FUNCTIONING OF THE STENTSOVSKY-ZHEBRIANSKY WETLANDS (SZW) – THE BUFFER ZONE OF DANUBE DELTA-UNDER ANTHROPOGENIC PRESS
Yu. Bogatova, G. Garkavaya, N. Berlinsky
Odessa Branch Institute of Biology of Southern Seas, National
Academy of Sciences of Ukraine
SZW - the part of the Danube wetland is under severe anthropogenic influence nowadays. This place is inhabited of rare and endangered birds. In 1999 SZW were included into the territory of the Danube Biosphere Reserve (Biodiversity, 1999).
The study of the SZW ecosystem was carried out in 1994-1998 in frame of the GEF project “Conservation of Biodiversity of the Ukrainian part of the Danube Delta”. Thirteen complex expeditions were carried out during the period 1994-1998. Investigations in frame of the INCO-Copernicus project “Fluxes of Greenhouse gases in the Northwestern region of the Black Sea coastal Zone: Influence of the Danube river system” was carried out in autumn of 1999. Hydrochemical parameters according to standard methods had been determined: mineralization, pH, Eh, oxygen, dissolved mineral and organic forms of phosphorus and nitrogen, silicon, labile organic matter (by permanganate oxidizability), BOD5, suspended matters. In bottom sediments (pore waters) mineral and organic forms of nitrogen and phosphorus, silicon and labile organic matter had been found.
The present SZW was silted ancient liman and separated from the sea by the Zhebriany bar. The Danube waters with considerable amount of suspended matters entering the SZW through Laptysh, Murza, Chatal and other arms (Hydrology, 1963). The water input is the cause of the mud accumulation in this part of the delta. Riverbed’s reconstruction, building of different constructions (canals, sluices, dams, roads etc.) led to violation of the natural wetlands conditions. Construction of the Danube–Sasyk canal influenced the wetlands water regime and formation of hydrochemical parameters. As the result, the wetlands were divided into two separate systems. Water exchange
between them is possible throw one siphon beneath the canal. At present, part of the wetlands is drained and turned into the rice fields. The water from the rice fields saturated fertilizers and pesticides comes into the wetland.
It was estimated that the Danube waters coming in to wetland contain 14-36 mln.m3 per year, 1048 tons of suspended matter, 36 tons of dissolved organic matter, 94 tons of nitrogen, 26 tons of silicon and about 2 tons of phosphorus. Irrigation system (7-19 mln.m3per year) gives 690 tons of suspended matter, 247 tons of dissolved organic matter, 120 tons of nitrogen and about 1,5tons of phosphorus to the wetlands. Precipitation (22-30mln.m3per year) gives to the wetlands 1900 tons of suspended matter, about 100 tons of dissolved organic matter, 80 tons of nitrogen, 5 tons of phosphorus. So the formation of hydrochemical regime of the SZW is under the natural and anthropogenic influence (Biodiversiti, 1999).
Seasonal dynamics of hydrochemical regime of SZW depends on the water input and intensity of the production - destruction processes (Tab. 1). Seasonal dynamics of nutrients is mainly correlated with the development of water vegetation. The decreasing of nutrients during the period takes place from spring to summer. In autumn nutrients increase in the SZW because of organic matter mineralization. Seasonal distribution of the organic matters has a contrary direction. It depends on the water regime and locks management.
Table 1. Seasonal fluctuations of hydrochemical parameters in the SZW (1994-1998)
Parameters
Spring
Summer
Autumn
О2, mg/l
1,3 – 11,0
0,5 – 11,4
2,5 – 15,0
pH
7,7 – 9,1
6,8 – 9,1
6,3 – 9,4
РО4, mg/l
0,010 – 0,073
0,010 – 0,140
0 – 0,090
Рorg., -“-
0,001 – 0,068
0,010 – 0,140
0,020 – 0,150
NH4, -“-
0,005 – 0,025
0 – 0,060
0,010 – 0,030
NO3, -“-
0,002 – 1,054
0 – 0,380
0 – 0,090
Norg., -“-
0,650 – 7,060
0,560 – 28,420
1,860 – 4,510
Si, -“-
0,750 – 1,790
0,620 – 5,130
0,940 – 2,900
SM*, -“-
4,6 – 25,1
2,6 – 265
3,9 – 42,8
LOM**, mgО/l
6,43 – 28,14
12,70– 47,10
2,87 – 72,70
*-suspended matter, ** -labile organic matter (by permanganate oxidizability)
Bottom sediments are one of the main factors that provide SZW with nutrients. It is the layer of liquid mud with the high concentrations of nitrogen, silicon, and phosphorus, which provide water vegetation with nutrients. The bottom sediments are forming from the two main sources. The first is the suspended matter input from the river and drainage runoff. It is an adsorbed organic compound on the inorganic particles. The second one is dead autochtonic organic matter. The condition providing the transformation of the process of nutrients from the bottom sediments to the water layers is wind mixing, biomixing in case of development of the reduction processes on the border between the water and bottom sediments. Intensity of the nitrogen and phosphorus compounds depend on the quantity of labile matter in bottom sediments. Comparison of the Data (Tab. 2) showed that values of phosphates are 1,8, organic phosphor 1,6, silicon 1,5 times more in pore waters of the Stentsovsky wetland than in Zhebriansky wetland. It could be explained that Stentsovsky wetland are under the direct influence of the Danube water runoff and irrigation systems. Zhebriansky wetland accumulated nitrates 1,6 times more than the Stentsovsky wetland because in the Zhebriansky wetland the oxidation processes take place while in the Stentsovsky wetland the reduction processes prevail. The average of ammonium nitrate in the pore waters of the Stentsovsky and Zhebriansky wetlands is the same. The specification of the poor waters of the SZW is the high level of the organic matter.
Table 2. The distribution of average Data of hydrochemical parameters in the pore waters of bottom sediments in the Stentsovsky- Zhebriansky wetlands
Stations
PO4
Porg.
Рtotal
NH4
NO2
NO3
N org.
Ntotal.
SiO3
LOM*
mgO/l
mg/l
Stentsovsky wetland
Ave-rage
1,788
1,489
3,277
1,964
0,009
0,166
19,13
21,15
22,09
49,0
Zhebriansky wetland
Ave-rage
1,020
0,925
1,945
1,931
0,000
0,268
18,63
20,46
15,37
49,8
* - labile organic matter (by permanganate oxidizability)
The result of the investigation of the bottom sediments is very important for the wetland ecosystem. The nutrients are the source of food for "air-water" vegetation. The vegetation is the storage for nutrients. In case of the certain condition in the wetland the nutrients can pass into the water and can be the main source of food for phitoplankton. That is the most important for the areas of wetlands where the water exchange and nutrients input is limited.
The result of investigation in autumn period of 1999 is the process of reduction, hypoxiya, H2S fluxes, organic matter accumulation into the water and bottom sediments took place. The state of the hydrochemical regime of the SZW ecosystem is destroyed by irregular high air and water temperature and low level of the Danube water.
The decreasing of water level in to the wetland depended on the irregular high temperature, evaporation increasing and decreasing of water comes from the irrigation systems. So the hydrochemical condition became worse. Mineralization of the water in to the wetland increased because of evaporation intensity.
So, it was established that into the wetland the destruction processes predominated. The main source of oxygen production was phytoplankton and periphiton. The improvement of hydrochemical conditions of the SZW wetlands could be provided in case of decreasing of water input from the rice fields and drainage system and increasing of the water input from the natural sources (Danube, precipitation etc.), flowage, water exchange between the Stentsovsky and Zhebriansky wetlands. In other cases the ecological conditions of the SZW will lead to the degradation of this unique part of the Danube delta.
References
1. Biodiversity of the Dunaisky Biosphere Reserve, protection and management.- Naukova dumka, Kiev,1999.-702p.
2. Hydrology of the Danube mouth.- Hydrometeoizdat, Moscow,1963.- 383p.
Related articles::