engleski

Ecological assessment of two karstic lakes (Plitvice lakes NP) using perennial data from phytoplankton and phytobenthic communities

According to requirements of the EU Water Framework Directive (WFD) ecological status of Lakes Kozjak and Prošće was assessed using biological quality elements (BQEs) - phytoplankton and phytobenthos, emphasizing diatoms as the main algal group characterizing both communities. Starting from 2009-2010, investigations resulted in designation of descriptor species for each of the two BQEs. For phytoplankton descriptor species were used to establish: 1) ecological quality ratio (EQR) based on Chl a and total phytoplankton biomass, and 2) phytoplankton assemblage index (Q). As for the phytobenthos, descriptor species were used to develop Croatian trophic diatom index (TIDRH), a mandatory biological tool in evaluating the ecological status of water. The results indicated that Lake Kozjak was characterized by a codon B centric Cyclotella distinguenda reaching maximum biomass in July (0.03 mg l-1), sharing codominance with group E (Dinobryon divergens/D. sociale/D. cylindricum), and with several descriptors from coda D and LO (Ulnaria ulna var. acus and Parvodinium inconspicuum/Peridinium cinctum). The following functional group (FG) succession pattern was noted: E→(B-E)→(B-D)→B. The phytobenthic community of Kozjak was characterized by species Achnanthidium minutissimum, Brachysira vitrea and Encyonema muelleri. According to TIDRH index (range 1.5-2.3) ecological status of Lake Kozjak was assessed as high. In Lake Prošće codon C associated Stephanodiscus neoastraea wasthe most dominant species with a maximum biomass in July (1.69 mg l-1). Codon B was also represented in Prošće with the species Cyclotella distinguenda Hustedt (max biomass 0.34 mg l-1, in September) and C. plitvicensis Hustedt (max biomass 0.14 mg l-1, in June). Apart from the centric diatoms, coda E, P and D were also noted coexisting with species Dinobryon divergens/D. sociale/D. cylindricum, Synedra sp./Fragilaria crotonensis and Asterionella formosa, respectively. According to dominant FGs, the following succession was recorded: (P- C-E-D)→(E-D)→C→(C-E)→C. The phytobenthic community was characterized by Achnanthidium minutissimum, Cyclotella meneghiniana, C. plitvicensis, Encyonopsis microcephala, E. minuta, Fragilaria capucina, F. crotonensis, Kobayashiella parasubtilissima and Stephanodiscus hantzschii. The range of TIDRH (2.2-2.5) indicated good ecological status of Lake Prošće. The assessments based on the EQR and the Q index indicated high ecological status of both lakes. The aim of recent ongoing investigation on Plitvice Lakes from 2015-2016 was to assemble perrenial data using the same sampling methodology during the same temporal interval and the same spatial position in order to produce a comparable and significant statistical evaluation of ecological status of the Lakes. Moreover, after the calibration process the aggregated data will be compared and the results will be further discussed in terms of ecological assessment status.

phytoplankton; phytobenthos; Water Framework Directive; karst lakes; water quality assessment

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