Littoral ecosystems of tropical lowland lakes : their structure and response to water level change

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We studied the mechanisms of maintaining biodiversity and material cycling in response to water level change in lowland oxbow and floodplain lakes of Borneo (Kalimantan).1.Bathymetrical maps were drawn for eight lakes along the Kahayan River. These lakes were categorized according to their hydrological connectivity with the main river at high and low water levels.2.Water quality changes were monitored in interconnected lakes during a period from dry season to wet season and confirmed the occurrence of vertical mixing of lake water during the high water level. Lake water quality changed greatly affected by the surface and ground waters from the surrounding peatlands and by the water from the main river. Measurement of phytoplankton primary production and litter flux indicated the dependence of lake ecosystem on the allochthonous organic matter.3.Diversity and biomass of organisms in oxbow and floodplain lakes were controlled by the lake's hydrological connectivity to the main river. Flo … More ating macrophyte such as water hyacinth harbored many invertebrates at its root system and playd an important role in maintaining zooplankton biomass.4.Forest clearing in the watershed basin deteriorated pond water quality in lowering water level and pH and increasing SO_4 concentration, which in turn, decreased zooplankton density. Both photosynthetically active radiation and UV light reaching lake surface are expected to increase after forest clearing. UV radiation enhanced DOC decomposition and community respiration during the incubation experiment of lake water. Possibility of increase in rotiferan biomass under enhanced bacterial loop should be examined in the future.5.Land development and the subsequent decrease in water level may finally reduce fish production, the mechanism of which should be studied further. Feasibility studies are needed to test the applicability of traditional farming and fishing methods using aquatic macrophytes such as water hyacinth for improving water quality. Less