The Identification, Characterization and Conservation Value of Isoetid Lakes in Ireland

1. Soft-water, oligotrophic isoetid lakes are vulnerable to eutrophication, acidification and alkalinization. As a result of these pressures a large proportion have undergone substantial deterioration in several European countries. The understanding of these systems has been limited by either a lack of lakes close to natural conditions or through receiving less focus in broader scale macrophyte surveys. This has resulted in a dearth of information on specific lake types in their natural condition. Sixty-eight soft-water lakes in Ireland were studied in order to achieve a better understanding of the biological and environmental conditions defining such lakes. 2. Eight groups of lakes were identified using cluster analysis and indicator species analysis. Three groups were representative of isoetid-rich lakes displaying a high frequency of occurrence of Isoetes lacustris, Lobelia dortmanna or Eriocaulon aquaticum together with the almost ubiquitous Littorella uniflora. Canonical variates analysis indicated that alkalinity, total phosphorus (TP), catchment area, altitude, moors and heathlands, mean transect depth, colour and lake area were significant variables discriminating among the eight groups. Soft-water lakes with high amounts of isoetids tended to be less exposed, have broad shallow littoral zones with a high transparency and be situated in smaller catchments. Total phosphorus and alkalinity were typically low, although one group of isoetid-rich lakes had higher mean TP and alkalinity values. This group may contain lakes under threat from nutrient enrichment and alkalinization and also lakes that have higher TP and alkalinity naturally. 3. Lakes with a prevalence of isoetids supported a greater diversity of macrophytes and chironomids indicating that such lakes may represent suitable conservation targets as they act as surrogates for soft-water lakes of high biodiversity. Other factors favouring a focus on isoetids in conservation strategies are their importance as a functional component in soft-water lakes and their sensitivity to lake and catchment environmental change. Copyright © 2008 John Wiley & Sons, Ltd.