Rivers are conduit that transport terrestrial matters to the ocean. Studying how the composition and transport mechanism of terrestrial matters influenced by tide, wave, wind and discharge is an important issue in the disparate of river-sea systems. The aim of this study is to understand the temporal and spatial variability of the grain size distribution of a river plume, using EOF (Empirical Orthogonal Function) to analyze the correlation between environmental processes and suspended sediments. We used CTD and LISST-100 to collect upper-colum profile data at Gaoping River mouth in five (R/V Ocean Research III) cruises from 2005 to 2009. We also deployed an instrumented tetrapods and a moored buoy at the inner Gaoping River mouth and the inner continental shelf off Gaoping River mouth for two days, respectively. In all the upper-column data, the volume concentration increased in surface column when the salinity decreased. The variability of volume concentration are dominant in grain sizes between 10-250 £gm. We used EOF to analyz the time series to investigate the correlations among the volume concentration of 5 grain-size groups (<3, 3-10, 10-63, 63-153, and 153-250 £gm), salinity, water temperature, and alongshore and across-shore winds. The first eigenmode explains about 50 % of the total correlations. This mode describes the dominant influence of the river runoff that affected all the grain-size classes within the plume. This mode suggests that the grain-sizes between 3-250 £gm are of terrestrial origin (low salinity, high water temperature) exported during the ebbing tide. The second eigenmode accounts for about 20 % of the total correlations. This mode describes the dominant influence of the wind. When under the upwelling-favorable across-shore wind, the upwelling brings low temperature and clay-sized suspended sediment from the submarine canyon to the surface. The results suggest that the size-classes greater than 3 £gm are terrestrial suspended sediment and transported by the river plume, the size-classes finer than 3 £gm are mostly from the submarine canyon by the upwelling-favorable winds.

A surf zone sediment transport study was conducted in Jamaica Beach, Texas, using new oceanographic equipment. A mini-sled was constructed and outfitted with an instrument package that consisted of two velocimeters, one current profiler, three OBS's (Optical Back Scatter), and a Sequoia Instruments LISST (Laser in situ Scatteroineter and Transinissoineter). This instrumented sled was used to measure sand concentration and flow velocity across the surf zone. Using these two parameters we were able to determine longshore sand transport. The study provided an accurate measurernent of sand transport on a muddy coast. Previous methods for measuring total longshore sediment transport did not quantify the effect that mud-sized particles would have on OBS's. To circumvent this issue we used the LISST to measure sand concentration in the water. The LISST can measure sand concentration despite the presence of mud. During this study it appeared that sand transport peaks 10 cm above the sea bottom. The measured total longshore transport rate closely matched results from one equation for determining total longshore transport (Kamphius, 199 1). The CERC equation was also compared to the measured result.

Laser in situ scattering and transmissometry (LISST) instruments are used to measure the particle size distributions (PSDs) and volume concentration of individual and groups of phytoplankton in water. The objective of this research was to test the LISST’s ability in detecting monospecific blooms in-situ and the ability to detect aggregation after diatoms were subjected to different temperatures and bacteria concentrations. The PSDs of ten harmful algal bloom (HAB) species were measured with the LISST characterizing the peak location, peak height, peak width, and peak range resulting in a scattering signature for each species. Each species had specific characteristics that would allow for their detection with the LISST, though microscope observations would be needed for complete accuracy. The LISST was able to detect HABs placed in natural seawater collected off the Texas coast. Blooms of four HAB species before they reached full” bloom concentrations were detected making the LISST a possible low cost, effective tool in the early detection and monitoring of HABs. The diatom, Odontella aurita, was used to test how well the LISST could monitor aggregation, an important process in the termination of many phytoplankton blooms. Increasing temperature causes an increase in transparent exopolymer particle (TEP) production in diatoms, which is a critical sticky particle that increases the probability of aggregation. An increase in temperature can also cause an increase in bacteria concentration that can positively effect TEP production and thus aggregation. O. aurita was grown at 20 °C and 28 °C and showed a significant increase in TEP abundance with temperature (p = 0.002), though no relationship between TEP production and bacteria concentration existed. Coomassie stained particles (CSP) are proteinaceous gel-like particles, which are currently understudied. CSP was consistently produced though it did not appear to be dependent upon any single factor. The increase in ocean temperatures has implications for an increase in phytoplankton blooms making the monitoring and understanding of these blooms even more important as they can affect the carbon cycle and potentially the microbial loop.

Kao-ping submarine canyon is straightly connected with Kao-ping River. Thus, it is influenced by the river¡¦s discharge. In order to investigate this seasonal difference in the canyon, we conducted several researches, which were based on temporal and spacial observations of the hydrological and dynamical characteristic of the canyon. We also studied the transport of suspended sediment particles in the canyon according to the distribution of SSC (suspended sediment concentration). In our research, we made along-canyon profile observations. We collected data by using CTD, ADCP and Transmissometer on R/V Ocean Researches Vessel ¢». The data include flood season cruises (CR536, CR248, CR552, CR634 and CR639), and dry season cruises (CR572, CR598, CR608). Based on the temporal and spacial observations, in June and July 1999 we found a cold pool at the location where canyon topography changed sharply. We also found the density disturbance and high concentration at the same location. When the tidal current was landward in the deep canyon, we can observes upwelling in the head region of the canyon. Conversely, we can observe downwelling while the tidal current was seaward. Moreover, we observed a strong vertical flow in the dry season, which can make resuspended easily. Besides, we deployed an instrument covey, including sediment traps, Recording Current Meter (RCM), wave gauge (S700) and Laser In-Suit Scattering and Transmissiometry (LISST-100), at the location where we previously observed SSC localizes high for one month (from June to July 2000) to investigate the temporal relations among temperature, salinity, flow, and suspended particles. From this time series observation we found a coincidence between cold temperature signal and the northward flow. It showed that the cold water from deep sea was transported to the head region of the canyon by a ¡¥Pump¡¦ process. We also observed the suspended particles at the top (195m), middle (245m), and the bottom (285m) of the ocean. According to their different sizes, we found that the upper depth has more sands which were from the continental shelf, and the middle and lower depth have more silt and clay. Subsequently, we used Empirical Orthogonal Function (EOF) analysis to explain the relationship among hydrological and flow factors of the canyon. We concluded that two major modes to explain the observed relationship: Submarine canyon seasonal effect, and dynamic stability.

Sediment, an integral part of rivers and watersheds, is eroded from, stored in, and transported through various watershed components. Rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes, this sediment can be transported downstream along the bed or suspended in the water column. Most sediment measurements are focused on the component suspended in the water column. Recent advances in data collection techniques have substantially increased both the resolution and spatial scale of data on suspended sediment dynamics, which is helpful in linking small, site-scale measurements of transport processes in the field with large-scale modeling efforts. Part of this research evaluates the accuracy of the latest laser diffraction instrument for suspended-sediment measurement in rivers, LISST-SL2 for measuring suspended sediment concentration (SSC), particle size distribution (PSD), and velocity by comparing to concurrent physical samples analyzed in a lab for SSC and PSD, and velocity measured using an acoustic Doppler current profiler (ADCP) at 11 sites in Washington and Virginia during 2018-2020. Another part of this work employs a 1-D river network, bed material transport model to investigate the magnitude, timing, and persistence of downstream changes due to the introduction of sediment pulses in a linear river network. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. Then the model capability is utilized to explore the control of hydrograph structure on debris flow sediment transport through a more complex river network at different time horizons. Another part of this work investigates the effect of differences in spatial distribution of debris flow sediment input to the network by analyzing corresponding tributary and mainstem characteristics. Based on an extensive dataset, our results highlight the need for a correction of the raw LISST-SL2 measurements to improve the estimation of effective density and particle size distribution with the help of a physical sample. Simulation results from the river network model show that bed response is primarily influenced by the sediment-pulse grain size and distribution. Intermediate mixed-size pulses are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed-size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform-size pulse. While investigating the hydrologic control on debris flow simulation, this study finds that differences between transport by a 30-year daily hydrograph and simplified hydrographs were greatest in the first few years, but errors decreased to around 10% after 10 years. Our simulation results highlight that the sequence of flows (initial high/low flow) is less important for transport of finer sediment. We show that such network-scale modeling can quantitatively identify geomorphically significant network characteristics for efficient transport from tributaries to the mainstem, and eventually to the outlet. Results suggest that watershed area and slope characteristics are important to predict aggradation hotspots in a network. However, to predict aggradation and fluvial geomorphic responses to variations in sediment supply from river network characteristics more confidently, more widespread (in several other river networks) model applications with field validation would be useful. This work has important implications for river management, as it allows us to better predict geomorphically significant tributaries and potential impact on downstream locations, which are important for river biodiversity. Model results lead the way to use of simplified flow hydrographs for different timescales, which is crucial in large-scale modeling as it is often restricted by computational capacity. Finally, given the ability for reliable quantification of a high-resolution time-series of different suspended-sediment characteristics, in-stream laser diffraction offers great potential to advance our understanding of suspended-sediment transport. / Doctor of Philosophy / Rivers receive sediment from different natural and human sources, and water moves this sediment in various ways. These ways include along the bottom of the stream or suspended in the water. Quantifying suspended sediment in streams is an important step to estimate the threat to riverine environments as suspended sediments not only carry chemicals and pollutants, but also interact with the river bottom to affect the characteristics of streams. Measurement of suspended-sediment concentration and particle-size is critical for many engineering, ecological, and river-structure issues, but obtaining an accurate measurement of sediment quantity in a river is challenging. The recent advancement of a laser diffraction instrument allows us to obtain frequent measurements of suspended-sediment concentration and particle size by volume. We applied the most recent such instrument at 11 sites in Washington and Virginia during 2018-2020, along with concurrent water samples to measure suspended-sediment concentration and particle size by mass in a laboratory. Our analysis suggests that at least one supporting physical mass measurement be obtained to improve the estimation from laser measurement. Beside this site-scale measurement, we apply a large-scale river network model to estimate how sediment moves along the bed of rivers at large spatial extents. We simulate how this added sediment results in downstream changes in the amount of sediment in the river channel. We compare observed changes in the elevation of the stream bottom and sediment accumulation rates in a downstream lake to model results. Then we investigate the magnitude, timing, and persistence of downstream changes due to the introduction of added sediment by comparing the changes against a baseline condition (without the added sediment). We find that the added sediment that is half as large as on the river bottom and with a range of sizes are likely to affect the largest downstream changes because smaller sizes move quickly and larger sizes move slowly. Furthermore, added sediment that is smaller than on the river bottom and with a range of sizes help more sediment on the river bottom move than if that sediment addition all had the same particle size. We also employ this model to explore the effect of flow variation and river characteristics on sediment movement. Comparing between a 30-year flow record and simplified flow records, we show that results from simplified flow records vary initially, but errors decrease after 10 years. That is, both flow records result in similar sediment movement in the long-term. In terms of aggradation from added sediment, results show that the characteristics of elevation change of the river bottom play a vital role along with the contributing landscape area. This work has important implications for river management, as it not only allows us to accurately measure suspended sediment with an advanced instrument, but also better understand how rivers and aquatic habitat are affected by variations in added sediment.