Jökull - 01.12.2007, Síða 39

Reviewed research article
Rates of carbon ingrowth and nutrient release from young
Icelandic basalts
Tamara McPeek1, Xianzhong Wang1, Kenneth Brown2 and Gabriel M. Filippelli2
1 Department of Biology, Indiana University-Purdue University Indianapolis (IUPUI),
723 West Michigan Street, Indianapolis, IN 46202–5132, USA
2 Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI),
723 West Michigan Street, Indianapolis, IN 46202–5132, USA
xzwang@iupui.edu, gfilippe@iupui.edu
Abstract – Formation of soil from the weathering of rocks is a dynamic process, affected by rock characteristics,
climate, biogenic activities and time. The objective of this project was to use biogeochemical analyses to
determine the interplay between biogenic activity and soil formation in historically dated basalts from southern
Iceland. Soil samples were taken from four lava flows and were analyzed for carbon (C) and phosphorus (P).
Organic carbon content totaled 3.30, 1.01, 0.80, and 0.21 kg m !2 for the 934, 1300, 1554, and 1783 AD flows,
respectively. The organic matter content in these Andisols is within but at lower end of the range of C content
of 0.1–14.9 kg m!2 found in other rocky and boreal ecosystems. The average C uptake in these soils was 1–3
g m!2yr!1, comparable to the 0.8–11.7 g m!2yr!1 C uptake for boreal ecosystems. Organic P in the soils
increased over time with the average being 13.7, 8.6, 6.5 and 4.5 mg cm!2 for the 934, 1300, 1554, and 1783
AD flows, respectively. Occluded P was variable over time and the average was 44.5, 9.4, 7.7, and 2.7 mg
cm!2 for the 934, 1300, 1554, and 1783 AD flows, respectively. Higher content of both C and P in older soils,
as found in our study, demonstrated that biological activity and weathering of parent rock increase with age of
exposure on the surface of southern Iceland.
INTRODUCTION
Southern Iceland is considered a sub-arctic ecosystem
because of its temperate climate, despite its geogra-
phic closeness to the Arctic Circle. Boreal and sub-
arctic ecosystems, although accounting for a small
percentage of the total land area of the world, are im-
portant ecologically and sensitive to global environ-
mental changes (Schlesinger, 1997). An examination
of the process of soil formation and nutrient accumu-
lation in the soil will enable us to better understand
the nutrient dynamics in soils, which support plants
and living organisms of higher trophic levels. Ice-
land is an excellent location to examine the effects of
weathering on the accumulation of essential nutrients
in the soil over time for a number of reasons. First,
Iceland has been settled by a human population with
written records since the early 10th century. Any vol-
canic eruption occurring after the 10 th century thus
has an approximate historical date. Second, the sur-
face of Iceland is primarily covered with basalt (Jak-
obsson, 1979). As a result, the range of geochemical
compositions of the parent material over Iceland is si-
gnificantly reduced, thus normalizing the rates of we-
athering for parent rocks. Third, southern Iceland has
a humid climate, which provides a continuous source
of water for rock weathering (Gislason et al., 1996).
Having similar parent materials and wet climate thro-
ughout southern Iceland ensures similar pedogenesis
at all sample sites in our study. Although airborne de-
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