MONITORING OF KEY EUTROPHICATION PARAMETERS AT THREE INSHORE STATIONS OF STRYMONIKOS GULF, NORTH AEGEAN SEA

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1 Volume 1 No REPRINT pp MONITORING OF KEY EUTROPHICATION PARAMETERS AT THREE INSHORE STATIONS OF STRYMONIKOS GULF, NORTH AEGEAN SEA N. Stamatis - D. Ioannidou - E. Koutrakis Angerstr Freising - Germany Phone: ++49 () Fax: () parlar@psp-parlar.de

2 by PSP Volume 1 No Fresenius Enviromental Bulletin MONITORING OF KEY EUTROPHICATION PARAMETERS AT THREE INSHORE STATIONS OF STRYMONIKOS GULF, NORTH AEGEAN SEA N. Stamatis, D. Ioannidou and E. Koutrakis N.AG.RE.F., Fisheries Research Institute (F.R.I.), N. Peramos,? avala, Greece SUMMARY Dissolved nutrients, chlorophyll-a, salinity and temperature were measured at three inshore stations of Strymonikos Gulf in order to monitor the eutrophication process. Monthly samplings were carried out for the period from December 1997 to June High mean concentrations of dissolved inorganic nitrogen (144.3 µg l -1 ), soluble reactive phosphorus (12.4 µg l -1 ) and dissolved silicon (716.5 µg l -1 ) classified the inshore Strymonikos Gulf within the eutrophic Greek marine areas. Agricultural run-off transferred by Strymon River was identified as the main source of the nutrients. Chlorophyll-a mean values ranged from.24 to 1.6 µg l -1, those of temperature and salinity between 8.8.and 29.1 o C and from 3.3 to 37.1 ppt, respectively. The eutrophication effect is spatially limited to inshore areas and it is not detectable at the offshore areas of Strymonikos Gulf. KEYWORDS: coastal eutrophication, nutrients, chlorophyll-a, temperature, salinity. INTRODUCTION The Mediterranean Sea is generally considered as oligotrophic due to its relatively low nutrient content [1]. However, coastal areas of the Mediterranean encounter increasing eutrophication caused mainly by anthropogenic influences. The Strymonikos Gulf, located at the Northern Aegean Sea (Eastern Mediterranean), is the potential final recipient of nutrients originating from agricultural and industrial activities as well as from urban population. The total catchment of Strymonikos Gulf is estimated at ca km 2. Main sources of nutrients are considered to be the run-off of Strymon, Richios and Mavrolakas rivers and the municipal effluents of Asprovalta, Stavros and Olympiada towns. From the three rivers flowing into the Strymonikos Gulf, Strymon is by far the biggest with a mean water flow of 6 m 3 /s. All coastal towns are mainly summer residences with more than 5. inhabitants during summer. From this point of view, Strymonikos Gulf is a particularly interesting ecosystem for the study of eutrophication. Considering that this coastal zone has not been adequately studied, the work presented herein is a first attempt to (1) present the seasonal variation of key eutrophication parameters at three inshore stations of Strymonikos Gulf, (2) classify the trophic state of inshore Strymonikos Gulf and (3) compare these results with data from other Greek coastal areas. STUDY AREA AND METHODS Sampling was done at three stations (St1, St2, St3) of Strymonikos Gulf in monthly intervals from December 1997 to June All samples were taken with a Ruttner 1l water sampler (Hydrobios, Kiel). Temperature and salinity were measured by a portable salinity meter (LF 34/WTW) equipped with a 2 m long cable. Sampling station 1 (1 m deep) is located about one nautical mile from the delta area of Strymon River (Fig. 1). From this station two sub-samples were taken in order to measure surface (St1a) and deep (St1b) water features. Sub-sample 1a comprised of a mixture of 5 l of water, each collected from meters -4 and sub-sample 1b comprised of a mixture of 5 l collected from meters 5-9. Temperature and salinity at this station were measured at 1 meter intervals. Sampling station 2 is located close to the town Stavros and about 1 n. mile distance from the river Richios. Sampling station 3 is located close to the town Olympiada and the river of Mavrolakas. From both stations, only surface water samples (1 m depth) were obtained from a distance of 1 m from the coast. 76

3 by PSP Volume 1 No Fresenius Enviromental Bulletin Chemical analyses of the water samples filtered through Whatman GF/C filters (.45 µm) were performed for N-NO 3, N-NO 2, N-NH 4, P-PO 4 and Si-SiO 2 by the methods of the Grasshoff s manual [2]. For the determination of chlorophyll-a the spectrophotometric absorbance of 9 % acetone extracts was measured [2]. The sum of N-NO 3, N-NO 2 and N-NH 4 gives the dissolved inorganic nitrogen (DIN) and the P-PO 4 corresponds to soluble reactive phosphorus (SRP). A Beckman Model DU-65 spectrophotometer was used for the absorbance measurements and all chemical reagents used were pro analysi (Merck, Riedel de Haen). FIGURE 1 - Map of the study area and the sampling stations. N higher than those measured by known eutrophic Greek areas like Kavala [3], Thermaikos [4] and Saronikos Gulfs [5, 6, 7]. Higher values of DIN were recorded in the period of high precipitation and river flow, i.e. winter and spring, as compared to summer and autumn (Fig. 2d). The most important form of DIN consisted of nitrate nitrogen (84.6 %), followed by ammonium (11.9 %) and nitrite nitrogen (3.5 %). Both results indicate that the main origin of nutrients is the agricultural run-off. The frequency distribution of D?? values is shown in Fig. 3a. Mean values of SRP were much higher at the station 1a (12.4 µg l -1 ) as compared to the other three stations (6.2 µg l -1 at each 1b, 2 and 3). SRP values in the three stations fluctuated during the whole sampling period without an obvious seasonality (Fig. 2e) and are at the same levels with those of Kavala [3], Thermaikos [4] and Saronikos Gulfs [5, 6, 7]. The frequency distribution of SRP values is shown in Fig. 3b. Mean values of dissolved silicon were higher in stations 3 ( µg l -1 ) and 1a (825.9 µg l -1 ) than those of stations 1b (387.1 µg l -1 ) and 2 (366.5 µg l -1 ). All mean concentrations of dissolved silicon in Strymonikos Gulf were higher than those measured in Thermaikos Gulf [4]. Seasonal variation of dissolved silicon concentrations displayed peaks, particularly in stations 1a and 3, during winter and spring (Fig. 2f). During the same sampling period, nutrient mean concentrations [C] at offshore areas of Strynonikos Gulf were measured at significantly lower levels (C [DIN] < 21.3 µg l -1, C [SRP] < 2. µg l -1, and C dissolved silicon < 3. µg l -1 )[8]. These values demonstrate that the offshore area of Strymonikos Gulf is not an eutrofic zone. RESULTS AND DISCUSSION Nutrients Seasonal variation of N-NO 3, N-NO 2, N-NH 4, DIN, SRP and Si-SiO 2 at the stations 1a, 1b, 2 and 3 of Strymonikos Gulf is shown in Fig. 2a-f. Mean values of DIN were by two times higher at stations 1a and 3 than at stations 1b and 2. Mean values of DIN were 144.3, 6.2, 51.8 and µg l -1 at stations 1a, 1b, 2 and 3, respectively. Mean values of DIN in inshore water of Strymonikos were at the same level or slightly N:P atomic ratio in open sea is close to 16:1 (Redfield ratio) [9]. Lower N:P values may indicate anthropogenic influences and in eutrophic conditions, nitrogen may act as a limiting factor. Higher N:P values may indicate phosphorus as a possible limiting factor [1]. Mean values of N:P atomic ratio in Strymonikos Gulf were relatively high (36.8) indicating possible phosphorus limitation of primary production. Chlorophyll-a Chlorophyll-a mean values were higher in stations 1a (1.6 µg l -1 ) and 3 (.9 µg l -1 ) as compared to the stations 1b (.24 µg l -1 ) and 2 (.62 µg l -1 ) (Fig. 4a). The higher concentrations of chlorophyll-a in stations 1a and 3 compared to stations 1b and 2, might be attributed to the higher concentrations of nutrients. Nevertheless, the highest value (11.1 µg l -1 ) was measured in station 3, in January Figure 4b shows the frequency distribution of chlorophyll-a. 77

4 by PSP Volume 1 No Fresenius Enviromental Bulletin FIGURE 2 a) - f) Seasonal variation of nutrient concentrations at three stations of Strymonikos Gulf. µg N-NO 3 /l a ) St 1a St 1b St 2 St 3 µg N-NO 2 / l b) µg N-NH 4 / l µg SRP / l c ) 8 d) e ) µg DIN / l µg Si-SiO 2 / l f) FIGURE 3 - Frequency distribution of a) TIN and b) SRP at inshore water of Strymonikos Gulf. FIGURE 4 - a) Seasonal variation of chlorophyll-a in surface water layer at three stations of Strymonikos Gulf and b) Frequency distribution of chlorophyll-a in inshore water of Strymonikos Gulf. Count TIN (µg l -1 ) n=76 x= a) µg chl-a /l a) St1a St2 St Count SRP (µg l -1 ) n=76 x= b) Count b) Chl-a (µg l -1 ) n=57 x=

5 by PSP Volume 1 No Fresenius Enviromental Bulletin FIGURE 5 - Vertical mean seasonal variation of a) temperature (in o C) and b) salinity (in ppt) at sampling station 1. a ) b ) Depth / m SPR 99 WIN 99 AUT 98 SUM 98 SPR 98 WIN 98 1 Chlorophyll values observed in the inshore area of Strymonikos Gulf are comparable to those observed in other eutrofic coastal areas, namely near the outflow of Evros River, in the Kavala Gulf, and in the middle part of Thermaikos Gulf [4], [11]. Chlorophyll-a values were generally higher during winter and spring than those in summer and autumn (Fig. 4a). The positive correlation (r =.48, n = 57) was found only between chlorophyll-a and the SRP values, and the high values of the N:P ratio have shown that phosphorus may constitute a major limiting factor in the increase of phytoplankton and eutrofication in the inshore Strymonikos Gulf. Temperature and Salinity Temperatures in the surface water layer ranged from 8.8 to 27.4? C at St1, 9.9 to 29.1? C at St2 and 1.9 to 28.8? C at St3. Salinity in the surface water layer ranged from 3.3 to 32.3 ppt at St1, from 1.2 to 37.1 ppt at St2 and from 1.9 to 35.3 ppt at St3. Temperature and salinity values are comparable to those detected in other estuarine systems of the Northern Aegean Sea [11]. The mean values of the temperatures of the surface layer of the station 1 (16.2? C) were lower than that of either station 2 (17.8? C) or 3 (18.1? C). This effect can be explained by the presence of cold, low salinity water masses from the Strymon River at station 1. Mean salinity values in the surface layer of the stations 1, 2 and 3 were 16.1, 31.7 and 28.8 ppt, respectively. Figure 4 shows the vertical distribution of the mean seasonal values of temperature and salinity in the water column at station 1. The highest variations of the mean seasonal values for the temperature (up to 3.4? C) and the salinity (up to 25.9 ppt) at station 1 were observed at the depth of 1 m, where the stratification of low and high salinity (density) waters occurs. CONCLUSIONS Based on the results of this study inshore water of Strymonikos Gulf can be classified as eutrophic. Nutrient concentrations and chlorophyll values together with temperature and salinity gradients showed that inshore water of Strymonikos Gulf seems to be affected principally from the Strymon River and to a lesser extent from the rivers Mavrolakas and Richios as well as from the coastal towns of Asprovalta, Stavros and Olympiada. High nutrient values were measured during the seasons of high precipitation, i.e. winter and spring. In addition, high percentage of N-NO 3 in DIN indicated agriculture as the main nutrients source. The results of this study indicated that monitoring programs provide useful information for the assessment of water quality and the management of a specific coastal zone. However, in the case of Strymonikos Gulf further research is needed in order to understand the causes and the effects of eutrophication and to make specific recommendations towards the protection of this coastal ecosystem. ACKNOWLEDGEMENTS We are grateful to the European Union and to the Greek Ministry for Environment for funding this investigation in the frame of program LIFE. Thanks are also due to Dr. S. Orfanidis for constructive comments on the manuscript. 79

6 by PSP Volume 1 No Fresenius Enviromental Bulletin REFERENCES 1. Krom, M. D., Kress, N., Bremmer, S. and Gordon, L. I., Limn. Oceanogr. 36, 424 (1991); 2. Grasshoff, K. (ed), Methods of seawater analysis, Verlag Chemie GmbH, D-694 Weinheim (1983); 3. Sylaios, G., Ioannidou, D., Stamatis, N. and Kallianiotis, A., Proc. 6 th Hel. Symp. Oceanorg. & Fish. 2, 424 (2); 4. Nikolaidis, G. and Moustaka-Gouni, M., Fresenius Envir. Bull. 1, 25 (1992); 5. Ignatiades, L., Karydis, M. and Vounatsou, P. Mar. Poll. Bull. 24, 238 (1992); 6. Karydis, M., Environ. Monitor. Assess. 41, 233 (1996); 7. Kitsiou, D., Karydis, M., J. Cost. Conserv. 4, 35 (); 8. Stamatis N. and Ioannidou D., Spatial and temporal distribution of nutrients in the whole area of Strymonikos and Ierissos Gulfs, In: Description of the coastal zone of Strymonikos and Ierissos Gulfs, E. Koutrakis, E. Lazaridou (eds). NAGREF-Fisheries Research Institute, Greek Biotope- Wetland Centre, N. Peramos, Kavala, Greece, , (1999); 9. Redfield, A. C., Ketchum, B. H. Richarrds, F. A. (eds.), The influence of organisms on the composition of seawater. In the sea, ideas and observations on progress in the study of the seas, Vol. 2, N. M. Hill (ed.) New York: Interscience, (1963); 1. Ryther, J.H. and Dunstan, W.M. Science 171, 18 (1971); 11. Nikolaidis, G., Moustaka-Gouni, M. and Tryfon, E. Fresenius Envir. Bull. 5, 9/1 (1996). Received for publication: December 15, 2 Accepted for publication: October 2, 21 CORRESPONDING AUTHOR N. Stamatis N.AG.RE.F. Fisheries Research Institute (F.R.I.) 647 N. Peramos,? avala - GREECE Phone: Fax: fri@mail.otenet.gr FEB/ Vol.1/ No.9/21 pages

Shen Zhen. New Territories. Stonecutters Island Kowloon. Victoria Harbor WM4 VM2 VM5 SM10. Hong Kong SM6. South China Sea.

Shen Zhen. New Territories. Stonecutters Island Kowloon. Victoria Harbor WM4 VM2 VM5 SM10. Hong Kong SM6. South China Sea. Shen Zhen Pearl River Estuary Latitude ( o N) New Territories Stonecutters Island Kowloon Victoria Harbor WM4 VM7 SM VM VM Hong Kong Lantau Islannd SM9 WM Island EM3 South China Sea Longitude ( o E) Fig..