Authors: B K Maulood G C F Hinton A D Boney
Publish Date: 1978/04/01
Volume: 58, Issue: 2, Pages: 99-117
Abstract
A study of diurnal variation over a 48 hour period was undertaken in July 1973 to ascertain the extent and timing of some major chemical physical and biological variables in Loch Lomond The phytoplankton population was dominated by the diatom Tabellaria fenestrata with a maximum abundance between 0400 and 0600 h in surface waters on both days A distinct diurnal variation in cell numbers was also recorded Chlorophyll a values also showed a regular pattern of variation with a single peak between 1000 and 1400 h each day Some chemical changes appeared to be a direct consequence of phytoplankton multiplication Nitratenitrogen showed a decrease in concentration coinciding with the period of cell multiplication whereas dissolved silica concentrations only fell on the completion of this process Other common diatoms displayed less distinct patterns of variation although Fragilaria crotonensis attained its maximum abundance in surface waters Considerable variation was recorded in the number of organisms and chlorophyll a levels at 25 cm intervals in the upper metre of the water column with large variations in standingcrop and chemical parameters in the space of one hour Diurnal oscillations in the position of the thermocline were recorded with the thermal discontinuity being at its greatest depth in the early hours of the morning The hypolimnion and thermocline regions clearly acted as a source of nutrient supply to the epilimnion From this investigation it is apparent that for the proper understanding of diurnal variation a 24 hour study alone is insufficient and may give rise to misleading results
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