Changing Water Quality in the Middle Mahakam Lakes: Water Quality Trends in a Context of Rapid Deforestation, Mining and Palm Oil Plantation Development in Indonesia’s Middle Mahakam Wetlands

The degradation of Indonesia’s wetlands is continuing at a rapid pace. People living in the Middle Mahakam Lakes (MML) region, part of a major wetland area in Indonesia, have observed various negative changes in their local environment, especially with regard to water quality. We verify these local perceptions with the support of water quality measurements (physical and chemical) taken in 1992–93, 1995, 1998 and 2006. We also aim to present data that can be used to determine future trends. We evaluated the water quality of the MML by comparing the 2006 measurements with data reported for similar water systems in Kalimantan and with water quality standards in the USA, and set by the World Bank, Australia, Malaysia and South Africa. Measurements show that the water quality of the MML improved considerably between 1998 and 2006 but there seems to be a delicate balance between the pH value and the levels of oxygen, nutrients and hydrogen sulphide. The low alkalinity values indicate that the system is prone to pH changes, which could be triggered by an increased input of acids, as a consequence of deforestation, mining activities or the drainage of peat lands, effects already occurring in one of the lakes