THE WEATHERING OF ICELANDIC BASALTS: RATES OF CARBON INGROWTH AND NUTRIENT RELEASE

The formation of soil from the weathering of rocks is a dynamic process, affected by rock characteristics, climate, biogenic activity, and time. The purpose of this project is to use biogeochemical analyses to determine the interplay between biogenic activity and soil formation in historically dated basalts with nearly identical geochemical compositions in southern Iceland.

Soil samples were taken from lava flows of four ages: 934 AD, 1300 AD, 1554 AD, and 1783 AD. Initial analyses have focused on the ingrowth of organic matter as a function of time in these young soils, an important factor in determining carbon uptake and sequestration during the weathering of volcanic rocks. We found an increase in the organic matter content with age of flow, reflecting the activity of surface plants and the ingrowth of soil microbial biomass. The soil derived from the 934 AD flow had an average of 3.3 kgC/m² and the soil derived from the 1783 AD flow had an average of 0.20kgC/m², which is within the range of carbon content range from 0.1 to 21.6 kgC/m² found in the rocky and tundra environments. The average carbon uptake in these soils was 1–3 gC/m²/yr, which are comparable to 0.2-2.4gC/m²/yr for tundras. Ongoing analyses will include SEM (Scanning Electron Microscope), microprobe, and phosphorus and nitrogen analyses. These tests will target the surface geochemical evidence of mineral weathering during soil formation, as well as potential changes in the storage of key nutrients, phosphorus and nitrogen, with time. This research will eventually provide insight into the impact of biogenic activity on the weathering of rocks and subsequent soil formation, and the rate at which these processes occur.