Effects of drying on aquatic invertebrate assemblages in the springbrook hyporheic zone of the Rječina River

Hiporeička zona spada među najugroženije vodene ekosustave u svijetu. Usprkos tome, hiporeička zona vodotoka koji presušuju započela se istraživati tek nedavno. Prikupljeni su uzorci vodenih beskralježnjaka hiporeičke zone izvorišnog toka rijeke Rječine u Republici Hrvatskoj kako bi se utvrdile sezonske razlike u brojnosti, sastavu i raznolikosti hiporeosa s obzirom na fizikalnokemijske i hidrološke uvjete u vodotoku. Uzorci su prikupljeni Bou-Rouch pumpom, a voda je profiltrirana kroz mrežicu promjera oka 100 μm čime je definirana minimalna veličina prikupljene faune (mikro- do meiofauna) koja je pohranjena u 96 %-tnom etanolu te specijalističkim ključevima pod laboratorijskom stereo lupom determinirana do najniže moguće sistematske razine. Presušivanje korita uzrokovalo je povišenje temperature vode u HZ te više vrijednosti organske tvari. Raznolikost hiporeosa najviša je tijekom ljeta kada je vodotok presušio, a najniža tijekom zime kada su vrijednosti protoka bile visoke do ekstremne. Veća je sličnost hiporeosa između zime i ranog proljeća te ljeta i rane jeseni s vrijednostima od 40 % do 60 % te odvojenim klasterima sezona tijekom kojih vodotok presušuje.The hyporheic zone is among the most endangered water ecosystems in the world. Nevertheless, researches of the hyporheic zone of intermittent streams started just recently. Samples of aquatic invertebrates of the springbrook hyporheic zone of the karst river Rječina in the Republic of Croatia were collected in order to determine seasonal differences in their abundance, composition and diversity with regard to the physiochemical and hydrologic conditions in the stream. A Bou-Rouch pump was used for sampling, and the water was filtered through a mesh with a hole diameter of 100 μm defining the minimum size of the collected fauna (micro- to meiofauna), which was stored in 96 % ethanol and later determined to the lowest possible systematic level under a laboratory stereo microscope using specialist keys. Drying of the riverbed led to an increase in the temperature of the water in the hyporheic zone and a higher organic matter content. The diversity of hyporheos is highest during summer when the watercourse dries up, and lowest during winter when discharge values are high to extreme. There is a greater similarity of hyporheos between winter and early spring and between summer and early autumn with values from 40 % to 60 % and separate clusters of seasons during which the watercourse dries up