Abstract
Chironomid head capsules were identified from sediment cores taken from Lake Gokyo (4750 m) and Lake Gosaikunda (4350 m) in the east-central Himalaya, to determine taxonomic composition of chironomid assemblages over time. The sedimentation rate of Lake Gosaikunda was estimated at 0.05 cm/yr and that of Gokyo was estimated at 0.07 cm/yr by 210Pb and 137Cs dating. Micropsectra sp. was dominant in the sediments of both lakes. Lake Gokyo sediments also contained Pseudodiamesa sp., Eukiefferiella/Tvetenia sp., Orthocladius/Cricotopus sp. and Rheocricotopus sp. The concentration of headcapsules was nearly an order of magnitude greater in the Lake Gosaikunda core, which contained mostly Micropsectra sp. and Pseudodiamesa sp. These taxa are typical of cold oligotrophic lakes. Differences in lake depth, dissolved minerals, plus epi- and hypolimnetic temperature and dissolved oxygen suggest that stratification and temperature-induced increases in primary production may affect chironomid assemblages in these pristine lakes. Palaeolimnological studies of Himalayan lakes should include replicate cores within lake, to increase headcapsule sample sizes given potentially high rates of sedimentation from glacial runoff. Key words: high altitude lakes, Himalaya, Chironomidae, palaeolimnology, Nepal
Highlights
High-altitude lakes are considered to be very sensitive to climate change (Parry et al 2007)
In Lake Gokyo, numbers decreased from the sediment surface to 4 to 5 cm depth; density started to increase towards 6 cm depth, and decreased at 15 to 10 cm depth in core 2
The natural sedimentation rate in Lake Gokyo was estimated at 0.07 cm, and in Lake Gosaikunda as 0.05 cm per annum on average
Summary
High-altitude lakes are considered to be very sensitive to climate change (Parry et al 2007). Palaeolimnological techniques present the possibility to infer change in environmental conditions over time, such as lake water temperature (Walker et al 1991) using sub-fossil chironomid head capsules preserved in lake sediments. Climate reconstruction modeling requires a calibration dataset based on samples of chironomid head capsules from a large number of lakes spanning a gradient of average temperature. A calibration dataset for Nepalese lakes has not yet been constructed: this study represents a necessary first step towards establishing the relationship between chironomid assemblages and temperature for Himalayan lakes by sampling two remote very high altitude lakes. There is hardly any information available on chironomid assemblages and temperature for Himalayan lakes and this study is a necessary first step, based on which several other high altitude lakes are planned to be studied in the future
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