Effects of EDTA, FeEDTA and soils on the phosphorus bioavailability for diatom and blue-green algal growth in oligotrophic waters studied by transplant biotests : Sediment: Water interaction 11

Biotests with dilute natural populations of blue-green algae and diatoms from the eutrophic Lake Arungen were performed to study the effects of EDTA and FeEDTA in combination with phosphate and soil total reactive phosphate (Tot-P r ) on the growth rate in filtered water samples from the ultraoligotrophic Lake Lutvann. The factor limiting growth other than phosphorus was termed X-limitation. The results showed that the addition of phosphate in combination with EDTA, or FeEDTA, was sufficient to obtain positive growth rates for the algal populations, i.e. for decreasing or removing X limitation. EDTA and FeEDTA had different effects on the growth rate both for different populations and for different samples from Lake Lutvann collected at different time. Low growth limiting concentrations of EDTA or FeEDTA and phosphate in combination was shown to be highly interactive. The optimum EDTA and FeEDTA concentrations for P- limited growth were often about 0.1-0.5 μm and 0.5-1.0 μm, respectively. At these concentrations, many populations were able to grow at very low phosphate concentrations (P < I μg l -1 ). Additions of soils may have similar stimulating effects as EDTA and FeEDTA. The soils (added as P-source) and EDTA had interactive effects on the growth rate both at low and high concentrations varying with the soil types. The optimum concentration of EDTA varied between 0.05 and 0.5 μm, but for the soil types it was very variable. The response of the populations varied considerably. This transplant biotest method, using an optimal concentration of FeEDTA and an optimal Fe:EDTA ratio to prevent X-limitation, should be useful for studying effects of soluble and adsorbed bioavailable phosphorus singly on the growth of diatoms and blue-green algal populations using oligotrophic lake water as medium.