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KRW-maatlatten [id:]

Method: WFD-metrics for natural watertypes [KRW-maatlatten voor natuurlijke watertypen]

1. General information

1.01 GIG: Central-Baltic
Relevant intercalibration types: R-C1 and R-C4 and R-C5
1.02 Category: Rivers
1.03 BQE: Benthic Diatoms
1.04 Country: Netherlands
1.05 Specification: none
1.06 Method name: WFD-metrics for natural watertypes
1.07 Original name: KRW-maatlatten voor natuurlijke watertypen
1.08 Status: Method is/will be used in First RBMP (2009)
1.09 Detected pressure(s):
Acidification, Eutrophication, General degradation, Pollution by organic matter Specification of pressure-impact-relationship:
The scores with the metric have very significant negative correlations with total phosphorous (n = 259) and total nitrogen (n=165) correlations, but these are too weak to allow confident predictions of phytobenthos quality from nutrient concentrations. Correlations as were done as Pearson correlations between logarithmically transformed nutrient concentrations and EQR, resulting in a confidence level of p ? 0.001, but correlation is less clear in the lager river types.

Reference: H. van Dam (2007). Een herziene KRW-maatlat voor het fytobenthos in stromende wateren (A revised WFD-metric for river phytobenthos in The Netherlands). In opdracht van (commissioned by): Rijkswaterstaat RIZA. Herman van Dam, Adviseur Water en Natuur. Amsterdam. 47p.
Yes, with quantitative data (e.g. against range of sites reflecting continuous gradient of pressure).
1.10 Internet reference:
1.11 Pertinent literature of mandatory character:
Besluit Kwaliteitseisen en Monitoring Water, 2009. Ministry of Housing, Spatial Planning and the Environment (presently under public consultation).
1.12 Scientific literature: n.a.
1.13 Method developed by:
Development by national expert group commissioned by STOWA, Bas van der Wal & RWS Waterdienst, Diederik van der Molen
Email of developer:,
Institute of developer:
STOWA Foundation for Applied Water Management Research & Rijkswaterstaat Waterdienst
1.14 Method reported by: Roel Knoben
Email of person reporting the method:
Email of institute reporting the method: Rijkswaterstaat Waterdienst
Description of KRWmaatlatten in Dutch.
Method and metrics derived from intercalibration for phytobenthos.

2. Data acquisition

Field sampling/surveying

2.01 Sampling/Survey guidelines:
Instructie; Richtlijn Monitoring Oppervlaktewater en Protocol Toetsen & Beoordelen (28 april 2009)
Quality Handbook Hydrobiology (in prep). 2009. STOWA.
2.02 Short description:
Living reed: gather reed stems (4-8 per replicate) by cutting at 15-20 cm below water level (paying attention to recent water level changes). Place reed stem in container for transfer to lab.
artificial substrate (consisting of dead reed stems): place 10 stems (attached to a floater) completely in the water. Remove after 7 weeks of incubation.
Extraction of phytobenthos in the lab by preferably chemical extraction.
2.03 Method to select the sampling/survey site or area: Expert knowledge Other method to select the sampling/survey site or area:
Sampling site should be in open water away from disturbances (e.g. bridges, tributary, spill overflow)
2.04 Sampling/survey device: Brush, Scraper
Other phytobenthos sampling device: Scissors to collect pieces of reed stems
Any other sampling device: Scissors to collect pieces of reed stems.
2.05 Specification:
Scissors to cut pieces of reed stems. If not possible use scraper(pocket knife or ice scraper) or a brush (tooth brush)
2.06 Sampled/surveyed habitat:
Specification of sampled habitat:
Reed (Phragmites australis); if not available, artificial substrate made from reed is placed on site.
Sampled habitat: All available habitats per site (Multi-habitat)
2.07 Sampled/surveyed zones in areas with tidal influence: not relevant
2.08 Sampling/survey month(s): April
2.09 Number of sampling/survey occasions (in time) to classify site or area:
Minimum one occasion per year, but classification preferably averaged over three years.
2.10 Number of spatial replicates per sampling/survey occasion to classify site or area:
At least one sampling location; several replicates from within 50 m from the sampling location.
2.11 Total sampled/surveyed area or volume or total sampling duration to classify site or area:
Reed: one location, several replicates. When using artificial substrate: incubation 7 weeks

Sample processing

2.12 Minimum size of organisms sampled and processed: n.a.
2.13 Sample treatment:

Suspension of extracted phytobenthos is used to prepare a microscope slide. The diatoms on this slide are identified and counted.
Sample is divided (sub-sampling) and organisms of a sub-sample are identified.
2.14 Level of taxonomical identification:
Level: Species/species groups
Specification of level of determination: n.a.
2.15 Record of abundance:
Determination of abundance: Relative abundance
Abundance is related to: n.a.
Unit of the record of abundance: % (relative abundance) or # per sample size (e.g. # / 200 individuals)
Other relation of abundance:
Count strategy is aimed to determine the relative abundance of most abundant species. Up to 200 individuals are identified and counted. Other species present beyond count of 200 scales are noted.
Other record of abundance:
expressed as relative abundance in the total counted sample size (this is most often a rounded number, e.g. 200).
2.16 Quantification of biomass: n.a.
2.17 Other biological data: none
2.18 Special cases, exceptions, additions: none
Biological WFD monitoring is performed by 26 regional water boards (local/regional water systems) and 1 national water board (large rivers, large lakes, estuaries and coastal waters). Small differences may occur in sampling strategies etc.

3. Data evaluation


3.01 List of biological metrics:
Metric is adapted from the IPS method (Indice de Polluosensitivité Spécifique).

IPS =( 4.75 x (sum (a x s x v)/ sum (a x v)) - 3.75

a = (relative) abundance of species i
s = sensitivity of species i
v = indicator value for species i

ISP values are in the range of 1-20 and can be converted to EQR.
3.02 Does the metric selection differ between types of water bodies: No
3.03 Combination rule for multi-metrics: Not relevant
3.04 From which biological data are the metrics calculated:
List of biological metrics: Data from single sampling/survey occasion in time

Reference conditions

3.05 Scope of reference conditions: Surface water type-specific
3.06 Key source(s) to derive reference conditions:
Scope of reference conditions: Expert knowledge, Historical data, Least Disturbed Conditions
Other reference source:
no actual existing natural sites in rivers in Netherlands. Only one least disturbed site; spatial references from foreign countries
3.07 Reference site characterisation:
Number of sites: 58
Geographical coverage: Germany, Belgium, France, Sweden, Estonia, United Kingdom
Location of sites:
Hierdense Beek, NL; Rotbach and Furlbach, Germany; 56 sites from CB-GIG Intercalibration database
Data time period:
NL: May 2006; Germany: September 2006; Belgium, France, Sweden, Estonia, United Kingdom: t.b.a.
Hierdense Beek is assigned as reference but this assignment is doubtful due to pressure from agricultural land use in the upstream part of the brook. Water in the lower stretch is cleaner due to tributaries coming form natural areas with very clean water.
Rotbach and Furlbach: selected by dutch hydrobiologists as reference for the original natural situation for dutch rivers regarding landscape, hydromorphology and physico-chemical characteristics (with minor human pressure).
Other reference sites are coming from the CB-GIG database with reference locations.
3.08 Reference community description:
Benthic diatoms are abundant on most of the available substrate. Areas with low current velocity are dominated by epipelic taxa, epiphytic taxa are abundant on macrophytes, branches and tree trunks.
Only epiphytic diatoms are collected for the phytobenthos metric, no species from other taxonomic groups.
Furthermore a general description is given (in Dutch) in:
STOWA (2009) Referenties en maatlatten voor natuurlijke watertypen. report 2007-32
3.09 Results expressed as EQR: No
Specification if results are not expressed as EQR:
ISP; ISP can be converted to EQR using a table presented in the metrics

Boundary setting

3.10 Setting of ecological status boundaries: Boundaries taken over from the intercalibration exercise
3.11 Boundary setting procedure:
By using similarities in geographic conditions the score on the IPS-scale in accordance with the reference condition is deduced for the Dutch situation. Next the scores of ten variants of an IPS-based metric were calculated for samples of CB-GIG type R-C1 and R-C4. For each of the ten variants the boundary values H/G and G/M at the intercalibration metric and several other performance characteristics were calculated, including the 95% confidence intervals of the boundary values. Finally a metric with a reference value has been chosen with boundary values which deviates less than the required 0.05 units from the mean values of all member states.
3.12 "Good status" community: The Good-moderate boundary is based on the Intercalibration Metric.


3.13 Consideration of uncertainty: Yes
Specification of uncertainty consideration:
Precision and uncertainty is regarded in Van Herpen, van Tongeren, Knoben, Baggelaar, van Loon (2009). Quick scan precision and confidence of KRW assessment (in Dutch). This study resulted in a statistical method to assess the level of precision and confidence monitoring results and status classifications (including identifying outliers and estimates for missing values). The confidence of a status classification is expressed as the probability of exceeding a chemical limit value or the biological status classification moderate/good. Recommendations from this study are incorporated in the Instructie; Richtlijn Monitoring Oppervlaktewater en Protocol Toetsen & Beoordelen (28 april 2009) (see question B.0). The new metric is validated by calculating the scores in the samples of the 56 foreign reference sites and by comparing the resulting quality classes with those which were originally inferred by the member state concerned.
The metric phytobenthos (as part of macrophytes) is a good indicator for acidification and eutrophication. Because phytoplankton is a good indicator as well for the eutrophication in lakes the multi-metric for phytobenthos is not used in lakes.

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