FACTORS INFLUENCING BIOMASS AND NUTRIENT CONTENT OF THE SUBMERSED MACROPHYTE EGERIA-DENSA PLANCH IN A PAMPASIC STREAM

We identified factors influencing biomass and nutrient content in E. d ensa in an enriched pampean stream of Argentina. Physical (current vel ocity, temperature), chemical (pH, conductivity, dissolved oxygen, nut rient content in water and sediments), and biological variables (bioma ss and nutrient content of E. densa, biomass of periphyton and other m acrophytes) were estimated at each sampling occasion, and mean monthly values estimated. Biomass and nutrient content in E. densa were corre lated with these physical-chemical and biological variables. Biomass w as positively correlated with ammonium in stream water (P < 0.05) and sediment total nitrogen (P < 0.01). Nitrogen showed a positive relatio nship with ammonium (P < 0.01), and a negative one with nitrate and pe riphyton biomass (P < 0.05). Phosphorus was positively correlated with soluble reactive phosphorus (P < 0.01). The growth of other macrophyt e species in the stream seemed to influence E. densa biomass, probably through competition for light. Current velocity was low and not signi ficantly related with E. densa biomass; however, a flood at the beginn ing of the study washed the macrophyte stand downstream.