Seasonality of chrysophyte cyst and diatom assemblages in varved Lake Nautajärvi – implications for palaeolimnological studies

Abstract

Phytoplankton species composition is strongly affected by seasons, which should be taken into account in palaeolimnological studies. Although chrysophyte cysts and diatoms are widely used as palaeobioindicators in palaeolimnological studies, only recently have attempts been made to use their modern deposition from sediment trap data to provide more detailed, seasonal-based environmental reconstructions. In this study sediment traps were used to record seasonality of chrysophyte cysts and diatoms during two climatically different years 2009 and 2010 in an annually laminated Lake Nautajärvi, Finland, and this seasonal data was then compared with the fossil record derived from the surface sediment of the lake. The overall changes in cyst and diatom assemblages between years and seasons are subtle. For both groups, no clear connection to any particular season could be detected in the sediment surface. Despite the climatological differences between the study years, the inter-annual accumulation rates of both algal groups were surprisingly similar, whereas the intra-annual accumulation rates differed substantially. This and the high amount of taxa occurring during all seasons in the trap samples implies that primary producers are more dependent on prevailing seasonal limnological conditions than on rapid, shortly lived episodes. Redundancy analysis (RDA) revealed that chrysophyte cyst assemblages from the spring sediment trap are mainly controlled by the spring discharge intensity, a surrogate variable of spring weather conditions, whereas precipitation and air temperature have the strongest impact on the summer assemblages. However, only discharge explains statistically significantly the variance in the cyst data. Precipitation and air temperature have the strongest impact on the diatom summer samples, whereas the spring sediment trap sample of the snowy and harsh winter of 2010 was strongly correlated with the spring discharge. However, none of the measured environmental variables explains the variance in the diatom data statistically significantly. The similarity between the algae found in the sediment traps and surface sediment sample suggests that within small and shallow lakes without any extreme environmental settings the surface sediment sample represents well the lake's overall algal composition and can thus be used in palaeolimnological studies.

Assessing environmental controls on the distribution of long-chain alkenones in the Canadian Prairies

“…Salinity has been suggested as an important factor on the occurrence and concentration of LCAs (D'Andrea and Huang, 2005;Lopez et al, 2005;Pearson et al, 2008;Toney et al, 2010;Liu et al, 2011;Chivall et al, 2014), with thresholds of salinity (< 3 g/L and > 100 g/L) considered unsuitable for LCA producers to prosper (Liu et al, 2011;Song et al, 2016). In addition, seasonality of environmental variables (e.g., temperature, salinity, nutrients), especially in high latitude regions where lakes are ice covered during winter, may have a strong effect on phytoplankton succession (e.g., Lampert and Sommer, 4 1997;Wetzel, 2001;Korkonen et al, 2017). In fact, lacustrine haptophytes experience sudden increase in abundance (bloom events), likely linked to seasonal changes in nutrient loading and irradiance levels (Toney et al, 2010;D'Andrea et al, 2011;Huguet et al, 2011;Theroux, 2012).…”

Biogeography and ecology of freshwater chrysophyte cysts in Finland

“…PEARL 11 has previously been observed at least in Svalbard (Betts-Piper et al, 2004) and in Arctic peat in Siberia, Russia (Gilbert et al, 1997). In a seasonality study of one particular lake in Finland (Korkonen et al, 2017), PEARL 11 occurred in small numbers mainly in spring cyst assemblages. Cyst Facher & Schmidt # 23 was also found in high numbers in Central European lakes with no clear ecological preference (Facher & Schmidt, 1996).…”

“…5b). In Finland, it has previously been linked with the summer season in a mesotrophic lake (Korkonen et al, 2017).…”

“…Dinobryon divergens has also been known to bloom under the ice cover, with the highest stomatocyst formation just before the onset of ice cover under oligotrophic, low-light, high-bacterial abundance conditions (Watson et al, 2001). In Finland, the highest accumulations of the cyst PEARL 161 were reported during summer (Korkonen et al, 2017). Our study indicates that in Finland, PEARL 116 prefers long icefree periods, unlike in Elk Lake, Minnesota (Zeeb & Smol, 1993), where this cyst was suggested to be more common in lakes with later-than-average ice-out and deep snow.…”

Control of diatom and chrysophyte cyst dynamics by a meteorologically driven mixing regime in eutrophic Lake Żabińskie, northern Poland

“…In this respect, seasonally collected and long‐term observational data are still scarce. In particular, there have been very few studies presenting diatom and chrysophytes seasonality (Hausmann & Pienitz, 2007; Interlandi et al, 1999; Korkonen et al, 2017; Pla‐Rabes & Catalan, 2011). Having in mind this research gap, for 3.5 consecutive years, with contrasting meteorological conditions, we conducted a high‐resolution observational study of the eutrophic Lake Żabińskie in northeastern Poland.…”