Browsing by Subject "sediment"

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Achieving Peak Flow and Sediment Loading Reductions through Increased Water Storage in the Le Sueur Watershed, Minnesota: A Modeling Approach
(2015-09) Mitchell, Nathaniel
Climate change, land clearing, and artificial drainage have increased the Minnesota River Basin’s stream flows and the rates at which channel banks and bluffs are eroded. Increasing erosion rates have contributed to higher sediment-loading rates, excess turbidity levels, and increases in sedimentation rates in Lake Pepin further downstream. These issues have motivated the discussion of flood management through either wetland restoration or the implementation of simple detention basins. This study uses the Soil and Water Assessment Tool (SWAT) to assess a wide variety of water retention site (WRS) implementation scenarios in the Le Sueur watershed in south-central Minnesota, a subwatershed of the Minnesota River Basin. Projected flows were used in conjunction with an empirical relationship developed from gauging data to assess changes in sediment-loading rates from near-channel features in the lower watershed. The WRS term is used as a general term for depressional storage areas, and sites could be made into wetlands or detention basins. Sites were delineated as topographic depressions with specific land uses, minimum areas (3000 m2), and relatively high compound topographic index (CTI) values. Contributing areas were manually measured for the WRS delineated. These contributing areas were used with existing depression depths, and different site characteristics to create 210 initial WRS scenarios. The contributing areas measured for the initial scenarios were used to create a generalized relationship between WRS area and contributing area. This relationship was used with different design depths, placement scenarios, and K values to create 225 generalized WRS scenarios. Reductions in peak flow volumes and sediment-loading rates are generally maximized by placing sites with high K values in the upper half of the watershed. High K values allow sites to lose more water through seepage, emptying their storages between precipitation events and preventing frequent overflowing. Reductions in peak flow volumes and sediment-loading rates also level off as WRS extent increases. This reduction in cost effectiveness with increasing site extent is due to the decreasing frequencies of high-magnitude events. The generalized WRS scenarios were used to create a simplified empirical model capable of generating peak flows and sediment-loading rates from near-channel features in the lower watershed. This simplified model is being incorporated into a decision-analysis model portraying a wide variety of management options in the Le Sueur watershed. This tool may better enable local stakeholders to evaluate, select, and promote management scenarios that best address the issues faced in the region.
Assessment of Lead and Beryllium Sorption To Exposed Stream Channel Sediment Under Varying Freshwater Channel Conditions
(2019-06) Pawlowski, Ethan
Purpose: Beryllium (Be) and lead (Pb) sorption is important to the utility of the radioisotopes of these elements for sediment fingerprinting. I examined the sorption of Be and Pb to exposed fluvial sediment under varying chemical conditions representative of freshwater streams draining two distinct Critical Zone environments in the eastern United States: the mid-Atlantic piedmont and heavily glaciated Great Lakes region. Materials and Methods: Batch experiments were completed using well-characterized in-stream deposit sediments collected from these two systems and varying solutions to reflect background and elevated levels of iron oxide in the form of goethite across times ranging from 0.25 to 360 h. The mid-Atlantic piedmont sediment had further treatments testing dissolved organic carbon (up to 11.86 mg L-1) and increased sediment to solution ratio (up to 8000 mg: 1 L) effects on Pb and Be sorption. Results and Discussion: Beryllium partition coefficients (Kd) ranged from a log Kd of 1.46 to 3.48 L kg-1 and Pb ranged from 0 to 5.03 L kg-1 across all treatments displaying several noticeable patterns. Two-stage sorption was observed such that sorption increased over time across all treatments and substrates. Goethite additions either enhanced or reduced sorption relative to the base treatment depending on the original sediment and mixing time. Lead sorption with the addition of 100 mg of goethite increased during shorter mixing times before being surpassed by the base treatment at longer mixing times for both the mid-Atlantic piedmont and glaciated Great Lakes sediment. Beryllium sorption was increased with the mid-Atlantic piedmont sediment whereas it was primarily decreased with the glaciated Great Lakes sediment. The 1 mg of goethite generally showed equal to or slightly enhanced sorption relative to the base treatment of both Pb and Be with the exception of Pb sorption to the Great Lakes sediment. The highest DOC concentration that I tested (11.86 mg L-1) retained a greater amount of Be and Pb in solution compared to other treatments after 360 h. Increasing the sediment to solution ratio showed decreased partition coefficients across all analogous times for Be compared to the base treatment whereas Pb sorption surpassed the unaltered treatment after 24 h. Conclusions: It is not recommended to use either 7Be or 210Pb in fluvial systems with high background concentrations of DOC because the DOC was shown to inhibit sorption to sediment surfaces and it could produce erroneous results in sediment fingerprinting studies unless that inhibition or loss is accounted for. The goethite treatments produced mixed results and further research is needed to parse out conditions that enhance or inhibit the sorption of fallout radionuclides in the presence of stream sediments with varying amounts of organic matter occlusion of surface binding sites. Increased sediment to solution ratios increased sorption of Pb suggesting that Pb would be a conservative tracer in fluvial systems with high sediment delivery. These results suggest that fluvial sediment mineralogy, organic matter concentration, and biogeochemical cycling of common stream chemical constituents may play a role in the mobilization or retention of these two trace metals and alter their utility for sediment fingerprinting.
C-59, Geologic Atlas of Pipestone County, Minnesota
(Minnesota Geological Survey, 2024) Retzler, Andrew J.; Mayer, Jordan A.; Bradley, Margeurite C.; Chandler, Val W.; Severson, Allison R.; Jirsa, Mark A.; Conrad, Daniel R.; Gowan, Angela S.; Van Berkel, Jordan T.; Francis, Sarah W.
A County Geologic Atlas project is a study of a county's geology and its mineral and groundwater resources. The information collected during the project is digitized and used to develop maps and database files. The map information is formatted as geographic information system (GIS) files with associated databases. The maps and reports are also reproduced as portable document files (PDFs).
Characterization of streams and rivers in the Minnesota River Basin Critical Observatory: water chemistry and biological field collections, 2013-2016
(2017-09-06) Dolph, Christine, L.; Hansen, Amy, T.; Kemmitt, Katie, L.; Janke, Ben; Rorer, Michelle; Winikoff, Sarah; Baker, Anna; Boardman, Evelyn; Finlay, Jacques, C.; dolph008@umn.edu; Dolph, Christine, L.
This dataset was collected to inform the Water, Sustainability and Climate Minnesota River Basin Observatory, and was supported by the National Science Foundation under Grant No. 1209402 Water, Sustainability and Climate (WSC) – Category 2, Collaborative: Climate and human dynamics as amplifiers of natural change: a framework for vulnerability assessment and mitigation planning. The dataset contains point locations, watershed areas and water quality information for 231 ditch, stream, river and wetland sites located in the Le Sueur River, Chippewa River, Cottonwood River, Cannon River, Wantonwan River and Blue Earth River basins of Minnesota. Study sites ranged in size from 1st order ditches and streams to an 8th order river. Each of these sites was sampled at least once between 2013-2016 (most sites were sampled multiple times) for one or more of the following parameters: 1) water chemistry (total dissolved nitrogen, nitrate-N, nitrite-N, ammonium-N, particulate nitrogen, soluble reactive phosphorus, total dissolved phosphorus, particulate phosphorus, total phosphorus, dissolved organic carbon, dissolved inorganic carbon, particulate carbon, chlorophyll a, total suspended solids, volatile suspended solids, delta-H-2 and delta-O-18 stable isotopes of site water, specific UV absorbance (SUVA) of site water, fluorescence index (FI) of site water); 2) stable isotopes (delta-C-13, delta-N-15, delta-H-2) of invertebrate consumers, particulate carbon and potential food sources; 3) denitrification rates and characteristics of benthic sediment in agricultural drainage ditches; and 4) stream discharge. This dataset also includes spatial data files containing study site locations and watershed areas delineated for each site.
Data for "Reducing High Flows and Sediment Loading through Increased Water Storage in an Agricultural Watershed of the Upper Midwest, USA"
(2018-08-08) Mitchell, Nate A; Kumarasamy, Karthik; Cho, Se Jong; Belmont, Patrick; Dalzell, Brent; Gran, Karen; mitc0388@d.umn.edu; Mitchell, Nate A; University of Minnesota Duluth Geomorphology Lab
Climate change, land clearing, and artificial drainage have increased the Minnesota River Basin’s (MRB) stream flows, enhancing erosion of channel banks and bluffs. Accelerated erosion has increased sediment loads and sedimentation rates downstream. High flows could be reduced through increased water storage (e.g., wetlands or detention basins), but quantifying the effectiveness of such a strategy remains a challenge. We used the Soil and Water Assessment Tool (SWAT) to simulate changes in river discharge from various water retention site (WRS) implementation scenarios in the Le Sueur watershed, a tributary basin to the MRB. We also show how high flow attenuation can address turbidity issues by quantifying the impact on near-channel sediment loading in the watershed’s incised reaches. WRS placement in the watershed, hydraulic conductivity (K), and design depth were varied across 135 simulations. The dominant control on site performance is K, with greater flow reductions allowed by higher seepage rates and less frequent overflowing. Deeper design depths enhance flow reductions from sites with low K values. Differences between WRS placement scenarios are slight, suggesting that site placement is not a first-order control on overall performance in this watershed. Flow reductions exhibit power-law scaling with exceedance probability, enabling us to create generalized relationships between WRS extent and flow reductions that accurately reproduce our SWAT results and allow for more rapid evaluation of future scenarios. Overall, we show that increasing water storage within the Le Sueur watershed can be an effective management option for high flow and sediment load reduction.
Experimental alluvial-river and landsliding response to base-level fall
(2020-04-24) Beaulieu, Olivia P; Wickert, Andrew D; Witte, Elizabeth D; Tofelde, Stefanie; awickert@umn.edu; Wickert, Andrew D; Saint Anthony Falls Laboratory; Department of Earth & Environmental Sciences; Universität Potsdam
We observed the incisional response of an alluvial river to base-level fall. We conducted the experiment in a 3.9 × 2.4 × 0.4 m box that we filled with uniform 0.140±0.04 mm sand. We dropped base level by lowering the elevation of an "ocean" pool at the river outlet. As the initial condition, we cut a 10±2 cm wide channel to a steadily increasing depth, from 3±0.5 cm at the inlet, where we supplied water and sediment, to 10±1 cm at the outlet. Input water and sediment discharge were 0.1 L/s and 0.0022 L/s (including pore space), respectively. As base level fell, the river incised and migrated laterally, forming a valley with abandoned terrace surfaces and walls that failed in mass-wasting events as they were undercut. We include a control case with no base-level fall, as well as experiments with 25 mm/hr, 50 mm/hr, 200 mm/hr, 300 mm/hr, and 400 mm/hr of base-level fall. We supply georeferenced overhead photos (0.89 mm resolution, every 20 seconds), digital elevation models (DEMs, 1 mm horizontal resolution, every 15–30 minutes), videos generated from the overhead photos, mapped landslides in GIS vector area (polygon) format, and landslide attributes. Relevant code to process and plot the data, as well as further information on grain size, is available from GitHub and Zenodo.
In search of the phosphorus legacy: merging hydrological and biogeochemical approaches to understand phosphorus dynamics in streams.
(2022-09) Pawlowski, Ethan
Nutrient and sediment pollution of surface waters remains a critical challenge for improving water quality. Phosphorus and sediment export to lakes and rivers has resulted in diminished water quality placing drinking water supplies, human health, recreation opportunities, and aquatic ecosystems at risk. Understanding both biogeochemical processing and transport of phosphorus and fine sediments (a major sorbent of phosphorus) in stream channels is required to understand the legacy effects of agricultural land management decisions and the effects of mitigation strategies. I focused my thesis on sediment and phosphorus dynamics in Midwestern USA watersheds by examining three parts: (1) using the Nutrient Tracking Tool (NTT) with physical site characteristics to target areas for revegetation, and to compare this field-scale tool with watershed export data; (2) a combination of tracer experiments with transient-storage modeling and biogeochemical assessment to understand phosphorus and sediment dynamics at base flow within Plum Creek, WI; and (3) the inventory and assessment of fallout radionuclides as a potential sediment fingerprint in the upper Midwest. To assess potential load reductions using revegetation, the nutrient tracking tool (NTT) was used with a scoring system to identify areas where vegetation mitigation could be implemented within three selected Fox River, WI sub-watersheds. A corn-soybean rotation, an implementation of a 10-m vegetated buffer, a full forest conversion, and tiling were modeled and assessed. The corn-soybean results were aggregated and compared to watershed level gauge data in two sub-watersheds. Edge of field data was compared to modeled results using multiple parameterization schemes. The agricultural areas that scored higher and were untiled showed greater potential nutrient and sediment export reduction when vegetation mitigation was implemented in the model. Aggregated watershed results showed disparities between modeled and measured phosphorus exports but modeled sediment export fell within observed gauge data ranges. Field specific parameter adjustments resulted in more accurate modeled results compared to measured edge of field data, but needed further refinement. Targeted mitigation using vegetation based on the scoring system was shown to be a helpful tool for nutrient and sediment reductions when modeled. Using a field scale model aggregated to the watershed scale presents tradeoffs regarding processes found beyond the edge of field. To understand in-channel processes, a fluorescent fine particle surrogate, bromide, and phosphate were injected and sampled under base flow conditions within two stream reaches that are representative of the lower and upper Plum Creek, WI, watershed. Grab samples were analyzed and breakthrough curves were modeled utilizing the one-dimensional transport with inflow and storage (OTIS) model. Sediment and stream water samples were analyzed for equilibrium phosphate concentration determination to gain a better understanding of phosphorus dynamics and the potential time lags associated with phosphorus delivery from agricultural fields to downstream water bodies when used in conjunction with transport parameters determined by OTIS. Results indicate sediments within Plum Creek have a large potential to sorb dissolved phosphorus entering the stream channel and reduce dissolved loads at the individual reach scale. These results suggest a large potential for discrepancies between mitigation implementation and noticeable water quality improvements when considering base flow transport and storage metrics. Fallout radionuclides beryllium-7 and lead-210 were measured at the St. Paul Weather Station, MN and at the Marcell Experimental Forest by collecting bulk deposition. Event-based sampling was completed in St. Paul whereas weekly sampling was done at the Marcell Experimental Forest in order to compare results with data from the National Atmospheric Deposition Program. Results showed that neither beryllium-7 nor lead-210 were correlated with precipitation inputs, but showed seasonal patterns with peak deposition occurring during the summer months. Beryllium-7 was weakly correlated with precipitation at the Marcell Experimental Forest and showed some correlation with sulfate and chloride deposition but the correlation was not strong enough that either sulfate or chloride could be used as a predictor of beryllium-7 deposition. Cumulative deposition followed a linear trend and could be useful for predicting deposition or filling data gaps in areas with scant depositional records or in remote settings.
Increasing transparency in the implications of variability in contaminant partitioning
(2021-11) Brennan, Amanda
Porewater concentrations of contaminants in aquatic sediment (Cfree) are often measured with passive sampling methods (PSM) to quantify the true contaminant activity more accurately. This Cfree correlates more closely with uptake and toxicity in benthic organisms than solid-phase contaminant concentrations (Ctotal) or model predictions of Cfree from Ctotal, and thus represent a better indicator of bioavailability and risk. While sediment managers rely on accurate measures of Cfree to estimate risk, they also rely on Ctotal as the basis for defining and monitoring clean-up goals for restoration and remediation. In real environments, the partitioning of contaminants between Cfree and Ctotal is highly variable among samples collected, even those in close proximity. The variability is due to intractable differences in adsorption capacity among different carbon phases; however, this variability can provide a quantitative basis for converting between Ctotal and Cfree in a stochastic approach. The stochastic approach can be used to estimate the likelihood that Ctotal would exceed a Cfree-based biological threshold in the case in which Cfree was not measured (or vice versa). When the stochastic approach to bioavailability is implemented at the beginning of the risk assessment process, screening-level evaluations can be refined and possibly reduce the number of sediments in which additional testing (e.g. toxicity testing) is required to elucidate risk. This dissertation uses field-collected measurements and statistical modeling to illustrate how PSM-measured Cfree and a stochastic view of contaminant partitioning can provide a more nuanced way of understanding the implications of variability in contaminant partitioning. This view can support more transparency in decision making at contaminated sediment sites.
Investigating the Use of Fallout Radionuclides Beryllium-7 and Excess Lead-210 as Short-Term Stream Sediment Chronometers in the Agricultural Upper Midwest, USA
(2023) Hankins, Ryan
Sediment pollution from agricultural fields is a concern for surface water quality in the Upper Midwest even with best management practices in place to prevent field erosion. Legacy stores of previously eroded field sediment may build up in streams over time and lead to persistent water quality degradation. It is thus important to understand sediment settling and resuspension behavior in streams. In the first chapter of my thesis, I use the fallout radionuclides beryllium-7 and excess lead-210 to estimate the relative time since precipitation exposure, or “age”, of suspended sediment at various points in a stream system in eastern Wisconsin during storms. The purpose of this work was to characterize patterns of sediment transport in Plum Creek. From the first chapter it was clear that the sediment aging technique I used is heavily influenced by the variation in radionuclide deposition by precipitation. Depositional fluxes and concentrations of beryllium-7 and excess lead-210 in rain and snow are assumed to be reasonably well-correlated in many sediment aging studies that use these nuclides. However, growing evidence suggests the depositional patterns of these FRNs vary with numerous environmental conditions. I expanded on these findings by using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to trace the back trajectories for storm series for which the beryllium-7 and lead-210 activities of precipitation were measured. I used this analysis to fill knowledge gaps that affect the sediment aging technique I employed in my first chapter.
Long-Term Population Growth And Food Web Impacts Of The Spiny Water Flea (Bythotrephes Longimanus) Revealed From Sediment Records
(2020-03) DeWeese, Nichole
The spiny water flea (Bythotrephes longimanus) is an invasive predacious zooplankton species that has well-documented impacts on aquatic food webs. However, few studies have examined long-term population dynamics and food web impacts of the species. This study used Bythotrephes subfossils, as well as subfossils from potential prey and competitor taxa (bosminids, daphniids, Simocephalus, and Leptodora kindtii) and pigment concentrations in 210Pb dated sediment cores from Mille Lacs Lake and Kabetogama Lake in Minnesota, USA to estimate first invasion and population growth of Bythotrephes and corresponding impacts on the lower food web. Bythotrephes evidence was found nearly 100 years prior to first detection in each lake, potentially making these lakes the earliest invaded lakes in North America. Bythotrephes subfossils slowly accumulated until around 1990, when accumulation rates rapidly increased. Two-piece linear models provided a good fit for Bythotrephes annual accumulation rates (a proxy for population size), and modelled lag phases lasted approximately 70 years in each lake. Of the native zooplankton species, Bosmina was the only species group that declined in correspondence with Bythotrephes population growth. Bosmina antennules and mucros were measured to analyze if morphological changes occurred as Bythotrephes populations grew, but these feature lengths did not consistently change over time. Sediment pigment concentrations did not increase with Bythotrephes population growth as expected in either lake. This research suggests that 1) Bythotrephes could be present in lakes decades before detection in zooplankton net samples, 2) populations take several decades to overcome lag phases, and 3) that other ecosystem factors may be more important than Bythotrephes in driving long-term food web changes in these lakes.
Measurement of Antibiotics in Water and Sediment: Determining Minnesota's Antibiotic Footprint
(2020-05-22) Frankson, Lara E; Arnold, William A; arnol032@umn.edu; Arnold, William A; University of Minnesota, Department of Civil, Environmental, and Geo- Engineering
Antimicrobial resistance is considered to be one of the greatest global public health threats of the 21st century. The discharge of antibiotics into the environment may increase antimicrobial resistance as well as disrupt proper ecosystem functioning. Thus, evaluating the antibiotics present in the environment as well as the contributing factors to their presence in the environment will provide invaluable information for improving water quality and protecting human and ecosystem health. This dissertation investigates the presence of antibiotics in water and sediment in both wastewater treatment effluent and agricultural animal affected areas throughout Minnesota. This is to provide a fine scale as well as a broadscale approach with multiple samples at each site at sites across Minnesota. Additionally, a snapshot of the antibiotics present and long term trends of antibiotics in the environment are investigated through water and sediment samples, respectively.
Measurement of Antibiotics In Water and Sediment: Determining Our Antibiotic Footprint
(2020-06) Frankson, Lara
Antimicrobial resistance is considered to be one of the greatest global public health threats of the 21st century. The discharge of antibiotics into the environment may increase antimicrobial resistance as well as disrupt proper ecosystem functioning. Thus, evaluating the antibiotics present in the environment as well as the contributing factors to their presence in the environment will provide invaluable information for improving water quality and protecting human and ecosystem health. This dissertation investigates the presence of antibiotics in water and sediment in both wastewater treatment effluent and agricultural animal affected areas throughout Minnesota. This is to provide a fine scale as well as a broadscale approach with multiple samples at each site at sites across Minnesota. Additionally, a snapshot of the antibiotics present and long term trends of antibiotics in the environment are investigated through water and sediment samples, respectively.
The morphodynamic influence of base-level change and waves on lake sediment
(2018-10) LaGarde, Michelle
Lakes continuously accumulate sediment, a process that has been ongoing since their formation. The sediment consists of soil particles and biological remains that runoff from the watershed and into the lake. The sediment may also contain particles from aeolian transported material from the “airshed” and biological and inorganic precipitated minerals. Thus, lake sediment is a continuous environmental archive, containing information about the history of the lake, and its surroundings. Unfortunately, lake sediment is subject to remobilization and mixing due to a variety of sediment transport processes, such as mass wasting. There has been limited research on how base-level change influences mass wasting, in particular, slope failure. Some studies suggest slope failures are correlated with base-level fall and/or base-level rise, while others suggest they don’t correlate at all. To address this controversy, I conducted flume experiments at the Saint Anthony Falls Laboratory (SAFL) to observe slope failure in sediment mixtures containing four different walnut-shell/kaolinite ratios. Three base-level change rates were tested, producing 12 base-level change experiments. Another set of experiments was also designed to investigate what effect, if any, the addition of waves would have on mass flow. Video recordings were taken during each experiment and were analyzed to study the geometry of each profile before and after base-level change had occurred. Results suggest that there is consistent sediment transport when waves are present, aiding in the transportation of walnut-shell downslope. Without waves, transport is limited, and the clinoform is subject to compaction, or slump formation, depending on clay content. This difference depends heavily on a sediment’s composition, where hydraulic conductivity (K) plays an important role in water transmission through the clinoform. My experiments suggest that slope failures in the field would occur in lake sediment with higher clay content. Base-level change itself has no effect on the occurrence of failures, but slope failures should occur during base-level change if clay content is high. With only base-level change, we can expect to see compacted lake sediment with lower clay content (~15-33% clay). Slope failures (slumps) occur in lake sediment with higher clay content (~50%). With the presence of waves, however, wavebase plays an important role in sediment transport. Wave-base greatly influences sediment transport downslope, which is seen in my experimental work. This suggests that waves in the field also transport lake sediment downslope while washing away any finegrained particles (i.e. clay).
OFR10-01, Sediment Source Apportionment to the Lake Pepin TMDL--Source Characterization
(Minnesota Geological Survey, 2010) Jennings, Carrie E.
The MGS portion of the project was specifically designed to help guide the selection and interpretation of lake-cores planned by the Science Museum of Minnesota that were intended to serve as reference sites (reference lakes) to document recent and historic erosion rates in the agricultural areas of the Middle Minnesota watershed. A second goal was to better predict the texture of surface sediment for input to a watershed model being used to address turbidity issues by the MPCA.
OFR18-03, Core Descriptions, Borehole Geophysics, and Unit Interpretations in Support of Phase I and II USGS Hydrologic Properties of Till Investigation
(Minnesota Geological Survey, 2018) Staley, Amie E; Wagner, Kaleb; Nguyen, Maurice; Tipping, Robert
This report summarizes the contributions of the Minnesota Geological Survey (MGS) to a three-year study conducted in two phases – Environmental and Natural Resources Trust Fund (ENRTF), M.L. 2014, Chp. 226, Sec. 2, Subd. 03h, and ENTRF, M.L. 2016, Chp. 186, Sec. 2, Subd. 04h, led by the United States Geological Survey (USGS) Minnesota Water Science Center, which seeks to further knowledge on the sources and rates of recharge to confined aquifers set within buried-valley sequences in Minnesota. Six cores (including one collected for a previous study) of unconsolidated Quaternary deposits were extracted from known confined glacial aquifer settings, in four regions across Minnesota, in order to target variability in the material properties of the aquitards that confine them.
OFR21-02, Pilot Multi-county Modeling Synthesis For Bonanza Valley Groundwater Management Area
(Minnesota Geological Survey, 2019) Tipping, Robert G
This report reviews current subsurface unconsolidated sediment modeling methods at MGS to address how model application to regional investigations can be improved in several fundamental ways: 1.) reduce errors and redundancy in final subsurface models that are artifacts of the modeling process itself, including linearity along cross-section lines in both elevation and map unit extent, unintended gaps in map units between cross sections, and lithostratigraphic formation subdivision to accommodate sand bodies within formations ; 2.) quantify uncertainty in modeling subsurface sand and gravel; and 3.) provide a work plan and method for subsurface models to remain current within shorter time frames as new data become available.
Phosphorus-sediment interactions and their implications for watershed scale phosphorus dynamics in the Le Sueur River Basin
(2018-08) Baker, Anna
Phosphorus is a leading pollutant of global surface waters, and sediment is a known driver of phosphorus loading to downstream receiving waters. This master’s thesis investigates sources and dynamics of phosphorus in the Le Sueur River basin in southern Minnesota, a highly agricultural watershed whose glacial history has rendered it vulnerable to massive erosion, and which contributes disproportionately to downstream sediment and phosphorus loading. We develop a mass balance for sediment-derived phosphorus, incorporating sediment-total and dissolved phosphorus into a robust sediment budget describing sources and sinks of sediment to this system. This budget explores the extent to which agricultural top soil and upland ditch-banks, and eroding near channel features such as bluffs, stream banks, and ravines, can be implicated for phosphorus loading to this basin. Further, we explore the extent to which in-stream processing alters the fate, bioavailability, and persistence of phosphorus in this system via the incorporation of sorption experimental data into this budget. Our results show that fine (silt and clay sized) source sediment can only account for at most 24% of the total phosphorus exported from the Le Sueur River. These results suggest that sediment and phosphorus sources are largely decoupled, and that if we managed 100% of fine sediment erosion we would only reduce phosphorus loading by 24% or less. Sorption tests were used to examine the role of fine sediment as a source or sink for phosphorus. Results of these tests demonstrate that agricultural sediments donate phosphorus, while near channel sediments bind phosphorus from the water column. Incorporation of these results into our budget indicates that 2-24% of total phosphorus may be in particulate form as a result of in-stream equilibrium processes between sediment and dissolved orthophosphate in the water column. Sorption of dissolved phosphorus by sediment may depress dissolved phosphorus load by as much as 31%. These results point to the importance of understanding dissolved phosphorus source and dynamics, and to the management of both sediment and dissolved phosphorus source being critical to addressing excess phosphorus in this basin.
RECOVERY OF SEDIMENT CHARACTERISTICS IN MORAINE, HEADWATER STREAMS OF NORTHERN MINNESOTA AFTER FOREST HARVEST
(2010) Merten, Eric, C.; Hemstad, Nathaniel, A.; Kolka, Randall, K.; Newman, Raymond, M.; Verry, Elon, S.; Vondracek, Bruce
We investigated the recovery of sediment characteristics in four moraine, headwater streams in north-central Minnesota after forest harvest. We examined changes in fine sediment levels from 1997 (preharvest) to 2007 (10 years postharvest) at study plots with upland clear felling and riparian thinning, using canopy cover, proportion of unstable banks, surficial fine substrates, residual pool depth, and streambed depth of refusal as response variables. Basin-scale year effects were significant (p < 0.001) for all responses when evaluated by repeated-measures ANOVAs. Throughout the study area, unstable banks increased for several years postharvest, coinciding with an increase in windthrow and fine sediment. Increased unstable banks may have been caused by forest harvest equipment, increased windthrow and exposure of rootwads, or increased discharge and bank scour. Fine sediment in the channels did not recover by summer 2007, even though canopy cover and unstable banks had returned to 1997 levels. After several storm events in fall 2007, 10 years after the initial sediment input, fine sediment was flushed from the channels and returned to 1997 levels. Although our study design did not discern the source of the initial sediment inputs (e.g., forest harvest, road crossings, other natural causes), we have shown that moraine, headwater streams can require an extended period (up to 10 years) and enabling event (e.g., high storm flows) to recover from large inputs of fine sediment.
River Bank Erosion in the Minnesota River Valley
(2015-12) Kessler, Andrew
Sediments remain one of the major causes of water quality impairments in the United States. Although soil erosion from agricultural lands has been viewed as the major source of sediment to rivers and lakes, in many watersheds, river banks are also contributing a significant amount of sediments to surface waters. Currently, limited research has been reported on the methods to quantify and to understand the causes and mechanisms that control river bank erosion. The research reported in this dissertation utilized emerging technologies and novel procedures to investigate (1) historic and modern rates of river bank erosion in the Blue Earth River Basin, a major source of sediment to the Minnesota River and Lake Pepin; (2) methods to delineate seeps (a major mechanism of bank sloughing) on the face of river banks and their impact on bank erosion; and (3) water retention capacity of depressional areas across the prairie pot hole regions of the Greater Blue Earth River Basin. The results of this research indicate that river bank erosion is and has been a major source of sediment in the Greater Blue Earth River Basin even before European immigrants began to settle in Minnesota; the return intensity from light detection and ranging (Lidar) can be used to delineate seepage areas on river banks and this along with lidar generated digital elevation model provides an opportunity to quantify seepage impacts on bank erosion; and the historic storage capacity of a prairie pothole landscape such as the Greater Blue Earth River Basin is relatively small (152 mm) and concentrated only in large depressions. This suggests that restoration of depressional areas will unlikely have a major impact on river flows without additional modifications.
Sand particle kinematics under different transport conditions
(2019-07-24) Guala, Michele; Liu, Mingxiao; mguala@umn.edu; Guala, Michele; St Anthony Falls Laboratory, University of Minnesota
The kinematics of sediment particles is investigated by non-intrusive imaging to provide a stochastic description of bedload transport in conditions near the threshold of motion. In particular, we focus on the cyclic transition between motion and rest regimes to quantify the statistical properties of the particles waiting times, inferred to be responsible for anomalous diffusion, and so far elusive. The probability distributions of the particle step time and step length, streamwise and spanwise velocity, acceleration, and waiting time are quantified experimentally. Results suggest that variables associated with the particle step motion are thin-tailed distributed while the waiting times exhibit a power law distribution. The experimental results shown here, under five different transport conditions, describe grain scale kinematics and dynamics at increasing shear stress and represent a benchmark dataset for the stochastic modeling of bedload transport.

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