engleski

Phytoplankton in a shallow lake: Vransko Jezero, Croatia.

Phytoplankton assemblages in the largest Croatian natural Lake, Vransko jezero were researched during 2003 and 2004. Lake Vransko jezero is a freshwater (salinity range 0.7-1.2 &#8240; ), polymictic, karstic cryptodepression connected at the South to the Sea by a narrow artificial channel. The preliminary research was done by collecting phytoplankton and water chemistry samples at seven sampling stations in the period from December 2002 to August 2003. No significant differences between stations (p>0.05) were observed, except for August (p<0.005). In 2004, phytoplankton was sampled monthly at four selected sites. Two dimensional MDS ordination indicated separation of the samples collected during 2004 into two large groups (stress 0.13). First group with dominate desmid species Cosmarium tenue was further differentiated into two subgroups corresponding to the winter and the spring species composition. Second group of MDS configuration corresponded to the samples collected during summer period where species Synedra sp. was frequently dominant. BIO-ENV procedure, using Primer 5.0, presented phytoplankton assemblages and abundances correlated with concentrations of nitrogen compounds (BIO-ENV, &#961; w=0.608). This was further supported by statistically highly significant correlation of chlorophyll a and nitrites values (r=0.42. p<0.05). These results suggest strong microbiological regeneration processes in the system.

phytoplankton; nutrients; nitrogen

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