Water quality
The term water quality (also water quality or water quality ) denotes, in a very general way, the usability of water for human or natural purposes and processes of all kinds. Accordingly, there is no generally applicable standard or index that could define water quality. The criteria result specifically from the respective use or quality component and are different depending on this, for example for use as drinking water, industrial water for agricultural irrigation, or technical processes, ecologically defined quality requirements for groundwater and standing or flowing surface water and many others. For each of these areas there are specific requirements, which are often laid down in manuals, guidelines or standards, often with definition of limit values (e.g. drinking water ordinance or bathing water directive ). These can have different legal obligations nationally or supra-nationally, from non-binding recommendations to individually enforceable personal rights. It is often between a rather related to water as usable environmental medium, water quality in the narrow sense and a rather ecological requirements considered water quality discriminated, the parameters such as the nature of the river bed or its biotic considered colonization by aquatic organisms. A decrease in water quality is water pollution. This can have natural causes or it can be caused by human influences (e.g. water pollution ).
Determination of water quality
Different methods are used to assess the quality of water in a natural environment, depending on whether it is groundwater or surface water . Because of the typical organisms that live in surface water, there are fundamental differences between flowing water and standing water (pond, lake). Water quality is often associated with processes that use up the oxygen present in the water . The benchmarks for total oxygen consumption are:
- Chemical oxygen demand (COD), which is determined by oxidation with potassium dichromate ,
- Biochemical oxygen demand (BOD), which is determined by measuring the decrease in oxygen content in a water sample in the dark.
As an alternative, the total organic carbon (TOC, from the English abbreviation total organic carbon) is mostly used today instead of these methodologically complex measurable quantities .
Physical, chemical and biological methods are used to determine the water quality.
Biological process
The biochemical oxygen demand 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 for the definition of the quality classes in 5 days is used as BOD 5 . Shorter periods of time are only used for highly stressed samples in which after five days there would be no oxygen at all.
In Germany, the use of quality classes for surface water has been common for decades . Hydrobiologist Hans Liebmann first introduced these grades in 1951. The water quality classes are used, for example, to be shown in the official water quality maps. With the saprobic system , the waters are divided into seven water quality classes based on the organisms found, 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. The pure saprobic system is also criticized. In this respect, long-term data on the physical and chemical parameters offer further criteria.
There is an almost unmanageable variety of biological assessment procedures for water quality in use internationally. An overview as part of a Europe-wide research project came up with 297 different procedures for the countries of the European Union alone. These methods have been made available in a database and are used to assess rivers, lakes, coastal waters and brackish water biotopes; the assessment is based on communities of phytoplankton , the bottom-living (or benthic ) microflora , the higher aquatic plants or macrophytes, the fish fauna and the bottom-living invertebrates ( Macrozoobenthos ). Almost all of the methods are based on the identification of species; a few manage with higher taxonomic groups (such as genera or families). The exception is phytoplankton, for which a sum parameter (the content of chlorophyll a ) is traditionally of great importance.
One technique that is widespread in the United States is limited to certain groups of organisms such as mayflies , stoneflies, and caddis flies .
Chemical process
The determination of the chemical oxygen demand (COD) and the biochemical oxygen demand (BOD) are ultimately also chemical processes, since the methods of analytical chemistry are used for this. Organically bound carbon (TOC) is also often examined.
Indications of pollution of the water from organic sources can be obtained from measurements of the nitrogen compounds ammonium , nitrite and nitrate or from the 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). 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 occurs particularly prominently in dammed river sections.
In the traditional quality classification, the individual chemical values were determined on the basis of numerous water samples. A chemical water quality classification was also proposed, but this no longer plays a role in Germany since the Water Framework Directive because of the different methodology .
In contrast, chemical processes still play a major role in drinking water hygiene.
Physical procedures
The physical methods for determining the water quality have the advantage that they can be used in most areas of application and - especially for numerous or continuous investigations - are more cost-effective than biological and chemical methods. The temperature, oxygen content, pH value , conductivity and sometimes radioactivity and other parameters are measured. The results of the measurements are mostly presented in environmental information systems and are available on the Internet thanks to today's measurement technology. In Germany, numerous measurement results from so-called quality measuring points on the five main rivers Elbe , Rhine , Oder , Danube and Weser are published in a specialist portal of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety implemented by the Federal Institute for Hydrology . This data has been available for some rivers since the 1980s.
Combined procedure according to the European Water Framework Directive
With the introduction of the European Union's Water Framework Directive in 2000, a new quality classification procedure was established. The aim of the directive is to bring all waters in Europe (at least) to “good status”. In principle, the waters are rated according to two conditions (“good” or “not good”, finer in five quality levels “very good”, “good”, “moderate”, “unsatisfactory”, “bad”). For all bodies of water that do not have a good status, measures are provided that are summarized in so-called management plans, so a bad classification is directly relevant to action. It is important that the overall quality does not result from the mean value of the individual quality parameters, but rather that the worst parameter determines the overall evaluation. The quality classification is based on a complicated procedure in which two parameters are considered, the “chemical status” and the “ecological status” of the water. The chemical status is primarily determined by the pollutant content of the water, with different classes of substances (heavy metals, pesticides, organic pollutants) being measured. The ecological status is in principle based on the cohabitation rates in the water, but auxiliary parameters like water structure quality and various chemical and physical parameters (such as oxygen content, nutrient content, temperature) also play a role. The ecological status is more broadly defined than the saprobial status measured with the help of the saprobial system, i.e. H. Even with a good saprobial status, a body of water can fail to achieve a good ecological status if the community is too far removed from what is naturally to be expected. All non-saprobial pollution factors, especially changes in the water structure and diffuse influences from land use in the catchment area, are summarized under the catchphrase “general degradation”. In addition, not only the community of the river bed called macrozoobenthos , which is the basis of the saprobic system, but also the fish fauna and the occurrence of aquatic plants play an important role in the assessment of the water body within the framework of the procedure.
Grades
The water quality of natural waters is divided into so-called quality classes. Since the saprobic system is relatively complex and is basically only defined for flowing waters, chemical parameters are mostly used. Standing water is mainly classified according to the trophy system. The following water quality classes result from the correlation of the water quality classes determined according to the saprobic system with chemical values measured at the same sample points:
| Grade | BOD 5 / mg O 2 · l -1 | O 2 content | Ammonium nitrogen content / mg · l |
|---|---|---|---|
| I. | < 1 | Close to saturation | ≈ 0 (at most present in traces) |
| I-II | < 2 | Small deficits of up to 20% in the course of the day are possible | |
| II | < 5 | Pronounced daily cycle through biogenic oxygen production | <0.5 |
| II-III | > 5 | Often permanently below 50% of saturation, but pronounced daily cycles | <1 |
| III | <10 | Often permanently below saturation, sometimes below 2 mg / l | > 1 (often formation of the highly toxic ammonia ) |
| III-IV | > 10 | At times only traces left, sludge formation | > 1 (long term) |
| IV | often ≫ 10 | Long-term below 1 mg / l, sediment anaerobic , covered by digested sludge |
See also
Web links
- How water quality can be improved in Europe - information from the Helmholtz Center for Environmental Research - UFZ
- Undine information platform for the Elbe, Oder, Rhine, Weser, Ems and Danube
Individual evidence
- ↑ M. Meybeck, E. Kuusisto, A. Mäkelä, E. Mälkki: Water Quality. Chapter 2 in Jamie Bartram & Richard Ballance (editors): Water Quality Monitoring. A practical guide to the design and implementation of freshwater quality studies and monitoring programs. Published on behalf of UNEP United Nations Environment Program. UNEP / WHO 1996. ISBN 0-419-22320-7 .
- ↑ Tanja Srebotnjak, Genevieve Carr, Alexander de Sherbinin, Carrie Rickwood (2012): A global Water Quality Index and hot-deck imputation of missing data. Ecological Indicators 17: 108-119. doi: 10.1016 / j.ecolind.2011.04.023 .
- ^ Geneviève M. Carr, with James P. Neary: Water Quality for Ecosystem and Human Health. prepared and published by the United Nations Environment Program Global Environment Monitoring System (GEMS) / Water Program, 2006. ISBN 92-95039-10-6 .
- ↑ 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.
- ↑ Lexicon of Biology , here it was called u. a. Regarding the saprobic system: "The determination of the water quality according to the saprobic system is a simplified procedure and is fraught with errors."
- ↑ Sebastian Birk, Wendy Bonne, Angel Borja, Sandra Brucet, Anne Courrat, Sandra Poikane, Angelo Solimini, Wouter van de Bund, Nikolaos Zampoukas, Daniel Hering (2012): Three hundred ways to assess Europe's surface waters: An almost complete overview of biological methods to implement the Water Framework Directive. Ecological Indicators 18: 31-41. doi: 10.1016 / j.ecolind.2011.10.009
- ↑ Methods database (work package 2.2). WISER (Water bodies in Europe: Integrative Systems to assess Ecological status and Recovery) , accessed on April 30, 2016.
- ↑ US federal biomonitoring publications, US EPA, "Whole Effluent Toxicity."
- ↑ US EPA. Washington, DC. "Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms." Document No. EPA-821-R-02-012. October 2002.
- ↑ 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 .
- ↑ a b Continuously measured parameters on the Weser ( Memento from June 4, 2016 in the Internet Archive )
- ↑ Information platform Undine Basics of Qualitative Hydrology
- ↑ J. Arle, K. Blondzik, U. Claussen; A. Duffek, S. Grimm, F. Hilliges, A. Hoffmann, W. Leujak, V. Mohaupt, S. Naumann, U. Pirntke, S. Richter, P. Schilling; C. Schroeter-Kermani, Christa; A. Ullrich, J. Wellmitz, S. Werner, R. Wolter: Water management in Germany. Part 2 water quality. published by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, November 2013. PDF
- ↑ 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.