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Reporting required for assessing the state of, and trends in, the water environment at the European level

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Comments on Draft Guidance on “Reporting required for assessing the state of, and trends in, the water environment at the European level”

Task 3 Guidance on scope of SOE-parameters
S. Poikane, P. Noges, W. van de Bund, A. Solimini, A. Solheim


26 September 2006

  1. Comments on the sheet NUT_ORG_RV_LK

  2. Comments on the sheet BIO_INV_RV

  3. Comments on the sheet BIO_AQU_LK

  4. Comments on Information on stations used for SOE reporting

1. Comments on the sheet NUT_ORG_RV_LK


State of rivers and lakes in terms of nitrogen, phosphorus, chlorophyll-a and organic pollution determinands in water

1.1. Determinand: Oxygen concentration, oxygen saturation
Determination of dissolved oxygen is a fundamental part of water quality since its major role in all chemical and biological processes. Concentrations below 5mg/l adversely affect biological communities and below 2 mg/l may lead to the death of most fish.
There are two factors which dramatically influence concentration and saturation of oxygen:

  1. the depth of measurement (epilimnion / hypolimnion)

  2. the season of measurement and ice cover

Picture 1. Vertical distribution of oxygen and temperature during the four main seasonal phases.
The dynamics of oxygen follow the rules:

  1. The dissolved oxygen concentration in the surface layers remains high throughout the year and doesn’t depend on lake status (because of photosynthesis and diffusion from the atmosphere will always provide oxygen);

  2. However, conditions in the hypolimnion vary with lake status. In more productive lakes, hypolimnetic dissolved oxygen declines during the summer because it is cut-off from all sources of oxygen, while organisms continue to respire and consume oxygen;

  3. Even surface layer can be totally devoid of oxygen under the ice cover when the water mass is cut-off from the atmosphere.

EEA Lake Base oxygen data contains no information of sampling depth, but evidently most of them are surface layer data. Analyze of EEA data set shows that 99 % of the mean values of dissolved oxygen measurements are higher than 6 mg/l, also 95% of minimal values are higher than 6.5 mg/l (Fig. 2), meaning that these measurement evidently are taken in the surface layer and don’t reflect the true situation of oxygen depletion in European lakes.

Fig 2 Dissolved oxygen data – minimal values mg/l (DE and FI, average per monitoring site)

Data collection of surface layers doesn’t make sense because oxygen values always will be in range 8 -12 mg/l, these measurements don’t provide any meaningful information.

It is important to collect oxygen data when and where oxygen depletion is expected - deeper layers (hypolimnion) and winter season under ice cover.


    • Sampling depth is obligatory parameter for oxygen data;

    • Focus on oxygen concentration in deeper layers (hypolimnion);

    • Calculation of depth-averaged concentration doesn’t apply to oxygen concentrations;

    • The best way is to collect all data (sampling dates, sampling depth) to get complete picture of oxygen depletion. The simplified way would be to focus on “occurrence of anoxia”.

1.2. Supportive determinands:

1) Alkalinity /conductivity:

For lakes both alkalinity and conductivity are included in the list of supportive determinands, for rivers – neither parameter is included.

It is necessary to include alkalinity (and conductivity) as supporting parameter also for rivers because it is an important typology factor differentiating siliceous and calcareous streams :

  • The composition of benthic macroinvertebrate assemblages is associated with catchment geology, with soft-water streams having restricted fauna and hard-water streams having greater diversity and abundance;

  • There are different ecological classification scales developed for different river types based on alkalinity;

  • Alkalinity is used as a proxy for siliceous/calcareous geology, with three classes: low alkalinity, medium and high alkalinity;

  • Conductivity can be used as a substitute of alkalinity in case of lack of alkalinity data

Proposal: to include alkalinity (and conductivity) as supporting parameter also for rivers due to its typological importance.

  1. Colour

Colour (determined by the content of humic substances) is the important parameter:

  • Colour of water determines light transmission depth and water transparency which in turn controls primary productivity, macrophyte colonization depth etc;

  • Colour is an important typology factor differentiating non-humic (clear water) and humic (brown water) lakes and rivers. These lakes/rivers have different ecological assessment tools due to their different chemical and biological features

Proposal: to include colour (mg Pt/l) because it is an important typology factor both for lakes and rivers.
3) Temperature

This measurement makes sense only if disaggregated, sample data are delivered.

2. Comments on the sheet BIO_INV_RV


State of river water bodies in terms of biological quality elements – benthic invertebrate fauna


A newly developed indicator on the requested data should include

National metrics compatible with ICMs (Intercalibration Common Metrics) defined in the WFD Intercalibration report.

3. Comments on the sheet BIO_AQU_LK


State of lake water bodies in terms of biological quality elements – other aquatic flora

What should be reported?

Proposal to include :

Presence and relative abundance of indicator taxa: Isoetids (Isoetes sp., Lobelia sp., Littorella sp) and Charophyta sp.

These taxa have been shown to decrease abruptly at a certain phosphorus threshold, and are therefore good indicators for eutrophication pressure (Penning et al. in prep. REBECCA project)

The large isoetids, such as Isoetes lacustris and Lobelia dortmanna for low-moderate alkalinity lakes, and Chara spp, for high alkalinity lakes, are good indicators for reference conditions, and also good ecological status. Both the assessments based on data and general expert judgement/literature suggest that these species are highly sensitive to an increase in eutrophication pressure (e.g. Blindow, 1992, Van den Berg et al, 1999).
Important: macrophyte vegetation survey and reporting method should be reported as well, including an explanation of abundance scale.

4. Information on stations used for SOE reporting
Proposal to include
Lake or River type: national type, and corresponding core type used for Intercalibration of assessment systems within the Geographical Intercalibration group (GIG) (when applicable), including data on typology factors (altitude, mean depth, alkalinity, water colour, etc.)

Lake or River types are essential for interpreting of the information because different types have different reference conditions and assessment schemes.

Please find enclosed the list of lake common Intercalibration types.

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