The development of a true riverine phytoplankton assemblage along a lake-fed lowland river
Yang, Jing-Rong; Basu, Ben K.; Hamilton, P. B.; Pick, Frances R.
published: Sep 25, 1997
ArtNo. ESP141014002006, Price: 29.00 €
Phytoplankton biomass, taxonomic composition and size structure were estimated at intervals along a lake-fed lowland river (Rideau River, Canada). Phytoplankton biomass decreased sharply from the headwater lake to the first riverine sampling site (at 14 km), and then increased downstream reaching a maximum at the last sampling station (90 km). At the upstream sites, the biomass was dominated by nanoplankton algae (< 22μm), which were gradually replaced by larger netplankton algae (> 64μm) at subsequent downstream sites. The downstream increase in total algal biomass was due primarily to an increase in abundance of netplankton which may have been favoured by the higher nutrient concentrations and longer water residence time. Diatoms usually dominated at all sites and the specific composition of the assemblages was influenced by water residence time, water depth and nutrient concentration. Although planktonic diatoms always dominated the diatom assemblage, nonplanktonic diatoms were observed in shallow waters or in fast flow conditions. Lacustrine diatom species such as Fragilaria crotonensis, Tabellaria Jenestrata and Cyclotella bodanica abundant at the headwater lake site, decreased sharply downstream where true riverine assemblages developed. At the first riverine sites, diatom assemblages were dominated by Aulacoseira italica, Cocconeis placentula, Cyclotella atomus and C. pseudostelligera. With increasing nutrient concentrations downstream, these species were replaced by taxa more typical of eutrophic conditions such as Aulacoseira granulata, Stephanodiscus parvus, and S. hantzschii. The latter taxa appear characteristic of large nutrient enriched temperature rivers.