title: Investigation of low-molecular weight organic acids and their spatiotemporal variation characteristics in Hongfeng Lake, China.
abstract: The identities and concentrations of low-molecular-weight organic acids (LMWOAs) were determined by ion chromatography throughout a 20-m water column in Hongfeng Lake, China. The spatiotemporal variations of LMWOAs and their contributions to dissolved organic matter (DOM) in a research period of 24 hr were also investigated. The results demonstrated that five LMWOAs (lactic, acetic, pyruvic, sorbic, oxalic acid) were detected, and their total concentration and proportion in DOC were 6.55 micromol/L and 7.47%. Their average levels were 2.50, 0.65, 2.35, 0.96 and 0.09 micromol/L, respectively. LMWOAs were higher during daytime (10:00-18:00 on Jun 13, 2008) than nighttime (21:00-6:00 the next morning), in particular 4.99 micromol/L high in the epilimnion (< or = 1 m water depth), reflecting the fact that direct import from terrigenous sources and photochemical production from humic materials were dominant during LMWOAs' origin and accumulation. The same factors caused LMWOAs to be 0.63 micromol/L in the epilimnion higher than in the hypolimnion. The rapid decrease of total organic acid (TOA) up until 18:00 mainly resulted from bio-uptake and mineralization in the hypolimnion (>1 m water depth). Pyruvic acid increased with time in the epilimnion and decreased in the hypolimnion, largely related to the two contrary processes of continuous degradation and synthesis of macromolecular organic matter during life materials' cycle mediated by organisms. Simultaneously, plankton behavior and thermal stratification played a pivotal role in LMWOAs' behavior in the water column, causing decreasing and increasing profiles. The distribution of LMWOAs represents an interesting resource for biogeochemical research of DOM in aquatic ecosystems.
authors.affiliation: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China. xiaomin@mails.gyig.ac.cn
authors.forename: Min
authors.initials: M
authors.lastname: Xiao
authors.forename: Fengchang
authors.initials: F
authors.lastname: Wu
authors.forename: Liying
authors.initials: L
authors.lastname: Wang
authors.forename: Xinqing
authors.initials: X
authors.lastname: Li
authors.forename: Rongsheng
authors.initials: R
authors.lastname: Huang
mesh_terms: D002681:China; D019344:Lactic Acid / Q000032:analysis; D060106:Lakes; D008970:Molecular Weight; D009930:Organic Chemicals / Q000032:analysis*; D019815:Oxalic Acid / Q000032:analysis; D019289:Pyruvic Acid / Q000032:analysis; D013011:Sorbic Acid / Q000032:analysis
chemical_list: D009930:Organic Chemicals; D019344:Lactic Acid; D019289:Pyruvic Acid; D019815:Oxalic Acid; D013011:Sorbic Acid