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  • 1
    Electronic Resource
    Electronic Resource
    Using ‘found’ data to augment a probability sample: Procedure and case study (1993)
    Springer
    Environmental monitoring and assessment 26 (1993), S. 65-83 
    Details
    ISSN: 1573-2959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract While probability sampling has the advantage of permitting unbiased population estimates, many past and existing monitoring schemes do not employ probability sampling. We describe and demonstrate a general procedure for augmenting an existing probability sample with data from nonprobability-based surveys (‘found’ data). The procedure, first proposed by Overton (1990), uses sampling frame attributes to group the probability and found samples into similar subsets. Subsequently, this similarity is assumed to reflect the representativeness of the found sample for the matching subpopulation. Two methods of establishing similarity and producing estimates are described: pseudo-random and calibration. The pseudo-random method is used when the found sample can contribute additional information on variables already measured for the probability sample, thus increasing the effective sample size. The calibration method is used when the found sample contributes information that is unique to the found observations. For either approach, the found sample data yield observations that are treated as a probability sample, and population estimates are made according to a probability estimation protocol. To demonstrate these approaches, we applied them to found and probability samples of stream discharge data for the southeastern US.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00555062
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Chemistry of lakes in designated wilderness areas in the western United States (1989)
    Springer
    Environmental monitoring and assessment 12 (1989), S. 3-21 
    Details
    ISSN: 1573-2959
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A synoptic survey of 719 lakes representing an estimated 10,393 lakes in mountainous areas of the western United States was conducted in autumn 1985. Nearly two-thirds of the study lakes were located in wilderness areas or national parks and were sampled by ground access. The results of a comparability study of 45 wilderness lakes accessed by helicopter and ground crews indicated that the data were generally indistinguishable, making it possible to use data from lakes sampled by ground crews without modification. Wilderness lakes had lower acid neutralizing capacity (ANC), base cations, sulfate, and dissolved organic carbon than nonwilderness lakes throughout the West. The highest estimated number (849) and percentage (42.1) of low ANC (≤50 μeq L-1) wilderness lakes were located in California; the lowest number (66) was located in the Southern Rockies. The Sierra Nevada contained an estimated 808 low ANC lakes, representing the largest subpopulation of low ANC lakes associated with an individual mountain range in the West. Wilderness lakes in selected geographic areas of the Rocky Mountains generally contained higher concentrations of major ions than lakes in the far West and the concentrations generally increased from the Northern to the Southern Rockies. Comparison of wilderness lakes in the West with lakes in the Adirondack Park, New York, and the Boundary Waters Canoe Area/Voyagers National Park in Northeastern Minnesota showed that western lakes are highly sensitive resources that currently exhibit little evidence of anthropogenic acidification. Although wilderness lakes do not exhibit symptoms of chronic acidification, short-term depression of pH and ANC from snowmelt and thunderstorms occur and episodic acidification influenced by anthropogenic sources cannot be discounted on the basis of this survey.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396724
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Variance estimation in the EMAP strategy for sampling discrete ecological resources (1994)
    Springer
    Environmental and ecological statistics 1 (1994), S. 133-149 
    Details
    ISSN: 1573-3009
    Keywords: double sampling ; EMAP ; Horvitz-Thompson estimator ; systematic sampling ; variable probability sampling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The United States Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) is designed to describe status, trends and spatial pattern of indicators of condition of the nation's ecological resources. The proposed sampling design for EMAP is based on a triangular systematic grid and employs both variable probability and double sampling. The Horvitz-Thompson estimator provides the foundation of the design-based estimation strategy used in EMAP. However, special features of EMAP designed to accommodate the complexity of sampling environmental resources on a national scale require modifications of standard variance estimation procedures as well as development of new techniques. An overview of variance estimation methods proposed for application to EMAP's sampling strategy for discrete resources is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02426656
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Regional chemical characteristics of lakes in North America Part II: Eastern United States (1986)
    Springer
    Water, air & soil pollution 31 (1986), S. 577-591 
    Details
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A survey of 1592 lakes ( 〉4 ha and ≤ 2,000 ha) was conducted in Fall, 1984. The study area was three regions of the eastern United States (Northeast, Upper Midwest, and Southeast) expected to contain the most lakes with acid neutralizing capacity (ANC) ≤400 μeq/L. The design of the survey provides statistically reliable estimates of the number, location and chemical characteristics of lakes in the study area. Frequency distribution statistics are presented for pH, ANC, sulfate and organic anion. The highest percentages and numbers of acidic lakes occurred in Florida, the Adirondaks, and the Upper Peninsula of Michigan. The highest percentages and numbers of lakes with high sulfate concentrations occurred in the Poconos/Catskills, Southern New England and Florida. The highest percentages and numbers of lakes with high organic anion concentrations occurred in Northeastern Minnesota, the Upper Great Lakes Area and Florida. The percentage of acidic lakes by sulfate concentration class revealed no discernable pattern across subregions. In contrast, the acidic lakes occur with the highest frequency in the lowest organic anion concentration class. The complex distribution of low ANC lakes cannot be explained simply by sulfate concentrations or organic acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00284214
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    Paper (German National Licenses)
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