Characterizing Rice Crop Hydrologic History and Implications for Arsenic Uptake Through the Use of Stable Isotopes and Remote Sensing

Rice provides 20% of the calories consumed by humanity and is thus central to the global food supply and human nutrition. However, rice often contains elevated levels of arsenic, which is toxic to humans consuming the rice and to the rice crop itself. Thus, high concentrations of arsenic in rice represent a significant human health risk and a threat to rice yields, posing a risk to food security. The mobilization of arsenic from the soil is dependent on redox conditions which are strongly influenced by soil moisture conditions of the rice paddy. However, understanding the role of soil moisture, which exhibits significant variation within and across growing seasons, on arsenic uptake into rice remains poorly understood. To address spatial and temporal variations in rice grain arsenic, we have collected paired rice and soil samples at over 80 rice farms in Cambodia. Here we use remotely sensed measurements of soil moisture throughout the growing season of the sampled rice, and we connect these soil moisture histories of each field to our measures of rice grain arsenic and stable isotopes of carbon and nitrogen in the rice grain. We aim to apply rice grain stable isotopes of C and N as proxies of the integrated environmental conditions experienced by the rice crop and to relate this to the uptake of arsenic into the grain – an important issue as a large fraction of Cambodians rely on rice farming for their livelihoods and nearly 70% of calories consumed within the country come from rice.