Processes controlling nitrogen release and turnover in Arctic tundra

Thesis (Ph.D.) University of Alaska Fairbanks, 1990This thesis provides data on nitrogen cycling among communities representative of the major vegetation types in arctic Alaska. Through field studies, I examined the pattern of nitrogen dynamics in four tundra ecosystems (dry lichen heath, wet meadow, tussock tundra, and deciduous shrub tundra) of contrasting structure and productivity near Toolik Lake, Alaska. In addition, through field and laboratory experiments, I sought to identify the major controls over nitrogen release and turnover in these nitrogen-limited systems. These ecosystems, representing extremes of productivity in arctic Alaska, show order-of-magnitude differences in biomass and net primary productivity, and likewise, exhibit order-of-magnitude differences in net nitrogen mineralization and nitrogen turnover. Decomposition, soil respiration, net nitrogen mineralization, and the turnover of soil inorganic nitrogen were all highly correlated with net primary production. These results show that nutrient availability, in particular nitrogen availability, is a major control over tundra ecosystem function. Soil pools of organic nitrogen are large, whereas the pools of inorganic nitrogen are small, and the net rate of nitrogen mineralization in situ is low. Thus, nitrogen mineralization represents a major control point in the nitrogen cycle. Net nitrogen mineralization is relatively insensitive to changes in soil temperature, but highly responsive to changes in available soil carbon and nitrogen. Thus, the effect of organic matter quality on microbial activity is a more important control of nitrogen release than is the direct effect of temperature. Free amino acids constitute a larger proportion of extractable soil nitrogen than do ammonium and nitrate. Tundra species have the capacity to absorb some amino acids directly at rates comparable to ammonium absorption. These experimental results contrast with the widely held assumption that mineral nitrogen is the only form of nitrogen available to plants. I conclude that we must examine the behavior of both inorganic and organic soil nitrogen in order to adequately understand nitrogen cycling in tundra soils and the functioning of arctic ecosystems

EFFECTS OF VARIABLE FIRE SEVERITY ON FORAGE PRODUCTION AND FORAGING BEHAVIOR OF MOOSE IN WINTER

The increasing frequency and extent of wildfires in Alaska over the last half century has spurred increased interest in understanding the role of post-fire succession on vegetation establishment. Our primary goal was to examine how wildfire affects production and distribution of winter forage for moose  (Alces alces) in interior Alaska, and how these changes in forage availability control forage offtake. Fire severity classification was based on post-fire depth of residual soil organic matter. We used a browse survey protocol to estimate the biomass of current year production (kg/ha) and overwinter offtake (kg/ha) by moose. Under the assumption of homogenous effects of fire severity on regeneration, we estimated that moose consumed 36% of all forage (current annual growth) across the study area. However, we found that moose exhibited significantly higher browse consumption relative to browse production in high fire severity sites than in low severity sites (P < 0.05). When we adjusted our estimates of forage production and consumption by accounting for the significant differences in browse consumption between severity classes and their distribution across the burn, moose consumed approximately 49% of available forage. Assessments of fire severity and its spatial distribution through remote sensing techniques and on-the-ground sampling provides improved projections of vegetation regeneration pathways following wildfires, and thus refined estimates of future browse production and habitat quality for moose

EFFECTS OF VARIABLE FIRE SEVERITY ON FORAGE PRODUCTION AND FORAGING BEHAVIOR OF MOOSE IN WINTER

The increasing frequency and extent of wildfires in Alaska over the last half century has spurred increased interest in understanding the role of post-fire succession on vegetation establishment. Our primary goal was to examine how wildfire affects production and distribution of winter forage for moose  (Alces alces) in interior Alaska, and how these changes in forage availability control forage offtake. Fire severity classification was based on post-fire depth of residual soil organic matter. We used a browse survey protocol to estimate the biomass of current year production (kg/ha) and overwinter offtake (kg/ha) by moose. Under the assumption of homogenous effects of fire severity on regeneration, we estimated that moose consumed 36% of all forage (current annual growth) across the study area. However, we found that moose exhibited significantly higher browse consumption relative to browse production in high fire severity sites than in low severity sites (P < 0.05). When we adjusted our estimates of forage production and consumption by accounting for the significant differences in browse consumption between severity classes and their distribution across the burn, moose consumed approximately 49% of available forage. Assessments of fire severity and its spatial distribution through remote sensing techniques and on-the-ground sampling provides improved projections of vegetation regeneration pathways following wildfires, and thus refined estimates of future browse production and habitat quality for moose

Permafrost Degradation Leaves Us On Thin Ice

The Tanana River flows through interior Alaska, a region characterized by discontinuous permafrost. Studies link degrading permafrost to increased winter river discharge due to increasing groundwater input. In winter, interior Alaskan rivers are exclusively fed by groundwater, which serves as an external source of heat. In fact, some portions of rivers fed by groundwater maintain thin ice throughout the winter, or remain altogether ice-free, despite very cold air temperatures. These ice conditions represent a significant danger to winter travellers who use rivers for wintertime travel, particularly in this largely roadless area. We developed a physically-based, numeric model to explore how fluctuations in groundwater discharge control ice thickness on the Tanana River. The model allows us to examine how changes in groundwater flow affect ice dynamics by addressing two questions: 1) What are the dominant factors controlling seasonal ice dynamics on the Tanana River? 2) What are the rates of change in ice thickness resulting from observed and projected changes in these factors?NSF, Alaska EPSCoR, Water and Environmental Research Center, Alaska Climate Science Center, Resilience and Adaptation Progra

Modeling the Thermal Balance Between Groundwater Springs and River Ice

We modeled the thermal balance between groundwater discharge and ice-free areas in the Tanana River near Fairbanks, Alaska, a region that is characterized by discontinuous permafrost. Under degrading permafrost conditions, these areas have been hypothesized to have increased winter discharge due to increasing contributions from groundwater flow. In the winter, interior Alaskan rivers are fed almost entirely by groundwater, which also serves as an external source of heat energy to the system. Several reaches of the river fed by groundwater springs remain ice-free or have dangerously thin ice throughout the winter despite air temperatures that dip below -40° C. These areas are dangerous for winter travelers who regularly use Alaskan rivers for wintertime travel. Our model allows us to explore the relationship between seasonal groundwater flows and ice thickness under changing atmospheric conditions. Our model results explore how local and regional changes in groundwater flow can affect ice thickness by addressing two primary research questions: 1) What physical factors influence seasonal ice dynamics on the Tanana River? 2) How is the thermal balance maintained between changing groundwater flow and cold air temperatures?NSF, US Army Corps of Engineers, Alaska EPSCoR, Resilience and Adaptation Program, Water and Environment Research Center, Alaska Climate Science Cente

Using local knowledge, hydrologic, and climate data to develop a driftwood harvest model in interior Alaska

Rural Alaskan residents are concerned that the character of the summer discharge in the Yukon River is changing, which is affecting their ability to harvest driftwood. The Yukon River flows northwesterly through British Columbia and the Yukon Territory before flowing southwest through Alaska. In most summers, residents of Tanana, Alaska harvest driftwood from the Yukon River during two different periods. Typically, driftwood accompanies high flows on the Yukon River associated with spring break‐up. A few weeks later, a second series of driftwood appears, associated with the “2nd rise,” which is reported to occur during early June. This study examines the nature of the differential timing of high flow events in the Yukon River. Many communities in interior Alaska have grown to rely upon driftwood as an important source of wood, which is used in construction, carving, and as a fuel source. Increasingly, villages in rural Alaska are trying to lessen their dependence upon expensive fossil fuels. To achieve this goal, a number of Alaskan villages have recently installed wood chip‐fired boilers to generate heat and/or electricity and additional boilers are slated to be installed in rural Alaska in the near future. These boilers are largely fed by driftwood, a cheap and easily processed wood source. Some Tanana residents have expressed concern that in recent years, driftwood was not readily available because the “2nd rise” flood event was absent. This is disconcerting for rural Alaskans that are becoming increasingly reliant upon the driftwood flows. Our goal is to determine if the perceived changes in driftwood availability are related to changes in river hydrology and if predicted changes in hydrology may affect driftwood flows and the livelihoods of rural Alaskans.NSF, Resilience and Adaptation Program, Water and Environmental Research Center, Alaska EPSCoR

Using Local Knowledge, Hydrologic, and Climate Data to Develop a Driftwood Harvest Model in Interior Alaska

Many rural Alaska residents rely on harvested driftwood from the Yukon River for fuel and construction materials, however they have stated that the character of the summer discharge in the Yukon River is changing and affecting their ability to harvest this resource. We examined whether the perceived changes in driftwood availability are related to changes in river hydrology and how changes in hydrology may affect future driftwood flows and the livelihoods of rural Alaskans.IAB, NSF, RAP, WERC, Alaska APSCo

Peer support in small towns: A decentralized mobile Hepatitis C virus clinic for people who inject drugs

Background & aims: New models of HCV care are needed to reach people who inject drugs (PWID). The primary aim was to evaluate HCV treatment uptake among HCV RNA positive individuals identified by point-of-care (POC) testing and liver disease assessment in a peer-driven decentralized mobile clinic. Methods: This prospective study included consecutive patients assessed in a mobile clinic visiting 32 small towns in Southern Norway from November 2019 to November 2020. The clinic was staffed by a bus driver and a social educator offering POC HCV RNA testing (GeneXpert®), liver disease staging (FibroScan® 402) and peer support. Viremic individuals were offered prompt pan-genotypic treatment prescribed by local hospital-employed specialists following a brief telephone assessment. Results: Among 296 tested individuals, 102 (34%) were HCV RNA positive (median age 51 years, 77% male, 24% advanced liver fibrosis/cirrhosis). All participants had a history of injecting drug use, 71% reported past 3 months injecting, and 37% received opioid agonist treatment. Treatment uptake within 6 months following enrolment was achieved in 88%. Treatment uptake was negatively associated with recent injecting (aHR 0.60; 95% CI 0.36-0.98), harmful alcohol consumption (aHR 0.44; 95% CI 0.20-0.99), and advanced liver fibrosis/cirrhosis (aHR 0.44; 95% CI 0.25-0.80). HCV RNA prevalence increased with age (OR 1.81 per 10-year increase; 95% 1.41-2.32), ranging from 3% among those <30 years to 55% among those ≥60 years. Conclusions: A peer-driven mobile HCV clinic is an effective and feasible model of care that should be considered for broader implementation to reach PWID outside the urban centres. Keywords: hepatitis C virus; peer support; people who inject drugs; point of care; treatment. © 2022 The Authors. Liver International published by John Wiley & Sons Ltd.publishedVersio

Terrain Features and Architecture of Wolverine (Gulo gulo) Resting Burrows and Reproductive Dens on Arctic Tundra

Burrowing species rely on subterranean and subnivean sites to fulfill important life-history and behavioral processes, including predator avoidance, thermoregulation, resting, and reproduction. For these species, burrow architecture can affect the quality and success of such processes, since characteristics like tunnel width and chamber depth influence access by predators, thermal insulation, and energy spent digging. Wolverines (Gulo gulo) living in Arctic tundra environments dig burrows in snow during winter for resting sites and reproductive dens, but there are few published descriptions of such burrows. We visited 114 resting burrows and describe associated architectural characteristics and non-snow structure. Additionally, we describe characteristics of 15 reproductive den sites that we visited during winter and summer. Although many resting burrows were solely excavated in snow, most incorporated terrain structures including cliffs, talus, river shelf ice, thermokarst caves, and stream cutbanks. Burrows typically consisted of a single tunnel leading to a single chamber, though some burrows had multiple entrances, branching tunnels, or both. Tunnels in resting burrows were shorter than those in reproductive dens, and resting chambers were typically located at the deepest part of the burrow. Reproductive dens were associated with snowdrift-forming terrain features such as streambeds, cutbanks on lake edges, thermokarst caves, and boulders. Understanding such characteristics of Arctic wolverine resting and reproductive structures is critical for assessing anthropogenic impacts as snowpack undergoes climate-driven shifts.Les espèces fouisseuses dépendent de lieux enfouis sous la terre et sous la neige pour satisfaire leurs importants processus de vie et de comportement, y compris l’évitement des prédateurs, la thermorégulation, le repos et la reproduction. Pour ces espèces, l’architecture des terriers peut avoir des effets sur la qualité et la réussite des processus, car des caractéristiques comme la largeur des tunnels et la profondeur des chambres influencent l’accès aux terriers par les prédateurs, l’isolation thermique et l’énergie dépensée pour creuser. L’hiver, les carcajous (Gulo gulo) qui vivent dans les environnements de la toundra de l’Arctique creusent des terriers dans la neige afin de s’en servir comme aires de repos et comme tanières de reproduction. Cependant, peu de descriptions de tels terriers ont été publiées. Nous avons visité 114 terriers de repos, puis nous avons décrit leurs caractéristiques architecturales et les structures connexes n’étant pas recouvertes de neige. Par ailleurs, nous décrivons les caractéristiques de 15 tanières de reproduction que nous avons visitées en hiver et en été. Même si de nombreux terriers de repos ont été uniquement creusés dans la neige, la plupart des terriers incorporaient des structures topographiques, dont des falaises, des talus, de la glace de banquise, des grottes thermokarstiques et des hautes berges de cours d’eau. En général, les terriers étaient composés d’un seul tunnel menant à une seule chambre, bien que certains avaient plusieurs entrées, des galeries, ou les deux. Les tunnels des aires de repos étaient moins longs que ceux des tanières de reproduction, et les chambres de repos étaient généralement situées dans la partie la plus profonde des terriers. Les tanières de reproduction étaient installées dans des caractéristiques topographiques où s’amoncelle la neige, comme les lits de cours d’eau, les hautes berges de lacs, les grottes thermokarstiques et les rochers. Il est essentiel de comprendre les caractéristiques des structures de repos et de reproduction des carcajous de l’Arctique afin d’être en mesure d’évaluer les incidences anthropiques au moment où le manteau neigeux subit des changements liés au climat