Water quality and hydrogeochemical characteristics of the River Buyukmelen, Duzce, Turkey

摘要

The River Buyukmelen is located in the province of Duzce in northwest Turkey and its water basin is approximately 470 km~2. The Aksu, Kucukmelen and Ugursuyu streams flow into the River Buyukmelen. It flows into the Black Sea with an output of 44 m~3 s~(-1). The geological succession in the basin comprises limestone and dolomitic limestone of the Yilanli formation, sandstone, clayey limestone and marls of the Akveren formation, elastics and volcano-elastics of the Caycuma formation, and cover units comprised of river alluvium, lacutrine sediments and beach sands. The River Buyukmelen is expected to be a water source that can supply the drinking water needs of Istanbul until 2040; therefore, it is imperative that its water quality be preserved. The samples of rock, soil, stream water, suspended, bed and stream sediments and beach sand were collected from the Buyukmelen river basin. They were examined using mineralogical and geochemical methods. The chemical constituents most commonly found in the stream waters are Na~+, Mg~(2+), SO_4~(2-), Cl~- and HCO_3~- in the Guz stream water, Ca~(2+) in the Abaza stream water, and K~+ in the Kuplu stream water. The concentrations of Na~+, K~+, Ca~(2+), Mg~(2+), SO_4~(2-), HCO _3~-, Cl~, As, Pb, Ni, Mn, Cr, Zn, Fe and U in the Kuplu and Guz stream waters were much higher than the world average values. The Dilaver, Gubi, Tepekoy, Maden, Celik and Abaza streams interact with sedimentary rocks, and the Kuplu and Guz streams interact with volcanic rocks. The amount of suspended sediment in the River Buyukmelen in December 2002 was 120 mg l~(-1). The suspended and bed sediments in the muddy stream waters are formed of quartz, calcite, plagioclase, clay (kaolinite, illite and smectite), muscovite and amphibole minerals. As, Co, Cd, Cr, Pb, Ni, Zn and U have all accumulated in the Buyukmelen riverbed sediments. The muddy feature of the waters is related to the petrographic features of the rocks in the basin and their mineralogical compositions, as most of the sandstones and volcanic rocks (basalt, tuffite and agglomerate) are decomposed to a clay-rich composition at the surface. Thus, the suspended sediment in stream waters increases by physical weathering of the rocks and water-rock interaction. Owing to the growing population and industrialization, water demand is increasing. The plan is to bring water from the River Buyukmelen to Istanbul's drinking-water reservoirs. According to the Water Pollution Regulations, the River Buyukmelen belongs to quality class 1 based on Hg, Cd, Pb, As, Cu, Cr, Zn, Mn, Se, Ba, Na~+, Cl~, and SO_4~(2-); and to quality class 3 based on Fe concentration. The concentration of Fe in the River Buyukmelen exceeds the limit values permitted by the World Health Organization and the Turkish Standard. Because water from the River Buyukmelen will be used as drinking water, it will have an adverse effect on water quality and humans if not treated in advance. In addition, the inclusion of Mn and Zn in the Elmali drinking-water reservoir of Istanbul and Fe in the River Buyukmelen water indicates natural inorganic contamination. Mn, Zn and Fe contents in the waters are related to geological origin. Moreover, the River Buyukmelen flow is very muddy in the rainy seasons and it is inevitable that this will pose problems during the purification process.