BS EN 14996-2006 pdf download.Water quality — Guidance on assuring the quality of biological and ecological assessments in the aquatic environment.
5 Design of biological and ecological studies
5.1 General aspects
Biological and ecological assessments of aquatic environments should start with a clear statement of the qualitative and quantitative goals of the study. Methods chosen should be fit for purpos& and should take account of their statistical power, in order to ensure that necessary spatial and temporal resolution is achievable and cost-effective, A written protocol for the method should be available.
NOTE I Wherever possible, the method used should be derived from an International or European Standard.
Biological and ecological analyses of aquatic environments should be performed within the context of programmes that recognise the complexity of ecological systems, including temporal and spatial variability. Those aspects of temporal and spatial variation which should be incorporated in the sampling regime will be determined by the objectives of the study. Efforts should be made to minimise the impact of spatial and temporal variation if they are no subjects of investigation.
NOTE 2 In some cases, a pilot study may be necessary in order to optimise the design, justify the choice of method or to provide an estimate of error and uncertainty appropriate to the system under study.
5.2 Error assessment
Users of a method should be aware of all likely sources of error associated with that method. As quantitative errors are additive (I.e. can be combined by standard addition rules) any attempt to reduce errors is desirable. Errors in identification may have an influence on the overall precision of a method, parttcularly when the error relates to a taxon that Is abundant in a sample. The relative contribution of each source to the total error should be assessed before the method is adopted. Results from investigations should be accompanied by estimates or measurements of the major sources of error from sampling, sample preparation, sample analysis, data handling and data analysis. Information is required for every parameter used In the analysis for both precision and accuracy. Possible sources of bias need to be understood, arid appropriate control measures described.
The result of a measurement or assessment deviates from the true value because of the existence of a number of systematic and random errors. Important sources of random error in ecology are those introduced by the sampling and sub-sampling of biological items. These errors are random by nature and should be considered separately from other components of uncertainty (see Clause 10). The calculation of these errors is an important tool in the design of biological and ecological studies. Where possible, errors should be assessed directly from monitoring data: however, this will not be practicable in some cases (e.g. sampling variability for invertebrates). In such cases, the size of the expected error should be estimated in advance, based on calibration studies performed by experienced personnel.
5.3 Spatial and temporal variability
Survey and sampling strategies should be designed to address the problem of non-random spatial or temporal distribution of organisms and features. Mechanisms for recognising and dealing with this problem should be specified in standard operating procedures. If there are no such procedures, then the type of distribution should be assessed before the survey starts, and an appropriate sampling strategy devised.
NOTE Refer to particular methods described In European standards for more details.
Predictable seasonal factors that influence the composition of the biota. or the phenology of particular taxa that are likely to be encountered between seasons should also be recognised during the design of studies. Periods during the year when samples shall not be collected should be stated in operating procedures. The role of short-term, unpredictable events such as floods on the composition of the biota in the period prior to sampling should also be recognised. Where such events have a significant effect on the biota, procedures should take account of the time period necessary for the biota to recover before field surveys can be undertaken.
The design of survey and monitoring programmes should take account the response times of biota to environmental change. This will depend upon factors such as the life-cycle duration and recolonisation rates
6 Surveys and sampling
Surveys are activities related to the collection of information in the field. These activities may include the collection of samples for immediate or later analysis. Survey and sample records should include sufficient information to enable the location of the sample or survey site to be identified precisely by future workers. Appropriate information may include Geographical coordinates, grid references, plus notes, sketch maps and photographs relating the sample site to permanent landmarks in the vicinity.
Survey and sample records should have unique identifiers linking them to the time and place of collection. Sufficient location metadata should be recorded to ensure traceability.
Many types of surveys involve taxonomic determination in the field. Quality aspects related to this are dealt with in 7.2. Operating procedures should specify those taxa that need to be determined in the laboratory, and describe appropriate procedures for sampling and preservation of this material prior to identification.
Special guidelines are required for situations where threatened or legally protected taxa are likely to be encountered (e.g. conservation assessments, studies of biodiversity). The appropriate level of verification of such taxa will depend upon the aims of the study. In situations where the presence of such a taxori may have regulatory implications or where records indicate new occurrences within a nationally recognised recording unit, then determinations should be confirmed by a recognised expert in the taxonomic group in question (see
7.3).BS EN 14996-2006 pdf download.

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