Quasi in situ separation of particulate matter from lakewater by hollow-fibre filters to overcome errors caused by short turnover times of dissolved compounds

Hollow-fibre modules combined with a pumping device are presented as a superior technique for obtaining particle-free lakewater as compared to conventional membrane filtration. The separation procedure as shown by chlorophyll a and ATP measurements is very efficient and gentle. The integrity of delicate flagellates as tested by the loss of their flagella is maintained at a very high percentage. The filtration process was shown to have no effects on the concentration of inorganic ions (ammonium, nitrite, o-phosphate), amino acids (alanine, phenylalanine) and sugars (glucose, maltotriose) in μM concentrations. This technology enables the preparation of large volumes of particle-free water from lakewater of eutrophic lakes with high phytoplankton densities that clog conventional membranes after passage of a few millilitres. The short turnover times of many inorganic and organic compounds in lakewater do not allow transport of water to the laboratory for separating the particulate fraction without essential changes in the water composition. With hollow-fibre filters a rapid separation can be conducted quasi in situ on the boat within seconds after taking samples, thus reducing the formation of artifacts in compound composition and concentration.