Importance of sampling frequency when collecting diatoms

Abstract

There has been increasing interest in diatom-based bio-assessment but we still lack a comprehensive understanding of how to capture diatoms’ temporal dynamics with an appropriate sampling frequency (ASF). To cover this research gap, we collected and analyzed daily riverine diatom samples over a 1-year period (25 April 2013–30 April 2014) at the outlet of a German lowland river. The samples were classified into five clusters (1–5) by a Kohonen Self-Organizing Map (SOM) method based on similarity between species compositions over time. ASFs were determined to be 25 days at Cluster 2 (June-July 2013) and 13 days at Cluster 5 (February-April 2014), whereas no specific ASFs were found at Cluster 1 (April-May 2013), 3 (August-November 2013) (>30 days) and Cluster 4 (December 2013 - January 2014) (<1 day). ASFs showed dramatic seasonality and were negatively related to hydrological wetness conditions, suggesting that sampling interval should be reduced with increasing catchment wetness. A key implication of our findings for freshwater management is that long-term bio-monitoring protocols should be developed with the knowledge of tracking algal temporal dynamics with an appropriate sampling frequency.

Hydrological and environmental variables outperform spatial factors in structuring species, trait composition, and beta diversity of pelagic algae

“…A previous study on the relations among 83 hydrological metrics and changes in algal communities of the United States was consistent with our study and demonstrated the importance of hydrological variables to the variance of specific algal community metrics (Steuer, Stensvold, & Gregory, ). Moreover, recent studies (Qu et al., ; Wu et al., ), which were in line with our finding, also found that hydrological conditions played an important role in temporal variations of pelagic algae communities. Skewness of flows was found to be one of the most consistently dominant indices across all stream types and may be a particularly important measure of flow condition for certain riverine taxa (Olden & Poff, ), for example, annual skewness of the flow has been linked to fish mobility and colonizing ability (Puckridge, Sheldon, Walker, & Boulton, ).…”

“…Nevertheless, previous studies and biomonitoring campaigns focused mostly on local environmental variables such as nutrients (Kelly & Whitton, ; Lange, Liess, Piggott, Townsend, & Matthaei, ), pH, temperature (Çelekli, Öztürk, & Kapı, ; Wu, Schmalz, & Fohrer, ), and recently also spatial factors (Heino & MykrÄ, ; Rezende, Santos, Henke‐Oliveira, & Gonçalves, ; Tang, Niu, & Dudgeon, ; Tang, Wu, Li, Fu, & Cai, ; Wu, Cai, & Fohrer, ). By comparison, little attention has been paid to hydrological factors such as flow regime (Qu, Wu, Guse, & Fohrer, ), although many studies have shown that riverine algal communities are linked to flow velocity and discharge (Biggs, Smith, & Duncan, ; Jowett & Biggs, ; Munn, Frey, & Tesoriero, ; Riseng, Wiley, & Stevenson, ; Wu et al., ) and catchment wetness (Wu et al., ). Yet, a profound understanding on the interaction of hydrological variables and river organisms, specifically algae, is still missing.…”

Terrestrial diatoms as tracers in catchment hydrology: a review

“…However, freshwater diatom communities are also strongly spatially structured 31,50 and pure spatial factors account sometimes for a high percentage in the total explainable community variation 53 and thereby suggest that diatoms lack strict ubiquitous dispersal. Wu et al 54 have recently advocated new (time-variant) sampling frequencies accounting for the strong seasonality in diatom population dynamics.…”

“…However, freshwater diatom communities are also strongly spatially structured 31,50 and pure spatial factors account sometimes for a high percentage in the total explainable community variation 53 and thereby suggest that diatoms lack strict ubiquitous dispersal. Wu et al 54 have recently advocated new (time-variant) sampling frequencies accounting for the strong seasonality in diatom population dynamics.In the Attert River basin, this is illustrated by the distinct spatial structure of diatom communities found in three experimental catchments with uniform bedrock geologies: schists in the Weierbach catchment, sandstone in the (upper) Huewelerbach catchment, and marls in the Wollefsbach catchment. These spatially structured diatom communities can be visualized along the DCA axis plotted against pH and conductivity (the two main measured parameters structuring diatom communities) ( Figure 5).…”

Technical note: A time-integrated sediment trap to sample diatoms for hydrological tracing

“…(both in December). The latter is also important, since diatoms exhibit seasonal succession and thus species composition could change significantly during the year (Wetzel, 2001;Wu et al, 2016). Klaus et al (2015) analysed 28 samples in which they found 221 different species, while we also observed 231 taxa.…”