巢湖沉积物磷铁硫形态记录及其环境变化指示

Fractions of phosphorus,iron and sulfur in lake sediments of Chaohu and its implication for environmental changes

分析了巢湖表层和柱状沉积物中磷(P)、铁(Fe)和硫(S)元素的形态组成、分布、相互关系及其指示的湖泊环境变化.西半湖S3采样点位柱状沉积物总磷(TP)记录表明,巢湖西半湖区自20世纪60年代开始受人类活动影响逐步明显,其中钙磷(Ca-P)指示的流域径流输入增加早于铁铝磷(Fe/Al-P)指示的居民生活污水输入;西半湖区沉积物15~0cm有机质埋藏持续增加伴随着pH值的逐步升高,指示了水体富营养化导致藻类生产力(光合作用)提高并显著影响pH值;而东半湖S7采样点位柱状沉积物磷形态则记录了东半湖区不同的环境变化特征.巢湖沉积物活性铁组分以Fe(Ⅱ)为主,S3和S7沉积剖面Fe(Ⅲ)/Fe(Ⅱ)值整体均呈上升趋势且与Fe(Ⅲ)同步变化,表明其比值由Fe(Ⅲ)变化驱动;Fe(Ⅲ)/Fe(Ⅱ)指示沉积物上层为弱氧化性,其余层位为还原性环境.沉积物还原性无机硫(RIS)以酸可挥发性硫(AVS)为主,沉积物高有机质含量、低元素硫和还原条件降低了AVS向黄铁矿硫(CRS)的转化.巢湖沉积物中与P,S结合的Fe占比很小,高Fe/P和Fe/S比值会抑制沉积物磷的释放,导致柱状剖面P,Fe和S之间的相互作用关系整体上并不显著.

Fractions of phosphorus,iron and sulfur in the surface sediments and two sediment profiles from Chaohu lake were analyzed to study their implication for the spatio-temporal environmental changes.Sedimentary records of total phosphorus(TP)in S3 sediment profile indicated an increasing pollution inputs from anthropogenic activities in the western lake since 1960s.The increase of watershed terrestrial runoff inputs indicated by calcium-bound phosphorus(Ca-P)was earlier than the domestic sewage inputs indicated by iron/aluminum-bound phosphorus(Fe/Al-P)in sediments.The synchronous increasing of organic matter and pH in the layer of 15~0cm in S3 sediment indicated an increasing lake primary productivity as well as the intensity of photosynthesis.Fractions of phosphorus in S7 profile,however,indicated different environmental changes in eastern lake.Fe(II)was the main fraction of total active iron in Chaohu lake sediments;the ratios of Fe(III)/Fe(II)in S3 and S7 profiles show an synchronous trend with Fe(III),indicating that the change of Fe(III)/Fe(II)was driven by Fe(III).Ratios of Fe(III)/Fe(II)indicated a weak oxidation condition for the upper sediment layer and reduction for the down layer in both of the S3 and S7 profiles.Acid volatile sulfur(AVS)was the main form of the reduced inorganic sulfur(RIS)in Chaohu lake sediments.High organic matter,low elemental sulfur and strong reducing condition in Chaohu lake sediments restricted the transformations of AVS to pyrite sulfur(CRS).The P-and S-bound iron proportioned only a very small part for the total iron in the sediments of Chaohu lake.The high ratios of Fe/P and Fe/S in the sediments of Chaohu lake weakened the release of internal phosphorus,and thus the correlation of P,Fe and S was insignificant on the whole.