The Effects of Blanket Bog Erosion on Aquatic Macrophytes in an Irish Soft Water Lake

The Irish Roundstone bog area is characterised by its many oligotrophic soft water lakes surrounded by blanket bogs. These lakes are mainly dominated by isoetid vegetation, adapted to limited nutrient and carbon availability. Peat erosion from surrounding bogs may lead to organic matter accumulation in these lakes, which could increase nutrient availability and pose a threat to isoetid vegetation. Here, we determined whether three distinct vegetation groups (dominated by Lobelia dortmanna, Eriocaulon aquaticum or Juncus bulbosus) in the Irish soft water lake Kankoge differed in sediment and (pore)water chemistry. Elemental composition of in-lake accumulated organic matter was compared with organic matter from blanket bogs to link peat erosion to differences in vegetation. Our results show that parts of the lake with accumulated organic matter had higher inorganic carbon and ammonium concentrations in the sediment pore water. These sites were mainly dominated by J. bulbosus, amounting to plant biomass more than 20 times higher than sites with no or low organic matter accumulation and isoetid dominated vegetation. Eriocaulon aquaticum was present at all sites, even those with high sediment organic matter. By comparing elemental composition of sediment organic matter to the surrounding blanket bog, we show that in-lake organic matter accumulation likely resulted from peat erosion.