<p dir="ltr">Globally, soils hold more carbon than both the atmosphere and aboveground terrestrial biosphere combined. Changes in land use and land cover have the potential to alter soil carbon cycling throughout the soil profile, from the surface to meters deep, yet most studies focus only on the near surface impact (< 25 cm deep). This research bias toward shallow soil carbon cycling has ramifications for understanding the full impacts of agricultural and restoration management practices on soil organic and inorganic carbon dynamics. The primary objective of my thesis research is to evaluate the factors controlling the impact of deep-rooting perennial grass on soil carbon cycling during prairie restoration of soil following long term, row crop agriculture. Paired soil pits were established to compare the effects of restoration on soil C dynamics in a corn-soy cropping system (minimal tillage) and restored prairie sites in Nebraska and Illinois. At each site, soil organic carbon (SOC) and inorganic carbon (SIC) content, stock, and stable carbon isotope analysis were preformed to ~2 m depth to assess long term integrated C dynamics. Estimating the contribution of prairie carbon inputs to the SOC in the soil profile was examined using stable carbon isotopic signatures in the SOC in relation to the above ground vegetation changes in C₃ and C₄ photosynthetic pathway plant community composition. Comparative analysis of edaphic properties and soil carbon suggests that deep loess deposits in Nebraska permit enhanced water infiltration and SOC deposition to depths of ~100 cm in 60 years of prairie restoration. In Illinois, poorly drained, clay/lime rich soils on glacial till and a younger restored prairie age (15 years) restricted the influence of prairie restoration to the upper 30 cm. Comparing the δ¹³C values of SOC and SIC in each system demonstrated that SIC at each site is likely of lithogenic origin. This work indicates that the magnitude of influence of restoration management is dependent on edaphic properties inherited from geological and geomorphological controls. Future work should quantify root structures and redox properties to better understand the influence of rooting depth on soil carbon concentrations. Fast-cycling C dynamics can be assessed using continuous, in-situ CO₂ and O₂ soil gas concentration changes. The secondary objective of my thesis was to determine if manual, low temporal resolution gas sampling and analysis are a low cost and effective means of measuring soil O₂ and CO₂, by comparing it with data from in-situ continuous (hourly) sensors. Manual analysis of soil CO₂ and O₂ from field replicates of buried gas collection cups resulted in measurement differences from the continuous sensors. Measuring CO2 concentration with manual methods often resulted in higher concentrations than hourly, continuous measurements across all sites. Additionally, O₂ concentrations measured by manual methods were higher than hourly values in the restored prairie and less in agricultural sites. A variety of spatial variability, pressure perturbations, calibration offsets, and system leakage influences on both analysis methods could cause the discrepancy.</p>

No description available.

The peri-Atlantic Arctic, one of the most sensitive components of the Earth climate system, experienced pronounced climatic fluctuations during the Holocene. Several external forcings were considered responsible for these variations, including decline of insolation on the Northern Hemisphere, changes in distribution of land ice mass, explosive volcanism, or changes in atmospheric and oceanic circulation. In order to explore the driving mechanisms of the peri-Atlantic Arctic environmental variability, three sites located in different parts of the region were selected for palaeoenvironmental reconstructions with focus on extracting the climatic information. With this intention, sedimentary cores from i) Lake Garmaksla, Central Svalbard, ii) Jarfjorden, northeastern Norway, and iii) Kobbefjord area, southwestern Greenland, were retrieved and subjected to multi-proxy investigation. The absolute chronostratigraphic framework was established by comprehensive radiocarbon (14 C) and short-lived radioisotopes (210 Pb, 137 Cs) dating. Further analyses include measurements of magnetic susceptibility, grain size distribution, element composition by means of X-ray fluorescence (XRF), and elements bound to organic matter, i.e. organic carbon, nitrogen, sulphur and biogenic silica. The relationships between the...

Methane (CH4) and carbon dioxide (CO2) are two greenhouse gases and main drivers of global climate change. Lakes are known to be a source of CH4 and CO2 to the atmosphere. While the importance of these emissions is clear, their magnitudes and regulation are still uncertain due to the scarcity of flux measurement data from lakes. Most previous flux measurements have been carried out on lakes &lt;10 km2 and the extrapolations are not representative of large lakes directly. Recent research has led to a growing recognition of the great importance of lakes as a source of emissions. Still, the relationship between environmental variables, lake properties and seasonal changes and the variability between and within lakes raises several question marks. Larger scale studies of greenhouse gases are needed to determine the spatial and temporal dynamics that exist. In this study, a floating chamber method and manual sampling was used to investigate the spatiotemporal variability and influencing variables of CH4 flux and concentration, as well as dissolved inorganic carbon (DIC) and pCO2aq (partial pressure of CO2 in the water). The sampling was conducted during five weeks in September and October 2020 in three large Swedish lakes. Our results generally showed varying CH4 values between the three lakes, indicating that nutrients affect the amount and emission of CH4. A pattern was found where the CH4 was higher near the shore and at a shallower depth. There was a correlation between CH4 concentration and the environmental variables wind speed and air- and water temperatures. Our DIC values were high in two of the lakes and low in one, all lakes’ DIC differed significantly from each other. The pCO2 did not have any difference within the lakes, and there was no difference between the lakes except in one case. Both DIC and pCO2 correlated with air- and water temperature. This study displays the large spatiotemporal variability within and between large lakes and that representative values for large lakes require more measurements under different conditions to distinguish how greenhouse gases emit and flux between lakes and atmosphere. / Metan (CH4) och koldioxid (CO2) är två växthusgaser och stora drivkrafter för globala klimatförändringar. Sjöar är kända för att vara en källa för CH4 och CO2 till atmosfären. Trots att betydelsen av dessa utsläpp är tydlig är deras storlek och reglering fortfarande osäker på grund av brist på flödesmätdata från sjöar. De flesta tidigare flödesmätningarna har utförts på sjöar &lt;10 km2 och det har påvisats att extrapoleringar inte är direkt representativa för stora sjöar. Ny forskning har lett till ett mer allmänt erkännande av sjöars stora betydelse som källa till utsläpp. Trots detta väcker förhållandet mellan miljövariabler, sjöegenskaper, säsongsförändringar och variationen mellan och inom sjöar flera frågetecken. Storskaliga studier om växthusgaser behövs för att bestämma den rumsliga och tidsmässiga dynamiken som finns. I denna studie användes en kammarmetod och manuell provtagning för att undersöka spatiotemporal variabilitet och miljövariabler som kan påverka CH4 flöde och koncentration, samt upplöst oorganiskt kol (DIC) och pCO2aq (partial trycket av CO2 i vattnet). Provtagningen genomfördes under fem veckor i september och oktober 2020 i tre stora svenska sjöar. Våra resultat visade generellt varierande CH4 värden mellan de tre sjöarna, vilket indikerade att näringsämnen påverkar mängd och utsläpp av CH4. Ett mönster noterades där CH4 var högre nära stranden och på ett grundare djup. Det fanns ett samband mellan CH4 koncentration och miljövariablerna vindhastighet och luft- och vattentemperatur. DIC-värdena var höga i två av sjöarna och låga i en, alla sjöarnas DIC skiljde sig signifikant från varandra. pCO2 hade ingen skillnad inom sjöarna, och det fanns ingen skillnad mellan sjöarna utom i ett fall. Både DIC och pCO2 korrelerade med luft- och vattentemperatur. Studien visar den stora spatiotemporala variationen inom och mellan stora sjöar och att representativa värden för stora sjöar kräver fler mätningar under olika förhållanden för att urskilja hur växthusgaser emitterar och flödar mellan sjöar och atmosfär.

Over the past decades, evidence show that the anthropogenetic greenhouse gases (GHG) emissions of carbon dioxide (CO₂) and methane (CH₄) are the main drivers behind global warming and are becoming stronger. Globally, hydropower is among the main sources of renewable energy and the popular notion that hydropower electricity is carbon neutral has been under debate as evidence from measurements in different regions of the globe show significant and highly variable carbon emissions from hydropower reservoirs. But these global estimates are still highly uncertain since they are restricted to a few locations in the south of Europe, North America, and South America, and lack both the temporal and spatial variability in addition to some of the flux pathways (often downstream emission and degassing). This study assesses the CH4 and CO₂ emissions from reservoirs associated to three small hydropower stations in the south of Sweden and aims to understand potential spatial and temporal variability in the temperate region. The study performed flux measurements of CH4 and CO₂, an analysis of CH4 and DIC concentration in the water, and a depth profile of temperature, DO, CH4 and DIC at the hydropower station’s reservoirs. In summation this study finds significant CH4 and DIC concentrations, as well as CH4 and CO₂emissions from the studied reservoirs. The findings of this study underline the notion that hydropower might be a `blind spot` in the Swedish GHG budget report, and if so, the carbon emissions from hydropower electricity need to be re-evaluated.