A PARTIAL BUDGET OF PRIMARY ORGANIC-CARBON FLOWS IN THE LITTORAL-ZONEOF A HARDWATER LAKE

Primary flows of particulate organic carbon were analysed within a sta nd of Phragmites australis (Cav.) Trin. ex Steud, in the littoral zone of a temperate, medium-sized, nutrient-rich hardwater lake. Primary c arbon flows refer to those fluxes of carbon which directly relate to t he supply and disappearance of organic matter (essentially primary pro duction, allochthonous input, decomposition and export), but without c onsidering the channelling of carbon through the food web. Epiphytic a nd planktonic production was estimated with the C-14 technique. Net ab ove-ground production of Phragmites was inferred from measurements of above-ground biomass, and allochthonous particulate inputs were estima ted from the amounts of litter collected in traps at the lake margin. Decomposition was studied with the litter-bag method, whereas the expo rt of coarse particulate organic matter to and its import from the pel agic zone were assumed to be insignificant. Annual above-ground reed p roduction was 689 g C m(-2) of reed bed and accounted for 88% of the c arbon becoming available within the littoral zone. Almost two-thirds o f the material consisted of stems and leaf sheaths, and although half of that fraction remained after 1 year, Phragmites also contributed su bstantially to heterotrophic lake metabolism (83% of the total), Extra polation of littoral and pelagic primary production indicated that 22% of total production in the lake was achieved in the littoral zone, wh ich covered only 4.5% of the lake area. Taken together, these findings illustrate the great potential of littoral zones to influence overall . lake metabolism.