Browsing by Subject "Erosion"

Now showing 1 - 17 of 17

Anthropogenically-intensified erosion in incising river systems.
(2012-07) Day, Stephanie S.
Anthropogenic alterations to landscapes, such as agriculture, can lead to accelerated erosion in incising (or incised) rivers threatening infrastructure and property, and causing unnaturally high sediment loads, which threaten ecosystems. Steep bluffs and ravines are characteristic landforms in incising river systems, and by understanding erosion on these landforms we can begin to mitigate the impacts of the altered landscape. The Le Sueur River watershed, in southern Minnesota, provides an ideal location for studying the impacts of agricultural land-use on erosion in an incising river. Agriculture in this watershed is made possible through the use of tile drains, which remove water from the uplands and route it directly into ravines or the river, reducing the water that pools on the landscape and increasing flows in the river. Using terrestrial laser scanning (TLS) and aerial photographs, bluff erosion rates in the Le Sueur River were measured and used to develop a watershed scale sediment budget. In the Le Sueur River bluffs account for 56 ± 12% of the 2000-2010 average measured total suspended solids load. These data were also used to interpret how changes in land-use and climate have accelerated bluff retreat in this watershed. The data collected paired with field observations show that over-steepening at the bluff toe drives bluff retreat, yet weakening due to groundwater seeps and freeze-thaw also contributes to erosion. The increases in flow rates and volumes brought on by tile drainage in this watershed have resulted in increased bluff erosion. To study ravine response to changing overland flow hydrology, brought on by tile drainage, small physical experiments were used to measure how changing the delivery rate of a fixed volume of water impacts erosion. The results of these experiments showed that regardless of flow rate the volume of sediment removed remained the same, suggesting that the tile drains installed in the Le Sueur River watershed may have decreased ravine growth. Results of each of these projects independently improves our understanding of bluff erosion and ravine growth processes, yet combined they provide insight into how changing hydrology impacts erosion throughout an incising watershed. While agricultural landscape alterations, especially tile drains, have decreased ravine growth they have resulted in increased bluff erosion. Because bluffs in the Le Sueur River watershed account for more than half of the total sediment load, there is a net increase in sediment loads as a result of anthropogenic landscape alterations.
Assessment of the Impacts of Various Grazing Management Strategies on Southern Minnesota Stream Channels
(2018-05) Kim, Seongjun
Stream riparian corridors are inherent to many farms in southern Minnesota. They are complex and diverse ecosystems, provide transportation for drainage from agricultural fields, and contribute to the quality of the larger watershed to which they belong. However, much of the 3.5 million miles of rivers in the United States are impacted, with sedimentation and excess nutrients being the most significant causes of degradation. The agricultural areas of southern Minnesota commonly use stream corridors as pasture since they are generally unsuitable for crops and provide a natural source of water for livestock. Traditional methods of grazing livestock can cause reduced vegetative cover, compacted soils, water contamination, sedimentation, and eroded banks. Managing livestock by limiting the location and duration of their grazing has seen some success in reducing the impact compared to conventional grazing methods. My research aims to further determine the impacts various grazing management strategies have had on streams. Geomorphic data from four sites across three streams are analyzed to evaluate effects of current grazing strategies and changes in grazing strategies. Grassed and wooded areas are also compared, as grazing directly influences the vegetative communities. The results suggest that both managed and grazing exclusion sites showed healthier channels than conventional grazing sites did, and that grassed bank areas contribute more to channel stability than wooded bank areas. In certain situations, managed grazing has the potential to be more beneficial to stream channel health than the prohibition of grazing.
Compaction Remediation for Construction Sites
(Minnesota Department of Transportation, 2008-01) Chaplin, Jonathan; Min, Min; Pulley, Reid
The goal of this project is to develop a sub-soiling regimen that will enhance and be compatible with existing erosion control measures. This project is important in minimizing the effect of construction-induced compaction on the urban and rural landscape. This activity, if successful, will become a building block for use in Best Management Practices (BMPs) that will ensure full vegetative growth post construction, and save on the cost of reapplication of erosion control measures. For a good comparative study, several sites were selected for typical slope and soil type. The study shows that there are low cost benefits to deep tillage of ROW. Heavy clay soils are problematic in that improvements in infiltration could not be detected after a single tillage operation. In lighter sandy soils, the benefits of tillage are such that significant increases in infiltration can be gained following a single pass tillage operation. The differences in tillage implement used could not be detected. The post-tillage aesthetic appeal when using a non-inverting plow (Kongskilde Paraplow) was apparent in this study. The vegetation was largely undisturbed following tillage, and this would be beneficial in preventing erosion on slopes. The ripper and the DMI inverted more soil, and therefore the tillage operation was less appealing to motorists. The relatively low cost of ownership and operation for the tillage is overshadowed by the high land cost when new roads are constructed. Tillage would be beneficial on lighter soils, however the "utility congestion" that is likely in such a scenario would make machinery management difficult.
Development and Evaluation of Effective Turbidity Monitoring Methods for Construction Projects
(Minnesota Department of Transportation Research Services & Library, 2014-07) Perkins, Rebekah Lynn; Hansen, Brad; Wilson, Bruce N.; Gulliver, John S.
Various agencies have discussed the possibility of using turbidity as an effluent standard for construction site. Turbidity monitoring can be difficult for dynamic construction sites. This project investigated turbidity relationships for conditions of Minnesota and developed protocols for the design and installation of cost-effective monitoring systems. Turbidity characteristics of fourteen different soils in Minnesota were investigated using the laboratory protocols. Trends in turbidity with sediment concentrations were well represented by power functions. The exponent of these power functions was relatively constant between soils and the log-intercept, or scaling parameter varied substantially among the different soils. A regression analysis for the scaling parameter was a function of percent silt, interrill erodibility, and maximum abstraction. A power value of 7/5 was chosen to represent all soils. The field studies were also used to develop turbidity monitoring systems that would be adaptable to construction sites and to collect turbidity data on construction site runoff. Construction site turbidities often exceeded 1000 NTUs and sometimes surpassed 3000 NTUs.
Erosion Forum Summary and Resource Guide
(2009) North Shore Management Board (NSMB)
This document gives a brief history and background to soil and bank erosion along the north shore of Lake Superior. It summarizes presentations made during the forum, and gives examples of erosion control projects near Two Harbors. The report gives practical examples and suggestions for planners, local governments and developers.
Erosion Hazard of Minnesota's Lake Superior Shoreline
(University of Minnesota. Minnesota Sea Grant, 1990) Johnston, Carol; Sales, James; Bonde, John; Aunan, Tim; Raby, Richard
The rugged beauty of bedrock cliffs rising from the waters of Lake Superior creates a memorable impression of Minnesota's Lake Superior coast. But unlike the resistant bedrock that creates beautiful vistas, some sections of the Minnesota shoreline are erosive sand or clay banks. Buildings and roads built in these areas are threatened by the gradual wearing away of the coast by the powerful waves of Lake Superior. While shoreline erosion can only be prevented at great expense, economic losses are minimized by knowing where and how fast shoreline erosion is likely to occur. Future problems are avoided by locating new structures and septic fields back from the bluff line to allow for the erosion that is expected to occur. Fortunately, the Minnesota Lake Superior shoreline has had relatively little development in comparison to other Great Lakes shorelines, so good planning can prevent future problems. There are several ways to identify erosion hazard areas. On-site monitoring of erosion is the most precise way to measure short-term erosion rates, but can be misleading as an indicator of long-term hazard if unusual conditions during the monitoring period cause uncharacteristically high or low erosion rates. Measuring shoreline recession from a time sequence of maps or aerial photos provides longer-term erosion rates. Shoreline geology also provides an indication of erosion hazard, because some types of geologic materials are more resistant to erosion than others. This study combined the latter two methods to produce maps of long-term shoreline erosion potential.
Erosion Study Aerial Photographs and Documentation
(1990) Johnston, Carol; Sales, James; Bonde, John; Aunan, Tim; Raby, Richard
Aerial photographs and documentation related to: Johnston, Carol; Sales, James; Bonde, John; Aunan, Tim; Raby, Richard. (1990). Erosion Hazard of Minnesota's Lake Superior Shoreline. University of Minnesota. Minnesota Sea Grant. Retrieved from the University of Minnesota Digital Conservancy, https://hdl.handle.net/11299/189149.
Factors influencing roadside erosion and in-stream geomorphic stability at road-stream crossings for selected watersheds, North Shore, Minnesota, USA.
(2012-07) Dutton, Patricia Danielle
Currently, 10 major watersheds in Minnesota's North Shore exceed state water quality standards for turbidity (10 NTU) a surrogate for total suspended solids. In this region, recent anthropogenic disturbances can be attributed to roadway construction and maintenance. The presence of roadways can pose a serious threat to ecosystem functions, altering local and landscape hydrology, fragmenting riparian areas, and delivering chemical pollutants and suspended sediments to nearby waterways via surface runoff and seepage. This study examined the current extent of hydrologic connectivity between roads and streams, by investigating roadside erosion for select sub-watersheds within the North Shore watershed of Minnesota, USA. Surveys were conducted at 54 road-stream crossings along 12.2 km of roadways in the summer of 2010. A Road-stream connectivity analysis found roads increase the drainage density of North Shore watersheds by approx. 1.45-9.47%. Measureable erosion was observed at 64.8% of survey sites (gully, or rill) totaling 93.26 m3, with an average loss per site of 1.73 m3, or 7.64 m3/km. Traffic intensity, road construction, parent material, stream order, soil k factor, hillslope gradient best predicted erosion for this dataset using logistic regression at local and watershed wide scales. The effect road-stream crossings as a localized stress on stream stability was also examined at seven sites, using Rosgen level I classification and Pfankuch stability metrics. This qualitative analysis of stream stability upstream and downstream of road-stream crossing structures indicated study road-stream crossings are causing localized instability. Assessments indicated stream segments are negatively impacted both upstream and downstream of crossing structures.
Field, experimental and numerical investigations into the mechanisms and drivers of lateral erosion in bedrock channels
(2014-01) Fuller, Theodore Kent
The process of lateral erosion in bedrock channels is poorly understood. This thesis sheds light on the mechanisms of lateral bedrock erosion as well as the larger scale drivers of lateral erosion. Contained in this thesis are three distinct studies: a field-based study that investigates the drivers of lateral planation of strath surfaces; an experimental study that seeks to identify specific mechanisms of lateral erosion; and a numerical modeling study that seeks to corroborate the findings of the experimental study and permit exploration of parameter space. The field study (Chapter 1) concludes that lateral planation of strath surfaces in the dominant channel erosion process during periods of elevated sediment supply. This study further concludes that the elevated sediment supply conditions were driven by changes in climate. The experimental study (Chapter 2) concludes that the deflection of saltating bedload particles by fixed roughness elements into the wall is an effective mechanism of erosion. In addition, the experimental study identifies a minimum roughness threshold that must be crossed before significant lateral erosion can occur. Finally, the experimental study suggests that once the roughness threshold is crossed (i.e. moving from a smooth bed devoid of roughness elements to a bed with roughness elements), further increases in bed roughness do not produce ever increasing rates of lateral erosion. Rather, an erosion rate plateau is reached shortly after the roughness threshold is crossed. The numerical modeling study (Chapter 3) corroborates the findings of the experimental study and demonstrates, from first principles, that lateral erosion by deflected bed load particles is an effective mechanism of lateral bedrock erosion. In addition, this study identifies an important trade-off between increased deflection surface area from larger roughness elements and the increased form drag associated with the larger roughness elements. Here, the increase in the number of particle deflections is offset by the decrease in particle kinetic energy on impact, resulting in the erosion rate plateau observed in the physical experiments.
Identifying erosional hotspots in streams along the North Shore of Lake Superior, Minnesota using high-resolution elevation and soils data
(2013-09) Wick, Molly Jane
Many streams on the North Shore of Lake Superior, Minnesota, USA, are impaired for turbidity driven by excess fine sediment loading. The goal of this project was to develop a GIS-based model using new, openly-available, high-resolution remote datasets to predict erosional hotspots at a reach scale, based on three study watersheds: Amity Creek, the Talmadge River, and the French River. The ability to identify erosional hotspots, or locations that are highly susceptible to erosion, using remote data would be helpful for watershed managers in implementing practices to reduce turbidity in these streams. Erosion in streams is a balance between driving forces, largely controlled by topography; and resisting forces, controlled by the materials that make up a channel's bed and banks. New high-resolution topography and soils datasets for the North Shore provide the opportunity to extract these driving and resisting forces from remote datasets and possibly predict erosion potential and identify erosional hotspots. We used 3-meter LiDAR-derived DEMs to calculate a stream power-based erosion index, to identify stream reaches with high radius of curvature, and to identify stream reaches proximal to high bluffs. We used the Soil Survey Geographic (SSURGO) Database to investigate changes in erodibility along the channel. Because bedrock exposure significantly limits erodibility, we investigated bedrock exposure using bedrock outcrop maps made available by the Minnesota Geological Survey (MGS, Hobbs, 2002; Hobbs, 2009), and by using a feature extraction tool to remotely map bedrock exposure using high-resolution air photos and LiDAR data. Predictions based on remote data were compared with two datasets. Bank Erosion Hazard Index surveys, which are surveys designed to evaluate erosion susceptibility of banks, were collected along the three streams. In addition, a 500-year flood event during our field season gave us the opportunity to collect erosion data after a major event and validate our erosion hotspot predictions. Regressions between predictors and field datasets indicate that the most significant variables are bedrock exposure, the stream power-based erosion index, and bluff proximity. A logistic model developed using the three successful predictors for Amity Creek watershed was largely unsuccessful. A threshold-based model including the three successful predictors (stream power-based erosion index, bluff proximity, and bedrock exposure) was 70% accurate for predicting erosion hotspots along Amity Creek. The limited predictive power of the models stemmed in part from differences in locations of erosion hotspots in a single large-scale flood event and long-term erosion hotspots. The inability to predict site-specific characteristics like large woody debris or vegetation patterns makes predicting erosion hotspots in a given event very difficult. A field dataset including long-term erosion data may improve the model significantly. This model also requires high resolution bedrock exposure data which may limit its application to other North Shore streams.
Identifying Erosional Hotspots in Streams along the North Shore of Lake Superior, Minnesota using High-Resolution Elevation and Soils Data
(2013) Wick, Molly Jane
This is a University of Minnesota Water Resources Science master’s thesis describing original research to determine fluvial erosion in three coastal streams (Amity, Talmadge and French) of Minnesota’s Lake Superior shoreline. All three streams have elevated levels of turbidity, with potential for damage to fisheries. The goal of this project was to develop a GIS-based model using new, openly-available, high-resolution LiDAR datasets to predict erosional hotspots at a reach scale. The abstract summarizing the study’s key findings is extracted and reproduced below. Abstract: “Many streams on the North Shore of Lake Superior, Minnesota, USA, are impaired for turbidity driven by excess fine sediment loading. The goal of this project was to develop a GIS-based model using new, openly-available, high-resolution remote datasets to predict erosional hotspots at a reach scale, based on three study watersheds: Amity Creek, the Talmadge River, and the French River. The ability to identify erosional hotspots, or locations that are highly susceptible to erosion, using remote data would be helpful for watershed managers in implementing practices to reduce turbidity in these streams. “Erosion in streams is a balance between driving forces, largely controlled by topography; and resisting forces, controlled by the materials that make up a channel’s bed and banks. New high-resolution topography and soils datasets for the North Shore provide the opportunity to extract these driving and resisting forces from remote datasets and possibly predict erosion potential and identify erosional hotspots. We used 3-meter LiDAR-derived DEMs to calculate a stream power-based erosion index, to identify stream reaches with high radius of curvature, and to identify stream reaches proximal to high bluffs. We used the Soil Survey Geographic (SSURGO) Database to investigate changes in erodibility along the channel. Because bedrock exposure significantly limits erodibility, we investigated bedrock exposure using bedrock outcrop maps made available by the Minnesota Geological Survey (MGS, Hobbs, 2002; Hobbs, 2009), and by using a feature extraction tool to remotely map bedrock exposure using high-resolution air photos and LiDAR data. “Predictions based on remote data were compared with two datasets. Bank Erosion Hazard Index surveys, which are surveys designed to evaluate erosion susceptibility of banks, were collected along the three streams. In addition, a 500-year flood event during our field season gave us the opportunity to collect erosion data after a major event and validate our erosion hotspot predictions. Regressions between predictors and field datasets indicate that the most significant variables are bedrock exposure, the stream power-based erosion index, and bluff proximity. A logistic model developed using the three successful predictors for Amity Creek watershed was largely unsuccessful. A threshold-based model including the three successful predictors (stream power-based erosion index, bluff proximity, and bedrock exposure) was 70% accurate for predicting erosion hotspots along Amity Creek. The limited predictive power of the models stemmed in part from differences in locations of erosion hotspots in a single large-scale flood event and long-term erosion hotspots. The inability to predict site-specific characteristics like large woody debris or vegetation patterns makes predicting erosion hotspots in a given event very difficult. A field dataset including long-term erosion data may improve the model significantly. This model also requires high resolution bedrock exposure data which may limit its application to other North Shore streams.”
The influence of vegetation and root density on erosion for Three Streams in Minnesota
(2013-08) Underhill, Benjamin Lawrence
Streambank erosion is a growing concern in Minnesota as hydrologic conditions continue to change throughout the state. Plant root anchoring and surface protection from vegetation play a role in reducing erosion. The Rosgen Bank Assessment for Non-point source Consequences of Sediment (BANCS) method of erosion prediction uses both root density and surface protection to estimate the resistance of a streambank to erosion. In order to understand how different types of vegetation can influence parameters within the BANCS system thirty sites were selected in the Glacial Lake Plain, Glacial Till, and Loess regions. Root sampling and vegetation surveys revealed no correlation between root density and erodibility factors from the BANCS system. Data from this study can assist restoration efforts in these regions in order to improve or refine current practices, reduce erosion and improve water quality.
Laboratory Debris Flow Experiments: A Study of Erosion
(2018-08) Maki, Laura
We investigate the dependence of net erosion on grain size distribution in experimental debris flows and erodible beds. We systematically and independently varied the composition of each the supply and erodible bed material and the flume inclination angle, ϕ. Then, we demonstrate that there is a unique neutral angle, ϕN (the angle at which erosion is equal to zero), for each bed and supply composition combination. We show that for each system, total net erosion increases roughly linearly with increasing ϕ and can be predicted based on ϕ-ϕN and the geometry of the erodible bed. Our other macroscopic findings include that ϕN is dependent on both the compositions of the bed and the supply; as davg,S increases, ϕN decreases; as davg,B increases, ϕN increases; and as davg,S/davg,B increases, ϕN generally decreases. We then consider particle scale dynamics that drive these macroscopic results including segregation mechanisms, inter-particle collisions, and relative roughness.
Late-stage exhumation of metamorphic core complexes and landscape development during orogenic collapse of the North American cordillera
(2014-02) Toraman, Erkan
Exogenic and endogenic processes control the exhumation of partially molten crust in extending orogens. Their relative contribution to total denudation is critical to evaluate different tectonic models. Therefore, assessing the timing, rates, style, and conditions of events from melt crystallization to cooling at near-surface temperatures is significantly important for understanding the thermo-mechanical evolution of orogenic crust and linking deep-to-shallow processes. Metamorphic core complexes (MCC) and gneiss domes located within the hinterland of orogenic belts expose a significant quantity of former partially-molten mid-to-lower crust in the form of migmatites. The Thor-Odin, Frenchman's Cap, and Okanogan domes are exposed in the biggest Cordilleran-style metamorphic core complex, the Shuswap MCC, where a series of migmatitic gneiss domes formed during collapse of the thickened crust in the Cenozoic. The Thor-Odin and Frenchman's Cap domes form the Shuswap MCC's narrow northern end where the present day topographic relief reaches up to 2.5 km with deeply incised valleys and ubiquitous glacial features. The Okanogan dome, on the other hand, represents the wider, lower-relief (≤ 1km) southern termination. In the Thor-Odin and Frenchman's Cap domes, zircon U-Th/He ages range from 45 to 37 Ma. Apatite fission track ages range between 48 to 14 Ma and increase with increasing sample elevation. Thermal modeling of samples from higher altitudes (~2100 to 1800 m) verify only rapid Eocene cooling, whereas the lower-elevation samples (~1800 to 500 m) reveal an additional Plio-Quaternary cooling event. The presence of the top of a fossil Eocene partial annealing zone at ~1800 m indicates that the migmatite dome reached near-surface depths (1-2 km) during its initial exhumation mainly by detachment tectonics. Apatite U-Th/He chronometry of these samples yields Miocene (26-5 Ma) ages. A number of low elevation (~500 m) samples collected from valleys reveal intra-sample single grain U-Th/He ages. Combined with the results of thermal modeling, these age variations indicate a rapid exhumation pulse at ca. 3 Ma, possibly related to continental glaciation. In the Okanogan dome, zircon U-Th/He ages range from 51 to 41 Ma and decrease towards the detachment fault zone, emphasizing up to 3.7 km/myr slip rate on the detachment zone. Apatite fission track and U-Th/He ages vary from 51 to 23 Ma, recording a very slow phase of erosional exhumation of the dome that removed ~ 2 km of rocks subsequently after its initial rapid ascent facilitated by detachment tectonics in the Eocene. Low-temperature data also document different cooling paths of rocks depending on their structural level; rocks closer to the detachment zone display rapid cooling rates (≥ 100 °C/myr), whereas deeper structural levels cool slowly (10-30 °C/myr). As in the North American Cordilleran hinterland, a series of migmatite-cored metamorphic core complexes is exposed in the Hellenides, where the geodynamic context of migmatitic dome formation is well known from previous research. Multiple low-temperature thermochronologic techniques combined with existing structural, geo- and thermochronologic, and petrologic data from Cordilleran and central Aegean migmatitic gneiss domes document rapid ascent of partially molten mid-to-lower crustal rocks, facilitating significant mass and heat advection to the shallow crust. Heat advection results in a high-geothermal gradient in shallow crust and shifts the brittle-ductile transition zone close to the surface. Percolation of surface-derived fluids through fault and fracture zones enables rapid cooling of rocks and enhances the brittle rheology.
Maps of wind-wave height on Minnesota lake shorelines
(2022-01-27) Herb, William; Janke, Ben; Cai, Meijun; Stefan, Heinz; Johnson, Lucinda; herb0003@umn.edu; Herb, William; University of Minnesota St. Anthony Falls Lab; University of Minnesota Duluth Natural Resources Research Institute
This data set provides maps of typical wind-wave height and energy on Minnesota lakes to inform shoreline and near-shore habitat restoration projects. The data set consists of a set of ArcMap shape files which map out simulated wave height and energy parameters for a series of points around the shoreline of 460 lakes in Minnesota, with separate files for annual wave statistics and monthly wave statistics. The wave statistics were calculated for each lake based on airport wind data and the open water distance (fetch) across the lake for each wind direction. Each shapefile contains information on multiple wave statistics, including the mean and significant wave height, the number of days wave height exceeds thresholds, and cumulative wave energy over the time period.
Prioritizing stream restoration: a decision support tool for use in restoring waters impaired by excess sediment in the Blue Earth River Basin of Minnesota
(2013-06) Presnail, Mary Louise
The hydrology of the Blue Earth River Basin has been dramatically altered following European settlement in the mid-to-late 1800's. Land use change has resulted in hydrologic instability leading to streambank and bluff erosion and increased sediment transport (Magner et al., 2003). Hydrologic change has led to an increase in Turbidity, or cloudiness of the river commonly measured as total suspended sediment (TSS). Excessive turbidity in water can be harmful to both humans (if used for drinking water) and aquatic life. In the Greater Blue Earth River Basin, there are 39 stream/river reaches that fail to meet the state's water quality standards for Turbidity, which is 90 parts per million TSS (MPCA, 2005). The purpose of this study is to create a tool that researchers can use to prioritize stream restoration in the Blue Earth River Basin in a relatively quick, productive and cost-effective way. The tool created will help prioritize stream sites for restoration based on a set of decision support metrics. A field test of the tool was conducted on two tributaries to the Blue Earth; Elm and Center Creek. The tool was tested on a total of 30 sites from these two tributaries. The future goal for this tool is for it to be used to help local officials prioritize restoration on unstable areas throughout the Blue Earth River Basin that are actively eroding and contributing sediment to the Blue Earth River.
Regional, Watershed, and Site-Specific Environmental Influences on Fish Assemblage Structure and Function in Western Lake Superior Tributaries
(2005) Brazner, John; Tanner, Danny K; Detenbeck, Naomi E; Batterman, Sharon L; Stark, Stacey L; Jagger, Leslie A; Snarski, Virginia M
This report assesses the impact of human activities and forest fragmentation on fish communities in the western Lake Superior basin. Human-induced activities noted in the report included temperature changes, siltation, erosion, forest cover and forest manipulation, and invasive species. Specific results are reproduced below. “The relative importance of regional, watershed, and in-stream environmental factors on fish assemblage structure and function was investigated in western Lake Superior tributaries. We selected 48 second- and third-order watersheds from two hydrogeomorphic regions to examine fish assemblage response to differences in forest fragmentation, watershed storage, and a number of other watershed, riparian, and in-stream habitat conditions. Although a variety of regional, fragmentation, and storage-related factors had significant influences on the fish assemblages, water temperature appeared to be the single most important environmental factor. We found lower water temperatures and trout–sculpin assemblages at lower fragmentation sites and higher temperatures and minnow–sucker–darter assemblages as storage increased. Factors related to riparian shading and flow separated brook trout streams from brown trout (Salmo trutta) – rainbow trout (Oncorhynchus mykiss) streams. Functionally, fish assemblages at lower fragmentation sites were dominated by cold-water fishes that had low silt tolerance and preferred moderate current speeds, while fishes with higher silt tolerances, warmer temperature preferences, and weaker sustained swimming capabilities were most common at higher storage sites. Our results suggest that site-specific environmental conditions are highly dependent on regional- and watershed-scale characters and that a combination of these factors operates in concert to influence the structure and function of stream fish assemblages. Key points: This study was completed within 160 km of Duluth, Minnesota, in the Northern Lakes and Forests Ecoregion and within two ecological units, the North Shore Highlands (north shore streams) and the Lake Superior Clay Plain (south shore streams)which provided excellent contrast in hydrogeomorphic types. Functionally, south shore fishes tended to be silt-dwelling, trophic generalists with slow current preferences and a tendency towards nest-guarding spawning behavior. North shore fishes tended to be single-bout spawners with fast current preferences. From a management perspective, our results suggest that both timber management and wetland restoration or degradation decisions will need to be considered by resource managers when fish community health is a concern. For example, increasing percentages of mature forest cover should allow for salmonid–sculpin assemblages to become more prevalent in streams with the potential for cool or cold waters. Similarly, increased wetland cover should allow for a greater predominance of healthy warmwater fish assemblages assuming that other landscape features are not too badly degraded. By understanding the species structure and functional character of an assemblage and its relationship to landscape features, managers should be able to make at least a rough assessment of watershed condition. Lacking fish data, it might be easier to simply characterize forest cover and storage as a first step in identifying which watersheds likely contain streams that are degraded. Our results suggest that although in-stream habitat rehabilitation should continue to be used an important tool to improve biological conditions in streams, restoration efforts will have greater success if the potential interactions with landscape conditions are factored into the decision-making process. In some situations, manipulation of forest cover or watershed storage may have a greater impact on fish assemblage integrity than in-stream habitat improvements.”

University Digital Conservancy

Browse by Subject

Browsing by Subject "Erosion"