Grassland Slope Research Articles

水土流失治理措施对小流域土壤有机碳和全氮的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 水土流失治理措施对小流域土壤有机碳和全氮的影响 DOI: 10.5846/stxb201108121182 作者: 作者单位: 西北农林科技大学资源环境学院,陕西杨凌,西北农林科技大学资源环境学院,中科院水利部水土保持与生态研究中心，陕西杨凌,西北农林科技大学资源环境学院,陕西杨凌,西北农林科技大学资源环境学院,陕西杨凌 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助(40771125) Effects of soil erosion control measures on soil organic carbon and total nitrogen in a small watershed Author: Affiliation: College of Resource and Environment,College of Resource and Environment,College of Resource and Environment,College of Resource and Environment Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:明确综合治理条件下小流域土壤有机碳(Soil organic carbon, SOC)和全氮(Total nitrogen, TN) 的空间分布特征及其影响因素,对科学评价水土流失区土壤固碳潜力具有重要意义。以黄土高原丘陵沟壑区典型小流域(砖窑沟流域)为对象,基于流域内3种典型地貌类型(梁峁坡、沟坡、沟谷)和3种典型水土流失治理措施(水平梯田、林地和草地措施,坡耕地为对照),采集土壤样品737个,研究地貌类型和水土流失治理措施对小流域SOC和TN变化的影响。结果表明,同一地貌类型上,水平梯田、林地和草地措施的SOC和TN(0-10 cm土层)含量均显著高于坡耕地(P<0.1)。梁峁坡上,水平梯田、林地和草地措施条件下的 SOC和TN含量较坡耕地依次提高了18%和24%、70%和59%、25%和21%;沟坡上,林地和草地措施的SOC和TN较坡耕地依次提高了76%和54%、25%和27%。同一治理措施在不同地貌类型间对0-10 cm土层SOC和TN的影响存在显著差异(P<0.1)。水平梯田条件下,沟谷的SOC和TN含量比峁坡提高了46%和43%;林地措施条件下,沟坡的SOC和TN含量比峁坡提高了18% 和6%;草地措施条件下,沟坡的SOC和TN含量比峁坡提高了14% 和18%。0-100 cm土层的SOC或TN在不同地貌类型或不同治理措施间的差异与土壤水分含量(Soil moisture, SM)的变化趋势基本一致,并且SOC或TN与SM呈指数关系y= aebx (y为SOC或TN,x为SM)。 Abstract:It is significance of assessing soil organic carbon (SOC) and total nitrogen (TN) sequestration potential to understand dynamics of soil organic carbon (SOC) and total nitrogen (TN) at a small watershed with comprehensive measures in the loess region of China. Based on three topographic positions (Ridge slope, Gully slope, Valley bottom) and three control measures for soil erosion (Level terrace,Woodland measures,Grassland measures), 737 soil samples were collected to investigate effects of topographic positions and soil erosion control measures on soil organic carbon and total nitrogen at Zhuan Yaogou watershed in the hilly region of Loess Plateau. Under the similar topographic positions, SOC and TN (0-10 cm soil layer) in level terrace, woodland and grassland were significantly higher than those in cropland on sloping land (P<0.1). For the ridge slope, SOC and TN in level terrace, woodland and grassland were 18% and 24%, 70% and 59%, and 25% and 21% higher than that in cropland on sloping land, respectively; For the gully slope, SOC and TN in woodland and grassland were 76% and 54%, and 25% and 27% higher than that in cropland on sloping land, respectively. The similar control measures for soil erosion produced significant differences among topographic positions (P<0.1). In the 0-10 cm soil layer, For the level terrace measure, SOC and TN in valley bottom were 46% and 43% higher than those in the ridge slope; For the woodland measures, SOC and TN in the gully slope were 18% and 6% higher than those in the ridge slope; For the grassland measures, SOC and TN in the gully slope were 14% and 18% higher than those in the ridge slope. In the 0-100 cm soil depth, SOC or TN had the similar change characteristics with soil moisture among the topographic positions and the soil erosion control measures. An exponential relationships of y= aebx (y is SOC or TN and x is soil moisture) were developed between SOC (TN) and soil moisture at the small watershed. 参考文献 相似文献 引证文献

사료작물 재배지에서 초지식생대를 이용한 NO3-N 저감효과에 관한 연구

The performance of grass filter strips (GFS) in abating NO3-N concentrations from the forage cropland was tested in an experiment on the 10% slope in Grassland and Forages Division, National Institute of Animal Science, Rural Development Administration (RDA) from October 2007 to September 2009. Forage croplands with rye-corn double cropping system applied with chemical fertilizer and livestock manure (LM) were compared in a natural condition. The plots were hydrologically isolated in a randomized block layout of 3 treatments × 2 factors × 3 replicates. Main plots consisted of the length of GFS, such as 0 m, 5 m, 10m and 15m. Sub plots consisted of the type of LM, such as chemical fertilizer (CF), cattle manure (CM) and swine manure (SM). Dry matter yields of rye and corn increased significantly in order of CF > CM > SM (p<0.05). Concentrations of NO3-N in surface runoff water were reduced as the length of GFS increased. Especially, GFS with 10 m and 15m reduced NO3-N concentrations significantly compared to that with 0 m and 5 m (p<0.05). The results from this study suggest that GFS improved the removal and trapping of manure nutrients from forage croplands. (Key words : Grass filter strips, Run-off, Manure, Forage, NO3-N)

사료작물 재배지에서 초지식생대가 PO4-P 및 토양유실 저감에 미치는 영향

The performance of grass filter strips (GFS) in reducing -P concentrations and soil loss from the forage cropland was tested in an experiment on the 10% slope in Grassland and Forages Division, National Institute of Animal Science, Rural Development Administration (RDA) from October 2007 to September 2009. Forage cropland with rye-corn double cropping system receiving inorganic fertilizer or livestock manure (LM) were compared in a natural condition. The plots were hydrologically isolated in a randomized block layout of 3 treatments 2 factors 3 replicates. Main plots consisted of the length of GFS, such as (), (), (). Sub plots consisted of the type of LM, such as chemical fertilizer (CF), cattle manure (CM) and swine manure (SM). Concentrations of -P in surface runoff water were reduced as the length of GFS increased. Especially, GFS with 10 m and 15 m reduced -P concentrations significantly compared to that with 0 m (p-P concentrations of GFS with 10m and that of GFS with 15 m. Moreover, Soil loss in surface runoff water were reduced as the length of GFS increased. GFS with 15 m reduced soil loss significantly compared to that with 5 m and 10 m (p-P and soil loss from forage cropland.

Spatial patterns of species distributions in grazed subalpine grasslands

Spatial patterns of species diversity have important influences on the functioning of ecosystems, and the effect of livestock grazing on spatial heterogeneity can differ depending on the scale of the analysis. This study examined the effects of grazing on the spatial patterns of species distributions and whether the effects of grazing on the spatial distributions of a species vary with the scale of the analysis. Data were collected at three locations in the subalpine grasslands of Ordesa-Monte Perdido National Park and Aisa Valley, Central Pyrenees, Spain, which differed in mean stocking rates. Aspect explained about one-third of the environmental variation in species distributions. In flat areas, spatial variation in species composition varied with grazing intensity at two scales. At a coarse scale (among vegetation patches), grazing promoted patchiness, and among-transect variation in species diversity and grazing intensity were positively correlated. At a fine scale (within vegetation patches), the disruption of the self-organizing processes of the species spatial distributions resulted in a reduction in the long-range spatial autocorrelations of some of the characteristic species and in the homogenization of species spatial distributions. The presence of encroaching Echinospartum horridum had a significant influence on the effect of grazing on south-facing grassland slopes.

Predicting assemblages and species richness of endemic fish in the upper Yangtze River

The present work describes the ability of two modeling methods, Classification and Regression Tree (CART) and Random Forest (RF), to predict endemic fish assemblages and species richness in the upper Yangtze River, and then to identify the determinant environmental factors contributing to the models. The models included 24 predictor variables and 2 response variables (fish assemblage and species richness) for a total of 46 site units. The predictive quality of the modeling approaches was judged with a leave-one-out validation procedure. There was an average success of 60.9% and 71.7% to assign each site unit to the correct assemblage of fish, and 73% and 84% to explain the variance in species richness, by using CART and RF models, respectively. RF proved to be better than CART in terms of accuracy and efficiency in ecological applications. In any case, the mixed models including both land cover and river characteristic variables were more powerful than either individual one in explaining the endemic fish distribution pattern in the upper Yangtze River. For instance, altitude, slope, length, discharge, runoff, farmland and alpine and sub-alpine meadow played important roles in driving the observed endemic fish assemblage structure, while farmland, slope grassland, discharge, runoff, altitude and drainage area in explaining the observed patterns of endemic species richness. Therefore, the various effects of human activity on natural aquatic ecosystems, in particular, the flow modification of the river and the land use changes may have a considerable effect on the endemic fish distribution patterns on a regional scale.

Relationships between cultivation techniques, vegetation, pedology and erosion on extensively cultivated and abandoned agricultural areas in the Putnok Hills

Pedological and coenological investigations were made around the villages of Alsószuha and Gömörszőlős, in the Putnok Hills microregion, which forms part of the Northern Hungarian Mountains. These were complemented with laboratory nutrient analyses, giving the opportunity to compare the pedological relationships and erosion of natural and ploughed areas. Arable lands can often be found on steep slopes. The brown forest soil types characteristic of these areas are less sensitive to erosion, but they suffer significant damage when cash crops are hoed regularly even on steep slopes.Coenological data indicative of the previous farming system are presented for three plots near Alsószuha. Regular mowing resulted in a large number of plant species even 10 years after cereal production was abandoned. The lack of regular mowing on a plot with a similar farming history, however, resulted in the dominance of aggressive weeds. The species on the third plot showed that the 42 years that had elapsed since cereal production was abandoned, followed by grazing until 1990, ensured enough time for revegetation and the generation of a secondary grassland (slope steppe) in a close-to-natural state. Invasive weeds were absent from all the observed plots.

HIERARCHICAL PLASTICITY OF CENTELLA ASIATICAIN RESPONSES TO MICROSITES WITH DIFFERENT HERBACEOUS COVERAGE OF FOREST EDGE AND ABANDONED GRASSLAND SLOPE

Aims In natural environments, resources of critical importance to plant growth are patchily distributed, even at a small spatial scale. The aims of this study are to address: 1) Centella asiatica exploitation of heterogeneous microsites in different habitats, 2) hierarchical effects of habitats and microsites with different herbaceous coverage on growth traits of C. asiatica, and 3) differences in hierarchical response patterns for large and small scales of heterogeneous habitats. Methods Microsites with low and high herbaceous coverage were selected in abandoned grassland slope and forest edge habitats. We measured morphological and physiological characteristics of C. asiatica in spring 2004 and 2005 at three levels: ramet population, clonal fragment and leaf. Environmental factors of different microsites were investigated again in September 2006. Important findings At the ramet population level, we observed no effect of habitat (forest edge vs. abandoned grassland slope). Root-shoot ratio of ramet population with low herbaceous coverage was significantly higher than that with high herbaceous coverage. At the level of clonal fragment, root dry weight, flower and fruit dry weight were significantly higher and internode length of primary and total stolons were shorter on abandoned grassland slope. Root-shoot ratio and number of primary stolons were significantly larger with low herbaceous coverage, but flower and fruit dry weight, internode length of secondary stolon and internode length of total stolon were lower. At the leaf level, lamina length, lamina width and lamina area were larger on abandoned grassland slope and with high herbaceous coverage. Plants with high herbaceous coverage had larger petiole length and specific petiole length. No significant effects of habitat and microsite on chlorophyll content were observed. These findings indicated that there were hierarchical effects of habitat and microsite on the growth traits of C. asiatica, and different hierarchical responses of C. asiatica to different habitats and microsites with different herbaceous coverage were observed. Plastic response to heterogeneous habitat is stronger at smaller scale than that at larger scale.

Aerating Grassland before Manure Application Reduces Runoff Nutrient Loads in a High Rainfall Environment

The effect of mechanically aerating grassland before liquid manure application in the fall on surface runoff and transport of nutrients and solids was studied in a high rainfall area. The two treatments were control and aeration, the latter receiving one pass with an aerator perpendicular to the slope before fall application of liquid manure (dairy in Years 1-3 and swine in Year 4). Treatments were randomly assigned on 3 to 5% sloping land with a silt loam surface soil (Aquic Dystroxerept) planted in orchardgrass (Dactylis glomerata L.). Runoff from natural rainfall events was sampled for nutrient and solids analysis. Aeration significantly reduced runoff and loads of suspended solids, total Kjeldahl N (TKN), and dissolved reactive P in all years. Annual runoff amounts were reduced by 47 to 81%, suspended and volatile solid loads by 48 to 69% and 42 to 83%, respectively, TKN loads by 56 to 81%, and total P (TP) loads by 25 to 75%. Loads of the soluble nutrient NH4-N, dissolved reactive P, and K were reduced by 41 to 83%. The first three runoff events after manure application accounted for approximately one-third of the annual total runoff and solid and nutrient loads when averaged across treatments, with loads of TKN, K, and NH4-N totaling 4.4, 3.3, and 1.9 kg ha-1, respectively. Aeration slightly increased downward movement of NO3-N, but not other nutrients in the soil. Thus mechanical aeration can be an effective tool for reducing runoff and loads of solids and nutrients after surface application of liquid manure on sloping grassland.

Abandonment in grazing systems: Consequences for vegetation and soil

Many dehesa zones in marginal areas are suffering from the abandonment of traditional farming practices. Herbivore grazing affects grassland dynamics, changing the species colonisation and extinction relationships via consumption, mechanical disturbance, seed dispersal and altered soil fertility due to dung-borne nutrient input. This paper analyses changes to floristic composition, species richness and heterogeneity as well as soil and light resources in relation to grazing abandonment in two characteristic topography-related types of dehesa habitat (upper slope and lower slope grasslands). Vegetation surveys were undertaken using five replicates in each habitat type in grazed and abandoned grasslands in the Guadarrama range in Central Spain with distric cambisol soils. Additional measurements of light and soil parameters were also undertaken. The results show an effect of grazing on resource availability. In general there was a smaller proportion of fine matter (clay), organic matter, total nitrogen, assimilable potassium and readily available water in abandoned as opposed to grazed zones. We did not find any effect of grazing on phosphorous availability. Abandonment reduces light availability at ground level in lower slope grasslands (wet meadows) but does not produce a significant reduction in upper slope (driest) grasslands, although there is an increased spatial heterogeneity in the availability of light associated with the presence of scattered shrubs. While the total number of species in abandoned zones did not significantly differ from grazed zones, floristic composition changed dramatically with abandonment in both habitat types, with less than 50% of common species. Also, floristic heterogeneity at the small scale increased with abandonment. Designers of agri-environmental policies applied to Mediterranean grasslands should be aware of the risk of widespread grazing abandonment and promote the diversification of grazing regimes across the landscape to maximize species diversity and take advantage of the benefits of low-density grazing in other functions of the ecosystem such as their productivity and stability.

Effects of microenvironment on net photosynthetic rate and growth of four tropical species in the La Mesa watershed

Seedlings of four tree species (Bischofia javanica, Dracontomelon dao, Erythrina orientalis, and Pterocarpus indicus) were planted in flat and sloping grassland in plantation sites established in May 2002 in the La Mesa watershed, Philippines. Tree growth and net photosynthetic rate (PN) were monitored. The height, diameter at the root collar, and PN of the four species grown in the sloping grass site were larger than those of seedlings grown in the flat grass site. In addition, soil moisture contents in the sloping grass site were higher than those of the flat grass site. Growth of the four species was probably strongly associated with microenvironments (e.g. air temperature) in both tested sites.

Comparison of different methods to measure and model actual evapotranspiration rates for a wet sloping grassland

Accurate measurements of the turbulent exchanges of mass and energy at the land surface are necessary for a good understanding of the various components of the hydrological cycle. The two most commonly used methods to measure evapotranspiration rates are the Bowen ratio energy balance (BREB) and the Eddy correlation (EC) methods. These methods are applicable when a number of requirements, mostly with respect to terrain topography and homogeneous fetch extension, are fulfilled. On the other hand, meteorological variables can be used to calculate evapotranspiration rates. The two most frequently used methods for this purpose are the Penman-Monteith (PM) combination equation and the Priestley-Taylor (PT) approximation. The objective of this paper is to compare these different methods under non-ideal conditions, more specifically for a wet sloping grassland. The BREB-based and EC-based latent heat fluxes are intercompared, and a good agreement between the estimates from both methods is found. A comparison between the results of the PM and PT methods and the measured latent heat fluxes is then done. A strong annual cycle in the calculated values for the PT alfa factor ( α), with a mean annual average value of 1.21 ± 0.79, has been observed. This annual cycle is related to the annual cycle of the humidity of the soil, which can be evaluated by either the soil moisture or the vapor deficit of the air. A strong annual cycle in the inverted surface resistances has also been observed. A relationship between the inverted surface resistances and α has been found, in which the highest values for α coincide with low surface resistances, and vice versa. The results indicate that the methods to measure and calculate latent heat fluxes are in a good agreement, and that imposing an annual cycle in the surface resistance and α leads to an improvement in the estimated evapotranspiration rates. The results suggest that it is possible to measure or model evapotranspiration rates in situations where the theoretical requirements (more specifically a non-sloping surface) are not met.

Correcting method of eddy covariance fluxes over non-flat surfaces and its application in ChinaFLUX

Although Eddy Covariance (EC) technique is one of the best methods for estimating the energy and mass exchanges between underlying surface and atmosphere in micrometeorology, errors and uncertainties still exist without necessary corrections. In this paper, we will focus on the effect of coordinate system on the eddy fluxes. Based on the data observed over four sites (one farmland site, one grassland site and two forest sites), the effects of three coordinate system transforming methods (Double Rotation-DR, Triple Rotation-TR and Planar Fit-PF) on the turbulent fluxes are analyzed. It shows that ( i ) the corrected fluxes are more or less than the uncorrected fluxes, which is related mainly to the sloping degree of surface, wind speed and wind direction; and ( ii ) pitch angle has a sinusoidal dependence on wind direction, especially in the regular sloping terrain; and ( iii ) PF method is something like the simplification of TR or DR, and there are not obvious distinctions in correction in sloping grassland and flat farmland, but PF method is not suitable for uneven and irregular forest sites.

Reforestation and Topography Affect Montane Soil Properties, Nitrogen Pools, and Nitrogen Transformations in Hawaii

Land use changes, such as deforestation and reforestation, modify not only the organisms inhabiting affected areas, but also above‐ and belowground environments. Topography further influences local vegetation and environment. Effects of topography and re‐establishment of N‐fixing koa (Acacia koaA. Gray) trees in +100‐yr‐old montane grassland on surface soil properties, N pools, and N transformations were assessed using standard and15N‐isotope pool dilution methods. Data were collected for soils on slopes and in drainage bottoms located in grassland, under 9‐ to 11‐yr‐old planted koa, and in nearby old‐growth koa‐ohia (Metrosideros polymorphaGaud.) forest. Soil under planted koa had significantly lower fine soil bulk density and pH than soil in grassland, and had concentrations of total C, total N, and extractable Mg and C/N ratio intermediate between grassland and forest. Topographic position affected pH and concentrations of total C, total N, and extractable P. Ten years after koa trees were re‐introduced to grassland, the concentration of soil NH4+–N had increased above levels found even in intact forest, and the concentration of NO3−–N was intermediate between forest and grassland. Ammonium dominated the inorganic N pools in grassland soil and NO3−dominated in forest soil. Under planted koa, NH4+domination was beginning to give way to NO3−domination. Soil microorganisms were potentially strong competitors for inorganic N on grassland slopes where they immobilized nearly all the inorganic N that was produced during short‐ and medium‐term field incubations, thus leaving little for plant growth. Re‐establishment of koa trees increased soil N availability.

Taxonomy, ecology and distribution of Hygrocybe (Fr.) P. Kumm. and Camarophyllopsis Herink (Fungi, Basidiomycota, Hygrocybeae) in Greenland,

This revision is based on critical macroscopic and microscopic studies of about 450 Greenlandic collections of the tribus Hygrocybeae, in Greenland represented by the genera Camarophyllopsis and Hygrocybe (s.l.). The collections are assigned to 29 taxa.&#x0D; Hygrocybe rubrolamellata and H. conica var. aurantiolutea are described as new. H. coccinea (Schaeff.: Fr.) P. Kumm., H. marchii (Bres.) F.H. Møller and H. coccineocrenata (P.D. Orton) M.M. Moser are excluded from the Greenlandic basidiomycota. The concepts of H. salicis-herbaceae Kühner, H. biminiata Kühner, H. occineocrenata (P.D. Orton) M.M. Moser, H. rhodophylla Kühner, H. substrangulata (P.D. Orton) P.D. Orton &amp; Watling and H. turunda (Fr.: Fr.) P. Karst. are revised.&#x0D; The phenology, ecology and distribution patterns of all species are discussed. The grassland slopes in S Greenland and the oceanic dwarf-shrub heaths and fens in S and SW Greenland are two centres of distribution. The species composition of tribus Hygrocybeae in Greenland shows much affinity to that of the Alps and NW Europe.

10Be, 14C Distribution, and Soil Production Rate in a Soil Profile of a Grassland Slope at Heshan Hilly Land, Guangdong

Concentrations of organic carbon, carbon isotopes (13C and 14C), atmospheric 10Be in soil, and in situ 10Be in bedrock and weathering rock were determined in a study of a profile of a grassland slope at the Heshan Hilly Land Interdisciplinary Experimental Station, Chinese Academy of Sciences, in Guangdong Province, China. A good linear relationship between depth and the 14C apparent age of the organic carbon demonstrates that the rock weathering process and the accumulation process of organic matter in the slope are relatively stable. Both 14C and 10Be results show that about 34% of soil in the grassland slope has been eroded during the past 3800 yr. The 10Be results for interstitial soil from weathered rocks show that the 90-cm-thick weathering rock layer above the bedrock has evolved over a period of 1.36 Myr. The concentrations of in situ 10Be in the weathered rock and bedrock are 10.7 × 104 atoms/g and 8.31 × 104 atoms/g, respectively. The weathering rate of the bedrock, equivalent to the soil production rate, was estimated at 8.8 × 10-4 cm/yr, and the exposure ages of the weathered rock and the bedrock were 72 kyr and 230 kyr, respectively.

Modelling butterfly distribution based on remote sensing data

AimWe tested the usefulness of satellite based remote sensing data and geographical information system (GIS) techniques (1) in explaining the observed distribution of the threatened clouded apollo butterfly (Parnassius mnemosyne) and (2) in predicting the occurrence of the butterfly in two independent test areas with different landscape structure.LocationThe three study areas are located along the rivers Rekijoki and Halikonjoki in a boreal agricultural landscape in south‐western Finland (60°40′ N; 23°20′ E).MethodsLandsat satellite images were used to generate habitat maps of the three study areas. Topographical variables were calculated from a digital elevation model. These data were used to construct a multiple logistic regression model fitted with the observed occurrence of clouded apollo in 126 grid squares of 0.25 km2 within an area of 31.5 km2 (model building area). The parameterized model was used to predict the occurrence of the butterfly in an adjacent test area with a similar landscape structure as in the model building area, as well as in a more distant test area with a more fragmented pattern of semi‐natural grassland.ResultsIn the model building area probability of clouded apollo occurrence increased with connectivity of semi‐natural grassland, cover of deciduous forest, cover of semi‐natural slope grassland and topographical heterogeneity. The model accuracy was high, the correct classification rate being 98.4% overall and 95.0% for the butterfly presence squares. In both test areas the overall correct classification of the model prediction was high (c. 92%). However, in predicting the actual butterfly presence squares the model succeeded substantially better in the adjacent than in the distant test area (correct classification rates 91.3% and 66.7%, respectively).Main conclusionsThe results showed that the distribution of a habitat specialized butterfly may be quite successfully explained and predicted based on pure satellite imagery and topographical data. Nevertheless, the decrease of accuracy of the model prediction when applied to a different landscape structure than the one in which the model was parameterized suggests that the useful application of such models is limited by the environmental variability of the original model building data.

Spatial Variability of Surface Soil Moisture and Investigation of the Local Sampling Sites Exhibiting Field Average in a Sloping Grassland Field

Spatial Variability of Surface Soil Moisture and Investigation of the Local Sampling Sites Exhibiting Field Average in a Sloping Grassland Field

Landscape Patterns of Tropical Forest Recovery in the Republic of Palau1

A GIS (geographic information systems) database was constructed from aerial photographs, a vegetation map, and topographic map data of the Ngeremeduu Bay Drainage Area (NBDA), Palau, to examine relationships between upland land cover dynamics, environmental variables, and past land use. In 1992, 82.9 percent of the NBDA was forest, 16.6 percent was grassland, and 0.5 percent consisted of village areas. Between 1947 and 1992, there was a 11.2 percent reduction of grassland area primarily due to a 10.9 percent increase in forest cover. These land cover changes led to larger, more continuous stretches of forest and numerous, highly fragmented grassland patches. Significant relationships (P < 0.001) were found between the spatial distribution of forest and grassland cover and slope, elevation, soil pH, and percent soil organic matter. These patterns, however, may have resulted from past farm site selection rather than from ecological relationships. Our results indicate that areas of forest expansion were significantly (P < 0.001) associated with the location of abandoned agricultural communities. In addition, over 92 percent of areas of forest expansion occurred within 100 m of established forest. These results suggest that the proximity of established forest facilitate forest recovery following human disturbance.

Temporal Stability of Spatial Patterns of Nitrous Oxide Fluxes from Sloping Grassland

AbstractInsight into the temporal and spatial variability of nitrous oxide (N2O) fluxes from soils is required to set up efficient sampling protocols of N2O fluxes and to set up strategies to reduce N2O fluxes. The aim of the present study was to assess the temporal stability of the spatial pattern of N2O fluxes along a transect (400 m) on a fertilized sloping grassland soil. Geostatistical analyses of flux chamber measurements over 4 d showed a clear spatial dependency of N2O fluxes. The spatial variability of N2O fluxes was much higher than the temporal variability during the 4 d. Despite the decreasing magnitude of the fluxes in time, the spatial pattern persisted during 4 d, that is, fluxes were always highest at the steepest part of the transect. The 15N natural abundance (δ15N) in soil N was significantly correlated with N2O fluxes, indicating a long‐term effect of N loss as N2O on the 15N abundance in the soil. It was suggested that topography played a role in the observed spatial patterns of N2O fluxes and Δ15N in soil N. The study showed that despite the persistent spatial pattern of N2O fluxes, flux magnitude may strongly fluctuate in time. Therefore, it is often not possible to combine N2O flux measurements made at different times in order to obtain enough data for geostatistical analysis.

Transport of nitrogen in soil water following the application of animal manures to sloping grassland

A field experiment was conducted on a sloping grassland soil in southwest England to investigate the downslope transport of nitrogen in soil water following the application of cattle manure, slurry and inorganic fertilizer. Transport of nitrogen (N) species was monitored on hydrologically isolated plots. Manure (50 t ha−1), slurry (50 m3 ha−1) and fertilizer (250 kg N ha−1) were applied in February/March 1992. Subsurface water movement, by both matrix and preferential flow, was the dominant flow route during the experiment. Subsurface and surface nutrient flow pathways were monitored by analysing soil water and surface runoff for NO3-N, NH4-N and total N. Subsurface flow chemistry was dominated by NO3-N, with concentrations usually between 2 and 5 mg NO3 −N dm−3. Differences between fertilizer and manure treatments and the untreated control were not significant. Significantly elevated NO3-N concentrations were observed in soil water in the buffer zone, indicating the importance of a buffer zone at least 10 m wide between manure spreading zones and an adjacent water course.