To better understand the Fe isotope characteristics of natural samples in the Karst area, the Fe isotope compositions of riverine suspended particulates, lake suspended particulates, lake sediments, porewaters, phytoplanktons, and aerosols in the watersheds of Lake Aha (a mineralized water system) and Lake Hongfeng (a mesotrophic water system), which are located in the Karst area, southwest China, were investigated. The studied samples displayed a variable range between (delta(56)Fe-2.03 parts per thousand and 0.36 parts per thousand. Aerosols and phytoplanktons have similar or slightly heavier Fe isotope compositions relative to the average of igneous rocks. Fe isotope compositions of riverine Suspended Particulate Matter (SPM) were mainly affected by the types of tributaries. Suspended particulates collected from tributaries seriously contaminated with coal mine drainages displayed negative delta(56)Fe values (-0.89 parts per thousand to -0.31 parts per thousand) during summer, and there were significant increases of delta(56)Fe values in winter, except AR2, which was polluted with both coal mine drainage and sewage effluent. Characteristics of lakes have important influences on Fe isotope compositions of suspended particulates, lake sediments, and porewaters. The epilimnetic particulate Fe of Lake Hongfeng had delta(56)Fe=-0.04 parts per thousand to 0.13 parts per thousand, while lighter Fe isotope compositions were measured for particulate Fe from Lake Aha, ranging from -0.42 parts per thousand to -0.09 parts per thousand. Sediments collected from Hon Wu (HW) station of Lake Hongfeng have an average delta(56)Fe value of 0.09 parts per thousand and their corresponding porewaters have lighter Fe isotope compositions, ranging from -0.57 parts per thousand to -0.31 parts per thousand; no significant variations have been observed. For the Liang Jiang Kou (LJK) station of Lake Aha, the content of reactive Fe and the concentration of sulfate were all high. Due to the reactive Fe recycling, including dissimilatory Fe reduction, adsorption, and Fe sulfide formation, porewaters sampled near the sediment surface have been found to have a delta(56)Fe value as low as -2.03 parts per thousand and an increase up to 0.12 parts per thousand, with a burial depth of 10 cm. In contrast, an opposite variation trend was found for LJK sediments. Sediments sampled at 1-cm depth had a value of delta(56)Fe=-0.59 parts per thousand and decrease as low as -1.75 parts per thousand with burial depth. This investigation demonstrated that significant Fe isotope fractionations occur in surface environments. Fe isotope compositions of particulate Fe were seriously affected by Fe sources, and Fe biogeochemical recycling has an important influence on Fe isotope fractionations in lake sediments, especially when there are significant amounts of reactive Fe and sulfate.

Publication name	ACTA GEOLOGICA SINICA-ENGLISH EDITION　Volume: 85 　Issue: 3 　Pages: 712-722 　Published: JUN 2011
Author(s)	Song Liuting; Liu Congqiang; Wang Zhongliang; Zhu Xiangkun; Teng Yanguo; Wang Jinsheng; Tang Suohan; Li Jin; Liang Lili
Corresponding author	SONG Liuting  songliuting@163.com  1. Beijing Normal Univ, Coll Water Sci, Beijing 100875, Peoples R China  2. Minist Educ, Engn Res Ctr Groundwater Pollut Control & Remedia, Beijing 100875, Peoples R China  3. Chinese Acad Sci, Inst Geochem, State Key Lab Environm Geochem, Guiyang 550002, Peoples R China  4. Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China