Best Practices in Collaborative Research with Northern Communities: A Synopsis from Early Career Researchers

Combining scientific and traditional knowledge is crucial to understand environmental systems across circum-Arctic regions, where climate change is most striking. However, building collaborative partnerships between visiting scientists and local, indigenous traditional knowledge holders in Northern communities presents challenges. The workshop “Community-based Research: Do`s and Don`ts of Arctic Research” was organized as an IASC cross-cutting initiative at ICOP2016 in Potsdam, Germany, to facilitate dialogue between Early Career Researchers (ECRs) and Northern residents. This workshop resulted in a diverse list of considerations and sustainable practices to improve traditional and scientific knowledge exchange, and collaborative Northern research. An extensive list of positive (Do`s) and few negative recommendations (Don`ts) was generated together with ECRs and Arctic representatives. Many good ideas on research design, active communication and community involvement developed from fruitful discussions. This study provides an example of bottom-up strategy development in order to enhance knowledge transfer between scientists and northern indigenous communities

Permafrost Landscape History Shapes Fluvial Chemistry, Ecosystem Carbon Balance, and Potential Trajectories of Future Change

Intensifying permafrost thaw alters carbon cycling by mobilizing large amounts of terrestrial substrate into aquatic ecosystems. Yet, few studies have measured aquatic carbon fluxes and constrained drivers of ecosystem carbon balance across heterogeneous Arctic landscapes. Here, we characterized hydrochemical and landscape controls on fluvial carbon cycling, quantified fluvial carbon fluxes, and estimated fluvial contributions to ecosystem carbon balance across 33 watersheds in four ecoregions in the continuous permafrost zone of the western Canadian Arctic: unglaciated uplands, ice-rich moraine, and organic-rich lowlands and till plains. Major ions, stable isotopes, and carbon speciation and fluxes revealed patterns in carbon cycling across ecoregions defined by terrain relief and accumulation of organics. In previously unglaciated mountainous watersheds, bicarbonate dominated carbon export (70% of total) due to chemical weathering of bedrock. In lowland watersheds, where soil organic carbon stores were largest, lateral transport of dissolved organic carbon (50%) and efflux of biotic CO2 (25%) dominated. In watersheds affected by thaw-induced mass wasting, erosion of ice-rich tills enhanced chemical weathering and increased particulate carbon fluxes by two orders of magnitude. From an ecosystem carbon balance perspective, fluvial carbon export in watersheds not affected by thaw-induced wasting was, on average, equivalent to 6%–16% of estimated net ecosystem exchange (NEE). In watersheds affected by thaw-induced wasting, fluvial carbon export approached 60% of NEE. Because future intensification of thermokarst activity will amplify fluvial carbon export, determining the fate of carbon across diverse northern landscapes is a priority for constraining trajectories of permafrost region ecosystem carbon balance

Meta-analysis of the detection of plant pigment concentrations using hyperspectral remotely sensed data

Passive optical hyperspectral remote sensing of plant pigments offers potential for understanding plant ecophysiological processes across a range of spatial scales. Following a number of decades of research in this field, this paper undertakes a systematic meta-analysis of 85 articles to determine whether passive optical hyperspectral remote sensing techniques are sufficiently well developed to quantify individual plant pigments, which operational solutions are available for wider plant science and the areas which now require greater focus. The findings indicate that predictive relationships are strong for all pigments at the leaf scale but these decrease and become more variable across pigment types at the canopy and landscape scales. At leaf scale it is clear that specific sets of optimal wavelengths can be recommended for operational methodologies: total chlorophyll and chlorophyll a quantification is based on reflectance in the green (550–560nm) and red edge (680–750nm) regions; chlorophyll b on the red, (630–660nm), red edge (670–710nm) and the near-infrared (800–810nm); carotenoids on the 500–580nm region; and anthocyanins on the green (550–560nm), red edge (700–710nm) and near-infrared (780–790nm). For total chlorophyll the optimal wavelengths are valid across canopy and landscape scales and there is some evidence that the same applies for chlorophyll a

Stream dissolved organic matter in permafrost regions shows surprising compositional similarities but negative priming and nutrient effects

Permafrost degradation is delivering bioavailable dissolved organic matter (DOM) and inorganic nutrients to surface water networks. While these permafrost subsidies represent a small portion of total fluvial DOM and nutrient fluxes, they could influence food webs and net ecosystem carbon balance via priming or nutrient effects that destabilize background DOM. We investigated how addition of biolabile carbon (acetate) and inorganic nutrients (nitrogen and phosphorus) affected DOM decomposition with 28-day incubations. We incubated late-summer stream water from 23 locations nested in seven northern or high-altitude regions in Asia, Europe, and North America. DOM loss ranged from 3% to 52%, showing a variety of longitudinal patterns within stream networks. DOM optical properties varied widely, but DOM showed compositional similarity based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. Addition of acetate and nutrients decreased bulk DOM mineralization (i.e., negative priming), with more negative effects on biodegradable DOM but neutral or positive effects on stable DOM. Unexpectedly, acetate and nutrients triggered breakdown of colored DOM (CDOM), with median decreases of 1.6% in the control and 22% in the amended treatment. Additionally, the uptake of added acetate was strongly limited by nutrient availability across sites. These findings suggest that biolabile DOM and nutrients released from degrading permafrost may decrease background DOM mineralization but alter stoichiometry and light conditions in receiving waterbodies. We conclude that priming and nutrient effects are coupled in northern aquatic ecosystems and that quantifying two-way interactions between DOM properties and environmental conditions could resolve conflicting observations about the drivers of DOM in permafrost zone waterways

The relative importance of climate and vegetation properties on patterns of North American breeding bird species richness

Recent advances in remote sensing and ecological modeling warrant a timely and robust investigation of the ecological variables that underlie large-scale patterns of breeding bird species richness, particularly in the context of intensifying land use and climate change. Our objective was to address this need using an array of bioclimatic and remotely sensed data sets representing vegetation properties and structure, and other aspects of the physical environment. We first build models of bird species richness across breeding bird survey (BBS) routes, and then spatially predict richness across the coterminous US at moderately high spatial resolution (1 km). Predictor variables were derived from various sources and maps of species richness were generated for four groups (guilds) of birds with different breeding habitat affiliation (forest, grassland, open woodland, scrub/shrub), as well as all guilds combined. Predictions of forest bird distributions were strong ( R ^2 = 0.85), followed by grassland (0.76), scrub/shrub (0.63) and open woodland (0.60) species. Vegetation properties were generally the strongest determinants of species richness, whereas bioclimatic and lidar-derived vertical structure metrics were of variable importance and dependent upon the guild type. Environmental variables (climate and the physical environment) were also frequently selected predictors, but canopy structure variables were not as important as expected based on more local to regional scale studies. Relatively sparse sampling of canopy structure metrics from the satellite lidar sensor may have reduced their importance relative to other predictor variables across the study domain. We discuss these results in the context of the ecological drivers of species richness patterns, the spatial scale of bird diversity analyses, and the potential of next generation space-borne lidar systems relevant to vegetation and ecosystem studies. This study strengthens current understanding of bird species–climate–vegetation relationships, which could be further advanced with improved canopy structure information across spatial scales

Low biodegradability of particulate organic carbon mobilized from thaw slumps on the Peel Plateau, NT, and possible chemosynthesis and sorption effects

Warming and wetting in the western Canadian Arctic are accelerating thaw-driven mass wasting by permafrost thaw slumps, increasing total organic carbon (TOC) delivery to headwater streams by orders of magnitude primarily due to increases in particulate organic carbon (POC). Upon thaw, permafrost carbon entering and transported within streams may be mineralized to CO2 or re-sequestered into sediments. The balance between these processes is an important uncertainty in the permafrost-carbon-climate feedback. Using aerobic incubations of TOC from streams affected by thaw slumps we find that slump-derived organic carbon undergoes minimal (g 1/4g 4g %) oxidation over a 1-month period, indicating that this material may be predominantly destined for sediment deposition. Simultaneous measurements of POC and dissolved organic carbon (DOC) suggest that mineralization of DOC accounted for most of the TOC loss. Our results indicate that mobilization of mineral-rich tills in this region may protect carbon from mineralization via adsorption to minerals and promote inorganic carbon sequestration via chemolithoautotrophic processes. With intensification of hillslope mass wasting across the northern permafrost zone, region-specific assessments of permafrost carbon fates and inquiries beyond organic carbon decomposition are needed to constrain drivers of carbon cycling and climate feedbacks within stream networks affected by permafrost thaw

Low biodegradability of particulate organic carbon mobilized from thaw slumps on the Peel Plateau, NT, and possible chemosynthesis and sorption effects

Warming and wetting in the western Canadian Arctic are accelerating thaw-driven mass wasting by permafrost thaw slumps, increasing total organic carbon (TOC) delivery to headwater streams by orders of magnitude primarily due to increases in particulate organic carbon (POC). Upon thaw, permafrost carbon entering and transported within streams may be mineralized to CO2 or re-sequestered into sediments. The balance between these processes is an important uncertainty in the permafrost-carbon-climate feedback. Using aerobic incubations of TOC from streams affected by thaw slumps we find that slump-derived organic carbon undergoes minimal (g 1/4g 4g %) oxidation over a 1-month period, indicating that this material may be predominantly destined for sediment deposition. Simultaneous measurements of POC and dissolved organic carbon (DOC) suggest that mineralization of DOC accounted for most of the TOC loss. Our results indicate that mobilization of mineral-rich tills in this region may protect carbon from mineralization via adsorption to minerals and promote inorganic carbon sequestration via chemolithoautotrophic processes. With intensification of hillslope mass wasting across the northern permafrost zone, region-specific assessments of permafrost carbon fates and inquiries beyond organic carbon decomposition are needed to constrain drivers of carbon cycling and climate feedbacks within stream networks affected by permafrost thaw

Physiographic Controls and Wildfire Effects on Aquatic Biogeochemistry in Tundra of the Yukon-Kuskokwim Delta, Alaska

Northern high-latitude deltas are hotspots of biogeochemical processing, terrestrial-aquatic connectivity, and, in Alaska’s Yukon-Kuskokwim Delta (YKD), tundra wildfire. Yet, wildfire effects on aquatic biogeochemistry remain understudied in northern delta regions, thus limiting a more comprehensive understanding of high latitude biogeochemical cycles. In this study, we assess wildfire impacts on summertime aquatic biogeochemistry in YKD tundra using a multi year (2015–2019) dataset of water chemistry measurements (n = 406) from five aquatic environments: peat plateau ponds, fen ponds, fen channels, lakes, and streams. We aimed to (i) characterize variation in hydrochemistry among aquatic environments; (ii) determine wildfire effects on hydrochemistry; and (iii) assess post-fire multi-year patterns in hydrochemistry in lakes (lower terrestrial-freshwater connectivity) and fen ponds (higher connectivity). Variation in hydrochemistry among environments was more strongly associated with watershed characteristics (e.g., terrestrial-aquatic connectivity) than wildfire. However, certain hydrochemical constituents showed consistent wildfire effects. Decreases in dissolved organic carbon (DOC) and CO2, and increases in pH, specific conductance, NH4 +, and NO3– indicate that, by combusting soil organic matter, wildfire reduces organics available for hydrologic transport and microbial respiration, and mobilizes nitrogen into freshwaters. Multi-year post-fire variation in specific conductance, DOC, and CO2 in lakes and fen ponds suggest that watershed characteristics underlie ecosystem response and recovery to wildfire in the YKD. Together, these results indicate that increasing tundra wildfire occurrence at northern high latitudes could drive multi-year shifts toward stronger aquatic inorganic nutrient cycling, and that variation in terrain characteristics is likely to underlie wildfire effects on aquatic ecosystems across broader scales

Impact of abrupt permafrost thaw on mineral elements release: case study in Peel Plateau, west Canadian Arctic

Abrupt thaw events in ice-rich permafrost regions lead to local landscape degradations (subsidence) known as thermokarst structures, which expand with present-day warming in the Arctic. Among these events, Retrogressive Thaw Slumps (RTS) expose deep material to erosion in addition to gradual permafrost thaw. The resulting eroded material comprises a mixture of organic-rich active layer and generally more mineral-rich deep perennially frozen permafrost. Exposing mineral-rich permafrost to weathering agents such as water is known to be a source of soluble elements release to local streams. However, soluble mineral element release may also influence mineral-organic carbon interactions within the resulting eroded material, thereby affecting the permafrost carbon feedback. More in-depth quantification of mineral element release from eroded material is needed for more precisely assessing the potential contribution of thermokarst-induced soluble element release to the carbon balance in these regions. Here we selected seven RTS structures from Peel Plateau, west Canadian Arctic, spanning a range of headwall height (2 to 25 m) and exposed land surface area (5 000 to 300 000 m²): we investigate RTS-affected permafrost soil profiles and sediments transported downstream from these disturbances. The organic carbon content, mineralogy, total elemental content and soluble element fractions were determined in soils at the slump headwall (active layer, Holocene permafrost, and Pleistocene permafrost) and in downstream eroded material (mud, and debris). The data support that RTS development is responsible for horizontal transfer of materials downstream from deep Pleistocene permafrost. Indeed, based on (i) a similar mineralogy comprising weatherable mineral phases, (ii) similar total content in Ca, K, Al and Sr, and (iii) similar soluble content in Ca, K, Mg, Na, downstream mud and debris are shown to be mainly fed by Pleistocene permafrost materials. The soluble element fraction from downstream eroded material is significantly higher than the one from previously thawed active layer soils. These soluble mineral elements may directly interact with organic carbon found in these mixed materials which were displaced by RTS and are now part of a new active layer developed on eroded materials

Deep material eroded from retrogressive thaw slump: case study in Peel Plateau, west Canadian Arctic

Ice-rich permafrost thaw is highly sensitive to the creation of local landscape subsidence in the Arctic, known as thermokarst structures. Upon thaw, these structures can erode, unlocking organic and mineral constituents and transferring this material downstream potentially affecting the ecosystem at larger scale. Such hillslope landscape processes have recently developed in Peel Plateau, west Canadian Arctic, as Retrogressive Thaw Slumps (RTS). We investigate whether material eroded from RTS and transported downstream originates from upper or deeper soil horizons with potentially distinct organic and mineral contents. The total elemental content and soluble element fractions were determined in soils from different depths at the slump headwall (active layer, Holocene permafrost, and Pleistocene permafrost) and in downstream eroded material (mud, and debris) for eight RTS structures. We observe a similar total content in Ca, K, Al and Sr, and soluble content in Ca, K, Mg, Na between the downstream mud and debris and the Pleistocene permafrost. The data highlight that the eroded material originates from the deeper Pleistocene permafrost, and contributes solute element concentrations that are significantly higher (by at least one order of magnitude) than in previously thawed active layer or locally Holocene permafrost. We hypothesize that RTS development is responsible for horizontal transfer of perennially frozen materials downstream originating from deep Pleistocene permafrost deposits. This means that in addition to exposing deep organic carbon to mineralization, modern RTS development likely affect local ecosystem chemistry by releasing soluble elements