Midge-and diatom-based palaeosalinity reconstructions for Mahoney Lake, Okanagan Valley, British Columbia, Canada

Abstract

Abstract. Salinity fluctuations in lakes of semi-arid regions have long been recognised as indicators of palaeoclimatic change, and have provided a valuable line of evidence in palaeoclimatic reconstruction. In the present study, fossil remains of diatoms and midges were used to reconstruct salinity changes at Mahoney Lake from the early postglacial, through the early, mid and late Holocene. A transition from midges typical of a freshwater community (Protanypus, Sergentia, Heterotrissocladius, Cladopelma, Dicrotendipes) during the early postglacial, to those indicative of saline environments (Cricotopus/Orthocladius, Tanypus) occurred in the early Holocene. The midge-inferred salinity values reflected the shift from freshwater (0.031 g/L) immediately after deglaciation, to saline water (2.4 to 55.2 g/L) in subsequent periods. A less saline period was found to have occurred after 1000 yr BP, suggesting a cooler or wetter period. The diatom record indicates similar trends, with freshwater taxa (e.g., Cyclotella bodanica var. aff. lemanica) dominating near the bottom of the core. Diatom-inferred salinities indicate that saline conditions (about 30 g/L) prevailed throughout subsequent Holocene time, although relatively fresh conditions are indicated following deposition of the Mazama Ash, and from about 1500 yr BP until the present day. Midge and diatom-inferred salinity reconstructions for Mahoney Lake compare favorably with each other, and with climate trends inferred from earlier palynological evidence. The palaeosalinity record thus contributes new data relevant to past climatic conditions, in a region where little data have previously been collected.

Holocene chironomid-inferred salinity and paleovegetation reconstruction from Kilpoola Lake, British Columbia

“…This may represent the rapid climatic warming that is well known to have occurred at the beginning of the Holocene (Hebda, 1995;Hebda and Whitlock, 1997;Mathewes, 1985). A similar, rapid salinity increase is evident in Mahoney Lake at this time (Heinrichs et al, 1997).…”

“…A few investigations have considered the impact of tephra deposition on chironomid communities (Boubée, 1983;Pienitz et al, 1992;Tsukada, 1967;Walker and Mathewes, 1987a, 1987b, 1989a, 1989bWarwick, 1989), but none has examined these changes in relation to salinity. Although Heinrichs et al (1997) have examined salinity changes at Mahoney Lake, in southern British Columbia, sampling resolution was insufficient to associate any faunal changes with deposition of an ash layer. We include reconnaissance level palynological analysis to assist in understanding the role of climatic vs. other factors on the aquatic ecosystem.…”

“…Recent investigations have used multiproxy approaches to investigate glacial recession, the evolution of limnic systems, vegetation succession and response, and the timing and severity of climate change in the south-central interior of British Columbia (Cumming et al, 1995;Evans, 1997;Hebda, 1982Hebda, , 1995Hebda, , 1996Heinrichs et al, 1997;Rück et al, 1998;Smith, 1997). Elsewhere, chironomid analysis of saline lake sediments has been demonstrated as a reliable method in reconstructing climate change (Mees et al, 1991;Vershuren 1994).…”

“…Elsewhere, chironomid analysis of saline lake sediments has been demonstrated as a reliable method in reconstructing climate change (Mees et al, 1991;Vershuren 1994). Many saline lakes in British Columbia have diverse chironomid communities (Cannings and Scudder, 1978) so we have been investigating their potential as indicators of paleosalinity and paleoclimate in British Columbia (Heinrichs, 1995;Heinrichs et al, 1997;Smith, 1997;Walker et al, 1995).…”

Changes of sub-fossil chironomid assemblages associated with volcanic sediment deposition in an Andean lake (38°S), Chile

“…Chironomids (Insecta: Diptera) have been used extensively, mainly in the northern hemisphere, to study the past climate, trophic status of lakes, oxygenation levels, and water quality, among others (Walker 1987, Walker et al 1991, Walker et al 1995, Heinrichs et al 1997, Olander et al 1997, Brooks & Birks 2000, Larocque et al 2001, Little & Smol 2001, Quinlan & Smol 2001, Adriaenssens et al 2004). These insects make good paleolimnological indicators because they are abundant in many water bodies, the larval head capsules preserve well in sediments, and the winged adult stages are highly mobile, enabling them to disperse over wide areas .…”