<p>Seasonally dry ecosystems cover large areas over the world, have high potential for carbon sequestration, and harbor high levels of biodiversity. They are characterized by high rainfall variability at timescales ranging from the daily to the seasonal to the interannual, and water availability and timing play key roles in primary productivity, biogeochemical cycles, phenology of growth and reproduction, and agricultural production. In addition, a growing demand for food and other natural resources in these regions renders seasonally dry ecosystems increasingly vulnerable to human interventions. Compounded with changes in rainfall regimes due to climate change, there is a need to better understand the role of climate variabilities in these regions to pave the way for better management of existing infrastructure and investment into future adaptations. </p><p>In this dissertation, the ecohydrological responses of seasonally dry ecosystem to climate variabilities are investigated under a comprehensive framework. This is achieved by first developing diagnostic tools to quantify the degree of rainfall seasonality across different types of seasonal climates, including tropical dry, Mediterranean, and monsoon climates. This global measure of seasonality borrows from information theory and captures the essential contributions from both the magnitude and concentration of the rainy season. By decomposing the rainfall signal from seasonality hotspots, increase in the interannual variability of rainfall seasonality is found, accompanied by concurrent changes in the magnitude, timing, and durations of seasonal rainfall, suggesting that increase in the uncertainty of seasonal rainfall may well extend into the next century. Next, changes in the hydrological partitioning, and the temporal responses of vegetation resulting from these climate variabilities, are analyzed using a set of stochastic models that accounts for the unpredictability rainfall as well as its seasonal trajectories. Soil water storage is found to play a pivotal role in regulating seasonal soil water hysteresis, and the balance between seasonal soil water availability and growth duration is found to induce maximum plant growth for a given amount of annual rainfall. Finally, these methods are applied in the context of biodiversity and the interplay of irrigation and soil salinity, which are prevailing management issues in seasonally dry ecosystems.</p> / Dissertation

Per- and polyfluoroalkyl substances (PFASs) are a group of emerging chemicals which havereceived increasing attention due to their toxicity, persistent properties, and global distribution.In this study, sorption coefficients (Kd and KOC) of PFASs in an industrial site in Sweden wereevaluated. Sorption is a measures of the mobility of a substance in the subsurface, and is a keyfactor in environmental risk assessments. Sorption coefficients were calculated both from fieldsamples processed in laboratory batch tests, and from a simplified approach involving the totalconcentrations in soil and groundwater (field-derived). Soil was sampled from two locations ofthe site; C8 and M6. Field-derived values were calculated based on concentrations which werehistorically measured. The aim was to compare the two methods, and to compare the valueswith literature values as well as guideline sorption values established by the SwedishGeotechnical Institute (SGI). Sorption coefficients for PFHxA, PFHpA, PFOA, PFHxS, PFOS, 6:2 FTS and PFBS could beestablished. Results showed that laboratory-derived sorption coefficients were significantlyhigher than field-derived sorption coefficients. Laboratory-derived sorption values were alsohigher than to SGI’s preliminary sorption values. Comparing C8 and M6 KOC values toliterature values, PFHpA, PFHxA, and PFBS exhibit values above literature values. PFOA,PFHxS, PFOS exhibit KOC values within the range of literature values. According to thesorption coefficients, predictive scenarios of leaching through the unsaturated zone weremodelled, and it was concluded that leaching was higher in M6 compared to C8. The resultsalso showed that an increase in precipitation increased the leaching. / Per- och polyfluorerade alkylsubstanser (PFAS) är en grupp nyligen uppkomna kemikalier somhar fått ökad uppmärksamhet pga. deras toxicitet, ihärdiga egenskaper och globala utbredning.Detta examensarbete har studerat fördelningskoefficienter (Kd och KOC) för PFAS inom ettindustriområde i Sverige. Fördelningskoefficienter är ett mått på mobilitet av en substans iunderjorden, och det är en viktig komponent i riskbedömningar inom förorenad mark.Fördelningskoefficienter beräknades dels utifrån jordprover som tagits i fält och analyserats ilaboratorium med extraktionsmetoder, och dels utifrån ett förenklat tillvägagångssätt därberäkning skett med hjälp av tidigare uppmätta koncentrationer i jord och grundvatten.Jordprover från två områden inom industriområdet; C8 och M6, togs och analyserades.Fältbaserade fördelningskoefficienter beräknades utifrån koncentrationer som tidigare mättsvid brunnsinstallation och vid grundvattenövervakning. Målet med studien var att jämföra detvå metoderna, och dessutom jämföra fördelningskoefficienterna med motsvarande i värdenlitteraturen samt riktvärden för fördelningskoefficienter som Statens Geotekniska Institutet(SGI) arbetet fram. Fördelningskoefficienter för PFHxA, PFHpA, PFOA, PFHxS, PFOS, 6:2 FTS and PFBS kundeberäknas. Resultatet visade att laboratorie-baserade fördelningskoefficienter var betydligthögre än fältbaserade fördelningskoefficienter. Laboratorie-baserade fördelningskoefficientervar även högre än de preliminära riktvärden för fördelningskoefficienter som SGI etablerat. Vidjämförelse av fördelningskoefficienter för C8 och M6 kunde det konstateras att PFHpA,PFHxA, and PFBS hade högre värden än motsvarande i litteraturen. PFOA, PFHxS, PFOSvisade på värden som var inom intervallet av värdena från litteraturen. Med hjälp av deberäknade fördelningskoefficienterna modellerades prediktiva utlaknings-scenarier. Utifrånresultatet sker utlakningen i större grad i M6 jämfört med C8. Utlakningen ökade även vidförhöjd nederbörd.