Using Hplc and Pcr-Dgge for the Assessment of Phytoplankton and Bacterioplankton Communities in Scottish Freshwater Lakes
The implementation of the European Water Framework Directive (Directive, 2000) prescribes the use of phytoplankton as a biological quality element for the determination of ecological status in surface waters. This study aimed to evaluate high performance liquid chromatography (HPLC) and a combination of polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) for the assessment of the plankton community in Scottish freshwater lakes. Phytoplankton composition and biomass were determined using microscopy and HPLC, while bacterioplankton density and diversity were assessed using flow cytometry (FC), epifluorescence microscopy (EPM), and PCR-DGGE respectively. HPLC and PCR-DGGE were initially applied to water samples from Loch Rannoch to test the applicability of the techniques during a spatio-temporal assessment of the plankton communities in the lake. The deep oligotrophic lake, which stratified over summer, contained a low phytoplankton biomass that was reflected by both, microscopy and HPLC. The variations in the phytoplankton data were related to changes in light, temperature and nutrients. Spatial heterogeneity in the bacterioplankton community compositions (BCCs) across and down the water column was mainly associated with stratification and dissolved organic carbon (DOC). An assessment of changes in the plankton communities was made fortnightly in mesotrophic Loch Calder, another heavily modified water body, which supplies drinking water to parts of Northern Scotland. Major peaks in cyanobacteria and diatoms occurred in summer 2009 and spring 2010 respectively, with lower phytoplankton biomasses noted over autumn and winter. Aspects of plankton eco-physiology could be assessed by the quantification of pigment degradation products and carotenoids, which showed evidence of photo-protection, grazing and senescence. Bacterioplankton density was positively correlated to phytoplankton biomass and BCC appeared to shift in accordance with transitions in ecological seasons. A geospatial study of 20 freshwater lakes across Northern Scotland using both techniques revealed a diverse range of lake types. The pigment profiles in the lakes corroborated their respective microscopy data, with lakes with pronounced differences in pH having distinct phytoplankton compositions. The study also revealed geospatial variations in bacterioplankton density and diversity. Bacterial densities determined using FC and EPM in both, Loch Calder and the Highland lakes showed some discrepancies, which could be explained by factors such as sample processing and the sensitivities of the respective techniques. The presence of at least 60 dominant bacterioplankton taxa in the northern Highland lakes showed that diversity in Scottish lakes was comparable to that in some northern European lakes. This work is the first to demonstrate the applicability of HPLC and PCR-DGGE as viable tools for the assessment of biomass, composition and diversity of phytoplankton and bacterioplankton in Scottish freshwater lakes. Furthermore, the study highlights the potential of the pigment data in assessing the ecological status of the freshwater lakes.
Networked Digital Library of Theses and Dissertations