The primary production of submerged macrophytes in West Blue Lake, Manitoba

Abstract

The primary productivity of 5 species of submerged macrophytes was determined by continuous cropping of plant biomass, and in situ by uptake of 14C. Both methods were studied by summed transect and random sampling procedures. Areas of the littoral zone colonized by macrophytes were marked off with floats and total area determined by planimetry. The carbon content of plant material per unit of organic weight was analyzed and found to be lower than previously published values. An "in-vial" combustion procedure was devised to allow the combustion of wet and dry samples and quantitatively determine the amount of 14CO2 fixed. The maximum difference between the activity of wet and dry samples was found to be 4.1% and not significant in order that a correction factor need by employed. When distribution and carbon content were applied to 14C experiments, only 2 species contributed significantly to the total macrophyte emergy input. These 2 species, Potamogeton Richardsonii (Benn.) Rydb. and Myriophyllum alterniflorum DC., along with Chara vulgaris L., also contributed to the majority of production determined from biomass changes. Maximum production from biomass changes for the summed transect method was 13.6 mgC m-2 day-1 and the random method was 11.0 mgC m-2 day-1. Maximum production from 14C uptake for the summed transect method was 93.7 mgC m-2 day-1 and for the random method was 102.0 mgC m-2 day-1. Cumulative net productivities for the random and summed transect methods were 8.0 mgC m-2 day-1 and 9.4 mgC m-2 day-1 respectively. These figures are lower than previous studies, although those studies were conducted on much shallower lakes in which the macrophytes occuppied a relatively larger area. Turnover times were calculated for 4 of the 5 macrophyte species and times ranged from 1.45 to 142.01 days. The turnover times were shown to be rather abstract numbers, the difference between any two being magnified by exponential growth.