Browsing by Subject "Diatoms"
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Item Climatic and anthropogenic influences on aquatic ecosystems in the valley of the Great Lakes, Mongolia.(2008-12) Shinneman, Avery Lynn CookClimate 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.Item Determining the impacts of damming, water-level fluctuations, climate, and landscape changes in Voyageurs National Park and vicinity.(2010-06) Bleser, Claire SerieyssolIn 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.Item Final Report on Sediment Diatom Reconstructions for Four Itasca County Lakes(University of Minnesota Duluth, 2009) Reavie, Euan DDue 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.Item An Integrated Approach to Assessing Multiple Stressors for Coastal Lake Superior(2011) Niemi, Gerald J; Reavie, Euan; Peterson, Gregory S; Kelly, John R; Johnston, Carol A; Johnson, Lucinda B; Howe, Robert W; Host, George; Hollenhorst, Thomas; Danz, Nick; Ciborowski, Jan H; Brown, Terry; Brady, Valerie; Axler, Richard PThis peer-reviewed article summarizes research conducted under the Great Lakes Environmental Indicators (GLEI) project initiated by the authors in 2001. The authors assessed the status of Lake Superior’s coastal ecosystem relative to over 200 environmental variables collected from GIS data sets for the enture US Great Lakes basin. These were assessed using gradients including atmosphereic deposition, agriculture, human population and development, land cover, point source pollution, soils and a cumulative stress index. Relationships of biological assemblages of birds, diatoms, fish and invertebrates, wetland plants, soils and stable isotopes to these gradients were then assessed. Key findings are extracted and reproduced below. Biological indicators can be used both to estimate ecological condition and to suggest plausible causes of ecosystem degradation across the U.S. Great Lakes coastal region. Here we use data on breeding bird, diatom, fish, invertebrate, and wetland plant communities to develop robust indicators of ecological condition of the U.S. Lake Superior coastal zone. Sites were selected as part of a larger, stratified random design for the entire U.S. Great Lakes coastal region, covering gradients of anthropogenic stress defined by over 200 stressor variables (e.g. agriculture, altered land cover, human populations, and point source pollution). A total of 89 locations in Lake Superior were sampled between 2001 and 2004 including 31 sites for stable isotope analysis of benthic macroinvertebrates, 62 sites for birds, 35 for diatoms, 32 for fish and macroinvertebrates, and 26 for wetland vegetation. A relationship between watershed disturbance metrics and 15N levels in coastal macroinvertebrates confirmed that watershed-based stressor gradients are expressed across Lake Superior’s coastal ecosystems, increasing confidence in ascribing causes of biological responses to some landscape activities. Several landscape metrics in particular—agriculture, urbanization, human population density, and road density—strongly influenced the responses of indicator species assemblages. Conditions were generally good in Lake Superior, but in some areas watershed stressors produced degraded conditions that were similar to those in the southern and eastern U.S. Great Lakes. The following indicators were developed based on biotic responses to stress in Lake Superior in the context of all the Great Lakes: (1) an index of ecological condition for breeding bird communities, (2) diatom-based nutrient and solids indicators, (3) fish and macroinvertebrate indicators for coastal wetlands, and (4) a non-metric multidimensional scaling for wetland plants corresponding to a cumulative stress index. These biotic measures serve as useful indicators of the ecological condition of the Lake Superior coast; collectively, they provide a baseline assessment of selected biological conditions for the U.S. Lake Superior coastal region and prescribe a means to detect change over time.” Key points: “In general, the U.S. Great Lakes coastal region of Lake Superior shows greater overall stress in the southern regions compared with relatively low overall stress in the northern regions. These patterns are primarily due to agricultural land use, higher human population densities, and point sources in the eastern and western portions on the south shore, while the north shore at the western end of Lake Superior is primarily forested with relatively sparse human population densities. Coastal regions of Lake Superior can be found at each of the extremes of the disturbance gradients. This includes relatively pristine watersheds in the northern regions with low human population densities and little agriculture that contrast with regions of relatively high populations with industrial activity such as Duluth-Superior in Minnesota-Wisconsin and Sault Ste. Marie Michigan at the other end of the gradient. The U.S. Lake Superior coastal region varies widely in the degree of human-related stress; generally, levels of stress decrease from south to north but with considerable variation, especially along the southern shore due to local agricultural activity and the presence of several population and industrial centers. In spite of a lack of latitudinal variation, there is human-induced, watershed scale variability across the Lake Superior coast. Compared to the other Great Lakes, Lake Superior coastal fish communities had more generally intolerant fish and more turbidity intolerant fish. Coastal fish community composition reflected the higher levels of suspended solids associated with human alteration to watersheds. The most disturbed sites on Lake Superior had greater proportions of non-native species and fewer bottom-feeding taxa.Item Monitoring Diatom Algae in Northeastern Minnesota(University of Minnesota Duluth, 2005) Reavie, Euan D; Kingston, John; Peterson, Morgan; Edlund, Mark BSurface 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.Item A Paleolimnological Comparison of Burntside and Shagawa Lakes, Northeastern Minnesota(1978-01) Bradbury, J. Platt; Waddington, Jean C BThe 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.Item 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 RTo 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.Item A Whole-Lake Assessment of Long-Term Human Impacts to Lake Superior(University of Minnesota Duluth, 2010) Reavie, Euan DObjectives: 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.