|This study uses limnological techniques and numerical methods to examine the periphyton and phytoplankton assemblages of Lough Atedaun, Cullaun and Inchiquin. Monthly and seasonal variations in periphyton and phytoplankton assemblages were examined from littoral and open water sites within each lake. Samples were taken on a monthly basis in each lake from November 2004 to October 2005. Cell biovolume values for the most abundant phytoplankton were calculated for each of the phytoplankton samples taken from Lough Atedaun, Cullaun and Inchiquin. Seasonal changes in environmental variables were described on a monthly and seasonal basis and the trophic status of each lake was examined. The influence of environmental variables, between site variation and time of sampling on the distribution and composition of the phytoplankton based on cell count data was investigated with the use of Canonical Correspondents Analysis. (CCA).
Results from physico-chemical analysis showed that a seasonal pattern of change existed for most variables. Very little inter lake differences were found in relation to variables concerned with ion exchange such as conductivity and alkalinity. Where as significant inter lake differences took place in relation to variables concerned with nutrient status such as TP, DMRP and NO3-N. A total of 100 phytoplankton species were identified within the three lakes, 72 of these 100 species were found in Lough Inchiquin, 54 in Lough Cullaun and 64 in Lough Atedaun. Of the 100 species identified 37 belonged to the phylum Chlorophyta, 25 to phylum Bacillariophyta, 23 to phylum Cyanophyta, 6 to phylum Chrysophyta, 3 to phylum Cryptophyta, 2 to phylum Pyrrophyta and 4 to phylum Euglenophyta. A total of 137 periphyton species been identified from all 3 lakes, 37 of these were Chlorophytes, 45 of these were Cyanophytes and 45 of these were diatoms.
CCA analysis identified two main groups of variables influencing algal diversity. The primary gradient consisted of a species response to temperature, water level variation and chlorophyll-a representing a seasonal gradient. The second gradient related to a
response to nutrient variables TP, N03-N and DMRP confirming that phytoplankton composition of is strongly influenced by trophic state.