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Estimation of sediment load from Himalayan basins is of considerable importance for the planning, designing, installation and operation of hydro-power projects, including management of reservoirs. In the present study, an assessment of physical and chemical load, sediment yield and erosion rate has been undertaken at eight different locations in the Sainj and Tirthan watersheds. The analysis revealed that the maximum load was transferred during the monsoon season. Moreover, the estimated average chemical erosion rate of the Sainj (83 t km− 2 yr− 1) and Tirthan (80 t km− 2 yr− 1) watersheds were higher than that of the Indian average (69 t km− 2 yr− 1) representing all the rivers. Both watersheds were eroding physically and chemically at a faster rate than that of the world global average erosion rate (185 t km− 2 yr− 1). The flattish nature of the channels in some segments of these watersheds showed a lower transport of sediments, where as the constricted segments having steep bed slopes increased the velocity of flow and the sediment transport rate. These findings have important implications for water resource management in the context of sediments mobilization, erosion, channel management, ecological functions and operation of the hydro-power projects in the Lesser Himalayan region. 相似文献
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玉米果穗粘连籽粒图像分割方法 总被引:6,自引:0,他引:6
为了对基于图像的玉米果穗穗粒数进行更精确的计算,给出了一种新的粘连籽粒图像分割方法。对粘连二值图像进行轮廓平滑和欧氏距离变换,将粘连籽粒的距离变换图视为地形学上的地形图,以地形图中的山谷线作为粘连二值图像的分割线。将欧氏距离变换图像的边界像素点视作水源点,根据山谷形态两边高、中间低的地形趋势设定水流的行进规则,使得水流在遇到山坡时自动绕行,但在遇到谷口点时可沿山谷线流动,从而将粘连籽粒分割开。该方法对单个未粘连籽粒不产生影响,不必在分割操作前依靠人工设定阈值进行籽粒是否粘连的判断,可以作为籽粒是否存在粘连的判断方法。用该方法对442个含不同粘连情况的籽粒连通分量进行判断与分割测试,粘连判断准确率为99.7%,粘连籽粒的分割准确率为94.9%。 相似文献
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Habitat connectivity is a central factor in shaping aquatic biological communities, but few tools exist to describe and quantify
this attribute at a network scale in riverine systems. Here, we develop a new index to quantify longitudinal connectivity
of river networks based on the expected probability of an organism being able to move freely between two random points of
the network. We apply this index to two fish life histories and evaluate the effects of the number, passability, and placement
of barriers on river network connectivity through the use of simulated dendritic ecological networks. We then extend the index
to a real world dendritic river system in Newfoundland, Canada. Our results indicate that connectivity in river systems, as
represented by our index, is most impacted by the first few barriers added to the system. This is in contrast to terrestrial
systems, which are more resilient to low levels of connectivity. The results show a curvilinear relationship between barrier
passability and structural connectivity. This suggests that an incremental improvement in passability would result in a greater
improvement to river network connectivity for more permeable barriers than for less permeable barriers. Our analysis of the
index in simulated and real river networks also showed that barrier placement played an important role in connectivity. Not
surprisingly, barriers located near the river mouth have the greatest impact on fish with diadromous life histories while
those located near the center of the river network have the most impact on fish with potadromous life histories. The proposed
index is conceptually simple and sufficiently flexible to deal with variations in river structure and biological communities.
The index will enable researchers to account for connectivity in habitat studies and will also allow resource managers to
characterize watersheds, assess cumulative impacts of multiple barriers and determine priorities for restoration. 相似文献
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A multi-scale assessment of human and environmental constraints on forest land cover change on the Oregon (USA) coast range 总被引:3,自引:0,他引:3
Human modification of forest habitats is a major component of global environmental change. Even areas that remain predominantly forested may be changed considerably by human alteration of historical disturbance regimes. To better understand human influences on the abundance and pattern of forest habitats, we studied forest land cover change from 1936 to 1996 in a 25000 km2 landscape in the Oregon (USA) Coast Range. We integrated historical forest survey data and maps from 1936 with satellite imagery and GIS data from 1996 to quantify changes in major forest cover types. Change in the total area of closed-canopy forests was relatively minor, decreasing from 68% of the landscape in 1936 to 65% in 1996. In contrast, large-conifer forests decreased from 42% in 1936 to 17% in 1996, whereas small-conifer forests increased from 21% of the landscape in 1936 to 39% in 1996. Linear regression models were used to predict changes in the proportion of large conifer forest as a function of socioeconomic and environmental variables at scales of subbasins (mean size = 1964 km2, n=13), watersheds (mean size = 302 km2, n=83), and subwatersheds (mean size = 18 km2, n=1325). The proportion of land in private ownership was the strongest predictor at all three spatial scales (partial R2 values 0.57–0.76). The amounts of variation explained by other independent variables were comparatively minor. Results corroborate the hypothesis that differing management regimes on private and public ownerships have led to different pathways of landscape change. Furthermore, these distinctive trajectories are consistent over a broad domain of spatial scales. 相似文献
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James D. Wickham Timothy G. Wade Kurt H. Riitters R.V. O'Neill Jonathan H. Smith Elizabeth R. Smith K.B. Jones A.C. Neale 《Landscape Ecology》2003,18(2):193-206
Nutrient export coefficients are estimates of the mass of nitrogen (N) or phosphorus (P) normalized by area and time (e.g.,
kg/ha/yr). They have been estimated most often for watersheds ranging in size from 102 to 104 hectares, and have been recommended as measurements to inform management decisions. At this scale, watersheds are often nested
upstream and downstream components of larger drainage basins, suggesting nutrient export coefficients will change from one
subwatershed to the next. Nutrient export can be modeled as risk where lack of monitoring data prevents empirical estimation.
We modeled N and P export risk for subwatersheds of larger drainage basins, and examined spatial changes in risk from upstream
to downstream watersheds. Spatial (subwatershed) changes in N and P risk were a function of in-stream decay, subwatershed
land-cover composition, and subwatershed streamlength. Risk tended to increase in a downstream direction under low rates of
in-stream decay, whereas high rates of in-stream decay often reduced risk to zero (0) toward downstream subwatersheds. On
average, increases in the modeled rate of in-stream decay reduced risk by 0.44 for N and 0.39 for P. Interactions between
in-stream decay, land-cover composition and streamlength produced dramatic changes in risk across subwatersheds in some cases.
Comparison of the null cases of no in-stream decay and homogeneously forested subwatersheds with extant conditions indicated
that complete forest cover produced greater reductions in nutrient export risk than a high in-stream decay rate, especially
for P. High rates of in-stream decay and complete forest cover produced approximately equivalent reductions in N export risk
for downstream subwatersheds.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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湘西北小流域不同植被恢复模式土壤养分库效应 总被引:5,自引:1,他引:4
研究了湘西北女儿寨小流域马尾松天然林(Ⅰ)、杉木人工林(Ⅱ)、杜仲人工林(Ⅲ)、油桐人工林(Ⅳ)、润楠次生林(Ⅴ)、毛竹杉木混交林(Ⅵ)及荒草灌丛(Ⅶ)等7种典型植被恢复模式土壤养分库含量、养分库有效性指数以及土壤团聚体分形维数和平均重量直径对养分库有效性的影响。结果表明:土壤养分库表聚效应明显,不同植被恢复模式全氮、水解氮质量分数为0.57×10-3~2.52×10-3、29.63×10-6~134.40×10-6,全磷、速效磷为0.02×10-3~0.12×10-3、0.93×10-6~14.55×10-6,速效钾为21.38×10-6~202.23×10-6;润楠次生林全氮、全磷、速效磷质量分数最高,杉木人工林水解氮质量分数最高,油桐人工林速效钾质量分数最高;森林植被模式下土壤养分库有效性指数均高于荒草灌丛,排序为EⅥ(1.2981)EⅣ(1.2855)EⅤ(1.2322)EⅡ(1.2141)EⅢ(1.2011)EⅠ(1.1986)EⅦ(1.1746);土壤团聚体分形维数与碱解氮、速效磷、速效钾均呈负相关,且与速效钾的相关关系达到显著水平(α=0.10);平均重量直径与碱解氮、速效磷为负相关,与速效钾为弱正相关,但均未达到显著水平;分形维数与速效钾之间线性回归关系极显著(R2=0.4901,p=0.0053),分形维数、平均重量直径与碱解氮、速效钾之间的通用线性方程也达到极显著(R2=0.6644,p=0.0014)和较显著(R2=0.4091,p=0.0426)。 相似文献
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