Sample Collection

4 Key excerpts on "Sample Collection"

• 

  eBook - ePub

  Field Sampling

  Principles and Practices in Environmental Analysis

  • Alfred R. Conklin, Jr.(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Analytical and instrumental methods of analysis are very precise and accurate, but the results of analyses of environmental samples are not. This means that the variability comes either from the sampling procedures or during sample handling and storage prior to analysis. Sampling is the most important source of variability, and both the sampling and handling process must be carried out with great attention to detail.

  Sampling is the act of isolating a portion of a larger entity, analyzing it, and using the analytical results to describe the characteristics of the whole entity. In statistical terms the sample is an individual, which is a member of a family of similar individuals. Analysis shows that even environmental samples taken from sites close together may not be individuals or members of a family. When samples are taken at progressively increasing distances from a specific location they change in one of several ways. Characteristics can change gradually until a very different individual is identified, or they may change in a repetitive manner over long distances.

  On the other hand, samples may show gradual or repetitive changes and all of a sudden show a dramatic change in a completely different direction. For example, a soil at the top of a hill might be well developed, with distinct A, E, and B horizons. As expected, the B horizon is high in clay, but there is good internal drainage. The hillside profile might have similar horizons except that they would be thinner and less well developed. At the bottom of the hill next to a stream the soil has a thick, dark, high organic matter A horizon underlain by a sandy B horizon with a small amount of clay in it. There is thus a gradual change down the hill and an abrupt change at the bottom.

  It is essential that such changes in the environment be kept in mind both when designing a sampling plan and during noninvasive and invasive sampling. If unexpected changes occur, they are recorded in the project notebook and accounted for in the sampling procedures, sample analysis, and the interpretation of sample analysis.

  In sampling, air and water variability is not as great as with soil. The atmosphere is particularly uniform, but the hydrosphere is more variable in that the salt content of water varies with location. It is important to remember, however, that there are layers and definite direction in movement in both of these spheres. Downwind or downstream from a source of contamination it is dramatically diluted, and thus changes in location, either horizontally or vertically, may lead to sampling different layers, and this may result in differing and perhaps confusing analytical results. These sources of possible variation and error must be kept in mind when designing sampling plans for air and water as well as soil [1

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Analytical Measurements in Aquatic Environments

  • Jacek Namiesnik, Piotr Szefer(Authors)
  • 2009(Publication Date)
  • CRC Press

    (Publisher)

  In most cases a small fraction of a given water population or sample is collected and analyzed. The aim of taking samples or sampling is to extract a fraction of the water body that has chemical, physical, and biological properties identical to those of the bulk of the system to be studied. Ideally, all the characteristics of the sample, or at least, the parameters that are to be deter-mined, should not change until the time of measurement. Only then can the results of the sample analysis be representative of the composition of the system under scrutiny. If analytical data are to be the source of reliable and valuable information on an aquatic environ-ment, the samples should not only be properly collected, preserved, transported, and stored, but should also be taken at the proper place, time, frequency, and so on. All these factors must be prop-erly planned, taking into account both the characteristics of the aquatic environment to be sampled and the feasibility of the task. This chapter looks at the sampling of different surface and ground waters. As sediments consti-tute an integral part of most aquatic environments, they too have been taken into consideration. It should be mentioned that precipitation and wet deposition also play an important role in the hydrological cycle, but the sampling problems are somewhat different and will not be dealt with here—they are comprehensively described elsewhere. 1,2 1.2 GENERAL CONSIDERATIONS Sampling is the critical step in the whole analytical process; indeed, it is often the weakest link in the procedure and needs special care if the analytical results obtained are to be a source of reliable analytical information on a system.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Essential Environmental Science

  Methods and Techniques

  • Simon Watts(Author)
  • 2003(Publication Date)
  • Routledge

    (Publisher)

  All that has been said about the desirability of random samples in the social environmental sciences applies equally to sampling in the physical environmental sciences. The difference is that, because of the nature of the physical system, random samples are very difficult to obtain (if possible at all). The following sections discuss the kinds of sampling frameworks available in the physical environmental sciences.

  see Section 2.2

  2.3a Sampling in areas

  Phenomena studied in the environmental sciences are often not accessible, individual ‘things’ which can be numbered and subjected to an ordinary probability sampling procedure. Geologists are perhaps in the worst position of all, as their subject matter is almost all buried at depth and they must take whatever evidence they can from outcrops or drill holes that happen to be available. Under these conditions it is very difficult to demonstrate that a sample is unbiased. In some branches of the environmental sciences populations are more accessible (like plants and animals), but the problem often is that they do not consist of identifiable and separate objects. Air, water, soil and rock are continuous media, and variables like air temperature, soil depth and water salinity are spread continuously. For this type of variable, location is often used as the basis of the sampling procedure. Consequently, measurements are taken at particular points, along lines or traverses, or in small areas (quadrats) (see Fig. 2.1 ).

  There are several methods for deciding the location of your sample points, traverses and quadrats. Here we shall describe the most commonly used methods for deciding the location of sampling points. The principles apply also to traverse and quadrat sampling. Fig. 2.2 illustrates the sampling designs.

  The methodology of simple random sample selection is given in Box 2.2

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Geoforensics

  • Alastair Ruffell, Jennifer McKinley(Authors)
  • 2008(Publication Date)
  • Wiley

    (Publisher)

  This spatial resolution of DEM may be especially relevant in search scenarios where a body deposition site is most likely to be in a certain vegetation or land-use type (vegetation such as bracken, peat bogs, etc.). In circumstances where overall elevation is more important than local variations in surface shape, mesoscale DEMs with a spatial resolution from 200 metres to 5 kilometres are more applicable. Macroscale DEMs (spatial resolution from 50–500 kilometres) provide generalized data and are applicable for broad-scale modelling or search scenarios. SAMPLE SIZE 157 6.2 Sampling for geological materials at urban and non-urban crime scenes Sample number, method of collection and storage, location and context are generally agreed to be critical in subsequent analysis. In the various branches of geoscience, sampling is a basic skill, practised in ways developed for efficient and representative solution to a problem but rarely written about from the perspective of criminal investigations. Remote sensing and geophysics are both completely dependent on representative sampling, otherwise only ground-truthing can be used to test what the method has acquired, making the procedure otherwise largely useless. The main reasons why physical samples are rarely discussed in the literature may be twofold: first is the implicit assumption that the qualified geoscientist will have been taught appropriate sampling methods; second is the trust placed on analysis. Murray (2004), Pye and Croft (2004) or Ruffell and McKinley (2004) are three recent overviews on how methods not data source , collection or integrity are central to the current practice of the science. A third reason, specific to geoforensics, is historical. When soil or sediment was observed/recovered from a scene of crime by investigators, with appropriate training and/or support they knew a geologist of some sort was required.

  Sign up to read

  Learn more about book