Responses of vegetation to a rise in water level at Kerkini Reservoir (1982–1991), a Ramsar site in northern Greece

Abstract

/ The floodplain of the river Strymon at Kerkini (northern Greece) was transformed into an irrigation reservoir by the construction of a dam in 1932 and subsequently enlarged in 1982. The aims of this study were to quantify the changes occurring in the various habitat types following raising of the waterlevel and to assess the stability of the plant communities present at this Ramsar site. The current hydrological regime, which has been stable since 1986, is typified by an increase in mean annual reservoir level of 2.2 m and by an increase in the annual range in level of 1.3 m. Landsat (1980, 1981, 1984, 1986, and 1988) and SPOT (1990) satellite images show a decrease in the area of grassland and shallow water areas, the very rapid disappearance of reedbeds, the appearance of beds of Nymphaea and the disappearance of half the forest area.The flooded forest, dominated by Salix alba, is a key habitat contributing to the biological richness of this wetland of international importance. The decrease in the forested area will continue because of the death of standing trees, the absence of regeneration under the new regime, the felling of trees and grazing. Management could be undertaken to ensure the survival of forested habitat and reedbeds at Kerkini, but this would require that the authorities take into account nature conservation and the protected status of the site and not raise the water level again.Lake Kerkini in northern Greece is situated on the floodplain of the River Strymon, which was transformed into a reservoir in 1932 by the construction of a dam. This reservoir (original maximum capacity: 289 x 106 mS; Babajimopoulos and Antonopoulos 1990) was designed to provide irrigation water for cultivation (maize, rice, etc.) on the Serres plain downstream and also for flood control. As a result of siltation of the lake by sediment brought down by the River Strymon, the reservoir lost 61% of its storage capacity in 50 years (Klossas 1975). For this reason and to expand irrigated crops, a new, higher dam and new dykes were built and came into operation in 1982. In order to be able to evaluate the impact of this new water management on the wildlife and the habitat of this wetland, an assessment of the impact of the changes since 1982 has been undertaken.

Damming effects on upstream riparian and aquatic vegetation: the case study of Nazzano (Tiber River, central Italy)

“…In other studies the formation of new habitats and significant changes in the vegetation types as a consequence of alterations in river water level, were observed (Crivelli et al, 1995;Springuel et al, 1997). Our study, in accordance with the latest investigations, shows how the dam construction has implied the formation of a new lacustrine habitat that has created optimal ecological conditions for the growth of various aquatic plant communities.…”

“…In this paper, we analyzed the structure and distribution changes of the vegetation along the Tiber River in Nazzano (Rome) resulting from the construction of a dam in 1956. This dam, which is associable with a run-of-river impoundment according to the our available data, is an interesting case study for the evaluation of alterations due to this type of plant, especially in the Mediterranean region, where the knowledge on this topic is very poor (Crivelli et al, 1995). Although it is known that this dam has contributed to the formation of a new sub-lacustrine ecosystem (the Nazzano Lake), and consequently of new habitats for the development of aquatic and riparian vegetation (AA.…”

“…Pasternack et al, 2004;Jacobson and Galat, 2006), and structure of food webs (Wootton et al, 1996). In the upstream stretch of a river, the main effect of damming is the increased water level and the consequent inundation and loss of habitats of the surrounding riparian areas (Crivelli et al, 1995;Nilsson and Berggren, 2000;New and Xie, 2008). The presence of a dam converts the free-flowing waters of the river into standing waters, creating conditions similar to a lacustrine ecosystem.…”

“…Analyses of the dam impact on the upstream vegetation have become a topic of scientific interest, mainly over the last decades (Nilsson and Berggren, 2000;New and Xie, 2008). Some studies addressed the identification of the main factors affecting the plant colonization of the riverbanks, such as the water level fluctuation (Springuel et al, 1991;Crivelli et al, 1995;Zhang and Lou, 2011) and the instability of the new shorelines (Johnson, 2002). Other studies focused on vegetation differences between river stretches at the reservoirs and those with natural hydrological conditions (Nilsson and Jansson, 1995;Jansson et al, 2000b;Johansson and Nilsson, 2002).…”

Quantitative evaluation of water-level effects on “regeneration safe-sites” for lakeshore plants in Lake Kasumigaura, Japan

“…In addition to these well-recognized impacts, manipulations of the water level of a lake and/or its patterns of fluctuation are other important factors affecting the abundance and species composition of lakeshore vegetation (Crivelli and Grillas 1995, Shay et al 1999, Coops and Hosper 2002.…”