ASSESSING THE EFFECT OF ACETOLYISIS ON DESMIDS, A POTENTIALLY VALUABLE PALEOLIMNOLOGICAL PROXY

A large body of research exists from Crawford Lake, Ontario illustrating the response of various microfossil communities to Iroquoian and later Euro-Canadian settlement and activity. Notably missing from the varved record of this well-studied meromictic lake to date is the NPP group desmids, although preliminary analysis at Brock University has shown them to be abundant in palynological preparations processed only using HCl to dissolve the marl. These charophycean algae have varied ecologies and life habits, making them excellent proxies of cultural eutrophication. This is emphasized through analysis of a core from Smith’s Bay (Lake Simcoe, Ontario), where desmids were used, along with other better-understood microfossils, to assess paleolimnological change associated with human impact. A decrease in desmid concentrations is associated with both Wendat (Huron) and Euro-Canadian land use in the watershed; resulting siltation and nutrient loading led to a shift toward eutrophic, predominantly planktonic taxa from oligo- to mesotrophic benthic taxa in the 20^th C. This reflects intensive agriculture and urbanization, as noted in desmid records from other parts of Lake Simcoe (Danesh et al., 2013; Volik and McCarthy in review). The omission of desmids from the majority of palynological records is likely due to the use of the acetolysis technique, which is commonly employed in palynological preparations. This oxidizing method is beneficial for analysis of pollen and other oxidation-resistant palynomorphs like Pediastrum, removing “unwanted” organic materials than can obscure them on slides. Analysis of samples pre- and post- acetolysis from Smith’s Bay demonstrates that use of this technique is destroys most desmids and skews the assemblage, particularly in organic-poor sediments. The use of this processing technique in paleolimnological studies warrants further investigation.