Monitoring water quality and quantity of national watersheds in Turkey.

National data from the hydrological network for 38 rivers out of 25 watersheds were used to detect spatial and temporal trends in water quality and quantity characteristics between 1995 and 2002. Assessment of water quality and quantity included flow rate, water temperature, pH, electrical conductivity, sodium adsorption rate, Na, K, Ca+Mg, CO(3), HCO(3), Cl, SO(4), and boron. Among the major ions assessed on a watershed basis, Turkish river waters are relatively high in Ca+Mg, Na and HCO(3), and low in K and CO(3). The watersheds in Turkey experienced a general trend of 16% decrease in flow rates between 1995 and 2002 at a mean annual rate of about 4 m(3) s(-1), with a considerable spatial variation. Similarly, there appeared to be an increasing trend in river water temperature, at a mean annual rate of about 0.2 degrees C. A substantial proportion of watersheds experienced an increase in pH, in particular, after 1997, with a maximum increase from 8.1 to 8.4 observed in Euphrates (P < 0.01). Kendall's tau test revealed increasing trends of EC and SAR concentrations that exceeded existing standards, particularly, in the Meriç, Kizilirmak and Big Menderes watersheds where intensive agricultural activities take place. Such continued levels may threaten biotic integrity and both drinking and irrigation water quality of rivers. Best multiple linear regression (MLR) models constructed both annually and monthly differed in R (2) values in accounting for variations of pH and water temperature only. The findings of the study can provide a useful assessment of controls over water quality and quantity and assist in devising integrated and sustainable management practices for watersheds at the regional scale in Turkey.