EFFECT OF ALDER ON NITROGEN TRANSPORT TO SURFACE WATERS AND CATION LOSSES IN NATURAL ECOSYSTEMS IN ŞiMŞiRLi WATERSHED

Plant species compositions in the ecosystem and soils developed under these species compositions cause nutrients to be fixed or transport away from the site. The change of plant species compositions of forest ecosystems in precipitation watersheds changes the quality of water produced from these watershed. Especially, the fact that species such as Alder with nitrogen fixation ability enter into plant species composition will be effective on nutrient cycling. In this study, the effect of Alder on nitrogen transport to surface waters and therefore the cation losses in the ecosystem in stands where it is dominant was investigated. For this purpose, 36 surface water samples from 3 sub-watersheds selected in Şimşirli stream watershed throughout 1 water year and 39 soil samples from 15 soil profiles opened in forest areas were taken. While water quality parameters such as pH, EC, total nitrogen (TN), nitrate (NO3-N), ammonium (NH4-N), Ca++, Mg++, K+ and Na+ were determined in surface waters, sand, silt, clay, pH, EC, soil organic matter, total nitrogen and exchangeable cations (Ca++, Mg++, K+ and Na+) were determined in soil samples. TN and NO3-N concentrations in surface waters have increased along with the increase in the rate of forest area in the lower watersheds. Increase of NO3-N concentration in surface waters increased the basic cation (Ca++, Mg++ and K+) concentrations. This situation shows that leaching of nitrate in the sub-watersheds increases the cation losses. Annual TN transport in the sub-watersheds varied between 6.17 - 95.09 kg N Ha-1 and was 44.93 kg N Ha-1Year-1 on the average. Findings obtained as a result of the study suggest that Alder might be an important species under the control of the ecosystem and provide valuable information about the possible eutrophication of Galyan-Atasu dam reservoir.