The sorption and desorption of phosphate-P, ammonium-N and nitrate-N in cacao shell and corn cob biochars.

The sorption of PO4-P, NH4-N and NO3-N to cacao shell and corn cob biochars produced at 300-350°C was quantified. The biochars were used; (i) as received (unwashed), (ii) after rinsing with Millipore water and (iii) following leaching with Millipore water. In addition to sorption, desorption of PO4-P from the unwashed biochars was quantified. There was no sorption of PO4-P to either washed or rinsed biochars, but following leaching, both biochars adsorbed PO4-P and distribution coefficients (Kd L kg(-1)) were very similar for both materials (10(1.1±0.5) for cacao shell biochar and 10(1.0±0.2) for corn cob biochar). The BET surface area and micropore volume increased 80% and 60% for the cacao shell and corn cob biochars following leaching. After 60 d, 1483±45 mg kg(-1) and 172±1 mg kg(-1) PO4-P was released from the cacao shell and corn cob biochars. NH4-N was sorbed by both unwashed biochars, albeit weakly with Kd values around 10(2) L kg(-1). We speculate that NH4-N could bind via an electrostatic exchange with other cationic species on the surface of the biochar. There was no significant release or sorption of NO3-N from or to either of the biochars.

Activation of old carbon by erosion of coastal and subsea permafrost in Arctic Siberia.

The future trajectory of greenhouse gas concentrations depends on interactions between climate and the biogeosphere. Thawing of Arctic permafrost could release significant amounts of carbon into the atmosphere in this century. Ancient Ice Complex deposits outcropping along the ~7,000-kilometre-long coastline of the East Siberian Arctic Shelf (ESAS), and associated shallow subsea permafrost, are two large pools of permafrost carbon, yet their vulnerabilities towards thawing and decomposition are largely unknown. Recent Arctic warming is stronger than has been predicted by several degrees, and is particularly pronounced over the coastal ESAS region. There is thus a pressing need to improve our understanding of the links between permafrost carbon and climate in this relatively inaccessible region. Here we show that extensive release of carbon from these Ice Complex deposits dominates (57 ± 2 per cent) the sedimentary carbon budget of the ESAS, the world's largest continental shelf, overwhelming the marine and topsoil terrestrial components. Inverse modelling of the dual-carbon isotope composition of organic carbon accumulating in ESAS surface sediments, using Monte Carlo simulations to account for uncertainties, suggests that 44 ± 10 teragrams of old carbon is activated annually from Ice Complex permafrost, an order of magnitude more than has been suggested by previous studies. We estimate that about two-thirds (66 ± 16 per cent) of this old carbon escapes to the atmosphere as carbon dioxide, with the remainder being re-buried in shelf sediments. Thermal collapse and erosion of these carbon-rich Pleistocene coastline and seafloor deposits may accelerate with Arctic amplification of climate warming.