About a source of nutrients in the tropical River Rajang (N Borneo) in relation to future impoundment

Summary

Rajang River has the general patterns of tropical flowing waters. It is poor in dissolved nutrients, slightly acid and exhibits dramatic changes of water level. The patchy distribution of heavy rains over the area grown with the primary and partly a secondary forest washes down the organic litter from the steep slopes of the shore. Abrupt changes in water discharge promote deposition of organic material close to the estuaries of small streams into the main river. Water level fluctuation moistens and drains the deposits layed in layers of compressed leaves and sand, respectively, accelerating the rate of decomposition along the shores. When the water recedes, semidecomposed organic material slides into the water current. The mineralization proceeds under aerobic conditions, simultaneously part of semidecomposed detritus provides food to several fish species and invertebrates. The proposed impoundment would disrupt this established system of supply, turnover and utilization of nutrients. This may have disastrous consequences in case that the rich existing vegetation would be submerged and, at the same time, the supply of organic drift would continue. Clearing of the vegetation and temporary retention of forest litter in tributaries to the future man- made lake was suggested.