2. surface water quality monitoring

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2. Surface water quality monitoring

This chapter aims at giving a short introduction to the basic principles of surface water monitoring. Additional information can be found in numerous textbooks, an example being "Design of Networks for Water Quality Monitoring" by Sanders et al. (1987).

The objective of water quality monitoring is to obtain quantitative information on the physical, chemical, and biological characteristics of water via statistical sampling (Sanders et al. 1987). The type of information sought depends on the objectives of the monitoring programme. Objectives and purposes range from detection of drinking water standard violations to determination of the environmental state and analysis of temporal water quality trends. Three categories of monitoring can be identified: (1) routine surface water monitoring, (2) periodic special surveys, and (3) special surveys performed to assess the extent of a pollution problem (eg. a survey of pesticide occurrence in surface waters).

The state of water quality is the result of complex natural and man-made conditions and the consequent interactions in both time and space. Consequently, abstracting the essence of water quality conditions is often very difficult. Monitoring and assessment of the environmental state of European surface waters are performed by numerous local, regional and national authorities. The wide variety of organizational structures pertaining at the national and local level in European countries means that administration of monitoring activities differs greatly. Looking at national large-scale regional surface water quality monitoring programmes as an important information source, it is important to know the main components of the organizational structure involved, eg. participating institutions and their responsibilities, the overall coordination principles of monitoring, data storage, reporting of information, etc.

Monitoring purposes

Any attempt to evaluate water quality monitoring programmes should begin with the question "Why do we monitor?" It is very important to be able to describe the purposes and objectives of monitoring as they create the background for the direct monitoring activities, ie. the set-up of sampling networks, variables to be measured, sampling frequency, data storage and information utilization, including data analysis and reporting.

The purpose of monitoring is generally laid down by laws or other regulatory actions (directives, water quality standards, action plans) and aim at assessing the environmental state and detecting trends. The regulatory actions set up water quality goals or standards (eg. a 50 per cent reduction of nitrogen loading to surface waters, no pesticides in drinking water, etc.), and the purpose of monitoring is to supply data and information on the water quality in relation to these regulatory actions.

Many monitoring programmes serve several purposes. One-purpose monitoring programmes may when new laws are passed deal with additional aspects of water pollution or new approaches to water quality management, and thus be expanded to supply additional data and information.

Objectives as the ones described above represent one dimension of the monitoring system. Another dimension is associated with the activities involved in data acquisition and utilization of information. These activities begin with the collection of samples and end with informing the public on the findings and using the results to implement measures to improve the environmental state of the waterbody.

Data acquisition can be described by the monitoring sampling network, the sampling frequency, and the water quality variables measured, while information utilization can be described by data storage, data analysis and reporting procedures. In the following these activities are described.

Monitoring network design

The monitoring network is above all described by the waterbodies (ie. springs, brooks, streams, rivers, river systems, ponds, lakes, reservoirs, fjords, estuaries, coastal area, or open marine water) and the geographical area (eg. country, river system, etc.) it covers. However, more specific information on the criteria for selection of sampling sites is often necessary to evaluate the information obtained from a monitoring programme. Two types of networks can be identified: (1) an extensive network involving many sampling sites, few annual samples, analyses of a few variables, and only one or few years of sampling, (2) an intensive network including sampling sites with detailed investigations, many annual sample or measurement of many variables, and many years of observations. Many monitoring networks are both intensive and extensive, for example, a sub-network consisting of many extensive sampling sites with few variables combined with a sub-network including relatively few sampling sites with frequent sampling and several variables measured.

River sampling networks must be described by the strategy for the selection of sampling sites; eg. major rivers in a country or frequent sampling downstream point sources. A general description of the total number of sampling sites, number of rivers, number of river systems and information on catchment areas (eg. catchment area size distribution) generally give a fair description of the sampling network. Many river sampling networks are composed of two or more sub-networks, eg. a few intensive sampling sites located in major rivers and numerous basic sampling sites located at less important tributaries and river reaches.

Lake sampling networks must also be described by the strategy for the selection of sampling sites (ie. largest lakes, or lakes from known problem areas featuring, for instance, eutrophication or acidification, etc.). Many lake monitoring programmes are based on surveys of the environmental state of lakes made at five year intervals, the lakes to be included into the survey either being fixed or selected by use of statistical criteria among the total number of lakes in a country. Often the survey programme is supplemented with an intensive lake monitoring programme involving annual studies of relatively few lakes..

Marine sampling networks are generally described by the specific marine areas in which sampling sites are located (eg. the name of estuarine areas or name of the sea), and the number of coastal and offshore sampling sites. Marine monitoring programmes often have several sub-networks, for example, one sampling network for taking water samples, one network for sampling bottom fauna, and one network for investigation of macrophytes.

Variables measured

The number of variables describing the quality of a waterbody have increased and are constantly being modified and further refined along with the expanding uses to which water is put, and also in pace with the development of analytical capabilities to measure more and more substances at ever lower concentrations.

The various groups of water users have, to some extent, developed their own approaches and methods to describe and measure water quality. For many decades river basin management and water pollution control have relied on summary variables, such as biochemical oxygen demand (BOD) and chemical oxygen demand (COD) to quantify sewage discharge and oxygen problems in rivers. For the purpose of 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.

The water quality variables can be grouped into the following broad categories:

  • Basic variables (eg. water temperature, pH, conductivity, dissolved oxygen, and discharge) used for a general characterization of water quality.
  • Suspended particulate matter (eg. suspended solids, turbidity and organic matter (TOC, BOD and COD)).
  • Organic pollution indicators (eg. dissolved oxygen, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), ammonium).
  • Indicators of eutrophication: nutrients (eg. nitrogen and phosphorus), and various biological effect variables (eg. chlorophyll a, Secchi disc transparency, phytoplankton, zoobenthos).
  • Indicators of acidification (eg. pH, alkalinity, conductivity, sulphate, nitrate, aluminium, phytoplankton and diatom sampling)
  • Specific major ions (eg. chloride, sulphate, sodium, potassium, calcium and magnesium) as essential factors in determining the suitability of water for most uses (eg. public water supply, livestock watering and crop irrigation)
  • Metals (eg. cadmium, mercury, copper and zinc)
  • Organic micropollutants such as pesticides and the numerous chemical substances used in industrial processes (eg. PCB, HCH, PAH).
  • Indicators of radioactivity (eg. total alpha and beta activity, 137Cs, 90Sr)
  • Microbiological indicator organism (eg. total coliforms, faecal coliforms and faecal streptococci bacteria)
  • Biological indicators of the environmental state of the ecosystem (eg. phytoplankton, zooplankton, zoobenthos, fish, macrophytes and birds and animals related to surface waters).

Matrices sampled

Most of the monitoring programmes measure the quality and pollution in the water column and some of the monitoring programmes also include sampling of other compartments of the aquatic environment, especially pollutant analysis of the sediment and of particulate matter. Biological indicator organisms and analysis of the various biological communities are used to assess the ecological state of the waterbodies. The biological indicators most employed in river quality investigations are large visible invertebrates (macroinvertebrates), while the biological indicators most employed in lake and coastal water investigations are studies of phytoplankton (algae) and zoobenthos.

Sampling frequency

The sampling frequency differs substantially depending on the purpose of the monitoring programme and the variables to be measured. Frequent samples are generally taken when the purpose of a monitoring programme is to observe trends, while programmes and surveys with the purpose of assessing the general state of many waterbodies generally are based on low sampling frequency. Some monitoring programmes include continuous registration of basic variables such as pH, conductivity, salinity and dissolved oxygen, while in most monitoring programmes measuring the quality and pollution in the water column, a number of annual samples are taken. Investigation of biological organisms such as macroinvertebrates in rivers and zoobenthos in lakes and marine areas is usually based on few annual samples. A large proportion of the costs of operating a monitoring programme is directly related to the sampling frequency.

The sampling frequency can be described by the total number of annual samples, for example 12/yr: twelve samples a year; or 2/5 yr: two samples every five years. Information on the timing of sampling may also be important, if sampling is evenly spread throughout the year (eg. monthly, weekly samples) or if stratified sampling is used (eg. sampling during summer, pesticide spraying seasons or peak flow periods; monthly sampling every fifth year).

Data storage and data analysis

Generally the national monitoring programmes are organized so that the local authorities are responsible for the data acquisition. For example, in the national French river monitoring programme the six basin agencies are responsible for data acquisition in their respective areas, or in Germany the Länder have the responsibility for environmental issues in their region including monitoring of surface waters. In many cases only summary data (eg. annual mean values or grades assigned to the quality of a specific waterbody) are reported to the organizations responsible for national reporting, while the raw data is stored at the organizations responsible for data acquisition. This accumulation of aggregated data at the national level often make comparison of results from the various countries difficult due to different methods used for data analysis and aggregation of data. Consequently, information on data analysis and data storage procedures is important when evaluating the national monitoring programmes.

Reporting and utilization of information

In the last five to ten years the number of national state of the environment reports have increased substantially. Nearly all countries prepare either annually or with intervals of two to five years various reports including a national assessment of the environmental state of surface waters. The reports are generally based on the information produced by the national monitoring programmes supplemented with additional information from more specific investigations.

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