Hydrochemistry and algal communities of turloughs (karstic seasonal lakes)

Abstract

This thesis deals with the hydrochemistry and the algal communities in a set of 22 Irish turloughs (karstic seasonal lakes) which represent a broad hydrogeological spectrum. During a flooding season (2006/2007) turloughs were sampled monthly from the onset of flooding (October) until they dried out (March to June). Temporal patterns in chemical characteristics amongst the turloughs were identified. Nitrogen (N) had a similar temporal pattern in all turloughs: a rise until peaking in mid winter and a steady decline thereafter. Phosphorus (P) and chlorophyll a (Chl a) did not show a common pattern amongst turloughs, with peaks of P and Chl a occurring at different times in different turloughs. A significant positive correlation was found between total phosphorus (TP) in the water and previously measured values of trophic sensitivity of the terrestrial plant communities, suggesting an influence of water P on plant community structure. Analyses of the concentrations of chemical variables revealed some discrete groups of turloughs with distinctive characteristics. In particular, a group of four deeper, hydrologically connected and more coloured turloughs in the Gort Lowlands was identified. The high colour in these tmloughs is thought to be related to larger proportions of peat areas in their catchments. Turloughs showed similar levels of nutrients and Chl a to those reported for Irish and international permanent lakes. Chlorophyll a, which peaked between November and February in the majority of turloughs, presented values at times higher than those measured in mesotrophic Irish lakes during the summer. A significant log-linear regression was found between TP and Chl a which suggests P- limitation of algal biomass in the majority of the turloughs (N=17). The regression characteristics were not significantly different to those described in similar studies of permanent lakes. Some turloughs were considered to have factors other than P limiting phytoplankton biomass.