- 3.5.3. Impacts on the Danube Delta in the Danube River Basin District

Major impacts on the delta ecosystem result from the changes both in the upstream conditions (retained sediments, increased pollution loads) as well as from the changes in the delta itself. The most significant activities in recent decades have been the artificial extension of the natural channel network (doubling their length from 1910 to 1990 up to altogether 3,400 km) to improve access and the circulation of water through the delta, as well as the re-construction of wetlands into huge agricultural polders and fishponds. The many canals bring more fine sediments and nutrient-laden river water into the lake complexes than before (the water discharge flowing through the delta lakes increased from about 160 m3/s in the 19th century to 620 m3/s in the period 1981-1990). As a result, biodiversity (fisheries) declined and the fundamentally important natural water and sediment transport system has been altered, diminishing the deltas capacity to retain nutrients and pollutants. The new regime allows much of the nutrient-containing silt to pass directly through the main canals into the Black Sea. Dredging is another important problem also here in the Danube Delta: In the delta of the Danube, the overall length of artificial water courses created by dredging amounts to 1,753 km ? equal to the total length of the natural water network. New channels created for transport purposes, like the Caraorman Channel and the Mila 23 Channel, have changed the natural runoff of the water in the delta and cause an increase of sedimentation. By 1990, one forth (974 km2) of the Danube delta has been diked in, including 400 km2 for agricultural purposes. The Tulcea-Sulina branch (81 km) is completely canalised with all former meanders and side channels being cut off, and its length reduced from 85 to 62 km. The 80 m wide navigation route has to be permanently dredged to secure a depth of 7.3 m. The southern Sfantu Gheorghe branch (109 km) is not used by sea ships but also affected by meander cutoffs since the 1960s (loss of app. 50 km) and by the ship waves destroying the unprotected banks.70 Other pressures and impacts on wetlands are gravel and sand excavation in many rivers of the DRB, contributing to the loss of riverine habitats and bed erosion, agricultural activities like drainage and irrigation systems, fishing and hunting and tourism. (4.5.3. Impacts on the Danube Delta in the Danube River Basin District - p.117)