Barcelona Field Studies Centre

ECOSTRIMED Protocol: Bioassessment to define a river's ecological status


Introduction: general procedure

The general procedure for rapid bioassessment to define a river's ecological status is as follows:


1. Selection of sampling sites


An appropriate series of sampling sites to be monitored must be defined as a preliminary step, prior to beginning the study, using topographical maps at a minimum scale of 1:50,000. Some considerations to take into account for selecting sites are:

  • The number of sampling sites will depend on the total length of the main river, and also on the objectives of the study.

  • The tributaries to the main river channel will be included if we plan a very detailed network of sites. However, only the most important tributaries or those which we can expect a priori to modify the characteristics of the main channel will be chosen.

  • The distance between sites should be between 1 and 10 kilometres. Shorter distances are suitable for local and detailed studies, while longer ones are better for broader studies (one or more drainage basins).

  • It is advisable for the subsequent interpretation of the results to select sites before and after cities or towns, as well as tributaries. The location should be at a certain distance from sewage inputs to avoid local pollution effects.

  • The first time a site is visited, a general examination of the reach is recommended in order to determine the possible modifying factors of water quality, which are impossible to predict or detect from a map.

  • When necessary, the exact location of the sampling site can be moved some metres up or downstream if this makes it more accessible or allows the detection of elements causing possible changes not observed from map studies.

  • In studies with a large number of sites, we would consider as suitable and efficient the sampling of at least 6 sites per day.


    2. Sampling point identification


    Each location should be identified (by name, code, etc.). The date, time of sampling and weather should be noted on the field data sheet provided in this protocol together with other observations which may be relevant for the study.


    3. Sampling procedure



    The hydrological regime of Mediterranean rivers is characterized by strong depletion of water discharge in summer, with the formation of intermittent streams (with disconnected pools) or even entirely dry channels. The discharge of the river or stream may modify the physical, chemical and biological characteristics of the water, and can give us an idea of its capacity to dilute runoff contaminants.



    Temperature, conductivity, pH and dissolved oxygen may be measured using field meters and recorded on the field data sheet. Remember to calibrate the meter before sampling. If these field measurements cannot be properly taken, a biological evaluation can still be done. On the other hand, if there is the possibility of studying a complete data set of physicochemical parameters in the field and in the laboratory, these can be useful for interpreting data, although they are not strictly necessary for a biological evaluation of water quality.



    The procedure for sampling macroinvertebrates is provided in section 5. We have included two sampling methods, one exclusively for lotic reaches , and the other to be used to obtain an integrative sample of all type of habitats present in the stream (lotic and lentic) .

    After the sampling, a preliminary field identification of the animals found may be performed, and the results annotated on the field data sheet (section 4), where the families present in Catalan rivers are listed. In section 8 and annex 1 we provide some keys and a set of illustrations of each family that should be useful in field recognition, but some previous knowledge is necessary for correct family identification in the field. If no taxonomical experience is available, the best alternative is to sort and identify the animals in the laboratory, using a stereoscope. Each sample should be labelled with the locality name and/or code and date of sampling.


    Riparian environment

    The riparian environment study should be performed on a 100 m long stretch of the river (although it can be shorter in small streams or when there are sudden changes in the sampling area; a waterfall, for example).


    4. Biological quality of the water and the status of the riparian environment


    If only lotic areas have been sampled, the FBILL index will be calculated.

    If all habitats have been included (riffles and pools) together with different kinds of substrates (stones, macrophytes, plant litter, etc.), 'BMWP' should be applied. The field sheet was designed for use with this index.

    The riparian environment status is an important element for the ecological assessment of Mediterranean rivers. The QBR method has to be used.


    5. Ecological status value

    The ecological status is obtained following the instructions in the ECOSTRIMED index and using the values of the water biological index selected and the QBR index.




    Sampling material

    Map with the sampling sites marked.

    Field sheets (several copies, at least one per sampling site)

    Field meters: to measure conductivity, solved oxygen (if available).

    Distilled water to clean the meters.

    Plastic tape-measure (minimum 10 m).

    pH and disDepth meter consisting of a long stick with graduated marks each centimeter.

    Hand net with a mesh size of 250 mm, at least 30 cm in diameter and 1 m long, to collect macroinvertebrates.

    White tray measuring approximately 1 5 x 20 x 5 cm, to observe the collected macroinvertebrates.


    250 g plastic jars to transport the samples to the lab.

    Plastic vials to collect and preserve animals not identified in the field.

    4% formalin or 70% ethanol to preserve the samples to be transported to the laboratory.

    Pencil, scissors, waterproof stickers and waterproof pens, to label and mark the samples.

    Paper labels to attach to the sample vials. They should be written in pencil and contain the following information: code or name of the sampling site, date, name of the collector, and the tentative taxonomical identification.

    Rubber gloves.

    Waders or boots.

    A towel.

    Sun protection: hat, sun cream, etc.


    Source: Diputació de Barcelona 2000 (Copyright)

    Developed by the Department of Ecology, University of Barcelona, with the collaboration of the Department of Environment of the Barcelona Council