Abstract
Rapid development and climate change in southeast Asia is placing unprecedented pressures on freshwater ecosystems, but long term records of the ecological consequences are rare. Here we examine one basin of Tasik Chini (Malaysia), a UNESCO‐designated flood pulse wetland, where human disturbances (dam installation, iron ore mining, oil palm and rubber cultivation) have escalated since the 1980s. Diatom analysis and organic matter geochemistry (δ13Corg and C/N ratios) were applied to a sediment sequence to infer ecological changes in the basin since c. 1900 CE. As the Tasik Chini wetland is a rare ecosystem with an unknown diatom ecology, contemporary diatom habitats (plant surfaces, mud surfaces, rocks, plankton) were sampled from across the lake to help interpret the sedimentary record. Habitat specificity of diatoms was not strongly defined and, although planktonic and benthic groupings were distinctive, there was no difference in assemblages among the benthic habitat surfaces. An increase in the proportion of benthic diatom taxa suggests that a substantial decrease in water level occurred between c. 1938 and 1995 CE, initiated by a decline in rainfall (supported by regional meteorological data), which increased the hydrological isolation of the sub‐basin. Changes in the diatom assemblages were most marked after 1995 CE when the Chini dam was installed. After this time both δ13Corg and C/N decreased, suggesting an increase in autochthonous production relative to allochthonous river flood pulse inputs. Oil palm plantations and mining continued to expand after c. 1995 CE and we speculate that inputs of pollutants from these activities may have contributed to the marked ecological change. Together, our work shows that this sub‐basin of Tasik Chini has been particularly sensitive to, and impacted by, a combination of human and climatically induced changes due to its hydrologically isolated position.
Highlights
Recent human impacts on natural ecosystems are unprecedented and have had a detrimental effect on freshwaters (WWF, 2018)
In zone 2 (47–11 cm, 1938– 2004 CE) diatom assemblages became more variable with smaller relative abundances of A. cf. muzzanensis as the relative abundance of F. saxonica increased to 16% (27 cm, 1980 ± 3 CE), B. brebissonnii increased to 6% (22 cm, 1989 ± 3 CE), and F. crassinervia increased to 7% (35 cm, 1965 ± 4 CE)
Decomposition of C. furcata has been associated with the reduction in pH at Tasik Chini (Shuhaimi‐Othman et al, 2008b), and low dissolved oxygen concentrations (87.5%) support the idea that organic matter decomposition is active at this site, and it is likely that water renewal times are slow
Summary
Recent human impacts on natural ecosystems are unprecedented and have had a detrimental effect on freshwaters (WWF, 2018). Freshwater, tropical wetlands are often important sites for biodiversity and provide vital ecosystem services, such as the provision of potable water, food supply, and flood protection (Mackay et al, 2012; Mir et al, 2010; Sharip et al, 2014) Such services are threatened by anthropogenic pressures, such as land conversion for agriculture, hydrological manipulation, climate change, and wastewater discharges, in the context of a rapidly expanding and developing population (Mackay et al, 2012; Mir et al, 2010; Sharip et al, 2014). 150 years; and (3) compare the diatom record with known climatic, hydrological, and land use changes to infer the causes of ecological change Together, this will provide the first detailed palaeoecological record for Tasik Chini and Peninsular Malaysia. This modification increased the overall size of the water body by 2.4 km and extended water retention times (Sujaul et al, 2010, 2013)
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