Yukon Flats National Wildlife Refuge Research Articles

Arctic-boreal lakes of interior Alaska dominated by contemporary carbon

Northern high-latitude lakes are critical sites for carbon processing and serve as potential conduits for the emission of permafrost-derived carbon and greenhouse gases. However, the fate and emission pathways of permafrost carbon in these systems remain uncertain. Here, we used the natural abundance of radiocarbon to identify and trace the predominant sources of methane, carbon dioxide, dissolved inorganic and organic carbon in nine lakes within the Yukon Flats National Wildlife Refuge in interior Alaska, a discontinuous permafrost region with high landscape heterogeneity and susceptibility to climate, permafrost, and hydrological changes. We find that although Yukon Flats lakes primarily process young carbon (modern to 1290 ± 60 years before present), permafrost-derived carbon is present in some of the sampled lakes and contributes, at most, 30 ± 10% of the dissolved carbon in lake surface waters. Apportionment of young carbon and legacy carbon (carbon with radiocarbon age ⩾5000 years before present) is decoupled among the dissolved inorganic and organic carbon species, with methane showing a stronger legacy signature. Our observations suggest that permafrost-thaw-related transport of carbon through Yukon Flats lacustrine ecosystems and into the atmosphere is small, and likely regulated by surficial sediments, permafrost distribution, wildfire occurrence, or masked by contemporary carbon processes. The heterogeneity of lakes across our study area and northern landscapes more broadly cautions against using any one region (e.g. Yedoma permafrost lakes) to upscale their contribution across the pan-Arctic.

Toward Alaska Native research and data sovereignty: Observations and experiences from the Yukon Flats

Indigenous Peoples research and data sovereignty is of paramount importance to a healthy relationship between Indigenous Peoples and the research enterprise. The development of Indigenous methods and methodologies lends itself to the hot discussion of research and data or, as we posit, knowledge born from Alaska Native communities’ experiences and observations since time immemorial. Within the context of climate change, Alaska Native communities in the Yukon Flats National Wildlife Refuge (Flats) are experiencing research fatigue. There are an extraordinary number of researchers applying constant pressure on Alaska Native communities on the Yukon Flats to engage with research ideas and pursuits that are not of their own needs. In concert with large and frequent grant dollars that are promoting research with Alaska Native Peoples and demand grant proposals have components of coproduction of knowledge intertwined with the research. With so much research directed at, not with, Alaska Native communities on the Yukon Flats, never has it been more important to shape research and data sovereignty with Alaska Native communities based on their needs and their worldviews. This article works to demonstrate how established Indigenous methods in collaboration with Alaska Native and Allies scholarship alongside Alaska Native communities inform the future of Alaska Native research and data sovereignty.

Airborne Hyperspectral Data Acquisition and Processing in the Arctic: A Pilot Study Using the Hyspex Imaging Spectrometer for Wetland Mapping

A pilot study for mapping the Arctic wetlands was conducted in the Yukon Flats National Wildlife Refuge (Refuge), Alaska. It included commissioning the HySpex VNIR-1800 and the HySpex SWIR-384 imaging spectrometers in a single-engine Found Bush Hawk aircraft, planning the flight times, direction, and speed to minimize the strong bidirectional reflectance distribution function (BRDF) effects present at high latitudes and establishing improved data processing workflows for the high-latitude environments. Hyperspectral images were acquired on two clear-sky days in early September, 2018, over three pilot study areas that together represented a wide variety of vegetation and wetland environments. Steps to further minimize BRDF effects and achieve a higher geometric accuracy were added to adapt and improve the Hyspex data processing workflow, developed by the German Aerospace Center (DLR), for high-latitude environments. One-meter spatial resolution hyperspectral images, that included a subset of only 120 selected spectral bands, were used for wetland mapping. A six-category legend was established based on previous U.S. Geological Survey (USGS) and U.S. Fish and Wildlife Service (USFWS) information and maps, and three different classification methods—hybrid classification, spectral angle mapper, and maximum likelihood—were used at two selected sites. The best classification performance occurred when using the maximum likelihood classifier with an averaged Kappa index of 0.95; followed by the spectral angle mapper (SAM) classifier with a Kappa index of 0.62; and, lastly, by the hybrid classifier showing lower performance with a Kappa index of 0.51. Recommendations for improvements of future work include the concurrent acquisition of LiDAR or RGB photo-derived digital surface models as well as detailed spectra collection for Alaska wetland cover to improve classification efforts.

Spawning Distribution of Bering Ciscoes in the Yukon River

AbstractBering CiscoesCoregonus laurettaeare anadromous salmonids with known spawning populations only in the Yukon, Kuskokwim, and Susitna rivers in Alaska. A commercial fishery for the species was recently initiated at the mouth of the Yukon River, inspiring a series of research projects to enhance our understanding of the exploited population. This study was designed to delineate the geographic spawning distribution of Bering Ciscoes in the Yukon River. One hundred radio transmitters per year in 2012 and 2013 were deployed in prespawning Bering Ciscoes at a site located 1,176 km upstream from the sea. A total of 160 fish survived fish wheel capture and tagging, avoided harvest and predation after tagging, and continued migrating upstream to their spawning destinations. Approximately 79% migrated to spawn in the upper Yukon Flats, upstream from the mouth of the Porcupine River, and 21% migrated to spawn in the lower Yukon Flats. Locating the Bering Cisco spawning area, which is almost entirely encompassed by the Yukon Flats National Wildlife Refuge, enhances our ability to protect it from anthropogenic disturbance and enables future biological research on the spawning population.Received July 25, 2014; accepted November 13, 2014

A Whole Ecosystem Approach to Studying Climate Change in Interior Alaska

Yukon River Basin Principal Investigators Workshop; Portland, Oregon, 18–20 January 2011; High latitudes are known to be particularly susceptible to climate warming, leading to an emphasis of field and modeling research on arctic regions. Subarctic and boreal regions such as the Yukon River Basin (YRB) of interior Alaska and western Canada are less well studied, although they encompass large areas that are vulnerable to changes in forest composition, permafrost distribution, and hydrology. There is an urgent need to understand the resiliency and vulnerability of these complex ecosystems as well as their feedbacks to the global climate system. Consequently, U.S. Geological Survey scientists, with other federal agency, university, and private industry partners, is focusing subarctic interdisciplinary studies on the Beaver Creek Wild and Scenic River watershed (http://www.blm.gov/pgdata/content/ak/en/prog/nlcs/beavercrk_nwsr.html) and Yukon Flats National Wildlife Refuge (http://yukonflats.fws.gov/ ) in the YRB, south and west of Fort Yukon, Alaska. These areas are national treasures of wetlands, lakes, and uplands that support large populations of wildlife and waterfowl and are home to vibrant native Alaskan communities that depend on the area for a subsistence lifestyle.

Percent surface water estimation from MODIS BRDF 16-day image composites

Four models for deriving percent surface water estimates were developed for use with MODIS16-day Bidirectional Reflectance Distribution Function (BRDF) corrected composite images. The models allow intra-annual surface water estimates to be produced with 1 km spatial resolution and an 8-day temporal resolution when applied to image composites from sensors on both the Aqua and Terra platforms. The surface water models are conceptually simple, relying on widely used indices (NDVI, NDWI, and tasseled cap), but computationally intensive. The models differ in the time and effort required to produce or acquire the inputs necessary for model training. The models were applied and tested in Yukon Flats National Wildlife Refuge, an area with varied surface water types including ponds, fens, and the Yukon River and its tributaries. Resulting accuracies peaked with an R 2 of approximately 0.625, and model accuracies were higher for pixels with higher percentages of water.

Monitoring a boreal wildfire using multi-temporal Radarsat-1 intensity and coherence images

Twenty-five C-band Radarsat-1 synthetic aperture radar (SAR) images acquired from the summer of 2002 to the summer of 2005 are used to map a 2003 boreal wildfire (B346) in the Yukon Flats National Wildlife Refuge, Alaska under conditions of near-persistent cloud cover. Our analysis is primarily based on the 15 SAR scenes acquired during arctic growing seasons. The Radarsat-1 intensity data are used to map the onset and progression of the fire, and interferometric coherence images are used to qualify burn severity and monitor post-fire recovery. We base our analysis of the fire on three test sites, two from within the fire and one unburned site. The B346 fire increased backscattered intensity values for the two burn study sites by approximately 5–6 dB and substantially reduced coherence from background levels of approximately 0.8 in unburned background forested areas to approximately 0.2 in the burned area. Using ancillary vegetation information from the National Land Cover Database (NLCD) and information on burn severity from Normalized Burn Ratio (NBR) data, we conclude that burn site 2 was more severely burned than burn site 1 and that C-band interferometric coherence data are useful for mapping landscape changes due to fire. Differences in burn severity and topography are determined to be the likely reasons for the observed differences in post-fire intensity and coherence trends between burn sites.

Lesser Scaup Breeding Probability and Female Survival on the Yukon Flats, Alaska

ABSTRACT Information on the ecology of waterfowl breeding in the boreal forest is lacking, despite the boreal region's importance to continental waterfowl populations and to duck species that are currently declining, such as lesser scaup (Aythya affinis). We estimated breeding probability and breeding season survival of female lesser scaup on the Yukon Flats National Wildlife Refuge, Alaska, USA, in 2005 and 2006. We captured and marked 93 lesser scaup with radiotransmitters during prelaying and nesting periods. Although all marked lesser scaup females were paired throughout prelaying and incubation periods, we estimated breeding probability over both years as 0.12 (SE = 0.05, n = 67) using telemetry. Proportion of lesser scaup females undergoing rapid follicle growth at capture in 2006 was 0.46 (SE = 0.11, n = 37), based on concentration of yolk precursors in blood plasma. By combining methods based on telemetry, yolk precursors, and postovulatory follicles, we estimated maximum breeding probability as 0.68 (SE = 0.08, n = 37) in 2006. Notably, breeding probability was positively related to female body mass. Survival of female lesser scaup during the nesting and brood‐rearing periods was 0.92 (SE = 0.05) in 2005 and 0.86 (SE = 0.08) in 2006. Our results suggest that breeding probability is lower than expected for lesser scaup. In addition, the implicit assumption of continental duck‐monitoring programs that all paired females attempt to breed should be reevaluated. Recruitment estimates based on annual breeding‐pair surveys may overestimate productivity of scaup pairs in the boreal forest.

Nest habitat selection of White-winged Scoters on Yukon Flats, Alaska

Breeding bird surveys indicate a long-term decline in numbers of scoters (Melanitta spp.) breeding in North America. Little is known about the breeding habitat and reproductive life history of White-winged Scoters (M. fusca) in their primary breeding areas in the boreal forest of Alaska and northern Canada. We characterized selection of nest habitats and attributes within those habitats by measuring variables at nests and random sites on the Yukon Flats National Wildlife Refuge, Alaska. White-winged Scoters avoided nesting in meadows, but nested in scrub or forested habitat types in proportion to their availability (χ25 = 9.7, P = 0.08). Nests of radio-marked females were farther from water and edge ( 210 ± 43 and 10 ± 4 m, respectively), and in slightly thicker cover ( 6 ± 4%) than nests located without aid of radio transmitters. Females selected sites with more variable and abundant overhead and lateral cover, and sites closer to edge and water than random sites. The results imply nearly random use of scrub and forested habitat types within the study area, but selective use of attributes within those habitat types. This generalist approach to nest site selection at a larger scale may be an adaptive response to reduce detection by nest predators. Nests located without use of radio-marked females may not be representative of the population of nests at a study site. White-winged Scoters often selected nest sites with dense cover far from water, which may increase nest survival. However, concealed sites are difficult for heavy-bodied birds to escape and females may be trading productivity against their own mortality.

Fire history and fire management implications in the Yukon Flats National Wildlife Refuge, interior Alaska

We conducted this investigation in response to criticisms that the current Alaska Interagency Fire Management Plans are allowing too much of the landscape in interior Alaska to burn annually. To address this issue, we analyzed fire history patterns within the Yukon Flats National Wildlife Refuge, interior Alaska. We dated 40 fires on 27 landscape points within the refuge boundaries using standard dendrochorological methods. Fire return intervals based on tree ring data ranged from 37 to 166 years (mean = 90 ± 32 years; N = 38) over the 250 year time frame covered by this study. We found no significant differences in the frequency of fire occurence over time. There was no evidence to suggest that changes in fire management policy have significantly altered the fire regime in the Yukon Flats area. However, the lack of significant differences over time may be due in part to the relatively short time period that fires were actively suppressed in Alaska. The full suppression era (1939–1984) may have been too short to significantly alter the fire regime in all areas of interior Alaska.

Contaminants in Lesser Scaup Eggs and Blood from Yukon Flats National Wildlife Refuge, Alaska

AbstractDocumented declines in Lesser Scaup (Aythya affinis) populations may be caused by several factors, including reduced reproductive success or survival from exposure to environmental contaminants during winter, migration, or breeding. We evaluated organochlorines and inorganic elements in Lesser Scaup blood (n = 14) and eggs (n = 10) from a breeding area in the relatively pristine Yukon Flats National Wildlife Refuge in interior Alaska. Most contaminants were not at concentrations of concern. Lead was detected in only four blood samples, with an average when detected (0.29 mg kg−1 wet weight [ww]) slightly above background levels (0.20 mg kg−1 ww). Our study area had little or no hunting, but since lead exposure is correlated with hunting pressure, lead should be evaluated in other Lesser Scaup breeding areas. Strontium in eggs (mean = 10.90 mg kg−1 dry weight [dw]) was significantly negatively correlated with eggshell thickness. Eggshell thickness was also 18% lower than in museum specimens, a percentage associated with population declines in other species, and was not correlated with other contaminants. Few comparative data in the literature exist, but productivity in this breeding area was low (mean nest success = 12%), so further research on the effects of strontium on productivity through the mechanism of eggshell thinning is needed. Most environmental contaminants are unlikely to be affecting Lesser Scaup populations breeding in interior Alaska, but lead and strontium should be studied further.

Lesser Scaup Nest Success and Duckling Survival on the Yukon Flats, Alaska

Abstract: Over the last 20 years scaup numbers have declined, and these declines have been greatest in the northern boreal forests of Canada and Alaska where most lesser scaup (Aythya affinis) nest. We studied nest success and duckling survival of lesser scaup over 3 field seasons, 2001–2003, on the Yukon Flats National Wildlife Refuge in northeastern Alaska, USA. Daily survival rate (DSR) of nests on our study area across all 3 years was 0.943 (n = 177 nests, 95% CI: 0.930–0.954), corresponding to a nest success of only 12.3%, considerably lower than published estimates of an average nest success as high as 57% for lesser scaup in the northern boreal forest. With Mayfield logistic regression, we investigated effects on nest survival of year, clutch initiation date, and nesting habitat type (large wetlands >10 ha, small wetlands <10 ha, and wooded creeks). Neither year nor clutch initiation date influenced nest survival; however, the odds of nest success on large wetlands was 49% lower than on wooded creeks (odds ratio = 0.512, 95% CI = 0.286, 0.918). Based on the model that used only habitat type for estimation, DSR on large wetlands was 0.931 (corresponding nest success = 7.6%), DSR on small wetlands was 0.941 (nest success = 11.1%), and DSR on wooded creeks was 0.963 (nest success = 26.2%). To estimate duckling survival, we monitored 10 broods (n = 75 ducklings) over 3 field seasons by radiotagging hens at nest hatch. Most duckling mortality (94%) occurred in the first 10 days after hatch. Average duckling survival during 1–10 days was 0.321 (95% CI: 0.122–0.772), during 11–20 days was 0.996 (95% CI: 0.891–1.040), and during 21–30 days was 0.923 (95% CI: 0.769–1.041). Three of 10 hens moved all or part of their broods overland between nesting and brood‐rearing wetlands for distances of 0.3–1.6 km. Our estimates of lesser scaup nest success and duckling survival on the Yukon Flats were among the lowest ever reported for ducks nesting at northern latitudes, even though the study site was in pristine boreal forest. Estimating and comparing scaup demographic rates from different geographic areas can contribute to improved conservation. Given the scarcity of information on scaup nesting in the boreal forest, basic nesting parameters are important to those trying to model scaup population dynamics.

CONTAMINANTS IN LESSER SCAUP EGGS AND BLOOD FROM YUKON FLATS NATIONAL WILDLIFE REFUGE, ALASKA

Abstract Documented declines in Lesser Scaup (Aythya affinis) populations may be caused by several factors, including reduced reproductive success or survival from exposure to environmental contaminants during winter, migration, or breeding. We evaluated organochlorines and inorganic elements in Lesser Scaup blood (n = 14) and eggs (n = 10) from a breeding area in the relatively pristine Yukon Flats National Wildlife Refuge in interior Alaska. Most contaminants were not at concentrations of concern. Lead was detected in only four blood samples, with an average when detected (0.29 mg kg−1 wet weight [ww]) slightly above background levels (0.20 mg kg−1 ww). Our study area had little or no hunting, but since lead exposure is correlated with hunting pressure, lead should be evaluated in other Lesser Scaup breeding areas. Strontium in eggs (mean = 10.90 mg kg−1 dry weight [dw]) was significantly negatively correlated with eggshell thickness. Eggshell thickness was also 18% lower than in museum specimens,...

Implications of Fire Policy on Native Land Use in the Yukon Flats, Alaska

Through a process of participatory mapping, this research assessed the impacts of the 1984 change in Alaska fire policy from one of exclusion to one of management on Native land use in the Yukon Flats National Wildlife Refuge. Findings suggest that while the change in policy has had little measurable effect on community land use the continued suppression of fire on Native owned lands is having a direct impact on the current availability of wildlife resources to the point of necessitating territorial expansion among Native resource users. However, given the complexity of human nature, the impacts associated with the 1984 policy change should not be reduced to a simplistic cause-and-effect relationship. Rather this analysis demonstrates the interaction as well as the contradiction that occur between policy, culture, and ecology as these factors together have come to influence Native land use.

Limnology of Shallow Lakes in the Yukon Flats National Wildlife Refuge, Interior Alaska

ABSTRACT Data from 129 shallow riverine lakes within the Yukon Flats National Wildlife Refuge (between 65° 45'N and 67° 30'N and 142° 30'W and 150° 00'W) are presented as a baseline contribution to the regional limnology of Alaska. Ion composition reflected the composition of carbonate alluvium within the region; in most lakes Ca > Mg and bicarbonate dominated the anions (~90%). In lakes where alkali deposits occurred, Na, Mg and bicarbonate were the principal ions. Some 25% of the lakes were slightly brackish (conductivity >500 μS) to brackish. The lakes are colored, with 18 to 447 Pt-units. And, they are fertile, with over 70% classified as eu-or hypereutrophic on the basis of their nutrient content. Ratios of N:P suggested nitrogen was potentially limiting in about half the study lakes and was increasingly important at high P values. The yield of algal chlorophyll (Chl) per unit of plant nutrient was low in these lakes and Chl-nutrient relations explained less of the variance relative to published models. Invertebrate grazing potentially regulates Chi in some lakes. Typically these lakes freeze to the sediments and most do not support a permanent fishery. High ratios of organic suspended solids to Chl indicate detrital carbon contributes to the filterable carbon pool of these shallow lakes.

Factors Influencing Depredation of Artificial Duck Nests

Because artificial nests can facilitate controlled experiments of nest success, we used them to assess whether human visitation, nest density, vegetation structure, and proximity to habitat edge could affect depredation of duck nests on Yukon Flats National Wildlife Refuge, Alaska. More (P 0.05) between depredated and undisturbed nests

A Line Transect Model for Aerial Surveys

We employ line transect methods to estimate the density of the common and Pacific loon in the Yukon Flats National Wildlife Refuge from aerial survey data. Line transect methods have the advantage of automatically taking into account visibility bias due to detectability differences of animals at different distances from the transect line. However, line transect methods must overcome two difficulties when applied to aerial surveys: (1) the existence of a or zone of zero detection below the aircraft, and (2) the inaccurate recording of sighting distances due to high travel speeds, so that in fact only a few reliable distance class counts are available. We propose a unimodal detection function that provides an estimate of the effective area lost due to the blind strip, under the assumption that a line of perfect detection exists parallel to the transect line. The unimodal detection function can also be applied when a blind strip is absent, and in certain instances when the maximum probability of detection is less than 100%. A simple bootstrap procedure to estimate standard error is illustrated. Finally, we present results from a small set of Monte Carlo experiments.