Depth-time distributions of detritus depositions in Lake Nemi (volcanic lake of central Italy)

Abstract

The depth-time distributions of detritus depositions onto lake bottom and the amount of resident organic matter on the upper layer of the bottom have been assessed in a volcanic lake. Depositions were sampled monthly across the lake at four depths (0.2 m; 2 m; 6 m; 30 m) during two years (1983–1984). Organic and ash fractions of sediment cores collected along a depth gradient were assessed in the summer of 1984. The result show: 1. The mean amount of organic matter deposition (size > 10 µm) is 1.24 gm−2 d−1 (dry weight) (i.e. 452.6 g m−2 year−1): 2. The metabolism of Large Particulate Organic Matter (L.P.O.M.)) occurs primarily in the littoral zones not farther than 30 m offshore and the dispersibility of the L.P.O.M. may be predicted by a negative exponential model; 3. The deposition on the bottom comprised under the perimeter of about 80% of the lake surface, is principally autochthonous (planktonic in origin); 4. The detritus settled out of the water column is not completely processed and about half of the total material enters the slow cycle of the sediment on the deepest zone of the lake.