Browsing by Subject "Paleolimnology"

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A 250-year assessment of human impacts on Lake Superior: an updated paleolimnological perspective
(2013-05) Chraibi, Victoria Lindsay Shaw
To understand environmental conditions in Lake Superior over the last two centuries, we conducted a paleolimnological study on two sediment cores collected in the eastern and western regions of the lake. We examined the diatom community assemblages, trace metals, sediment characteristics, and GIS-reconstructed human land use to evaluate the historical impacts of human activities. During European settlement and agricultural development, there is clear indication the diatom community reorganized due to nutrient enrichment. Trace metal profiles tracked a period of mining and ore processing which temporarily increased metal loads to the lake in the mid- to late-20th century. In recent decades, more oligotrophic diatom species were favored, suggesting nutrient decreases associated with remedial activities. The diatom community has reorganized to be dominated by Cyclotella species, providing evidence that water quality changes are being influenced by atmospheric nitrogen deposition and changes in the lake's physical and chemical processes associated with climate change.
Climatic and anthropogenic influences on aquatic ecosystems in the valley of the Great Lakes, Mongolia.
(2008-12) Shinneman, Avery Lynn Cook
Climate warming and major land use changes have profoundly affected the Mongolian landscape in the past several decades. As in many arid and semi-arid regions, water resources are critically important for ecological, social, and economic viability. In Mongolia, traditional semi-nomadic pastoralism contributes substantially to the national economy as well as to individual subsistence and depends on limited freshwater resources to provide for grazing herds and human needs. Yet, because of substantial variability across this immense region, its remoteness, and recent political transitions, little work has been done to monitor water quality or to set baseline standards against which to measure future changes. Compounding the problem is a lack of well-resolved paleo-ecological and paleo-climatological work. These data are necessary to provide a foundation for understanding the natural variability in the aquatic systems of the region, especially with recent changes in climate and land use. This work is a contribution to developing these records by first, developing diatom-based inference models for total phosphorus and salinity, and second, applying the models to investigate lacustrine sediment records of past changes. The diatom-based inference models were based on a survey of the water chemistry, physical characteristics, and diatom flora of 64 lakes in western Mongolia. The region had a diverse diatom flora with over 300 species, nearly 100 of which had not been previously reported from Mongolia, from lakes ranging from fresh to hypersaline. The many isolated lake basins provided unique ecosystems where multiple unique communities, novel species distributions, and new and endemic flora were found. Three of these new species are described here in a careful examination of the genus Cyclotella in western Mongolia. Canonical correspondence analysis (CCA) was used to identify four variables (specific conductivity, total phosphorus, bicarbonate, and lake morphology) that were significantly related to the distribution of diatoms; predictive models were developed for specific conductivity and total phosphorus using weighted averaging regression and calibration methods. The application of these models to dated lake sediment cores, along with interpretations of other geochemical and sediment characteristics, was then used to develop records of variability in lake salinity and nutrient flux. The interpretation of diatom and sedimentary records demonstrated increases in nutrient fluxes to the lakes related to climate warming and major changes in land-use over the last 20 years. Diatom-inferred lake salinity was correlated with changes in temperature over the past 2000 years, as inferred from tree-ring records, demonstrating a positive relationship between increased warming and increased lake salinity in recent geologic history. Changes in warm-season temperature, as inferred from tree-rings, in the most recent decades were less-well correlated with inferred changes in salinity than over most of the 2000 year record. However, instrumental records of winter temperature were well correlated with recent shifts in inferred salinity, perhaps suggesting recent changes in climate that are unique from those over the past several thousand years.
Completion Report Jessie Lake Paleolimnology Project
(University of Minnesota Duluth, 2002) Kingston, John
Jessie Lake is a high-priority lake in terms of the Itasca County Water Plan, recognized as an important resource for multiple-use recreation and for its walleye (Stizostedium vitreum (Mitchill)) fishery in particular. The Jessie Lake Watershed Association has been particularly active in promoting and participating in research to understand and improve the resource. The major concern in the watershed is increasing nutrient loading, according to recent lakewater phosphorous studies. Internal loading is also implicated in keeping the algal growth in the lake at high levels. We are presently using diatoms for paleolimnological interpretations of past baselines, trends, and magnitudes of change in lakewater phosphorous. Jessie Lake has been eutrophic since before European settlement of the area, though phosphorus concentrations were higher in the middle of the 20th century than they are now.
Completion Report Mille Lacs Lake Paleolimnology Project
(University of Minnesota Duluth, 2003) Kingston, John
Mille Lacs Lake is a high-priority lake in terms of its size and premier walleye fishery, and it has a relatively small watershed compared to the size of the lake surface. Expected future increases in development of the lakeshore have prompted a desire to know about water quality baselines for this important lake. This paleolimnological study examines a sediment core collected in late winter of 2002 using radioisotope dating, loss-on-ignition analysis of organic and inorganic sediment components, and diatom analysis as a proxy for nutrient loading. Land use changes in the watershed have caused accelerating soil erosion from 1960 until the present day. Diatom counts show a decline of benthos-dominated assemblages starting by the 1950s, with greater dominance of planktonic species for the last 60 years. This indicates nutrient loading increases and water transparency decreases. The core-top, representing conditions in 2001, shows the highest relative abundance of planktonic diatom species, indicating that nutrient loading is still increasing. Preliminary diatom- based reconstructions of past lakewater total phosphorus concentrations show that nutrient loading in Mille Lacs has increased approximately 30% during the past half century and remains at an historical high level.
Determining the impacts of damming, water-level fluctuations, climate, and landscape changes in Voyageurs National Park and vicinity.
(2010-06) Bleser, Claire Serieyssol
In the past century, the border lakes in and near Voyageurs National Park have been subject to anthropogenic and natural stressors. These stressors include logging, damming, hydromanagement, human population growth, and climate change, which can be broadly categorized into three groups: land use, hydromanagement, and climate. In order to determine how these stressors have impacted the lakes, we developed a before-after control-impact paleolimnological study. Lakes included in the study were the dammed lakes of Namakan, Rainy, and Kabetogama, which are all in the Voyageurs National Park region, and undammed Lac La Croix, which is upgradient in protected wilderness lands. One sediment core was retrieved from each lake and analyzed for 210Pb inventory, loss-on-ignition, and diatoms. Multiple statistical analyses (species richness and turnover, cluster analysis, multivariate ordination, diatom-inferred water quality, and variance partitioning) were used to provide a more comprehensive picture of how these lakes were affected uniquely and interactively by the different stressors. Among the various stressors, land use generally explained the greatest amount of variance in diatom communities. Nevertheless, it is important to note that the interactive effects among land use, climate, and hydromanagement were also highly significant. Although hydromanagement is a primary source of concern in this region, multiple stressors and their interactions were identified as drivers of change in the diatom community and therefore must be considered in the management of the border lakes. The International Joint Commission who has been managing this system since 1940 has been mostly re-active in its decision making. However, in the late 1990s enough awareness was raised in regards to the deterioration of biological communities that they choose to modify the water-level rules in the border lakes. This step created a new decision-making process in this region; a move from being re-active to been pro-active. As part of this new rule change, the IJC required local agencies to evaluate the change in the rule curve. The ruling board located in the Rainy-Namakan System also has taken part in the new International Watershed Initiative which approaches the management of watersheds in an ecosystem approach. This step is extremely important as it promotes interactions between all stakeholders and therefore is able to fully integrate concerns in decision-making. Nevertheless, there are still concerns for the management of the resources in a sustainable way. Repeatedly, agencies in the region have raised concerns in the lack of funding from the IJC to maintain monitoring station. These stations are extremely important when making sustainable decisions especially during a time of unprecedented climate change. Thus, it is important that the IJC not only pro-active in its decision-making but also consider long-term sustainability.
The geologic history of Lake of the Woods, Minnesota, reconstructed using seismic-reflection imaging and sediment core analysis
(2014-07) Hougardy, Devin D.
The history of glacial Lake Agassiz is complex and has intrigued researchers for over a century. Over the course of its ~5,000 year existence, the size, shape, and location of Lake Agassiz changed dramatically depending on the location of the southern margin of the Laurentide Ice Sheet (LIS), the location and elevation of outflow channels, and differential isostatic rebound. Some of the best-preserved sequences of Lake Agassiz sediments are found in remnant lake basins where erosional processes are less pronounced than in adjacent higher-elevation regions. Lake of the Woods (LOTW), Minnesota, is among the largest of the Lake Agassiz remnant lakes and is an ideal location for Lake Agassiz sediment accumulation.High-resolution seismic-reflection (CHIRP) data collected from the southern basin of LOTW reveal up to 28 m of stratified lacustrine sediment deposited on top of glacial diamicton and bedrock. Five seismic units (SU A-E) were identified and described based on their reflection character, reflection configuration, and external geometries. Three prominent erosional unconformities (UNCF 1-3) underlie the upper three seismic units and indicate that deposition at LOTW was interrupted by a series of relatively large fluctuations in lake level. The lowermost unconformity (UNCF-1) truncates uniformly draped reflections within SU-B at the margins of the basin, where as much as four meters of sediment were eroded. The drop in lake level is interpreted to be contemporaneous with the onset of the low-stand Moorhead phase of Lake Agassiz identified from subaerial deposits in the Red River Valley, Rainy River basin, and Lake Winnipeg. A rise in lake level, indicated by onlapping reflections within SU-C onto UNCF-1, shifted the wave base outwards and as much as 11 m of sediment were deposited (SU-C) in the middle of the basin before a second drop, and subsequent rise, in lake level resulted in the formation of UNCF-2. Reflections in the lower part of SU-D onlap onto UNCF-2 only near the margins of the basin, suggesting that water occupied much of the middle of the southern basin after lake level drawdown. The reflection character and configuration of SU-C and SU-D are genetically different indicating that the depositional environment had changed following the formation of UNCF-2. Piston-type sediment cores collected from the southern basin of LOTW at depths that correspond to the middle of SU-D contain high amounts of organic material and charcoal fragments and sediment that are probably not related to Lake Agassiz. Instead, they were likely deposited during a transitional phase between when Lake Agassiz left the LOTW basin (UNCF-2) and inundation of LOTW from the northern basin due to differential isostatic rebound (UNCF-3). All sediment cores collected from the southern basin of LOTW record the uppermost unconformity, analogous in depth to UNCF-3 in the seismic images, which separates modern sediments from mid to late-Holocene sediments. The lithology of sediments below this unconformity varies across the basin from gray clay to laminated silt and clay. Radiocarbon ages from two peat layers immediately below the unconformity indicate that subaerial conditions had existed prior to the formation of UNCF-1, at about 7.75 ka cal BP. The timing correlates well with other lakes in the upper Midwest that record a prolonged dry climate during the mid-Holocene. UNCF-3 is planar and erosional across the entire survey area but erosion is greatest in the northern part of the basin as the result of a southward transgressing wave base driven by differential isostatic rebound. Deposition in the southern basin probably resumed around 3.3 ka cal BP, though no radiocarbon dates were collected directly above UNCF-3. The lithology of sediment above UNCF-3 is highly uniform across the basin and represents modern sedimentation. Late-Holocene sedimentation rates were calculated at about 0.9 mm year-1 and are roughly double the sedimentation rates in the NW Angle basin, suggesting that erosion of the southern shoreline contributes significantly to deposition in the southern basin.
Late Holocene sediments of the western Sea of Galilee
(2016-03) Williams, Abigail
A 143-cm UWITEC percussion core, collected from a water depth of ~10 m, about 1 km from the city of Ginosar on the western shore of the Sea of Galilee, was studied to infer input from East Galilee over the last ~4000 years. The core location is offshore the mouths of Amud and Tsalmon, two of the larger streams that drain the northeastern part of the Galilee Mountains and have formed Holocene alluvial deposits. Today these streams are seasonal and during some years have no flow. Changes in core lithology, grain size, elemental chemistry, and bulk carbonate-free 87Sr/86Sr ratios and εNd values indicate changes in lake levels and sediment delivery from the Galilee. The presence of mm- to cm-thick laminations in the bottom 20 cm of the core indicate that the lake was deeper than today from ~4000 to ~3500 cal yrs BP and became shallower reaching near modern depth by ~3250 cal yrs BP. Summertime daily afternoon windwaves caused by westerly wind coming across the Galilee Mountains creates counterclockwise gyres and sediment resuspension to the depth of about 10 m resulting in accumulation of massive sediments in zones shallower than ~10 m (Serruya, 1978). Two thick flood units were identified, one on top of the other, between 104 and 60 cm. Both show a fining upward trend. The earlier flood shows lithology and 87Sr/86Sr ratios and εNd values similar to Amud drainage basin rocks and soils whereas the later flood shows affinity to Tsalmon drainage basin. Additional minor sediment delivery events are suggested by the presence in the sediment of Late Cretaceous to Eocene marine foraminifer fossils that are known to occur in carbonate rocks and their weathering products (Terra Rossa and Rendzina soils) exposed in the Galilee Mountains. An event that resulted in a hiatus occurred sometime between ~530 and ~1200 cal yrs BP.
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.
Modern Limnological and Paleolimnological Applications of Diatoms in Minnesota Lakes
(2021-05) Burge, David
The following chapters represent a continuity of diatom research in Minnesota lakes. In Chapter 2, the study on Upper and Lower Red Lakes demonstrates the use of well-established paleolimnological proxies to assess eco-limnological change in a pair of large shallow lakes and inform management of the lakes by the Red Lake Tribal Department of Natural Resources and the Minnesota Pollution Control Agency. Highlighted here was the use of diatoms using traditional morphological and geochemical approaches to reconstructing limnological history. In Chapter 3, I present a review on resurrection ecology as a new tool in the paleolimnological tool belt. This chapter highlights diatoms as prime candidates for resurrection ecology studies and the use of sediment eDNA to guide such studies. Chapter 4 uses the recommendations in Chapter 3 to leverage diatom microfossils and their DNA to examine the influence of 20th century dust deposition on productivity and community composition. This study highlights the first use of sediment DNA to characterize diatom assemblage changes in a North American lake, and furthermore highlights the beneficial uses of paired microfossil-DNA diatom proxies. In Chapter 5, I used sediment DNA to describe the genomic diversity of diatoms across lakes of Minnesota. The diatom diversity described here corresponds to the distribution of lake types across Minnesota that can be characterized by diatoms observed in light microscopy or by their DNA signatures. Furthermore, the paired use of diatom microfossils and sediment DNA showed similar limnological trends in the paleolimnological record of two lakes.
A Paleolimnological Comparison of Burntside and Shagawa Lakes, Northeastern Minnesota
(1978-01) Bradbury, J. Platt; Waddington, Jean C B
The paleolimnological records of Burntside and Shagawa Lakes in northeastern Minnesota reveal that these two adjacent lakes have been limnologically distinct for many years prior to the late 19th century activities of white men that polluted Shagawa Lake. Although both lakes occur within the same vegetation type and share much of their water, the diatom stratigraphy of their bottom sediments indicates that Burntside Lake was less productive in its natural state than Shagawa Lake. The causes for this natural difference are not clearly known, but differences in relative size of drainage area and in bedrock geology may be responsible. Intensive white settlement around Shagawa Lake beginning in 1866 supplied nutrients that increased its productivity and finally supported the massive blooms of blue-green algae that characterize culturally eutrophic lakes. Burntside Lake was spared such intensive eutrophication, but its diatom record shows that nutrients derived from shoreside recreational cabins and related construction activity are increasing the lake's productivity. The results of this study show that paleolimnological studies may provide better comparative information for lake rehabilitation programs than do biological and chemical analyses of contemporary unpolluted water bodies. This report is contribution #155 of the Limnological Research Center, University of Minnesota and was submitted in fulfillment of P.O. 04J1P0-0605 under the sponsorship of the U.S. Environmental Protection Agency.
Paleolimnological Reconstructions for the White Iron Chain of Lakes
(University of Minnesota Duluth, 2013) Reavie, Euan D
To quantify the environmental history of the White Iron Chain of Lakes (Lake and St. Louis Counties, Minnesota), five lakes were selected for retrospective analyses. Primary goals were to determine pre- European settlement conditions and track the timing and extent of anthropogenic impacts and remediation. Sediment cores were collected from each lake and sediment intervals were dated using isotopic analyses. Fossil remains, in concord with other stratigraphic indicators (organic and inorganic materials, sedimentation rates, other biological entities), were used to reconstruct the ~200-year history of each lake. Pollen analyses allowed for reconstruction of local and regional terrestrial conditions. Geochemical analyses provided data on historical flux of elemental trace metals to the sediments. Diatom assemblages were assessed from sediment intervals and inferred trophic conditions in the profiles were derived using a regional diatom-based model for Minnesota lakes. Eutrophication apparently occurred following settlement, particularly in White Iron Lake, but reconstructed phosphorus trends indicate more recent nutrient reductions. Pollen data track the decrease in pine abundance in the region and the rise of birch. Sedimentary metals largely reflect physical changes in the system, such as a change in sediment deposition regimes resulting from damming. Recent increases in metals are probably a result of increasing accumulation of soil and bedrock materials, a trend that is supported by increasing accumulation rates of overall organic and inorganic material. These recent increases in the last 30-40 years, which include increased algal deposition in Birch, Farm and Fall lakes, are not well explained at this time, but may be due to shifting water quality unrelated to phosphorus and possibly hydrological changes.
Paleolimnology of the Lake of the Woods southern basin
(University of Minnesota Duluth, 2015) Reavie, Euan D; Edlund, Mark B; Andresen, Norman A; Engstrom, Daniel R
To quantify the environmental history of the southern basin of Lake of the Woods (Ontario, Manitoba and Minnesota), seven core locations were selected for retrospective analyses. Primary goals were to determine pre-European settlement conditions and track the timing and extent of anthropogenic impacts and remediation. Sediments were dated using isotopic analyses and fossil remains, in concord with other stratigraphic indicators (organic and inorganic materials, sedimentation rates, other biological entities), were used to reconstruct the ~150-year history of the lake. Diatom assemblages were assessed from sediment intervals and inferred trophic conditions in the profiles were derived using a regional diatom-based model for Minnesota lakes. Nutrient reconstructions indicated a period of cultural eutrophication throughout much of the 20th century. Despite a known reduction in anthropogenic nutrient flux to the lake in recent decades, there has been no apparent reversal in eutrophication in the pelagic system. Contemporary observations indicate that blooms of blue-green algae are becoming a greater problem. It appears that legacy nutrient recycling and other environmental drivers are maintaining the current condition of pelagic nutrient enrichment. Sedimentary analyses also indicated that physical changes to the lake resulting from warming may be contributing in small part to the recent reorganization of algal assemblages.
Water Quality (2000-08) and Historical Phosphorus Concentrations from Paleolimnological Studies of Swamp and Speckled Trout Lakes, Grand Portage Reservation, Northeastern Minnesota
(2010) Christensen, Victoria G; Jones, Perry M; Edlund, Mark B; Ramstack, Joy M
A paleolimnological approach was taken to aid the Grand Portage Reservation, in northeastern Minnesota, in determining reference conditions for lakes on the reservation. The U.S. Geological Survey, in cooperation with the Grand Portage Band of Chippewa Indians and the Science Museum of Minnesota, conducted a study to describe water quality (2000–08) and historical total phosphorus concentrations (approximately 1781–2006) for Swamp and Speckled Trout Lakes. Results from this study may be used as a guide in establishing nutrient criteria in these and other lakes on the Grand Portage Reservation. Historical phosphorus concentrations were inferred through paleolimnological reconstruction methods involving diatom analysis and lead-210 dating of lake-sediment cores. Historical diatom-inferred total phosphorus concentrations in Swamp Lake ranged from 0.017 to 0.025 milligrams per liter (mg/L) based on diatom assemblages in sediment samples dated 1781–2005. Historical diatom-inferred total phosphorus concentrations in Speckled Trout Lake ranged from 0.008 to 0.014 mg/L based on diatom assemblages in sediment samples dated 1825–2006. In both lakes, historical changes in diatom-inferred total phosphorus concentrations did not exceed model error estimates, indicating that there has been minimal change in total phosphorus concentrations in the two lakes over about two centuries. The pH and alkalinity values of waters in both lakes indicate that general water-quality conditions likely are not threatening fish or acid-intolerant forms of aquatic life. Lake-sediment cores from Swamp and Speckled Trout Lakes were collected in 2006 and dated back to 1781 for Swamp Lake and 1825 for Speckled Trout Lake. A large increase in sediment accumulation rate after 1960 likely was a result of logging along the northeastern shore of Swamp Lake in 1958. The diatom flora of Swamp Lake is very diverse with more than 280 diatom taxa found in the core samples. These diatoms included many rare or uncommon species and several unknown taxa. Minor increases in sediment accumulation rates in the Speckled Trout Lake core occurred between 1840 and 1880. These increases may have resulted from fires following droughts in northeastern Minnesota. Heinselman (1973) identified five periods of fire in the 1800s for the Boundary Waters Canoe Area, Minnesota: 1801, 1824, 1863–64, 1875, and 1894. Most of these fire periods followed prolonged droughts of subcontinental extent, including the 1864 drought. Similar to the Swamp Lake core, the diatom flora of the Speckled Trout Lake core was very diverse and dominated by softwater diatoms. More than 215 diatom taxa were found in the core samples including many rare or uncommon species and several unknown taxa. Results of loss-on-ignition analyses indicated that sediment from Swamp Lake historically has been dominated by the inorganic component with a shift to an organic component in modern sedimentation. Median values of recent (2000–08) total phosphorus concentrations in water-quality samples and diatom-inferred phosphorus in recent sedimentation in Swamp and Speckled Trout Lakes were similar. These similarities, coupled with strong analogues for subfossil diatom communities for both lakes within the 89 Minnesota lakes diatom transfer function, indicate that recent and historical diatom-inferred phosphorus reconstructions might be used to help establish reference conditions and nutrient criteria for Grand Portage Reservation lakes when a sampling program is designed to ensure representative phosphorus concentrations in water samples are comparable to diatom-inferred concentrations.
A Whole-Lake Assessment of Long-Term Human Impacts to Lake Superior
(University of Minnesota Duluth, 2010) Reavie, Euan D
Objectives: 1) To find the driving factors behind changes occurring in Lake Superior. 2) To determine the effect of rehabilitation efforts on lake conditions. 3) To determine whether historical changes in the lake were related to anthropogenic impacts. 4)To investigate the spatial variation in historical pelagic conditions.

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