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Nitrous oxide (N2O) is a powerful greenhouse gas and the main driver of stratospheric ozone depletion. Since soils are the largest source of N2O, predicting soil response to changes in climate or land use is central to understanding and managing N2O. Here we find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3−), water content and temperature using a global field survey of N2O emissions and potential driving factors across a wide range of organic soils. N2O emissions increase with NO3− and follow a bell-shaped distribution with water content. Combining the two functions explains 72% of N2O emission from all organic soils. Above 5 mg NO3−-N kg−1, either draining wet soils or irrigating well-drained soils increases N2O emission by orders of magnitude. As soil temperature together with NO3− explains 69% of N2O emission, tropical wetlands should be a priority for N2O management.

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Abstract. Peatland restoration may provide a potential afteruse option to mitigate the negative climate impact of abandoned peat extraction areas; currently, however, knowledge about restoration effects on the annual balances of carbon (C) and greenhouse gas (GHG) exchanges is still limited. The aim of this study was to investigate the impact of contrasting mean water table levels (WTLs) on the annual C and GHG balances of restoration treatments with high (Res H ) and low (Res L ) WTL relative to an unrestored bare peat (BP) site. Measurements of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) fluxes were conducted over a full year using the closed chamber method and complemented by measurements of abiotic controls and vegetation cover. Three years following restoration, the difference in the mean WTL resulted in higher bryophyte and lower vascular plant cover in Res H relative to Res L . Consequently, greater gross primary production and autotrophic respiration associated with greater vascular plant cover were observed in Res L compared to Res H . However, the means of the measured net ecosystem CO 2 exchanges (NEE) were not significantly different between Res H and Res L . Similarly, no significant differences were observed in the respective means of CH 4 and N 2 O exchanges. In comparison to the two restored sites, greater net CO 2 , similar CH 4 and greater N 2 O emissions occurred in BP. On the annual scale, Res H , Res L and BP were C sources of 111, 103 and 268 g C m −2 yr −1 and had positive GHG balances of 4.1, 3.8 and 10.2 t CO 2 eq ha −1 yr −1 , respectively. Thus, the different WTLs had a limited impact on the C and GHG balances in the two restored treatments 3 years following restoration. However, the C and GHG balances in Res H and Res L were considerably lower than in BP due to the large reduction in CO 2 emissions. This study therefore suggests that restoration may serve as an effective method to mitigate the negative climate impacts of abandoned peat extraction areas.

This paper describes the runoff water quality of Light Weight Aggregates (LWA)-based extensive green roofs and sod roofs in Estonia. Samples were taken from August 2004 to April 2009 from 10 different green roofs to determine what level of water quality may be found. The results presented here show that green roofs influenced water quality to a considerable degree. The runoff water of LWA-based green roofs generally had higher values of pH, BOD 7 , TP and PO 4 -P than that from sod roofs. However, COD, TN, SO 4 and Ca-Mg salt were higher in the sod roofs than in the green roofs. The results for NH 4 -N and NO 3 -N were similar for both roof types. According to the results, the character of the runoff and the contents in the substrate layer at the moment the samples were taken affected runoff quality more than the age and location of the green roof. The use of NPK-nutrients in the substrate or in the soil caused much higher values of COD and concentrations of TP, PO 4 -P, TN, NH 4 -N and NO 3 -N in runoff water than on non-fertilized green roofs. The results of samples taken from the Tartu LWA-based green roof each spring in the period 2005-2009, at a time when the snow had almost melted, showed that concentrations of compounds in runoff water generally decreased gradually. The pH value and Ca-Mg salt concentration were, however, stable, and this was caused by the LWA material.