Trophic characteristics of the Sapanca lake (Turkey)

Abstract

Systematic measurements of optical properties, concentrations of major and minor chemicals and primary production throughout 1989?1992 enabled us to identify the oligotrophic state of Sapanca lake, Marmara region, Turkey. Lake waters which have low concentrations of major anions and cations (total = 49 M) overturn every February?March, ventilating the bottom waters and enriching the surface waters with nutrients. Surface waters cool down to 6.5 °C by late winter and then warm steadily to 26 °C by late summer, while temperatures in deep waters range between 6.5 and 10.0 °C throughout the year. When the seasonal thermocline develops, the dissolved oxygen profiles exhibit a subsurface maximum in the thermocline, while in the hypolimnion water, the content varies seasonally from 11.5?12.0 ppm (350?375 M) in March to 0.5?1.7 ppm (16?56M) in late autumn. Surface nitrate concentrations vary markedly with season, from < 0.15 M in summer to 5.7 M in early March, whilst the bottom water concentrations range from 13.5?14.0M in late autumn to 5.7M after the winter