Within-lake variability of subfossil chironomid assemblage in a large, deep subtropical lake (Lugu lake, southwest China)

The present study analysed the distribution of subfossil chironomid larval head caspules in a suite of surface sediment samples from a large deep subtropical lake, i.e. Lugu lake, located in southwest China. In order to identify the relationships between environmental variables and the chironomid assemblages ordination methods were used. A total of 41 chironomid taxa were found across the 46 samples, 21 of which had a minimum abundance >1% and were present in more than one site. The samples were dominated by 12 taxa, which together accounted for 97% of the fauna. Redundancy analysis (RDA) revealed that the predominant drivers of chironomid distribution within Lugu lake were bottom water temperature, water depth, loss-on-ignition (LOI) and water total phosphorus (TP) concentration. Abrupt changes in chironomid assemblages occurred at 10 m of water depth, which is closely related to the macrophyte distribution and the position of the thermocline. The chironomid assemblages became uniform below a water depth of ca. 15 m, and the anthropogenic impact on the chironomid fauna was then limited to the edge of Lugu lake. The depth-related faunal shifts primarily reflect the dominant controls of temperature and macrophyte distribution on the chironomids in Lugu lake. This is the first within-lake subfossil chironomid study from this region and the understanding of key environmental influences on contemporary faunas within the lake will aid interpretations of palaeolimnological datasets to reconstruct past trends and magnitude of environmental change over a range of timescales.