Geochemical Journal, Vol. 46 (No. 6), pp. e47-e52, 2012EXPRESS LETTER
Takaaki Itai,1 Michio Kumagai,2 Yuika Hyobu,1 Daisuke Hayase,1 Sawako Horai,3 Michinobu Kuwae1 and Shinsuke Tanabe1
1Center for Marine Environmental Studies, Ehime University, Bunkyo-cho 2-5, Matsuyama, Ehime 790-8577, Japan
2Lake Biwa Environmental Research Institute, 5-34 Yanagasaki, Otsu, Shiga 520-0022, Japan
3Faculty of Regional Sciences, Tottori University, 4-101 Koyama-Minami, Tottori 680-8551, Japan
(Received August 24, 2012; Accepted October 16, 2012; Online published October 31, 2012)
An apparent temporal increase in Mn and As in a thin surface layer (ca. 2 cm) of sediments in Lake Biwa, Japan, was observed by comparing depth profile data from 1977 and 2009. By our estimation, several thousand tonnes of Mn and a few hundred tonnes of As newly accumulated during the 32 years to 2009. Given various methodological concerns and geochemical factors associated with Mn and As dynamics, this phenomenon is believed to have been caused by increased Mn and As influxes to the lake rather than by redistribution induced by the intra-annual decrease in the level of dissolved oxygen. Mass balance calculations indicated that it is unlikely that the recently accumulated quantities of Mn and As were supplied via rivers as dissolved phases; rather, ground-water is the more likely source of these quantities. Further monitoring surveys will be important for assessing the environmental impact of this temporal change.
Key words: Lake Biwa, manganese, arsenic, temporal variation, environmental change