STRIVE - Environmental Protection Agency

Molecular Diversity and Dynamics of Toxigenic Blue-green Algae in Irish Lakes
Figure 3.27. Microphytoplankton concentrations determined from surface samples in Lough Corrib (a) and
Ballyquirke Lough (b) collected during summer 2010.
3.7.2 Phytoplankton Analysis and Relationships
with Environmental Variables
Surface phytoplankton community dynamics were
investigated in preserved water samples for both Lough
Corrib and Ballyquirke Lough by light microscopy. Only
the most abundant taxa that were recognisable at
×100 magnification were considered (Fig. 3.27). There
was little microphytoplankton observed in the samples
collected from Lough Corrib and only the following
taxonomic units were enumerated: unidentified
dinoflagellates, spherical cyanobacterial colonies and
Asterionella sp. In general, Asterionella sp. was the
most abundant and frequent taxon, with a maximum
concentration of ~6,500 cells l-1 achieved on 25 August
(sample 369). However, unidentified dinoflagellates
were numerically more abundant on 22 July (sample
342) with a maximum concentration of ~12,000 cells l-1 .
Phytoplankton concentrations reached greater levels
in Lough Ballyquirke, where the taxa Oscillatoria sp.,
Tabellaria sp., Ceratium sp. and Asterionella sp. were
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enumerated. The four taxa were relatively abundant
with a cumulated average concentration of 20,000 cells
l-1 until 5 July, after which the concentrations remained
below 3,000 cells l-1 .
The relationships between phytoplankton
concentrations and other environmental variables
were assessed using Pearson’s parametric correlation
analysis for both lakes. Significant correlations were
found between temperature and chlorophyll-a in
Lough Corrib (p = 0.04, r = 0.59, n = 12), and between
chlorophyll-a and cumulated phytoplankton abundance
for Ballyquirke Lough (p = 0.05, r = 0.395, n = 17).
3.7.3 Water Column Profiling and Surface Nutrient
Concentrations
Water column profiling was carried out at each station
during summer 2010 using a YSI Pro Quatro instrument
which was lowered overboard from the side of the
sampling platform (Fig. 3.28).
Figure 3.28. Maps of Lough Corrib (a) and Ballyquirke Lough (b) showing in each lake the locations sampled
on a near-weekly basis during summer 2010.