Saprobic system

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The saprobic system (in ancient Greek σαπρός sapros , German 'lazy' , βίος bios 'life', σύστεμα systema 'structure') is a rating system for determining the biological water quality of rivers and their classification in water quality classes .

Organisms found in water are used as bioindicators for the pollution of a water body by degradable organic substances, this is known as its saprobia . The various types of organisms recorded, also called saprobians or saprobians , are assigned a species-specific indicator value according to the more or less saprobiotic way of life, which, taking into account their respective frequency, allows the calculation of a so-called saprobic index to which a water quality class is assigned.

With the saprobic system only the pollution of a running water with organic, easily degradable, oxygen-consuming substances, e.g. B. from domestic sewage , measured. As these under oxygen degrade -Consumption, this is closely related to the oxygen content of the water and the redox potential . Other water pollution are not indicated with the saprobic system. These are e.g. B .: Exposure to toxic substances ( heavy metals , pesticides ), exposure to nutrient salts ( trophies ), acidification of the water , unnatural increase in water temperature (thermal exposure), exposure to "structural degradation" ( expansion and straightening of the water ) and by changing the hydraulics (low water lowering and drying out phases, increased high water peaks due to canal tees ). For some of these pressures, separate indication systems have been set up, which can be used in addition to the saprobic system for water monitoring , for example the SPEARpesticides procedure for the indication of pesticide contamination.

When assessing rivers for the European Water Framework Directive , it is required that bodies of water achieve “good ecological status”. This is defined more comprehensively than the water quality according to the saprobic system, for example all aquatic organisms, e.g. also aquatic plants, algae and fish, are taken into account. The soil-living, invertebrate organisms, which are the basis of the saprobial system, are further considered as one of the quality components, but non-saprobial changes in the natural community now also lead to a devaluation. The saprobic system will continue to be used within the framework of the new methodology, but it now only forms one of several assessment “ modules ”.


The saprobic system is based on the observation that the biological community of a water body changes in a predictable manner with organic pollution. While some water dwellers are insensitive and robust to organic pollution, others only occur in unpolluted or slightly polluted waters, whereby their tolerance ranges are very different. Other species become more common in organically polluted waters. These observations can be explained from the biology of the organisms. Some species and groups of species are extremely in need of oxygen and perish when the oxygen content drops. Other species require a high supply of nutrients (e.g. organically enriched mud), but they can sometimes tolerate very low levels of oxygen. The occurrence and frequency of such water dwellers who react strongly to organic pollution can be used to measure this pollution if the tolerance ranges for the individual species are known. In the saprobic system, each type of indicator is assigned a value, the index value. This is empirically derived from the observation of numerous polluted and unpolluted bodies of water (i.e. not based on laboratory measurements). The mean value (weighted according to the frequency of occurrence) of the index values ​​of all indicator species living there results in a numerical value for an examined sample site, the so-called saprobic index. The species that occur are used to a certain extent as measuring instruments for organic pollution. By using numerous types of indicators, the measurement is ideally very well secured.

To determine the water quality class, the saprobic index of the examined stretch of water is compared with a standardized list of such indices. The running water is classified in water quality classes.

The saprobic system in the form described was first set up by Kolkwitz and Marsson a good hundred years ago and has been further developed since then. The procedure in Germany is mostly based on DIN 38410. The procedure is traditionally used in Austria and the Czech Republic in a slightly modified form (in Austria: Önorm M6232, in the Czech Republic CSN 757716 and 757221). When the evaluation procedure for the Water Framework Directive of the European Union (Perlodes) was introduced, the saprobic system served as a model for biological factors. Otherwise z. B. the British BMWT / ASPT system. (An overview of common rating systems can be found in.)

Investigation method

To determine the saprobic index, the following procedure is (somewhat simplified) necessary (only macro-samples):

  • Selection of the sampling point: As a comprehensive sampling of the water would be impossible, representative sampling points are to be selected at which the index is to be determined. The index determined here is transferred to a longer, homogeneous stretch of water. The selection of the correct sample locations has a serious impact on the relevance of the results. A sampling point must be representative of the stretch of water to be assessed (e.g. not the only rapids in a sluggishly flowing lowland stream). Their location to known wastewater discharges or confluences of tributaries is naturally important. For larger water systems, sample sites are usually selected according to a given grid (e.g. on the basis of the waterways).
  • Collect the aquatic organisms. All organisms living in the water that could be indicator species are to be collected at the selected sampling point. The sampling should depict the stretch of water as representative as possible. Since most of the indicator species could not be determined with sufficient certainty in the field, the organisms must usually be killed and preserved so that the species can later be determined in the laboratory. Since not only the presence but also the frequency of the species must be known for the saprobic index, the sampling must be carried out in such a way that it can be determined. In the procedure, classification into frequency classes is sufficient. Above all, within the Perlodes method, quantitative samples are also taken, in which the absolute frequency is determined (by counting).
  • Determination of the collected species in the laboratory. Most saprobic species can only be determined using a microscope or a stereo magnifying glass, sometimes only after preparation. Identifying many species is difficult and demanding. Various simplified methods that make less demands on the determination are in use for laypersons. These provide less precise, but mostly usable results of the order of magnitude.
  • List the indicator types of the sample with their frequency (as an abundance class or by counting)
  • Calculation of the index

Macro and microsaprobies

The indicator organisms used to determine the saprobic index are called saprobic or saprobic.

Two lists are used in the context of the procedure. A list contains microorganisms (micro saprobia). These are small, often single-celled animal species, e.g. B. ciliates (ciliates) and flagellates ( flagellates ). The other list includes macroscopically recognizable, bottom-living invertebrates (macroinvertebrates or macro-saprobia), e.g. B. Insect larvae (such as stonefly larvae , mayfly larvae , caddis fly larvae ), crustaceans (such as woodlice and amphipods ), snails, clams, leeches and some annelids are listed; these are summarized as macrozoobenthos . In the currently valid version of the DIN procedure, around 200 micro-probes and more than 600 macro-probes are listed. The saprobic index is to be set up separately for micro and macrosaprobic, both may not be averaged or offset against each other. In practice, the more important value is that for the macro probes. The value for the micro-probes is particularly important in organically very heavily polluted waters, because only very few types of macro-probes live in them and the result is therefore very poorly secured.

Organisms of the free water body (pelagic) are not used for either the macro or the micro index. This applies e.g. B. also for the fish species.

Saprobic index

The following rule is used to calculate the saprobic index:

Each type of indicator found in a sample is assigned a frequency level, the so-called abundance ( A ). It ranges from ( A ) = 1 (single finding) to ( A ) = 7 (occurring in large numbers) (in the case of absolute count values, the values ​​are converted into frequency classes).

The saprobic value ( s ) is a number between 1 and 4, where e.g. B. s = 1.0 indicates an indicator organism for oligosaprobia, s = 4.0 an indicator organism for polysaprobia. The value is given with one decimal place. It can be read from the list of indicator organisms.

The indication weight ( g ) can assume the value 1, 2, 4, 8 or 16, whereby an organism with a higher g has a smaller tolerance and thus represents an indicator that is all the more specific for the quality class in question. Only organisms with an indication weight of 4 or higher are used in the saprobic system.

The saprobial index is calculated from the numbers for all indicator organisms found in the sample using the following formula:

The index number calculated in this way is given to two decimal places after the comma. In fact, the reliability of your statement must be determined in each individual case using the methods of mathematical statistics . It strongly depends on the sample size and the number of types of indicator found. According to the procedure, the saprobic index is only valid if the cumulative abundance sum of all indicator organisms reaches at least 20. This is intended to exclude very sparsely populated or species-poor sample sites because the index determined here would be too uncertain. In addition, such a low abundance value usually indicates the presence of other, non-saprobial stress factors that could distort the result.

Water quality classes and levels of saprobicity

The saprobic index determined using the method is initially only a numerical value. In order to illustrate these abstract numerical values ​​and to facilitate comparisons, the values ​​are grouped as value classes into saprobic levels. In Germany, the classification into quality classes has been common for decades; this was first introduced by the hydrobiologist Hans Liebmann in 1951. The water quality classes were used, for example, to be shown in the official water quality maps.

As part of the re-evaluation by the European Water Framework Directive , the procedure was also extended to other biological quality elements in addition also to saprobial stress about the water acidification and the species impoverishment due to hydraulic structures (called "general degradation") procedures and use influences are supposed to measure. In order to standardize the procedure, the values ​​were also adapted to the respective type of river , as each type naturally has a certain type-specific different autosaprobicity.

According to the results of the saprobic system, the waters are traditionally divided into seven water quality classes, each for a certain range of values ​​of the saprobic index. The originally four quality classes were increased to seven by adding three intermediate classes in order to enable a finer differentiation. In the course of the classification as part of the "Saprobia module" according to the Water Framework Directive, five new classes were created from the seven quality classes.

The following list shows the seven water quality classes, supplemented by the classification according to the assessment procedure for the Water Framework Directive. (The gradation of the saprobic index is shown here without the differentiation according to the type of flowing water, so it might have to be modified slightly depending on the type.)

  • Water quality class I: unpolluted to very lightly contaminated. oligosaprobe zone. Representation in the quality card: dark blue. Saprobic index less than 1.5. "very good condition.
  • Water quality class I-II: low pollution. oligo- to β-mesosal sample zone. Representation in the quality card: light blue. Saprobic index from 1.5 to less than 1.8. "very good condition.
  • Water quality class II: moderately polluted. β-mesosal sample zone. Representation in the quality card: dark green. Saprobia index 1.8 to less than 2.3. "good condition.
  • Water quality class II-III: critically polluted. Β-mesosaprobe to the α-mesosaprobe zone. Representation in the quality card: light green. Saprobia index 2.3 to less than 2.7. "Moderate" condition.
  • Water quality class III: heavily polluted. α-mesosal sample zone. Representation in the quality card: yellow. Saprobia index 2.7 to less than 3.2. "Unsatisfactory" condition.
  • Water quality class III-IV: very heavily polluted. α-mesosaprobe to polysaprobe zone. Representation in the quality card: orange. Saprobic index 3.2 to less than 3.5. "bad condition.
  • Water quality class IV: excessively polluted. polysaprobe zone. Representation in the quality card: red. Saprobic index 3.5 to 4.0. "bad condition.

Especially in Austria and the Czech Republic, a xenosa sample zone (with its own fauna) is distinguished. This includes bodies of water without any pollution, so it would have to be connected above the oligosa-sample zone. Sometimes the term "katharob" is used for this (by definition, katharob would be saprobic zero. That would not be measurable in the context of the procedure).

In the Czech procedure (due to the extremely high water pollution that was customary at the time) further stages were added which are worse than the polysaprobe condition. This "eusaprobe" area applies to more or less undiluted wastewater. In ascending order, an isosaprobe, metasaprobe, hypersaprobe and ultrasaprobe should be added. These areas only differ in their micro-colonization (life would no longer be possible in the ultra-sampled area) and are not recorded by the common saprobic system. Even a water quality class V (ecologically destroyed), which used to be temporarily different, is no longer used because water bodies that are heavily polluted with wastewater no longer play a role in Germany due to legal regulations.

Other factors

Saprobia is associated with all processes that use up oxygen in water . Are measures of total oxygen consumption

  • Chemical oxygen demand (COD), which is determined by oxidation with potassium dichromate , and the
  • Biochemical oxygen demand (BOD), which is determined by measuring the decrease in oxygen content in a water sample in 2 or 5 days at 20 ° C in the dark. Traditionally, the load indicator used to define the quality classes is the BOD5. Shorter periods of time are only used for highly stressed samples in which after five days there would be no oxygen at all.

Organically bound carbon (TOC) is also often used as a measure of pollution.

It is not permitted to derive a quality classification of the water from selective chemical measurements. Attempts at a chemical water quality classification were proposed, but are no longer relevant today because of the different methodology within the framework of the Water Framework Directive.

For the German water quality atlas 1995, typical value ranges for a series of pollution parameters were determined based on the water quality according to the saprobic index and a series of chemical values ​​measured at the same sample points and their correlation was determined. These are shown in the following list.

  • Quality class I: BOD5 less than 1 mg O 2 per liter. O 2 content close to saturation. Ammonium present at most in traces.
  • Quality class I-II: BOD5 less than 2 mg O 2 per liter. Small oxygen deficits of up to 20 percent during the day are possible. Ammonium present at most in traces.
  • Quality class II: BOD5 less than 5 mg O 2 per liter. Pronounced daily cycle of O 2 concentrations due to biogenic oxygen production. Ammonium nitrogen concentration below 0.5 mg per liter.
  • Quality class II-III: BOD5 higher than 5 mg O 2 per liter. O 2 concentrations often permanently below 50 percent of saturation, but pronounced daily cycles. Ammonium nitrogen concentration reaches 1 mg per liter.
  • Quality class III: BOD5 up to 10 mg O 2 per liter. O 2 concentrations are often permanently below saturation, sometimes below 2 mg per liter. Ammonium nitrogen concentration exceeds 1 mg per liter, often formation of highly toxic ammonia .
  • Quality class III-IV: BOD5 over 10 mg O 2 per liter. Only traces of oxygen remain at times, digested sludge is formed . The ammonium nitrogen concentration also exceeds 1 mg per liter in the long term.
  • Quality class IV: BOD5 often well over 10 mg O 2 per liter. Long-term oxygen below 1 mg per liter, sediment anaerobic , covered by digested sludge. The ammonium nitrogen concentration also exceeds 1 mg per liter in the long term.

Indications of pollution of the water from organic sources can also be obtained from measurements of the nitrogen compounds ammonium , nitrite and nitrate or from total phosphorus. These fertilizing compounds (important for plants as macronutrients ) define the trophy of the water. Only the contents of the reduced nitrogen fractions ammonium and nitrite are directly significant for the saprobic index, because these can be oxidized to nitrate by microorganisms (with consumption of oxygen), i.e. they are saprobial. Indirect correlations can often result from the fact that in well-exposed water bodies, increased nutrient content leads to strong plant growth. If these plants later die, the biomass formed (through the consumption of oxygen) leads to increased saprobia. This phenomenon is called “secondary pollution” and is particularly pronounced in dammed river sections.

The chemical parameters can be measured faster than the saprobic index. They represent a momentary picture of the load, while the biologically determined index gives a statement about the load that has arisen over a longer period and is therefore averaged.

Web links

Individual evidence

  1. Kolkwitz, R. & Marsson, M. (1902): Principles for the biological assessment of water according to its flora and fauna. Communications from the royal testing institute for water supply and wastewater disposal 1: 33–72 (Berlin-Dahlem).
  2. a b c d DIN 38410. German standard methods for water, waste water and sludge examination - Biological-ecological water examination (group M) - Part 1: Determination of the saprobic index in flowing waters (M 1) (2004).
  3. DIN 38410 validation document ( PDF ).
  4. a b Rolauffs, P. et al .: Development of a model-oriented saprobic index for the biological assessment of rivers. Environmental research plan of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety Research report 200 24 227. published as UBA texts 11/03 ( PDF ).
  5. ^ Matthias Schaefer: Dictionary of Ecology. Springer-Verlag, 2012. ISBN 978-3-8274-2562-1 p. 255 limited preview on Google Books .
  6. Hans Liebmann: Handbuch der Frischwasser- und Abwasserbiologie (biology of drinking water, bathing water, fish water, receiving waters and waste water), Volume 1. Verlag R. Oldenbourg, Munich 1951. 539 pp.
  7. Carolin Meier, Jürgen Böhmer, Regina Biss, Christian Feld, Peter Haase, Armin Lorenz, Claudia Rawer-Jost, Peter Rolauffs, Karin Schindehütte, Franz Schöll, Andrea Sundermann, Armin Zenker, Daniel Hering: Further development and adaptation of the national evaluation system for macrozoobenthos to new international guidelines. Report on behalf of the Federal Environment Agency. Essen 2006. download at .
  8. a b c LAWA regional working group on water: Water quality atlas of the Federal Republic of Germany. Biological water quality map 1995. Berlin, 1996. 52 pages + maps.
  9. cf. Biological water quality in the Hessen Environmental Atlas .
  10. Sladecek, Vladimir (1973): System of water quality from the biological point of view. Results of Limnology 7 ISBN 978-3-510-47005-1 .
  11. LAWA working group target specifications, in cooperation with LAWA working group Qualitative Hydrology of Waters (publisher): Assessment of the water quality of flowing waters in the Federal Republic of Germany - Chemical Water Quality Classification. Berlin, August 1998. ISBN 3-88961-224-5 .