Synthesis Report - ERTDI Report 50 - Cruikshanks et al
Summary: Evaluates the efficacy of the SDI approach to site designation under Irish conditions. The water chemistry of 257 sites across Ireland were examined during base flow. A further 65 sites were sampled at base and elevated flow and more detailed hydrological events were monitored at a smaller number of sites.
The identification of acid-sensitive waters currently uses coarse methods of designation, i.e. pH (<5.5) and low alkalinity (<10 mg/l CaCO3).
While these measures are clearly indicative of low buffering capacity, they are extremely variable within any one catchment, depending on flow conditions and geology.
The contribution of sodium (Na+) to the sum of the major cations (Sodium Dominance Index, SDI, or Weathering Index) in river waters has been proposed as an indicator of the acid sensitivity of rivers in upland Scotland, particularly where sea-salt inputs dominate the base cation composition.
The extent of the SDI is considered a quantitative indication of catchment weathering rate, incorporating the effects of diverse geological composition.
This project set out to evaluate the efficacy of the SDI approach to site designation under Irish conditions.
Two hypotheses were tested:
These hypotheses were tested by examining the water chemistry of 257 sites across Ireland, encompassing a range of underlying geologies, during base flow.
A further subset of 65 sites were sampled at both base and elevated flow and a number of more detailed hydrological events were monitored at a smaller number of sites.
Full executive summary in report.
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