 Hi, I'm Fumiko Nakagawa. This article is done by Dr. Tsunogai, Mr. Miyawuchi, Mr. Oyama, Dr. Kumatsu, Dr. Ito, and me. This article focuses on the nitrate, which is a key nutrient in aquatic environments, and proposes a new method to estimate the gross production rate of nitrate via nitrification. Traditionally, the gross nitrification rate has been estimated via incubation experiments using artificial tracers such as N15. The N15 method, however, is a snapshot tracer approach and needs time series observations to estimate long-term average rate. Here, we would like to propose an alternative simple method using the natural O17 excess of dissolved nitrate as a tracer. The average O17 excess of nitrate in a lakeswater column reflects relative supply rate of nitrate between atmospheric deposition and nitrification. Besides, the position rate of atmospheric nitrate can be easily obtained through the air quality monitoring. As a result, we can deduce long-term average nitrification rate for an internal between observations. In 2011, we successfully applied this new method to Lake Mashu, the lake with no inflows and outflows. So, the aim of our present study is to quantify nitrification rates in a more general lake with inflows and outflows. Lake Biwa, the largest freshwater lake in Japan. We successfully applied this new method to the lake and revealed that nitrate supplied by inflows occupies only less than 30% of nitrate supplied into the lakeswater column. Besides, about 80% of the metabolized nitrate was reminulized to nitrate again via rapid turnover of nitrate in the lake. If you want to know more, please read the article.