Algal growth and loss rates in Lake Loosdrecht: first evaluation of the roles of light and wind on a basis of steady state kinetics

Abstract

Lake Loosdrecht (The Netherlands) is shallow, highly eutrophic and subject to frequent wind-induced resuspension of settled algae and detritus . The summer phytoplankton consists of filamentous prokaryotic species . Chlorophyll a levels are rather stable over the summer at a concentration of ca. 160 mg m -3 ;losses due to grazing and sinking are small . Epipelic chlorophyll a concentrations range from 0 to 250, but ca . 50 mg m -2 is typical . In situ rates of change of chlorophyll a in the water column were related to specific growth rates predicted by a model for light-limited growth . In the model, incident light is partitioned among algae, tripton and background colour, to determine the light available for algal growth and cell maintenance . Model coefficients were derived primarily from laboratory studies of the growth of Prochlorothrix hollandica, an abundant species in the lake in summer . Presuming constant rates of loss due to grazing and sinking, for summers 1985 and 1986 some 56% of the variation in the chlorophyll a in the lake water was explained by change in light conditions alone and 77% by light and wind-driven resuspension of epipelic chlorophyll a together . These factors had little influence on the phytoplankton biomass in 1983 and 1984 ; other environmental conditions, e .g. phosphorus availability, may have been important . Also, the laboratory-derived growth kinetics of P. hollandica may not have been equally suitable for modelling in the four summers . Fig. 2 . Daily insolation (kJ m -' day'), resuspension frequency (% lake area day -' ), and concentrations of sestonic dry weight (g m -3 ), sestonic chlorophyll a (mg m -3 ) and epipelic chlorophyll a (mg m -2 ) of L. Loosdrecht during summers 1983-1986 .

An assessment of the importance of emergent and floating-leaved macrophytes to trophic status in the Loosdrecht lakes (The Netherlands)

“…Further, the effect of phosphorus on phytoplankton growth in these lakes may be reduced or even lacking as light limitation appears to limit further increases in phytoplankton growth (Gons & Rijkeboer, 1990) . In these lakes, however, chlorophyll a concentra-tions remain high until December and it is possible that macrophyte decomposition helps to maintain high autumn levels .…”

Population dynamics of planktonic rotifers in Lake Loosdrecht, the Netherlands, in relation to their potential food and predators

“…This permitted reasonable estimations on egg development rates because the water column was generally completely mixed (Gons et al, 1991). This permitted reasonable estimations on egg development rates because the water column was generally completely mixed (Gons et al, 1991).…”

“…Despite a decrease in the external phosphorus-load from about 1.0 to 0.35 g P m ±2 year ±1 , the phytoplankton (Van and zooplankton had shown no obvious responses by 1990. The mean seston (< 150 mm) mass varies between 8 and 12 mg C L ±1 , between 50% and 75% of which is detritus (Gons & Rijkeboer, 1990). Because the lake is shallow and exposed to wind action, it is well-mixed (Gons, Otten & Rijkeboer, 1991).…”

The first biomanipulation conference: a synthesis

“…Besides, effect ofbenthivorous fish is likely to be important because nutrients accumulating at the lake bottom, including faeces offish and benthic organisms will be brought back (A)). This can, however, also be established by wind action (Gons & Rijkeboer, 1990), particulary in large lakes where waves can develop. Probably the combination of wind and benthivorous feeding has a larger impact than the seperate effects because only little wind is needed to keep already disturbed sediments in suspension.…”