It has been common in forestry and agriculture to drain waterlogged areas through ditching in order to cultivate them. The ditches that drain water are usually connected to some watercourse, such as a river. When the water flow of the river decreases and becomes more still, particles will settle and fall to the bottom of the water body and form sediment. If there is an increasing amount of nutrients and metals transported with the water, it could affect the water quality negatively, since an increased amount of nutrients could result in eutrophication and many metals are toxic in high amounts. In the Sangis River there is an increased amount of sediment deposited at the mouth of the river and inside the estuary, which has resulted in the river and the estuary becoming shallower. The origin of the deposited sediments is believed to partly be from ditching. The residents of the village of Sangis have said that it is difficult to cross the estuary by boat because of the deposited sediments, therefore, their wish is for a channel dredged in the Sangis River and its estuary that they can use. The main aim of this master's thesis was to analyse the geochemical status of the surface water and the sediment in the estuary of the Sangis River and to give recommendations for future actions preventing sedimentation of the river channel. The analyse of the geochemical status of the sediment was achieved by sampling six sediment- cores in the estuary and analysing for different parameters. The analyse of the geochemical status of the surface water was achieved by comparing the water quality regarding metal concentrations in the estuary with other nearby rivers and classifying the concentration of phosphorous in the estuary, to determinate if there was an ongoing eutrophication. The following analyses were conducted for the sediment-cores: Element distribution were analysed with P-XRF, pH and electrical conductivity were measured and loss on ignition was also calculated trough combustion of the sub-samples. The results showed for the P-XRF that the dominating main elements were iron, sulfur, calcium and potassium. Iron and sulfur were correlated to each other in all profiles and had a peak between 20-35 cm in the sediment. This indicated that there could be formation of iron sulfides at that depth. Therefore, sub-sample 4.D was analysed with SEM-EDS instrument and framboidal pyrite (FeS2) was detected in the sample. The results from the pH and conductivity showed that the pH-value varies greatly both with depth and between the sediment cores. However, for the conductivity it could be seen how it peaked at around 20-35 cm in all profiles, with the highest EC-value in profile 4. It could be concluded that the surface water in the estuary contains elevated concentrations of copper and that there is an ongoing eutrophication as well. Due to the eutrophication, it has most likely resulted in an increased amount of aquatic plants during the summer. The increased amount of organic material has probably resulted in oxygen-free bottoms, since all the oxygen has been consumed when the organic material has been decomposed. The formation of framboidal pyrite shows that the redox ladder has reached the two last steps, since framboidal pyrite (FeS2) consists of reduced sulfur and dissolved iron and is formed during anoxic conditions. Reduced sulfur forms when sulfate is reduced in order to oxidize organic matter and dissolved iron forms when iron-oxide hydroxides are reduced in order to oxidize organic matter. If dredging is carried out in the Sangis river and its estuary, oxidation of framboidal pyrite will occur, this could result in formation of acid and leachate of metals that were previously bound to framboidal pyrite. The consequences if it leaches into the river and the estuary is that it creates an acidic environment with elevated metal concentrations, where marine life would find it hard to live. The extent and impact of leached acidity and metals needs to be studied further.

Estuaries are valuable ecosystems that are easily affected by human activities within the watershed. One determinant of water quality for in an estuary is the presence of suspended sediments. The use of satellite sensors to remotely sense visible and near-infrared reflectance allows for suspended particulate matter (SPM) and suspended particulate inorganic matter (SPIM) concentrations to be monitored on a repetitive synoptic scale. Previously presented algorithms for relating remote sensing reflectance (Rrs) and SPM/SPIM concentrations were evaluated for the Weeks Bay estuary in Alabama. Additionally, numerous potential SPM/SPIM concentration retrieval algorithms using the Landsat-8 satellite were determined through regression analysis, as well as through the consideration of the inherent optical properties of the water body. The most robust empirical algorithm produced an RMSE of 12.50% and utilized the band combination of Ln(Band4)/Ln(Band3), while the most robust semi-analytical algorithm produced an RMSE of 16.34% and utilized the band combination of Band4/Band3.

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Many chemicals are released into surface water and biodegradation is one important mechanismto remove the contaminants. Their actual concentrations in water depend on their persistence.The OECD 309 test is the most recognized method to assess the persistence of chemicals in theaquatic environment. However, the quantity of sediment used in the OECD 309 suspensiontests is not clearly defined. To investigate the influence of sediment concentrations and thebacterial cell count on the biodegradation, we compared the biodegradation rate constants of amixture of organic chemicals in suspension tests with 5 different water-sediment ratios. Thesediment concentrations were 125, 50, 20, 8 and 3 g L-1. The 5 test systems were spiked with129 chemicals including pharmaceuticals, agrochemicals, food additives, and cosmetics at aconcentration of 1 μg mL-1 each. The chemical degradation was monitored by analyzing thewater subsamples collected at different time points during the 14-day incubation period. It wasthe first time that the effects of sediment concentrations on biodegradation were systematicallystudied for a broad range of chemicals. The bacterial cell count was measured to test whether itcorrelated with sediment concentration and biodegradation rate constant. In the present study,k could be quantified for at least 2 sediment concentrations for 10 chemicals. The resultsshowed that the biodegradation rate constants of the chemicals, k, were positively correlatedwith sediment concentration for 10 chemicals; 6 of these correlations were significant. The totalbacterial cell count showed a positive correlation with sediment concentration, but it was notsignificant. Also, k was positively correlated with total cell count, but these correlations werenot significant for any of 10 chemicals. It is concluded that sediment plays an important role inchemical biodegradation. Sediment-associated total cell count can be one factor contributing tothis effect. The variable results of chemical biodegradation rate constants caused by differentsediment concentrations in the present suspension tests suggest the need for a standardizedsediment concentration in OECD 309 tests.

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The presence of fine muddy sediment (grain size < 0.1 mm) in streams has many impacts on the fluvial system and those relying on it, both humans and aquatic biota. Previously, fine sediment was considered a washload and has been ignored in transport models. More recently, it has been treated as being transported once the surface gravel layer that stores it is able to be mobilized. We propose that the surface layer need not be mobilized in order for muddy sediment to travel through the fluvial system in a series of erosive and depositional events. Our first study uses a new in situ device to show how mud entrainment from immobile gravel beds behaves cohesionlessly and can be modeled using the framework of classic sand-based models modified to account for hiding effects present in the stream bed. It also provides a method to predict how deep into the surface layer of gravel entrainment of fine sediment will occur given flow and stream bed characteristics. The second study investigates the primary pathway that fine sediment is traveling to get captured within bluehead chub fish nests. It was determined that more deposition of mud occurred in the upstream half of the nest concluding that the primary pathway was hyporheic pumping through the nest. Capture efficiencies of the nests were also found to increase as the length of nests increased. Both of these studies provide supporting evidence in the need to transition modeling fine sediment transport as a series of deposition and resuspension. / Master of Science / Fine muddy sediment (grain size < 0.1 mm) is present in natural streams and has many impacts on the stream system and those relying on it, including humans, plants, animals, and other organisms in the ecosystem. Previously, fine sediment was treated as being too small to consider in models that aid in understanding how a stream transports sediment. This is because small sediment stays suspended in the water column more easily than larger sediment. Therefore, it was just assumed to pass through the system and never deposit into the stream bed. However, in nature we observe large quantities of fine sediment being stored within the stream bed. More recently, it has been assumed that the sediment that does deposit will be transported once the surface gravel layer that stores it is able to be mobilized. That is, the surface gravel layer shields the fine sediment trapped between it and that the mud will stay put until that gravel is moved. We propose that the surface layer need not be mobilized for muddy sediment to travel through the fluvial system in a series of erosive and depositional events. Our first study uses a new device that forces erosion of mud to show how mud entrainment, or the process of how a fluid picks something up and carries it, from immobile gravel beds can be modeled using the framework of classic sand-based entrainment models modified to account for hiding effects, or protection against entrainment of a smaller sediment by a larger sediment shielding it, present in the stream bed. It also provides a method to predict how deep into the surface layer of gravel that fine sediment will be eroded given flow and stream bed characteristics. This is beneficial in estimating the amount of sediment that will be eroded during a given storm event. The second study investigates the primary pathway that fine sediment is traveling to get captured within bluehead chub gravel fish nests used for spawning their eggs and reproducing. It was determined that more deposition of mud occurred in the upstream half of the nest. This leads us to believe that the primary pathway of sediment traveling through the nest was hyporheic pumping through the nest, or the process of water flowing down through the surface layers of sediment in the stream bed. Capture efficiencies, or the ratio of how much of the sediment that traveled through the nest was captured, of the nests were also found to increase as the length of nests in the downstream direction increased. Both of these studies provide supporting evidence in the need to transition modeling fine sediment transport as a series of deposition and resuspension.

yes / A two dimensional (2D) RNG k-ε sediment model including the effects of secondary currents is developed to simulate sediment transport and bed deformation in rivers with continuous bends. Nonuniform suspended and bedload sediment transports and variation of effective bed material size distribution are included in the model. A semi-coupled scheme for sediment model is proposed, which can be used for simulating both the long- and short-term sediment transport whenever riverbed changes. The model is applied to simulate the flow and sediment transport in the Shapotou reservoir in the upper reach of the Yellow River which is a typical natural river reach with continuous bends. River bed deformations caused by suspended and bedload sediment transport are investigated. Good agreement between the numerically simulated results and the field measurements is obtained, indicating that the model is capable of simulating the sediment transport and predicting the bed deformation of rivers having continuous bends with reasonable accuracy. / the Major Research Plan Project, National Natural Science Foundation of China(Grant No.: 91230111 and 51279071); National Key BasicResearch Development Program of China (973 Program, Grant No.: 2010CB429002);Project of Science and Technology of Colleges in Ningxia, China (Grant No.:NGY2012097)

Yes / Ice cover formed on an alluvial channel can significantly alter the flow characteristics, such as the vertical distributions of streamwise velocity and shear stress, and hence the water and sediment transport process. The vertical profile of the suspended sediment concentration in the ice-covered alluvial channels with steady uniform flows is investigated in this study. To calculate the suspended sediment concentration, we are based on the Schmidt O’Brien equation and deduce an analytical model that employs an existing eddy viscosity model and a modified formula of the sediment fall velocity considering the common effects of the upper and lower boundaries. The proposed analytical model is then validated by using available experimental data reported in the literature. The predicted accuracy of the proposed model is evaluated through error statistics by comparing to previous modeled results. The relative concentration profiles of the suspended sediment are subsequently simulated by applying the validated analytical model with different characteristic parameters. Results show that the relative concentration decreases with the increase of both the ice cover roughness and the sediment fall velocity. The uniformity of the relative concentration distribution is closely related to the value of the proportionality parameter σ, revealing the physical mechanism that the more prominent the turbulent diffusion effect is, the more uniform the relative concentration profile is. / This work was supported by the National Natural Science Foundation of China (grant 604 numbers 52020105006 and 11872285) and the Open Funding of State Key Laboratory of Water Resources and Hydropower Engineering Science (WRHES), Wuhan University (Project number 2018HLG01).