K.A. Moser - Academia.edu (original) (raw)
Papers by K.A. Moser
ABSTRACT The Uinta Mountains are situated in northeastern Utah, USA and contribute ~ 10% of Color... more ABSTRACT The Uinta Mountains are situated in northeastern Utah, USA and contribute ~ 10% of Colorado River Flow at Lees Ferry. Instrumental data suggest that this region is sensitive to major modes of Pacific Ocean variability as well as North American Monsoon dynamics. This work examines multidecadal hydroclimate variability since circa 13,000 cal yrs BP using diatom species assemblage changes in a lake sediment core. Results are suggestive of a Younger Dryas signal and a relatively wet middle Holocene, perhaps associated with enhanced monsoon activity. Detailed analysis of the last ~ 1,000 years using tree-ring reconstructions for snowpack and flow in the Duchesne River, the largest river draining the southern slope of the Uinta Mountains, indicates statistically significant relationships between hydrology and certain phase combinations of the El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO). However, results also indicate that connections between Uinta Mountains hydrology and major modes of ocean variability are inconsistent over time, suggesting changes in the nature of teleconnections to this region.
Limnology and Oceanography, 2014
We use multiple proxies from lake sediment records of six remote alpine lakes in the Uinta Mounta... more We use multiple proxies from lake sediment records of six remote alpine lakes in the Uinta Mountains, Utah, to investigate primary production and potential drivers of changes in trophic status over the last two centuries. Chlorophyll a, chlorophyll a flux, and percentage of organic matter (determined by loss on ignition) increase beginning in the mid-20th century in five of the six alpine study lakes, indicating increasing production. These changes tend to coincide with decreasing sedimentary d 15 N and increasing abundance of the nitrophilous diatom Asterionella formosa. An earlier, more subtle change in diatom community composition and d 15 N indicates that human activities prior to 1950 had measurable effects on these lake ecosystems, although no corresponding increase in primary production was observed at this time. Multiple factors can lead to increased primary production at alpine sites, but the evidence presented shows that enhanced atmospheric deposition of nitrogen and phosphorus explain the recent, more prominent increase in production. Although previous research has suggested that alpine lakes are nitrogen limited, our results suggest nutrient limitation varies spatially and temporally, and is complex in these oligotrophic systems. This and other factors, such as catchment characteristics, will affect the sensitivity of a lake to atmospheric deposition-fertilizing effects. The changes observed show that remote lakes are vulnerable to long-distance transport of nutrients, and that the risk of eutrophication could be intensified by increased nutrient inputs from expanding mining, fossil fuel combustion, and agriculture and by rapid warming predicted for the southwest.
Progress in Physical Geography, 2014
This editorial is the product of the Progress in Physical Geography lecture at the April 2013 mee... more This editorial is the product of the Progress in Physical Geography lecture at the April 2013 meeting of the Association of American Geographers. The paper was presented by George Malanson, the North American Editor, and the co-authors presented critiques based on a draft. Subsequently, the manuscript was developed and revised based on discussion at the meeting and additional exchange among the co-authors.
Marine Pollution Bulletin, 1988
Concrete cinder blocks and Pleistocene coral limestone rubble were submerged in the East Back Ree... more Concrete cinder blocks and Pleistocene coral limestone rubble were submerged in the East Back Reef lagoon at Discovery Bay, Jamaica for 13 years. In 1986, they were collected, slabbed, and examined for bioeroding infauna. Taxa varied in their ability to penetrate the non-calcareous cement matrix. Polychaetes and the bivalve, Lithophaga, bored all substrata easily, although the polychaetes preferred the cement. The sponges, Cliona and Damiria, only occurred in calcium car
Journal of Paleolimnology
Global and Planetary Change, 2019
Mountain lakes are often situated in protected natural areas, a feature that leads to their role ... more Mountain lakes are often situated in protected natural areas, a feature that leads to their role as sentinels of global environmental change. Despite variations in latitude, mountain lakes share many features, including their location in catchments with steep topographic gradients, cold temperatures, high incident solar and ultraviolet radiation (UVR), and prolonged ice and snow cover. These characteristics, in turn, affect mountain lake ecosystem structure, diversity, and productivity. The lakes themselves are mostly small and shallow, and up until recently, have been characterized as oligotrophic. This paper provides a review and update of the growing body of research that shows that sediments in remote mountain lakes archive regional and global environmental changes, including those linked to climate change, altered biogeochemical cycles, and changes in dust composition and deposition, atmospheric fertilization, and biological manipulations. These archives provide an important record of global environmental change that pre-dates typical monitoring windows. Paleolimnological research at strategically selected lakes has increased our knowledge of interactions among multiple stressors and their synergistic effects on lake systems. Lakes from transects across steep climate (i.e., temperature and effective moisture) gradients in mountain regions show how environmental change alters lakes in close proximity, but at differing climate starting points. Such research in particular highlights the impacts of melting glaciers on mountain lakes. The addition of new proxies, including DNAbased techniques and novel stable isotopic analyses, provides a gateway to addressing novel research questions about global environmental change. Recent advances in remote sensing and continuous, high-frequency, limnological measurements will improve spatial and temporal resolution and help to add records to spatial gaps including tropical and southern latitudes.
Nature Communications, 2016
Humans have altered Earth's nitrogen cycle so dramatically that reactive nitrogen (Nr) has double... more Humans have altered Earth's nitrogen cycle so dramatically that reactive nitrogen (Nr) has doubled. This has increased Nr in aquatic ecosystems, which can lead to reduced water quality and ecosystem health. Apportioning sources of Nr to specific ecosystems, however, continues to be challenging, despite this knowledge being critical for mitigation and protection of water resources. Here we use D 17 O, d 18 O and d 15 N from Uinta Mountain (Utah, USA) snow, inflow and lake nitrate in combination with a Bayesian-based stable isotope mixing model, to show that at least 70% of nitrates in aquatic systems are anthropogenic and arrive via the atmosphere. Moreover, agricultural activities, specifically nitrate-and ammonium-based fertilizer use, are contributing most (B60%) Nr, and data from other North American alpine lakes suggest this is a widespread phenomenon. Our findings offer a pathway towards more effective mitigation, but point to challenges in balancing food production with protection of important water resources.
We use multiple proxies from lake sediment records of six remote alpine lakes in the Uinta Mounta... more We use multiple proxies from lake sediment records of six remote alpine lakes in the Uinta Mountains, Utah, to investigate primary production and potential drivers of changes in trophic status over the last two centuries. Chlorophyll a, chlorophyll a flux, and percentage of organic matter (determined by loss on ignition) increase beginning in the mid-20th century in five of the six alpine study lakes, indicating increasing production. These changes tend to coincide with decreasing sedimentary d15N and increasing abundance of the nitrophilous diatom Asterionella formosa. An earlier, more subtle change in diatom community composition and d15N indicates that human activities prior to 1950 had measurable effects on these lake ecosystems, although no corresponding increase in primary production was observed at this time. Multiple factors can lead to increased primary production at alpine sites, but the evidence presented shows that enhanced atmospheric deposition of nitrogen and phosphor...
Drought has had disastrous impacts on western North American ecosystems, economies and society, a... more Drought has had disastrous impacts on western North American ecosystems, economies and society, and for many regions is predicted to be a likely consequence of future climate change. The instrumental record, however, spans too short a period to provide the full range of drought variability (including frequency, duration and magnitude), which is critical information to anticipate and prepare for future drought events. Paleolimnology provides a means to reconstruct long-term (1000s of years) climate records from which to determine drought variability. Here we present a Holocene drought record from the eastern Sierra Nevada, CA, USA, and compare this record to similar records from western North America in order to explore spatial variability of Holocene drought. A 3.1 m sediment core was retrieved from Kirman Lake (2,174 m a.s.l.), located west of Bridgeport, CA. At present, Kirman Lake is a relatively small (11.9 ha), shallow (3.8 m), slightly alkaline (pH=7.6), freshwater (salinity=9...
Aquatic systems in alpine and sub-alpine areas of the western United States are potentially impac... more Aquatic systems in alpine and sub-alpine areas of the western United States are potentially impacted by atmospheric pollution and climate change. Because these mountainous regions are an important water resource for the western United States, it is critical to monitor and protect these systems. The Uinta Mountains are an east- west trending mountain range located on the border between Utah, Wyoming and Colorado and downwind of the Wasatch Front, Utah, which is characterized by a rapidly expanding population, as well as mining and industry. This alpine area provides water to many areas in Utah, and contributes approximately nine percent of the water supply to the Upper Colorado River. Our research is focused on determining the impacts of climate change and pollution on alpine lakes in the Uinta Mountains. The results presented here are based on limnological measurements made at 64 Uinta Mountain lakes spanning a longitude gradient of one degree and an elevation gradient of 3000 feet....
Instrumented lake and watershed climatic data along with lake sediment surface samples and cores ... more Instrumented lake and watershed climatic data along with lake sediment surface samples and cores are being used to develop and apply paleolimnological transfer functions to reconstruct climate change and ecosystem response in the eastern Sierra Nevada Mountains of California and the Unita Mountains of Utah. The selection of the two ranges provides a circum Great Basin perspective on natural climate variability in the western mountains. The California study sites are located in the eastern Sierra Nevada. Surface sediment samples and water samples have been analyzed from 57 lakes extending across an altitudinal gradient of 1360 m. Transfer functions that estimate water temperature, salinity and depth on the basis of lake diatom flora or chironomid fauna have been developed and published. Long cores have been obtained from 8 lakes that provide a transect from treeline down to the sagebrush dominated Great Basin. The lake records extend back between 9000 and 15,000 Cal yr BP. Pronounced...
Physical and chemical variables were measured in 35 lakes from Wood Buffalo National Park, northe... more Physical and chemical variables were measured in 35 lakes from Wood Buffalo National Park, northern Alberta and the Northwest Territories, Canada. Of these lakes, 22 were sinkholes, situated on limestone and gypsum, five were situated on the Canadian Shield and eight were shallow 'muskeg' lakes located on calcareous shales. All of the lakes were small to moderate in size. For
Diatoms (Bacillariophyceae) are a widely distributed group of microscopic, unicellular algae that... more Diatoms (Bacillariophyceae) are a widely distributed group of microscopic, unicellular algae that are characterized by siliceous cell walls (frustules). The size, shape and sculpturing of diatom frustules are taxonomically diagnostic. Moreover, because of their siliceous composition, diatoms are often well preserved in stratigraphic deposits, where they can be used to infer (quantitatively or qualitatively) past environmental conditions. The sensitivity of diatoms to a wide variety of environmental variables provides geographers with a multitude of research opportunities. This review focuses on palaeoecological reconstructions that are based on freshwater diatoms. Geographical applications including studies of climatology, hydrology, geomorphology, bio geography, and water-quality assessment and monitoring are discussed.
Quaternary Research, 1990
Two radiocarbon-dated cores from small lakes located approximately 25 km north of the mapped boun... more Two radiocarbon-dated cores from small lakes located approximately 25 km north of the mapped boundary between forest-tundra and tundra provide records of postglacial vegetation change at the treeline near Yellowknife, NWT, Canada. Basal radiocarbon dates of 6180 and 7470 yr B.P. were obtained from the cores. The fossil pollen evidence suggests that the initial vegetation was Betula tundra with a peatland component. Alnus became an important constituent of the pollen assemblages between 6900 and 5500 yr B.P. Both lakes record sharp increases in Picea cf. mariana pollen at approximately 5000 yr B.P., suggesting the establishment of forest-tundra. By 3500 yr B.P. Picea mariana forest-tundra had withdrawn. The proportion of organic to inorganic sediment in the cores was at a maximum between 5000 and 3500 yr B.P. Tundra has dominated the region since 3500 yr B.P. In northwestern Canada, the maximum northward advance of treeline occurred between 9000 and 5000 yr B.P. The asynchrony in treeline advance in central and northwestern Canada may reflect that glacial ice persisted in the interior NWT longer than previously believed. Alternatively, the asynchronous history of the treeline may be a result of the geometric properties of the long-wave westerly disturbance that is manifest in the median summer position of the arctic front and ultimately controls the geographic location of the treeline. 0 l!Bll University of Washington.
Diatom assemblages and biogenic silica concentrations in a ~200 year, varved sediment record from... more Diatom assemblages and biogenic silica concentrations in a ~200 year, varved sediment record from Rainbow Lake A (RLA), located in the northern boreal forest of Wood Buffalo National Park, straddling northern Alberta and the Northwest Territories (Canada), were investigated in order to determine the impacts of recent climate warming to a remote northern lake. Diatom community composition, trends in diatom-inferred total phosphorus (TP) and biogenic silica levels all showed significant changes, beginning between circa 1830 and 1840, coincident with the onset of increasingly warm June/July temperatures in northern Canada. We test several hypotheses which may have caused these nutrient changes, including local anthropogenic disturbances, forest fires, increased atmospheric deposition of nutrients or pollen, and internal sources of nutrient regeneration. We conclude that the most likely explanation of the observed changes is enhanced internal cycling of phosphorus due to increased thermal stratification in response to warmer summer temperatures and/or decreased meromictic stability. These results, in combination with other recent paleolimnological research at high latitude regions, suggest significant and widespread aquatic response to increasingly warm temperatures beginning in the nineteenth century.
Several recent studies have successfully applied diatom-based paleolimnological techniques to inf... more Several recent studies have successfully applied diatom-based paleolimnological techniques to infer past hydrological changes in arctic and subarctic regions. For example, we summarize arctic studies that attempt to determine changes in peat water content, flood frequency, river discharge, effective moisture and ice cover in northern regions. Some of the investigations are still in preliminary stages, but represent innovative approaches to study arctic and subarctic paleohydrology. New data demonstrate that lake depth, which may be related to changing hydrological conditions, is a significant variable influencing the distributions of diatom taxa in lake surface sediment calibration sets from Wood Buffalo National Park (WBNP), on the border of Alberta and the Northwest Territories, Canada, and from Fennoscandia (mainly northwest Finland). Weighted averaging regression and calibration methods were used to develop quantitative inference models for lake depth using diatom assemblages preserved in surface sediments. The predictive abilities of the transfer functions were relatively high (for WBNP r 2 = 0.70 and RMSE = 2.6 m, and for Fennoscandia r 2 = 0.88 and RMSE = 1.8 m). However, evaluating the transfer functions using jack-knifing procedures indicated lower predictive abilities, possibly reflecting the relatively small sample size and/or short gradients used in these calibration sets. Such transfer functions can be used to track overall trends in lake levels, and provide an objective assessment as to directions of changing lake levels. Any interpretations of inferred lake levels, especially those related to climate change, must be made cautiously and must include some understanding of the local, present-day hydrological system.
To investigate the response of a remote boreal lake to recent climate warming, a |200-year varved... more To investigate the response of a remote boreal lake to recent climate warming, a |200-year varved sediment record from Rainbow Lake A (RLA), located in the northern boreal forest of Wood Buffalo National Park, straddling northern Alberta and the Northwest Territories (Canada), was investigated using diatom assemblages and biogenic silica concentrations. Diatom community composition, trends in diatom-inferred total phosphorus (TP) and biogenic silica levels all showed significant changes beginning between circa 1830 and 1840, coincident with the onset of increasingly warm June / July temperatures in northern Canada. We evaluated several hypotheses which may have caused these nutrient changes, including local anthropogenic disturbances, forest fires, increased atmospheric deposition of nutrients or pollen, and internal sources of nutrient regeneration. We concluded that TP is likely increasing as a result of enhanced internal cycling of phosphorus due to either increased thermal stratification in response to warmer summer temperatures and / or decreased meromictic stability. The results presented here, in combination with other recent paleolimnological research in northern latitude regions, suggest widespread aquatic response to increasing temperatures beginning in the 19th century.
ABSTRACT The Uinta Mountains are situated in northeastern Utah, USA and contribute ~ 10% of Color... more ABSTRACT The Uinta Mountains are situated in northeastern Utah, USA and contribute ~ 10% of Colorado River Flow at Lees Ferry. Instrumental data suggest that this region is sensitive to major modes of Pacific Ocean variability as well as North American Monsoon dynamics. This work examines multidecadal hydroclimate variability since circa 13,000 cal yrs BP using diatom species assemblage changes in a lake sediment core. Results are suggestive of a Younger Dryas signal and a relatively wet middle Holocene, perhaps associated with enhanced monsoon activity. Detailed analysis of the last ~ 1,000 years using tree-ring reconstructions for snowpack and flow in the Duchesne River, the largest river draining the southern slope of the Uinta Mountains, indicates statistically significant relationships between hydrology and certain phase combinations of the El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO). However, results also indicate that connections between Uinta Mountains hydrology and major modes of ocean variability are inconsistent over time, suggesting changes in the nature of teleconnections to this region.
Limnology and Oceanography, 2014
We use multiple proxies from lake sediment records of six remote alpine lakes in the Uinta Mounta... more We use multiple proxies from lake sediment records of six remote alpine lakes in the Uinta Mountains, Utah, to investigate primary production and potential drivers of changes in trophic status over the last two centuries. Chlorophyll a, chlorophyll a flux, and percentage of organic matter (determined by loss on ignition) increase beginning in the mid-20th century in five of the six alpine study lakes, indicating increasing production. These changes tend to coincide with decreasing sedimentary d 15 N and increasing abundance of the nitrophilous diatom Asterionella formosa. An earlier, more subtle change in diatom community composition and d 15 N indicates that human activities prior to 1950 had measurable effects on these lake ecosystems, although no corresponding increase in primary production was observed at this time. Multiple factors can lead to increased primary production at alpine sites, but the evidence presented shows that enhanced atmospheric deposition of nitrogen and phosphorus explain the recent, more prominent increase in production. Although previous research has suggested that alpine lakes are nitrogen limited, our results suggest nutrient limitation varies spatially and temporally, and is complex in these oligotrophic systems. This and other factors, such as catchment characteristics, will affect the sensitivity of a lake to atmospheric deposition-fertilizing effects. The changes observed show that remote lakes are vulnerable to long-distance transport of nutrients, and that the risk of eutrophication could be intensified by increased nutrient inputs from expanding mining, fossil fuel combustion, and agriculture and by rapid warming predicted for the southwest.
Progress in Physical Geography, 2014
This editorial is the product of the Progress in Physical Geography lecture at the April 2013 mee... more This editorial is the product of the Progress in Physical Geography lecture at the April 2013 meeting of the Association of American Geographers. The paper was presented by George Malanson, the North American Editor, and the co-authors presented critiques based on a draft. Subsequently, the manuscript was developed and revised based on discussion at the meeting and additional exchange among the co-authors.
Marine Pollution Bulletin, 1988
Concrete cinder blocks and Pleistocene coral limestone rubble were submerged in the East Back Ree... more Concrete cinder blocks and Pleistocene coral limestone rubble were submerged in the East Back Reef lagoon at Discovery Bay, Jamaica for 13 years. In 1986, they were collected, slabbed, and examined for bioeroding infauna. Taxa varied in their ability to penetrate the non-calcareous cement matrix. Polychaetes and the bivalve, Lithophaga, bored all substrata easily, although the polychaetes preferred the cement. The sponges, Cliona and Damiria, only occurred in calcium car
Journal of Paleolimnology
Global and Planetary Change, 2019
Mountain lakes are often situated in protected natural areas, a feature that leads to their role ... more Mountain lakes are often situated in protected natural areas, a feature that leads to their role as sentinels of global environmental change. Despite variations in latitude, mountain lakes share many features, including their location in catchments with steep topographic gradients, cold temperatures, high incident solar and ultraviolet radiation (UVR), and prolonged ice and snow cover. These characteristics, in turn, affect mountain lake ecosystem structure, diversity, and productivity. The lakes themselves are mostly small and shallow, and up until recently, have been characterized as oligotrophic. This paper provides a review and update of the growing body of research that shows that sediments in remote mountain lakes archive regional and global environmental changes, including those linked to climate change, altered biogeochemical cycles, and changes in dust composition and deposition, atmospheric fertilization, and biological manipulations. These archives provide an important record of global environmental change that pre-dates typical monitoring windows. Paleolimnological research at strategically selected lakes has increased our knowledge of interactions among multiple stressors and their synergistic effects on lake systems. Lakes from transects across steep climate (i.e., temperature and effective moisture) gradients in mountain regions show how environmental change alters lakes in close proximity, but at differing climate starting points. Such research in particular highlights the impacts of melting glaciers on mountain lakes. The addition of new proxies, including DNAbased techniques and novel stable isotopic analyses, provides a gateway to addressing novel research questions about global environmental change. Recent advances in remote sensing and continuous, high-frequency, limnological measurements will improve spatial and temporal resolution and help to add records to spatial gaps including tropical and southern latitudes.
Nature Communications, 2016
Humans have altered Earth's nitrogen cycle so dramatically that reactive nitrogen (Nr) has double... more Humans have altered Earth's nitrogen cycle so dramatically that reactive nitrogen (Nr) has doubled. This has increased Nr in aquatic ecosystems, which can lead to reduced water quality and ecosystem health. Apportioning sources of Nr to specific ecosystems, however, continues to be challenging, despite this knowledge being critical for mitigation and protection of water resources. Here we use D 17 O, d 18 O and d 15 N from Uinta Mountain (Utah, USA) snow, inflow and lake nitrate in combination with a Bayesian-based stable isotope mixing model, to show that at least 70% of nitrates in aquatic systems are anthropogenic and arrive via the atmosphere. Moreover, agricultural activities, specifically nitrate-and ammonium-based fertilizer use, are contributing most (B60%) Nr, and data from other North American alpine lakes suggest this is a widespread phenomenon. Our findings offer a pathway towards more effective mitigation, but point to challenges in balancing food production with protection of important water resources.
We use multiple proxies from lake sediment records of six remote alpine lakes in the Uinta Mounta... more We use multiple proxies from lake sediment records of six remote alpine lakes in the Uinta Mountains, Utah, to investigate primary production and potential drivers of changes in trophic status over the last two centuries. Chlorophyll a, chlorophyll a flux, and percentage of organic matter (determined by loss on ignition) increase beginning in the mid-20th century in five of the six alpine study lakes, indicating increasing production. These changes tend to coincide with decreasing sedimentary d15N and increasing abundance of the nitrophilous diatom Asterionella formosa. An earlier, more subtle change in diatom community composition and d15N indicates that human activities prior to 1950 had measurable effects on these lake ecosystems, although no corresponding increase in primary production was observed at this time. Multiple factors can lead to increased primary production at alpine sites, but the evidence presented shows that enhanced atmospheric deposition of nitrogen and phosphor...
Drought has had disastrous impacts on western North American ecosystems, economies and society, a... more Drought has had disastrous impacts on western North American ecosystems, economies and society, and for many regions is predicted to be a likely consequence of future climate change. The instrumental record, however, spans too short a period to provide the full range of drought variability (including frequency, duration and magnitude), which is critical information to anticipate and prepare for future drought events. Paleolimnology provides a means to reconstruct long-term (1000s of years) climate records from which to determine drought variability. Here we present a Holocene drought record from the eastern Sierra Nevada, CA, USA, and compare this record to similar records from western North America in order to explore spatial variability of Holocene drought. A 3.1 m sediment core was retrieved from Kirman Lake (2,174 m a.s.l.), located west of Bridgeport, CA. At present, Kirman Lake is a relatively small (11.9 ha), shallow (3.8 m), slightly alkaline (pH=7.6), freshwater (salinity=9...
Aquatic systems in alpine and sub-alpine areas of the western United States are potentially impac... more Aquatic systems in alpine and sub-alpine areas of the western United States are potentially impacted by atmospheric pollution and climate change. Because these mountainous regions are an important water resource for the western United States, it is critical to monitor and protect these systems. The Uinta Mountains are an east- west trending mountain range located on the border between Utah, Wyoming and Colorado and downwind of the Wasatch Front, Utah, which is characterized by a rapidly expanding population, as well as mining and industry. This alpine area provides water to many areas in Utah, and contributes approximately nine percent of the water supply to the Upper Colorado River. Our research is focused on determining the impacts of climate change and pollution on alpine lakes in the Uinta Mountains. The results presented here are based on limnological measurements made at 64 Uinta Mountain lakes spanning a longitude gradient of one degree and an elevation gradient of 3000 feet....
Instrumented lake and watershed climatic data along with lake sediment surface samples and cores ... more Instrumented lake and watershed climatic data along with lake sediment surface samples and cores are being used to develop and apply paleolimnological transfer functions to reconstruct climate change and ecosystem response in the eastern Sierra Nevada Mountains of California and the Unita Mountains of Utah. The selection of the two ranges provides a circum Great Basin perspective on natural climate variability in the western mountains. The California study sites are located in the eastern Sierra Nevada. Surface sediment samples and water samples have been analyzed from 57 lakes extending across an altitudinal gradient of 1360 m. Transfer functions that estimate water temperature, salinity and depth on the basis of lake diatom flora or chironomid fauna have been developed and published. Long cores have been obtained from 8 lakes that provide a transect from treeline down to the sagebrush dominated Great Basin. The lake records extend back between 9000 and 15,000 Cal yr BP. Pronounced...
Physical and chemical variables were measured in 35 lakes from Wood Buffalo National Park, northe... more Physical and chemical variables were measured in 35 lakes from Wood Buffalo National Park, northern Alberta and the Northwest Territories, Canada. Of these lakes, 22 were sinkholes, situated on limestone and gypsum, five were situated on the Canadian Shield and eight were shallow 'muskeg' lakes located on calcareous shales. All of the lakes were small to moderate in size. For
Diatoms (Bacillariophyceae) are a widely distributed group of microscopic, unicellular algae that... more Diatoms (Bacillariophyceae) are a widely distributed group of microscopic, unicellular algae that are characterized by siliceous cell walls (frustules). The size, shape and sculpturing of diatom frustules are taxonomically diagnostic. Moreover, because of their siliceous composition, diatoms are often well preserved in stratigraphic deposits, where they can be used to infer (quantitatively or qualitatively) past environmental conditions. The sensitivity of diatoms to a wide variety of environmental variables provides geographers with a multitude of research opportunities. This review focuses on palaeoecological reconstructions that are based on freshwater diatoms. Geographical applications including studies of climatology, hydrology, geomorphology, bio geography, and water-quality assessment and monitoring are discussed.
Quaternary Research, 1990
Two radiocarbon-dated cores from small lakes located approximately 25 km north of the mapped boun... more Two radiocarbon-dated cores from small lakes located approximately 25 km north of the mapped boundary between forest-tundra and tundra provide records of postglacial vegetation change at the treeline near Yellowknife, NWT, Canada. Basal radiocarbon dates of 6180 and 7470 yr B.P. were obtained from the cores. The fossil pollen evidence suggests that the initial vegetation was Betula tundra with a peatland component. Alnus became an important constituent of the pollen assemblages between 6900 and 5500 yr B.P. Both lakes record sharp increases in Picea cf. mariana pollen at approximately 5000 yr B.P., suggesting the establishment of forest-tundra. By 3500 yr B.P. Picea mariana forest-tundra had withdrawn. The proportion of organic to inorganic sediment in the cores was at a maximum between 5000 and 3500 yr B.P. Tundra has dominated the region since 3500 yr B.P. In northwestern Canada, the maximum northward advance of treeline occurred between 9000 and 5000 yr B.P. The asynchrony in treeline advance in central and northwestern Canada may reflect that glacial ice persisted in the interior NWT longer than previously believed. Alternatively, the asynchronous history of the treeline may be a result of the geometric properties of the long-wave westerly disturbance that is manifest in the median summer position of the arctic front and ultimately controls the geographic location of the treeline. 0 l!Bll University of Washington.
Diatom assemblages and biogenic silica concentrations in a ~200 year, varved sediment record from... more Diatom assemblages and biogenic silica concentrations in a ~200 year, varved sediment record from Rainbow Lake A (RLA), located in the northern boreal forest of Wood Buffalo National Park, straddling northern Alberta and the Northwest Territories (Canada), were investigated in order to determine the impacts of recent climate warming to a remote northern lake. Diatom community composition, trends in diatom-inferred total phosphorus (TP) and biogenic silica levels all showed significant changes, beginning between circa 1830 and 1840, coincident with the onset of increasingly warm June/July temperatures in northern Canada. We test several hypotheses which may have caused these nutrient changes, including local anthropogenic disturbances, forest fires, increased atmospheric deposition of nutrients or pollen, and internal sources of nutrient regeneration. We conclude that the most likely explanation of the observed changes is enhanced internal cycling of phosphorus due to increased thermal stratification in response to warmer summer temperatures and/or decreased meromictic stability. These results, in combination with other recent paleolimnological research at high latitude regions, suggest significant and widespread aquatic response to increasingly warm temperatures beginning in the nineteenth century.
Several recent studies have successfully applied diatom-based paleolimnological techniques to inf... more Several recent studies have successfully applied diatom-based paleolimnological techniques to infer past hydrological changes in arctic and subarctic regions. For example, we summarize arctic studies that attempt to determine changes in peat water content, flood frequency, river discharge, effective moisture and ice cover in northern regions. Some of the investigations are still in preliminary stages, but represent innovative approaches to study arctic and subarctic paleohydrology. New data demonstrate that lake depth, which may be related to changing hydrological conditions, is a significant variable influencing the distributions of diatom taxa in lake surface sediment calibration sets from Wood Buffalo National Park (WBNP), on the border of Alberta and the Northwest Territories, Canada, and from Fennoscandia (mainly northwest Finland). Weighted averaging regression and calibration methods were used to develop quantitative inference models for lake depth using diatom assemblages preserved in surface sediments. The predictive abilities of the transfer functions were relatively high (for WBNP r 2 = 0.70 and RMSE = 2.6 m, and for Fennoscandia r 2 = 0.88 and RMSE = 1.8 m). However, evaluating the transfer functions using jack-knifing procedures indicated lower predictive abilities, possibly reflecting the relatively small sample size and/or short gradients used in these calibration sets. Such transfer functions can be used to track overall trends in lake levels, and provide an objective assessment as to directions of changing lake levels. Any interpretations of inferred lake levels, especially those related to climate change, must be made cautiously and must include some understanding of the local, present-day hydrological system.
To investigate the response of a remote boreal lake to recent climate warming, a |200-year varved... more To investigate the response of a remote boreal lake to recent climate warming, a |200-year varved sediment record from Rainbow Lake A (RLA), located in the northern boreal forest of Wood Buffalo National Park, straddling northern Alberta and the Northwest Territories (Canada), was investigated using diatom assemblages and biogenic silica concentrations. Diatom community composition, trends in diatom-inferred total phosphorus (TP) and biogenic silica levels all showed significant changes beginning between circa 1830 and 1840, coincident with the onset of increasingly warm June / July temperatures in northern Canada. We evaluated several hypotheses which may have caused these nutrient changes, including local anthropogenic disturbances, forest fires, increased atmospheric deposition of nutrients or pollen, and internal sources of nutrient regeneration. We concluded that TP is likely increasing as a result of enhanced internal cycling of phosphorus due to either increased thermal stratification in response to warmer summer temperatures and / or decreased meromictic stability. The results presented here, in combination with other recent paleolimnological research in northern latitude regions, suggest widespread aquatic response to increasing temperatures beginning in the 19th century.