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You are here: Home / Publications / European Freshwater Monitoring Network Design / 13. Assessment of Information Gaps in Existing Monitoring

13. Assessment of Information Gaps in Existing Monitoring


13.1 Introduction

A more detailed assessment of gaps and differences that will compromise the aims of the proposed monitoring network should be possible during the pilot implementation project to be undertaken during 1996.

13.2 Rivers

13.2.1 Major gaps

In most of the national river monitoring networks the number of stations in existing national programmes are greater than the proposed number of stations to be included into the general surveillance river network (Section 8.2). However, the number of stations in the national river monitoring programmes in the Netherlands, Germany, Norway, Sweden and Finland are generally lower than the proposed number. In these countries the local authorities are monitoring numerous river stations and some of these stations may be selected to achieve the proposed number of stations. The national river monitoring programmes generally include stations on the major rivers, while the number of stations in small rivers and at reference sites may be low. For many countries it may be necessary to establish some stations covering small river catchments and reference areas.

Most countries conduct annual sampling at their river stations and most of the stations for this network can be selected from the existing national river monitoring programmes. Many of the river stations in the national monitoring programmes are not located at or near gauging stations and the requirement for water flow data on a continuous basis may reduce the number of possible stations, especially in the case of small rivers and reference sites. Hydrological forecasting of flows may be useful here.

Many national monitoring networks are established for estimating the riverine loads from land areas into coastal areas or loads in transboundary rivers. Generally these networks consist of sampling at downstream sites on all major river systems. The aims of these networks will have to be established before the gaps can be evaluated. However, in most countries frequent measurement of important water quality variables at downstream points in the largest rivers are undertaken. This network should not duplicate the work done for the existing international networks but be based on the results from these networks. There is a need for harmonisation/standardisation of the various methods of calculating the loading as well as descriptions of human activities in the catchment and estimating the source apportionment.

The ecological quality network should be established on basis of the national reporting in relation to the proposed Directive on Ecological Quality. In sparsely populated countries it will not be possible to make a census of the ecological quality of all water courses. However, a representative sub-sample should be selected to describe the ecological quality. The river stations in the extensive water quality network could be the basis for this sub-sample.

13.2.2 Gaps in required determinants

Basic physical variables

Information about water flow is an important variable when the state of the environment is to be evaluated. In the river network water flow should either be measured at each sampling site or at a nearby gauging station. In the riverine loading network the water flow should be measured continuously at a gauging station. Water temperature, pH, and conductivity are measured at low cost and may be used for general characterisation the rivers. Many of the river stations in the national monitoring programmes are not located at or near gauging stations and the requirement of water flow data on a continuous basis may reduce the number of possible stations, especially in the case of small rivers and reference sites.

Organic pollution indicators

From an ecological perspective, the estimate of average oxygen concentration based on monitoring programmes may not be the best descriptor of oxygen conditions in rivers. Oxygen levels vary throughout the year and individual days, and the status of aquatic fauna will often reflect episodic or systematic minima in these levels rather than average conditions. The lowest oxygen concentration are generally found during the night and the summer months. Nearly all monitoring of oxygen is undertaken during the day for logistical reasons, so that there is little chance of recording the true annual minimum. However, dissolved oxygen is measured at low cost, and it is measured at the majority of river stations often with a long time series. This variability is also a characteristic of other chemical indicators.

Biochemical oxygen demand (BOD) and ammonium levels can give an indication of organic pollution in rivers. However, especially in the Nordic countries chemical oxygen demand (COD) is measured instead of BOD and dissolved oxygen is not measured at all. In addition, for BOD and COD many different analytical methods are used. For example, BOD can be measured with or without addition of a nitrification inhibitor, and COD is measured either by the potassium dichromate or by the sodium permanganate method. Some standardisation will be necessary to ensure that these data are comparable at an EEA level.


There is generally a close relationship between phosphorus concentration and catchment population density, and between nitrate levels and the percentage of the catchment used for agricultural purposes. It has been recommended that the state of eutrophication at the river stations are evaluated on the basis of measurements of nitrate (oxidised nitrogen, nitrate plus nitrite) and total phosphorus. In some countries total nitrogen is measured instead of nitrate, especially in the Nordic countries with relatively low nitrate levels and relatively high organic nitrogen levels. In some countries soluble reactive phosphate (SRP) is measured instead of total phosphorus.

13.3 Lakes

13.3.1 Major gaps

An extensive lake/reservoir monitoring network with up to 8 samples taken over one year in each reporting period of 3 to 5 years has been proposed. The network should include reference lakes, typical lakes/reservoirs and the largest and most important lakes and reservoirs in each country. In several countries there is no national lake/reservoir monitoring programme, however, in some of these countries local authorities monitor the water quality of lakes/reservoirs, and it should be possible to select the required number of water bodies for the extensive network from the local networks. Several countries are creating inventories of the environmental state of lakes and reservoirs by collating the results from local authority monitoring activities and it may be possible to use this information in producing the EEA extensive lake network.

13.3.2 Variables measured in existing lake monitoring programmes

Basic variables

Variables describing the basic chemical and physical properties of lake water are included in most programmes. Generally, the analysis programmes include measurement of water temperature, pH, dissolved oxygen and conductivity.

Trophic status

Nearly all the lake monitoring programmes include measurement of total phosphorus, total nitrogen, oxidised nitrogen and chlorophyll-a. Measurement of soluble reactive phosphate, ammonium nitrogen and Secchi disc transparency are included in most of the monitoring programmes. In those lake monitoring programmes with more than one annual sample, the sampling frequency of trophic status indicators varies from 3 to 4 samples to 19 samples a year.


Up to ten metals are measured in the various national lake-monitoring programmes.

Biological assessment of lake water quality

Biological variables are included in many general lake-monitoring programmes as well as programmes concerning specific localities (e.g. large important lakes). Sampling and investigation of phytoplankton and zooplankton are components of several monitoring programmes. Apart from a general evaluation of the phytoplankton community, the objectives of some programmes are more specific such as assessment of the occurrence of potentially toxic blue-green algae in waterbodies used for bathing or drinking water supply. Bottom fauna, macrophytes and fish are also objects of study in some of the lake monitoring programmes.

13.4 Groundwater

Unlike for groundwater quality, there are no current EC directives with specific requirements for groundwater quantity monitoring, in spite of the intimate relationship between quantity and quality, especially in impacted areas. Consequently difficulties arise in evaluating representativeness of the networks. Conscious of this serious gap, the EC has established through the GAP (Groundwater Action Programme) an urgent priority to formulate the required criteria for the establishment of an EC groundwater (quality and quantity) monitoring network.

A full analysis of gaps in existing monitoring networks was not possible because of the lack of supportive information provided by the EEA Member countries in the MW2 questionnaires. This is particularly so for sampling density evaluation of the baseline and impact networks. There was also no information on the hydrogeological characteristics of each groundwater region and the spatial distribution of the monitoring stations, only general data were provided. Also no characterisation was made of the type of impacted areas, for example, heavily exploited areas or areas particularly subject to interactions with other systems (rivers, sea, lakes, estuaries).

Large differences were found in sampling frequencies among the EEA countries although no interpretative information was provided on the objectives of each monitoring programme which might explain these differences. It will, therefore, be necessary during the pilot implementation of the network to go into more specific details on national networks when selecting sites and other aspects of the EEA network for groundwater.

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