AME 34:291-299 (2004)  -  doi:10.3354/ame034291

ABSTRACT: Respiratory activity in sediments was studied in 3 Slovenian mountain lakes and 1 subalpine lake. Electron transport system (ETS) activity was measured in the sediments to assess the potential mineralisation of organic matter (OM), while oxygen consumption rate (R), induced under laboratory conditions, was used to assess the actual mineralisation of OM in these sediments. The lakes are situated at different altitudes, with different water temperatures. They also have different trophic status. It was found that higher lake water temperatures and more productive lakes, having higher contents of labile autochthonous OM, caused higher microbial respiratory activity, reflected in higher ETS activities and R. Subsurface peak values of ETS activity and R were observed in the mountain lakes, most probably indicating slower degradation of OM; in particular, the more refractory terrestrial OM, and the presence of anaerobic microorganisms. In the case of the lowland eutrophic Lake Bled, no such distribution was observed. In this lake, OM is effectively degraded in the water column and surface sediments due to high lake water temperatures and high content of autochthonous OM. A high correlation between ETS activity and R was observed in all the sediments, while correlations between ETS activity and organic carbon (OC) concentration, and between R and OC concentration were lower.

KEY WORDS: ETS activity · Oxygen consumption rate · Mineralisation · Organic matter · Alps