Rangas Lake Expedition: Uncovering Environmental Change in a Floodplain Oxbow Lake

Rangas Lake is a shallow oxbow lake with a maximum depth of approximately 6 meters, formed through the separation of a former river meander from the Rungan River in Palangka Raya, Central Kalimantan. As a product of natural fluvial processes, the lake represents an integral component of the Rungan River floodplain system.

Although Rangas Lake remains hydrologically connected to the Rungan River, its water level is highly dynamic, fluctuating in response to tidal influences and seasonal hydrological changes. These fluctuations shape the lake’s physical and ecological characteristics, influencing nutrient exchange, sediment deposition, and biological productivity.

The lake holds significant socio-ecological value for surrounding communities. It is widely used as a fishing ground, providing an important source of livelihood and protein for local residents. In addition, the Rungan River serves as a vital transportation corridor, supporting daily mobility through paddle boats and small motorized vessels that connect villages along the floodplain.

However, increasing human activities pose growing challenges to the ecological integrity of Rangas Lake. Of particular concern is gold mining activity in and around the lake. The release of pollutants associated with gold extraction, especially the suspected use of mercury (Hg) during ore processing, presents a serious risk to water quality and aquatic life. Mercury contamination can accumulate in sediments and biomagnify through food webs, potentially threatening both ecosystem health and human well-being.

Key scientific questions remain unresolved: When did Rangas Lake form, and since when have significant environmental changes occurred? These questions are best addressed through paleolimnological investigations, which analyze sediment cores to reconstruct historical changes in hydrology, pollution inputs, and ecosystem conditions over time.

Accordingly, this study forms part of the Oxbow Lakes Expedition: Rangas Lake, aimed at generating critical baseline data to understand the lake’s environmental history and to support evidence-based management of floodplain lakes under increasing anthropogenic pressure.