Abstract:
Palakaimunai, positioned at North Western coast of Sri Lanka, has been shaped and influenced by
oceanic, terrestrial and anthropogenic activities to varying extent. The natural vegetation in this
deltatic system is dominated with mangroves with intermittently spreading saltmarsh patches at the
foreground and littoral woodland species at the back. The extent which the mangroves in such
seasonally dry tropical climates would provide sediment-grounds for soil carbon and other nutrients
is yet to be revealed. Therefore, spatial variation of soil carbon and carbon fractions, and the
associations of these to available nutrients in Palakaimunai mangals were examined in this study.
Stratified random sampling adhering to 10 m × 10 m grids based on ArcGIS were laid and soil
sampling (n=30) was done from the layer of 0-15 cm from surface. Samples were analyzed for
available nitrate, phosphate and ammonium, microbial biomass carbon (MBC), permanganate
oxidizable carbon (POC), water soluble carbon (WSC) and soil organic carbon (SOC), soil macro and
micro nutrient cations. Principal component (PC) analysis and agglomerative hierarchical clustering
based on geometric positioning under PCs revealed five clusters indendogram, despite there was a
high spatial heterogeneity examined soil parameters over the area. Interdependencies were
unreciprocated among pH (+) to SOC (-) and WSC (-) and ammonium (-) and zinc (-) to MBC (+).
The samples in the clusters with the highest mean SOC content of 11.3%- 14.0% and was associated
with low MBC (0.005% ± 0.007) , high POC (712.23 ± 6.97 mg/kg), high WSC (0. 15% - 0.16%)
and high ammonium (14.2 ± 8.5 mg/kg) contents. Nevertheless, the samples in the cluster with the
lowest SOC content of 1.99 ± 1.54 was found to be associated with the highest availability of nitrate
(2.90 ± 0.78) and lowest of phosphate (14.98 ± 6.02 mg/kg) contents. These highest SOC contents
were recorded at proximate substratum with Avicenia and Rhizophora species and within frequently
saturated substratum. Simultaneously, low MBC content was related with the above prevailing
aneroxic condition. Thereby, generalization over in-site SOC may not verify the carbon sink
potentiality thus varied by geomorphological traits.
Keywords: Blue carbon ecosystems; MBC; WSC; Cluster analysis; SOC
