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Journal Articles - UP - MSI

Permanent URI for this collectionhttps://repository.unesco.gov.ph/handle/123456789/50

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1995 - 19983

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    Changes in community structure and biomass of seagrass communities along gradients of siltation in SE Asia
    Terrados, J.; Duarte, C. M.; Fortes, M. D.; Borum, J.; Agawin, N.; Bach, S.; Thampanya, U.; Kamp-Nielsen, L.; Kenworthy, W. J.; Geertz-Hansen, O.; Vermaat, J. (Elsevier BV, 1998-05)
    The patterns of change in species richness and biomass of Southeast Asian seagrass communities along siltation gradients were compared at different sites in The Philippines and Thailand. Seagrass species richness and community leaf biomass declined sharply when the silt and clay content of the sediment exceeded 15%. Syringodium isoetifolium and Cymodocea rotundata were present only in multispecific meadows, while Enhalus acoroides was the only species remaining in heavily silted sediments. The following ranking of species sensitivity to siltation is proposed (from the least to most sensitive): S. isoetifolium→C. rotundata→Thalassia hemprichii→Cymodocea serrulata→Halodule uninervis→Halophila ovalis→Enhalus acoroides. Positive correlations were found between species richness and both community leaf biomass and the leaf biomass of individual seagrass species. The increase in community biomass with increasing species richness was associated with a more even distribution of the leaf biomass among seagrass species. The relationships between percent silt and clay in the sediment and seagrass community leaf biomass and species richness provide useful dose–response relationships which can be used to set allowable or threshold siltation loads in SE Asian coastal waters, and indicate that species loss from seagrass meadows is an early warning of detrimental siltation loads.
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    Relationship between sediment conditions and mangrove Rhizophora apiculata seedling growth and nutrient status
    Duarte, C. M.; Geertz-Hansen, O.; Thampanya, U.; Terrados, J.; Fortes, M. D.; Kamp-Nielsen, L.; Borum, J.; Boromthanarath, S. (Inter-Research Science Center, 1998)
    The growth rate and nutritional status of Rhizophora apiculata seedlings were analyzed across mangrove stands with different sediment composition in The Philippines and Southern Thailand. Plant growth differed 10-fold and the production of new leaves, roots and branches varied between 50- and 100-fold across sites. Most (>60%) of the variance in mangrove growth rate across systems could be accounted for by differences in the nutrient concentration of the leaves, which was in turn related to the interstitial nutrient concentration and the silt plus clay content of the sediments. Nutrient-poor coarse sediments were characteristic of mangroves located in the mouths of rivers draining small watersheds, while sediments at the mouths of large rivers had high silt, clay, and nutrient contents, thus allowing the development of nutrient-sufficient, fast-growing R. apiculata seedlings. The growth of R. apiculata seedlings increased significantly when the plants grew adjacent to rivers draining areas >10 km2. The results provide evidence that growth of R. apiculata seedlings at the edge of the progressing mangrove forests is often nutrient limited, and that the extent of nutrient limitation depends on the delivery of silt and nutrients from the rivers. The coastal zones adjacent to small (<10 km2) drainage areas seem unsuitable to support adequate growth of R. apiculata seedlings, and afforestation programmes should, therefore, target mud flats adjacent to large rivers instead.
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    Heavy metal fluxes in Bang Pakong River Estuary, Thailand: Sedimentary vs diffusive fluxes
    Cheevaporn, V.; Jacinto, G. S.; San Diego-McGlone, M. L. (Elsevier BV, 1995-04)
    Estimates of the flux of heavy metals into the sediments (sedimentary flux) of Bang Pakong River Estuary and the diffusive flux of these metals across the sediment-water interface provide quantitative approximations on the movement of heavy metals from the water column into the sediments, and vice versa. Results showed higher sedimentary flux of Cu, Pb, Zn, Cd, Cr and Ni (0.1–16.8 μg cm−2 yr−1) relative to the diffusive flux of these metals (0.01–4.8 μg cm−2 yr−1). The percentage diagenetic contribution (ratio of diffusive flux to sedimentary flux) of these metals ranged from 10–91%. This suggests that diagenetic remobilization and release of these metals from the sediments into the overlying water may contribute to the subsequent redeposition of these metals into the sediments. Metal enrichment at the surface sediments when compared with deeper sections of the sediment may not necessarily be interpreted as evidence of recent natural, anthropogenic inputs alone, but may also be a consequence of the deposition of metals previously released from the sediments through diagenesis.