B - Convention on Biological Diversity

the biodiversity point of view are replaced, to a certain degree, by fish-pond systems, which form an essentialpart of the Czech cultural landscape. The number of fish ponds currently exceeds 21 000. Artificial or highlymodifi ed ecosystems also include flooded quarries, sand pits and gravel pits, abandoned peat deposits, channels,mill races and amelioration ditches. Dam lakes are elements of discontinuity in river systems and constitutea special transitional body between still and flowing water, depending on the period of retention. The ecologicalstate of water and wetland ecosystems is substantially determined by the character and condition of terrestrialecosystems in their river basin.Human activities, particularly in the recent decades, have markedly affected the state and functions of aquaticand wetland habitats (only approx. 1/4 has remained of the estimated total area of 1 300 thousands hectaresof wetlands). The greatest impact was caused by extensive drainage of the landscape (over 1 mil. hectares ofagriculturally utilized land has been extensively drained in the territory of the Czech Republic during the last 50years) for the purposes of agriculture and forestry, intensive farming, physical modification of both the longitudinaland transverse profiles of water courses, their regulation and canalization, construction of transverse structures(discontinuities), discharging of municipal and industrial wastewater and atmospheric deposition.The total length of water courses in the Czech Republic has been reduced through past modifications of thechannels by at least one third. Regulation of water courses leads to a substantial loss of their environmentalfunctions and to marked disturbance of the water regime of the landscape. Technical modifications of channels,including unsuitable flood-protection measures, still remain a fundamental problem in management of inlandwater ecosystems. Numerous structures on water courses cause obstacles preventing drifting and migration ofaquatic organisms, which caused disappearance of, e.g., Atlantic salmon (Salmo salar) from the territory of theCzech Republic.After 1989, the volumes of industrial and agricultural production substantially decreased and a number ofwastewater treatment plants were built, resulting in fast and radical improvement of water quality. However,point and also diffuse pollution sources have not yet been fully eliminated and the effects of the eutrophicationprocess are still marked. In spite of substantial reduction of emissions, the impact of acidification on biodiversityis still clear, particularly in oligotrophic mountain ecosystems.Since the period of the greatest development of fish ponds at the beginning of modern times, the number offi sh ponds in the territory of the Czech Republic has gradually decreased. The greatest reduction in their areaoccurred during the reign of Maria Theresia and Joseph II. (1740 – 1790) and also in the period since the 1950swhen, due to insufficient care and increased erosion, a number of minor ponds have entirely vanished and thesize of others has substantially decreased. Although a number of these artificial reservoirs were renewed after1989, such minor water reservoirs that can increase biodiversity and improve water retention in the landscapeare still lacking in a number of areas. In certain cases, the condition of fish ponds is unfavourably affected byeutrophication caused by pollution of water by municipal waste, and partly also by infl ow of nutrients washedout from agricultural land.Unsuitable interventions in the landscape have resulted in devaluation of aquatic and wetland habitats asimportant landscape features. The joint action of anthropogenic effects led to such damage of fresh-waterecosystems that ichtyocenoses have become the most endangered group in Europe. However, apart from theabove, other communities of aquatic organisms are also substantially endangered. Certain species of aquaticfauna, such as the original species of crayfish stone crayfi sh (Austropotamobius torrentium) and freshwatercrayfi sh (Astacus astacus) or freshwater pearl mussel (Margaritifera margaritifera) have already disappearedfrom a majority of original localities.90