Consistent patterns in diatom assemblages and diversity measures across water‐depth gradients from eight Boreal lakes from north‐western Ontario (Canada)

Abstract

Summary 1. Until recently, the distribution of diatom species assemblages and their attributes (e.g. species richness and evenness) in relation to water depth have been identified but not quantified, especially across several lakes in a region. Here, we examined diatom assemblages in the surface sediment across a water‐depth gradient in eight small, boreal lakes in north‐western Ontario, minimally disturbed by human activities. 2. Surface‐sediment diatom assemblages were collected within each lake along a gentle slope from near‐shore to the centre deep basin of the lake, at a resolution of ∼1 m water depth. Analysis of sedimentary samples provided an integrated view of assemblages that were living in the lake over several years and enabled a high‐resolution analysis of many lakes. The study lakes ranged in water chemistry, morphology and size and are located along an east–west transect approximately 250 km long in north‐western Ontario (Canada). 3. The majority of diatom species were distributed along a continuum of depth, with those taxa having similar habitat requirements forming distinct, though overlapping, assemblages. Three major zones of diatom assemblages in each lake were consistently identified: (i) a near‐shore assemblage of Achnanthes (sensu lato), Nitzschia, Cymbella (sensu lato) and other benthic species; (ii) a mid‐depth assemblage of small Fragilaria (sensu lato)/small Aulacoseira and various Navicula taxa; and (iii) a deep‐water assemblage of planktonic origin (mainly Discotella spp.). 4. The depth of the transition between assemblage zones varied between the eight lakes. The boundary between the deep‐water planktonic zone and the mid‐depth benthic zone varied according to water chemistry and was probably related to light attenuation. The boundary was deeper in lakes with the lower dissolved organic carbon and total phosphorus (TP) (i.e. less light attenuation) and vice versa. 5. Generally, species richness, species evenness and turnover rate of species as a function of depth were significantly lower in the planktonic assemblage zone in comparison with the two zones nearer the shore. Reproducibility of species and assemblage distributions across the depth gradient of the lakes illustrated that, despite potential for sediment transport, detailed ecological characterisation of diatom species can be gleaned from sedimentary data. Such data are often lacking, particularly for near‐shore benthic species.

Diatom-based evidence of regional aridity during the mid-Holocene period in boreal lakes from northwest Ontario (Canada)

“…Laird and Cumming (2008) suggest that ELA Lake 239 declined by at least 8 m during the mid-Holocene period. The consistently high percent abundance and concentrations of benthic taxa in Meekin Lake and Gall Lake strongly suggests much lower water levels than present between ~8000 and 5000 years ago ( Figure 5), likely by as much as 2-3 m in Meekin Lake and 3-5 m in Gall Lake based on the modern distribution of S. pinnata, other benthic taxa, and D. stelligera (Laird and Cumming, 2008;Laird et al, 2011;Kingsbury et al, 2012). The nMDS ordination also clearly showed that the diatom assemblages of the mid-Holocene period were unique in all three lakes in comparison with the early-Holocene and late-Holocene periods ( Figure 6).…”

“…The watershed is mostly forested with minimal anthropogenic activities in the catchment (Kingsbury et al, 2012). The predominant vegetation around Meekin Lake is balsam fir (Abies balsamea), poplar (Populus spp.…”

“…Similar to Meekin Lake, the watershed of Gall Lake is mostly forested with minimal anthropogenic activities in the catchment (Kingsbury et al, 2012). However, the vegetation is quite different being dominated by black spruce (Picea mariana), jack pine (Pinus banksiana), and poplar, with lesser amounts of white birch, balsam fir, and larch (Larix spp.).…”

“…Retrieval of a core near this boundary provides a means of tracking this movement and inferences of changes in lake level. The depth of the B-P diatom boundary in both of our study lakes was established by Kingsbury et al (2012) and occurs at a depth of ~10 m in Meekin Lake and a depth of ~6 m in Gall Lake, the difference thought to be related to the greater light transparency in Meekin Lake (Kingsbury et al, 2012). Consequently, the targeted depths for coring were set at 11.5 m for Meekin Lake and a depth of 7.5 m for Gall Lake.…”

Staurosira longwanensis sp. nov., a new araphid diatom (Bacillariophyta) from Northeast China.

“…Previous studies focusing on diatom distribution along a water-depth gradient also reported a middepth assemblage dominated by small Fragilariaceae in various lakes from Europe (Cantonati et al 2009) and North America (kingsbuRy et al 2012). Light availability and water turbulence, which decrease as water depth increases, strongly influence diatom depth zonation (FloWeR et al 2004).…”