Seasonality of Dissolved Nitrogen from Spring Melt to Fall Freezeup in Alaskan Arctic Tundra and Mountain Streams PDF Download
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Author: Thomas A. Douglas Publisher: ISBN: Category : Alaska Languages : en Pages : 20
Book Description
Predicting the response of dissolved nitrogen export from Arctic watersheds to climate change requires an improved understanding of seasonal nitrogen dynamics. Recent studies of Arctic rivers emphasize the importance of spring thaw as a time when large fluxes of nitrogen are exported from Arctic watersheds, but studies capturing the entire hydrologic year are rare. We examined the temporal variability of dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) concentrations in six streams/rivers in Arctic Alaska from spring melt to fall freezeup (May through October) in 2009 and 2010. DON concentrations were generally high during snowmelt and declined as runoff decreased. DIN concentrations were low through the spring and summer and increased markedly during the late summer and fall, primarily due to an increase in nitrate. The high DIN concentrations were observed to occur when seasonal soil thaw depths were near maximum extents. Concurrent increases in DIN and DIN‐to‐chloride ratios suggest that net increases from nitrogen sources contributed to these elevated DIN concentrations. Our stream chemistry data, combined with soil thermistor data, suggest that downward penetration of water into seasonally thawed mineral soils, and reduction in biological nitrogen assimilation relative to remineralization, may increase DIN export from Arctic watersheds during the late summer and fall. While this is part of a natural cycle, improved understanding of seasonal nitrogen dynamics is particularly important now because warmer temperatures in the Arctic are causing earlier spring snowmelt and later fall freezeup in many regions.
Author: Thomas A. Douglas Publisher: ISBN: Category : Alaska Languages : en Pages : 20
Book Description
Predicting the response of dissolved nitrogen export from Arctic watersheds to climate change requires an improved understanding of seasonal nitrogen dynamics. Recent studies of Arctic rivers emphasize the importance of spring thaw as a time when large fluxes of nitrogen are exported from Arctic watersheds, but studies capturing the entire hydrologic year are rare. We examined the temporal variability of dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) concentrations in six streams/rivers in Arctic Alaska from spring melt to fall freezeup (May through October) in 2009 and 2010. DON concentrations were generally high during snowmelt and declined as runoff decreased. DIN concentrations were low through the spring and summer and increased markedly during the late summer and fall, primarily due to an increase in nitrate. The high DIN concentrations were observed to occur when seasonal soil thaw depths were near maximum extents. Concurrent increases in DIN and DIN‐to‐chloride ratios suggest that net increases from nitrogen sources contributed to these elevated DIN concentrations. Our stream chemistry data, combined with soil thermistor data, suggest that downward penetration of water into seasonally thawed mineral soils, and reduction in biological nitrogen assimilation relative to remineralization, may increase DIN export from Arctic watersheds during the late summer and fall. While this is part of a natural cycle, improved understanding of seasonal nitrogen dynamics is particularly important now because warmer temperatures in the Arctic are causing earlier spring snowmelt and later fall freezeup in many regions.
Author: Matthew Solomon Khosh Publisher: ISBN: Category : Languages : en Pages : 316
Book Description
Climate-linked changes in hydrology and biogeochemical processes within Arctic watersheds are likely already affecting fluvial export of waterborne materials, including organic matter (OM) and dissolved inorganic nitrogen (DIN). Our understanding of Arctic watershed OM and DIN export response to climate change is hampered by a lack of contemporary baselines, as well as a dearth of seasonally comprehensive studies. This work focuses on characterizing OM and DIN concentrations and sources in six streams/rivers on the North Slope of Alaska during the entirety of the hydrologic year (May through October) in 2009 and 2010. The highest OM concentrations occurred during spring snowmelt, with results indicating that terrestrial vegetation leachates are the major source of dissolved OM, while particulate OM originates from a degraded soil source. Over the hydrologic year, soils became a progressively increasing source of dissolved OM, while autochthonous production made up a sizeable proportion of particulate OM during base flow conditions. DIN concentrations were low throughout the spring and summer and increased markedly during the late summer and fall. Our findings suggest that penetration of water into thawed mineral soils, and a reduction in nitrogen assimilation relative to remineralization, may increase DIN export from Arctic watersheds during the late summer and fall. Although recent studies of Arctic rivers have emphasized the importance of the spring thaw period on OM export, our understanding of the mechanisms that control water chemistry observations during this time are still lacking. Experimental leaching results, from experiments conducted in 2014, suggest that aboveground plant biomass is a major source of dissolved OM in Arctic catchments during the spring, and that the timing of freezing and drying conditions during the fall may impact dissolved OM leaching dynamics on that same material the following snowmelt. Improved knowledge of OM and DIN temporal trends and the mechanisms that control seasonal concentrations is essential for understanding export dynamics of these water constituents in Arctic river systems. Perhaps more importantly, increased understanding of the seasonal controls on OM and DIN export in Arctic rivers is critical for predicting how these systems will respond under future climate change scenarios.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Climate change has resulted in warmer soil temperatures, earlier spring thaw and later fall freeze-up, resulting in warmer soil temperatures and thawing of permafrost in tundra regions. While these changes in temperature metrics tend to lengthen the growing season for plants, light levels, especially in the fall, will continue to limit plant growth and nutrient uptake. We conducted a laboratory experiment using intact soil cores with and without vegetation from a tundra peatland to measure the effects of late freeze and early spring thaw on carbon dioxide (CO2) exchange, methane (CH4) emissions, dissolved organic carbon (DOC) and nitrogen (N) leaching from soils. We compared soil C exchange and N production with a 30 day longer seasonal thaw during a simulated annual cycle from spring thaw through freeze-up and thaw. Across all cores, fall N leaching accounted for similar to 33% of total annual N loss despite significant increases in microbial biomass during this period. Nitrate(NO3- ) leaching was highest during the fall (5.33 ± 1.45 mgNm-2 d-1) following plant senescence and lowest during the summer (0.43 ± 0.22 mg Nm-2 d-1). In the late freeze and early thaw treatment, we found 25% higher total annual ecosystem respiration but no significant change in CH4 emissions or DOC loss due to high variability among samples. The late freeze period magnified N leaching and likely was derived from root turnover and microbial mineralization of soil organic matter coupled with little demand from plants or microbes. Furthermore, large N leaching during the fall will affect N cycling in low-lying areas and streams and may alter terrestrial and aquatic ecosystem nitrogen budgets in the arctic.
Author: John E. Hobbie Publisher: Oxford University Press ISBN: 0199860408 Category : Science Languages : en Pages : 354
Book Description
The latest volume in the LTER series, this book presents the results and finding of the Long-Term Ecological Research site in the Alaskan Arctic, discussing Arctic ecology from a variety of perspectives and disciplines.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Soil nitrogen availability to plants is a fundamental control on the structure and functioning of arctic tundra ecosystems. Despite recent evidence that biogeochemical and microbial dynamics during the non-growing season impact nitrogen availability to plants in tundra ecosystems, very little is known about soil microbial patterns and mechanisms for nutrient mobilization in the winter, spring and fall. In this dissertation I have examined the environmental and microbial controls on seasonal nitrogen mobilization in a widespread Canadian low arctic birch hummock tundra ecosystem. In particular, I have investigated the potential for increased winter snow depth and different above-ground vegetation-types to alter soil microbial community patterns and nutrient mobilization from organic matter into plant-available pools. First, I demonstrated that experimentally deepened winter snow altered soil microbial physiology during winter, defined as increased microbial carbon limitation to growth and activity. Second, I established that deepened snow enhanced spring nutrient mobilization during distinct environmental phases, producing large peaks in the soil microbial biomass and soil solution carbon, nitrogen and phosphorus during snow thaw. Third, I showed that laboratory predictions of early-spring air temperature freeze-thaw cycles promoting tundra soil nitrogen loss are not relevant, as the soil environment and soil biogeochemistry were relatively stable after snow melt and before plant growth began. Fourth, I demonstrated that microbial functional groups did not differ strongly under different tundra vegetation types, but higher quality shrub litter induced positive feedbacks on soil carbon availability and soil nitrogen mineralization in the late summer. Finally, I illustrated that annual patterns of tundra soil microbial community structure and composition were strongly linked to soil biogeochemistry and that significant shifts in fungal/bacterial ratios occur during sno.
Author: Andrew P. Borner Publisher: ISBN: Category : Plant phenology Languages : en Pages : 94
Book Description
"This study was part of the International Tundra Experiment (ITEX) and examined the effects of increased winter snow depth and decreased growing season length on the phenology of four arctic plant species (Betula nana, Salix pulchra, Eriophorum vaginatum, and Vaccinium vitis-idaea) and seasonal nitrogen availability in arctic snowbed communities. Increased snow depth had a large effect on the temporal pattern of first date snow-free in spring, bud break, and flowering, but did not affect the rate of plant development. By contrast, snow depth had a large qualitative effect on N mineralization in deep snow zones, causing a shift in the timing and amount of N mineralized compared to ambient snow zones. Nitrogen mineralization in deep snow zones occurred mainly overwinter, whereas N mineralization in ambient snow zones occurred mainly in spring. Concentrations of soil dissolved organic nitrogen (DON) were approximately 5 times greater than concentrations of inorganic nitrogen (DIN) and did not vary significantly over the season. Projected increases in the depth and duration of snow cover in arctic plant communities will likely have minor effects on plant phenology, but potentially large effects on patterns of N cycling"--Leaf iii.
Author: Charles R. Goldman Publisher: John Wiley & Sons ISBN: 1118470613 Category : Science Languages : en Pages : 481
Book Description
Effects of global warming on the physical, chemical, ecological structure and function and biodiversity of freshwater ecosystems are not well understood and there are many opinions on how to adapt aquatic environments to global warming in order to minimize the negative effects of climate change. Climatic Change and Global Warming of Inland Waters presents a synthesis of the latest research on a whole range of inland water habitats – lakes, running water, wetlands – and offers novel and timely suggestions for future research, monitoring and adaptation strategies. A global approach, offered in this book, encompasses systems from the arctic to the Antarctic, including warm-water systems in the tropics and subtropics and presents a unique and useful source for all those looking for contemporary case studies and presentation of the latest research findings and discussion of mitigation and adaptation throughout the world. Edited by three of the leading limnologists in the field this book represents the latest developments with a focus not only on the impact of climate change on freshwater ecosystems but also offers a framework and suggestions for future management strategies and how these can be implemented in the future. Limnologists, Climate change biologists, fresh water ecologists, palaeoclimatologists and students taking relevant courses within the earth and environmental sciences will find this book invaluable. The book will also be of interest to planners, catchment managers and engineers looking for solutions to broader environmental problems but who need to consider freshwater ecology.
Author: Robin Dublin Publisher: ISBN: 9781890692100 Category : Languages : en Pages : 250
Book Description
Covers elements of alpine and lowland ecosystems, the role of wind, cold, snow and permafrost, animal and plant survival techniques, tundra food chains and food webs, the fragility and resistance of plants, animals and the land, and conservation issue investigations.
Author: U.S. Global Change Research Program Publisher: Cambridge University Press ISBN: 0521144078 Category : Business & Economics Languages : en Pages : 193
Book Description
Summarizes the science of climate change and impacts on the United States, for the public and policymakers.
Author: Thomas A. Douglas
Author: Thomas A. Douglas
Author: Matthew Solomon Khosh
Author: 
Author: John E. Hobbie
Author: 
Author: Andrew P. Borner
Author: Charles R. Goldman
Author: Hui Li
Author: Robin Dublin
Author: U.S. Global Change Research Program