This study analyzed the water quality dynamics in the coastal zone of Boracay Island in relation to anthropogenic activities and natural factors. Seven sites were studied where possible sources of nutrient inputs on spatial and temporal basis were identified. Water samples were evaluated using the Philippine Department of Environment and Natural Resources (DENR) regulatory standards. The coastal water quality was generally influenced by nutrient loading coming from untreated and partially treated waste water from households and commercial establishments not connected to the sewerage system of the island. Natural cleansing mechanisms attributed to activities of autotrophs in the coastal water and biogeochemical processes of mangrove swamps are operational. Coastal waters adjacent to mangrove swamp impoverished of mangrove trees showed poor water quality, while coastal water adjacent to mangrove swamp with relatively good mangrove cover exhibited good water quality. The months of February to June with highest number of tourist arrival proved to be the critical periods. Lugotan Cove close to Mangrove Swamp 6 impoverished of trees was the critical area in the Island. Puka Beach close to Mangrove Swamp 1 with good mangrove cover showed the cleanest water quality, followed by Long Beach with most of the commercial establishments connected to the sewerage system.
This study investigated the impacts of natural and anthropogenic factors on the coastal water quality dynamics in the Island of Boracay, Malay, Aklan, Central Philippines particularly the effects of nutrient pollution on phytoplankton population. The samples were gathered at two month interval for a total of five samplings by filtering 10 liter buckets of surface water through a net with 25μm mesh bag. There were 35 identified genera of phytoplankton belonging to four taxonomic groups. Diatoms had 26 genera, cyanophycean and silicoflagellate and dinoflagellates had one and seven genera, respectively. Diatoms were the dominant group with the highest mean density of 1,588 ind.L-l, followed by silicoflagellate at 399 ind.L-1 represented by Tintinnopsis, cynophycean was represented by Trichodesmium at 204 ind.L-1, while the dinoflagellates had 132 ind.L-l. Genera richness was high when N and P concentrations were relatively lower. Phytoplankton density was highest in Lugotan Cove and Long Beach where nutrients readings were relatively high. This research clearly demonstrated that the growth of Trichodesmium reaching carrying capacity is an indication that the island ecosystem is near its ecological thresholds. The level of nitrate N acts as the limiting nutrient in the coastal water of the island controlling the growth of Trichodesmium and phytoplankton diversity. Changes in phytoplankton assemblages and density in the coastal waters were associated to variations on intensity and frequency of water mixing along with nutrient loading coming from anthropogenic activities and land uses in the island.
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