Cladocera responses to climate changes and treeline shifts in an alpine lake-catchment since the Last Glacial Maximum

Abstract

The study of alpine lake ecosystem ontogeny provides an understanding of how climate dynamics and the associated catchment changes impact on lake functioning. Here, a high-resolution subfossil Cladocera sedimentary record, together with geochemistry proxies, from an alpine, treeline lake (Cuoqia Lake) in SW China were analyzed to understand the lake ecosystem response to changes in the regional Indian summer monsoon (ISM) climate and the local mountain environment since the Last Glacial Maximum (LGM, ca. 19.5 cal kyr BP to present). The results show that the cladoceran record from Cuoqia Lake clearly responds to long-term climate change and significant climate events. The lake was depauperate in cladoceran species throughout the late glacial period (ca. 16–11 cal kyr BP) but Daphnia longispina-group and Chydorus sphaericus were the pioneer taxa when the lake was formed. The rapid proliferation of open-water and littoral cladoceran taxa began with increasing water temperature. The Younger Dryas (YD) cold event was recorded by high abundance of the cold-tolerant taxon C. sphaericus during ca. 12–11 cal kyr BP. At the onset of the Holocene (ca. 11 cal kyr BP), Alona spp. and macrophyte-associated taxa became dominant while numbers of C. sphaericus decreased dramatically. In the mid- to late-Holocene, the productivity of Cuoqia Lake seemed to have increased as reflected by higher Cladocera concentration and the appearance of Ceriodaphnia spp. and raptorial P. pediculus which are common in high nutrient waters. Partial Redundancy Analysis (partial-RDA) results highlight the strong effect of indirect climate change (mediated via catchment processes) on cladoceran assemblages during the Holocene. Abrupt shifts in sediment geochemical proxies and regional catchment vegetation at ca. 11 cal kyr BP indicate that substantial nutrient inputs, treeline advancement, and soil development in catchment resulted from the intensified ISM. Therefore, the cladoceran community changes suggest a long-term direct response of the alpine lake ecosystem to climate change since the LGM, but one that was strongly mediated by catchment-vegetation processes, such as the treeline shifts.