Application of a coupled ecosystem-chemical equilibrium model, DayCent-Chem, to stream and soil chemistry in a Rocky Mountain watershed

Atmospheric deposition of sulfur and nitrogen species have the potential to acidify terrestrial and aquatic ecosystems, but nitrate and ammonium are also critical nutrients for plant and microbial productivity. Both the ecological response and the hydrochemical response to atmospheric deposition are of interest to regulatory and land management agencies. We developed a non-spatial biogeochemical model to simulate soil and surface water chemistry by linking the daily version of the CENTURY ecosystem model (DayCent) with a low temperature aqueous geochemical model, PHREEQC. The coupled model, DayCent-Chem, simulates the daily dynamics of plant production, soil organic matter, cation exchange, mineral weathering, elution, stream discharge, and solute concentrations in soil water and stream flow. By aerially weighting the contributions of separate bedrock/talus and tundra simulations, the model was able to replicate the measured seasonal and annual stream chemistry for most solutes for Andrews Creek in Loch Vale watershed, Rocky Mountain National Park. Simulated soil chemistry, net primary production, live biomass, and soil organic matter for forest and tundra matched well with measurements. This model is appropriate for accurately describing ecosystem and surface water chemical response to atmospheric deposition and climate change.     

Land use change around protected areas: management to balance human needs and ecological function.

Protected areas throughout the world are key for conserving biodiversity, and land use is key for providing food, fiber, and other ecosystem services essential for human sustenance. As land use change isolates protected areas from their surrounding landscapes, the challenge is to identify management opportunities that maintain ecological function while minimizing restrictions on human land use. Building on the case studies in this Invited Feature and on ecological principles, we identify opportunities for regional land management that maintain both ecological function in protected areas and human land use options, including preserving crucial habitats and migration corridors, and reducing dependence of local human populations on protected area resources. Identification of appropriate and effective management opportunities depends on clear definitions of: (1) the biodiversity attributes of concern; (2) landscape connections to delineate particular locations with strong ecological interactions between the protected area and its surrounding landscape; and (3) socioeconomic dynamics that determine current and future use of land resources in and around the protected area.     

Genetic Structure and Migration in Native and Reintroduced Rocky Mountain Wolf Populations

Gray wolf (Canis lupus) recovery in the Rocky Mountains of the U.S. is proceeding by both natural recolonization and managed reintroduction. We used DNA microsatellite analysis of wolves transplanted from Canada to two reintroduction sites in the U.S. to study population structure in native and reintroduced wolf populations. Gene flow due to migration between regions in Canada is substantial, and all three recovery populations in the U.S. had high genetic variation. The reintroduced founders were moderately genetically divergent from the naturally colonizing U.S. population. These findings corroborate that the reintroduction more than meets generally accepted genetic guidelines. Maintaining this variation, however, will depend on ample reproduction in the first few generations. In the long term genetic variation will best be retained if migration occurs among the recolonizing and the two transplanted populations. Evidence from field observation and genetic studies shows extensive dispersal by wolves, and we conclude that exchange among these groups due to natural dispersal is likely if public tolerance and legal protection are adequate outside lands designated for wolf recovery.     

Possible Effects of Acidic Deposition on a Rocky Mountain Population of the Tiger Salamander Ambystoma tigrtinum

Para investigar los posibles efectos biológicos de lluvia ácaida en el oeste de los Estados Unidos, se llevaron a cabo censos poblacionales de salamandras y experimentos deevaluación de respuesta a varias dosijicaciones en una cuenca subalpina en las Montañas Rocosas del Estado de Colorado. Una población adulta de salamundras tigre (Ambystoma tigrinum nebulosum) tuvo un descenso de 65% ensiete años, mientras el reclutamiento de larvas disminuyó en general salvo en el ultimo año de este perí'odo. Huatos de A. tigrinum tuvieron un pH de 5.6(LD-50), valor que se encuentra en el rango usual para este luagar medido durante el período de desahielo. Aunque el descenso de A. tigrinurn en esta cuenca puede deberse a una fluctuación natural la evidencia disponible es consistente con la hipótesis de que su causa se debe a las deposiciones por lluvia ácida Por. lo tanto, el descenso de A. tigrinurn en la cuenca puede ser la primera indicación de daño biológico de los llivia acida en el oeste de los Estados Unidos.     

Scale-dependent responses of plant biodiversity to nitrogen enrichment

Experimental studies demonstrating that nitrogen (N) enrichment reduces plant diversity within individual plots have led to the conclusion that anthropogenic N enrichment is a threat to global biodiversity. These conclusions overlook the influence of spatial scale, however, as N enrichment may alter beta diversity (i.e., how similar plots are in their species composition), which would likely alter the degree to which N-induced changes in diversity within localities translate to changes in diversity at larger scales that are relevant to policy and management. Currently, it is unclear how N enrichment affects biodiversity at scales larger than a small plot. We synthesized data from 18 N-enrichment experiments across North America to examine the effects of N enrichment on plant species diversity at three spatial scales: small (within plots), intermediate (among plots), and large (within and among plots). We found that N enrichment reduced plant diversity within plots by an average of 25% (ranging from a reduction of 61% to an increase of 5%) and frequently enhanced beta diversity. The extent to which N enrichment altered beta diversity, however, varied substantially among sites (from a 22% increase to an 18% reduction) and was contingent on site productivity. Specifically, N enrichment enhanced beta diversity at low-productivity sites but reduced beta diversity at high-productivity sites. N-induced changes in beta diversity generally reduced the extent of species loss at larger scales to an average of 22% (ranging from a reduction of 54% to an increase of 18%). Our results demonstrate that N enrichment often reduces biodiversity at both local and regional scales, but that a focus on the effects of N enrichment on biodiversity at small spatial scales may often overestimate (and sometimes underestimate) declines in regional biodiversity by failing to recognize the effects of N on beta diversity.     

基于氮磷指数的小流域氮磷流失风险评价

识别区域氮磷流失综合风险分布状况并对氮磷流失进行综合调控是控制非点源污染的有效措施。但传统的研究往往局限于氮或磷流失风险的单独评估和调控,以密云水库沿湖集约化农区东庄小流域为例,应用氮指数、磷指数及氮磷综合指数法,对区域氮磷流失风险进行综合评价。结果表明:流域氮、磷流失风险总体上较小,80%以上的区域均处于氮、磷流失的无风险或低风险区,但氮、磷流失的空间分布存在较大差异。其中氮流失的高度风险区集中在山地中土壤侵蚀指数较大的果园;而磷流失的高风险区域主要分布在河流沿岸的农业用地。氮磷综合风险指数显示,93.1%的区域处于无风险和低风险区,中度以上风险区占总面积的6.9%,主要集中在流域中部有着较高的肥料施用、地势陡峭且处在河流沿岸的农业用地或山地中。单独考虑氮指数或磷指数都难以反映区域氮磷流失的综合风险状况,容易忽略磷指数高氮指数低、氮指数高和磷指数低以及氮、磷风险在中等的区域。因此,在氮、磷流失风险评估基础上,进行氮磷流失风险的综合评价,可为氮磷流失的综合调控提供指导。     

基于氮磷指数的小流域氮磷流失风险评价

识别区域氮磷流失综合风险分布状况并对氮磷流失进行综合调控是控制非点源污染的有效措施。但传统的研究往往局限于氮或磷流失风险的单独评估和调控,以密云水库沿湖集约化农区东庄小流域为例,应用氮指数、磷指数及氮磷综合指数法,对区域氮磷流失风险进行综合评价。结果表明：流域氮、磷流失风险总体上较小,80%以上的区域均处于氮、磷流失的无风险或低风险区,但氮、磷流失的空间分布存在较大差异。其中氮流失的高度风险区集中在山地中土壤侵蚀指数较大的果园;而磷流失的高风险区域主要分布在河流沿岸的农业用地。氮磷综合风险指数显示,93.1%的区域处于无风险和低风险区,中度以上风险区占总面积的6.9%,主要集中在流域中部有着较高的肥料施用、地势陡峭且处在河流沿岸的农业用地或山地中。单独考虑氮指数或磷指数都难以反映区域氮磷流失的综合风险状况,容易忽略磷指数高氮指数低、氮指数高和磷指数低以及氮、磷风险在中等的区域。因此,在氮、磷流失风险评估基础上,进行氮磷流失风险的综合评价,可为氮磷流失的综合调控提供指导。     

Land use/cover change effects on floods with different return periods: a case study of Beijing, China

In this study, an approach integrating digital land use/cover change (LUCC) analysis, hydraulic modeling and statistical methods was applied to quantify the effect of LUCC on floods in terms of inundation extent, flood arrival time and maximum water depth. The study took Beijing as an example and analyzed five specific floods with return periods of 20-year, 50-year, 100-year, 1000-year and 10000-year on the basis of LUCC over a nine-year period from 1996 to 2004. The analysis reveals that 1) during the period of analysis Beijing experienced unprecedented LUCC; 2) LUCC can affect inundation extent and flood arrival time, and floods with longer return periods are more influenced; 3) LUCC can affect maximum water depth and floods with shorter return periods are more influenced; and 4) LUCC is a major flood security stressor for Beijing. It warns that those cities having experienced rapid expansion during recent decades in China are in danger of more serious floods and recommends that their actual land use patterns should be carefully assessed considering flood security. This integrated approach is demonstrated to be a useful tool for joint assessment, planning and management of land and water.     

Land use and land cover in a transitioning militarized landscape

The repurposing of military lands is common in many parts of the world and presents a variety of conservation opportunities. This study examines land cover at Big Oaks National Wildlife Refuge, Indiana (U.S.A.) as it transitioned from military proving ground to wildlife refuge from 1985 to 2013. We use remote sensing, semi-structured interviews, and a review of planning and management documents to examine this transition. Limited change in land cover composition and distribution are detected, despite changes in use and management. This landscape similarity relates to similarities in land management practices, and the impact of landscape history on current management practices. The findings suggest that military use and conservation objectives at this site yield similar land covers and are not necessarily in contrast to each other. As military base closures continue, the potential to maintain and expand conservation opportunities on these lands will likely grow in importance.     

皖南低山丘陵地区流域氮磷径流输出特征

通过对安徽南部宣城地区梅村小流域的定位监测,研究了该小流域地表径流中氮磷输出特征。结果表明:氮输出以NO-3N为主,占氮素输出总量的60%,磷输出以悬浮颗粒结合态磷(PAP)为主,占磷输出总量的92%;各类形态氮素输出量间存在极显著线性正相关关系;PAP随悬浮颗粒输出量的增加而增加,PAP与水溶性磷(DP)输出量间存在着极显著的对数关系;氮磷输出具有明显的季节性变化规律,夏季输出量最大,其次是春季,再次是秋季,冬季最少,这是由降雨量的季节性变化所引起的。而且暴雨对氮磷输出的贡献率极大,因此控制雨季土壤侵蚀是有效控制氮磷通过径流输出的最重要方式。     

土地利用方式对紫色土丘陵区土壤剖面碳、氮影响

采取野外调查与室内分析相结合的方法研究了紫色土丘陵区林地、撂荒地、水田、旱地土壤剖面(0～40 cm)有机碳、全氮变化特征.结果表明.有机碳、全氮均随土层深度增加而逐渐减小,且林地、撂荒地有机碳递减幅度高于水田、旱地.相对于撂荒地和旱地,水田、林地更利于有机碳、全氮的积累.林地有机碳和全氮在0～5 cm土层表现出绝对优势;随土层递增,与水田、撂荒地和旱地的差异逐渐减小.水田有机碳和全氮在大于10 cm土层显示最大值.而撂荒地有机碳和全氮仅在土壤表层高于旱地.有机碳与全氮存在显著正相关关系;w(C)/w(N)随土层深度增加而降低,且林地、撂荒地降低幅度较大.因此相对于水田、旱地,林地和撂荒地w(C)/w(N)仅在0～10 cm显示较大值.可见,土地利用方式对陆地生态系统碳、氮蓄积有明显影响,通过旱地还林或撂荒可以增加土壤特别是表层土壤对碳、氮的积累.     

Litterfall 15N abundance indicates declining soil nitrogen availability in a free-air CO2 enrichment experiment

Forest productivity increases in response to carbon dioxide (CO2) enrichment of the atmosphere. However, in nitrogen-limited ecosystems, increased productivity may cause a decline in soil nitrogen (N) availability and induce a negative feedback on further enhancement of forest production. In a free-air CO2 enrichment (FACE) experiment, the response of sweetgum (Liquidambar styraciflua L.) productivity to elevated CO2 concentrations [CO2] has declined over time, but documenting an associated change in soil N availability has been difficult. Here we assess the time history of soil N availability through analysis of natural 15N abundance in archived samples of freshly fallen leaf litterfall. Litterfall delta15N declined from 1998 to 2005, and the rate of decline was significantly faster in elevated [CO2]. Declining leaf litterfall delta15N is indicative of a tighter ecosystem N cycle and more limited soil N availability. By integrating N availability over time and throughout the soil profile, temporal dynamics in leaf litterfall delta15N provide a powerful tool for documenting changes in N availability and the critical feedbacks between C and N cycles that will control forest response to elevated atmospheric CO2 concentrations.     

冻融对长白山森林土壤碳氮矿化的影响

长白山地区秋末春初常常存在冻融过程,冻融过程影响土壤水分分布而改变土壤理化性质。通过室内模拟实验,研究了冻融过程（-20~15℃）对长白山阔叶红松（Pinus koraiensis）林和白桦（Betula platyphylla）林土壤有机碳和氮矿化过程的影响。结果表明,经过3次冻融循环,冻融处理土壤矿化速率显著高于对照处理,但经过多次冻融循环过程,冻融处理抑制土壤有机碳矿化过程,对照处理土壤有机碳矿化速率高于冻融处理（P=0.019）。在培养结束后,冻融处理的阔叶红松林和白桦林土壤无机氮质量分数,分别是对照处理的1.88倍和1.96倍;冻融次数也是影响土壤有机氮矿化的一个重要因素,35次冻融循环后,阔叶红松林和白桦林土壤中无机氮分别提高了2.10倍和2.81倍。冻融循环促进了土壤有机氮的矿化,有利于土壤中有效氮的累积,为春季植物生长提供足够的氮素,但也潜在增加了土壤中无机氮流失的风险。     

九龙江流域典型汇水区地表径流氮磷流失特征分析

选取九龙江流域5个典型汇水区,通过流域主要雨季天然降雨径流过程监测,对所获得的氮磷营养盐的监测数据进行归纳与分析,着重探讨了暴雨事件下径流氮磷流失及其形态的变化规律。结果表明:暴雨事件下农业汇水区地表径流氮输出以水溶态为主,磷以泥沙结合态为主,天然林地为主的汇水区则相反,前者以泥沙结合态为主,后者以水溶态为主;5个汇水区暴雨事件中总氮最高浓度值为日常采样浓度值的2.9～11.3倍,暴雨事件中总磷最高浓度值为日常采样浓度值的2.9～20.5倍;氮磷输出量均值的差异反映氮磷输出量大小受土壤质地、施肥量、土壤氮磷含量、土壤保水保肥性能等因素的综合影响。整个径流过程中水量和氮磷浓度随时间变化幅度较大,且2者变化呈大体相同的趋势。氮磷及其各形态的浓度多数在相同时间内达到峰值。泥沙结合态氮、水溶态磷变化幅度较小,水溶态氮和泥沙结合态磷浓度变化幅度较大。统计各汇水区雨量不同的降雨事件下氮磷流失负荷表明,特大暴雨对汇水区氮磷负荷的贡献非常显著。     

Effect of land use and land cover change on soil erosion and the spatio-temporal variation in Liupan Mountain Region, southern Ningxia, China

The Liupan Mountains are located in the southern Ningxia Hui Autonomous Region of China, that forms an important divide between landforms and biogeographic regions. The populated part of the Liupan Mountain Region has suffered tremendous ecological damage over time due to population pressure, excessive demand and inappropriate use of agricultural land resources. To present the relationship between land use/cover change and spatio-temporal variation of soil erosion, data sets of land use between the late 1980s and 2000 were obtained from Landsat Thematic Mapper (TM) imagery, and spatial models were used to characterize landscape and soil erosion conditions. Also, soil erosion in response to land use and land cover change were quantified and analyzed using data from geographical information systems and remote sensing. Soil erosion by water was the dominant mode of soil loss, while soil erosion by wind was only present on a relatively small area. The degree of soil erosion was classified into five severity classes: slight, light, moderate, severe, and very severe. Soil erosion in the Liupan Mountain Region increased between the late 1980s and 2000, both in terms of acreage and severity. Moderate, severe, and very severe eroded areas accounted for 54.86% of the total land area. The lightly eroded area decreased, while the moderately eroded area increased by 368817 ha (22%) followed by severe erosion with 146552 ha (8.8%), and very severe erosion by 97067.6 ha (5.8%). Soil loss on sloping cropland increased with slope gradients. About 90% of the cropland was located on slopes less than 15°. Most of the increase in soil erosion on cropland was due to conversion of steep slopes to cropland and degradation of grassland and increased activities. Soil erosion was severe on grassland with a moderate or low grass cover and on dry land. Human activities, cultivation on steep slopes, and overgrazing of pastures were the main reasons for the increase in erosion severity.     

Soil erosion and significance for carbon fluxes in a mountainous Mediterranean-climate watershed.

In topographically complex terrains, downslope movement of soil organic carbon (OC) can influence local carbon balance. The primary purpose of the present analysis is to compare the magnitude of OC displacement by erosion with ecosystem metabolism in such a complex terrain. Does erosion matter in this ecosystem carbon balance? We have used the Revised Universal Soil Loss Equation (RUSLE) erosion model to estimate lateral fluxes of OC in a watershed in northwestern Mexico. The watershed (4900 km2) has an average slope of 10 degrees +/- 9 degrees (mean +/- SD); 45% is >10 degrees, and 3% is >30 degrees. Land cover is primarily shrublands (69%) and agricultural lands (22%). Estimated bulk soil erosion averages 1350 Mg x km(-2) x yr(-1). We estimate that there is insignificant erosion on slopes < 2 degrees and that 20% of the area can be considered depositional. Estimated OC erosion rates are 10 Mg x km(-2) x yr(-1) for areas steeper than 2 degrees. Over the entire area, erosion is approximately 50% higher on shrublands than on agricultural lands, but within slope classes, erosion rates are more rapid on agricultural areas. For the whole system, estimated OC erosion is approximately 2% of net primary production (NPP), increasing in high-slope areas to approximately 3% of NPP. Deposition of eroded OC in low-slope areas is approximately 10% of low-slope NPP. Soil OC movement from erosional slopes to alluvial fans alters the mosaic of OC metabolism and storage across the landscape.