Changes in the diatom community structure and impact on water quality from 2005-2017 - Great Lake (Lurë National Park, Albania)

Abstract

Great Lake is the largest of the 6 lakes situated in the eastern part of Lura Mountain in the Lurë National Park. Samples were collected in July 2005, June and August 2013 and August 2017. In 2005 and August 2013 epiphytic samples were collected from one locality, while in Jun 2013 was collected epilithic sample. However, in August 2017 no macrophytes were found which caused the collection of epilithic samples from 6 localities (LM1-LM6) around the lake with the aim of establishing ecological status. After laboratory analysis 52 taxa were identified in July 2005, 67 in June 2013 and 111 in August 2013. In August 2017 the number of identified taxa was higher, in total 126 taxa. Dominant taxa in July 2005 were Achnanthidium minutissimum (13.01%), Diatoma vulgaris (13.84%) and Meridion circulare (11.76%). A. minutissimum was also dominant in 2013 (22.26% in June and 21.48% in August). In 2017, dominant taxa differed among localities: LM1 Cyclotella cretica var. cyclopuncta (29.38%), LM2 and LM3 Encyonopsis microcephala (21% at both sites), LM4 Cyclotella cretica var. cyclopuncta (17.41%) and Encyonopsis krammeri (18.91%), LM5 and LM6 A. minutisimum (27.79% and 30.47%, respectively). The genera Diatoma, Epithemia, Fragilaria and Surirella were not recorded in 2017, contrary to previous years. The ecological status of the Great Lake was assessed by using diatom indices. Most European countries have established lake assessment systems based on diatoms. However, the Albanian National Monitoring System does not include biological parameters and therefore no officially accepted diatom index is in place. We compared the values of IPS (Indice de Polluo-sensibilité) and TDIL (Trophic Diatom Index for lakes) indices using boundary values given by the authors. Values of IPS index indicated very good water quality in all years at all sites, while the TDIL indicated moderate water quality in 2005 and 2013 and good water quality in 2017. The reason for this deviation probably is the low relative abundance of indicator species used to calculate TDIL index. The TDIL was developed 2007 in Hungary, and it includes significantly fewer indicator taxa than the IPS. More comprehensive ecological investigations of lakes in Albania are necessary to be able to fulfill the demands of the Water Framework Directive.