Boreal mire carbon exchange

Boreal peatlands are important long-term sinks of atmospheric carbon and in the same time the largest natural source of methane to the atmosphere. A changing climate as well as deposition of anthropogenically derived pollutants, such as nitrogen and sulfur, has the potential to affect the processes that control the carbon exchange in peatlands. Many of the biogeochemical responses to changed environmental conditions, such as changed plant community composition, are slow and therefore long-term studies are required. In this thesis I have investigated the long-term effects of nitrogen addition, sulfur addition and greenhouse enclosures on carbon exchange by using a field manipulation experiment in a boreal minerogenic, oligotrophic mire after 10-12 years of treatment. Treatment effects on CH4 emissions, gross primary production (GPP), ecosystem respiration (Reco) and net ecosystem exchange (NEE) were estimated from 1-2 seasons of chamber flux measurements. Treatment effects on potential CH4 production and oxidation were estimated in incubations of peat from different depth intervals. The effect of nitrogen deposition on carbon accumulation was evaluated in peat cores at different depth intervals. The long-term nitrogen additions have: shifted plant community composition from being dominated by Sphagnum to being dominated by sedges and dwarf shrubs; changed mire surface microtopography so that mean water table is closer to the surface in plots with high nitrogen; increased CH4 production and emission; increased Reco slightly but have not affected GPP or NEE; reduced the peat height increment, but increased both peat bulk density and carbon content, leading to an unchanged carbon accumulation. The long-term sulfur additions have not reduced CH4 emissions, only slightly reduced CH4 production and did not have any effect on the CO2 carbon exchange. The greenhouse treatment, manifested in increased air and soil temperatures, reduced both CH4 emissions and CH4 production by approximately 30%, decreased Reco slightly, but had no effect on either GPP or NEE. Many of these results oppose to earlier findings, and this suggests that long-term field manipulations are important when evaluating effects with a long time constant

Variations in bioavailability of dissolved organic matter during a spring flood episode in northern Sweden

This study of spring flood episodes was performed within the catchment of Krycklan, in Svartberget, northern Sweden. The purpose was to better understand changes in total organic carbon (TOC) concentrations and the bioavailability of dissolved organic matter (DOM) during the spring flood and how they differ between stream sites, ranging in size and characteristics. DOM bioavailability was estimated from CO2 production rates (PrRs) and total CO2 production (TPrs), derived by applying standardized bacterial bioassays during approximately 90 days. TOC concentrations in most of the forested streams increased during spring flood. Furthermore, the PrRs per unit of TOC increased by up to 95% when comparing discharge before and after spring flood. These patterns can be explained by the activation of new superficial flow paths in the riparian zone, increasing not only the DOM concentration per se, but also its susceptibility to biological degradation. At a mire-influenced headwater stream, TOC concentrations decreased during peak flow and no differences in DOM bioavailability per unit TOC was observed before and during spring flood. This suggests that the hydrological flow paths in the mire are superficial during most of the year and do not provide any new sources of DOM to the stream during spring flood. Instead, existing sources are diluted due to higher discharge. PrRs and TPrs ranged from 0.10% to 0.43 % of total C pool per day and from 6% to 20% of total C pool over 80 days, respectively. PrRs and TPrs were low in headwaters and increased further downstream. This downstream change was observed during all three bioassays, but was largest before and during spring flood. PrRs were up to four times higher in the outlet of the catchment of Krycklan than in the forest and mire headwaters. The residence time of water in streams within the catchment is small and water temperatures during spring flood are low. Therefore, it is likely that most of the bioavailable DOM will be utilized outside the catchment of Krycklan and spring-flood contributions can, consequently, play an important role for carbon and nutrient cycling in rivers, lakes and the ocean further downstream

Impact of 4D channel distribution on the achievable rates in coherent optical communication experiments

We experimentally investigate mutual information and generalized mutual information for coherent optical transmission systems. The impact of the assumed channel distribution on the achievable rate is investigated for distributions in up to four dimensions. Single channel and wavelength division multiplexing (WDM) transmission over transmission links with and without inline dispersion compensation are studied. We show that for conventional WDM systems without inline dispersion compensation, a circularly symmetric complex Gaussian distribution is a good approximation of the channel. For other channels, such as with inline dispersion compensation, this is no longer true and gains in the achievable information rate are obtained by considering more sophisticated four-dimensional (4D) distributions. We also show that for nonlinear channels, gains in the achievable information rate can also be achieved by estimating the mean values of the received constellation in four dimensions. The highest gain for such channels is seen for a 4D correlated Gaussian distribution

Gender, Productivity and the Nature of Work and Pay: Evidence from the Late Nineteenth-Century Tobacco Industry

Women have, on average, been less well-paid than men throughout history. Prior to 1900, most economic historians see the gender wage gap as a reflection of men's greater strength and correspondingly higher productivity. This paper investigates the gender wage gap in cigar making around 1900. Strength was rarely an issue, but the gender wage gap was large. Two findings suggest that employers were not sexist. First, differences in earnings by gender for workers paid piece rates can be fully explained by differences in experience and other productivity-related characteristics. Second, conditioning on those characteristics, women were just as likely to be promoted to the better paying piece rate section. Neither finding is compatible with a simple model of sex-based discrimination. Instead, the gender wage gap can be decomposed into two components. First, women were typically less experienced, in an industry in which experience mattered. Second there were some jobs that required strength, for which men were better suited. Because strength was so valuable in the other jobs at this time, men commanded a wage premium in the general labour market, raising their reservation wage. Hiring a man required the firm to pay a 'man's wage'. This implies that firms that were slow to feminise their time rate workforce ended up with a higher cost structure than those that made the transition more quickly. We show that firms with a higher proportion of women in their workforce in 1863 were indeed more likely to survive 35 years later.gender, productivity, discrimination, piece-rates, time-rates, labour markets, firm survival

Deep Learning of Geometric Constellation Shaping including Fiber Nonlinearities

A new geometric shaping method is proposed, leveraging unsupervised machine learning to optimize the constellation design. The learned constellation mitigates nonlinear effects with gains up to 0.13 bit/4D when trained with a simplified fiber channel model.Comment: 3 pages, 6 figures, submitted to ECOC 201

Four-Dimensional Estimates of Mutual Information in Coherent Optical Communication Experiments

Mutual information is experimentally investigated for long-haul coherent transmission. Receivers that consider memoryless four-dimensional noise distributions can achieve significantly higher rates than receivers assuming two-dimensional symmetric distributions