SOIL CARBON CONTENT AND CO2 FLUX IN EXPERIMENTAL REVEGETATION PLOTS, SOUTHERN ICELAND: IMPLICATIONS FOR SEQUESTRATION AND SOIL STABILIZATION

Experimental plots established at Geitasandur in 1999 to study the effectiveness of various soil treatments in revegetating heavily eroded land surfaces also provide information on the rates and limits of soil carbon sequestration during restoration. We measured the soil carbon and soil CO₂ flux in plots with four treatments: control (untreated), fertilizer-grass seeding, fertilizer-grass-birch-willow and unfertilized lupine seeded. The carbon content of the soils in all four treatment areas is quite low; none yielded soils with a mean C_soil of 1.0 % or greater. The control plots exhibit the lowest carbon content of the treatments (mean C_soil = 0.39%), and a carbon stock of 0.36 kg m^-2. Plots treated with fertilizer and grasses demonstrated slightly higher carbon levels (mean C_soil = 0.40%) compared to the control plots and a carbon stock of 0.38 kg m^-2. Plots seeded with grass, birch and willow display higher levels of soil carbon (mean C_soil = 0.57%), and carbon stocks of 0.52 kg m^-2. The highest soil carbon levels were observed in samples from plots seeded with lupine;(mean C_soil = 0.66%, and the carbon stock is 0.61 kg m^-2.

The carbon content in treated soils increased substantially during the initial eight years in plots for which the treatment included both fertilizer and seeding with grasses, concomitant with the increase in vegetative cover. In the following seven years, however, the soil carbon accumulation rates declined to negligible for most treatments and the carbon content in soils mainly remained constant. The only plots that displayed significant and consistent increase in soil carbon content were those seeded with lupine. These plots also exhibited substantially higher root respiration, as measured by soil CO₂ flux (mean CO_2soil = 2.90 μmol m^-2 s^-1). The lupine-treated plots are also distinctive in being the only plots displaying a positive correlation between soil carbon content and soil CO₂ flux with r² > 0.1. These results suggest that lupine may have utility in reclamation and stabilization of eroded land surfaces and in promoting carbon sequestration, but other ecological factors require consideration. This work has implications for development of long-term strategies for land reclamation and carbon sequestration in high latitude regions.