Wat. Res. Vol. 35, No. 5, pp. 1334–1337, 2001 # 2001 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/01/$ - see front matter PII: S0043-1354(00)00380-8 RESEARCH NOTE REGENERATION OF N, P AND Si NEAR THE SEDIMENT/ WATER INTERFACE OF LAKES FROM SOUTHWESTERN CHINA PLATEAU F. WU 1,2 *, H. QING 3 and G. WAN 1 1 State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, People’s Republic of China; 2 Institute of Hydrospheric-Atmospheric Sciences, Nagoya University, Chikusa-Ku, Nagoya 464-8601, Japan and 3 Department of Geology, University of Regina, Regina SK, Canada S4S 0A2 Abstract}Lake water, pore water, and sediments were sampled in both polluted and unpolluted lakes from Southwestern (SW) China Plateau. The results show that although the mechanisms of nutrient regeneration were similar in the polluted and unpolluted lakes, the processes, however, were much stronger in the polluted lakes. Nitrogen regeneration was mainly of organic process. Phosphorus regeneration was essentially controlled by iron redox cycling near sediment/water interface. Nutrient upward fluxes were in the order SiO 2 > NH þ 4 > PO 3 4 . This study has significance for further investigating the response of nutrient biogeochemistry to the increasing nutrient levels in aquatic environments. # 2001 Elsevier Science Ltd. All rights reserved Key words}nutrient regeneration, lakes, sediment/water interface, southwestern China Plateau INTRODUCTION Nutrient biogeochemistry has been studied in aquatic environments (Brzezinski et al., 1997; Lyons et al., 1996; Sundby and Gobeil, 1992; Landing et al., 1991; Nixon, 1981). The results, however, sometimes were controversial. There is a need for comparative investigation, and general models require examining each aspect in a variety of locations. The results reported here represent a comparative study of nutrient regeneration between the polluted and unpolluted lakes in SW China Plateau. There are more than 30 lakes in SW China, few have been reported. Although some of these lakes are seldom polluted, most of them have been heavily contaminated by recent human activities and they are experiencing a major deterioration of the water quality and decrease in aquatic species. The increase of nutrient levels is believed to be an important factor of these problems (Wu, 1997). The fundamentals pertaining to nutrient biogeochemistry, however, are poorly documented. Based on previous lake chemistry survey (Wu et al., 1997; Wu, 1997), one unpolluted lake (Lake Lugu) and two polluted lakes (Lakes Baihua and Erhai) were chosen in this region as the case study. Lake Lugu is isolated from industrial areas due to its high sea level, and is regarded as one of the best naturally preserved lakes in China (Wu, 1997). Lakes Erhai and Baihua, however, are two polluted lakes. N and P contents in Lake Baihua were the highest among the lakes in this region (Wu, 1997). In this study, N, P and Si regeneration processes between the polluted and unpolluted lakes were comparatively investigated by studying detailed profiles of N and P species and dissolved SiO 2 in the overlying water, sediments, and pore water, and by comparison of calculated nutrient fluxes near the sediment/water interface. MATERIALS AND METHODS Water samples were filtered through a polycarbonate filter (0.45 mm pore-size) for chemical analyses. The sediment/water interface samples were collected in the center of these lakes in 1991 and 1994. The sediments were sliced into 0.5–2.0 cm intervals, pore water was then filtered through 0.45 mm membrane filters following centrifugation. The residue was lyophilized and ground, and stored frozen until analysis. NO  3 contents were analyzed by ionic chromatography. Dissolved NH þ 4 , SiO 2 and PO 3 4 concentrations were deter- mined using colorimetric method (Strickland and Parson, 1972). N and C org concentrations in the sediments were determined by elemental analyzer after the removal of carbonate. Nitrogen in the sediments was operationally analyzed for three forms: exchangeable nitrogen (NH þ 4 and NO  3 ), effective nitrogen and residual nitrogen (Wu, 1997; Jackson, 1976). Total inorganic and organic P in the sediments was analyzed following the procedures outlined in Jackson (1976). RESULTS AND DISCUSSION Nitrogen regeneration in the overlying water and sediments The average total nitrogen (TN) in the overlying water was 1.26 mg l 1 in Lake Baihua, 0.70 mg l 1 *Author to whom all correspondence should be addressed. Fax: +81-52-7893436; e-mail: wu@ihas.nagoya-u.ac.jp; fcwu@hotmail.com 1334