جستجوی مقالات مرتبط با کلیدواژه « Selective deposition » در نشریات گروه « کشاورزی »

River sediments are the major component of the aquatic ecosystems and play an important role in the nutrients cycle and contaminants transformation in river systems. Sediment particles are transported in the forms of the suspended and bed sediment depending on the river flow regime and the size distribution of the particles. Sediments in the river are in equilibrium with the pore water and river flow. Therefore, the composition of sediments strongly affects water quality and the biological activities in the aquatic systems. Release of the organic and inorganic contaminants and nutrients from the sediments to the river flow is mainly influenced by the physical and chemical properties of the sediments. Thus, understanding of the basic physical and chemical properties of river sediments is essential for sustainable management of the watershed. The aim of this study was evaluate and compare the physical and chemical properties of the suspended and bed sediments of the Roze-Chay river in the Urmia region.
Total of the 19 bed sediments were collected along the river. Bed sediments were sampled from three parts of the river including up-stream (6 samples), mid-stream (6 samples), and down-stream (7 samples). In addition, six suspended sediments were sampled from the river during a flood event. Sediment samples were passed through a 2000 micron sieve and were analyzed for their basic physical and chemical properties. Hierarchical cluster analysis and principle component analysis were preformed for grouping the sediment samples and identifying the most effective properties of them.
Results indicated that the sand and silt particles are very dominant in bed and suspended sediments, respectively. The average silt and very fine sand content in bed sediments were 15.8 and 15.5 percents, while the silt and very fine sand particles content in suspended sediments were 44 and 25 percent, respectively. However, bed sediment have coarse texture due to their higher sand content in comparison with suspended sediments. The average values of organic matter and electrical conductivity of bed sediments were 1.7 and 2.5 times greater than the suspended samples. The organic matter content in up-stream bed sediments were higher than the middle and downstream parts, which may due to the discharge of the domestic sewage in this part of the watershed. Principle component and the hierarchical cluster analysis showed that the organic matter, EC, and particle size distribution are the most effective properties of the sediments.
Discharge of the domestic sewage to the river bed may has led to the accumulation of the organic matter and soluble salts in the bed sediments of the upstream part. As a result, the basic physical and chemical properties of the upstream bed sediments are different from the middle and downstream parts. Preventing the entry of the sewage into the river bed especially at the upstream part has an essential role in sustainable management of the Roze-chay river ecosystem. Multivariate analysis of the sediment samples revealed that there was a significant difference between the properties of the suspended and bed sediments.

Check dams have been widely used in erosion control projects of upland areas especially in arid and semi arid regions. These structures control and reduce the amount of sediments entering main rivers by trapping the sediment load of floods. Trapped sediments by check dam systems reduce the slope of gully and provide ideal condition to starting biological measures of erosion control such as vegetation cover establishment. Physical and chemical properties of check dam sediments have major role in determining the different aspects of their behavior like water holding capacity, water infiltration rate, and controlling nutrient loss and pollutants transportation. This study aims to analyze physicochemical properties of sediments in some successive check dam systems. The study was carried out in four seasonal waterways from two different region of Urmia city, northwestern Iran. Results indicated that the average sand content of the sediments in waterways lies between 54.4 and 88.4 percent. Sediments samples with sandy and loamy sand texture were coarser than the original soils of the adjacent hillslopes. Sediments were poor in macronutrients in comparison with original soils and the enrichment ratio of the N, P, and K were 0.53, 0.66 and 0.60 respectively. In the partially filled check dam systems, as a result of selective sediment deposition, sediment characteristics change regularly and the amount of clay and macro nutrients were higher in the downstream dams than the upstream dams. Results indicated that the check dam systems are not able to trap all sediment sizes and the great amounts of particles smaller than 2 micrometer in diameter, passed through the system in the form of suspended load. Principle component analysis of sediment properties strongly suggested the importance of macronutrients with sand and silt content in characterization of sediment properties.

Particle size distribution of sediment is one of the key factors which affects many other physical and chemical characteristics of the sediments. In this study, particle size distribution of the sediments trapped behind successive check dams was evaluated. Two waterways (G1 and G2) were selected in Noshan region of Urmia which have three and four check dams respectively. In each waterway, particle size distribution of sediment samples was compared with the original soil of the adjacent hill slope. Results indicated that the sediments have loamy-sand to sandy texture and have coarser particles than the adjacent soil samples. Selective deposition of sediment particles was observed in half full successive check dams of G1 waterway and the sediments of the check dam located at the downstream have a similar particle size distribution with adjacent soil sample. In filled dams of G2 waterway, considerable amounts of particles coarser than 0.124 mm in diameter were passed through dams. Some mathematical models were used to describe the particle size distribution of sediment samples and performance of them was evaluated by several efficiency criteria. Hierarchical cluster analysis of models, based on selected efficiency criteria, indicated that the Fredlund, ORL and ONL models have good performance in describing the particle size distribution of sediment samples. Coefficient of determination for these models was 0.99 and the Akaike’s Information Criterion (AIC) for these models were -44.13, -43.92, and -41.46 respectively. It can be concluded that these models are applicable for quantifying the particle size distribution of sediment samples.