Diurnal primary production patterns in seven lakes and ponds in Alberta (Canada)

Series of consecutive short-term experiments using the¹⁴C-radio-isotope technique indicated that diurnal primary production patterns were different for lakes and ponds. Surface waters of lakes usually gave a morning maximum and a midday or afternoon depression, and deeper water layers gave a midday production peak. Ponds showed little midday depression, and afternoon maxima predominated. There was a significant correlation between solar radiation and phytoplankton production during part-day intervals, except in surface waters of lakes. Primary production between 08.00 h and 12.00 h appeared to be the best short-term indicator of total daily production in lakes. The estimation of total daily production by extrapolation from short-term midday production was fairly accurate for ponds, but was less accurate and less consistent for lakes, especially in surface waters. Relative to solar radiation received, ectrapolations from shortterm incubations near midday were likely to give underestimates of total daily net primary production.