Natural and anthropogenic transformations of water and marsh vegetation in Lake Zb chy (Wielkopolska Region)

Lake Zb chy is situated in the General Ch apowski Landscape Park, which is the model of a rural area that has been subjected to agricultural pressure for many years. Over a thirty-year period (1976-2006) serious changes in the plant associations of Lake Zb chy have occurred. The maximal depth of plant occurrence decreased from 3.6 m in 1976 to 2 m at present. The area overgrown by submerged macrophytes decreased from 13 to 0.2 ha. The community of Nitellopsidetum obtusae that dominated the belt of submerged plants during the 1970s has entirely disappeared from the lake. The decreasing phytolittoral area in the lake is the result of progressive lake eutrophication and water pollution. The transformations of reed and sedge communities are of a partially natural and partially anthropogenic character. The ecological status of the lake has deteriorated significantly. The ecological state of the lake in 1976 was good according to the Water Framework Directive. Currently, it is sufficient, but the ESMI value of 0.21 only slightly exceeds that of a bad ecological state (0.20-0.00). The level of lake development in the succession process was between mature and aged in 1976; now it is classified as definitely aged.