SQUEEZE-WATER ANALYSIS FOR THE DETERMINATION OF MICROBIAL METABOLITES IN LAKE-SEDIMENTS - COMPARISON OF METHODS

We compared methods for extracting interstitial water from stratified sediments in Lake Geneva and Lake Zurich. Microbial metabolites (NH4+, NO3-, NO2-, SO42-, Mn2+, Fe2+, PO43-, DOC), pH, conductivity, and VFA (volatile fatty acids such as acetate and propionate) as well as more conservative chemical species (Na+, K+, Ca2+, Mg2+, and H4SiO4) were analyzed in pore-water samples collected with a high-pressure squeezing-filtration method and an in situ equilibrium diffusion technique. Both methods are useful if the limitations of their applicability are appreciated. Among the nonvolatile compounds, squeezing leads to increased concentrations of Na+, K+, HPO42-, H4SiO4, NO2-, and DOC. Intracellular metabolites from only partially lysed or still living sediment organisms may be released into the aqueous extract under the influence of very high pressures. The squeezing technique needs to be optimized for pressures that yield pore-water sample volumes large enough for the required analyses but do not disrupt cells.