Magnusson B.,Icelandic Institute of Natural History |
Magnusson S.H.,Icelandic Institute of Natural History |
Olafsson E.,Icelandic Institute of Natural History |
Sigurdsson B.D.,Agricultural University of Iceland
Biogeosciences | Year: 2014
Plant colonization and succession on the volcanic island of Surtsey, formed in 1963, have been closely followed. In 2013, a total of 69 vascular plant species had been discovered on the island; of these, 59 were present and 39 had established viable populations. Surtsey had more than twice the species of any of the comparable neighbouring islands, and all of their common species had established on Surtsey. The first colonizers were dispersed by sea, but, after 1985, bird dispersal became the principal pathway with the formation of a seagull colony on the island and consequent site amelioration. This allowed wind-dispersed species to establish after 1990. Since 2007, there has been a net loss of species on the island. A study of plant succession, soil formation and invertebrate communities in permanent plots on Surtsey and on two older neighbouring islands (plants and soil) has revealed that seabirds, through their transfer of nutrients from sea to land, are major drivers of development of these ecosystems. In the area impacted by seagulls, dense grassland swards have developed and plant cover, species richness, diversity, plant biomass and soil carbon become significantly higher than in low-impact areas, which remained relatively barren. A similar difference was found for the invertebrate fauna. After 2000, the vegetation of the oldest part of the seagull colony became increasingly dominated by long-lived, rhizomatous grasses (Festuca, Poa, Leymus) with a decline in species richness and diversity. Old grasslands of the neighbouring islands ElliÄ'aey (puffin colony, high nutrient input) and Heimaey (no seabirds, low nutrient input) contrasted sharply. The puffin grassland of ElliÄ'aey was very dense and species-poor. It was dominated by Festuca and Poa, and very similar to the seagull grassland developing on Surtsey. The Heimaey grassland was significantly higher in species richness and diversity, and had a more even cover of dominants (Festuca/Agrostis/Ranunculus). We forecast that, with continued erosion of Surtsey, loss of habitats and increasing impact from seabirds a lush, species-poor grassland will develop and persist, as on the old neighbouring islands. © 2014 Author(s).
Sigurdsson B.D.,Agricultural University of Iceland |
Magnusson B.,Icelandic Institute of Natural History
Biogeosciences | Year: 2010
When Surtsey rose from the North Atlantic Ocean south of Iceland in 1963, it became a unique natural laboratory on how organisms colonize volcanic islands and form ecosystems with contrasting structures and functions. In July, 2004, ecosystem respiration rate (Re), soil properties and surface cover of vascular plants were measured in 21 permanent research plots distributed among the juvenile communities of the island. The plots were divided into two main groups, inside and outside a seagull (Larus spp.) colony established on the island. Vegetation cover of the plots was strongly related to the density of gull nests. Occurrence of nests and increased vegetation cover also coincided with significant increases in Re, soil carbon, nitrogen and C:N ratio, and with significant reductions in soil pH and soil temperatures. Temperature sensitivity (Q10 value) of Re was determined as 5.3. When compared at constant temperature the Re was found to be 59 times higher within the seagull colony, similar to the highest fluxes measured in drained wetlands or agricultural fields in Iceland. The amount of soil nitrogen, mainly brought onto the island by the seagulls, was the critical factor that most influenced ecosystem fluxes and vegetation development on Surtsey. The present study shows how ecosystem activity can be enhanced by colonization of animals that transfer resources from a nearby ecosystem. © 2010 Author(s).
Ingimundardottir G.V.,Lund University |
Ingimundardottir G.V.,Icelandic Institute of Natural History |
Weibull H.,Naturcentrum AB |
Cronberg N.,Lund University
Biogeosciences | Year: 2014
The island Surtsey was formed in a volcanic eruption south of Iceland in 1963-1967 and has since then been protected and monitored by scientists. The first two moss species were found on Surtsey as early as 1967 and several new bryophyte species were discovered every year until 1973 when regular sampling ended. Systematic bryophyte inventories in a grid of 100m×100m quadrats were made in 1971 and 1972: the number of observed species doubled, with 36 species found in 1971 and 72 species in 1972. Here we report results from an inventory in 2008, when every other of the grid's quadrats were searched for bryophytes. Despite lower sampling intensity than in 1972, distributional expansion and contraction of earlier colonists was revealed as well as the presence of new colonists. A total of 38 species were discovered, 15 of those were not encountered in 1972 and eight had never been reported from Surtsey before (Bryum elegans, Ceratodon heterophyllus, Didymodon rigidulus, Eurhynchium praelongum, Schistidium confertum, S. papillosum, Tortula hoppeana and T. muralis). Habitat loss due to erosion and reduced thermal activity in combination with successional vegetation changes are likely to have played a significant role in the decline of some bryophyte species which were abundant in 1972 (Leptobryum pyriforme, Schistidium apocarpum coll., Funaria hygrometrica, Philonotis spp., Pohlia spp, Schistidium strictum, Sanionia uncinata) while others have continued to thrive and expand (e.g. Schistidium maritimum, Racomitrium lanuginosum, R. ericoides, R. fasciculare and Bryum argenteum). Some species (especially Bryum spp.) benefit from the formation of new habitats, such as grassland within a gull colony, which was established in 1984. Several newcomers are rarely producing sporophytes on Iceland and are unlikely to have been dispersed by airborne spores. They are more likely to have been introduced to Surtsey by seagulls in the form of vegetative fragments or dispersal agents (Bryum elegans, Didymodon rigidulus, Eurhynchium praelongum, Ceratodon heterophyllus and Ulota phyllantha). The establishment of the gull colony also means that leakage of nutrients from the nesting area is, at least locally, downplaying the relative importance of nitrogen fixation by cyanobacteria growing in bryophyte shoots. © 2014 Author(s).
Brynjolfsson S.,Icelandic Institute of Natural History |
Schomacker A.,e Arctic University of Norway |
Korsgaard N.J.,Copenhagen University |
Korsgaard N.J.,University of Iceland |
And 2 more authors.
Earth and Planetary Science Letters | Year: 2016
Surface elevation and volume changes of the Drangajökull surge-type glaciers, Reykjarfjarðarjökull and Leirufjarðarjökull, were studied by comparing digital elevation models that pre-date and post-date their most recent surges. Annual glacier-frontal measurements were used to estimate average ice velocities during the last surge of the glaciers. The observations show a distinct ice discharge, most of which was from the upper reservoir areas, down to the receiving areas during the surges. The surface draw-down in the reservoir areas was usually 10–30 m during the surges, while the thickening of the receiving areas was significantly more variable, on the order of 10–120 m. Despite a negative geodetic net mass balance derived from the digital elevation models, the reservoir areas have been gaining mass since the surge terminations. This surface thickening along with considerable ablation of the receiving areas will most likely return the glacier surface profiles to the pre-surge stage. Our results indicate that (a) greatest surface thinning in the upper reservoir areas of Drangajökull rather than proximal to the equilibrium line during Vatnajökull surges and (b) development of Drangajökull surges that resembles Svalbard surge-type glaciers rather than Vatnajökull surge-type glaciers. The contrasting surge characteristics could be explained by differences in glacier geometry, topography and substratum of the Drangajökull and Vatnajökull surge-type glaciers. © 2016 Elsevier B.V.
Romagnoli C.,University of Bologna |
Jakobsson S.P.,Icelandic Institute of Natural History
Geomorphology | Year: 2015
Surtsey is a small volcanic island in the Vestmannaeyjar archipelago, off the south coast of Iceland. The eruption leading to the island's emersion lasted for 3.5 yr (1963-1967) while destructive forces have been active for over 50 yr (1963-present-day) during which Surtsey has suffered rapid subaerial and submarine erosion and undergone major morphological changes. Surtsey is a well-documented modern example of the post-eruptive degradational stage of island volcanoes, and has provided the unique opportunity to continuously observe and quantify the effects of intense geomorphic processes. In this paper we focus on coastal and marine processes re-shaping the shoreline and shallow-water portions of the Surtsey complex since its formation and on the related geomorphological record. Analogies with the post-eruptive morphological evolution of recently active island volcanoes at the emerging stage, encompassing different climatic conditions, wave regimes and geological contexts, are discussed. © 2015 Elsevier B.V.
Del Moral R.,University of Washington |
Magnusson B.,Icelandic Institute of Natural History
Biogeosciences | Year: 2014
Surtsey and Mount St. Helens are celebrated but very different volcanoes. Permanent plots allow for comparisons that reveal mechanisms that control succession and its rate and suggest general principles. We estimated rates from structure development, species composition using detrended correspondence analysis (DCA), changes in Euclidean distance (ED) of DCA vectors, and by principal components analysis (PCA) of DCA. On Surtsey, rates determined from DCA trajectory analyses decreased as follows: gull colony on lava with sand > gull colony on lava, no sand g« lava with sand > sand spit > block lava > tephra. On Mount St. Helens, plots on lahar deposits near woodlands were best developed. The succession rates of open meadows declined as follows: Lupinus-dominated pumice > protected ridge with Lupinus > other pumice and blasted sites > isolated lahar meadows > barren plain. Despite the prominent contrasts between the volcanoes, we found several common themes. Isolation restricted the number of colonists on Surtsey and to a lesser degree on Mount St. Helens. Nutrient input from outside the system was crucial. On Surtsey, seabirds fashioned very fertile substrates, while on Mount St. Helens wind brought a sparse nutrient rain, then Lupinus enhanced fertility to promote succession. Environmental stress limits succession in both cases. On Surtsey, bare lava, compacted tephra and infertile sands restrict development. On Mount St. Helens, exposure to wind and infertility slow succession. © 2014 Author(s).
Wasowicz P.,Icelandic Institute of Natural History
PeerJ | Year: 2016
The highlands and mountains of Iceland are one of the largest remaining wilderness areas in Europe. This study aimed to provide comprehensive and up-to-date data on non-native plant species in these areas and to answer the following questions: (1) How many non-native vascular plant species inhabit highland and mountainous environments in Iceland? (2) Do temporal trends in the immigration of alien species to Iceland differ between highland and lowland areas? (3) Does the incidence of alien species in the disturbed and undisturbed areas within Icelandic highlands differ? (4) Does the spread of non-native species in Iceland proceed from lowlands to highlands? and (5) Can we detect hot-spots in the distribution of non-native taxa within the highlands? Overall, 16 non-native vascular plant species were detected, including 11 casuals and 5 naturalized taxa (1 invasive). Results showed that temporal trends in alien species immigration to highland and lowland areas are similar, but it is clear that the process of colonization of highland areas is still in its initial phase. Non-native plants tended to occur close to man-made infrastructure and buildings including huts, shelters, roads etc. Analysis of spatio-temporal patterns showed that the spread within highland areas is a second step in non-native plant colonization in Iceland. Several statically significant hot spots of alien plant occurrences were identified using the Getis-Ord Gi* statistic and these were linked to human disturbance. This research suggests that human-mediated dispersal is the main driving force increasing the risk of invasion in Iceland's highlands and mountain areas. © 2016 Wasowicz.
Skarphedinsdottir H.,University of Stockholm |
Gunnarsson K.,Iceland Marine Research Institute |
Gudmundsson G.A.,Icelandic Institute of Natural History |
Nfon E.,University of Stockholm
Archives of Environmental Contamination and Toxicology | Year: 2010
Organochlorine (OC) bioaccumulation and biomagnification were studied in a marine food web at a pristine site in Iceland. The species studied were the gastropod and grazer chink shell (Lacuna vincta), the filter feeding bivalve blue mussel (Mytilus edulis), the predators butterfish (Pholis gunnellus), and the seabird black guillemot (Cepphus grylle), all sampled and analysed in 1996-1997. Individual OC levels were generally low in chink shell and blue mussels, somewhat elevated in the fish, and an order of a magnitude higher in the top predator black guillemot, except for ∑HCH (hexachlorocyclohexane isomers) and ∑chlordane levels, which were similar in all organisms, ranging from 10 to 36 ng/g lipid weight (lw). In the molluscs and fish, mean concentrations of ∑PCB (polychlorinated biphenyl) ranged from 111 to 377 ng/g lw, ∑DDT (dichlorodiphenyltrichloroethane) ranged from 19 to 65 ng/g lw, and HCB (hexachlorobenzene) ranged from 21 to 30 ng/g lw. The levels of same OCs in the black guillemot were on average 2352, 361, and 283 ng/g lw, respectively. The OC tissue concentrations in blue mussel and black guillemot are comparable to levels in Arctic and sub-Arctic regions, but OC levels in blue mussel tissue were an order of magnitude lower than found in the North Sea and the Baltic Sea. The relative composition of OCs were generally similar among species with the PCB congeners emerging as the most abundant compounds with levels an order of magnitude higher than the other compounds in all species. Food web magnification factors (FWMFs) were determined for the OCs by using trophic levels determined from δ15N. FWMFs >1, indicating biomagnification, were found for ∑PCB, penta- or higher chlorinated PCBs (e.g., PCB 101, 118, 138, 153, 180), β-HCH, HCB, ∑DDT, p,p-DDE, and transnonachlor. The highest FWMF was observed for PCB 180 at FWMF = 5.8. © 2009 Springer Science+Business Media, LLC.
Ingimarsdottir M.,Lund University |
Ingimarsdottir M.,Icelandic Institute of Natural History |
Ripa J.,Lund University |
Magnusdottir T.B.,University of Iceland |
Hedlund K.,Lund University
Basic and Applied Ecology | Year: 2013
Allochthonous arthropods can sustain a local food web on seemingly barren land, but are nevertheless often neglected in studies of community assembly. In the present study, we investigated primary food web assembly on nunataks (ice-free areas) in a retreating glacier in Iceland. Nunataks enable studies that take into account both the temporal factor of the assembly and the influx of allochthonous organisms. Arthropods were collected on sites of different age on five nunataks younger than 70 years, as well as the youngest parts of one old nunatak. The youngest sites had no vegetation and were dominated by detritivores and predators along with allochthonous arthropods. The arthropod biomass, that was considered established, increased with vegetation cover and site age but also differed among nunataks. To investigate whether or not the assembly of arthropods was consistent with the predictions of assembly rules, we tested whether, (1) the proportion of each trophic level changed non-randomly, (2) predator-prey ratio remained constant, and (3) larger species replaced smaller ones. We could only verify that proportions of trophic levels changed non-randomly. As assembly rules only apply for established organisms, it is possible that difficulties in determining whether e.g. generalist predators were established or not may affect the outcome of analyses of assembly rules. It is thus important to be aware that unintentional inclusion of allochthonous arthropods in models of community assembly may affect whether or not the community can be explained and predicted by assembly rules. © 2013 Gesellschaft für Ökologie.
Jakobsson S.P.,Icelandic Institute of Natural History |
Johnson G.L.,University of Alaska Fairbanks
Bulletin of Volcanology | Year: 2012
The Western Volcanic Zone in Iceland (64.19° to 65.22° N) has the morphological characteristics of a distinct Mid-Atlantic ridge segment. This volcanic zone was mapped at a scale of 1:36.000, and 258 intraglacial monogenetic volcanoes from the Late Pleistocene (0.01-0.78 Ma) were identified and investigated. The zone is characterized by infrequent comparatively large volcanic eruptions and the overall volcanic activity appears to have been low throughout the Late Pleistocene. Tholeiitic basaltic rocks dominate in the Western Volcanic Zone with about 0.5 vol. % of intermediate and silicic rocks. The basalts divide into picrites, olivine tholeiites, and tholeiites. Three main eruptive phases can be distinguished in the intraglacial volcanoes: an effusive deep-water lava phase producing basal pillow lavas, an explosive shallow-water phase producing hyaloclastites and an effusive subaerial capping lava phase. Three evolutionary stages therefore charcterize these volcanoes; late dykes and irregular minor intrusions could be added as the fourth main stage. These intrusions are potential heat sources for short-lived hydrothermal systems and may play an important role in the final shaping of the volcanoes. Substantial parts of the hyaloclastites of each unit are proximal sedimentary deposits. The intraglacial volcanoes divide into two main morphological groups, ridge-shaped volcanoes, i. e., tindars (including pillow lava ridges) and subrectangular volcanoes, i. e., tuyas and hyaloclastite or pillow lava mounds. The volume of the tuyas is generally much larger than that of the tindars. The largest tuya, Eiríksjökull, is about 48 km 3 and therefore the largest known monogenetic volcano in Iceland. Many of the large volcanoes, both tuyas and tindars, show a similar, systematic range in geochemistry. The most primitive compositions were erupted first and the magmas then changed to more differentiated compositions. The ridge-shaped tindars clearly erupted from volcanic fissures and the more equi-dimensional tuyas mainly from a single crater. It is suggested that the morphology and structure of the intraglacial volcanos mainly depends on two factors, (a) tectonic control and (b) availability of magma at the time of eruption. © 2012 Springer-Verlag.