Carbon Sink

Urbanisation is increasing tremendously in some parts of the world. Consequently, many rural forests may become depleted, although many opportunities exist for urban forests to increase. However, few studies have quantified the carbon (C) sequestration capacities of urban and rural forests in specific climatic zones. The present study compared carbon sequestration in two temperate deciduous forests located in Nagoya and

Drainage for forestry purposes increases the depth of the oxic peat layer and leads to increased growth of shrubs and trees. Concurrently, the production and uptake of the greenhouse gases carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) change: due to the accelerated decomposition of peat in the presence of oxygen, drained peatlands are generally considered to lose peat carbon (C). We measured CO 2 exchange with the eddy covariance (EC) method above a drained nutrient-poor peatland forest in southern Finland for 16 months in [2004][2005]. The site, classified as a dwarf-shrub pine bog, had been ditched about 35 years earlier. CH 4 and N 2 O fluxes were measured at 2-5-week intervals with the chamber technique. Drainage had resulted in a relatively little change in the water table level, being on average 40 cm below the ground in 2005. The annual net ecosystem exchange was −870 ± 100 g CO 2 m −2 yr −1 in the calendar year 2005, indicating net CO 2 uptake from the atmosphere. The site was a small sink of CH 4 (−0.12 g CH 4 m −2 yr −1 ) and a small source of N 2 O (0.10 g N 2 O m −2 yr −1 ). Photosynthesis was detected throughout the year when the air temperature exceeded −3 • C. As the annual accumulation of C in the above and below ground tree biomass (175 ± 35 g C m −2 ) was significantly lower than the accumulation observed by the flux measurement (240 ± 30 g C m −2 ), about 65 g C m −2 yr −1 was likely to have accumulated as organic matter into the peat soil. This is a higher average accumulation rate than previously reported for natural northern peatlands, and the first time C accumulation has been shown by EC measurements to occur in a forestry-drained peatland. Our results suggest that forestry-drainage may significantly increase the CO 2 uptake rate of nutrient-poor peatland ecosystems.

Anthropogenic greenhouse gas emissions may be offset by sequestering carbon dioxide (CO 2 ) through the carbonation of magnesium silicate minerals to form magnesium carbonate minerals. The hydromagnesite [Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O] playas of Atlin, British Columbia, Canada provide a natural model to examine mineral carbonation on a watershed scale. At near surface conditions, CO 2 is biogeochemically sequestered by microorganisms that are involved in weathering of bedrock and precipitation of carbonate minerals. The purpose of this study was to characterize the weathering regime in a groundwater recharge zone and the depositional environments in the playas in the context of a biogeochemical model for CO 2 sequestration with emphasis on microbial processes that accelerate mineral carbonation. Regions with ultramafic bedrock, such as Atlin, represent the best potential sources of feedstocks for mineral carbonation. Elemental compositions of a soil profile show significant depletion of MgO and enrichment of SiO 2 in comparison to underlying ultramafic parent material. Polished serpentinite cubes were placed in the organic horizon of a coniferous forest soil in a groundwater recharge zone for three years. Upon retrieval, the cube surfaces, as seen using scanning electron microscopy, had been colonized by bacteria that were associated with surface pitting. Degradation of organic matter in the soil produced chelating agents and acids that contributed to the chemical weathering of the serpentinite and would be expected to have a similar effect on the magnesium-rich bedrock at Atlin. Stable carbon isotopes of groundwater from a well, situated near a wetland in the southeastern playa, indicate that ∼ 12% of the dissolved inorganic carbon has a modern origin from soil CO 2 . The mineralogy and isotope geochemistry of the hydromagnesite playas suggest that there are three distinct depositional environments: (1) the wetland, characterized by biologically-aided precipitation of carbonate minerals from waters concentrated by evaporation, (2) isolated wetland sections that lead to the formation of consolidated aragonite sediments, and (3) the emerged grassland environment where evaporation produces mounds of hydromagnesite. Examination of sediments within the southeastern playa-wetland suggests that cyanobacteria, sulphate reducing bacteria, and diatoms aid in producing favourable geochemical conditions for precipitation of carbonate minerals. The Atlin site, as a biogeochemical model, has implications for creating carbon sinks that utilize passive microbial, geochemical and physical processes that aid in mineral carbonation of magnesium silicates. These processes could be exploited for the purposes of CO 2 sequestration by creating conditions similar to those of the Atlin site in environments, artificial or natural, where the precipitation of magnesium carbonates would be suitable. Given the vast quantities of Mg-rich bedrock that exist throughout the world, this study has significant implications for reducing atmospheric CO 2 concentrations and combating global climate change.

Based on theories of mire development and responses to a changing climate, the current role of mires as a net carbon sink has been questioned. A rigorous evaluation of the current net C-exchange in mires requires measurements of all relevant fluxes. Estimates of annual total carbon budgets in mires are still very limited. Here, we present a full carbon budget over 2 years for a boreal minerogenic oligotrophic mire in northern Sweden (64111 0 N, 19133 0 E). Data on the following fluxes were collected: land-atmosphere CO 2 exchange (continuous Eddy covariance measurements) and CH 4 exchange (static chambers during the snow free period); TOC (total organic carbon) in precipitation; loss of TOC, dissolved inorganic carbon (DIC) and CH 4 through stream water runoff (continuous discharge measurements and regular C-concentration measurements). The mire constituted a net sink of 27 AE 3.4 ( AE SD) g C m À2 yr À1 during 2004 and 20 AE 3.4 g C m À2 yr À1 during 2005. This could be partitioned into an annual surfaceatmosphere CO 2 net uptake of 55 AE 1.9 g C m À2 yr À1 during 2004 and 48 AE 1.6 g C m À2 yr À1 during 2005. The annual NEE was further separated into a net uptake season, with an uptake of 92 g C m À2 yr À1 during 2004 and 86 g C m À2 yr À1 during 2005, and a net loss season with a loss of 37 g C m À2 yr À1 during 2004 and 38 g C m À2 yr À1 during 2005. Of the annual net CO 2 -C uptake, 37% and 31% was lost through runoff (with runoff TOC4DIC ) CH 4 ) and 16% and 29% through methane emission during 2004 and 2005, respectively. This mire is still a significant C-sink, with carbon accumulation rates comparable to the long-term Holocene C-accumulation, and higher than the C-accumulation during the late Holocene in the region.