Carbon stored in human settlements: the conterminous United States

Urban areas are home to more than half of the world's people, responsible for >70% of anthropogenic release of carbon dioxide and 76% of wood used for industrial purposes. By 2050 the proportion of the urban population is expected to increase to 70% worldwide. Despite fast rates of change and potential value for mitigation of carbon dioxide emissions, the organic carbon storage in human settlements has not been well quantified. Here, we show that human settlements can store as much carbon per unit area (23–42 kg C m −2 urban areas and 7–16 kg C m −2 exurban areas) as tropical forests, which have the highest carbon density of natural ecosystems (4–25 kg C m −2 ). By the year 2000 carbon storage attributed to human settlements of the conterminous United States was 18 Pg of carbon or 10% of its total land carbon storage. Sixty-four percent of this carbon was attributed to soil, 20% to vegetation, 11% to landfills, and 5% to buildings. To offset rising urban emissions of carbon, regional and national governments should consider how to protect or even to increase carbon storage of human-dominated landscapes. Rigorous studies addressing carbon budgets of human settlements and vulnerability of their carbon storage are needed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75157/1/j.1365-2486.2009.02002.x.pd

Impact of sewage sludge application on the long-term nutrient balance in acid soils of Scots pine (Pinus sylvestris, L.) forests

The objective of the investigation was to determine the effects of sewage sludge application on nutrient concentrations in soil and plant biomass fractions in Scots pine forests (Pinus sylvestris, L.), situated on sandy soils with low pH, in a south to north temperature gradient in Sweden. Twenty tons dw ha(-)1 of sewage sludge was applied in 50 to 60 yr old pine forests at four sites from Brosarp in South Sweden to Jukkasjarvi in the northern parts of the country. Application of 20 ton dw ha(-1) of sewage sludge significantly increased the concentrations of extractable N, P, K, Ca, Mg and Na, in both the mor layer and in the upper 10 cm of the mineral soil. Three years after sludge application K concentrations were only significantly increased in the upper 10 cm of the mineral soil. After 11 yr the concentrations of P were still at the same level in the mor layer as after three years. The concentrations of Ca, Mg and Na had slightly decreased only in the mor layer. There was, in most cases, a statistically significant positive correlation between the amount of applied sludge and nutrient concentrations in the soil, as well as in pine needles and in leaves of Vaccinium vitis-idaea. In all sites, Mg concentrations in the mor layer was positively and significantly correlated with Mg concentrations in current-year pine needles. Similarly, concentrations of Ca, Mg, and P in the mor layer were correlated with concentrations of these elements in current-year shorts of Vaccinium vitis-idaea