四川省草地生态系统破坏损失价值评估

本文建立了四川省草地生态系统服务价值评价指标体系,初步估算其年度服务价值,并通过确定人为破坏率来评估四川省草地生态系统破坏损失价值。结果表明,目前,四川省由于人为破坏造成草地生态破坏损失达到370.55亿元,占2010年全省地区GDP的2.16%,其中,水土保持贡献率最大,达到34.52%。过度放牧是造成四川省草地生态系统破坏的重要原因。     

Developing an Environmental Indicator System for Sustainable Development in China: Two Case Studies of Selected Indicators

Environmental indicator systems are a fundamental tool in quantifying the environmental component of sustainable development. They are useful because they quantify the status and trends of key environmental parameters and provide information on the environment that allows authorities and communities to make informed decisions. This article analyzes the basic framework for Chinese environmental indicator systems and presents a “core” set of environmental indicators. In our research, we used a theme approach to develop the environmental indicator systems. We performed two case studies of selected indicators. In the first, we used an urban ambient air pollution composite index and an urban ambient air pollution indicator for three main pollutants to examine trends in urban air pollution in China from 1990 to 2000 at regional and national levels. The results indicate that China has made some progress towards controlling urban air pollution, but must do more in order to reach acceptable pollution levels. We think that an aggregated index and disaggregated indicators have important complementary roles in the policy-making processes. In the second case study, we developed and constructed a grassland degradation index that aggregates information on the extent and severity of grassland degradation. Taking the Xilinhaote region of Inner Mongolia as the study area, we calculated this index by combining remote-sensing data, a geographical information system (GIS), and field investigation. Based on these results, we provide recommendations regarding further development and measurement of environmental indicators in China.     

Patterns of bird abundance along the agricultural gradient of the Pampean region

Bird and land-use surveys were conducted along the agricultural gradient covering from pure croplands through mixed-farming to pure pastoral-farming scenario in the Pampean region of Argentina. Simple regression analyses were performed to analyse the responses of bird abundance to the percentage of land devoted to crop-production. The specific variables associated to bird abundance within both the crop and pastoral-farming landscapes were identified by running redundancy analyses (RDA). The abundance of 20 out of 43 species (47%) was significantly related to the percentage of cropland, finding negative (65%), positive (25%) unimodal (5%) and bimodal (5%) responses of birds to increasing intensity of crop production. The results showed three types of negative and two types of positive responses of bird abundance to the agricultural gradient. RDA revealed the importance of crop-field types in the crop-production scenario and of cattle presence and grass height in the pastoral-farming scenario for the structuring of the grassland bird community. As most species were negatively affected by crop production, the current land-use homogenisation towards high-intensity croplands will most likely result in population decline of many birds in the region.     

试论四川省草地资源开发利用与可持续发展

四川省草地资源丰富,是我国五大牧区之一。本文从可持续发展理论对草地资源开发利用的指导作用、草地资源在开发利用中存在的主要问题以及如何实现草地资源开发利用的可持续发展进行了探讨     

Factors affecting nitrate distribution in shallow groundwater under a beef farm in South Eastern Ireland

Groundwater contamination was characterised using a methodology which combines shallow groundwater geochemistry data from 17 piezometers over a 2 yr period in a statistical framework and hydrogeological techniques. Nitrate–N (NO₃-N) contaminant mass flux was calculated across three control planes (rows of piezometers) in six isolated plots. Results showed natural attenuation occurs on site although the method does not directly differentiate between dilution and denitrification. It was further investigated whether NO₃-N concentration in shallow groundwater (<5 m below ground level) generated from an agricultural point source on a 4.2 ha site on a beef farm in SE Ireland could be predicted from saturated hydraulic conductivity (K_sat) measurements, ground elevation (m Above Ordnance Datum), elevation of groundwater sampling (screen opening interval) (m AOD) and distance from a dirty water point pollution source. Tobit regression, using a background concentration threshold of 2.6 mg NO₃-N L⁻¹ showed, when assessed individually in a step wise procedure, K_sat was significantly related to groundwater NO₃-N concentration. Distance of the point dirty water pollution source becomes significant when included with K_sat in the model. The model relationships show areas with higher K_sat values have less time for denitrification to occur, whereas lower K_sat values allow denitrification to occur. Areas with higher permeability transport greater NO₃-N fluxes to ground and surface waters. When the distribution of Cl⁻ was examined by the model, K_sat and ground elevation had the most explanatory power but K_sat was not significant pointing to dilution having an effect. Areas with low NO₃ concentration and unaffected Cl⁻ concentration points to denitrification, low NO₃ concentration and low Cl⁻ chloride concentration points to dilution and combining these findings allows areas of denitrification and dilution to be inferred. The effect of denitrification is further supported as mean groundwater NO₃-N was significantly (P < 0.05) related to groundwater N₂/Ar ratio, redox potential (Eh), dissolved O₂ and N₂ and was close to being significant with N₂O (P = 0.08). Calculating contaminant mass flux across more than one control plane is a useful tool to monitor natural attenuation. This tool allows the identification of hot spot areas where intervention other than natural attenuation may be needed to protect receptors.     

Effect of diet manipulation in dairy cow N balance and nitrogen oxides emissions from grasslands in northern Spain

Dietary modifications in dairy cattle have been reported as a useful strategy to alter the composition of manure. Many reports have been published on how changes in dietary crude protein content and forage-to-concentrate ratio reduces animal nitrogen (N) excretion, but little information exists about the effect of diet modification on nitrous oxide (N₂O) and nitric oxide (NO) emission when the subsequent slurry is applied on grassland. Two diets differing in forage:concentrate ratio (high forage or HF diet, 75:25; low forage or LF diet, 55:45) were tested to detect the improvement of N use efficiency in milk and the reduction of urinary and fecal N excretion. Triticale silage and barley grain were used as the main forage and concentrate sources in the diets. The subsequent slurries were characterized for N and ammonium-N content (NH₄⁺-N) and applied on grassland in order to study total and pattern of emission of N₂O and NO.The HF diet reduced the voluntary dry matter intake of the cows, N intake and urinary and fecal N excretion. However, the reduction of N intake did not improve the N use efficiency in milk (NUE) (21.0%) and did not reduce N excretion per unit of milk produced (15 g N l⁻¹) due to the lower milk yield. Slurries were similar in N content but differed in NH₄⁺ content, being lower in HF. Therefore, different slurry amounts were needed to be applied on grassland to reach the correct fertilisation rate (120 kg NH₄⁺-N ha⁻¹). Total emissions of N₂O (5.8 and 5.0 kg N₂O-N ha⁻¹) and NO (507.2 and 568.6 g NO-N ha⁻¹), and the pattern of emissions were not affected by dietary treatments. When fertilisation management depends on the collected volume to empty the slurry pit, higher N₂O and NO emissions per kg of slurry could be expected from LF slurry. Nevertheless, if slurry is applied following recommendation rates, N₂O and NO emission per unit of milk produced might be slightly lower from LF slurry. Grass yield (1.5 t dry matter ha⁻¹) and N uptake (50 kg N ha⁻¹) did not vary due to the applications of different slurries, and was attributed to low rainfalls. The correct management of the slurries on grasslands may justify an adequate nutritional strategy of dairy herds from an environmental and productive point of view.     

生态空间定量识别及时空演变特征分析——以呼伦贝尔市为例

生态空间作为国土空间的重要组成部分,是人类生产和生活的基础。以内蒙古呼伦贝尔市为例,系统构建了综合生态空间重要性指数评价指标体系,进行生态空间的定量识别研究。并在此基础之上,对生态空间的动态演变特征进行分析,找寻研究区生态空间的时空分异规律。研究表明：（1）研究区生态空间重要性指数整体偏高,研究期间核心型和重要型生态空间占总面积的比例始终处于50%水平之上,且呈现逐渐上升的趋势。（2）研究区生态空间的综合活跃程度经历了一个逐渐变大的过程,其中2015—2018年生态空间的综合活跃程度尤为强烈。（3）核心型、重要型和非关键型生态空间的稳定性较好,并且各类生态空间都主要向着重要性指数较高的生态空间类型进行转换。（4）生态空间重要性变化具有明显的空间异质性,研究期间重要性持续处于较高水平的生态空间主要分布在中部大兴安岭林区和核心水体区,而重要性持续处于较低水平的生态空间主要分布在西部牧区和东部农区。     

Biodiversity of the ground-dwelling spider fauna of afforestation habitats

The aim of this study was to assess spider diversity among habitats that are typically used for afforestation in Ireland, and to identify habitat parameters which could potentially be used as indicators of their biodiversity value. Ground-dwelling spiders were surveyed in 24 sites across Ireland, with eight sites of each of the following habitat types: improved grassland, wet grassland and peatland. The spiders were sampled using pitfall traps which were located within the major vegetation types present in each site as well as within supplementary habitat features which may add to biodiversity value of the whole site such as hedgerows, flushes and the edges of ditches and streams.Each habitat supported distinct spider assemblages that reflect major differences in both environmental conditions and management regime. The improved grasslands had low spider species richness and low variation in assemblage structure which is probably related to the intensive management of this habitat. In this case hedgerows maybe an important aspect of the spider diversity within agricultural landscapes. The peatlands, and to a lesser extent wet grasslands, supported a diverse and specialist spider fauna, including a number of rare species; this may be due to differences in soil moisture and plant architecture. Indicators of biodiversity value identified included wet flushes in the peatlands and low grazing pressure in the wet grasslands. This study suggests that in terms of biodiversity value improved grassland is the preferable habitat for afforestation, because of the poor baseline spider diversity. However, it may be unrealistic to expect land owners to afforest their most productive agricultural land, so the management and habitat indicators identified in this study may be of use for assessing habitat quality among the wet grassland and peatlands to allow sites with lower biodiversity value to be identified.     

High fluxes but different patterns of nitrous oxide and carbon dioxide emissions from soil in a cattle overwintering area

Cattle overwintering areas common in central Europe may represent significant point sources of the important greenhouse gases, nitrous oxide (N₂O) and carbon dioxide (CO₂). A 2-year field study was carried out in order to estimate the emissions of N₂O and CO₂ from soil in a cattle overwintering area located in the southwest of the Czech Republic. The measurements were performed at three sampling locations along a gradient of animal impact (severe, moderate, slight) to test the hypothesis that emissions of CO₂ and N₂O are positively related to the degree of impact. In addition to CO₂ and N₂O fluxes determined by using non-vented manual closed chambers, soil mineral nitrogen (NH₄⁺ and NO₃⁻), pH and temperature were determined to assess their regulatory role and impact on gas fluxes. The overwintering area was about 4 ha and it had been used for overwintering of about 90 cows since 1995. Deposition of animal excreta resulted in a significant accumulation of nitrogen in the soil during winter, but most of the N₂O was emitted during a few short periods in spring and/or in late autumn. Maximum N₂O fluxes of up to 2.5 mg N₂O-N m⁻² h⁻¹ were recorded at the most impacted location near the animal house, where the highest concentrations of soil mineral nitrogen also occurred. The emissions of CO₂ showed a completely different pattern to those of N₂O, being correlated with soil temperature; the highest emissions thus occurred in June–July, while very low fluxes were found in winter. Emission values ranged from about 0 to 700 mg C-CO₂ m⁻² h⁻¹. Furthermore, the effect of animal impact on CO₂ emissions was opposite to that on N₂O fluxes, as the highest CO₂ fluxes were mostly recorded at the least impacted location, where respiration of plants most likely increased overall CO₂ production. The results show that cattle overwintering areas are important sources of greenhouse gases, including N₂O and CO₂. Fluxes of these two gases are, however, differently distributed over the year, which also suggests that they are controlled by different environmental and soil factors.     

Grass feedbacks on fire stabilize savannas

Savannas commonly consist of a discontinuous cover of overstory trees and a groundcover of grasses. Savanna models have previously demonstrated that vegetation feedbacks on fire frequency can limit the density of overstory trees, thereby maintaining savannas. Positive feedbacks of either savanna trees alone or trees and grasses together on fire frequency have been shown to result in a stable savanna equilibrium. Grass feedbacks on fire frequency, in contrast, have resulted in stable equilibria in either a grassland or forest state, but not in a savanna. These results, however, were derived from a system of differential equations that assumes that fire occurrence is strictly deterministic and that vegetation losses due to fire are continuous in time. We develop an alternative formulation of the grass-fire feedback model that assumes that fires are discrete and occur stochastically in time to examine the influence of these assumptions on the predicted state of the system. We show that incorporating fire as a discrete event can produce a recurring temporal refuge in which both grass and trees co-occur in a stable, bounded savanna. In our model, tree abundance is limited without invoking demographic bottlenecks in the transition from fire-sensitive to fire-resistant life history stages. An increasing strength of grass feedback on fire results in regular, predictable fires, which suggests that the system can also be modeled using a set of difference equations. We implement this discrete system using modified Leslie/Gower difference equations and demonstrate the existence of a bounded savanna state in this model framework. Our results confirm the potential for grass feedbacks to result in stable savannas, and indicate the importance of modeling fire as a discrete event rather than as a loss rate that is continuous in time.