Biogeochemistry of particulate organic matter from lakes of different trophic levels in Switzerland

Differences in OM degradation processes are reflected in slightly higher chlorin index values and higher relative proportions of saturated vs. unsaturated n-FAs in Lake Lugano. Higher contents of branched chain FAs, 16:1ω7 n-FA, and enhanced 18:1ω7/18:1ω9 n-FA ratios suggest enhanced bacterial biomass in the water column of Lake Lugano close to the chemocline. Increasing proportions of saturated n-FAs and n-alkanols with increasing water depth, most distinct in the autumn for both lakes, argue for intensified bacterial activity and degradation of OM during autumn. High relative contents of sterols and low n-alkanol concentrations in POM close to the chemocline at Lake Lugano during spring are interpreted to reflect higher primary productivity in the photic zone, OM export to the deeper parts and enhanced degradation rates of more labile constituents (i.e. C13-C20n-alkanols), as compared to Lake Brienz.