The effect of water table depth on emissions of N2O from a grassland soil

Nitrous oxide (N₂O) emissions were measured by the closed chamber technique from five plots along a transect in a nitrogen‐fertilised grassland, together with soil water content, soil temperature and water table depth, to investigate the effect of water table depth on N₂O emissions. N₂O fluxes varied from <1 g N₂O‐N ha^?1 day^?1 to peaks of around 500–1200 g N₂O‐N ha^?1 day^?1 after N fertiliser applications. There was no significant difference in overall average water table depth between four of the five plots, but significant short‐term temporal variations in water table depth did occur. Rises in the water table were accompanied by exponential increases in N₂O emissions, through the associated increases in the water‐filled pore space of the topsoil. Modelling predicted that if the water table could be managed such that it was kept to no less than 35 cm below the ground surface, fluxes during the growing season would be reduced by 50%, while lowering to 45 cm would reduce them by over 80%. The strong implication of these results is that draining grasslands, so that the water tables are only rarely nearer to the surface than 35 cm when N is available for denitrification, would substantially reduce N₂O emissions.     

Nitrous Oxide Emissions from Newly Created Littoral Marshes in the Drawdown Area of the Three Gorges Reservoir, China

This study aimed to understand the seasonal and spatial variations of N₂O emissions from newly created littoral marshes in the drawdown area of the Three Gorges Reservoir (TGR), China. We measured N₂O emissions at 10-day intervals during the growing season (early July to late September) in 2008. N₂O emissions were measured with static chambers in four typical vegetation stands. The results showed great spatial variations of N₂O emissions among the four stands. The greatest N₂O emissions (0.052?±?0.063 mg N₂O m^?2?h^?1) were from Scirpus triqueter stand, while the lowest N₂O emissions (0.020?±?0.020 mg N₂O m^?2?h^?1) were from Typha angustifolia stand. To such spatial variations in N₂O emissions, standing water depths and soil water content may be important explaining factors. Besides spatial variations, we also found significant temporal variations of N₂O emissions in this area. The temporal variation of N₂O emissions in the growing season was not found significantly related to any measured factor in the study. However, based on principal component analysis, we consider it partly caused by thermal conditions and the marked temporal variation of the standing water depth in the growing season, which to some degree influenced the process of denitrification and N₂O emissions. These results about TGR enable us to make a more reasonable estimate of N₂O emissions from large dam reservoirs, particularly those with a large drawdown area in the growing season in an agricultural landscape.     

Influence of nitrogen fertilization on soil ammonia oxidizer and denitrifier abundance,microbial biomass,and enzyme activities in an alpine meadow

Terrestrial ecosystems are predicted to experience an increasing level of atmospheric nitrogen (N) deposition, which may cause significant shifts in plant community composition and concomitantly stimulate soil acidification. However, little is known concerning the effects of N deposition on belowground microbial communities in alpine grassland ecosystems such as on the Tibetan Plateau. This study examined the responses of soil N-transforming microbes (measured after DNA extraction and quantitative PCR), soil microbial biomass C (SMBC) and N (SMBN), and soil enzyme activities to different forms (NH₄ ⁺-N, NO₃ ^?-N, and NH₄NO₃-N) and rates (1.5 and 7.5 g N m^?2 year^?1, denoted as low and high N, respectively) of N fertilization (addition) in two successive plant growing seasons. The N rate, not N form, influenced the abundance of ammonia-oxidizing archaea (AOA). High N addition significantly increased ammonia-oxidizing bacteria (AOB) abundance which differed across different N form treatments. Nitrogen addition had no significant impact on the abundance of soil denitrifiers. The SMBC and SMBN were significantly decreased by high N additions, but no difference was found among different N forms. Despite higher urease activities being detected in the late plant growing season, the activities of invertase and alkaline phosphomonoesterase stayed unchanged irrespective of the different N amendments and plant growing season. Significant positive correlations were found between potential nitrification rates and AOB abundances. These results highlight that AOB seemed to respond more sensitively to different N fertilization and might have prominent roles in soil N cycling processes in this Tibetan Plateau alpine meadow than AOA.     

Functional dependencies of soil CO2 emissions on soil biological properties in northern German agricultural soils derived from a glacial till

Agricultural soil CO₂ emissions and their controlling factors have recently received increased attention because of the high potential of carbon sequestration and their importance in soil fertility. Several parameters of soil structure, chemistry, and microbiology were monitored along with soil CO₂ emissions in research conducted in soils derived from a glacial till. The investigation was carried out during the 2012 growing season in Northern Germany. Higher potentials of soil CO₂ emissions were found in grassland (20.40 µg g^?1 dry weight h^?1) compared to arable land (5.59 µg g^?1 dry weight h^?1) within the incubating temperature from 5°C to 40°C and incubating moisture from 30% to 70% water holding capacity (WHC) of soils taken during the growing season. For agricultural soils regardless of pasture and arable management, we suggested nine key factors that influence changes in soil CO₂ emissions including soil temperature, metabolic quotient, bulk density, WHC, percentage of silt, bacterial biomass, pH, soil organic carbon, and hot water soluble carbon (glucose equivalent) based on principal component analysis and hierarchical cluster analysis. Slightly different key factors were proposed concerning individual land use types, however, the most important factors for soil CO₂ emissions of agricultural soils in Northern Germany were proved to be metabolic quotient and soil temperature. Our results are valuable in providing key influencing factors for soil CO₂ emission changes in grassland and arable land with respect to soil respiration, physical status, nutrition supply, and microbe-related parameters.     

Factors Affecting the Growth of Microalgae on Blackwater from Biosolid Dewatering

This paper discusses the possibility of including the culturing of microalgae within a conventional wastewater treatment sequence by growing them on the blackwater (BW) from biosolid dewatering to produce biomass to feed the anaerobic digester. Two photobioreactors were used: a 12 L plexiglas column for indoor, lab-scale tests and a 85 L plexiglas column for outdoor culturing. Microalgae (Chlorella sp. and Scenedesmus sp.) could easily grow on the tested blackwater. The average specific growth rate in indoor and outdoor batch tests was satisfactory, ranging between 0.14 and 0.16 day^?1. During a continuous test performed under outdoor conditions from May to November, in which the off-gas from the combined heat and power unit was used as the CO₂ source, an average biomass production of 50 mgTSS L^?1 day^?1 was obtained. However, statistical analyses confirmed that microalgal growth was affected by environmental conditions (temperature and season) and that it was negatively correlated with the occurrence of nitrification. Finally, the biochemical methane potential of the algal biomass was slightly higher than that from waste sludge (208 mLCH₄ gVS^?1 vs. 190 mLCH₄ gVS^?1).     

Seasonal Biomass Accumulation and Nutrient Uptake of Pea and Lentil on a Black Chernozem Soil in Saskatchewan

ABSTRACT

Close relationships usually exist among biomass accumulation, nutrient uptake, and seed yield during the growing season. Field experiments with pea (Pisum sativum L.) and lentil (Lens cultinaris L.) were conducted in 1998 and 1999 at Melfort, Saskatchewan, Canada, to determine relationships of biomass accumulation and nutrient uptake with days after emergence (DAE) or growing degree days (GDD). For both biomass accumulation and nutrient uptake, maximum rates and amounts increased with time at early growth stages and reached a maximum value at late growth stages. The R² values for cubic polynomial regressions were highly significant, indicating their suitability to estimate the progression of biomass accumulation and nutrient uptake as a function of days after emergence (DAE). Both pulse crops followed a similar pattern in biomass accumulation and nutrient uptake, which increased in the early growth stages and reached a maximum late in the growth cycle. Pulse crops usually reached their maximum biomass accumulation rate and amount at early to late bud formation (42–56 DAE or 390–577 GDD) and at medium pod formation to early seed filling (75–82 DAE or 848–858 GDD) growth stages, respectively. Maximum biomass accumulation rate was 175–215 kg ha^{? 1}d^?1 for pea and 109–140 kg ha^{? 1}d^{? 1} for lentil. Maximum nutrient uptake rate and amount usually occurred at branching to early bud formation (28–49 DAE or 206–498 GDD) and at the flowering to seed filling (66–85 DAE or 672–986 GDD) growth stages, respectively. Maximum uptake rate of nitrogen (N), phosphorus (P), potassium (K), and sulfur (S), respectively, was 4.6–4.9, 0.4–0.5, 5.0–5.3 and 0.3 kg ha^{? 1}d^{? 1} for pea, and 2.4–3.8, 0.2–0.3, 2.0–3.4 and 0.2 kg ha^{? 1}d^{? 1} for lentil. In general, maximum nutrient uptake rate and amount occurred earlier than maximum biomass accumulation rate and amount, respectively; and the maximum accumulation rates of both biomass and nutrients occurred earlier than maximum amounts. The findings suggest that adequate supply of nutrients from soil and fertilizers at early growth stages, and translocation of biomass and nutrients to seed at later growth stages are of great importance for high seed yield of pulse crops.     

Denitrification loss from a grassland soil in the field receiving different rates of nitrogen as ammonium nitrate

Denitrification loss from a loam under a cut ryegrass sward receiving 0, 250 and 500 kg N ha^?1 a^?1 in four equal amounts was measured during 14 months using the acetylene-inhibition technique. The rate of denitrification responded rapidly to changes in soil water content as affected by rain. Mean rates of denitrification exceeded 0.2 kg N ha^?1 day^?1 only when the soil water content was >20% (w/w) and nitrate was >5μ N g^?1 in the upper 20 cm of the profile and when soil temperature at 2 cm was >5–8°C. When the soil dried to a water content <20%, denitrification decreased to <0.05 kg N ha^?1 day^?1. Highest rates (up to 2.0 kg N ha^?1 day^?1) were observed following application of fertilizer to soil at a water content of about 30% (w/w) in early spring. Denitrification in the control plot during this period was generally about a hundredth of that in plots treated with ammonium nitrate. High rates of N₂O loss (up to 0.30 kg N ha^?1 day-1) were invariably associated with high rates of denitrification (> 0.2 kg N ha^?1 day^?1). However, within 2–3 weeks following application of fertilizer to the plot receiving 250 kg N ha^?1 a^?1 the soil acted as a sink for atmospheric N₂O when its water content was >20% and its temperature >5–8°C. Annual N losses arising from denitrification were 1.6, 11.1 and 29.1 kg N ha^?1 for the plots receiving 0, 250 and 500 kg N ha^?1 a^?1, respectively. More than 60% of the annual loss occurred during a period of 8 weeks when fertilizer was applied to soil with a water content >20%.     

Seasonal Biomass Accumulation and Nutrient Uptake of Canola,Mustard, and Flax on a Black Chernozem Soil in Saskatchewan

ABSTRACT

Seed yield and nutrient use efficiency are related to biomass accumulation and nutrient uptake in the growing season. Biomass accumulation and nutrient uptake of canola (Brassica napus L. and Brassica rapa L.), mustard (Brassica juncea L.) and flax (Linum usitatissimum L.) and the relationship to days after emergence (DAE) or growing degree days (GDD) were determined during the 1998 and 1999 growing seasons in field experiments at Melfort, Saskatchewan, Canada. In general, biomass accumulation and nutrient uptake increased with time at early growth stages and reached a maximum at late growth stages. Significant R² values for both biomass accumulation and nutrient uptake indicated that a cubic polynomial type equation was suitable to represent these parameters as a function of DAE. All oilseed crops maximized biomass at mid way to the end of pod forming stages (74–84 DAE or 750–973 GDD). Maximum biomass accumulation rate occurred at the early to late bud forming stage (42–49 DAE or 390–498 GDD), and it was 146–190 kg ha^?1d^?1 for canola, 158–182 kg ha^?1d^?1 for mustard, and 174–189 kg ha^?1d^?1 for flax. Maximum nutrient uptake occurred during flowering to early ripening (59–82 DAE or 597–945 GDD). Maximum nutrient uptake rate normally occurred at branching to early bud formation (21–42 DAE or 142–399 GDD). There was a close correlation between biomass accumulation and nutrient uptake, and among nutrients, suggesting interrelated absorption. For nitrogen (N), phosphorus (P), potassium (K), sulfur (S), and boron (B), respectively, maximum nutrient uptake rate was 2.3–4.5, 0.3–0.5, 2.5–5.7, 0.7–1.1, and 0.005–0.008 kg ha^?1d^?1 for canola; 2.3–3.9, 0.4–0.5, 2.6–4.9, 1.2–1.4, and 0.006–0.008 kg ha^?1d^?1 for mustard; and 3.2–4.0, 0.3–0.4, 2.9–4.1, 0.3–0.5, and 0.004–0.009 kg ha^?1d^?1 for flax. In general, maximum nutrient uptake rate and amount occurred earlier than maximum biomass accumulation rate and amount, and maximum rates of both nutrient uptake and biomass accumulation occurred earlier than their maximum amounts. The findings suggest that for high seed yields, there should be adequate supply of nutrients for plants, particularly to sustain high nutrient uptake rate at branching to bud forming stage and high biomass accumulation rate at early to late bud forming stage.     

Full-Scale Experiment on Domestic Wastewater Treatment by Combining Artificial Aeration Vertical- and Horizontal-Flow Constructed Wetlands System

To improve domestic wastewater treatment for total nitrogen (TN) removal, a full-scale constructed wetlands combining an artificially aerated vertical- (AVCW) and a horizontal-flow constructed wetland (HCW) was completed in July 2007. The system covered a total area of 7,610?m². From 2 July 2007 to 7 August 2008, the treatment capacity was 2,076?m³?day^?1 with an aeration quantity of 7,400?m³?day^?1. The system effectively reduced the average annual output of BOD₅ (52.0?%), NH₄?CN (58.41?%), and TP (41.61?%), although the percentage reductions of other pollutants, including chemical oxygen demand (34.1?%), suspended solid (38.9?%), and TN (31.05?%) were lower. The purpose of the HCW was for denitrification of the effluent from the AVCW, and annual average of 34.27?% of NO₃?CN was removed compared with the reading at the AVCW outlet. With hydraulic loading increased to 4,152?m³?day^?1 from 9 September to 23 November 2007, the removal rate for NO₃?CN from the HCW decreased substantially from 48.80 to 18.86?%. The total removal rates of NH₄?CN showed significant positive correlation with DO content in the AVCW and with total TN removal rates for the combined system (P?<?0.05). The study indicated that, even with limited artificial aeration, nitrification was very effective for NH₄?CN removal.     

Ammonia,Nitrous Oxide,Carbon Dioxide and Methane Emissions from Commercial Broiler Houses in Mediterranean Portugal

Limited data are available on ammonia (NH₃), nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) emissions from poultry housing in Mediterranean countries. The aim of the present study was to assess the NH₃, N₂O, CO₂ and CH₄ emission rates from commercial breeding hen and broiler houses under Mediterranean climate conditions. Research was conducted at one commercial breeding hen house and in two commercial broiler houses located in central Portugal. The environmental conditions, gas concentrations and ventilation rates were measured in the cold (8.0?±?2.1 °C) and hot (20.7?±?1.9 °C) season for the breeding hen house, whereas for the two broiler houses, measurements were made during one fattening cycle in the fall (17.3?±?1.7 °C) season. Results showed that the annual average emission rates for breeding hen and broiler houses were 0.52?±?0.27 and 0.06?±?0.01 for NH₃, 0.030?±?0.042 and 0.006?±?0.001 for N₂O, 169.6?±?56.2 and 58.0?±?15.1 for CO₂ and 0.092?±?0.131 and 0.0113?±?0.0002 g day^?1 bird^?1 for CH₄, respectively. The N₂O emission rates observed in breeding hen houses may have been overestimated, being higher than previously reported for Mediterranean countries.     

三江源地区植被覆盖度变化及其与气候因子的关系

为揭示气候变化对三江源地区草地生态系统的影响及适应机制,研究以SPOT-VGT为基础数据,利用像元二分模型估算了三江源地区1998—2012年的植被覆盖度,分析了年最大覆盖度的变异特征,并对植被覆盖度与气候因子之间的响应关系进行了深入探讨。结果表明:在区域尺度上,15 a来研究区生长季植被覆盖度呈极显著增加的趋势（P < 0.01）,平均每年增加0.004。在草地生态系统类型上,高寒草甸植被覆盖度与生长季温度的相关关系更加密切（r=0.802,P < 0.01）;高寒草原植被覆盖度与生长季温度呈显著相关关系（r=0.515,P < 0.05）。与生长季降水量相比较,5—7月降水量对高寒草原植被覆盖度变化的影响更加关键,但在高寒草甸上却不存在这种差异。     

Contribution of dissolved organic nitrogen deposition to nitrogen saturation in a forested mountainous watershed in Tsukui, Central Japan

Nitrogen (N) budget was estimated with dissolved inorganic N (DIN) and dissolved organic N (DON) in a forested mountainous watershed in Tsukui, Kanagawa Prefecture, about 50 km west of Tokyo in Central Japan. The forest vegetation in the watershed was dominant by Konara oak (Quercus serrata) and Korean hornbeam (Carpinus tschonoskii), and Japanese cedar (Cryptomeria japonica). Nitrate (NO₃ ^?) concentration in the watershed streamwater was averagely high (98.0 ±± 19 (±± SD, n = 36) μmol L^?1) during 2001–2003. There was no seasonal and annual changes in the stream NO^? ₃ concentration even though the highest N uptake rate presumably occurred during the spring of plant growing season, a fact indicating that N availability was in excess of biotic demands. The DON deposition rates (DON input rates) in open area and forest area were estimated as one of the main N sources, accounting for about 32% of total dissolved N (TDN). It was estimated that a part of the DON input rate contributed to the excessive stream NO^? ₃ output rate under the condition of the rapid mineralization and nitrification rates, which annual DON deposition rates were positively correlated with the stream NO₃ ^? output rates. The DON retention rate in the DON budget had a potential capacity, which contributed to the excessive stream NO^? ₃ output rate without other N contributions (e.g. forest floor N or soil N).     

Natural disaster in the mountainous region of Rio de Janeiro state,Brazil: Assessment of the daily rainfall erosivity as an early warning index

Rainfall erosivity is defined as the potential of rain to cause erosion. It has great potential for application in studies related to natural disasters, in addition to water erosion. The objectives of this study were: i) to model the R_day using a seasonal model for the Mountainous Region of the State of Rio de Janeiro (MRRJ); ii) to adjust thresholds of the R_day index based on catastrophic events which occurred in the last two decades; and iii) to map the maximum daily rainfall erosivity (R_maxday) to assess the region's susceptibility to rainfall hazards according to the established R_day limits. The fitted R_day model presented a satisfactory result, thereby enabling its application as a R_day estimate in MRRJ. Events that resulted in R_day > 1500 MJ ha^?1.mm.h^?1. day^?1 were those with the highest number of fatalities. The spatial distribution of R_maxday showed that the entire MRRJ has presented values that can cause major rainfall. The R_day index proved to be a promising indicator of rainfall disasters, which is more effective than those normally used that are only based on quantity (mm) and/or intensity (mm.h^?1) of the rain.     

No significant difference in N2O emission,fertilizer-induced N2O emission factor and CH4 absorption between anaerobically digested cattle slurry and chemical fertilizer applied timothy (Phleum pratense L.) sward in central Hokkaido,Japan

Abstract

Nitrous oxide (N₂O) and methane (CH₄) fluxes from a fertilized timothy (Phleum pratense L.) sward on the northern island of Japan were measured over 2?years using a randomized block design in the field. The objectives of the present study were to obtain annual N₂O and CH₄ emission rates and to elucidate the effect of the applied material (control [no nitrogen], anaerobically digested cattle slurry [ADCS] or chemical fertilizer [CF]) and the application season (autumn or spring) on the annual N₂O emission, fertilizer-induced N₂O emission factor (EF) and the annual CH₄ absorption. Ammonium sulfate was applied to the CF plots at the same application rate of NH₄-N to the ADCS plots. A three-way ANOVA was used to examine the significance of the factors (the applied material, the application season and the year). The ANOVA for the annual N₂O emission rates showed a significant effect with regard to the applied material (P?=?0.042). The annual N₂O emission rate from the control plots (0.398?kg N₂O-N ha^?1?year^?1) was significantly lower than that from the ADCS plots (0.708?kg N₂O-N ha^?1?year^?1) and the CF plots (0.636?kg N₂O-N ha^?1?year^?1). There was no significant difference in the annual N₂O emission rate between the ADCS and CF plots. The ANOVA for the EFs showed insignificance of all factors (P?>?0.05). The total mean?±?standard error of the EFs (fertilizer-induced N₂O-N emission/total applied N) was 0.0024?±?0.0007 (kg N₂O-N [kg N]^?1), which is similar to the reported EF (0.0032?±?0.0013) for well-drained uplands in Japan. The CH₄ absorption rates differed significantly between years (P?=?0.014). The CH₄ absorption rate in the first year (3.28?kg CH₄?ha^?1?year^?1) was higher than that in the second year (2.31?kg CH₄?ha^?1?year^?1), probably as a result of lower precipitation in the first year. In conclusion, under the same application rate of NH₄-N, differences in the applied materials (ADCS or CF) and the application season (autumn or spring) led to no significant differences in N₂O emission, fertilizer-induced N₂O EF and CH₄ absorption.     

Seasonal variations in natural 13C abundances in C3 and C4 plants collected in Thailand and the Philippines

Abstract

The natural ¹³C abundance (δ ¹³C) of plant leaves collected from fields in Thailand and the Philippines (Asian Monsoon tropics) was analyzed, and changes in the δ ¹³C values of C₃ and C₄ plants in wet and dry seasons were characterized. In Thailand, the δ ¹³C values of C₃ plants were ?29.2?±?1.04 (mean?±?standard deviation) ‰ in July and August (wet season) and ?28.6?±?1.05‰ in February and March (dry season): these values are not significantly different, whereas the values of C₄ plants were ?12.7?±?0.56‰ in the wet season and ?14.5?±?0.68‰ in the dry season (P?<?0.01, t-test). In the Philippines, where plants were collected only in October (late wet season), the δ ¹³C values of C₃ plants were ?29.5?±?1.28‰, whereas those of C₄ plants were ?12.6?±?1.11‰. These results suggest that under an Asian Monsoon climate, C₄ plants exhibit more negative δ ¹³C values in the dry season than in the wet season, whereas C₃ plants as a whole show no clear seasonal changes in δ ¹³C values.     

Grazing intensity alters soil respiration in an alpine meadow on the Tibetan plateau

Grazing intensity may alter the soil respiration rate in grassland ecosystems. The objectives of our study were to (1) determine the influence of grazing intensity on temporal variations in soil respiration of an alpine meadow on the northeastern Tibetan Plateau; and (2) characterise the temperature response of soil respiration under different grazing intensities. Diurnal and seasonal soil respiration rates were measured for two alpine meadow sites with different grazing intensities. The light grazing (LG) meadow site had a grazing intensity of 2.55 sheep ha⁻¹, while the grazing intensity of the heavy grazing (HG) meadow site, 5.35 sheep ha⁻¹, was approximately twice that of the LG site. Soil respiration measurements showed that CO₂ efflux was almost twice as great at the LG site as at the HG site during the growing season, but the diurnal and seasonal patterns of soil respiration rate were similar for the two sites. Both exhibited the highest annual soil respiration rate in mid-August and the lowest in January. Soil respiration rate was highly dependent on soil temperature. The Q₁₀ value for annual soil respiration was lower for the HG site (2.75) than for the LG site (3.22). Estimates of net ecosystem CO₂ exchange from monthly measurements of biomass and soil respiration revealed that during the period from May 1998 to April 1999, the LG site released 2040 g CO₂ m⁻² y⁻¹ to the atmosphere, which was about one third more than the 1530 g CO₂ m⁻² y⁻¹ released at the HG site. The results suggest that (1) grazing intensity alters not only soil respiration rate, but also the temperature dependence of soil CO₂ efflux; and (2) soil temperature is the major environmental factor controlling the temporal variation of soil respiration rate in the alpine meadow ecosystem.     

Climatic controls and ecosystem responses drive the inter-annual variability of the net ecosystem exchange of an alpine meadow

Seven years of continuous eddy covariance measurements at an alpine meadow were used to investigate the impacts of climate drivers and ecosystem responses on the inter-annual variability (IAV) of the net ecosystem exchange (NEE). The annual cumulative value of NEE was positive (source) in 2003, 2005 and 2009 (50, 15 and 112 g m⁻² respectively) and negative (sink) in 2004, 2006, 2007 and 2008 (29, 75, 110 and 28 g m⁻² respectively). The IAV of carbon dioxide fluxes builds up in two phenological phases: the onset of the growing season (triggered by snow melting) and the canopy re-growth after mowing. Respiratory fluxes during the non-growing season were observed to increase IAV, while growing season uptake dampened it. A novel approach was applied to factor out the two main sources of IAV: climate drivers’ variability and changes in the ecosystem responses to climate. Annual values of carbon dioxide fluxes were calculated assuming (a) variable climate and variable ecosystem response among years, (b) variable climate and constant ecosystem response and (c) constant climate and variable ecosystem response. The analysis of flux variances calculated under these three assumptions indicates the occurrence of an important negative feedback between climate and ecosystem responses. Due to this feedback, the observed IAV of NEE is lower than one would expect for a given climate variability, because of the counteracting changes in ecosystem responses. This alpine meadow therefore demonstrates the ability to acclimatise and to limit the IAV of carbon fluxes induced by climate variability.     

Winter soil CO2 efflux and its contribution to annual soil respiration in different ecosystems of a forest-steppe ecotone, north China

Most soil respiration measurements are conducted during the growing season. In tundra and boreal forest ecosystems, cumulative winter soil CO₂ fluxes are reported to be a significant component of their annual carbon budgets. However, little information on winter soil CO₂ efflux is known from mid-latitude ecosystems. Therefore, comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of ecosystem carbon budgets and the response of soil CO₂ efflux to climate changes. In this study we measured winter soil CO₂ efflux and its contribution to annual soil respiration for seven ecosystems (three forests: Pinus sylvestris var. mongolica plantation, Larix principis-rupprechtii plantation and Betula platyphylla forest; two shrubs: Rosa bella and Malus baccata; and two meadow grasslands) in a forest-steppe ecotone, north China. Overall mean winter and growing season soil CO₂ effluxes were 0.15-0.26 μmol m⁻² s⁻¹ and 2.65-4.61 μmol m⁻² s⁻¹, respectively, with significant differences in the growing season among the different ecosystems. Annual Q₁₀ (increased soil respiration rate per 10 °C increase in temperature) was generally higher than the growing season Q₁₀. Soil water content accounted for 84% of the variations in growing season Q₁₀ and soil temperature range explained 88% of the variation in annual Q₁₀. Soil organic carbon density to 30 cm depth was a good surrogate for SR₁₀ (basal soil respiration at a reference temperature of 10 °C). Annual soil CO₂ efflux ranged from 394.76 g C m⁻² to 973.18 g C m⁻² using observed ecosystem-specific response equations between soil respiration and soil temperature. Estimates ranged from 424.90 g C m⁻² to 784.73 g C m⁻² by interpolating measured soil respiration between sampling dates for every day of the year and then computing the sum to obtain the annual value. The contributions of winter soil CO₂ efflux to annual soil respiration were 3.48-7.30% and 4.92-7.83% using interpolated and modeled methods, respectively. Our results indicate that in mid-latitude ecosystems, soil CO₂ efflux continues throughout the winter and winter soil respiration is an important component of annual CO₂ efflux.     

Metal fluxes at the sediment–water interface in rivers in the Turvo/Grande drainage basin, S?o Paulo State, Brazil

Purpose

The Turvo/Grande drainage basin (TGDB), located in the northwestern region of S?o Paulo state, covers an area of 15,983?km². The region is typically regarded as agricultural by the S?o Paulo State Environmental Agency, but the industrial area is expanding, and some studies have shown that metal concentrations in water can be higher than the values regulated by Brazilian law. Therefore, the aim of this study was to assess the role of sediments as a source or a sink of metals for drainage basin management.

Materials and methods

Interstitial water from different sediment depths (0?C42?cm) and the sediment?Cwater interface and sediment core samples were collected in February and July 2010 from the Preto, Turvo, and Grande rivers. Quantification of Cr, Cu, Fe, Mn, Ni, and Pb in these samples was performed by graphite furnace or flame atomic absorption spectrometry. Metal diffusive flux estimation from sediment into the overlying water was calculated by Fick??s First Law of Diffusion.

Results and discussion

The fluxes of all metals for the three rivers were positive, indicating diffusion into the overlying water. Ni and Pb showed the lowest diffusive fluxes, which ranged from 2.4 to 3,978???g?m^?2?day^?1 for Ni and from ?0.1 to 1,597???g?m^?2?day^?1 for Pb. In turn, Cu and Cr were subject to the largest transfer to water, especially in the dry season (Cr, 4.5?C7,673???g?m^?2?day^?1; Cu, 1.3?C14,145???g?m^?2?day^?1). The Preto River (urban area) showed smaller fluxes than the Grande River (agricultural area), and the values of the latter were higher than those found in other impacted areas of the world.

Conclusions

The diffusive fluxes indicate that sediments from the TGDB act as a source of metals for the water column, with increased export of metals, particularly Cr and Ni, from the sediment into the overlying water during the dry season.     

GREENHOUSE GAS EMISSIONS FROM AN ALKALINE SALINE SOIL CULTIVATED WITH MAIZE (ZEA MAYS L.) AND AMENDED WITH ANAEROBICALLY DIGESTED COW MANURE: A GREENHOUSE EXPERIMENT

Sludge derived from cow manure anaerobically digested to produce biogas (methane; CH₄) was applied to maize (Zea mays L.) cultivated in a nutrient-low, alkaline, saline soil with electrolytic conductivity 9.4 dS m^?1 and pH 9.3. Carbon dioxide (CO₂) emission increased 3.1 times when sludge was applied to soil, 1.6 times when cultivated with maize and 3.5 times in sludge-amended maize cultivated soil compared to the unamended uncultivated soil (1.51 mg C kg^?1 soil day^?1). Nitrous oxide (N₂O) emission from unamended soil was -0.0004 μg nitrogen (N) kg^?1 soil day^?1 and similar from soil cultivated with maize (0.27 μg N kg^?1 soil day^?1). Application of sludge increased the N₂O emission to 4.59 μg N kg^?1 soil day^?1, but cultivating this soil reduced it to 2.42 μg N kg^?1 soil day^?1. It was found that application of anaerobic digested cow manure stimulated maize development in an alkaline saline soil and increased emissions of CO₂ and N₂O.