BIO-OPTICAL INVESTIGATION ON THE ALBANO LAKE

Water quality parameters, such as Particulate and Dissolved Organic Matter and phytoplankton characteristics, have been investigated by optical (absorption and fluorescence) and biological techniques. The Italian Albano Lake, near Rome, has been chosen as a test site being a well-known place for tourism. Different water samples were collected monthly, from June 1999 to April 2000, at the same station and depth of the lake. Filtration has played a crucial rule due to the necessity to prepare the samples for the subsequent analyses. Primary productivity and photosynthetic activity of the natural phytoplankton community were investigated by using a Pulsed Amplitude Modulated fluorometer. These analyses were carried out on a GF/F filter (0.7 µm). Concentrated samples on the filter were placed in a quartz cuvette and excited with red and white actinic light. A lamp spectrofluorometer was used to perform analysis, both on unfiltered and filtered samples by using filters of different pore size (0.7, 0.45, 0.22 µm). All the water samples were also analysed for phytoplankton taxonomic identification. Samples were fixed in formaline 2% and observed on a reverse optic-microscope, after sedimentation in a specific sedimentation chamber. Different optical techniques have been applied for chlorophyll pigments determination. Results have shown a good correlation coefficient (r=0.86) between absorption and fluorescence techniques. The Chlorophyll a detected by spectrofluorometer showed a significant correlation (r=0.71) with the phytoplankton biomass determined at the microscope. Dissolved Organic Matter and its components were observed and better analysed in filtered samples than in the unfiltered ones.