ORIGINAL PAPER Spatial and temporal variation of suspended sediment concentration versus turbidity in the stream Harşit Watershed, NE Turkey Adem Bayram & Hızır Önsoy & Murat Kankal & Murat İhsan Kömürcü Received: 23 May 2013 /Accepted: 10 September 2013 # Saudi Society for Geosciences 2013 Abstract Suspended sediment related studies based on direct measurements for Turkish rivers and streams are very few for various reasons such as cost, time, or fewer operational sedi- ment gauging stations, and thus the researchers tend to look for indirect methods. Turkey is a developing country and in need of many investments, which resulted in engineering and management modifications in its river and stream systems. This paper investigates the spatial and temporal variations of suspended sediment concentration (SSC, mg/L) versus turbid- ity (NTU) in the stream Harşit watershed having a length of the main branch at 143 km and catchment area of 3,280 km 2 , Eastern Black Sea Basin of Turkey. Subsequently, the effect of the all kinds of anthropogenic activities was evaluated, name- ly, dam operation, levee construction, municipal wastewater discharge, sand–gravel mining on SSC, and turbidity in the watershed. In situ turbidity monitoring and water sampling studies were semimonthly conducted at ten stations from March 2009 to February 2010. On a semimonthly basis, it was revealed that SSC and turbidity values having significant correlation varied spatially and temporarily. The municipal wastewater discharge from the city of Gümüşhane together with the decreasing flow rate revealed itself with a significant increase in the turbidity and SSC, especially in the summer months. Torul Dam having a reservoir volume of 168 hm 3 could trap 78.6 % of the SSC and could remove 66.6 % of the turbidity, thanks to its long hydraulic residence time; however, Kürtün Dam released the suspended sediment as a result of its sluiceway tunnel operation. Sand–gravel mining activities between the last two stations severely affected the water quality by increasing the SSC and turbidity. Keywords Kürtün Dam . Sand–gravel mining . Stream Harşit . Suspended sediment concentration . Torul Dam . Turbidity Introduction Fluvial systems are key elements for operating Earth surface change because they convey most of the global fluxes of water and sediment from land to oceans (Meybeck and Ragu 1997). It is likely that these systems have suffered the single most intensive onslaught of all the world's ecosystems over the past 50 years of human history (Davies et al. 2000). Common anthropogenic activities as well as climate change have in- creasingly altered the water discharge and sediment load of the rivers and their catchments. Over recent decades, interest in suspended sediment dy- namics has increased, and many issues such as the transport of the pollutants adsorbed onto the fluvial sediments, reservoir sedimentation, channel and harbor silting, soil erosion and loss as well as the ecological and recreational impacts of sediment management relate to suspended sediment concen- tration (SSC), implying the requirement to understand its occurrence and transport process. Furthermore, study on SSC can provide important information on processes of ero- sion and deposition as well as different erosion sources within basins, such as hill slope erosion and channel erosion, runoff from agricultural land, construction activities and sewage, and industrial effluents. Thus, more and more work on suspended sediment dynamics in temporal scales have been conducted in many regions around the world (Fang et al. 2008). Yang et al. (2002) examined the temporal variability in the sediment load of Yangtze River, China, and the influences of human activities. It was concluded that human activities, especially dam construction, were responsible for the decrease in sediment load because no natural cause (e.g., water A. Bayram (*) : H. Önsoy : M. Kankal : M. İ. Kömürcü Department of Civil Engineering, Faculty of Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey e-mail: adembayram@gmail.com Arab J Geosci DOI 10.1007/s12517-013-1122-z