Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 7 3 2010 10.5194/bg-7-883-2010 http://www.biogeosciences.net/7/883/2010/ http://www.biogeosciences.net/7/883/2010/bg-7-883-2010.html http://www.biogeosciences.net/7/883/2010/bg-7-883-2010.pdf 883 891 2010-03-05 Effects of seagulls on ecosystem respiration, soil nitrogen and vegetation cover on a pristine volcanic island, Surtsey, Iceland B. D. Sigurdsson bjarni@lbhi.is B. Magnusson Agricultural University of Iceland, 112 Keldnaholt, Reykjavik, Iceland Icelandic Institute of Natural History, P. O. Box 5320, 125 Reykjavik, Iceland 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. 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