太湖沉积物铁形态分布特征及磷铁相关性分析

通过对太湖藻型湖区、草藻过渡型湖区、草型湖区柱状沉积物进行铁的形态分级分析沉积物中不同提取态磷铁含量,获得不同形态铁的空间分布特征.结果表明:沉积物总铁含量藻型湖区31.57mg/g(SD=8.51) >过渡型湖区30.34mg/g(SD=11.97) >草型湖区25.25mg/g(SD=4.59),不同湖区沉积物中铁形态的含量依次为可还原(晶型)铁氧化物Fe_ox2 >碳酸盐铁Fe_carb >易还原(无定形)铁氧化物Fe_ox1 >低活性硅酸铁Fe_prs >磁铁矿Fe_mag >可吸附性Fe(Ⅱ),Fe_carb、Fe_ox1、Fe_ox2,3种铁形态属于高活性铁Fe(Ⅲ),含量为7.79,6.16,8.18mg/g,分别占总铁含量的28.56%,21.54%,29.53%,表明高活性铁(Ⅲ)是沉积物中最主要的铁形态;沉积物中各提取态磷含量大小比较为NH₂OH·HCl-P >MgCl₂-P >NaAc-P >Na₂S₂O₄-P >浓HCl-P >(NH₄)₂C₂O₄-P,含量较高的MgCl₂-P(0.067mg/g)、NaAc-P(0.061mg/g)、NH₂OH·HCl-P(0.068mg/g),分别占总提取磷的35.28%、31.97%和22.55%,是沉积物铁分级提取态磷中最主要的形态.磷-铁相关性分析表明,二者之间呈显著的正相关(P<0.05),进一步从铁形态分级角度证实铁是沉积物內源磷释放的关键因子.

Distribution of iron forms and their correlations analysis with phosphorus forms in the sedimentary profiles of Taihu Lake.

Occureneces and distributions of iron forms in the sediment cores from three typically zones of Lake Taihu, i.e. phytoplankton dominated zone, macrophyte dominated zone, and phytoplankton-macrophyte transition zone, were investigated using the sequential extraction procedure. Generally, the total iron contents decreased in the order:phytoplankton dominated zone(31.57±8.51mg/g) >phytoplankton-macrophyte transition zone(30.34±11.97mg/g) >macrophyte dominated zone(25.25±4.59mg/g), while the contents of different iron forms in the interest sites followed the variations:reducible oxides Fe_ox2 >carbonate associated Fe Fe_carb >easilyreducible oxidesFe_ox1 >poorly reactive sheet silicate FeFe_prs >magnetite Fe_mag >Absorbed Fe(Ⅱ), Fe_carb、Fe_ox1、Fe_ox2 weremeasured to be7.79mg/g, 6.16mg/g, 8.18mg/g, accounting for 28.56%, 21.54%, 29.53% of total iron respectively, suggesting those highly reactive iron Fe(Ⅲ) were the dominated iron forms. The concents of different extracted phosphorus in sediment decreased in the order:NH₂OH·HCl-P >MgCl₂-P >NaAc-P >Na₂S₂O₄-P >Concentrated HCl-P >(NH₄)₂C₂O₄-P. Three dominated phosphorus fractions including MgCl₂-P、NaAc-P、NH₂OH·HCl-Pwere measured to be 0.067mg/g, 0.061mg/g, 0.068mg/g, accounting for 35.28%、31.97% and 22.55% of the total extracted phosphorus.Significantly positive relationships were observed between the extracted phosphorus and iron fractions using the sequential extraction(P<0.05), further confirming the concomitant release of phosphorus from reduction dissolution ofFe(oxyhydr) oxides in sediments.