Introduction and overview of monitoring activities
Monitoring network design
The monitoring network is described by the water bodies (i.e. springs, brooks, streams, rivers, river systems, ponds, lakes, reservoirs, fjords, estuaries, coastal area, or open marine water) and the geographical area (e.g. country, river basin, etc.) it covers.
Two types of networks can be identified: i). an extensive network involving many sampling sites, few annual samples, analyses of a few determinands, and only one or few years of sampling, ii). an intensive network including sampling sites with detailed investigation, many annual samples or measurement of substantial numbers of determinands, and many years of observations.
The number of determinands which describe water quality is continuously increasing. Moreover, determinands are constantly being modified and refined in line with the expanding uses to which water is being put and in pace with the development of analytical capabilities for measuring more substances at ever lower concentrations.
For many decades river basin management and water pollution control have relied on summary determinands, such as biochemical oxygen demand (BOD) and chemical oxygen demand (COD), to quantify sewage discharge and oxygen problems in rivers. For human consumption and public water supply, a set of microbiological indicator organisms (eg. faecal coliform bacteria) have been identified and their enumeration is now commonly applied to determine the hygienic suitability of water for drinking.
Determinands can be grouped into the following broad categories:
- Basic determinands, e.g. water temperature, pH, conductivity, dissolved oxygen, and discharge, used for a general characterisation of water quality.
- Suspended particulate matter, e.g. suspended solids, turbidity and organic matter (Total Organic Carbon - TOC), Biochemical Oxygen Demand -BOD and Chemical Oxygen Demand - COD).
- Indicators of pollution with oxygen consuming substances, e.g. dissolved oxygen, BOD, COD and ammonium.
- Indicators of pollution with nutrients and eutrophication effects, e.g. nitrogen and phosphorus, and various biological effect variables, e.g. chlorophyll a and Secchi-disc transparency.
- Indicators of acidification, e.g. pH, alkalinity, conductivity, sulphate, nitrate, aluminium, phytoplankton and diatom sampling
- Specific major ions, e.g. chloride, sulphate, sodium, potassium, calcium and magnesium. These are essential factors in determining the suitability of water for most uses, such as public water supply, livestock watering and crop irrigation
- Metals, e.g. cadmium, mercury, copper and zinc
- Organic micro-pollutants, such as pesticides and the numerous chemical substances used in industrial processes, products and households.
- Indicators of radioactivity, e.g. total alpha and beta activity, 137Cs, 90Sr
- Microbiological indicator organisms, e.g. total coliforms, faecal coliforms and faecal streptococci bacteria.
- Biological indicators of the ecological quality, e.g. phytoplankton, zooplankton, zoobenthos, fish and macrophytes.
Most monitoring programmes measure the quality and pollution in the water column. Some monitoring programmes also include sampling of other compartments of the aquatic environment, especially pollutant analysis of the sediment and organism.
Biological indicator organisms and analysis of the various biological communities are used to assess the ecological status of the water bodies. Most biological indicators employed in river quality investigations are large visible invertebrates (macro-invertebrates), while the biological indicators used in lake and coastal water investigations are studies of phytoplankton (algae) and zoobenthos.
The sampling frequency differs substantially depending on the purpose of the monitoring programme and the determinands to be measured. Frequent samples are generally taken when the purpose of a monitoring programme is to observe trends. In cases where programmes aim to assess the general state of many water bodies, monitoring is based on low sampling frequency. Some monitoring programmes include continuous registration of a selection of determinands.
Investigation of ecological quality elements, such as macro-invertebrates in rivers, is usually based on a few annual samples. A large proportion of the costs of operating a monitoring programme are directly related to the sampling frequency.
For references, please go to www.eea.europa.eu/soer or scan the QR code.
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