High rates of production and mortality of submerged Sparganium emersum Rehman during its short growth season in a Eutrophic Danish stream

Abstract

Above-ground production and mortality of submerged Sparganium emersum Rehman were investigated during its short summer growth season, when water discharge is low, in the Danish lowland stream, River Suså. Production and mortality followed the same seasonal pattern with a time-lag for mortality of about 1 month. The life time of individual leaves was only from 31 to 39 days. In one population, the mortality rate constituted more than 50% of the production rate before the maximum biomass was attained This mortality was mainly due to a successive loss of individual, old leaves, and loss of entire shoots was small until late in the season. Ratios of annual production to maximum standing crop were from 2.2 to 2.4 and therefore, standing crop cannot be used as a measure for annual production. The maximum daily production rates were from 4 to 6% of the biomass in late June and mean rates for the growth season were from 2.5 to 2.7% day −1. The maximum daily productivity ranged from 11.5 to 15.4 g dry wt. m −2 and the annual production realized during 5 months was from 500 to 1000 g dry wt m −2. These values show that leaf growth and leaf mortality of Sparganium emersum are concurrent and rapid processes in eutrophic, temperate streams.