eutrophication level indicators in Romanian seawater

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1 Journal of Environmental Protection and Ecology 10, No 3, (2009) Recent data concerning evolution of the eutrophication level indicators in Romanian seawater A. Cociasu a, L. Varga b, L. Lazar a, D. Vasiliu a * Marine ecology a Grigore Antipa National Institute for Marine Research and Development, 300 Mamaia Blvd., Constantza, Romania b Ministry of Environment and Sustainable Development, 12 Libertatii Blvd., Sector 5, Bucharest, Romania Abstract. Eutrophication, the most sever pollution form referring to the Romanian marine waters, began in the early 70 s and reached the upper limit in the 80 s. During this period, all environmental factors suffered important changes with disastrous effects on the entire ecosystem. The increasing of the nutrients and organic matter inputs by major rivers and wastewaters resulted in the increase of primary plankton production, of frequency and magnitude of the blooms phenomenon, released chain disturbances in the ecosystem with impact on biodiversity, resources and balneal qualities. After 1990, particularly after 1995, due to the decreased nutrients input, marine waters quality was considerably improved as a proof being the diminishing of frequency and magnitude of the blooms phenomenon and the diminishing of the hypoxic areas found that the ecosystem get better. During last years, the main physical and chemical parameters of the marine ecosystem from the sampled area, recorded natural fluctuation limits for their concentrations proving a net tendency of stabilisation. The paper presents recent data as for level of the general and state indicators of the eutrophication phenomenon in Constantza area sea water, reference area for the Romanian coast. Data concerning temperature, salinity, nutrients and chlorophyll a for the year 2006 were processed and compared with those for the last ten years. Data analysis demonstrated the improvement of the eutrophication phenomenon and of the Romanian sea water quality. Keywords: eutrophication, level indicators, Romanian Black sea water, nutrients. aims and background The present paper is doing an assessment of the eutrophication general and state indicators level in coastal Romanian waters in 2006 in comparison with the previous ten years, (Ref. 1). The aim of the paper is to highlight the particularities of the abiotic factors seasonal dynamic and spatial distribution into the coastal waters, which are controlling the eutrophication phenomenon. * For correspondence. 701

2 Experimental The analysed data refer to the Romanian coastal waters sampled as follows: every working day from Cazino-Mamaia station; seasonal in 2006 from EST Constanta one transect of five stations with depths within 0-50 m perpendicular to the Romanian shoreline; seasonal in 2006 from Sulina, Sf. Gheorghe, Zaton transects of stations with depths within 0-50 m, perpendicular to the Romanian shoreline near the Danube mouths (Fig. 1). SULINA SF. GHEORGHE ZATON CONSTANTA Fig.1. Stations network After sampling, sea water was analysed by the Analysis and Measurement Laboratory of the Romanian Marine Research Institute Grigore Antipa, Con- 702

3 stanta, Romania using methods from Refs 1 and 2. The laboratory is accredited by SR ISO We have analysed eutrophication general and status indicators: temperature, salinity, oxygen, nutrients and chlorophyll a. Results and Discussion The Black sea, most isolated and largest inland sea, permanently occupied by anoxic water below m, possesses various oceanographic features that make it distinctively different from other basins. It is a land-locked sea, constituting an unicum hydrobiologicum by virtue of its physical, chemical and biological conditions. Owing to strong thermohaline stratification and the long residence time of its water masses, the ecosystem is highly sensitive to increased production of organic matter 3. The most important Black Sea s degradation phenomenon was the eutrophication with dramatic changes in the coastal ecosystem, living resources, tourism and recreation. It is well known that the main cause was the increasing of the nutrients and organic matter input from the Danube (more than 75%). Even if starting with 1990 nutrients level had considerable decrease and some positive changes in the ecosystem were recorded, eutrophication is still an important issue for the ecosystem fragility. In accordance with the background of general tendency of stabilisation and coming back to the normal status the paper presents the natural variability proportions in the 2006 characteristic conditions. Sea water temperature at Constanta, reference area for the Romanian shore, was recorded as usual important seasonal variations from -1.3 o C in January to 26.8 o C in June. The extreme values were close to those from last year, the annual average (13 o C) outrunning with 0.2 o C the 2005 annual average. During 2006, excep February, the monthly average was close or little higher than the multi-annual averages from , maximum difference being in December (Fig. 2). The annual average shows an increase with 0.54 o C of the coastal waters temperature comparing with the same period, mainly due to the slow and continuous process of air temperature warming. Sea water salinity at Constanta recorded important variations within normal limits for the Romanian shoreline, psu. The lower value was in July after three months of very high Danube flows due to the abundant precipitations. The upper level was in December following decreased flows from the last part of the year. The monthly average evolution shows important deviations from the annual cycle according with the river flow oscillations. In this sense, we are mentioning May July period and September, when mean salinity decreased below 13 psu and October December period when the monthly averages, higher than

4 psu, were superior than mean value of coastal zone (Fig. 3). We must mention here the salinity from July, 9.90 psu, the lower July monthly average in last 45 years. This situation is explained by the high Danube freshwater inputs in March-July when the monthly averages were not superior to average condition from the last ten years (Fig. 4). temperature evolution ( C) I II III IV V VI VIIVII IX X XI XII month Fig. 2. Temperature evolution in coastal waters at Constanta during salinity evolution (psu) I II III IV V VI VII VIII IX X XI XII month Fig. 3. Salinity evolution in coastal waters at Constanta during flow evolution (km 3 /month) I II III IV V VI VII VIIIIX X XI XII month Fig. 4. Danube flow evolution (km 3 /month) at Sulina during Dissolved oxygen presented usual important variations, mainly controlled by the sea water temperature evolution. The recorded values were within µm in 704

5 August and µm in March, the annual average being closer to those of year Following the annual cycle, the monthly averages decreased continuously from µm in February when it was recorded the lowest temperature monthly average and µm in August corresponding to the highest sea water temperature. Comparative with the recorded situation in we can appreciate that in 2006, with two exceptions, coastal waters were better oxygenated (Fig. 5a). dissolved oxygen (µm) a I II III IV V VI VII VIII IX X XI XII month oxygen saturation (%) I II III IV V VI VII VIII IX X XI XII Fig. 5. Dissolved oxygen (a) and oxygen saturation (b) in coastal waters at Constanta during b month Oxygen saturation recorded a narrow range than usual, %, showing the tendency of entering into normality, without plentiful biological events. The monthly averages were in most of cases superior to those of , highest differences below to the cold season. Except August, coastal waters were saturated and supersaturated with oxygen and were no anoxia or hypoxia cases (Fig. 5b). Nutrients, the mainly coastal waters eutrophication indicators recorded as usual important variations with the annual cycle perturbation. In this sense, phosphate oscillated within 3.59 µm in March and 0.01 µm in August, the latter being the method limit of detection, and silicates reached maximum, 52.6 µm in April and decreased below 1µM in October. The extremely high maximum values for the coastal zone were determined by the Danube high flows from 2006 s spring. Even so, the monthly averages were below multi-annual averages from , due to their decreased concentration in the river waters. The monthly averages of inorganic phosphorus concentrations did not exceed 0.6 µm. They did not highlight important seasonal changes while silicates had a net seasonal distribution with decreasing concentrations during the warm season (Figs 6 and 7). 705

6 phosphates concentration (µm) I II III IV V VI VIIVIIIIX X XI XII month Fig. 6. Phosphates concentration evolution in coastal waters at Constanta during silicates concentration (%) I II III IV V VI VII VIII IX X XI XII month Fig. 7. Silicates concentration evolution in coastal waters at Constanta during Generally, the three inorganic nitrogen forms recorded variations in a wide range values. For nitrates the maximum level reached µm in May. The monthly averages show nitrates being prevalent in the first nine months of the year and only in October December the ammonia form being prevalent (Fig. 8a) (µm) a N NO 3 N NH 4 N NO 2 NO 3+NO 2+NH4 (µm) b I II III IV V VI VII VIII IX X XI XII 5 I II III IV V VI VII VIII IX X XI XII Fig. 8. Inorganic nitrogen concentration evolution in coastal waters at Constanta during Despite the mentioned situation of phosphates and silicates, the inorganic nitrogen recorded a significant increase in 2006 outrunning in January September the level from (Fig. 8b). This situation was characteristic only for the coastal waters where, due to the favourable weather conditions, the high Danube flow from 2006 spring and summer, it was felt. 706

7 The main indicator of primary production, chlorophyll a recorded important variations in June-October suggesting intense biological processes. In this sense, the maximum value was in July, 51.2 µg/l exceeding well the upper limit from anterior years in coastal zone. The annual average was much superior to annual averages from the last five years showing a slow refresh of biological processes from coastal zone following the highest Danube flow (Fig. 9). The oxygen supersaturation of the superficial waters, mentioned before, is confirmation of this statement. chlorophyll a concentration (µg/l) I II III IV V VI VII VIII IX X XI XII month Fig. 9. Chlorophyll a concentration evolution in coastal waters at Constanta during The results of the oceanographic expeditions inside the Romanian shelf continental zone in 2006 were within specific variability range with small changes due to weather and hydrological conditions during the investigations. Sea water temperature recorded seasonal normal values with an appreciable increase from spring to August. Like in the coastal zone, the upper limits were in August, exceeding 25 o C at the surface, highlighted at Sulina, Sf. Gheorghe and Zaton transects. The autumn cooling process was slower up to the north where temperatures did not decrease below 15 o C in the water column (Figs 10-13). Salinities measured in the superficial layer usually reflect the Danube influence degree. In 2006, the very big freshwater input was not proper felt in the open sea area due to the dominant winds from northeast favouring freshwater flowing close to the shore. So, only on Sulina transect the superficial layer salinity decreased in April and August below 12 psu. In the rest of the researched zone, superficial layer salinity increased slowly from psu at Sf. Gheorghe to psu at Constanta. It was highlighted a slow decrease of the values with the depth within the known range for the Romanian shoreline (Figs 14-17). Dissolved oxygen recorded higher values in April when the most were within µm, slow higher on Sf. Gheorghe transect. Due to very high temperature from August, the oxygen concentration decreased generally to µm without hypoxia. Decreasing temperature from August induced the slow values increase, which exceeded 350 µm on Sf. Gheorghe transect at surface (Figs 18-21). 707

8 Fig. 10. Seawater temperature evolution at Sulina in Fig. 11. Seawater temperature evolution at Sf. Gheorghe in 2006

9 Fig. 12. Seawater temperature evolution at Zaton in

10 Fig. 13. Seawater temperature evolution at Constanta 710

11 Fig. 14. Salinity evolution at Sulina in 2006 Fig. 15. Salinity evolution at Sf. Gheorghe in

12 Fig. 16. Salinity evolution at Zaton in

13 Fig. 17. Salinity evolution at Constanta in

14 Fig. 18. Dissolved oxygen evolution at Sulina in 2006 Fig. 19. Dissolved oxygen evolution at Sf. Gheorghe in

15 Fig. 20. Dissolved oxygen evolution at Zaton in

16 Fig. 21. Dissolved oxygen evolution at Constanta in 2006 The oxygen saturation shows a good oxygenation of the water column for all observations, with normal values for the respective period. The highest value was at Sf. Gheorghe transect, 150%, at surface in August. That oxygen excess resulted in following moderate biological processes (Figs 22-25). 716

17 Fig. 22. Oxygen saturation evolution at Sulina in 2006 Fig. 23. Oxygen saturation at Sf. Gheorghe in

18 Fig. 24. Oxygen saturation evolution at Zaton in

19 Fig. 25. Oxygen saturation evolution at Constanta in 2006 Among main nutrients, nitrates reached the highest values in April. In the superficial layer they exceeded 10 µm at Sulina. Advancing in warm season nitrates concentrations considerably decreased to 2-3 µm, spatial distribution being more homogeneous. The slow increase of the values from autumn was more pronounced in the superficial layer from the north part of the researched area (Figs 26-29). 719

20 Fig.26 evolutia nitratilor pe sectiunea sulina Fig. 26. Nitrates evolution at Sulina in 2006 Fig.27 evolutia nitratilor pe sectiunea sf.ghe. 720 Fig. 27. Nitrates evolution at Sf. Gheorghe in 2006

21 Fig. 28. Nitrates evolution at Zaton in

22 PDF Created with deskpdf PDF Writer - Trial :: Fig. 29. Nitrates evolution at Constanta in 2006 Ammonia recorded lower and more homogeneous values, with small differences between transects and seasons most of them within 2-3 µm (Figs 30-33). Phosphates had a different evolution, the most decreased values, below 0.1 µm recorded in April. Then, in August reached higher values exceeding 0.2 µm in the water column. A slow decreasing was recorded in autumn especially in the north part (Figs 34-37). 722

23 Fig. 30. Ammonia evolution at Sulina in 2006 Fig. 31. Ammonia evolution at Sf. Gheorghe in

24 Fig. 32. Ammonia evolution at Zaton in

25 Fig. 33. Ammonia evolution at Constanta in

26 Fig. 34. Phosphates evolution at Sulina in 2006 Fig. 35. Phosphates evolution at Sf. Gheorghe in

27 Fig. 36. Phosphates evolution at Zaton in

28 Fig. 37. Phosphates evolution at Constanta in 2006 Silicates, like nitrates, reached the upper limit in April, when at surface in north exceeded 20 µm. A decreasing below 10 µm was distinguished in August in water column, except some small bottom area where it was some silicates excess from the detritus mineralisation processes (Figs 38-41). 728

29 Fig. 38. Silicates evolution at Sulina in 2006 Fig. 39. Silicates evolution at Sf. Gheorghe in

30 Fig. 40. Silicates evolution at Zaton in 2006 Fig. 41. Silicates evolution at Constanta in

31 Conclusions During the last years, the main physical and chemical parameters of the marine ecosystem from the sampled area recorded natural fluctuation limits for their concentrations proving a net stabilisation tendency. The environmental factors evolution was strong affected by the very high Danube flows from spring and summer 2006, which determined the appreciable decrease of salinity and increase of nitrates level. This situation was also confirmed by the high values of planktonic primary productivity expressed through chlorophyll a. The other nutrients registered values in decreasing concentrations general tendency from the previous ten years ( ). Inside the continental shelf, all parameters recorded decreased values within characteristic natural variability. The continuous decrease of nutrients level, returning to the 60 conditions and the oxygenation degree improvement entailed the Romanian sea water quality improvement, proved by the reduction as frequency and magnitude of the phytoplankton blooms phenomenon. References 1. K. GRASSHOFF, K. KREMLING, M. EHRHARDT: Methods of Seawater Analysis A. COCIASU, A. PETRANU, P. E. MIHNEA: Ecological Indicators of the Romanian Coastal Waters in the Black Sea. Black Sea Pollution Assessment. Black Sea Environmental Series, 10 (1998). 3. Regional Seas: Manual Techniques for Nutrient and Phytoplankton Pigment Analysis in Seawater Received 5 March 2008 Revised 15 April