Breakdown of mangrove leaf litter in a replanted mangrove forest in Kalpitiya, Puttlam lagoon

Abstract

The mangroves in Puttlam Lagoon were exploited by coastal communities for various purposes such as for fuel wood, for construction timber fencing and for shrimp farms. In order to protect and expand the mangrove vegetation the Turtle Conservation Project (TCP) has initiated a mangrove rehabilitation program in Puttlam Lagoon. By this project Rhizopora mucronata was replanted as it is the dominant species in the area. The present study was conducted with a view to assess the decomposition rate of R. mucronata leaves under replanted conditions.

Decomposition of the selected sp leaves was studied in situ using litter bags in 5 years old replanted sites in Kalpitiya, Puttlam lagoon. Four sites were selected for the study as Eththala, Palakuda, Palliwasathurai and Anawasala in Kalpitiya. Litter samples were placed in 0.5 x 0.5 m litter bags and placed on the plantation floor to assess the litter decomposition rate.

During 123 days decomposition experiment in each site, Eththala(83.95%), Palakuda(71.99%), Palliwasathurai(82.51%) and Anawasala (92.10 %) weight loss of fresh mass was recorded. According to the p-value (0.452) there were no significant differences in dry weight mass loss among these 5 year old replanted sites.

A single exponential decay model was used to describe the rate of decomposition in each site. According to the results obtained from the exponential model rate of decomposition constant per day was 0.02, 0.01, 0.01 and 0.02 in Anawasala, Palakuda, Palliwasthurai and Eththala respectively. There was no significant difference of rate of decomposition constant in each site. The time in days required for the loss of half of the initial dry mass was 34, 67, 49 and 49 in Anawasala, Palakuda, Palliwasthurai and Eththala respectively.

In order to calculate the maximum decomposition limit for litter decomposition for a period of one year, time spent in data collection data was not sufficient. Therefore, it was forecasted the limit value according to the pattern of decomposition and trend analysis with Minitab 14. The maximum decomposition values for Rhizophora mucronata replanted sites were 99.99%.