MONO LAKE DIATOMS – THE PRESENT IS NOT NECESSARILY THE KEY TO THE PAST

Although a great deal of literature on the algal flora of Mono Lake, California has been published, few of those reports have presented data on diatoms. Kociolek and Herbst (1992) collected 18 sediment samples from three sites on the western side of the lake in water up to 10 m deep. The assemblages in all the samples were dominated by benthic species preferring brackish, alkaline conditions.

These assemblages differ markedly from those present in two cores also collected on the western side of the lake. When combined, the records from the cores, one shallow water (2.8 m water depth, Early through Late Holocene) and the other deep water (18 m water depth, late Pleistocene through Middle Holocene) cores, which when combined, provide a record spanning the last 16,000 years.

While present throughout both cores, the taxa that are dominant in modern Mono Lake sediments comprise only a small part of the assemblages in the late Pleistocene and most of the Holocene. In the deep-water core, freshwater eutrophic planktic Stephanodiscus comprise as much as 97% of the diatom assemblage during late glacial and Younger Dryas highstands. A variety of benthic taxa, including epiphytic species attached to aquatic macrophytes become increasing abundant in the Early and Middle Holocene sediments of the deep-water core, but are only a major component in isolated samples. Due to the proximity to the shoreline, the abundance of Stephanodiscus is lower (<70%) in the shallow-water core, and the number of freshwater taxa decrease rapidly near the end of the Early Holocene and remains low for the remainder of the Holocene. This indicates the possibility of seasonal variations in salinity that become more evident as lake level decreases.

In-sample comparison of the abundance of Stephanodiscus to total organic carbon, total inorganic carbon, δ¹³C_org, δ¹⁵N_org, C_org:N_total, and biogenic silica in the deep-water core show no relationship between diatom abundance and productivity, indicating that productivity is tied to other non-diatom algal and cyanobacterial components.

Kociolek, J.P., and Herbst, D.B., 1992, Taxonomy and distribution of benthic diatoms from Mono Lake, California, U.S.A.: Transactions of the American Microscopical Society, v. 111, n. 4, p. 338-355.