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close this bookBasic Concepts in Environment, Agriculture and Natural Resources Management: An Information Kit (IIRR, 1993, 151 p.)
close this folderFreshwater and marine ecosystems
View the documentFreshwater ecosystems
View the documentEstuarine-mudflat ecosystems
View the documentSeagrass ecosystems
View the documentMangrove ecosystems
View the documentCoral reef ecosystems
View the documentHuman intrusions into the water cycle
View the documentDiversity of coastal and marine resources
View the documentPhilippine marine fisheries
View the documentMarine turtles
View the documentMarine food web
View the documentOcean pastures
View the documentThe menace of algal bloom
View the documentRed tide (Dynamics and public health aspects)

The menace of algal bloom


Upsetting the ecological balance causes algal blooms

· In natural conditions, relatively small quantities of nutrients and sediments are leached or eroded from the land into waterways. In turn, fed by clear rivers and streams, the natural condition of lakes and estuaries is generally nutrient-poor. This limits the growth of PHYTOPLANKTON (from phyto=plant and plankton = floating) an aquatic plant which consists of numerous species of algae. Algae grow as microscopic, single cells or small groups or threads of cells that maintain themselves near or even on the surface. Since they are not connected to the bottom, populations of phytoplankton must get their nutrients from the water. Lack of nutrients in the water limits their growth accordingly.

· As erosion and leaching occur, a body of water is gradually filled in with sediments and enriched with nutrients. Algal and plant growth steadily increases as the lake shallows and is slowly filled in. This natural ageing process of lakes is called eutrophication.

· Human activities, however, can rapidly speed up this long-term natural process. Logging and agriculture increase sediments and nutrients in runoff flowing into lakes. This speeds up the process of eutrophication leading to large and frequent algal blooms and subsequent fish kills. This human-induced process is known as cultural eutrophication.

· Laguna de Bay is an example of a lake experiencing cultural eutrophication. Industrial, domestic and agricultural wastes all contribute to the pollution of the lake. Siltation from land use, including logging in surrounding hills, has reduced the lakes depth from 7 to 2.8 meters. Algal blooms are becoming more frequent causing larger fish kills.