The Exchange of Energy, Water and Carbon Dioxide Between Wet Arctic Tundra and the Atmosphere at the Lena River Delta, Northern Siberia

The ecosystem-scale exchange fluxes of energy, water and carbon dioxide (CO2) between wet arctic tundra and the atmosphere were investigated by the micrometeorological eddy covariance method. The investigation site was situated in the centre of the Lena River Delta in Northern Siberia (72°22'N, 126°30'E). The micrometeorological campaigns were performed from July to October 2003 and from May to July 2004. The combined datasets of the two campaigns were used to characterise the seasonal course of the energy, water and CO2 fluxes and the underlying processes for the synthetic measurement period May 28…October 21 2004/2003 which included the period of snow and soil thawing as well as the beginning of refreezing. The cumulative summer (June…August) energy partitioning was characterised by low net radiation (607 MJ m-2), large ground heat flux (163 MJ m-2), low latent heat flux (250 MJ m-2) and very low sensible heat flux (157 MJ m-2) compared to other tundra sites. These findings point out the major importance of the very cold permafrost (due to extreme winter cooling) for the summer energy budget of the tundra in Northern Siberia. Despite a high cumulative precipitation of 201 mm during summer, the cumulative summer evapotranspiration of 98 mm was low compared to other tundra sites. In summer 2003, heavy rainfall initiated severe thermoerosion phenomena and in the consequence increased drainage and run-off at the wet polygonal tundra thus demonstrating the sensitivity of permafrost landscapes to degradation by changes in hydrology. The CO2 budget of the wet polygonal tundra was characterised by a low intensity of the main CO2 exchange processes, namely the gross photosynthesis and the ecosystem respiration. The gross photosynthesis accumulated to -432 g m-2 over the photosynthetically active period (June…September). The ecosystem respiration accumulated to +327 g m-2 over the photosynthetically active period, which corresponds to 76 % of the magnitude of the gross photosynthesis. The wet polygonal tundra of the Lena River Delta was observed to be a substantial CO2 sink with an accumulated net ecosystem CO2 exchange of -119 g m-2 over the summer (June…August) and an estimated annual net ecosystem CO2 exchange of 71 g m-2. The analysis of the qualitative relationships between the processes and environmental factors, which control the energy, water and CO2 budget, suggested that the wet arctic tundra will experience severe perturbations in response to the predicted climatic change. The alterations of the tundra ecosystems would in turn exert pronounced mainly positive feedbacks on the changing climate on the regional and global scale

Utility Cost of Formal Privacy for Releasing National Employer-Employee Statistics

National statistical agencies around the world publish tabular summaries based on combined employer-employee (ER-EE) data. The privacy of both individuals and business establishments that feature in these data are protected by law in most countries. These data are currently released using a variety of statistical disclosure limitation (SDL) techniques that do not reveal the exact characteristics of particular employers and employees, but lack provable privacy guarantees limiting inferential disclosures. In this work, we present novel algorithms for releasing tabular summaries of linked ER-EE data with formal, provable guarantees of privacy. We show that state-of-the-art differentially private algorithms add too much noise for the output to be useful. Instead, we identify the privacy requirements mandated by current interpretations of the relevant laws, and formalize them using the Pufferfish framework. We then develop new privacy definitions that are customized to ER-EE data and satisfy the statutory privacy requirements. We implement the experiments in this paper on production data gathered by the U.S. Census Bureau. An empirical evaluation of utility for these data shows that for reasonable values of the privacy-loss parameter ϵ≥1, the additive error introduced by our provably private algorithms is comparable, and in some cases better, than the error introduced by existing SDL techniques that have no provable privacy guarantees. For some complex queries currently published, however, our algorithms do not have utility comparable to the existing traditiona

Seasonal progression of active-layer thickness dependent on microrelief

Introduction Active-layer thickness is a major factor for all physical and biological processes in permafrost soils. It is closely related to the fluxes of energy, water and carbon between permafrost landscapes and the atmosphere. Active-layer thickness is mainly driven by air temperature, but also influenced by snow cover, summer rainfall, soil properties and vegetation characteristics (Nelson et al., 1998). The typical polygonal tundra of the Lena Delta is characterised by a pronounced microrelief, which causes a high small-scale heterogeneity of soil and vegetation properties. Consequently, also the active-layer thickness varies substantially across small lateral distances of decimetres to metres. In order to up-scale results of process studies to the landscape scale, a quantification of the heterogeneity of active-layer thickness is of great interest

Assessing the long‐term carbon‐sequestration potential of the semi‐natural salt marshes in the European Wadden Sea

Salt marshes and other blue carbon ecosystems have been increasingly recognized for their carbon (C)‐sink function. Yet, an improved assessment of organic carbon (OC) stocks and C‐sequestration rates is still required to include blue C in C‐crediting programs. Particularly, factors inducing variability in the permanence of sequestration and allochthonous contributions to soil OC stocks require an improved understanding. This study evaluates the potential for long‐term C sequestration in the semi‐natural salt marshes of the European Wadden Sea (WS), conducting deep (1.3 m) down‐core OC‐density assessments in sites with known site histories and accretion records. Because these young marshes have developed from tidal‐flat ecosystems and have undergone rapid succession during the last 80–120 yr, the identification of different ecosystem stages down‐core was crucial to interpret possible changes in OC density. This was conducted based on the down‐core distribution of different foraminiferal taxa and grain sizes. Comparisons of historic and recent accretion rates were conducted to understand possible effects of accretion rate on down‐core changes in OC density. δ13C in OC was used to assess the origin of accumulated OC (autochthonous vs. allochthonous sources). We show that large amounts of short‐term accumulated OC are lost down‐core in the well‐aerated marsh soils of the WS region and thus emphasize the importance of deep sampling to avoid overestimation of C sequestration. Despite steep declines in OC‐density down‐core, minimum values of OC density in the salt‐marsh soils were considerably higher than those of the former tidal‐flat sediments that the marshes were converted from, illustrating the greater C‐sequestration potential of the vegetated ecosystem. However, our data also suggest that marine‐derived allochthonous OC makes up a large fraction of the effectively, long‐term preserved OC stock, whereas atmospheric CO2 removal by marsh vegetation contributes relatively little. The implication of this finding for C‐crediting approaches in blue C ecosystems has yet to be clarified

Permafrost Thaw and Liberation of Inorganic Nitrogen in Eastern Siberia

The currently observed climate warming will lead to widespread degradation of near-surface permafrost, which may release substantial amounts of inorganic nitrogen (N) into arctic ecosystems. We studied 11 soil profiles at three different sites in arctic eastern Siberia to assess the amount of inorganic N stored in arctic permafrost soils. We modelled the potential thickening of the active layer for these sites using the CryoGrid2 permafrost model and representative concentration pathways (RCPs) 4.5 (a stabilisation scenario) and 8.5 (a business as usual emission scenario, with increasing carbon emissions). The modelled increases in active-layer thickness (ALT) were used to estimate potential annual liberation of inorganic N from permafrost soils during the course of climate change. We observed significant stores of inorganic ammonium in permafrost, up to 40-fold higher than in the active layer. The modelled increase in ALT under the RCP8.5 scenario can result in substantial liberation of N, reaching values up to the order of magnitude of annual fixation of atmospheric N in arctic soils. However, the thaw-induced liberation of N represents only a small flux in comparison with the overall ecosystem N cycling