6 litter fall loss-rate,
since there may be removal by the tide was calculated as the ratio of annual litter-fall mass L to litter-layer or standing crop X
ss
, k = L X
ss
. Turnover rate, the rate of the amount of a substance released by or entering into a compartment in a given time
was defined as the inverse form of decomposition rate 1k. Half-lives t
0.5
assuming an exponential model applies, were calculated as 0.693k Olson, 1963.
2. Litter-fall and litter-layer
The total small litter-fall was 18.65 thay for upper plants and 4.23 thay for lower plants, giving a total number of 22.88 thay. For upper plants leaf-litter was by far the
biggest contributor 65.16, followed by reproductive parts 15.48, wood 12.26, trash 3.23 and stipules 2.58. In contrast wood litter productivity 70.81 was by far the
highest for lower plants, followed by Derris 16.44 and Acanthus leaves 10.90. September to December was the most productive months for upper plant litter-fall but in
contrast the least for the lower plant. The lowest litter-fall for upper plants was in July- August. The total number of litter-fall in Segara Anakan was amazingly much higher than the
range reported for any other mangrove sites in South-East Asia such as Matupore Island, Papua New Guinea with total production of 14.30 Leach and Burgin, 1985, Bintuni Bay,
Papua 11.1 thay Pribadi, 1998, Kuala Selangor, Malaysia 15.8 thay Sasekumar and Loi, 1983, Matang Mangrove Reserve, Malaysia 11.4 thay Gong et al., 1984 and Ranong
Mangrove Forest, Thailand 10.88 thay Aksornkoae et al., 1991. There are several factors which influence litter-fall in mangroves: latitude Saenger and Snedaker, 1993; freshwater
input Pool et al., 1975, Flores-Verdugo et al., 1987; salinity Clough et al., 1982; Clough 1984; the ratio of precipitation to evaporation Clough et al., 1982; Clough, 1984; soil
nutrients Boto and Wellington, 1983; and the age or state of maturity of the forest Clough, 1985. The mangroves of Segara Anakan were not extreme as far as the above factors are
concerned and but surprisingly produced a very high litter-fall. It should be noted, however, that there might be overriding factors that can influence litter-fall in Segara Anakan in the
short term. As it was mentioned above the lagoon presently has a serious threat by a rapid accelerated sedimentation and infilling from the inlet rivers which of course influence water
salinity, and possibly other physical and chemical factors.
The amounts of nutrient returned through small litter-fall were estimated to be kg ha yr: N 255.5, P 41.0 and K 145.5. These values are higher than those reported by Pribadi
1998 for Bintuni Bay i.e. N 240.4, P 6.1 and K 43.2 and Gong et al. 1984 for Matang mangrove forest, Malaysia i.e. N 46.6, P 4.7, K 25.6. The lower values for both forests must
be viewed in the light of their lower annual litter-fall of Bintuni Bay 11.1 tha and Matang 7.8 tha than in Segara Anakan 22.88 tha.
3. Leaf-litter decomposition The
