A TYPOLOGICAL CLASSIFICATION OF HEADWATER STREAMS IN IRELAND

This article addresses the lack of knowledge with regards to the macroinvertebrate communities of Irish headwater streams. The main objective of this study was to describe the macroinvertebrate communities of 74 headwater sites representing a range of geological and geographical settings with the focus on reference systems and to propose a typological classification of these sites. Four main groups of headwaters were identified using multivariate clustering and ordination techniques to develop groups and to determine the environmental factors associated with macroinvertebrate assemblages. The groups identified are largely grouped according to environmental variables. Group 1 sites drained softer geology with non-peaty soils, with a higher conductivity and total hardness than any other group. Group 2 had a similar geology and again drained mainly non-peaty soils but had lower conductivity levels than Group 1 and had the greatest representation of cobble/pebble substrate among the groupings. Group 3 sites drained mainly siliceous geology with peaty soils and were characterized by predominately bedrock and boulder substrates. Finally, Group 4 sites drained siliceous geology with peaty soils and were located at the highest elevations and had the lowest pH. A Canonical correspondence analysis (CCA) was conducted to determine the relationships between the macroinvertebrate communities and the physico-chemical variables. It was clear that geology and its co-variables, including conductivity and pH, played a considerable role in defining the groups. A one-way ANOVA also highlighted the significance of some of these variables in the grouping of these sites. This study highlights the importance of defining headwater typologies so that reference conditions for each type can be established and thus form a baseline against which future changes in biodiversity or water quality can be measured.