Ronald Daanen

Vegetation on mesic loamy and sandy soils along a 1700-km maritime Eurasia Arctic Transect

Abstract Questions How do plant communities on zonal loamy vs. sandy soils vary across the full maritime Arctic bioclimate gradient? How are plant communities of these areas related to existing vegetation units of the European Vegetation Classification? What are the main environmental factors controlling transitions of vegetation along the bioclimate gradient? Location 1700‐km Eurasia Arctic Transect (EAT), Yamal Peninsula and Franz Josef Land (FJL), Russia. Methods The Braun‐Blanquet approach was used to sample mesic loamy and sandy plots on 14 total study sites at six locations, one in each of the five Arctic bioclimate subzones and the forest–tundra transition. Trends in soil factors, cover of plant growth forms (PGFs) and species diversity were examined along the summer warmth index (SWI) gradient and on loamy and sandy soils. Classification and ordination were used to group the plots and to test relationships between vegetation and environmental factors. Results Clear, mostly non‐linear, trends occurred for soil factors, vegetation structure and species diversity along the climate gradient. Cluster analysis revealed seven groups with clear relationships to subzone and soil texture. Clusters at the ends of the bioclimate gradient (forest–tundra and polar desert) had many highly diagnostic taxa, whereas clusters from the Yamal Peninsula had only a few. Axis 1 of a DCA was strongly correlated with latitude and summer warmth; Axis 2 was strongly correlated with soil moisture, percentage sand and landscape age. Conclusions Summer temperature and soil texture have clear effects on tundra canopy structure and species composition, with consequences for ecosystem properties. Each layer of the plant canopy has a distinct region of peak abundance along the bioclimate gradient. The major vegetation types are weakly aligned with described classes of the European Vegetation Checklist, indicating a continuous floristic gradient rather than distinct subzone regions. The study provides ground‐based vegetation data for satellite‐based interpretations of the western maritime Eurasian Arctic, and the first vegetation data from Hayes Island, Franz Josef Land, which is strongly separated geographically and floristically from the rest of the gradient and most susceptible to on‐going climate change.

Thermo- and Hydrodynamic Simulation of Variably Saturated Flow in Northern Latitude Peatlands

Peatlands store an estimated one quarter of the Earth’s terrestrial soil carbon. Predominantly found within northern latitudes, peatlands contribute an estimated 17-28% of global methane emissions and therefore play an important role in the global carbon cycle. The application of models attempting to accurately represent the energy and hydrologic mass transfer in peatlands have been limited with application of generic functions of moisture retention and thermal conductivity. We have collected environmental data over a four year period from the Alaska Peatland Experiment (APEX) site, a heavily instrumented fen located in interior Alaska. The objective of this research is to develop several deterministic models of complex energy transfer and multiphase hydrologic processes, simulate and apply them to organic variably saturated soils in peatlands. More complex representations of the unsaturated subsurface and energy transfer within organic soils have the potential to provide insight on the dynamics of subterranean microbiological processes associated with carbon transformations, atmospheric emissions of greenhouse gases, and hydrologic transport. We have used finite element and volume analyses to account for seasonal variations of mass and energy transport. The application of a modified van Genuchten equation for variably saturated flow modeling has been used to account for all hydrologic processes. The results illustrate that the water table has a distinctive non-linear effect on heat transfer and phase change. Results of our study also indicate the importance of variability in thermal conductivity of organic soils and quantify the effect of porosity within application of coupled models.

Application of Geophysical and Spectral Methods in Non-invasive Characterization of Porous Media : A Critical Review

The objective of this research is to use geophysical methods and spectral analysis techniques for non-invasive characterization of the subsurface in cold regions under isothermal conditions. As a component of the research, this paper provides a critical review of the various geophysical techniques used for characterization with special mention of the application of spectral methods and discussion on the choice of suitable surrogates. Traditional methods of porous media characterization such as pumping tests are invasive and unsuitable for many reasons including the high-cost involved, inability for local scale characterization, and possible contamination problems due to alteration of flow regime. Attempts for non-destructive characterization of subsurface hydraulic properties have resulted in the development of many conceptual and theoretical models. Attributes of the porous media such as porosity, grain size, packing, and geological texture and structure, are known to have direct control on permeability and may be used as surrogates for its estimation. Since complete three-dimensional information of the subsurface is very difficult to obtain, two-dimensional maps of the surrogates aided by heuristic knowledge of the geologic controls on hydraulic properties may be useful for characterization. Most of the non-invasive characterization methods have utilized correlation of such inexpensive, measurable surrogate(s) with permeability in conjunction with one or more geophysical methods (e.g. GPR). Success of such methods depends largely on the choice of suitable surrogate(s) and strength of their correlation with the target property (viz. permeability). Researchers have used spectral analysis techniques to enhance and extrapolate signatures from the images or maps of the surrogates to study possible correlation with permeability for continuous mapping of the permeability.

The Effect of Vegetation on Simulated Differential Ice Accumulation in Non-Sorted Circles Ecosystems

Changes in the Arctic landscape due to climate warming are evident in greening of the tundra, formation of permafrost thaw lakes and erosion of ice wedge polygons. The changes are caused by atmospheric as well as soil and permafrost warming trends. Freezing and thawing drive many landscape features in the Arctic; cryoturbation being the major force that moves the soil. The interaction between vegetation development and cryoturbation is the objective of our research. In particular we simulate the effects of vegetation on the freezing rate in soils in three-dimensions in order to model non-sorted circle ecosystems that are prevalent in the Arctic. Differential insulation at the soil surface causes the soil to freeze irregularly and determines the strength and location of cryoturbation, caused by ice lens formation. Redistribution of water causes ice accumulation where the soil freezes first, while the thickness of the vegetation and its organic layer slows the freezing process, which dries the soil below vegetated patches. For our research we combined two simulation models, 1) the WIT3D model that simulates the hydrology in the active layer during freezing, and 2) the ArcVeg model that simulates vegetation succession in the tundra. We have analyzed vegetation types along a bioclimatic gradient in the arctic tundra and determined an insulation factor for these vegetation types. The insulation values were used in the combined models and the results show that warming conditions simulated with bare ground, as initial condition, would form a vegetation pattern that is more uniform and would develop fewer non-sorted circles. However when an existing pattern is simulated with a warmer climate as the initial condition, then the pattern does not disintegrate but the vegetation dominates and makes the non-sorted circles smaller. Over a longer time frame the vegetation can eventually dominate the non-sorted circles completely.