Bonaire is a Caribbean Island that is part of the Dutch Kingdom. The island is currently facing serious challenges. One of the defined issues is the lack of local food production which leads to expensive fruit and vegetables in the supermarket. This results in unhealthy diets of the citizens which leads to 60% of overweighted inhabitants in Bonaire (Verweij et al., 2020). To fight this problem, the local government of Bonaire is starting agricultural projects such as community gardens. However, there is a need for examples and knowledge on how to set up successful agricultural projects. This information is currently missing in Bonaire, which makes providing guidance in such projects the main aim of this thesis. To achieve this goal, I in my role as a researcher, became a member of an ongoing communal food initiative project in the agricultural department of Bonaire called “Nos mes por”. My integration into the community created a unique opportunity to gain real-world experiences by using participatory action research (PAR) as a methodology. In short, there are two objectives namely (1) implementing actions for “Nos mes por” (gaining action) while also (2) generating information for the process and product design of community gardens in Bonaire (gaining knowledge). This research methodology in this dissertation is compiled by using interviews, observations, and focus groups as research methods. This study resulted in both real-world actions which are applied in “Nos mes por” and specific guide-lines defined by the members of the community garden to make the project successful. Moreover, strategies to set up and design communal urban agriculture initiatives in Bonaire specifically and SIDS generally are developed. However, future research in Bonaire and SIDS should test the guidelines to see how they work in practice.

Cable bacteria (Deltaproteobacteria, Desulfobulbaceae) are long filamentous sulfur-oxidizing bacteria that generate long-distance electric currents running through the bacterial filaments. This way, they couple the oxidation of sulfide in deeper sediment layers to the reduction of oxygen or nitrate near the sediment-water interface. Cable bacteria are found in a wide range of aquatic sediments, but an accurate procedure to assess their abundance is lacking. We developed a qPCR approach that quantifies cable bacteria in relation to other bacteria within the family Desulfobulbaceae. Primer sets targeting cable bacteria, Desulfobulbaceae and the total bacterial community were applied in qPCR with DNA extracted from marine sediment incubations. Amplicon sequencing of the 16S rRNA gene V4 region confirmed that cable bacteria were accurately enumerated by qPCR, and suggested novel diversity of cable bacteria. The conjoint quantification of current densities and cell densities revealed that individual filaments carry a mean current of ∼110 pA and have a cell specific oxygen consumption rate of 69 fmol O2 cell–1 day–1. Overall, the qPCR method enables a better quantitative assessment of cable bacteria abundance, providing new metabolic insights at filament and cell level, and improving our understanding of the microbial ecology of electrogenic sediments.@en

Iron, manganese, and trace elements play an important role in the marine carbon cycle as they are limiting nutrients for marine primary productivity. Water column concentrations of these bio-essential elements are controlled by the balance between input and removal, with burial in marine sediments being the main sink. The efficiency of this burial sink is dependent on the redox state of the water column, with sediments underlying a sulphidic (euxinic) water column being the most efficient sinks for Fe, but also Mn and trace elements (Co, Cd, Ni, Mo, As, W, V, and U). Transient changes in ocean redox state can hence affect trace element burial, and correspondingly, the ocean's trace element inventory, but the impact of transient oxygenation events on trace element cycling is currently not well understood. Here, we investigate the impact of a natural oxygenation event on trace element release and burial in sediments of the Eastern Gotland Basin (EGB), a sub-basin of the Baltic Sea. After being anoxic (<0.5 µM O2) for ∼10 years, the deep waters of the EGB experienced a natural oxygenation event (Major Baltic Inflow, MBI) in 2015. Following this oxygenation event, we deployed benthic chamber landers along a depth transect in the EGB in April 2016, 2017 and 2018. We complemented these in situ flux measurements with analyses of water column, solid phase and pore water chemistry. Overall, the event increased the benthic effluxes of dissolved trace elements, though particular responses were element-specific and were caused by different mechanisms. Enhanced fluxes of Cd and U were caused by oxidative remobilisation, while Ni showed little response to the inflow of oxygen. In contrast, enhanced release of Co, Mo, As, W, and V was caused by the enhanced transient input of Mn oxides into the sediment, whereas Fe oxides were of minor importance. Following the dissolution of the oxides in the sediment, Mn and W were nearly completely recycled back to the water column, while fractions of Fe, Co, Mo, As, and V were retained in the sediment. Our results suggest that transient oxygenation events in euxinic basins may decrease the water column inventory of certain trace elements (Fe, Co, Mo, As, and V), thus potentially affecting global marine primary productivity on longer timescales.@en