Multi-scale assessment and simulation of sediment biogeochemical cycles in coastal areas: implications for ecosystem functioning and provision of services

Abstract

Marine coastal sediments and associated communities provide benefits to humans through natural processes such as nitrate removal via denitrification (prevention or mitigation of eutrophication), burial of toxic substances (pollution control), and sediment stabilization (coastal protection). However, sediments can also have negative impacts on the environment, for example throughout the production of toxic hydrogen sulfide, and emission of greenhouse gases (CH4, N2O). Understanding sediment biogeochemical cycles in coastal areas and responses to natural and anthropogenic forcing can provide important insight into the functioning of marine coastal ecosystems, as well as tools to manage positive (desired) and negative (undesired) interactions with human systems. This thesis aimed to explore the linkages and interactions among biological, geochemical and human systems in coastal sediments at sub-seasonal and meter to kilometer scales. Two major projects were conducted. The first project focused on understanding (Chapter 2) and predicting (Chapter 3) the patterns of, and controls on the C and N cycling in sediments of two shallow coastal systems of Nova Scotia, Canada. The second project focused on the study of aquaculture – sediment interactions, particularly, on the modeling and prediction of the deposition, degradation, and accumulation of organic wastes in sediments underlying fish farm cages (Chapter 4). The integration of statistical and deterministic modeling, field and laboratory observations, and benthic habitat mapping provided a means to study benthic processes at multiple spatial scales. Results of Chapter 3 and 4 highlight the important role of habitat diversity and sediment-biological interactions (e.g., autotrophic activity) on diagenetic processes in coastal sediments. Chapter 4 provided new conceptual and modeling tools to manage aquaculture-sediment interactions in coastal areas.