Guðrún Gísladóttir

Life on the periphery is tough: Vegetation in Northwest Iceland and its responses to early-Holocene warmth and later climate fluctuations

Long- and short-term climate variations in the North Atlantic have been of sufficient magnitude to leave a discernible mark on the history of vegetation and landscape stability in Iceland during the Holocene. A reconstruction of early- and mid-Holocene vegetation around Lake Kagaðarhóll, Northwest Iceland, examines how climate fluctuations have affected the terrestrial ecosystem. A thorough reconstruction has been made using pollen and plant macrofossil analyses combined with proxies for organic and inorganic matter. The record shows the development from a period of pioneer vegetation towards a woodland ecosystem. The deposition of the Saksunarvatn tephra at c. 10,300 cal. yr BP caused a 100-year period of instability, followed by a gradual trend of stabilization over several centuries while material left behind by retreating glaciers and tephra was being contained by expanding and developing vegetation. Early-Holocene warmth is indicated by high pollen production of Juniperus communis around the lake by c. 10,100 cal. yr BP and birch woodland being established around the lake by c. 9200 cal. yr BP, much earlier than previously believed for this locale. Cooling climate between c. 8700 and 8200 cal. yr BP halted woodland development, with reduced plant reproduction likely caused by cold spring and summer temperatures. Woodlands became re-established from c. 7900 cal. yr BP before entering a decline from c. 6000 cal. yr BP, with harsher environmental conditions apparent after c. 4200 cal. yr BP. The Kagaðarhóll record compares favourably with other palaeoclimatic data from the North Atlantic, demonstrating the potential of pollen and macrofossil data for reconstructions of environmental change in Iceland and as an indicator of climate variability in the North Atlantic during the Holocene.

Inundation extent as a key parameter for assessing the magnitude and return period of flooding events in southern Iceland

Abstract River flow conditions in many watersheds of Iceland are particularly disturbed during winter by the formation, drifting and accumulation of river ice, whose impact on water encroachment and extent of inundations is not reflected in the discharge records. It is therefore necessary to use river discharge with great caution when assessing the magnitude of past inundations in Iceland, and to give attention to other flood magnitude parameters. A GIS-based methodology is presented that focuses on inundation extent as an alternative parameter for the assessment and ranking of the magnitude of past flooding events in the Ölfusá-Hvítá basin, known as one of the most dangerous flood-prone river complexes in Iceland. Relying ultimately on a macro-scale grid, the method enabled the reconstruction of the extent of inundations, the delineation of the flood plain, and, finally, some estimation of the likelihood of flooding of exposed areas that include marine submergences and river floods for both open water and ice conditions. Citation Pagneux, E., Gísladóttir, G. & Snorrason, Á. (2010) Inundation extent as a key parameter for assessing the magnitude and return period of flooding events in southern Iceland. Hydrol. Sci. J. 55(5), 704–716.

Aggregation and organic matter in subarctic Andosols under different grassland management

Quantity and quality of soil organic matter (SOM) affect physical, chemical, and biological soil properties, and are pivotal to productive and healthy grasslands. Thus, we analyzed the distribution of soil aggregates and assessed quality, quantity, and distribution of SOM in two unimproved and improved (two organic and two conventional) grasslands in subarctic Iceland, in Haplic and Histic Andosols. We also evaluated principal physicochemical and biological soil properties, which influence soil aggregation and SOM dynamics. Macroaggregates (>250 µm) in topsoils were most prominent in unimproved (62–77%) and organically (58–69%) managed sites, whereas 20–250 µm aggregates were the most prominent in conventionally managed sites (51–53%). Macroaggregate stability in topsoils, measured as mean weight diameter, was approximately twice as high in organically managed (12–20 mm) compared with the conventionally managed (5–8 mm) sites, possibly due to higher organic inputs (e.g., manure, compost, and cattle urine). In unimproved grasslands and one organic site, macroaggregates contributed between 40% and 70% of soil organic carbon (SOC) and nitrogen to bulk soil, whereas in high SOM concentration sites free particulate organic matter contributed up to 70% of the SOC and nitrogen to bulk soil. Aggregate hierarchy in Haplic Andosols was confirmed by different stabilizing mechanisms of micro- and macroaggregates, however, somewhat diminished by oxides (pyrophosphate-, oxalate-, and dithionite-extractable Fe, Al, and Mn) acting as binding agents for macroaggregates. In Histic Andosols, no aggregate hierarchy was observed. The higher macroaggregate stability in organic farming practice compared with conventional farming is of interest due to the importance of macroaggregates in protecting SOM and soils from erosion, which is a prerequisite for soil functions in grasslands that are envisaged for food production in the future.

Cereal cultivation as a correlate of high social status in medieval Iceland

Utilising a multi-profile palynological approach and a rapid scanning technique, this paper examines whether or not cereal cultivation is representative of a medieval Icelandic farmstead’s social status; first as a correlate by confirming that cereals were grown in association with the archaeological features characteristic of high status and second, as an indicator in its own right through comparison with other datasets from inferred lower status farms in the same valley. The results suggest that medieval cereal cultivation in Mosfellsdalur was confined to the landholding of the Mosfell Estate. This is probably a direct consequence of the locale being settled early during Iceland’s colonisation and thereby allowing settlers there to secure the prime location in the valley for agriculture. The later abandonment of cereal cultivation on the Estate also appears to be linked to social circumstances in Mosfellsdalur c. ad 1200. An evaluation of other pollen studies and historical sources intimates a transition in cereal cultivation from inland toward coastal (and perhaps geothermal) sites in the mid-13th century, probably as a consequence of the onset of the Little Ice Age. These sites may also be linked with high status institutions. Despite this effort to adapt to altered climate conditions, cereal cultivation in Iceland is believed to have been completely abandoned by ad 1500. Overall, the temporal and spatial dynamics of cereal cultivation are shown to be complex, subject to both societal and environmental changes.

Holocene environmental change and development of the nutrient budget of histosols in North Iceland

Backround and aimsLittle is known about vegetation changes in Icelandic peatlands in the context of soil chemical properties. By connecting soil chemical and physical characteristics with palaeobotanical data we examined interactions between climate, histosols, vegetation and land use during the Holocene.MethodsExchangeable base cations, cation exchange capacity (CEC), base saturation (BS), decomposition rates, using carbon:nitrogen ratio (C:N) and von Post humification, and soil physical properties were determined. Vegetation development was reconstructed based on pollen analysis. The impact of geographic location was examined by comparing results from three sloping fens (coastal, inland and highland fringe).ResultsMinerogenic content was highest in the proximity of the active volcanic zone, reflected in higher C:N and nutrient content in the histosol profiles of the fens inland and at the highland fringe. The coastal site revealed exceptionally high BS. C:N was either stable throughout the profile or increased with depth. Plant species richness, and evenness based on pollen data, and pollen concentrations were greatest at the site with lowest nutrient levels.ConclusionsMinerogenic content facilitates the ability of histosols to bind nutrients. Plant growth is optimised at the sites with lower fertility levels. C:N alone is not a reliable indicator of decomposition rates, but depends on the quality of the organic parent material. Environmental conditions driven by climate changes caused alterations in vegetation and soil properties before the human settlement of Iceland (c. AD 870), but overall the histosols showed resilience towards severe degradation. After the settlement, the histosols struggled to buffer the impact caused by destruction of vegetation and increased erosion. This study increases our understanding of environmental and anthropogenic determinants of soil- and vegetation development.

Hekla Volcano, Iceland, in the 20th Century: Lava Volumes, Production Rates, and Effusion Rates

Lava flow thicknesses, volumes, and effusion rates provide essential information for understanding the behavior of eruptions and their associated deformation signals. Preeruption and posteruption elevation models were generated from historical stereo photographs to produce the lava flow thickness maps for the last five eruptions at Hekla volcano, Iceland. These results provide precise estimation of lava bulk volumes: V1947–1948 = 0.742 ± 0.138 km , V1970 = 0.205 ± 0.012 km , V1980–1981 = 0.169 ± 0.016 km , V1991 = 0.241 ± 0.019 km , and V2000 = 0.095 ± 0.005 km 3 and reveal variable production rate through the 20th century. These new volumes improve the linear correlation between erupted volume and coeruption tilt change, indicating that tilt may be used to determine eruption volume. During eruptions the active vents migrate 325–480 m downhill, suggesting rough excess pressures of 8–12 MPa and that the gradient of this excess pressure increases from 0.4 to 11 Pa s 1 during the 20th century. We suggest that this is related to increased resistance along the eruptive conduit. Plain Language Summary The sizes of volcanic eruptions are key parameters to understand eruption precursors and eruption hazard scenarios. Hekla is one of Iceland’s most active volcanoes and erupted five times (1947–1948, 1970, 1980–1981, 1991, and 2000) during the 20th century. Here we use an archive of historical aerial photographs to reconstruct the topography before and after each eruption in order to provide the first precise lava thickness maps and volume estimates of Hekla volcano. Our results reveal that the last three eruptions ranged significantly in size unlike earlier estimates, indicating that the production rate at the volcano is more variable than previously thought. Furthermore, this suggests that geophysical measurements of the volcano deformation now correlate with the eruption size and therefore may be important to determine eruption size.

A chronosequence approach to estimate the regional soil organic carbon stock on moraines of two glacial fore-fields in SE-Iceland

ABSTRACT SOC has received increased attention over the last decades because of its role as an option to mitigate the effects of increased anthropogenic greenhouse gas emissions. In Iceland, the loss of vegetation and soil due to land-use and natural processes has left large areas as barren deserts. Land restoration actions have the primary goals to prevent land degradation and restore lost ecosystems but the ancillary benefits of SOC accumulation with regard to COP 21 are obvious. Natural vegetation succession is active in areas being exposed by glacial recession since the end of the Little Ice Age in ∼1890. Here, we attempt to estimate the current regional SOC stock on undisturbed moraines in front of two glaciers in SE-Iceland, using surface age, soil properties and vegetation cover data. RapidEye images were used to estimate the surface area of two vegetation classes with <50% and >50% cover. Regional SOC stock was calculated using soil data and the sum of the area of each cover class for each time-zone. The rates of SOC accretion reached the maximum values of 0.004−0.009 kg C m−2 yr−1. The regional SOC stock for the two glacier fore-fields was estimated at 1605 Mg C (0−10 cm) for Skaftafellsjökull (396 ha) and 1106 Mg C (0−5 cm) for Breiðamerkurjökull (632 ha). The current annual increase in the moraine SOC stocks was estimated at 20.7 Mg C yr−1 for Skaftafellsjökull and 19.7 Mg C yr−1 for Breiðamerkurjökull.

Southern Iceland: Volcanoes, Tourism and Volcanic Risk Reduction

Tourists flock to southern Iceland to experience the impressive landscapes surrounding the Hekla, Eyjafjallajokull, Katla and Grimsvotn volcanoes. This chapter describes these volcanic systems and their recent activity. It also provides detail on strategies implemented by government agencies to reduce volcanic risk in this region.

Of mosses and men: Plant succession, soil development and soil carbon accretion in the sub-Arctic volcanic landscape of Hekla, Iceland

Lava flows pose a hazard in volcanic environments and reset ecosystem development. A succession of dated lava flows provides the possibility to estimate the direction and rates of ecosystem development and can be used to predict future development. We examine plant succession, soil development and soil carbon (C) accretion on the historical (post 874 AD) lava flows formed by the Hekla volcano in south Iceland. Vegetation and soil measurements were conducted all around the volcano reflecting the diverse vegetation communities on the lavas, climatic conditions around Hekla mountain and various intensities in deposition of loose material. Multivariate analysis was used to identify groups with similar vegetation composition and patterns in the vegetation. The association of vegetation and soil parameters with lava age, mean annual temperature, mean annual precipitation and soil accumulation rate (SAR) was analysed. Soil carbon concentration increased with increasing lava age becoming comparable to concentrations found on the prehistoric lavas. The combination of a sub-Arctic climate, gradual soil thickening due to input of loose material and the specific properties of volcanic soils allow for continuing accumulation of soil carbon in the soil profile. Four successional stages were identified: initial colonization and cover coalescence (ICC) of Racomitrium lanuginosum and Stereocaulon spp. (lavas <70 years of age); secondary colonization (SC) – R. lanuginosum dominance (170−700 years); vascular plant dominance (VPD) (>600 years); and highland conditions/retrogression (H/R) by tephra deposition (70−860 years). The long time span of the SC stage indicates arrested development by the thick R. lanuginosum moss mat. The progression from SC into VPD was linked to age of the lava flows and soil depth, which was significantly deeper within the VPD stage. Birch was growing on lavas over 600 years old indicating the development towards birch woodland, the climax ecosystem in Iceland.

Pollen, Plague & Protestants: The Medieval Monastery of Þingeyrar (Þingeyraklaustur) in Northern Iceland

Until recently, Icelandic monasticism has been considered remote from European monasticism and that it had little impact upon medieval Icelandic society. Focussing upon a monastic site in northern ...