Effects of forest canopy cover and floor on chemical quality of water in broad leaved and coniferous forests of Istanbul, Turkey

Abstract

The objective of this study was to determine how the canopy cover and forest floor of sessile oak, oriental beech, and Anatolian black pine stands affect the rainwater chemical parameters. The chemical parameters investigated were pH, electrical conductivity, total nitrogen (N), total phosphorus (P), sulfate (SO4)2-, nitrate (NO3)-, ammonia (NH3)+, permanganate index (PI), chloride (Cl−), sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), iron (Fe), aluminum (Al), and lead (Pb). Forest canopy covers significantly affected pH, total N, total P, SO42-, Na+, and K+ contents in the throughfall, while forest floors influenced all chemical properties, except for NH3+ and Pb in the forest floor solution. While rainwater pH changed from medium acid (5.79) to strongly acid for both the throughfall (5.48) and forest floor solution (5.50) in the pine stand, it increased to neutral (6.57) in the oak and slightly acid (6.15) in the beech forest floor solution for the throughfall. Regardless of forest stand types, mean total P values of rainwater significantly decreased after passing through the canopy, but a change was not detected in the forest floor solution. A significant amount of SO42- was retained in the forest floor. Average SO42- values decreased from 4.90mgL−1 in the rainwater to 1.14–1.04mgL−1 in the forest floor solution of oak, beech and pine stands. Forest floor under the beech stand had significantly higher nitrate leaching than that under other two stands. Canopy covers of oak, beech and pine stands did not significantly influence the concentrations of Ca2+, Mg2+, Fe, and Al in the throughfalls. However, the same chemical parameters significantly increased in the forest floor. Given that the forest canopy cover and floor of all three stands had significantly different effect on rainwater chemistry, various tree species appear to differently influence the stream water chemistry. Therefore, selection of tree species for afforestation projects in fresh water producing watersheds becomes important to maintain water quality in streams for aquatic life and fresh water consumers.