Indices of phytoplankton diversity as an indicator of the ecological state of karst lakes

Istraživanja fitoplanktonske zajednice provedena su u jezerima Kozjak, Visovac, Prošće, Crniševo i u Vranskom jezeru na otoku Cresu. Uzorci su sakupljani mjesečno od travnja do rujna 2009. i 2010. godine na dubinama od 1, 5, 10, 15, 20 i 25 metara te analizirani Uthermöl-ovom metodom. Glavni ciljevi ovog istraživanja su 1) na osnovi taksonomskog sastava vrsta, brojnosti i biomase fitoplanktona odrediti indekse bioraznolikost i definirati ih prema HR tipu jezera, 2) prema količini ukupnog fosfora definirati indekse raznolikosti kao moguće pokazatelje ekološkog stanja pojedinog tipa jezera i 3) definirati indeks koji na osnovi fitoplanktona najbolje opisuje ekološko stanje pojedinog jezera. Utvrđeno je da se reprezentativna fitoplanktonska zajednica nalazi u eufotičkoj zoni jezera. Prema koncentracijama ukupnog fosfora definirane su tri kategorije dubokih jezera Dinaridske ekoregije: TP MAX 0,005 (HR_J-2), TP MAX 0,05 ( HR_J-1A, HR_J-1B, HR_J-5) I TP MAX 0,1 (HR_J-3).Zaključeno je da zbog prirodnih specifičnosti svakog od pet proučavanih jezera u Hrvatskoj nije moguće koristiti samo jedan od navedenih indeksa raznolikosti koji bi bio primjenjiv u pokazivanju ekološkog stanja svih jezera.Studies of the phytoplankton community were carried out in the lakes Kozjak, Visovac Prošće, Crniševo and Vrana Lake on the Cres island. Samples were collected monthly from April to September in 2009 and 2010, at depths of 1, 5, 10, 15, 20 and 25 meters and analyzed by Uthermöhl-method. The main objectives of this study were 1) on the basis of taxonomic species composition, abundance and biomass, determine and define phytoplankton biodiversity indices according to the HR type of lake, 2) by the amount of total phosphorus define diversity indices as possible indicators of the ecological status of each type of lake and 3) define phytoplankton based index that best describes the ecological status of each lake. It is determined that representative phytoplankton community was found in eufotic lake zone. According to total phosphorus concentrations three categories of Dinaridic ecoregion deep lakes have been defined: TP MAX 0,005 (HR_J-2), TP MAX 0,05 ( HR_J-1A, HR_J-1B, HR_J-5) I TP MAX 0,1 (HR_J-3). Due to the natural characteristics of each of the five studied lakes in Croatia, it has been concluded that is not possible to use only one index of diversity that would be applicable in assessing the ecological status for all of them