Articles | Volume 11, issue 22
Biogeosciences, 11, 6237–6250, 2014

Special issue: Geological and biological development of volcanic islands

Biogeosciences, 11, 6237–6250, 2014

Research article 17 Nov 2014

Research article | 17 Nov 2014

Effects of seabird nitrogen input on biomass and carbon accumulation after 50 years of primary succession on a young volcanic island, Surtsey

N. I. W. Leblans1,2, B. D. Sigurdsson2, P. Roefs1, R. Thuys1, B. Magnússon3, and I. A. Janssens1 N. I. W. Leblans et al.
  • 1Univ. of Antwerp, Dept. of Biology, 2610 Wilrijk, Belgium
  • 2Agric. Univ. of Iceland, Hvanneyri 311 Borgarnes, Iceland
  • 3Icelandic Inst. of Nat. Hist., 210 Gardabaer, Iceland

Abstract. What happens during primary succession after the first colonizers have occupied a pristine surface largely depends on how they ameliorate living conditions for other species. For vascular plants the onset of soil development and associated increase in nutrient (mainly nitrogen; N) and water availability is especially important. Here, we report the relationship between N accumulation and biomass and ecosystem carbon (C) stocks in a 50-year-old volcanic island, Surtsey, Iceland, where N stocks are still exceptionally low. However, a 28-year-old seagull colony on the island provided nutrient-enriched areas, which enabled us to assess the relationship between N stock and biomass and ecosystem C stocks across a much larger range in N stock. Further, we compared areas on shallow and deep tephra sands as we expected that deep-rooted systems would be more efficient in retaining N. The sparsely vegetated area outside the colony had accumulated 0.7 kg N ha−1 yr−1, which was ca. 50–60% of the estimated N input rate from wet deposition. This approximates values for systems under low N input and bare dune habitats. The seagulls have added, on average, 47 kg N ha−1 yr−1, which induced a shift from belowground to aboveground in ecosystem N and C stocks and doubled the ecosystem N-use efficiency, determined as the ratio of biomass and C storage per unit N input. Soil depth did not significantly affect total N stocks, which suggests a high N retention potential. Both total ecosystem biomass and C stocks were strongly correlated with N stock inside the colony, which indicated the important role of N during the first steps of primary succession. Inside the colony, the ecosystem biomass C stocks (17–27 ton C ha−1) had reached normal values for grasslands, while the soil organic carbon (SOC) stocks (4–10 ton C ha−1 were only a fraction of normal grassland values. Thus, it will take a long time until the SOC stock reaches equilibrium with the current primary production, during which conditions for new colonists may change.

Short summary
We studied the influence of allochthonous N inputs on primary succession and soil development of a 50-year-old volcanic island, Surtsey. Seabirds increased the ecosystem N accumulation rate inside their colony to ~47 kg ha-1 y-1, compared to 0.7 kg ha-1 y-1 outside it. A strong relationship was found between total ecosystem N stock and both total above- and belowground biomass and SOC stock, which shows how fast external N input can boost primary succession and soil formation.
Final-revised paper