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.