Classification of Danube Delta lakes based on aquatic vegetation and turbidity

The aquatic vegetation present in lakes in the delta of the River Danube was studied using field survey data and satellite image. Based on the spectral information from satellite images, three categories of lakes were distinguished: clear / macrophyte-dominated, intermediate and turbid / poorly vegetated. The satellite-based classification was consistent with vegetation cover and water transparency measured in the field. Cluster analysis of vegetation data from 235 releves made in 22 lakes (1996-1998, each year in June) identified ten submerged vegetation types. The lakes were characterised by the frequency of occurrence of each vegetation type and ordinated, using Principal Components Analysis (PCA). A strong relationship appeared between the composition and density of aquatic vegetation and water transparency. Isolated lakes within the extensive beds of floating reed (plaur lakes) formed a separate group. Based on the ordination analysis, connectivity of lakes in the Danube Delta was concluded to be a major factor for the development of dense macrophyte vegetation.