Effect of Timber Harvest on Physical Water Quality Characteristics

The effect of 11% thinning on selected stream water properties in an oak-beech forest ecosystem in the Belgrad Forest of Istanbul, Turkey was studied with a paired catchment experiment. Regression equations for some physical properties of the stream water were developed between control (W-I) and treatment (W-II) watersheds for calibration (with their 95% confidence limits) and treatment periods. The study discovered significant linear regressions between control and treatment watersheds for color, turbidity, air and water temperatures, suspended sediment concentration, pH and electrical conductivity in the calibration period but not turbidity and suspended sediment concentration in the treatment period. The impact of the timber removal was calculated as the difference between measured and predicted values derived from calibration equations. Results showed that timber harvest caused significant decreases in the color, turbidity, temperature, pH, and electrical conductivity values of the stream water and air temperature under the canopy but did not affect the suspended sediment concentration in the stream water.     

Effects of recreational activities on the soil and water components of a deciduous forest ecosystem in Turkey

Impacts of recreational activities on some hydrological properties of a deciduous forest ecosystem related to water production have been evaluated with an inclusive soil study, coupled with a two‐year water quality monitoring program. Spatial variations of water quality parameters did not indicate a statistically significant deterioration caused by the recreational activities in the stream water, but the effects of trampling on physical soil properties were clear. The bulk density of the soils increased with the intensity of recreation from 1.18 to 1.29 g cm^?3, while the percentage of clay fraction decreased, as an indicator of erosion. The soils of the stream banks in the recreation area had reasonable saturated hydraulic conductivity values, and were affected sharply by the intensity of recreational use. The low inclination (0.5%) and the coarse texture of the soils were possibly the main factors diminishing or concealing the trampling effects not observed on the water quality of the stream passing through the recreation area.     

Evapotranspiration from a Mixed Deciduous Forest Ecosystem

The objectives of this paper were to determine evapotranspiration (ET) from an oak-beech dominated forest ecosystem in Belgrad Forest near Istanbul, Turkey by using catchment water balance method and compare it with potential evapotranspiration (PET) computed by using Thornthwaite method. Data, in this study, were derived from a long-term hydrological research conducted in Belgrad Forest. Long-term stream flow measurements (1979–1995) were conducted with concrete sharp-crested V-notch weirs instrumented with automatic water level recorders in two close experimental watersheds. ET values of the watersheds were determined by using water balance equation. Average annual ET values from the old growth oak-beech forest ecosystem during the monitoring period of 17 years were around 833.20 mm for W-I and 752.07 mm for W-IV whereas PET estimated according to Thornthwaite method was found to be 726.14 mm. In other words, 79.68%, and 71.93% of mean annual precipitation evaporated from W-I and W-IV, respectively while 69.45% of precipitation evaporated according to Thornthwaite method. PET estimated with Thornthwaite method differed significantly only from W-I whereas W-I and W-IV had similar ET values.     

Effect of Selective Cutting on Streamflow in an Oak-Beech Forest Ecosystem

Calibration equations for streamflow between the control (W-I) and the treatment (W-II) watersheds as an integral part of a paired experimental watershed study in Belgrad Forest are presented. Correlation coefficients of the calibration equations were found to be highly significant. The effect of 11% removal of the standing volume by regular selective cutting in old-growth oak-beech forest ecosystems was discussed. Streamflow hydrographs were developed for March, April, May, and June of 1986, and for the long-term period from 1986 to 1996. Increase in water yield immediately after the treatment was detected as the difference between measured and predicted values. Significant increases occurred in streamflow in March 1986 and in the long-term period (1986–1996).     

Comparison of Rainfall-Runoff Relationship Modeling using Different Methods in a Forested Watershed

The daily rainfall-runoff relationship in an experimental watershed was modeled using a statistical method and an artificial neural network method. The estimations were examined and a performance evaluation was done. It was seen that the ANN method, FFBP (Feed Forward Back Propagation), provided closer flow estimations reproducing the shape of the observed hydrograph more realistic. The superiority of FFBP was reflected in the performance evaluation criteria. The extreme flows, i.e., high and low flows, were relatively better approximated by FFBP indicating its promise as a useful tool for hydrologic studies such as flood modeling. The Rational Method was also used, as a conventional tool, to predict the maximum discharge for selected return periods. It was found to be realistic for the forested watershed under consideration when the C coefficient was taken as 0.20 for the 10-year period.

     

Effect of Forest Thinning on Water Yield in a Sub-Humid Mediterranean Oak-Beech Mixed Forested Watershed

Forested watersheds provide fresh water with best quality and forestry practices play important role on the water production in the watersheds. Therefore, the objective of this study was to investigate the effect of 18 % thinning, which was under the 20 % threshold value reported in the literature on water yield in a forested watershed. Two experimental watersheds with similar ecological conditions in the Belgrad Forest of Istanbul were studied. Following a 6-year calibration period from December 2005 to October 2011, a simple linear regression equation was developed between the monthly streamflows of two watersheds with a significantly high correlation coefficient (r = 0.95). After 18 % of standing volume was removed from one watershed and the other was left untreated as a control, the streamflow was monitored for 2 years starting in January 2012 in both watersheds. The change in the monthly runoff was estimated as the difference between measured and values calculated with the linear regression equation. Average monthly streamflows were about 19, 15 and 10 mm in the control and 21, 20, and 11 mm in the treatment watersheds for calibration, first and second post-treatment periods, respectively. Paired watershed analysis showed that monthly streamflow did not significantly increase in either watershed for the first or the second year after the harvest. The results revealed that thinning intensity had to be greater to increase water yield significantly in this forest ecosystem and the threshold value for a streamflow increase was greater than 18 % for this region.