MACROPHYTES OFTHE LIVEROVIC RESERVOIR NEAR THE CITY OF NIKSIC IN MONTENEGRO

Reservoirs represent specific habitats characterized by a number of unique features unfavorable for macrophytedevelopment, above all frequent and sudden changes of the water level. For this reason, reservoirs usually lack a zone of emerged and floating plants, and the vegetation of swampy meadows develops in the littoral, in which terrestrial forms of aquatic plants are often abundantly represented (Randjelovi6 and Blazenci6, 1997).

Plants of aquatic and swampy habitats are increasingly becoming a subject of interest to botanists, not only on account of their significance in aquatic ecosystems, but also due to their use as a means of protecting these ecosystems from unfavorable factors such as drying up and pollution of the biotope.
In contrast to increasingly numerous data on aquatic and swampy plants of natural aquatic biotopes, very little is known about the macrophytes of reservoirs ( Bl Reservoirs represent specific habitats characterized by a number of unique features unfavorable for macrophytedevelopment, above all frequent and sudden changes of the water level.For this reason, reservoirs usually lack a zone of emerged and floating plants, and the vegetation of swampy meadows develops in the littoral, in which terrestrial forms of aquatic plants are often abundantly represented (Randjelovi6 and Blazenci6, 1997).
Although reservoirs belong to the category of lake ecosystems inasmuch as they are most often formed by construction of dams on brooks and rivers, they have a special hydrological regime characterized by numererous sub lacustrine springs and underwater currents.For this reason, plants characteristic ofrunning waters and springs are found in them, in addition to typical lake plants.
In view of the specificity of reservoirs as biotopes and lack of knowledge about their flora and vegetation, we decided to investigate the SIano (Bl az cnc i c and Hl az e n c i c , 1991), Krupac, and Liverovic Reservoirs near Niksic, The Liverovic Reservoir was built in 1961/62 in the middle of the course of the Gracanica River about 20 km southeast of Niksic at an elevation of around 800 m above sea level.The lake's basin is elongated in the form of a trough extending in a southeast-to-northwest direction.Water depth increases in the same direction up to the dam, where the lake is deepest.Investigations were carried out on 12 August 1987, and the results presented herein will be of use to future researchers as a basis for monitoring the state and succession of macrophytic populations.The measured air temperature in the morning hours (8:00 h) was 14.2 C, while that of water in the surface layer was 22.0 C. Water clarity was 4.5 m.Botanical investigations were initiated from wet meadows of the southeast part of the lake, were continued in its shallowest 15P part, and then followed the lake's long axis in a northwesterly direction to the dam itself, where a depth of 12.0 m was measured.Moving in this manner and using the method of transects and cross profiles, we collected numerous samples that are stored in the conserved state in the collection of the Biology Faculty'S Instutute of Botany in Belgrade.
On its southeast side, the lake is gradually entered over gently sloping terrain cut by many streamlets.The presence of cracked dry ground gradually overgrown by plants characteristic of wet meadows suggests that the water only recently retreated from it.This conclusion is also supported by a white surface covering of dried macroscopic algae (Chara contraria) between the meadow plants.
In the shallow part of the lake (to a depth of 1.0 m), fields of Chara contraria replace meadow vegetation.This species of Chara occurs in the form of pure populations or in combination with the species Teucrium scordium and Alisma plantago-aquatica in shallow parts of the lake.In some places, the bottom is covered by mosses together with occasional rare specimens of Potamogeton pusillus and Nitella opaca.The presence of these species points to the existence of sublacustrine springs in the vicinity.Moving toward greater depths, populations of Chara contraria are regularly replaced by Nitella opaca and Chara deliculata.At shallower depths (about 2.5 m), the population of Chara contraria is dominant.At depths of from 3.0 to 4.5 m, it is replaced by a zone with a mixed population of Chara contraria and Nitella opaca.Starting from a depth of 4.5 to 5.5 m, the next zone consists of dense meadows of Nitella opaca.This species continues into deeper parts of the lake to a depth of 11.8 m, but the population becomes thinner with increase of depth.The species Chara delicatula is recorded in the same places as N. opaca, but in considerably smaller numbers.Thus, these two species at a depth of 11.8 m form the lower boundary ofmacrophyte distribution in the Liverovic Reservoir.
On the basis of floristic composition and vegetation of Charetum contrariae Corillion 1957 and Nitellum opaceae Corillion 1957 communities, the Liverovic Reservoir can be called areservoir of the Nitella type.This at the same time means that the given reservoir is rich in sub lacustrine springs and cold underwater currents.
aze n c i c and Bt az e n c i c , 1991; Ran dj e l o v i c and Bl az e n c ic , 1997; St ev a n o v i c et aI., 2003), especially in Montenegro (Bt az e.nc ic and Bf az e n c ic , 1997).