Temporal and Spatial Differences in Phytoplankton Productivity in Marion Lake, British Columbia

Abstract

As shown by the C14 method, the primary productivity of phytoplankton in Marion Lake, a small shallow coastal lake, was very low and was concentrated almost entirely in the 5-month period June to October. Even on the sunniest days, productivity of the surface was not inhibited in contrast to results from most freshwater and marine studies. No explanation could be given. Measurements made simultaneously at 0.5 m at 20 stations covering the lake showed a trend to lower productivity as the water flowed from the inlet to the outlet except when the water passed a large spring. Here productivity increased, suggesting that nutrients were definitely limiting productivity. There was a close relationship between productivity and temperature but not between productivity and light. This suggested that the water temperature prevents full utilization of the available light energy and nutrients during 7 months of the year. The average producivity under a square metre of lake surface was estimated as only 8 g C/m2 per year, and efficiency of conversion of available sun's energy to plant material as only 0.0009%. The low efficiency reflected the very low concentrations of nutrients in the lake water, the high flushing rate, and the low water temperature during 7 months of the year.