Multi-proxy Holocene paleoenvironmental reconstruction from Tha Kum Peat Swamp, Eastern Thailand

Coastal regions across Southeast Asia were drastically transformed during the post glacial period due to sea level rise, yet the paleoenvironmental development of eastern Thailand remains poorly understood compared to other regions. As peat swamp ecosystems are highly sensitive to climate variability and hydrological changes, they can serve as an important archive of past environmental shifts. This study presents a high-resolution 8,100-year multi-proxy record from three sediment sequences retrieved from the Tha Kum peat swamp located 15-km from the modern shoreline in eastern Thailand. We used elemental geochemistry (XRF), total organic carbon (TOC), stable isotopes (δ13C, δ15N, and C/N ratios), and n-alkane distributions to reconstruct the landscape development. 

The stratigraphic sequence of the oldest core (NU4) is divided into four distinct units. The basal Unit 4 (~8100-7600 cal yr BP) exhibits highly variable organic matter provenance, with δ13C and C/N ratios spanning freshwater, marine, and terrestrial sources, reflecting a lake that was indirectly influenced by early Holocene sea-level rise and tidal back water effects. A significant shift occurs in Unit 3 (7600–7350 cal yr BP), characterized by peaks in Sulfur (S) and TOC, alongside lower aquatic proxy (Paq​) values, representing the establishment of shallower lake or wetland system due to coastal progradation following the mid-Holocene sea-level highstand. Unit 2 (7350–2600 cal yr BP) exhibits prolonged geochemical stability following the highstand. High resolution radiocarbon dating indicates a hiatus between 2600 and 200 cal yr BP, which could be the result of relatively dry conditions. This hiatus is followed by the deposition of the most recent sediment (Unit 1), which is characterized by a sharp decrease in Ti and a maximum TOC, signaling a transition to a modern organic-dominated peat swamp system. This shift was likely driven by a stabilization of the local water table or sea level. 

While the study area is currently managed by the Forest Industry Organization to balance plantation, industry, and conservation, the stability of this ecosystem is threatened by future sea-level rise and fluctuating precipitation patterns. These could potentially lead to ecosystem degradation through the modification of local hydrological and geochemical conditions.