Markus Saari

Bio: Markus Saari is an academic researcher from University of Oulu. The author has contributed to research in topics: Environmental science & Peat. The author has an hindex of 3, co-authored 6 publications receiving 15 citations.

What conditions favor the influence of seasonally frozen ground on hydrological partitioning? A systematic review

Abstract: The influence of seasonally frozen ground (SFG) on water, energy, and solute fluxes is important in cold climate regions. The hydrological role of permafrost is now being actively researched, but the influence of SFG has received less attention. Intuitively, SFG restricts (snowmelt) infiltration, thereby enhancing surface runoff and decreasing soil water replenishment and groundwater recharge. However, the reported hydrological effects of SFG remain contradictory and appear to be highly site- and event-specific. There is a clear knowledge gap concerning under what physiographical and climate conditions SFG is more likely to influence hydrological fluxes. We addressed this knowledge gap by systematically reviewing published work examining the role of SFG in hydrological partitioning. We collected data on environmental variables influencing the SFG regime across different climates, land covers, and measurement scales, along with the main conclusion about the SFG influence on the studied hydrological flux. The compiled dataset allowed us to draw conclusions that extended beyond individual site investigations. Our key findings were: (a) an obvious hydrological influence of SFG at small-scale, but a more variable hydrological response with increasing scale of measurement, and (b) indication that cold climate with deep snow and forest land cover may be related to reduced importance of SFG in hydrological partitioning. It is thus increasingly important to understand the hydrological repercussions of SFG in a warming climate, where permafrost is transitioning to seasonally frozen conditions.

Postglacial Spatiotemporal Peatland Initiation and Lateral Expansion Dynamics in North America and Northern Europe: Implications to Carbon Uptake

Abstract: Peatlands are major ecosystems of the Northern Hemisphere and have a significant role in global biogeochemical processes. Consequently, there is growing interest in understanding past, present and future peatland dynamics. However, chronological and geographical data on peatland initiation are scattered, impeding the reliable establishment of postglacial spatiotemporal peatland formation patterns and their possible connection to climate. In order to present a comprehensive account of postglacial peatland formation histories in North America and northern Europe, we collected a data set of 1400 basal peat ages accompanied by below-peat sediment-type interpretations from literature. Our data indicate that all peatland initiation processes (i.e. primary mire formation, terrestrialization and paludification) co-occurred throughout North America and northern Europe during the Holocene, and almost equal amounts of peatlands formed via these three processes. Furthermore, the data suggest that the processes exhibited some spatiotemporal patterns. On both continents, primary mire formation seems to occur first, soon followed by terrestrialization and later paludification. Primary mire formation appears mostly restricted to coastal areas, whereas terrestrialization and paludification were more evenly distributed across the continents. Primary mire formation seems mainly connected with physical processes, such as ice sheet retreat. Terrestrialization probably reflected progressive infilling of water bodies on longer timescales but was presumably drought driven on shorter timescales. Paludification seems affected by climate as it slowed down in Europe during the driest phase of the Holocene between 6 and 5 ka. Lateral expansion of existing peatlands accelerated c. 5000 years ago on both continents, which was likely connected to an increase in relative moisture.

Hillslope-scale variability in seasonal frost depth and soil water content investigated by GPR on the southern margin of the sporadic permafrost zone on the Tibetan Plateau

Abstract: Ground temperature data show that permafrost has recently been absent at a site on the southern edge of the sporadic permafrost zone on the Tibetan Plateau (TP). A detailed survey of seasonal frost depth (SFD) and soil water content (SWC) here is significant for understanding the hydrological response to thawing permafrost. However, little is known about the spatial heterogeneity of SFD and SWC at the hillslope scale in this vulnerable permafrost region. Thus, high-frequency ground-penetrating radar (GPR) was applied to a field site that varied in terms of topography (slope, aspect and elevation) and surface environments (vegetation cover and stream presence). The GPR data and accompanying field observations of gravimetric water content and frost depth revealed a spatial variation at the hillslope scale in SFD and SWC, and indicated that topography, vegetation and stream distribution significantly influence the patterns observed. The average SFD was much deeper along the north-facing slope, compared to the south-facing slope in early May, and its thickness varied considerably with altitude along each slope. An increase in the extent of vegetation cover correlated with decreasing SFD. The SWC at shallow depth was higher along the south-facing slope than along the north-facing slope at the beginning of the thawing period. For slopes of both aspects, the SWC vertical profiles exhibited a similar variability, with SWC decreasing with depth, but at different rates. This study demonstrates that GPR provides an appropriate method for quantifying SWC at the hillslope scale on the TP. Copyright © 2015 John Wiley & Sons, Ltd.

Carbon dioxide and methane exchange of a patterned subarctic fen during two contrasting growing seasons

Abstract: . The patterned microtopography of subarctic mires generates a variety of environmental conditions, and carbon dioxide (CO 2 ) and methane (CH 4 ) dynamics vary spatially among different plant community types (PCTs). We studied the CO 2 and CH 4 exchange between a subarctic fen and the atmosphere at Kaamanen in northern Finland based on flux chamber and eddy covariance measurements in 2017–2018. We observed strong spatial variation in carbon dynamics between the four main PCTs studied, which were largely controlled by water table level and differences in vegetation composition. The ecosystem respiration (ER) and gross primary productivity (GPP) increased gradually from the wettest PCT to the drier ones, and both ER and GPP were larger for all PCTs during the warmer and drier growing season 2018. We estimated that in 2017 the growing season CO 2 balances of the PCTs ranged from − 20 g C m −2 (Trichophorum tussock PCT) to 64 g C m −2 (string margin PCT), while in 2018 all PCTs were small CO 2 sources (10–22 g C m −2 ). We observed small growing season CH 4 emissions ( 1 g C m −2 ) from the driest PCT, while the other three PCTs had significantly larger emissions (mean 7.9, range 5.6–10.1 g C m −2 ) during the two growing seasons. Compared to the annual CO 2 balance ( − 8.5 ± 4.0 g C m −2 ) of the fen in 2017, in 2018 the annual balance ( − 5.6 ± 3.7 g C m −2 ) was affected by an earlier onset of photosynthesis in spring, which increased the CO 2 sink, and a drought event during summer, which decreased the sink. The CH 4 emissions were also affected by the drought. The annual CH 4 balance of the fen was 7.3 ± 0.2 g C m −2 in 2017 and 6.2 ± 0.1 g C m −2 in 2018. Thus, the carbon balance of the fen was close to zero in both years. The PCTs that were adapted to drier conditions provided ecosystem-level resilience to carbon loss due to water level drawdown.