Haliç yüzey sularında biyojeokimyasal aktivite

Abstract

ÖZET Haliç (İstanbul)'te yapılmış bu çalışmada, yüzey suyunun biyojeokimyasal aktivitesi ve sonucunda oluşan reaksiyonların jeokimyasal ortama olan etkisi araştırılmıştır. Bu amaçla, 2.2.1997 tarihinden 20.7.1997 tarihine kadar toplam 103 adet su numunesi alınmıştır. Alınan örneklerde, amonyum, nitrat, nitrit, fosfat ve sülfat analizleri, toplam koliform bakteri, anaerobik sülfür bakterisi tayinleri ve iletkenlik, pH, Eh, çözünmüş oksijen testleri yapılmıştır. Analizler sonucunda değerlerin birbirinden farklı iki farklı populasyonu temsil ettiği görülmüştür. Sarayburnu-Cibali arasındaki bölgede, Eh, pH, çözünmüş oksijen miktarının ve iletkenliğin yüksek, amonyum, fosfatın düşük olduğu tespit edilmiştir. Cibali-Alibeyköy arasındaki bölgede Eh, pH, çözünmüş oksijen miktarının ve iletkenliğin düşük, amonyum, fosfatın ve bakteriyel faaliyetlerin oldukça yüksek olduğu tesbit edilmiştir.. Özellikle Balat'tan sonra çözünmüş oksijen miktarının hızla düşmesiyle birlikte, ortamın özelliğinin tamamen değiştiği görülmüştür. Bütün bu değişimler, su koşullarındaki ani bir değişimi düşündürmektedir. Haliç'te çözünmüş oksijen miktarının düşük çıkmasının en önemli nedenlerinden biri, alık sularla ortama gelen organik maddelerin duraylı hale gelmek için çözünmüş oksijeni kullanmasıdır. Balat'tan sonra artan bakteriyel faaliyetle birlikte oksijen miktarının da azalması bunu desteklemektedir. Ayrıca ortamdaki su hareketlerinin son derece azalmış olması, yeni oksijen girişlerini de engellemiştir. Oksijen miktarının düşmesiyle birlikte, Eh değeri hızla düşerek ortam indirgen bir özellik kazanmıştır. Reaksiyonların yoğun olduğu Hasköy civarında Eh değeri -399 'a ulaşmıştır. Yapılan anaerobik sülfür bakterisi analizleri sonucunda, reaksiyonların Balat'tan sonra hızla arttığı görülmüştür. Artan reaksiyonlarla birlikte H2S oluşumuda hızlanmıştır. Anaerobik faaliyetlerin yoğun olduğu bölgelerde yapılan metal analizleri sonucunda, elementlerin saptanamayacak kadar düşük konsantrasyonlarda olması ve ortamda sülfür derişiminin artması, metallerin sülfür şeklinde dibe çökerek dip çamurlarında zenginleşmiş olabileceğini düşündürmektedir. Haliç bölgesinde pH değeri 6.7S-8.26 arasında okunmuştur. En düşük pH değeri 6.75 olarak Silahtarağa civarında, en yüksek pH değeri 8.26 olarak Sarayburnu civarında okunmuştur. Önceki çalışmalarda okunmuş pH değerleri ile karşılaştırıldığında, hafif baziğe geçiş tespit edilmiştir. Bunun nedeni atık sularla ortama gelen deterjanlardır. Deterjanların yapısında bulunan sodyum perborat ve ağartma etkeni olarak kullanılan sodyum sülfatın bu artışa neden olduğu düşünülmektedir. Yapılan toplam koliform bakteri tayinleri sonucunda, özellikle Cibali'den sonra ortalama değerin 10 -1 07 bakteri/ml arasında değişliği tespit edilmiştir. Bu değer, su ile karışmamış kanalizasyonlarda bulunan koli sayısı olan, l O6- 1 08 bakteri/ml ile karşılaştırıldığında, Haliç'in kirlilik derecesinin ne kadar artmış olduğu kolayca görülebilir. Amonyum ve fosfat analizleri sonucunda, en yüksek konsantrasyonlar Haliç köprüsü civarında okunmuştur. Atık suların yoğun olduğu kesimde, konsantrasyonların yüksek çıkması atık su kaynaklı olduğunu desteklemektedir. X

BIOGEOCHEMICAL ACTIVITY OF SURFACE WATER OF GOLDEN HORN(HALİÇ) SUMMARY In the presented contribution, the biogeochemical activities surface water of Golden Horn and geochemical reactions have been investigated. For this purpose, 103 water samples were taken up using the special cups from February 1997 to July 1997. The determinations of ammonium, nitrogen, sulfate, orthophosphate have been analyzed insitu by RQ-reflectoquant. Dissolved oxygen, electrical conductivity, Eh and pH have been measured by using the special electrods. The analyses of TTC (total coliform bacteria) and anaerobic sulfur bacteria have been made by special tubes. In order to identify the contents of trace element from surface water samples of Golden Horn it was added one mole hydrogen fluor and two mol hydrogen sulfur in water samples. As a result of analysis, it is shown that values represent two different populations. Dissolved oxygen decrease in the estuary region particularly from Balat to Alibeyköy with increasing waste water and also including reduction potential, conductivity. Generally, organic compounds in waste water use dissolved oxygen to be stable in environment. Organic compounds are normally composed of a combination of carbon, hydrogen, sulphur, oxygen and nitrogen. In some cases other important elements such as phosphorus and iron may also be present. The principal groups of organic substances found in waste water are proteins, carbohydrates, fats and addition with some clays. Organic compounds are decomposed by bacterial reaction and new substances may be occur. Dissolved oxygen is required for the respiration of aerobic microorganisms as well as other aerobic life forms. However, oxygen is only slightly soluble in water. The actual quantity of oxygen that can be present in solution is governed by the solubility of the gas, the partial pressure of the gas in the atmosphere, the temperature and salinity suspended solids of the water. Since there are not enough water circulations in the estuary region, the oxygen content from atmosphere by diffusion decrease. Because biogeochemical reactions increase associated with progressive temperature, dissolved oxygen level tend to be more critical during summer months in the Golden Horn. The problem is complex in summer months because stream flows are usually slow, and thus the total quantity of oxygen available is also lower summer. XIThe minimum dissolved oxygen concentration is of 0.2 mg/lt,in the Silahtarağa area and maximum 5.6 mg/lt (Figure: 1). The dissolved oxygen content decrease from Sarayburnu to Alibeyköy with increasing organic compounds. Hydrogen sulfide is formed from the anaerobic decomposition of organic matter containing sulfur or from the reduction of mineral sulfides and sulfates. İt is not formed in the presence of an abundant supply of oxygen. Hydrogen sulfide forms widespreadly in the Haliç region particularly from Balat to Alibeyköy with increasing anaerobic reaction. Because anaerobic reaction increase, dissolved oxygen content decrease and hydrogen sulfides form much more This gas is a colorless, inflammable compound with the characteristic odor of rotten eggs. The blackening of wastewater and sludge as in Haliç usually result from the formation of hydrogen sulfide. However, if there is iron in the environment, these hydrogen sulfide form ferrous sulfide. Various other metallic sulfides are also formed. In the determination of the metals it is establish that metals show interference due to the organic compouns and hydrogen sulfides. It is very difficult to observe the water samples in the regions having dominant domestic waste waters as in Haliç. Metals were not measurable because of interference exerted by the sodium, calcium and organic compounds and metals settle down as a metallic sulfide because the existence of much hydrogen sulfide in the estuary region. Trace quantities of many metals, such as nickel (Ni), manganese (Mn), lead (Pb), chromium (Cr), cadmium (Cd), zinc (Zn), copper (Cu), iron (Fe) and mercury (Hg) are important constituents of most water. Some of these metals are necessary for growth of biological life and absence of sufficient quantities of them could limit growth. The presence of any of these metals in excessive quantities will intervene with many beneficial uses of the water because of their toxicity. Orthophosphate measured in the estuary show a very high concentration. Maximum intense of orthophosphate in the estuary is 75 mg/lt. and minimum concentration of the Orthophosphate is 0.2 mg/lt. Since the Orthophosphate in the water comes from waste water, its principal supply is considered as detergents associated with domestic waste water. The usual forms of phosphorus found in aqueous solutions include orthophosphate polyphosphate and organic phosphate. The orthophosphate ( PO4`3, H PO4*2, H2 PO4`, H3 PO4 ) are available for biological metabolism without break down. Polyphosphates undergo hydrolysis in aqueous solutions and revert to the orthophosphate forms, this hydrolysis is usually quite slow. XIIFigure: 1 The dissolved oxygen content of Haliç water from Alibeyköy to Sarayburnu area. AB: Alibeyköy, EC: Eyüp BC: Balat, GK: Galata Bridge, SB: Sarayburnu Figure: 2 pH change from Alibeyköy to Sarayburnu area AB: Alibeyköy, EC: Eyüp, BC: Balat, GK: Galata Bridge, SB: Sarayburnu XIIIAt low pH ranges sulfides and cyanides show more toxic effects than higher pH values because they are converted to their acids at low pH values and these acids are more toxic than its anions. pH range was determineted to be 6.75-8.26 in the Estuary water sample. Minimum pH was analyzed as a 6.75 in the Silahtarağa and as maximum 8.26 in the Sarayburnu area. pH ranges exhibit a slight basic feature, particularly from Balat to Hasköy (Figure: 2). pH range of this study which is determineted to be 6.75-8.26 does not increase the toxicity of sulfides and cyanides. Ammonium and orthophosphat content of the samples taken from Balat and Hasköy were found to be exceedingly high being 80 mg/lt, 42 mg/lt and 60 mg/lt, 3 1 mg/lt. Ammonia nitrogen exists in aqueous solutionas either the ammonium ion or ammonia, depending on the pH of the solution. There is a reaction between ammonia and ammonium ions as following. NH3 + H20 -> NH+4 + OH` At pH levels above 7, the equilibrium is displaced to the left, at levels below and slightly basic condition the ammonium ion is predominant. Total colilform bacteria content of the samples from Haliç surface water were found to be above of the permitted level of 1 0s- 1 06 bacteria /ml. Sulfate content of the samples taken from Sarayburnu were found high being 1600-1200 mg/lt. The samples contents taken from Hasköy area that of the samples from Sarayburnu because of anaerobic reactions. The sulfate ion occurs naturally in most waters supplies and is present in waste water as well. Sulfur is required in the syntesis of proteins released in their degradation. Sulfate is reduced biologically under anaerobic conditions to sulfide, which in turn can combine with hydrogen to form hydrogen sulfide (H2S). the following generalized reactions are typical. organic matter + S04 ~2 -> S`2 + H20 +C02 S`2 + 2H+-> H2S Hydrogen sulfide released to the atmosphere above the wastewater. The minimum sulfate value is of 200 mg/lt in Halıcıoğlu, maksimum value 1600 mg/lt. Sulfate ions decreased with particularly anaerobic reaction in Hasköy. XIVAlthough, sulphur is important component of the biosphere, its most important biogeochemical reactions are those in which sulphur remains in inorganic form and, by interchanging between its -2 and +6 oxidation states, acts as an electron donors and acceptorin a variety of key redox reactions. For example, in organic rich, anoxic waters, sulphate-reducing bacteria can use sulfate ions (SO4`2 ) as in Haliç. In shallow water systems, the gaseous H2S often escapes into the atmosphere and give rise to the rotten eggs smell that is charecterisrtic of salt marshes and tidal mudflats. As a result of Eh determination, it is found that the minimum Eh value is of -399 which is higher than -260 permitted level of the deep water. Maximum value is 283 in Sarayburnu. Eh values decrease from Sarayburnu to Alibeyköy associated with increasing domestic waste water. Domestic and industrial waste water implicate organic compounds. Organic compounds in waste water settle down and give rise to actual muds with clay material. Generally, organic compounds use dissolved oxygen to be stable so the oxygen content of environment decrease and reduction condition is formed. Eh is one of the most important parameters to define the environmental condition oxidation or reduction. Reduction condition is dominant in Haliç so hydrogen sulfide is formed basicly. Forming hydrogen sulfide cause the changing of the geochemical condition. For instance, the oxidation state of this element varies from its most reduced state of -2 to its most oxidized state of +6. Moreover, in its -2 oxidation state the element's chemical make up can vary from its most acidic form of hydrogen sulfide to its most deprotonated or basic form its most deprotonated or basic form as the sulfide ion, while in its +6 oxidation state it may vary from its most acidic form of sulfuric acid to its most basic form as the sulfate ions.