but removal of total-N was higher in the beds planted with Canna than in beds with Heliconia because of the higher growth rate of Canna. It is concluded that ornamental species like Canna and Heliconia can be used to enhance the aesthetic appearance and hence the public acceptance of wastewater treatment systems in tropical climates. Canna is the preferred species from a treatment perspective because of its more vigorous growth, but since Heliconia has an economic potential as cut flowers may be preferred in many cases.     

Structure and seasonal dynamics of the protozoan community (heterotrophic flagellates,ciliates, amoeboid protozoa) in the plankton of a large river (River Danube,Hungary)

Seasonal dynamics of all major protozoan groups were investigated in the plankton of the River Danube, upstream of Budapest (Hungary), by bi-weekly sampling over a 1-year long period. Sixty-one heterotrophic flagellate, 14 naked amoeba, 50 testate amoeba, 4 heliozoan and 83 ciliate morphospecies were identified. The estimated abundance ranges of major groups throughout the year were as follows: heterotrophic flagellates, 0.27–7.8×10⁶ ind. l^?1; naked amoebae, max. 3300 ind. l^?1; testaceans, max. 1600 ind. l^?1; heliozoans, max. 8500 ind. l^?1; ciliates, 132–34,000 ind. l^?1. In terms of biovolume, heterotrophic flagellates dominated throughout the year (max. 0.58 mm³ l^?1), and ciliates only exceeded their biovolume in summer (max. 0.76 mm³ l^?1). Naked amoeba and heliozoan biovolume was about one, and testacean biovolume 1–3, orders of magnitude lower than that of ciliates. In winter, flagellates, mainly chrysomonads, had the highest biomass, whilst ciliates were dominated by peritrichs. In 2005 from April to July a long spring/summer peak occurred for all protozoan groups. Beside chrysomonads typical flagellates were choanoflagellates, bicosoecids and abundant microflagellates (large chrysomonads and Collodictyon). Most abundant ciliates were oligotrichs, while Phascolodon, Urotricha, Vorticella, haptorids, Suctoria, Climacostomum and Stokesia also contributed significantly to biovolume during rapid succession processes. In October and November a second high protozoan peak occurred, with flagellate dominance, and slightly different taxonomic composition.     

Tillage effects on carbon footprint and ecosystem services of climate regulation in a winter wheat–summer maize cropping system of the North China Plain

Inappropriate farm practices can increase greenhouse gases (GHGs) emissions and reduce soil organic carbon (SOC) sequestration, thereby increasing carbon footprints (CFs), jeopardizing ecosystem services, and affecting climate change. Therefore, the objectives of this study were to assess the effects of different tillage systems on CFs, GHGs emissions, and ecosystem service (ES) values of climate regulation and to identify climate-resilient tillage practices for a winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) cropping system in the North China Plain (NCP). The experiment was established in 2008 involving no-till with residue retention (NT), rotary tillage with residue incorporation (RT), sub-soiling with residue incorporation (ST), and plow tillage with residue incorporation (PT). The results showed that GHGs emissions from agricultural inputs were 6432.3–6527.3 kg CO₂-eq ha⁻¹ yr⁻¹ during the entire growing season, respectively. The GHGs emission from chemical fertilizers and irrigation accounted for >80% of that from agricultural inputs during the entire growing season. The GHGs emission from agricultural inputs were >2.3 times larger in winter wheat than that in the summer maize season. The CFs at yield-scale during the entire growing season were 0.431, 0.425, 0.427, and 0.427 without and 0.286, 0.364, 0.360, and 0.334 kg CO₂-eq kg⁻¹ yr⁻¹ with SOC sequestration under NT, RT, ST, and PT, respectively. Regardless of SOC sequestration, the CFs of winter wheat was larger than that of summer maize. Agricultural inputs and SOC change contributed mainly to the component of CFs of winter wheat and summer maize. The ES value of climate regulation under NT was ¥159.2, 515.6, and 478.1 ha⁻¹ yr⁻¹ higher than that under RT, ST, and PT during the entire growing season. Therefore, NT could be a preferred “Climate-resilient” technology for lowering CFs and enhancing ecosystem services of climate regulation for the winter wheat–summer maize system in the NCP.     

Regulating effects of climate,net primary productivity,and nitrogen on carbon sequestration rates in temperate wetlands,Northeast China

Temperate wetlands in the Northern Hemisphere have high long-term carbon sequestration rates, and play critical roles in mitigating regional and global atmospheric CO₂ increases at the century timescale. We measured soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) from 11 typical freshwater wetlands (Heilongjiang Province) and one saline wetland (Jilin Province) in Northeast China, and estimated carbon sequestration rates using ²¹⁰Pb and ¹³⁷Cs dating technology. Effects of climate, net primary productivity, and nutrient availability on carbon sequestration rates (R_carbon) were also evaluated. Chronological results showed that surface soil within the 0–40 cm depth formed during the past 70–205 years. Soil accretion rates ranged from 2.20 to 5.83 mm yr⁻¹, with an average of 3.84 ± 1.25 mm yr⁻¹ (mean ± SD). R_carbon ranged from 61.60 to 318.5 gC m⁻² yr⁻¹ and was significantly different among wetland types. Average R_carbon was 202.7 gC m⁻² yr⁻¹ in the freshwater wetlands and 61.6 gC m⁻² yr⁻¹ in the saline marsh. About 1.04 × 10⁸ tons of carbon was estimated to be captured by temperate wetland soils annually in Heilongjiang Province (in the scope of 45.381–51.085°N, 125.132–132.324°E). Correlation analysis showed little impact of net primary productivity (NPP) and soil nutrient contents on R_carbon, whereas climate, specifically the combined dynamics of temperature and precipitation, was the predominant factor affecting R_carbon. The negative relationship observed between R_carbon and annual mean temperature (T) indicates that warming in Northeast China could reduce R_carbon. Significant positive relationships were observed between annual precipitation (P), the hydrothermal coefficient (defined as P/AT, where AT was accumulative temperature ≥10 °C), and R_carbon, indicating that a cold, humid climate would enhance R_carbon. Current climate change in Northeast China, characterized by warming and drought, may form positive feedbacks with R_carbon in temperate wetlands and accelerate carbon loss from wetland soils.     

Determination of metoclopramide in human plasma by LC–ESI-MS and its application to bioequivalance studies

An LC–MS method for the determination of metoclopramide in human plasma was developed and validated. Sample preparation involved extraction with ethyl acetate. Chromatographic separation was performed on a Thermo Hypersil-Hypurity C₁₈ (150 mm × 2.1 mm, 5 μm) with the mobile phase consisting of 40 mM ammonium acetate–methanol–acetonitrile. A single-quadrupole mass spectrometer with an electrospray interface was operated in the selected-ion monitoring mode to detect the [M+H]⁺ ions at m/z 300 for metoclopramide and at m/z 384 for the internal standard (prazosin). The method was validated over 0.78–50.00 ng mL^?1 for metoclopramide. The recovery was 67.8–83.1%, and the limit of quantitation (LOQ) detection was 0.78 ng mL^?1 for metoclopramide. The intra- and inter-day precision of the method at three concentrations was 5.0–13.6% with accuracy of 99.2–104.0%. Stability of compounds was established in a battery of stability studies. The method was successfully applied to bioequivalence studies of metoclopramide hydrochloride tablets to obtain the pharmacokinetic parameters.     

Treatment of high-strength wastewater in tropical vertical flow constructed wetlands planted with Typha angustifolia and Cyperus involucratus

The ability of vertical flow (VF) constructed wetland systems to treat high-strength (ca. 300 mg L^?1 of COD and ca. 300 mg L^?1 total-nitrogen) wastewater under tropical climatic conditions was studied during a 5-month period. Nine 0.8-m diameter experimental VF units (depth 0.6 m) were used: three units were planted with Typha angustifolia L., another three units were planted with Cyperus involucratus Rottb and three units were unplanted. Each set of units were operated at hydraulic loading rates (HLRs) of 20, 50 and 80 mm d^?1. Cyperus produced more shoots and biomass than the Typha, which was probably stressed because of lack of water. The high evapotranspirative water loss from the Cyperus systems resulted in higher effluent concentrations of COD and total-P, but the mass removal of COD did not differ significantly between planted and unplanted systems. Average mass removal rates of COD, TKN and total-P at a HLR of 80 mm d^?1 were 17.8, 15.4 and 0.69 g m^?2 d^?1. The first-order removal rate constants at a HLR of 80 mm d^?1 for COD, TKN and total-P were 49.8, 30.1 and 13.5 m year^?1, respectively, which is in the higher range of k-values reported in the literature. The oxygen transfer rates were ca. 80 g m^?2 d^?1 in the planted systems as opposed to ca. 60 g m^?2 d^?1 in the unplanted systems. The number of Nitrosomonas was two to three orders of magnitude higher in the planted systems compared to the unplanted systems. Planted systems thus had significantly higher removal rates of nitrogen and phosphorus, higher oxygen transfer rates, and higher quantities of ammonia-oxidizing bacteria. None of the systems did, however, fully nitrify the wastewater, even at low loading rates. The vertical filters did not provide sufficient contact time between the wastewater and the biofilm on the gravel medium of the filters probably because of the shallow bed depth (0.6 m) and the coarse texture of the gravel. It is concluded that vertical flow constructed wetland systems have a high capacity to treat high-strength wastewater in tropical climates. The gravel and sand matrix of the vertical filter must, however, be designed in a way so that the pulse-loaded wastewater can pass through the filter medium at a speed that will allow the water to drain before the next dose arrives whilst at the same time holding the water back long enough to allow sufficient contact with the biofilm on the filter medium.     

Diversity and spatial clustering of shade trees affect cacao yield and pathogen pressure in Costa Rican agroforests

The importance of the spatial organisation of individuals in explaining species coexistence within a community is widely recognised. However, few analyses of spatial structure have been performed on tropical agroforests.The main objective of this study was to highlight the links between spatial organisation of shade trees on the one hand, and shade tree species richness and cacao yield on the other, using data from 29 cacao agroforests in Costa Rica.A method of spatial statistics, Ripley's K-function, was used to analyse the spatial organisation of shade and cacao trees in the study plots. For each stand, the X and Y coordinates of ≥2.5-m-tall trees were recorded. In each plot we also assessed shade tree species richness and cacao yield (with total number of pods = number of pods damaged by frosty pod rot + number of healthy pods).Three types of stands were identified: the first was characterised by significant clustering of shade trees, the highest shade tree species richness (S = 6), and the highest number of damaged pods (139 pods ha^?1 year^?1). The second type was characterised by random spatial organisation of shade trees. The third type showed a trend towards regular organisation. Species richness of shade trees did not differ significantly between the last two types (S = 4 for both), nor did the number of damaged pods (56 pods ha^?1 year^?1 and 67 pods ha^?1 year^?1 respectively).Although the trends were not statistically significant for all the variables in our data set, the clustered spatial structure appears to favour a synergy between environmental (tree species richness), and provisioning (cacao production) services.     

Potential of dendrochronology in assessing carbon sequestration rates of Vitellaria paradoxa in southern Mali,West Africa

This study aimed to investigate the applicability of dendrochronology for assessing the growth dynamics and response to climate variability and to estimate the aboveground carbon stock and carbon sequestration potential of Vitellaria paradoxa in southern Mali. Twenty stem disks were collected from three land-use types (parklands, fallows and protected areas) in Koutiala and Yanfolila districts. We combined a standard dendrochronological approach with biomass allometric equations to estimate the growth and carbon stocks. The results showed that V. paradoxa forms distinct growth ring boundaries but most of the disks from parklands did not successfully cross-date due to management operations like pruning. The tree-ring width showed a significant standardized coefficient of regression with rainfall (r² = 0.66, p < 0.001) but insignificant correlation with temperature. One-way analysis of variance showed no significant difference (p > 0.05) for C-sequestration as well as for carbon stocks in aboveground biomass for both land-use types and sites. Mean values of the amount of C-sequestered in Yanfolila were 0.112 ± 0.0.065 Mg C ha⁻¹ yr⁻¹ in parklands, 0.075 ± 0.018 Mg C ha⁻¹ yr⁻¹ in fallows and 0.064 ± 0.028 Mg C ha⁻¹ yr⁻¹ in protected areas. In Koutiala, the values were 0.068±0.020 Mg C ha⁻¹ yr⁻¹ in the parklands and 0.053 ± 0.017 Mg C ha⁻¹ yr⁻¹ in the fallows. These results clearly indicate that dendrochronology can be applied to assess growth and carbon sequestration potential of V. paradoxa. These results also suggest that climate change could affect the growth and carbon sequestration potential of V. paradoxa. Given the limited size of our sample, figures on the amount of carbon are indicative calling for applying the tested approaches to larger samples and also to other tree species in West Africa.     

Nonspecific inhibition of nitric oxide synthesis evokes endothelin-dependent increases in myocardial contractility

The role of endogenous nitric oxide (NO) in modulating myocardial contractility is still unclear, in part because of unknown, secondary effects of blocking NO release. We hypothesized that the nonspecific inhibition of nitric oxide synthase (NOS) enhances endothelin-1 (ET-1) effects, which can play a role in ET-A receptor-dependent myocardial contractile responses. The myocardial contractility was estimated from the slope of the left ventricular end-systolic pressure–diameter relationship in closed-chest, pentobarbital-anesthetized dogs. Group 1 (n = 7) was the saline-treated control, while in groups 2 (n = 7) and 3 (n = 7) N-nitro-l-arginine (NNA, 4 mg kg^?1), a nonselective NOS blocker, was administered with or without pretreatment with the ET-A receptor antagonist ETR-P1/fl peptide (100 nmol kg^?1 iv). Plasma ET-1, nitrite/nitrate (NO_x) and blood superoxide levels were measured, and myocardial ET-1 content and xanthine oxidoreductase (XOR) activity were determined from myocardial biopsies. The infusion of NNA over 120 min decreased the plasma NO_x, significantly elevated the plasma ET-1 and blood superoxide levels, and in parallel greatly increased the left ventricular contractility as compared with the untreated controls [47.5 vs 30 mm Hg mm^?1]. The myocardial ET-1 content decreased simultaneously, while the XOR activity and blood superoxide level were significantly elevated. These effects, including NNA-induced positive inotropy, were significantly suppressed by pretreatment with ETR-P1/fl peptide. These results demonstrate that a diminished NO synthesis leads to a preponderant ET-1 effect, which increases myocardial contractility through an ET-A receptor-dependent mechanism.     

Effect of hydraulic retention time on the treatment of secondary effluent in a subsurface flow constructed wetland

This study evaluates the potential of subsurface flow (SSF) constructed wetlands (CWs) for tertiary treatment of wastewater at four shorter HRTs (1–4 days). The CWs were planted with Typha angustata, which was observed in our earlier study to be more efficient than Phragmites karka and Scirpus littoralis. The CWs comprised four rectangular treatment cells (2.14 m × 0.76 m × 0.61 m) filled with layers of gravel of two different sizes (approximately 2.5 cm and 1.5 cm diameter) to a depth of 0.61 m. The inflow rates of the secondary effluent in the four cells were accordingly fixed at 300 L d^?1, 150 L d^?1, 100 L d^?1 and 75 L d^?1, respectively, for 1, 2, 3 and 4 days HRT. The hydraulic loads ranged between 59.05 mm d^?1 and 236.22 mm d^?1.The wastewater inflow into the CW system as well as the treated effluent were analyzed, using standard methods, at regular intervals for various forms of nitrogen (NH₄-N, NO₃-N and TKN), orthophosphate-P and organic matter (BOD and COD) concentrations over a period of five weeks after the development of a dense stand.The higher HRT of 4 days not only helped maximum removal of all the pollutants but also maintained the stability of the treatment efficiency throughout the monitoring period. For the nutrients (NH₄-N, NO₃-N and TKN), HRT played a more significant role in their removal than in case of organic matter (BOD₃ and COD). More than 90% of NO₃-N and TKN and 100% of NH₄-N were removed from the wastewater at 4 days HRT.At lower HRTs, the mass loading rate was higher with greater fluctuation. However mass reduction efficiency of the T. angustata CW for all forms of nitrogen was >80% with the HRTs of 2, 3 and 4 days.     

Ecological re-engineering of a freshwater impoundment for salt marsh restoration in a hypertidal system

The purpose of this paper was to examine the vegetative, sedimentary, nekton and hydrologic response to ecological re-engineering of a freshwater impoundment in the Upper Bay of Fundy. The dyke was breached in five locations and one channel initiated to connect the river to the borrow pit behind the dyke. This triggered significant self-organization within the restoration site. Existing channels (e.g. borrow pit) were incorporated within the newly excavated and developing creek system, increasing the hydraulic connectivity within the marsh and increasing fish habitat. Vegetation colonization, primarily by Spartina alterniflora, was rapid with almost 100% coverage by the end of the third year. Species associated with high marsh communities such as Juncus gerardii, Scirpus robustus, Ranunculus cymbalaria and Puccinellia maritima were present in increasing abundance post-restoration at the restoration site. The constructed channel eroded downward 2.3 m and the head of the channel retreated 35 m in response to the increased tidal prism. In the year immediately following the breach (2006), the surface of the marsh was unconsolidated and rates of change in surface elevation measured at RSET stations ranged from ?0.7 (±0.1) to 1.7 (±0.2) cm yr^?1 (±1SE). Measurements between years are highly variable. By year 3 the rate of surface elevation change decreased to a more moderate but variable mean of 0.3 (±0.6) cm yr^?1 with the marker horizons recording mean accretion rates of 0.7 cm yr^?1. This implies subsurface consolidation as the sediments dewatered or organic matter decomposed and vegetation became more established. Fish density decreased after restoration, however, remained higher than at the reference site for most years.     

Purification,kinetic and thermodynamic characterization of soluble acid invertase from sugarcane (Saccharum officinarum L.)

We report for the first time kinetic and thermodynamic properties of soluble acid invertase (SAI) of sugarcane (Saccharum officinarum L.) salt sensitive local cultivar CP 77-400 (CP-77). The SAI was purified to apparent homogeneity on FPLC system. The crude enzyme was about 13 fold purified and recovery of SAI was 35%. The invertase was monomeric in nature and its native molecular mass on gel filtration and subunit mass on SDS-PAGE was 28 kDa. SAI was highly acidic having an optimum pH lower than 2. The acidic limb was missing. Proton transfer (donation and receiving) during catalysis was controlled by the basic limb having a pKa of 2.4. Carboxyl groups were involved in proton transfer during catalysis. The kinetic constants for sucrose hydrolysis by SAI were determined to be: k_m = 55 mg ml^?1, k_cat = 21 s^?1, k_cat/k_m = 0.38, while the thermodynamic parameters were: ΔH* = 52.6 kJ mol^?1, ΔG* = 71.2 kJ mol^?1, ΔS* = ?57 J mol^?1 K^?1, ΔG*_E–S = 10.8 kJ mol^?1 and ΔG*_E–T = 2.6 kJ mol^?1. The kinetics and thermodynamics of irreversible thermal denaturation at various temperatures 53–63 °C were also determined. The half -life of SAI at 53 and 63 °C was 112 and 10 min, respectively. At 55 °C, surprisingly the half -life increased to twice that at 53 °C. ΔG*, ΔH* and ΔS* of irreversible thermal stability of SAI at 55 °C were 107.7 kJ mol^?1, 276.04 kJ mol^?1 and 513 J mol^?1K^?1, respectively.     

Carbon sequestration potential of green roofs using mixed-sewage-sludge substrate in Chengdu World Modern Garden City

Green roofs which use sewage sludge to sequestrate urban carbon dioxide may represent a potential opportunity to evaluate carbon sequestration benefits for the urban development under increasing global climate change. In this study, green roofs composed of 6 small green segments with two different substrates, mixed-sewage-sludge substrate (MSSS, volume ratio of sewage sludge and local-natural soil 1:1), and local-natural soil (LNS), three different substrate depths (20 cm, 25 cm and 30 cm), and three types of native plants (Ligustrum vicaryi, Neottia auriculata, and Liriope spicata) in Chengdu City were established to determine carbon sequestration from July 2012 to July 2013 through assessment of the carbon storage and sequestration. Results show that the average carbon storage of MSSS and LNS on green roofs was respectively 13.15 kg C m⁻² and 8.58 kg C m⁻², and the average carbon sequestration followed the order of LNS (3.89 kg C m⁻² yr⁻¹) > MSSS (3.81 kg C m⁻² yr⁻¹). Thus MSSS could be considered as a potential material for carbon sequestration. The carbon storage and carbon sequestration by native plants on the green roofs followed the order of L. vicaryi > L. spicata > N. auriculata. The whole green roof had a mean carbon storage of 18.28 kg C m⁻² and average carbon sequestration of 6.47 kg C m⁻² yr⁻¹ in the combined biomass and substrate organic matter. The best green roof configuration was L. vicaryi together with MSSS substrate, with a middle-high level of carbon sequestration. It will be feasible and worthwhile to scale-up the adaptable green roof configurations in Chengdu World Modern Garden City.     

Ecosystem functions as indicators for heathland responses to nitrogen fertilisation

Anthropogenic deposition of reactive nitrogen (N) has increased during the 20th century, and is considered an important driver of shifts in ecosystem functions and biodiversity loss. The objective of the present study was to identify those ecosystem functions that best evidence a target ecosystem’s sensitivity to N deposition, taking coastal heathlands as an example. We conducted a three-year field experiment in heathlands of the island Fehmarn (Baltic Sea, North Germany), which currently are subject to a background deposition of 9 kg N ha⁻¹ yr⁻¹. We experimentally applied six levels of N fertilisation (application of 0, 2.5, 5, 10, 20, and 50 kg N ha⁻¹ yr⁻¹), and quantified the growth responses of different plant species of different life forms (dwarf shrubs, graminoids, bryophytes, lichens) as well as shifts in the C:N ratios of plant tissue and humus horizons. For an applicability of the experimental findings (in terms of heathland management and critical load assessment) fertilisation effects on response variables were visualised by calculating the treatment ‘effect sizes’. The current year’s shoot increment of the dominant dwarf shrub Calluna vulgaris proved to be the most sensitive indicator to N fertilisation. Shoot increment significantly responded to additions of ≥ 5 kg N ha⁻¹ yr⁻¹ already in the first year, whereas flower formation of Calluna vulgaris increased only in the high-N treatments. Similarly, tissue C:N ratios of vascular plants (Calluna vulgaris and the graminoids Carex arenaria and Festuca ovina agg.) only decreased in the highest N treatments (50 and 20 kg N ha⁻¹ yr⁻¹, respectively). In contrast, tissue C:N ratios of cryptogams responded more quickly and sensitively than vascular plants. For example, Cladonia spp. tissue C:N ratios responded to N additions ≥ 5 kg N ha⁻¹ yr⁻¹ in the second study year. After three years we observed an increase in cover of graminoids and a corresponding decrease of cryptogams at N fertilisation rates of ≥ 10 kg N ha⁻¹ yr⁻¹. Soil C:N ratios proved to be an inappropriate indicator for N fertilisation at least within our three-year study period. Although current critical N loads for heathlands (10−20 kg N ha⁻¹ yr⁻¹) were confirmed in our experiment, the immediate and highly sensitive response of the current year’s shoots of Calluna vulgaris suggests that at least some ecosystem functions (e.g. dwarf shrub growth) also might respond to low (i.e. < 10 kg N ha⁻¹ yr⁻¹) but chronic inputs of N.     

Relationship between microbial activity and microbial community structure in six full-scale anaerobic digesters

High activity levels and balanced anaerobic microbial communities are necessary to attain proper anaerobic digestion performance. Therefore, this work was focused on the kinetic performance and the microbial community structure of six full-scale anaerobic digesters and one lab-scale co-digester. Hydrolytic (0.6–3.5 g COD g^?1 VSS d^?1) and methanogenic (0.01–0.84 g COD g^?1 VSS d^?1) activities depended on the type of biomass, whereas no significant differences were observed among the acidogenic activities (1.5–2.2 g COD g^?1 VSS d^?1). In most cases, the higher the hydrolytic and the methanogenic activity, the higher the Bacteroidetes and Archaea percentages, respectively, in the biomasses. Hydrogenotrophic methanogenic activity was always higher than acetoclastic methanogenic activity, and the highest values were achieved in those biomasses with lower percentages of Methanosaeta. In sum, the combination of molecular tools with activity tests seems to be essential for a better characterization of anaerobic biomasses.     

Treatment of high-strength wastewater in tropical constructed wetlands planted with Sesbania sesban: Horizontal subsurface flow versus vertical downflow

Treatment of various types of wastewaters is an urgent problem in densely populated areas of many tropical countries. We studied the potential of using Sesbania sesban, an N₂-fixing shrub, in constructed wetland systems for the treatment of high-strength wastewater. A replicated horizontal subsurface flow system and a saturated vertical downflow system was established with planted and unplanted beds to assess the effects of system design and presence of plants on treatment performance. The systems were loaded with a mixture of domestic and pig farm wastewater at three hydraulic loading rates of 80, 160 and 320 mm d^?1. The S. sesban plants grew very well in the constructed wetland systems and produced 17.2–20.2 kg dry matter m^?2 year^?1 with a high nitrogen content. Mass removal rates and removal rate constants increased with loading rate, but at 320 mm d^?1 the effluent quality was unacceptable and hydraulic problems appeared. Mass removal rates and removal rate constants were much higher than reported in other studies probably because of the high-strength wastewater, the high loading rates and the tropical conditions. Planted systems removed pollutants much more efficiently than the unplanted controls. Direct plant uptake constituted only up to 8% of the total-N removal and 2% of the P removal at the lowest loading rate, and was quantitatively of low importance compared to other removal processes. The significant effects of plants were therefore related more to their indirect effects on the removal processes. This study for the first time documents that S. sesban can be used in constructed wetland systems for the treatment of polluted water while at the same time producing a valuable N rich biomass that can be used for animal fodder or soil amendment.     

Responses to climate change in radial growth of Picea schrenkiana along elevations of the eastern Tianshan Mountains,northwest China

Tree growth is largely driven by climate conditions in arid and alpine areas. A strong change in climate from warm-dry to warm-wet has already been observed in northwest China. However, little is known about the impacts of regional climate variability on the radial growth of trees along elevations of the eastern Tianshan Mountains. Consequently, we developed three tree-ring width chronologies of Schrenk spruce (Picea schrenkiana Fisch. et Mey.) ranging in elevation from 2159 to 2552 m above sea level (a.s.l.), which play an important role in the forestry ecosystem, agriculture, and local economy of Central Asia. In our study, the correlation analyses of growth-drought using the monthly standardized precipitation-evapotranspiration index (SPEI) at different temporal scales demonstrated that drought in growing season was the main factor limiting tree growth, regardless of elevation. The relationships between radial growth of Schrenk spruce and main climate factors were relatively stable by moving correlation function, and the trend of STD chronologies and basal area increment (BAI) also showed a synchronous decline across the three elevations in recent decades. And meanwhile, slight differences in responses to climate change in radial growth along elevations were examined. The drought stress increased as elevations decreased. Radial growth at the higher elevation depended on moisture availability due to high temperature, as indicated by the significant negative correlation with mean temperature in the late growing season of the previous year (August-September, p < 0.001). However, radial growth at the lower elevation were restricted by drought stress due to less precipitation and higher temperatures, as demonstrated by the significant negative correlation with mean temperature but positive with total precipitation in the early growing season of the current year (April-May, p < 0.05). In addition, the decline of radial growth (BAI) at the higher elevation (3.710 cm² yr⁻¹/decade, p < 0.001) was faster than that of the middle elevation (2.344 cm² yr⁻¹/decade, p < 0.001) and the lower elevation (3.005 cm² yr⁻¹/decade, p < 0.001) since 2000, indicating that the trees at higher elevation of a relatively humid environment were more susceptible to the effects of climate change due to their poor adaptability to water deficit. Therefore, the forest ecosystems would be suppressed as a result of increasing drought stress in the future, especially in the high-elevation forests of arid and semi-arid areas.     

Management scenario evaluation for a large treatment wetland using a spatio-temporal phosphorus transport and cycling model

This paper describes the development of a two-dimensional, spatially distributed model to simulate coupled hydrologic and phosphorus (P) biogeochemical processes in a 147-ha cell of a 1544-ha stormwater treatment wetland designed to help protect the greater Everglades, FL, USA. The model was used to assess the effects of a suite of feasible management alternatives on the long-term ability of the wetland to sustain total P (TP) removal. The spatial and temporal dynamics of TP retention were simulated under historical (1995–2000) conditions, and under assumptions of removal of short-circuiting channels and ditches, changes in external hydraulic and TP loading, and long-term (>20 years) impacts on soil and water column TP dynamics under current and reduced load conditions. Internal hydrology and transport processes were calibrated against measured tracer concentrations, and subsequently validated against outflow discharge and spatial chloride concentration data. Cycling of P was simulated as first-order uptake and release, with different uptake coefficients for open water/sparse submerged aquatic vegetation (SAV) areas (0.2 day^?1) and dense SAV areas (0.4 day^?1), and a much lower, uniform release coefficient (1.97 × 10^?4 day^?1). The calibration and validation of the P model showed good agreement with field measurements of water column TP concentrations measured at the wetland outlet (calibration RMSE = 10.5 μg L^?1; validation RMSE = 15.6 μg L^?1). Under simulated conditions of preferential channels eliminated, average annual TP treatment effectiveness increased by 25%. When inflow TP loads were assumed to be eliminated after 6 years of loading, the release of accumulated soil P sustained predicted annual average outlet concentrations above 6.7 μg L^?1 for 18 years, decreasing at a rate of 0.16 μg L^?1 yr^?1. Sensitivity analyses indicate that the most critical model input factors include flow resistance parameters, initial soil TP content, and P cycling parameters compared to initial water level, initial TP concentration in water column, ET and transport parameters.     

Grazing-induced morphological and growth rate changes in Anarthrophyllum rigidum,a Patagonian leguminous shrub

Grazing influences the morphology and growth rate of shrubs, and consequently, their population dynamics. It has been shown that grazing directly affects the growth of shrubs. On the other hand, the reduction of grass biomass by herbivores reduces soil–water competition between grasses and shrubs, and indirectly, could enhance the growth of shrubs. However, the assessment of the long-term effects of grazing on the growth of shrubs in the arid Patagonia has been hampered by the lack of long and homogeneous records of plant population dynamics and primary production. In this study, we combined growth-ring and allometric analyses to assess the long-term effect of grazing on individuals of Anarthrophyllum rigidum, a leguminous shrub widely distributed across the Patagonian steppe. A. rigidum has evergreen leaves rich in proteins that constitute an important complement to the diet of sheep, particularly in winter when the abundance of grasses is reduced. Our observations indicate that individuals of A. rigidum nearby the water source used by livestock were smaller in size (35.5 cm vs. 67.39 cm), presented a larger number of basal branches (23 vs. 12), and showed slower rates of growth (8.2 mm year^?1 vs. 14.3 mm year^?1) than individuals located far from the water source. This first quantification of the long-term effects of grazing on A. rigidum in the dry Patagonian steppe suggests that beneficial effects of grazing through the reduction of grasses that compete with shrubs for soil–water should be more obvious for livestock non-preferred than preferred shrubs