Terrain plays a key role in landscape pattern formation, particularly in the transition zones from mountains to plains. Exploring the relationships between terrain characteristics and landscape types in terrain-complex areas can help reveal the mechanisms underlying the relationships. In this study, Qihe River Basin, situated in the transition zone from the Taihang Mountains to the North-China Plain, was selected as a case study area. First, the spatial variations in the relief amplitudes (i.e., high-amplitude terrain undulations) were analyzed. Second, the effects of relief amplitudes on the landscape patterns were indepth investigated from the perspectives of both landscape types and landscape indices. Finally, a logistic regression model was employed to examine the relationships between the landscape patterns and the influencing factors (natural and human) at different relief amplitudes. The results show that with increasing relief amplitude, anthropogenic landscapes gradually give in to natural landscapes. Specifically, human factors normally dominate the gentle areas (e.g., flat areas) in influencing the distribution of landscape types, and natural factors normally dominate the highly-undulating areas (e.g., moderate relief areas). As for the intermediately undulating areas (i.e., medium relief amplitudes), a combined influence of natural and human factors result in the highest varieties of landscape types. The results also show that in micro-relief areas and small relief areas where natural factors and human factors are more or less equally active, landscape types are affected by a combination of natural and human factors. The combination leads to a high fragmentation and a high diversity of landscape patterns. It seems that appropriate human interferences in these areas can be conducive to enhancing landscape diversity and that inappropriate human interferences can aggravate the problems of landscape fragmentation. 相似文献
The persistence effect contribution of legacy nutrients is often cited as a reason for little or no improvement in water quality following extensive implementation of watershed nutrient mitigation actions, yet there is limited knowledge concerning factors influencing this response, often called the “persistence effect.” Here, we adopted detrended fluctuation analysis and Spearman analysis methods to assess the influence of land use on the watershed phosphorus (P) persistence effect, using monthly water quality records during 2010–2016 in 13 catchments within a drinking water reservoir watershed in eastern China. Detrended fluctuation analysis was used to calculate the Hurst exponent α to assess watershed legacy P characteristics (α ≈ 0.5, α > 0.5, and α < 0.5 indicate white noise, persistence, and anti‐persistence, respectively). Results showed weak to strong P persistence (0.60–0.81) in the time series of riverine P in the 13 catchments. The Hurst exponent α had negative relationships with agricultural land (R = ?.47, p = .11) and developed land (R = ?.67, p = .01) and a positive relationship with forest land cover (R = .48, p = .10). The persistence effect of riverine P was mainly determined by retention ability (biogeochemical legacy) and migration efficiency (hydrological legacy). A catchment with strong retention capacity (e.g., biomass uptake/storage and soil PO4 sorption) and low migration efficiency results in a stronger persistence effect for riverine P. In practice, source control is more effective in catchments with weak persistence, whereas sink control (e.g., riparian buffers and wetlands) is preferred in catchments with strong persistence effects. 相似文献
Using the 7 100 absolute first arrivals of P waves and 91 513 relative P arrival times of 726 events at the northeastern margin of the Ordos block since 2009, the 3D fine structure of P wave velocity within the depth of 15km in the crust was inverted by the double difference seismic tomography method. The results show that there exist obvious high-speed continuous bodies in the northwest of the study area, and their lateral areas increase gradually with depth, while the velocity of east and south is relatively low. The velocity inhomogeneity exists and differs at different depths. The lateral differences of velocity are related to seismicity and faults. The 5~15km depth profile shows that earthquakes tend to occur in the area with relatively high velocity or high speed transition zones, which to some extent reflects the fragility of regional crustal media and the strong differential movement of faults in vertical and horizontal directions where the crust body is easy to absorb and store strain energy and generate major earthquakes. A "Y"-shape low-velocity channel is present in the lower crust around Liangcheng, corresponding to the NW-trending Heilaoyao-Shahukou fault set, which may reveal the migration path of the Late Tertiary-Quaternary basalt eruption. The Helingeer M6.2 earthquake in 1976 was related to the formation of the locking section of the thermal welding in this area. The three-dimensional fine structure of P wave velocity presented in this paper provides intuitive seismological evidence for physical and chemical properties of crustal media and the deep tectonic environment of earthquake preparation. 相似文献
The control of soil pollution in China has become an issue, and in this study, a compound contaminated site was selected and focus on the site and its nearby environment, organochlorine pesticides (OCPs) were investigated in both soil (top and deep soil) and air samples. The main pollutants in top soils at site are dichlorodiphenyltrichloroethane (DDTs, 0.05–104 mg/kg d.w., avg: 14.5 mg/kg d.w.) and hexachlorobenzene (HCB, 0.02–4.85 mg/kg d.w., avg: 0.72 mg/kg d.w.) which is in accordance with its production history. As for the deep soils, ΣOCPs at site were found concentrated at workshops especially the technical pesticide workshop (5.29–22.1 mg/kg d.w., avg: 9.15 mg/kg d.w.) and the history DDTs’ workshop (4.00–64.8 mg/kg d.w., avg: 20.4 mg/kg d.w). Around site, OCPs were mainly concentrated at layers of −20 cm and the −40 cm and decreased with distance being far away, at 5000 m, the ΣOCPs was comparable with normal agriculture soil (22.1−91.4 ng/g d.w., avg: 55.4 ng/g d.w.). ΣOCPs in the air samples ranged 64.6–823 ng/m3 (avg: 459 ng/m3) at site and 9.93–176 ng/m3 (avg: 50.8 ng/m3) around site which are all dominated with DDTs and HCHs. Soil–air exchange fugacity was calculated to judge the transportation of the OCPs and the results showed soils at the site and its nearby areas (within 5000 m) are releasing most of the OCPs into air, and accordingly through evaluation, inhalation was found to be the major source for human health risk, which is a great threat to the workers at site and the nearby residents.
By using the digital observations of the pendulum tiltmeter, water tube tiltmeter,extensometer and volumetric strainmeter at Huzhou station and with the power spectrum density estimation method,we acquired the_0S_5-_0S_50 fundamental sphere free oscillations caused by the Japan earthquake on March 11,2011,then compared it with the PREM model. The relative errors are mostly bigger than 1.2‰. The extensometer and volume strainmeter can clearly detect _0S_2,_0S_3and_0S_4,which are closely related to the deep structure and earth's interior. 相似文献
Quasi-static testing is one of the most commonly used experimental methods for examining the seismic performance of structural members. However, consistent loading protocols for experimental seismic qualification of members in emerging steel frames such as self-centering braced frames (SCBFs) as well as in some conventional ones including buckling-restrained braced frames (BRBFs) are still lacking. This paper aims to propose standardized loading protocols based on time-history dynamic analysis on a series of prototype building frames, including steel SCBFs, BRBFs, and moment-resisting frames (MRFs), where both far-field and near-fault earthquakes are considered. The methodology for the development of the loading protocols involves ground motion selection and scaling, design and analysis of prototype buildings, analysis results processing, and rainflow cycle counting, together with extra justification steps. The proposed loading protocols are consistently derived based on the MCE-level seismic hazard and 84th percentile values of key seismic demand parameters. These parameters are number of damaging cycles Nt, maximum inter-story drift θmax, inter-story drift range Δθi, sum of inter-story drift range ΣΔθi, and residual inter-story drift θr. The analysis confirms the variations in these seismic demands imposed on the different structural systems under different types of ground motions, highlighting the necessity of developing separate loading protocols for the different cases. The assumptions, decisions, and judgments made during the development of the loading protocols are elaborated, and the conditions and restrictions are outlined. The rationality of the proposed loading protocols is further justified through demonstrating the cumulative distribution function and energy dissipation demand of the systems. 相似文献
Regression-based methods are commonly used for riverine constituent concentration/flux estimation, which is essential for guiding water quality protection practices and environmental decision making. This paper developed a multivariate adaptive regression splines model for estimating riverine constituent concentrations (MARS-EC). The process, interpretability and flexibility of the MARS-EC modelling approach, was demonstrated for total nitrogen in the Patuxent River, a major river input to Chesapeake Bay. Model accuracy and uncertainty of the MARS-EC approach was further analysed using nitrate plus nitrite datasets from eight tributary rivers to Chesapeake Bay. Results showed that the MARS-EC approach integrated the advantages of both parametric and nonparametric regression methods, and model accuracy was demonstrated to be superior to the traditionally used ESTIMATOR model. MARS-EC is flexible and allows consideration of auxiliary variables; the variables and interactions can be selected automatically. MARS-EC does not constrain concentration-predictor curves to be constant but rather is able to identify shifts in these curves from mathematical expressions and visual graphics. The MARS-EC approach provides an effective and complementary tool along with existing approaches for estimating riverine constituent concentrations. 相似文献