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Intermittent rivers and ephemeral streams (IRES) experience drying events, and they are becoming increasingly common due to climate change and anthropogenic water withdrawal. Despite their prevalence, IRES have been less studied than non-drying rivers, and more research is needed to understand their dynamics. This dissertation examines drying events' effects on the sediment microbial community structure and biogeochemistry in temperate IRES. First, a research study was carried out using an outdoor mesocosm setup to track changes in bacterial and fungal communities, microbial functions and properties of sediment-dissolved organic carbon during three different drying events. Results showed that drying duration and intensity and sediment organic matter content regulated river Spree sediment microbial community composition and biogeochemical processes during drying. The associated sediment respiration, assessed as CO2 flux, rapidly declined during all drying treatments, and Bacilli class became the most dominant bacteria after 90 days of drying, except in non-enriched sediment under the most intense drying. Second, a microcosm experiment was conducted to understand how sediment drying history and properties influence biogeochemical dynamics during an IRES expansion phase. Sediment respiration and nutrient release/retention rates were measured through flow resumption, and results showed that drying duration and intensity and sediment organic matter content regulated the dynamics of nutrients and respiration upon flow resumption. Under the most intense and prolonged drying, non-enriched sediment showed a lag response in respiration during the first day after flow resumption, while all other treatments had either a linear increase or a fast pulse in respiration. Finally, the long-term microbial succession in IRES sediment and soil in the experimental catchment of Chicken Creek was investigated. In 2008 and 2018, the sediment of three ephemeral streams and their adjacent soil was analyzed for the structure of the bacterial and fungal communities and microbial functions across different seasons. Results showed that environmental factors, such as vegetation type and organic matter content, mediated sediment and soil microbial succession in Chicken Creek. Ephemeral streams under spare and sporadic flow events remained unique ecosystems with distinctive microbial communities and biogeochemical dynamics, different from its riparian soil. Overall, this dissertation concludes that temperate IRES are dynamic ecosystems where dry-wet cycles and environmental factors modulate their sediment microbial community structure and function trajectories in the short- and long term.
Unlike many areas of the world where agricultural producers exhibit the physical, economic and social resources to moderate, or adapt, subsistence agriculture in the Sudano-Sahel region of Cameroon is seem to be particularly vulnerable to the impacts of climatic variability. This is in part due to the fact that the majority of the population depends on rain-fed agriculture for their livelihood. Adapting to climate change in the subsistence agricultural sector is therefore very imperative in providing food security and concomitantly protecting the livelihood of rural communities. This study examined the patterns of current climatic variables on some selected subsistence staple crops namely; millet and sorghum in the Cameroon´s Sudano-Sahel. It also valorized and documented the community based adaptation strategies used by local farmers to cope with current climate change, explored the constraints and opportunities in adaptation and mitigation that could facilely be integrated and incorporated into policies and programs. The guiding premises were that climatic change impacts subsistence crop yields as the lower the rainfall, the higher the vulnerability of the yields of staple crops. It also hypothesized that the present community-based strategies used by the local farmers are relevant and crucial to the present day quest for climate change adaptation strategies. Analyses of agricultural droughts using the Standardized Precipitation Index (SPI), spatio-temporal land use and land cover dynamics via remote sensing were utilized as well as the application of statistical tools for the investigation of pressure and state indicators. A participatory research approach was used in exploring adaptation patterns perceived by the ruralites in the face of variable climatic condition via administered questionnaires. The results suggested critical impact asymmetries due to climatic and socio-economic factors affected subsistence crops in the Sudano-Sahel of Cameroon. Furthermore, SPI results indicated incidences of droughts; with the Multilinear Regression (MLR) models showing temperature and rainfall to an extent determined agricultural crop productivity in the Sudano-Sahel. However, other factors such as population growth have undoubtedly caused enormous impacts on the agricultural system as seen in remote sensing analyses. Questionnaire survey findings also connoted that subsistence farming communities have a rich repertoire of strategies ranging from changing of planting dates, changing of crop varieties, switching from crops to livestock, use of local indicators, movement from rural to urban areas, increment in cultivated lands, irrigation soil conservation practices among many others as they perceive varying climatic conditions. Additionally, some of these indigenous strategies are inherent in ecological agricultural practices that offer a win-win scenario for the simultaneously tackling of climate change adaptation and mitigation and hence meeting the development goals. The results further highlighted the lack of money, poor access to climate information, the encroachment of desert and shortage of man power as some of the factors hindering subsistence farmers’ ability to adapt. The study concluded that adaptation measures in subsistence agriculture were highly significant for poverty reduction, thus improving on the well-being of the ruralites. The key to the ability of farmers to adapt would be access to relevant knowledge and information. Following the rich repertoire of strategies by local farmers, adaptation needed to be mainstreamed and institutional networks strengthened in order for effective community based adaptation.