Structure of the tychoplanktonic and epipelic diatom communities in the Zelenci spring

Abstract ID: 3.13318 | Accepted as Talk | Requested as: Talk | TBA | TBA

Igor Zelnik
Anastasija, Videska (1); Mateja, Ger (1); Igor, Zelnik (1)

(1) University of Ljubljana - Biotechnical faculty, Jamnikarjeva 101, 1000 Ljubljana, SI

Categories: Biodiversity, Ecosystems, Water Resources
Keywords: epipelon, tychoplankton, diatoms, limnocrene spring

Categories: Biodiversity, Ecosystems, Water Resources
Keywords: epipelon, tychoplankton, diatoms, limnocrene spring

Abstract

Authors: Anastasija Videska, Mateja Germ, Igor Zelnik
The seasonal dynamic of diatom communities was studied in the limnocrene spring Zelenci, located at the foothills of the Julian Alps (Slovenia). The research was conducted between November 2023 and October 2024 at four sampling sites, where tychoplanktonic and benthic samples were collected. A plankton net was used in the open water part of the limnocrene spring for the collection of tychoplankton samples, while epipelon samples were obtained from the soft substrate in its shallow areas. At all sampling sites, selected abiotic factors were measured. A total of 167 diatom species were identified, peaking in June 2024 when their density was the highest. The Shannon-Wiener diversity index was relatively high throughout the year in most of the samples, especially in the epipelic ones, where the similarity of the diatom communities between the samples was greater and more consistent. As the water level increased, the diversity index of the tychoplankton rose consistently, likely due to greater activity of the underwater springs, which brought diatoms up to the water column, and vice versa. Previous studies conducted at this site in 2014 and 2015 indicate that the trophic index is now considerably higher in certain months, suggesting that the spring is occasionally enriched with nutrients from the catchment area. Concentrations of NO₃⁻ and NH₄⁺ were slightly elevated in the spring and summer months, whereas the concentrations of orthophosphate were mostly below the detection limit. Planktonic species were found only in the tychoplankton community. High-profile species were mostly found in the epipelon samples due to their size and fragileness. Motile and low-profile species were dominant in the epipelon. However, they were also abundant in the tychoplanktonic samples, indicating that the species diversity in the tychoplankton is increasing due to the influence of the underwater springs. Achnanthidium minutissimum and Navicula cryptocephala reached the highest abundance in most of the samples, while the most species-rich genera were: Navicula, Gomphonema and Nitzschia. The high diversity of diatom communities in the Zelenci spring, is another good reason to preserve this valuable ecosystem and prevent further nutrient enrichment due to mass tourism or agriculture.