Changes of phosphorus and nitrogen concentration and of phytoplankton in enriched lake enclosures1

Abstract

Enclosures isolating 17 m3 water with the underlying sediments in the mesotrophic area of Lake Balaton were used to simulate the main processes taking place in its hypertrophic area. In an enclosure with both P and N added the ~production and the biomass of phytoplankton increased immediately. Algae rapidly took up the added nutrients, transporting a third of the loadings from the water to the sediments and supplying a large amount of organic substrate for denitrification. As a result of N loss from the system, Aphanizomenonflos-aquae formed a second bloom. In an enclosure with only N added the production and the biomass of algae remained similar to those in the open water. NO,-accumulated in the water for a long time. In an enclosure with only P added the algal production and biomass showed a moderate increase, followed by an outburst of A. flos-aquae. POd3-accumulated in the water during the first part of the experiment and was used up during the second.

The influence of different disturbance frequencies on the species richness, diversity and equitability of phytoplankton in shallow lakes

“…Its phytoplankton is limited primarily by nutrients, namely N or P or both. Silicon has never been found to be limiting for diatoms (Istv&novics & Herodek, 1985;Istvanovics et al, 1986). When the algal biomass is high, or after storms the plankton may be subject to light limitation through self-shading or resuspended turbidity.…”

Macronutrient controls on nitrogen fixation in planktonic cyanobacterial populations

“…Experimental studies of the effect of nutrient additions on nitrogenase activity in natural plankton assemblages have utilised a variety of approaches. Some studies relied on large but unreplicated mesocosms including limnocorrals and sections of, or even entire, small lakes (Lean et al 1978;Flett et al 1980;Istvanovics et al 1986). Several largescale experiments were continued for one or two seasons (Lean et al 1978) or even a few years (Flett et al 1980).…”

“…Several largescale experiments were continued for one or two seasons (Lean et al 1978) or even a few years (Flett et al 1980). Other workers used replicated laboratory or field enclosures in experiments which typically lasted days or weeks (Home 1975;Horstmann 1975;Wurtsbaugh & Home 1983;Istvanovics et al 1986).…”

Nearshore abundance of dissolved and sedimented forms of phosphorus

“…were observed during the postmudbank than the premudbank period. Since the content of phosphate in water is influenced by the dynamics of biological activity under natural conditions (Istvanovics et al, 1986), the high biouptake in premudbank period (since primary productivity is very high) and low primary productivity during post period make the postmudbank period dissolved organic phosphate concentration to be about ten times larger than that of premudbank value. The comparatively high biouptake of organic phosphate in the premudbank period is explained by the high primary production reducing the concentration of both inorganic and organic forms of this nutrient to their lowest values in mudbank.…”

“…The mudbanks act as a store of phosphate and with respect to overlying water it is a 'reservoir of phosphate' (Damodaran & Hridayanathan, 1969). The content of phosphate in water is shown to be influenced by the dynamics of biological activity under natural conditions (Istvanovics & Herodek, 1985;Istvanovics et al, 1986).…”