Masterarbeit

Arsenic speciation and methane release from a paddy soil chronosequence under changing climate conditions

Alejandra Higa Mori (10/2020-09/2021)

Betreuer: Britta Planer-Friedrich, José Miguel León Ninin

Climate change will exacerbate environmental, health and food safety risks that arise from soils that are used for rice cultivation under flooded conditions, known as paddy soils. Arsenic is a relevant contaminant in paddies as soil management favors its release, and consequently uptake by rice. On the other side, paddy soils are important contributors to global CH4 release. Effects of rising temperatures due to climate change will be observed on the dynamics of As, Fe and S and on methanogenesis, processes which are closely related. These effects, however, have not been studied together among paddy soils of different age. Here, we studied the effect of rising temperatures and soil age, based on future climate scenarios projected by the IPCC using a paddy soil chronosequence, on the changes in As, Fe and S concentration and As speciation in pore water together with CH4 production. Non-paddy soils were used as reference. After incubation experiments, we determined that in pore water from young paddy soils, the share of methylated oxyarsenates increased with rising temperatures; whereas inorganic oxyarsenic species increased in older paddies. Also, CH4 production was enhanced with temperature in all paddy soils. The oldest paddy was the most susceptible to temperature in terms of CH4 production and As and Fe concentration increases in pore water. Possible explanations for the differences in the dynamics of CH4 production, As, Fe and S concentrations, and As speciation could be the stimulation of certain groups of microbes, changes in the structure and abundance of microbial communities, and the diverse complexity of carbon substrates. Overall, rising temperatures related to climate change will be a key driver of increasing CH4 release from older paddies, as well as of intensifying health risks due to higher shares of inorganic oxyarsenic species; whereas, in younger paddies, higher risks for crop production could be expected due to higher shares of methylated oxyarsenates with rising temperatures.