A whole‐lake experiment confirms a small centric diatom species as an indicator of changing lake thermal structure

Abstract

In many lakes across the Northern Hemisphere, paleolimnological records have revealed that the relative abundances of the small centric diatom, Discostella stelligera, changed over the past century, with these widespread shifts attributed to climate change. Specifically, small‐scale experiments and current spatial distribution patterns suggested that this species is more abundant when lake mixing depths are shallower, but a direct test of this hypothesis at the whole‐lake scale was lacking. We conducted a whole‐lake mixing manipulation in a remote arctic lake that normally has relatively shallow thermal stratification and abundant D. stelligera populations during the summer. We employed a “Before‐After‐Control‐Impact” design using an experimental lake and a control lake. Lake thermal structure and diatom populations were monitored in both lakes in summer 2013 without manipulating either lake, and again in summer 2014 when the experimental lake was manipulated to achieve deeper mixing depths. The abundance of D. stelligera declined during the manipulated period of deeper mixing in 2014, while it increased during the same time frame in the control lake. The same pattern was not observed for the four other diatom taxa found in both lakes in both years. Our results confirm the use of D. stelligera as an indicator of changing lake thermal structure, and suggest that the broader application of this tool to lake sediment records will yield greater insight into longer‐term variability in the response of lake ecosystems to climate.

How Does Changing Ice-Out Affect Arctic versus Boreal Lakes? A Comparison Using Two Years with Ice-Out that Differed by More Than Three Weeks

“…Cell densities of D. stelligera and L. radiosa were lower during the early ice-out year, with deeper mixing depths, compared to the late ice-out year. Discostella stelligera is more abundant in lakes with shallower mixing depths [40], and L. radiosa is more abundant under high light conditions typical of shallower mixing depths [71]. In contrast, cell densities of L. bodanica were higher during the early ice-out year with deeper mixing depths; this taxon has a deeper mixing depth optimum than other Cyclotella taxa [46].…”

“…Continuous permafrost underlies the region [38] and surface inflow and outflow are not typically apparent [39]. Mean summer temperature is 10.2 • C from June to August and precipitation averages 173 mm per year [40]. Ice-out typically occurs between late May and late June with thermal stratification occurring very quickly thereafter [41].…”

Potential anthropogenic regime shifts in three freshwater lakes in Tropical East Asia

“…Small centric species such as Discostella demonstrate lower sinking rates than larger and heavier planktonic species, such as Aulacoseira (Yang, Stenger‐Kovács, Padisák, & Pettersson, ). Recent increases in the relative abundance of small centric taxa have been attributed to warmer temperatures, and thus enhanced thermal stability of higher latitude lakes (Perren, Douglas, & Anderson, ; Rühland, Paterson, & Smol, ; Saros, Northington, Anderson, & Anderson, ; Saros et al., ; Smol et al., ). Similar changes, possibly also driven at least in part by warming, appear to be occurring in lakes located in the warm tropics, at least on the basis of the data presented here.…”

Alder, Nitrogen, and Lake Ecology: Terrestrial-Aquatic Linkages in the Postglacial History of Lone Spruce Pond, Southwestern Alaska

“…This rise at the expense of larger planktonic or benthic forms has been linked with the onset of Anthropocene regime shifts, but attribution of the cause (i.e. climate warming, nutrient loading, or both) is still widely debated [18–22]. In many cases, stronger thermal stratification appears to be a common feature of these lakes [20, 22] but the role of allochthonous (atmospheric) nutrient additions have yet to be systematically ruled out, and in-lake bioassays suggest a significant response of these organisms to additional epilimnetic N in addition to climate-related parameters [23, 24].…”