Reference Conditions for Irish Rivers – Description of River Types and Communities




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Reference Conditions for Irish Rivers – Description of River Types and Communities


Draft Document - 22 December 2004.

Background


The Irish Article 5 Characterisation Report for the Water Framework Directive (WFD) identifies 12 primary river types in Ireland. The typology used is a System B Typology based primarily on geology and river slope. The typology chosen has been shown to be more discriminating than the System A typology on a statistical basis – i.e. for Macroinvertebrates, Phytobenthos and Macrophytes, both individually and in combination. Thus, the chosen 12-Type typology has been shown to produce statistically significant differences between types for these elements that are more significant than a similar analysis undertaken for the System A typology based on geology, size and altitude outlined in Annex II of the WFD.
The basic 12-Type typology is based on the results of a large-scale project funded under the Environmental Research, Technological Development and Innovation (ERTDI) Programme – The RIVTYPE Project (Kelly-Quinn et al., 2004) which studied the ecology of 50 high or reference status sites in detail and related the plant and animal species found to river type over the period 2002-2004. An additional study of reference condition macroinvertebrates in the headwaters of rivers undertaken for the Heritage Council of Ireland has also helped in the overall description of reference conditions for the major types (Baars et al., 2004).
This document outlines the macroinvertebrate communities for the 12 major types. The basic types are outlined in Table 1. Figs. 1 to 6 map the distribution of the 12 river types in the six River Basin Districts under consideration.


Table 1. Irish River Types based on geology and river slope.

(The type codes have two-digits codes with the first digit indicating the geology of catchment and the second digit river slope)

Code:

Catchment Geology (% bedrock in upstream catchment by type)

Description




Hardness/Alkalinity


1


100% Siliceous


Soft water


<35 mg CaCO3/l


2

1-25% Calcareous (Mixed Geology)

Medium hardness

35-100 mg CaCO3/l

3

>25% Calcareous

Hard water

>100 mg CaCO3/l















Code:

Slope (m/m)







1

<=0.005

Low Slope




2

0.005-0.02

Medium Slope




3

0.02-0.04

High Slope




4

>0.04

Very High Slope




Examples of Type Codes:

The two codes from above are combined in order geology first digit and slope second digit

e.g. A code of 31 indicates a calcareous low-slope site

e.g. A code of 23 indicates a mixed geology and high slope of between 2 and 4% gradient







Maps of river types within the six River Basin Districts. (Click on the thumbnails to see the maps on www.WFDIreland.ie)







Fig. 1. Eastern RBD

Fig. 2. Southeastern RBD

Fig. 3. Southwestern RBD







Fig. 4. Shannon IRBD

Fig. 5.Western RBD

Fig. 6. Northwestern IRBD

The 12-Type typology was slightly less significant than a 24-Type typology which had two size/discharge categories and this in turn was slightly less again than a 48-type system which had two peat categories. All three potential typologies, however, performed significantly better than the System A typology. The 12-Type typology was chosen partly in order to reduce the overall number of potential water body types but also because of the inherently high variance of ecological communities and the difficulty in delineating true reference communities for large numbers of closely related types. The question of site-specific conditions and element-specific responses to physical, chemical and biotic factors is dealt with further below. In addition to the 12 major types a number of unusual or rare types are noted and treated separately (See Appendix 2 of this document).




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