The marine edge of the Danube Delta (MED) and its estuarial coast is intensively changing with time. Additive natural factors, forming MED, include: carry over of river sediments, alongshore sea currents and connected with them transport of solid fractions as well as deformations caused by sea roughness. Depending on the extent of influence of the river and the sea coastal part of the delta can crow, retreat or be relatively stable. MED is an efficient indicator of direction and intensity of delta-formation processes, interaction of river and sea basins.
Organization of monitoring
In 2011 together with workers of the DHMO it was extended a network of benchmark observations on dynamics of the delta marine edge for Kiliya Branch of the Danube. The benchmarks were installed and surveying azimuths were designated for 14 profiles (Trimble R3 GPS system), botanical observations were done on accumulative new formations of the avandelta with a precise spatial affixment.
Figure 1: (See map) Scheme of location of profiles and polygons at the marine edge of the Kiliya Delta. Notes: red colour indicates profiles established in 2011.
Analysis of dynamics of the marine edge of the delta
Deformations of the marine edge can be short-term and often reversible-they are mainly determined by storms and high water, and long- term changes which connected with variability of water drainage, runoff of river sediments, processes of drainage redistribution, climate impact on the wind rose. As a separate group it can be distinguished the changes caused by direct anthropogenic influence on the marine edge: construction of dams and spur dykes, dredging of bars (Fig. 2).
Figure 2: (See map) Dynamics of the marine edge of the delta.
In addition to decrease of sediment runoff of the Danube and redistribution of drainage between the Tulcha and Kiliya Branches, the dynamics of the Kiliya Delta marine edge of is influenced by the growth of the Black Sea level.
Last years the drainage of the Ochakovsky Branch reduced the most intensively; along the marine edge there are observed stabilization and even wash-out of the bank, aging of delta bays (kuts). The middle and southern parts of MED are actively moving forward into the sea, with appearance of above-water bars and formation of new delta bays.
New MED formations are very dynamic. An example of the meridionally located spit which developed from products of a bar erosion in Bystry Branch is a good demonstration of changes in the coastline during 3 successive years (Fig. 3).
Figure 3: (See map) Location of Ptichya Spit in 2009, 2010, 2011 and 2012.
Development of flora
An important factor, influencing on new accumulative formations along the outer delta edge, is the development on them a pioneer vegetation cover which assists to fixation and stabilization of microrelief. The structure of vegetation cover determines the resistance of new formations to wave erosion.
A strong flow of the Danube water, especially during periods of floods, carries out a vast quantity of fragments of vegetatively propagating plants (reed, willows, poplars, etc) which are able to fix themselves and participate in development of pioneer vegetation on coastal new formations. This is the reason of high percentage of perennial grassy and shrubby species on the new formations (Fig. 4).
|Figure 4. Biomorphological structure of flora on profiles in the marine part of the Kiliya Delta of the Danube (figures show the quantity of species).|
When describing profiles we chose the sites equal in their length but nevertheless their species composition greatly differed. The analysis of flora structure on 12 profiles, located meridionally along the delta edge, has shown that the highest portion of perennial grasses and tree- shrub vegetation (Fig. 5) was observed on the islands and spits which grow with a slow rate (profile 3, 4, 5, 9 and 12); and the highest number of species, especially annual grasses, is recorded on the sites with an active delta growth (profile 6 and 11). In general, the southern part of MED is presently characterized by a more intensive growth.
Figure 5. Distribution of flora species of higher vascular plants on profiles in the marine part of the Kiliya Delta of the Danube.
Profiles: 1 - Taranova Spit ; 2 - Dalnya Spit (Potapovsky Branch); 3 - Dalnya Spit (Poludenny Branch); 4 - Delyukova Spit (Poludenny Branch); 5 - Delyukova Spit (Sredny Branch); 6 - Stambulsky Island (Bystry Branch); 7 - Ptichya Spit (Bystry Branch); 8 - Ptichya Spit (Vostochny Branch); 9 - Parokhodnaya Spit (Tsyganka Branch); 10 – Parokhodnaya Spit (Osinka Branch); 11 - The end of Tsyganka Island; 12 - Island Kubanu (Zavodnensky Branch).
A weak growth of some spits (profile 1) leads to absence of tree-shrub species on them. Sometimes this reason is also added with penetration of marine salt water.
Finally, the MED dynamics determines the formation of new vegetation communities and sites of biotopes which are used by various groups of animals. Thus, vanguard biocoenoses contribute to increase and conservation of general biodiversity.
Development of new accumulative islands and spits also has an important socio- economic value, because it means new areas for camping and stable recreation at the Azov-Black Sea coast.
In case of some climate scenarios, growth of the Danube water content will have predictable positive effects to rise buffer capacity of ecosystems and increase recreation potential of the seacoast.