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131.
Aquatic macroinvertebrate diversity in the Nanda Devi Biosphere Reserve (NDBR) was monitored for a period of twelve months (September 2000 to August 2001). All the important hydrological attributes were measured monthly for one year. Macroinvertebrates were sampled from three sites (S1$, S2$, & S3$) of the headwater stream Dhauliganga of NDBR. The present study revealed that the velocity of the water current, hydromedian depth, turbidity and dissolved oxygen in addition to nature and size of the bottom substrates have their significant impact on benthic invertebrate diversity. The ecological relevance of the measured hydrological attributes was investigated by comparing their degree of correlation with invertebrate density and diversity. Macroinvertebrate diversity was found to be highest (3.096 ± 0.03) in winter months (November–January) and lowest (2.816 ± 0.02) in monsoon months (July–August). The high diversity of macroinvertebrates may be due to low turbidity, high water transparency, optimum water temperature, high dissolved oxygen, low water velocity and suitable composition of the bottom substrates. 相似文献
132.
Manoliadis OG 《Environmental management》2001,28(4):497-504
Irrigation management calls for objective criteria capable of representing the economy, reliability, and productivity of irrigation
systems. These criteria must be compatible with long-term sustainability and conservation goals. The criteria representing
the above goals are the economic effect of management on yield reduction, economic effect, and reliability referring to plant
growth and operation of the network. In this study environmental indices are introduced to express the above criteria in quantitative
terms. The inclusion of these indices at the farm and network level create a multicriteria framework for decision-making based
on composite programming. An experimental study was conducted during the irrigation periods of 1989 and 1990 in Chania, Greece,
concerning water delivered to 40 experimental plots, soil moisture content at the rootzone, and irrigation system operational
failures. The data collected in real time were used for the calculation of the corresponding environmental indices. The variation
in time and space is high and resulted in up to 62% of yield loss and low system performance (up to 7% of system temporal
reliability). The study indicated that environmental indices could be incorporated to select alternatives and also to develop
policies on water delivery. The final decision involves a trade-off analysis between cost of application and desired system
performance. Measures of both primary objectives can be obtained using environmental indices that represent system operation
aggregation at its basic levels (on farm and network). 相似文献
133.
Past tree colonization dynamics of a powerline-right-of-way (ROW) corridor in the Haut-Saint-Laurent region of Quebec was studied based on the present age distribution of its tree populations. This colonization study spans 20 years, from 1977 (ROW clearance) to 1996. The sampled quadrats were classified into six vegetation types. Tree colonization dynamics were interpreted in each type, and three distinct patterns were identified. (1) Communities adapted to acidic conditions were heavily colonized by Acer rubrum, at least for the last 12 years. (2) Communities adapted to mesic or to hydric conditions were more intensely colonized in the period 1985-1987 than in the following 9 years; this past success in tree colonization may have been caused by herbicide treatments, which could have facilitated tree establishment by damaging the herbaceous and shrub vegetation. (3) Cattail, vine-raspberry, and reed-dominated communities contained few tree individuals, with almost all trees establishing between 1979 and 1990; those three vegetation types appear as the most resistant to tree invasion in the ROW studied. This study supports the need for an integrated approach in ROW vegetation management, in which the selection of vegetation treatment methods would depend on the tree colonization dynamics in each vegetation type. Minimizing disturbances inflicted on ROW herbaceous and shrub covers should be the central strategy because disturbances jeopardize natural resistance to future tree invasion, except in communities adapted to acidic conditions where the existing vegetation does not prevent invasion by A. rubrum. Many trees are surviving the successive cutting operations by producing new sprouts each time, particularly in communities adapted to mesic and hydric conditions. In these cases, mechanical cutting should be replaced by a one-time stump-killing operation, to avoid repeated and unsuccessful treatments of the same individuals over time. 相似文献
134.
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136.
Vehicular and pedestrian traffic decreased top and root production, percent cover, and diversity of vegetation, and modified species composition on beach and foredune areas of Padre Island National Seashore and Nueces County Park. Degradation of vegetal cover was directly related to the type and intensity of traffic; species in heavily trafficked areas represented earlier successional stages than those in comparable undisturbed areas. 相似文献
137.
P. H. Anderson M. W. Lefor W. C. Kennard 《Journal of the American Water Resources Association》1980,16(2):248-255
ABSTRACT: The delineation of inland wetlands requires close field examination of the biological and physical gradients (transition zones) between wetlands and bordering uplands. As part of a study on the detection and delineation of inland wetlands in eastern Connecticut by remote sensing techniques, this effort was designed to investigate vegetation distribution and composition and selected physical and chemical properties of the soils of wetland to upland transition zones in deciduous wetland forests. Field research was conducted during the growing season of 1975 within a test area consisting of the 45 mi2 Town of Mansfield, Connecticut. Changes in vegetation composition and structure, soil pH, and soil water content were determined along line transects extended over wetland to upland transition zones. Differences in soil pH occurred along the transects but were of such magnitude that they probably have little impact on plant distribution. There were significant changes in soil water content along the wetland to upland gradients. Discriminant analysis applied to statistical “index of abundance” data describing vegetation distribution among the various zones (wetland, transition, upland) showed which plant species best distinguish wetlands from uplands. Of the criteria studied, vegetation composition and distribution, soil water content, and relief are the most useful criteria for delineating deciduous wetland forests. 相似文献
138.
Bruce J. Blanchard Marshall J. McFarland Thomas J. Schmugge Edd Rhoades 《Journal of the American Water Resources Association》1981,17(5):767-774
Large area soil moisture estimations are required to describe input to cloud prediction models, rainfall distribution models, and global crop yield models. Satellite mounted microwave sensor systems that as yet can only detect moisture at the surface have been suggested as a means of acquiring large area estimates. Relations previously discovered between microwave emission at the 1.55 cm wavelength and surface moisture as represented by an antecedent precipitation index were used to provide a pseudo infiltration estimation. Infiltration estimates based on surface wetness on a daily basis were then used to calculate the soil moisture in the surface 0–23 cm of the soil by use of a modified antecedent precipitation index. Reasonably good results were obtained (R2= 0.7162) when predicted soil moisture for the surface 23 cm was compared to measured moisture. Where the technique was modified to use only an estimate of surface moisture each three days an R2 value of 0.7116 resulted for the same data set. Correlations between predicted and actual soil moisture fall off rapidly for repeat observations more than three days apart. The algorithms developed in this study may be used over relatively flat agricultural lands to provide improved estimates of soil moisture to a depth greater than the depth of penetration for the sensor. 相似文献
139.
E. Earl Whitlatch Peggy L. Asplund 《Journal of the American Water Resources Association》1981,17(2):310-314
ABSTRACT: The cost of water service to rural residents is very high compared to urban areas. This is true even after subsidization by Farmers Home Administration (FmHA) loans and grants. Capital cost data on 44 projects financed by the Ohio office of the FmHA during the period August 1968 to January 1977 are used to derive cost equations for 26 components of rural water distribution systems. These components represent 92 percent of the capital cost of the pipeline distribution systems studied. The data can be used to economically design rural water supply systems from a capital cost viewpoint. More data are needed on operation and maintenance costs as well as central and cluster well costs before totally economic system designs can be undertaken. 相似文献
140.
Vegetation changes associated with barrier-dune construction on the outer banks of North Carolina 总被引:1,自引:0,他引:1
Manmade dunes are used to stabilize the barrier islands of the mid-Atlantic coast of the United States so that they are more amenable to development. Although this strategy has stabilized extensive sections of the barrier-island substrate, it has also caused significant ecological changes. The rate and pattern of the resulting vegetation changes along the Outer Banks of North Carolina were determined using sequential aerial photography. Successional trends have been altered in favor of more stable woody communities. 相似文献