Objectives of the study

1. Variations of pH Values ofStreamWater in Mature Oak-Beech Forest Ecosystems in the Belgrad Forest Near Istanbul,Turkey Ferhat Gökbulak, Yusuf Serengil, Süleyman Özhan, Ahmet Hızal Istanbul University, Faculty of Forestry, Dept. of Watershed Management,Bahçeköy 34473, Istanbul - TURKEY

2. Objectives of the study • to presentlongterm variation of pH values of the waters from both stream and precipitation • to determine how precipitation affected pH ofthe streamwater in the long term

3. Background • rain waters generally does not reach the streamflows with the same pH value and stay close to neutral level (Serengil, 2002; Silveria,1999) • e.g.; although Hong Kong experienced acid rains, streams had a pH much more higher than those of precipitation (Peart, 2000). • precipitation is not the only factor responsible for stream pH level (Serengil,1997)

4. Background • mostly, pH is higher when streamflow is lower and fed from ground water (Neal et al., 2000) • acid rains were observed (down to 3.5) in winter months and the probability is high (0ver 80 %) for a precipitation having a pH less than 5.6 (Serengil, 2003).

5. Study site • The study site islocated in the Belgrad Forest (41° N, 28° E) which has been preserved as the only old-growth oak-beech natural forest near Istanbul provides domestic water for Istanbul.

6. Experimental watersheds N 1 25 000

7. precipitation, temperature and potential evapotranspiration in the study site • Mean annual temperature: 12.8 °C • Mean annual precipitation: 1090.5 mm • Mean annual potential ET.: 698.3 mm

8. Soil and topography • soils derived from carboniferous clay schists: • usually shallow to deep, • gravelly, loamy clay in texture, • rich in organic matter with medium to good permeability rates

9. Soil and topography • soils developed from neogene deposits: • deep, loamy clay in surface horizons • clay in the subsoil with medium permeability rates.

10. Soil and topography • both soils have high erodobility potentials with no carbonate reaction • mull type forest floor has an average depth of 5 cm

11. Soil and topography • subsurface and base flows feed the streams in the watersheds • topography is generally gentle • mean elevation is around 140 m

12. Soil and topography • about 3 or 4 km from the Black Sea • under the influence of prevailing northern maritime winds • vegetation is composed of oak (Q. frainetto Ten., Q. cerris L.) and beech (F. orientalis Lipsky.)

13. Some characteristics of the experimental watersheds

14. Water Sampling and Analysis • two experimental watersheds in the Belgrad Forest, Istanbul have been monitored for eighteen years • water samples were collected from precipitation and two streams on weekly basis • analyzed at the same samplecollection day

15. Statistical design • experiment was a randomized complete block design with two replications • data were analyzed by using analysis of variance • means were compared with Duncan multiple range test (P<0.05)

16. Results and Discussion • no significant difference between pH of the streams in the watersheds • overall mean monthly pH values of the stream was 7.39 and ranged from 7.04 to 7.60 • overall mean monthly pH values of the precipitation was 5.75 and variedbetween 4.52 to 6.91

17. Results and Discussion • numerically not big differences between monthly pH values of the streamwater, however, they were significantly different from each other • summer and wintermonths significantly differred from each other

18. Results and Discussion • pH levels of both precipitation and streamwater followed the same trend • they started decrasing after August and this trend continued until February

19. Results and Discussion • regardless of the months, stream water had greater pH values than precipitation • they were always over neutral level. • amount of precipitation affected acidity of the both stream and rain waters. • duringthe months with higher precipitation, lower pHs were measured in the both water samples

20. Mean monthly pH values for precipitation and streamwater during the study period

21. Results and Discussion • average monthly pH values of mostly winter months covering December through March were lower than those of mostly summer months from June to September • in other words, pH values were lower when streamflow and precipitation were higher and vegetation was dormant

22. Mean monthly precipitation and runoff coefficient during the study period

23. Conclusion • acid rains fall in the region and acidity of rain and stream waters increases especially in the rainy winter months • pH level of the precipitation affected pH level of the stream water because the pH level in the streamflow followed similar trend that of precipitation

24. Conclusion • pH level was always below neutral level for the precipitation and over neutral level for streamflow