Thesis advisor: Noah P. Snyder / Salt marshes are hotspots for biodiversity, important carbon sinks, pollutant filtration systems, and buffers which strengthen coastal resiliency. Detailed geomorphic and sedimentary observations are vital to understanding the stability and sustainability of salt marshes in response to sediment placement restoration projects. Marsh stability is dependent on the suspended sediment and nutrients that are delivered to the marsh platform by meandering tidal channels. This study observed suspended-sediment fluxes at the mouth of Southeast Creek on Gull Island at Seven Mile Island Innovation Lab in coastal, southern New Jersey. The mesotidal, almost entirely low marsh, southern Gull Island received a recent dredge placement in fall 2020 of approximately 30,600 cubic meters of sediment from the adjacent New Jersey Intracoastal Waterway. Wetland instrumentation platforms to monitor post-dredge conditions were deployed summer 2021 and were removed in summer 2022. This instrumentation measured current velocity and depth time series at all platforms and suspended-sediment concentration using acoustic backscatter techniques at the mouth of Southeast Creek. This study is motivated by understanding the ongoing transport and deposition of dredged material placed on the marsh island. I found that velocities were ebb-dominant during all conditions. Concentrations on the flood phase of the tide were approximately half the magnitude of those seen on the ebb phases of the tide for normal circumstances while elevated concentrations were observed on ebbing and flooding currents for storms. A net export of 6.27 x 105 kg suspended sediment was observed through the tidal channel for all timescales throughout the deployment period. / Thesis (MS) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

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.

This research incorporates streambank erosion and failure processes into a distributed watershed model and evaluates the impacts of climate change on the processes driving streambank sediment mobilization at a watershed scale. Excess sediment and nutrient loading are major water quality concerns for streams and receiving waters. Previous work has established that in addition to surface and road erosion, streambank erosion and failure are primary mechanisms that mobilize sediment and nutrients from the landscape. This mechanism and other hydrological processes driving sediment and nutrient transport are likely to be highly influenced by anticipated changes in climate, particularly extreme precipitation and flow events. This research has two primary goals: to develop a physics-based watershed model with more inclusive representation of sediment by including simulation of streambank erosion and geotechnical failure; and to investigate the impacts of climate change on unstable streams and suspended sediment mobilization by overland erosion, erosion of roads, and the erosion as well as failure of streambanks. This advances mechanistic simulation of suspended sediment mobilization and transport from watersheds, which is particularly valuable for investigating the impacts of climate and land use changes, as well as extreme events. Model development involved coupling two existing physics-based models: the Bank Stability and Toe Erosion Model (BSTEM) and the Distributed Hydrology Soil Vegetation Model (DHSVM). This approach simulates streambank erosion and failure in a spatially explicit environment. The coupled model is applied to the Mad River watershed in central Vermont as a test case. I then use the calibrated Mad River model to predict the response in watershed sediment loading to future climate scenarios that specifically represent local temperature and precipitation trends for the northeastern US, particularly changing trends in the frequency and magnitude of extreme precipitation. Overall the streambank erosion and failure processes are captured in the coupled model approach. Although the presented calibration of the model underestimates suspended sediment concentrations resulting from relatively small storm/flow events, it still improves prediction of cumulative loads and in some cases suspended sediment concentrations during elevated flow events in comparison to model results without including BSTEM. Increases in temperature affect the timing and magnitude of snow melt and spring flows, as well as associated sediment mobilization, in the watershed. Increases in annual precipitation and in extreme precipitation events produce increases in annual as well as peak discharge and sediment loads in the watershed. This research adds to the body of evidence indicating that streambank erosion and failure can be a major source of suspended sediment, and thereby a major source of phosphorus as well. It also shows that local climate trends in the Northeast are likely to result in higher peak discharges and sediment yields from meso-scale, high-gradient watersheds that encompass headwater forested streams and agricultural floodplains. One limitation was that we could not drive the model with meteorological data that represented changes in both temperature and precipitation, highlighting the need for improved climate predictions. This coupled model approach could be parameterized for alternative watersheds and be re-applied to answer various questions related to erosion processes and sediment transport in a watershed. These findings have important implications for resource allocation and targeted watershed management strategies.

Master of Science / Department of Biological and Agricultural Engineering / Naiqian Zhang / A real time wireless, optical sensor network was tested for long-term, remote monitoring of suspended sediment concentrations (SSC) in streams. The sensor and control board assembly was calibrated using a two-stage calibration procedure, including a pre-calibration conducted in the laboratory to adjust the sensitivity of the sensor and a field calibration using grab samples to establish an effective statistical model to predict SSC from the sensor signals. The assembly was installed in three military bases around the United States. These bases were Fort Riley, Kansas; Fort Benning, GA; and Aberdeen Proving Ground, MD. The types of water bodies and watersheds varied greatly among the sites, which allowed the sensor to be tested under versatile conditions for potential widespread use. The results show that the sensor was capable of measuring SSC at each watershed independently. The calibration model developed for each sensor can be used to predict SSC from real-time sensor data. A data processing algorithm was developed to lessen the effect of fouling and clogging on sensor signals, along with eliminating anomalies in the data gathered. The results of this study displayed meaningful prediction data that can be used to estimate SSC in a stream over a long period of time. Information obtained in this study can be used as a launching point for future work and understanding of stream processes.

<p>U radu je ispitana distribucija metala u sistemu sediment/voda na najugroženijim vodotocima u<br />AP Vojvodini. Na osnovu dobivenih podataka urađena je procena rizika na osnovu analize<br />porne vode, kiselog volatilnog sulfida i simultano ekstrahovanih metala i sekvencijalne<br />ekstrakcione procedure. Procena mobilnosti metala u sistemu sediment/voda određena je<br />promenom fizičko-hemijskih uslova u realnom sistemu (vodotok) i u laboratorijskim uslovima.<br />Ispitana je efikasnost in-situ (aeracijom sistema sediment/voda) i ex-situ remedijacije<br />sedimenta metodama termičkog tretmana i solidifikacije/stabilizacije.<br />Rezultati su ukazali da u svakom vodotoku i za&scaron;tićenoj zoni postoji lokacija u kojoj je sediment<br />barem po jednom metalu klasifikovan (holandski sistem klasifikacije sedimenata) kao zagađen<br />(klasa 3) ili izuzetno zagađen sediment (klasa 4). Generalno, kvalitet sedimenta manjih<br />vodotoka (Krivaja, Nadela, Kudo&scaron;, Veliki Bački kanal i Begej) je lo&scaron;iji u odnosu na ostale<br />ispitivane vodotoke.<br />Procena dostupnosti metala u sedimentu Velikog Bačkog kanala ukazala je da na svakom<br />ispitivanom profilu postoji minimum jedan metal i jedna metoda koja defini&scaron;e sediment kao<br />visoko rizičan. Takođe je zaključeno da je sediment na delu od 2+000 do 4+900 km zagađeniji,<br />jer postoji veći broj metala i metoda koji ga defini&scaron;u kao visoko rizičnim. Ovako dobijeni<br />rezultati ukazuju da nije dovoljan jednostavan i samo jedan pristup u oceni kvaliteta sedimenta<br />i proceni rizika koji metali mogu da ispolje u akvatičnom ekosistemu.<br />Ukazano je da pomeranje sedimenta (npr. otvaranja ustave), dovodi do promene fizičkohemijskih<br />uslova u sistemu sediment/voda, resuspenzije i transporta sedimenta. Usled ovih<br />promena povećava se dostupnost metala i dolazi do povećanja njihove koncentracije u vodenoj<br />fazi čime se znatno povećava rizik i mogućnost ispoljavanja negativnih efekata na akvatični<br />ekosistem.<br />U slučaju resuspenzije sedimenta u sistemu sediment/voda pronađena je zavisnost između<br />koncentracije metala u suspendovanim materijama i vodi od sadržaja određenih frakcija u<br />suspendovanim materijama (sadržaj organskih materija i frakcije do 63 &mu;m).<br />Remedijacione tehnike često su ekonomski neprihvatljive zbog velike zapremine zagađenog<br />sedimenta. Ukazano je da primena in-situ aeracije, omogućava smanjenje količine sedimenta<br />(čime se smanjuju tro&scaron;kovi eventualno naknadnog tretmana sedimenta), a da je tretman<br />solidifikacije/stabilizacije sedimenta sa glinom i termičke remedijacije zadovoljavjući sa<br />aspekta izluživanja metala. Dobijeni rezultati izvedenih testova izluživanja ukazali su na<br />moguću primenu ovih tretmana u pogledu re&scaron;avanja problema sedimenta koji je zagađen<br />metalima, bilo u pogledu sigurnog odlaganja na deponiju ili u smislu njegove upotrebe kao<br />dodatka pri proizvodnji građevinskog materijala (opeke), osnove za puteve, uređenje obale<br />(nasipa) itd. Na taj način mogu se znatno umanjiti tro&scaron;kovi izmuljivanja i manipulacije<br />kontaminiranog sedimenta, a sama remedijacija učiniti mnogo prihvatljivijom</p> / <p> This work investigates the distribution of metals in the sediment / water systems of the most<br /> endangered rivers in Vojvodina. Utilizing the data obtained, risk assessments are carried out<br /> based on analysis of pore water, acidic volatile sulphides and simultaneously extracted metals<br /> and sequential extraction procedure. The assessment of metal mobility in the sediment / water<br /> system is determined by the changing physical and chemical conditions in real systems<br /> (waterways) and under laboratory conditions. The effectiveness of in-situ (aeration of sediment<br /> / water) and ex-situ remediation of sediment by thermal treatment methods and solidification /<br /> stabilization are investigated.<br /> The results show that in each waterbody and protected area, certain locations have sediment<br /> which for at least one metal, is classified (by the Dutch system of sediment classification ) as<br /> polluted (class 3) or highly polluted (class 4). In general, the quality of sediment in smaller<br /> rivers (Krivaja, Nadela, Kudo&scaron;, Veliki Bački canal and Begej) is inferior to the other rivers<br /> studied.<br /> Assessment of the metals availability in the sediments of the Veliki Bački canal indicates that<br /> in each profile examined, at least one metal and one method defines the sediment as very<br /> hazardous. It is also shown that the sediment at the section from 2 +000 to 4 +900 km is the<br /> most polluted, with a number of metals and methods that define it as a high risk. The results<br /> indicate that it is inadequate to have a simple singular approach to sediment quality assessment<br /> and the assessment of the risks posed by metals detected in aquatic ecosystems.<br /> This work shows that sediment movement (e.g. from opening a sluice gate) leads to changes in<br /> the physical-chemical conditions of the sediment / water system, with resuspension and<br /> sediment transport. These changes increase metals availability and increase their<br /> concentrations in the aqueous phase, significantly increasing the posed risk and the possibility<br /> of adverse effects on aquatic ecosystems.<br /> In the case of sediment resuspension in the sediment / water system, a relationship was found<br /> between the concentration of metals in suspended matter and the concentration in the water for<br /> certain fractions of suspended matter (organic matter content and the fraction up to 63 &mu;m).<br /> Remediation techniques are often not economically viable due to the large volume of<br /> contaminated sediments involved. It is shown that the implementation of in-situ aeration<br /> reduces the amount of sediment (which reduces the costs of subsequent sediment treatment),<br /> and that solidification / stabilization treatment with clay and thermal remediation results in<br /> satisfactory remediation with respect to metals leaching. Leaching test results show the<br /> potential of these treatments to solve the problem of sediments which are contaminated with<br /> metals, either in terms of safe disposal in landfill or in terms of its use as a supplement in the<br /> production of building materials (brick), as road foundation, or for river bank reinforcement<br /> (dams), etc.. Thus, the costs of dredging and manipulating contaminated sediments can be<br /> significantly reduced, making remediation itself much more applicable.</p>

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<p>Projektet baserades på analyser av Munksjöns sediment. Munksjön är belägen i centrala Jönköping och har under många decennier omgivits av miljöbelastande verksamheter. Detta har resulterat i att sjön är så starkt förorenad att den ligger på första plats i Länsstyrelsens 30-lista över prioriterade objekt i det regionala programmet för undersökning, utredning och åtgärder av förorenade områden i Jönköpings län. Den mest förorenade delen av sjön, fiberbanken, är belägen utanför Munksjö AB som tidigare släppt ut stora mängder fibermaterial och kvicksilver med sitt processvatten från papperstillverkningen.</p><p>Analyserna har omfattat syreförbrukning och svavelinnehåll. Sedimentprovertogs från fyra lokaler i olika områden och djup. Metoden för syreförbrukningenarbetades fram genom olika försök för att få en linjär hastighet som motsvarar sjöns naturliga tillstånd. Den slutliga metoden utfördes med E-kolvar där botten täcktes med sediment och flaskan sedan fylldes med Milli-Q-vatten till kanten och förslöts med en gummipropp. Mätningar utfördes varje vardag med syrgaselektrod i två veckor, och därefter utfördes en mätning efter ytterligare en vecka. Metoden för svavelinnehåll innebar natriumhydroxidfusion och spektrofotometrisk analys.</p><p>Resultatet för syreförbrukningen visade att områden kring fiberbanken har enhögre syreförbrukningshastighet än den södra, mindre förorenade, delen avsjön. Den högsta syreförbrukningshastigheten, 4,07*10^-3 mg O₂ per gram och timme, uppmättes på sedimentet från området närmast fiberbanken. Den lägsta hastigheten, 1,61*10^-3 mg O₂ per gram och timme, uppmättes i södra delen av sjön. Syreförbrukningshastigheten bestämdes också per cm².</p><p>Resultatet för svavelinnehållet visade att en lokal vid djupområdet i sjön hade högst svavelinnehåll, 15,2 g/kg torrsubstans. Eftersom den ligger nära fiberbanken är det höga svavelinnehållet bra, då det binder till sig förekommande metaller så att de inte påverkar de levande organismerna i sjön.</p> / <p>The project was based on analyses of the sediments of Lake Munksjön in Jönköping, Sweden. Lake Munksjön is located in central Jönköping and has for many decades been surrounded by environmentally damaging enterprises. This has resulted in the lake being so strongly polluted that it is placed first on a list from The County Administrative Board over priority objects in the regional programme for inquiry, investigation and intervention of polluted areas in Jönköping County. The most heavily polluted part of the lake, the fibre bank, is situated outside Munksjö Inc. which has previously emitted large amounts of fibre and mercury with the process water from the paper mill’s manufacturing process.</p><p>The analyses have covered oxygen consumption rate and sulphur content. Sediment samples were taken from four sampling points in different areas andat different depths. The method for measuring oxygen consumption rate was developed through several tests to achieve a linear velocity that also corresponds to the natural condition of the lake. The final method was performed using E-flasks were the bottom was covered with sediment and the flask filled with Milli-Q-water and stopped with a rubber plug. Measurements were taken every weekday with an oxygen electrode for two weeks, with one extra measurement after another week. The method for analysing sulphur content included sodium hydroxide fusion and spectrophotometric analysis.</p><p>The result for oxygen consumption showed that the areas around the fibre bank have a higher oxygen consumption rate than the area in the southern, less polluted, part of the lake. The highest oxygen consumption rate, 4.07*10^-3 mg O₂ per gram dry substance and hour, was found in the sediment from the area closest to the fibre bank. The lowest rate, 1.61*10^-3 mg O₂ per gram dry substance and hour, was found in the sediments from the southern part of the lake. Oxygen consumption per cm² and hour was also determined.</p><p>The result for sulphur content showed that a sampling point by the deep area of the lake had the highest sulphur content, 15.2 g/kg dry substance. Due to the close proximity of the fibre bank the high sulphur content is good, as sulphides bind metals so they do not affect the living organisms in the lake.</p>

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