Browsing by Subject "Sediment core sampling"

Now showing 1 - 5 of 5
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    Final Report on Sediment Diatom Reconstructions for Four Itasca County Lakes
    (University of Minnesota Duluth, 2009) Reavie, Euan D
    Due to potential threats to water quality and fishery health, four lakes in Itasca County (Minnesota) were selected for retrospective analyses. Primary goals were to determine background conditions and track probable long-term degradation, timing of impacts and remediation. The lakes range from developed (Buck, Shallow and Round lakes) to currently undeveloped (Willeys Lake). Sediment cores were collected from each lake and sediment intervals were dated using isotopic analyses. 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. 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 system. Buck Lake experienced eutrophication and other anthropogenic impacts, but in recent decades the lake has at least partly remediated. Shallow Lake has apparently undergone numerous nearshore anthropogenic shifts, but development has not resulted in an overall increase in nutrient concentrations. Water quality response to early watershed modifications of Round Lake was limited but eutrophication became a problem in the latter portion of the 20th century due to historic and recent land use activities. Despite being selected as an “undeveloped” lake, Willeys Lake showed some subtle impacts due to likely deforestation in the lake’s catchment.
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    Monitoring Diatom Algae in Northeastern Minnesota
    (University of Minnesota Duluth, 2005) Reavie, Euan D; Kingston, John; Peterson, Morgan; Edlund, Mark B
    Surface sediment samples from 37 Itasca region lakes were appended onto an existing Minnesota lakes diatom calibration set to create a new 145 lake diatom training set with better representation of lakes throughout Minnesota and better reconstruction performance for total phosphorus values above 60 μg/L. Relationships among 15 chemical, physical and spatial (i.e., region) variables and 170 diatom species distributions in the new 145 lake training set were explored using canonical correspondence analysis (CCA), a multivariate ordination technique. Environmental variables that independently explained a significant portion of variation in species distribution were identified using forward selection. Total phosphorus (TP) was one of the most explanatory variables in the refined calibration set, including pH, lake depth, color, chloride, Secchi depth, conductivity, mean lake depth, lake area, and ANC. Weighted averaging partial least squares regression and calibration was identified as the appropriate method for model evaluations. A transfer function for inferring TP was generated from three versions of the lake calibration set: 1) the full 145-lake calibration set; 2) a reduced, 129-lake set where lakes with pH ≥ 9.0 removed to better represent conditions in the Itasca region; and 3) a further-reduced model that eliminated five lakes with poor diatom-inferred (DI) total phosphorus concentrations. The 124-lake calibration set produced a total phosphorus transfer function covering a gradient spanning lakes from 5-364 μg/L TP, and strong predictive ability for TP (r2 = 0.87, r2 jack = 0.77, RMSEP = 0.210 log(μg/L+1)). The transfer function was applied to estimate historical epilimnetic total phosphorus from subfossil diatom assemblages in a sediment core recovered from Jessie Lake, Itasca region. Pre-settlement conditions in Jessie Lake were inferred to be eutrophic, with a temporary augmentation in nutrient load between ~1950 and ~1980.
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    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.
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    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.
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    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.