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river-catchments


Typical mangrove forest in Timor Leste after small-scale cutting by refugees along the north coast.

The Timor Leste Government has recognised that land-use practices in the nation's river catchments have accelerated coastal erosion which may be degrading the quality of waterways and coastal zone habitats along both the north and south coasts. At the Government's invitation, scientists from AIMS, Charles Darwin University and the Australian National University assessed biophysical and social elements of two major river systems (Laclo and Betano) draining to the north and south coasts, respectively. The Timor Leste Government and the United Nations Development Programme (UNDP) funded the necessary fieldwork and community consultations.

In the Laclo catchment, scientists measured nutrients and recycling processes near the river mouth and established permanent study sites in tidal forests dominated by different mangrove species, many of which are used for fuel wood. Measurements in the Laclo catchment confirmed that historical deforestation has caused severe gully erosion and siltation of the river system. The downstream impact upon the marine environment was less significant, however, because almost all of the extra sediment and nutrients are transported quickly across a narrow continental shelf and sunk in the deep ocean. As a result, mangroves along the nearby coast are growing in muds derived from the ocean rather than from the catchment. Similarly, nutrients for the inshore food web are derived as much from the ocean as by release from sediments deposited on the shelf and upper continental slope. One result is that marine production near the mouth of the Laclo River has little dependence, if any, upon river-derived materials.

Scientists are now analysing data from the Betano catchment, which was sampled in June 2007. The conclusions about coastal impacts are expected to be quite different, as the southern coast is fringed by a broader continental shelf. Satellite images show extensive plumes of muddy waters extending along the coast, apparently trapped against the coast by prevailing winds, as is the case in north Queensland and Gulf of Papua.