-Not to be cited without prior reference to the authors- ICES CM 2010/F:52 ASSESSMENT OF ECOLOGICAL STATUS OF THE DELTA () BY PHYTOPLANKTON Julia GORBUNOVA1& Alevtina GORBUNOVA2 1Atlantic Branch of P.P.Shirshov Institute of Oceanology Russian Academy of Sciences , Kaliningrad, 236022, Prospect Mira, 1, e-mail: [email protected] 2Astrakhan State Nature Biosphere Reserve, Russia, , 414021, Naberejnaya Reki Tsarev, 119

Total area Introduction of the Volga Delta ≈25000 km2 The Volga River flows into the Caspian Sea and forms one of the largest deltas in the world. Biological resources of the Volga delta are unique and are Delta (upper) characterized by great richness and diversity of flora and fauna. There are the Astrakhan 2 10000-12000 km Reserve that included in the UNESCO's Man and the Biosphere Programme and the Fore-delta Ramsar Site in the Volga delta. 8000-10000 km2 Primary production of phytoplankton and allochthonous organic matter are Ilmen region material and energy basis for the functioning of the aquatic ecosystem of the Volga delta 6000 км2 and its biological productivity. Hydrology and water runoff are important factors that determine the primary production of phytoplankton of the Volga delta. Average long-term runoff of the Volga River at During the second half of the 20th century there has been a significant the apex of the delta – 250 km-3 change in hydrological conditions in the Volga River and its delta under the effect of during the spring-summer climate changes and anthropogenic factors. One of the most important impacts was the flood – 150 km-3 construction of the Volga-Kama cascade reservoirs.

Results and Discussion Material and methods The annual variability of phytoplankton primary The researches ware carried out production is related to hydrological seasons in in the Lower part of the Volga the Volga delta. In channels of the lower zone of Delta and fore-delta on the base the delta seasonal dynamics of phytoplankton of the Astrakhan Biosphere productivity indicators (photosynthesis intensity, Reserve during the period of chlorophyll a concentration and phytoplankton 1996-2007. The concentration of biomass) is characterized by an increase in the chlorophyll a was determined by period of spring-summer flooding and summer- standard spectrophotometric autumn mean water period. In the fore-delta area – method (SCOR-UNESCO, 1966; in spring before the spring-summer flooding and Lorenzen, Jeffrey, 1980). The during the summer-autumn mean water period in photosynthesis intensity was local costal zones. In the spatial characteristic of measured applying the oxygen these indicators the most even distribution is in modification of the bottle method spring-summer flooding and the greatest with 24 hours exposition of differentiation is in the summer-autumn mean samples (Winberg, 1960). water period. During the period of research integral phytoplankton primary production for vegetation season ranged from 106 to 199 gO2·m‑ 2 in channels of the lower zone of the delta. Observed over the year photosynthesis intensity ranged from 0.1 to 3.5 gO2∙m‑‑ 3∙day 1, content of chlorophyll a – 0.2-65.5 mg⋅m-3. In the fore-delta the observed photosynthesis intensity of phytoplankton ranged from 0.2 to 7.3 gO2∙m‑‑ 3∙day 1, chlorophyll a – 0.2-113.2 mg⋅m-3. Our studies of primary production of phytoplankton completed the long-term time series data (1960-1990) for channel of the lower zone of the Volga delta. The methodology was consistent. Analysis of long-term data for second half of the twentieth century showed that under the regulated flow conditions from the beginning of the 1960's to early 1990's there was a rise of average quantity of phytoplankton primary production. The process of eutrophication was observed. At the end of last century and the beginning of present there was a decrease of primary productivity in comparison with the previous period. On the average the level of primary production reduced to the values of the 1960 – 1970th. It allows to ascertain the fact of de-eutrophication process in the beginning of the 21st century. At present the trophic status of channels of the lower zone of the Volga delta assessed as mesotrophic. Some of the fore-delta coastal areas are of some eutrophic character.

SPATIAL DISTRIBUTION OF CHLOROPHYLLa PRIMARY PRODUCTION OF PHYTOPLANKTON (INTEGRAL FOR VEGETATION before the spring-summ er SEASON ) IN THE LOWER ZONE OF THE VOLGA DELTA summ er-autu mn floo d sp ring-summ er flood mean water (1960-1990 years. - Gorbunov (1976, 1991), 1997-2006 - own data) Over-regulated regime 180 of the Volga River runoff 160 I II III IV I - 1961-1970 – medium 140 r

runoff; a 120 e y

II - 1971-1977 – small runoff;

2 100 ⋅ -3

mg m III - 1978-1994 – large runoff; m

/ 80

2

O 60

IV - 1995-2007 – modern g period (generally 40 characterized as large runoff) 20 0 0 2 6 8 0 2 6 2 4 6 8 0 4 8 0 2 4 6 2 4 6 8 0 4 6 6 6 7 7 7 7 8 8 8 8 8 9 9 9 9 0 0 0 6 6 7 9 0 9 9 9 9 9 9 9 9 0 0 Conclusions 9 9 9 9 9 9 9 9 9 9 9 9 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2

The primary production of phytoplankton varied greatly during the second half of the 20th century and the beginning of the 21st century in the Volga delta. Hydrology conditions and the Volga river runoff are important factors that determine the phytoplankton primary production in the delta. There was the eutrophication of the Volga delta in 1980th. On the one hand the reason is the increase of fertilizers application in agriculture that caused their significant draining into water bodies, on the other hand extra load of nutrients from the areas of floodplain and delta that were not flooded for a long time during the previous years of a small river runoff. At modern period the process of de-eutrophication of the Volga delta is caused both the reduction of a drain of fertilizers due to an economic depression and because of effect of “wash-out” of nutrient during the previous phase of large river runoff. At present the trophic status of channels of the lower zone of the Volga delta assessed as mesotrophic. Some of the fore-delta coastal areas are of some eutrophic character. Usually the larger spring-summer runoff volume makes condition for higher annual phytoplankton primary production. At that the alternation of years of different spring-summer runoff volume is important.